Cermic Matrix Composites - Toughening Mechanisms and Processing Problems: "Cermic Matrix Composites – Toughening Mechanisms and Processing Problems
Topics Covered
Background
Ceramic Matrix Composites
Toughening Mechanisms for Ceramic Matrix Composites
How Fibre Reinforcement Toughening Mechanisms Work
Short-Fibre or Whisker Reinforcement versus Long Fibre Reinforcement
Problems Associated with Powder Processing of Ceramic Matrix Composites
Fibre Agglomeration
Density differences
Background
Technological advances are continually placing greater demands on the performance characteristics of engineering materials. Traditionally, engineering ceramics have been considered for heat containment, wear resistant, static load bearing, and electro-optical applications owing to the generalised properties of ceramics which include hardness, corrosion resistance, stability at high temperatures, creep resistance, high elastic modulus, and electrical and thermal resistivity. Unfortunately, these properties come at the expense of toughness. While metals typically have toughness values of 15 to 150 MPa.m½ ceramics usually have toughness values below 5 MPa.m½ frequently below 2 MPa.m½.
Ceramic Matrix Composites
Significant research effort has been directed toward the development of tough ceramics, since such materials have the potential to open up a large range of specialised engineering applications. Toughness can
Wednesday, June 25, 2008
Avalon Instuments - Raman FAQs
Avalon Instuments - Raman FAQs: "What is Raman?
A technique which uses a laser to identify the chemical composition of almost anything.
click here for more details
Can Raman work on... solids..liquid... etc.?
Raman spectra can be obtained from molecular samples, i.e. solids, liquids, gels, slurries, powders, etc.
Raman spectra can even be obtained from some metals! It is possible to obtain Raman spectra of gases but this typically requires specialist equipment.
What does a Raman spectrum look like?
A series of peaks, very like a FT-IR transmission spectrum. Here is an example of a Raman Spectrum, in this case o-, m- & p-xylene, this spectrum is of 33% p-xylene, 33% o-xylene, 33% m-xylene in a glass bottle.
raman spectrum
Can I do Raman spectroscopy on mixtures?
Yes, see the Raman spectrum above.
A Raman spectrum is a spectral “finger print”. If there are a number of different compounds in a mixture, the Raman spectrum will be a superposition of the spectra of each of the components.
The relative intensities of the peaks can be used to give quantitative information on the composition of a mixture of known compounds. If the identity of the components is not known, simple software-based protocols can be used to identify them even if the spectra are too complex to resolve by the naked eye.
Is Raman q"
A technique which uses a laser to identify the chemical composition of almost anything.
click here for more details
Can Raman work on... solids..liquid... etc.?
Raman spectra can be obtained from molecular samples, i.e. solids, liquids, gels, slurries, powders, etc.
Raman spectra can even be obtained from some metals! It is possible to obtain Raman spectra of gases but this typically requires specialist equipment.
What does a Raman spectrum look like?
A series of peaks, very like a FT-IR transmission spectrum. Here is an example of a Raman Spectrum, in this case o-, m- & p-xylene, this spectrum is of 33% p-xylene, 33% o-xylene, 33% m-xylene in a glass bottle.
raman spectrum
Can I do Raman spectroscopy on mixtures?
Yes, see the Raman spectrum above.
A Raman spectrum is a spectral “finger print”. If there are a number of different compounds in a mixture, the Raman spectrum will be a superposition of the spectra of each of the components.
The relative intensities of the peaks can be used to give quantitative information on the composition of a mixture of known compounds. If the identity of the components is not known, simple software-based protocols can be used to identify them even if the spectra are too complex to resolve by the naked eye.
Is Raman q"
Monday, June 23, 2008
The Smalley Group - Rice University - Sent Using Google Toolbar
The Smalley Group - Rice University
Autobiography
Richard Errett Smalley
Biographical Sketch
I was born in Akron, Ohio on June 6, 1943, one year to the day before D-Day, the allied invasion at Normandy. The youngest of four children, I was brought up in a wonderfully stable, loving family of strong Midwestern values. When I was three my family moved to Kansas City, Missouri where we lived in a beautiful large home in a lovely upper-middle class neighborhood. I grew up there -- at least to the extent one can be considered to be grown up on leaving for college at age 18 -- and was convinced that Kansas City, Missouri was the exact center of the known universe.
My mother, Esther Virginia Rhoads, was the third of six children of Charlotte Kraft and Errett Stanley Rhoads, a wealthy manufacturer of furniture in the Kansas City area. She liked the unusual name Errett so much that she gave it to me as my middle name. She picked the name Richard after the crusading English king (the Lion-Hearted), but being a good American and suitably suspicious of royalty, she was fond of calling me "Mr. President" instead. She had big plans for me, and loved me beyond all reason.
My father, Frank Dudley Smalley, Jr., was the second of four children born to Mary Rice Burkholder and Frank Dudley Smalley (Sr.), a railroad mail clerk in Kansas City. Although my father went by the name of June (short for Junior), he never quite forgave his father for not having given him a name of his own, and for not having aspired to more in life. My father started work as a carpenter, and then as a printer's devil, working for the local newspaper, The Kansas City Star, and later for a farm implement trade journal, Implement and Tractor. By the time he retired in 1963 he had long since risen to be CEO of this company, and a group of several others that published trade journals in the booming agriculture industry throughout the Western Hemisphere. He was incredibly industrious, talented, and fascinated with both business and technology. He had a wonderfully analytic mind, and loved argument, open discussion, and homespun philosophy. During the depression in the early 1930's he married my mother (who fell in love with his blue eyes) and was promptly laid off from work. The story of his career is one of total dedication to both his work and his family, a dedication that held steady through a series of tribulatons, many of which I am only now beginning to appreciate. He loved me too, but he could see himself in me, and knew my failings through and through. Until late in life I was never quite good enough for my father, and I suppose that is part of what drives me even now, well after his death in 1992.
My interest in Science had many roots. Some came from my mother as she finished her B.A. Degree studies in college while I was in my early teens. She fell in love with science, particularly as a result of classes on the Foundations of Physical Science taught by a magnificent mathematics professor at the University of Kansas City, Dr. Norman N. Royall, Jr. I was infected by this professor second hand, through hundreds of hours of conversations at my mother's knees. It was from my mother that I first learned of Archimedes, Leonardo da Vinci, Galileo, Kepler, Newton, and Darwin. We spent hours together collecting single-celled organisms from a local pond and watching them with a microscope she had received as a gift from my father. Mostly we talked and read together. From her I learned the wonder of ideas and the beauty of Nature (and music, painting, sculpture, and architecture). From my father I learned to build things, to take them apart, and to fix mechanical and electrical equipment in general. I spent vast hours in a woodworking shop he maintained in the basement of our house, building gadgets, working both with my father and alone, often late into the night. My mother taught me mechanical drawing so that I could be more systematic in my design work, and I continued in drafting classes throughout my 4 years in high school. This play with building, fixing, and designing was my favorite activity throughout my childhood, and was a wonderful preparation for my later career as an experimentalist working on the frontiers of chemistry and physics.
The principal impetus for my entering a career in science, however, was the successful launching of Sputnik in 1957, and the then-current belief that science and technology was going to be where the action was in the coming decades. While I had been a rather erratic student for many years, I suddenly became very serious with my education at the beginning of my Junior year in the fall of 1959. I set up a private study in the partly furnished, unheated attic of our home, and began to spend long hours in solitude studying and reading (and smoking cigarettes). This happened to be the year when I began to study chemistry for the first time. Luckily, these years were some of the best ever for the public school system in Kansas City, and my local high school, Southwest High, was one of the most effective anywhere in the US as measured by scores on standard achievement tests, and the fraction of students going on to college. My teacher, Victor E. Gustafson, was a great inspiration. He had just begun to teach the preceding year, and was full of love for his subject and for teaching, and had an as yet unblunted ambition to reach even the slowest of students. In addition, this was the first class I had ever taken with my sister, Linda, who was a year older than I, and was a far better student than I had ever been. The result was that by the end of the year, my sister and I finished with the top two grades in the class. We hardly ever missed a question on an exam. It was an exhilarating experience for me, and still ranks as the single most important turning point in my life, even from my current perspective of nearly four decades later. It was the proof of an existence theorem. After my junior year, I knew I could be successful at science. The next year I did equally well in physics with a wonderful professor, J. C. Edwards, but my soul had already been imprinted by my exposure to chemistry the year before.
My mother's youngest sibling, Dr. Sara Jane Rhoads, was one of the first women in the United States to ever reach the rank of full Professor of Chemistry. After earning her Ph.D. in 1949 with William von Eggars Doering, who was then at Columbia University, she devoted her life to teaching and research in the Department of Chemistry of the University of Wyoming. She received the Garvan Medal of the American Chemical Society in 1982 for her contributions to physical organic chemistry, particularly in the study of the Cope and Claisen rearrangements. She was the only scientist in our extended family and was one of the brightest and, in general, one of the most impressive human beings I have ever met. She was my hero. I used to call her, lovingly, "The Colossus of Rhoads". Her example was a major factor that led me to go into chemistry, rather than physics or engineering. One of the most enjoyable memories of my early life was the summer (1961) I spent working in her organic chemistry laboratory at the University of Wyoming. It was at her suggestion that I decided to attend Hope College that fall in Holland, Michigan. Hope had then (and still has now) one of the finest undergraduate programs in chemistry in the United States.
At Hope College I spent two years in fruitful study, but decided to transfer to the University of Michigan in Ann Arbor after my favorite professor, Dr. J. Harvey Kleinheksel, died of a heart attack, and the organic chemistry professor with whom I had hoped to do research, Dr. Gerrit Van Zyl, announced his retirement. While the next two years in Ann Arbor were successful, I had become so entangled in a stormy love affair with a lovely girl back at Hope College, that I was not able to concentrate as much on science as I should have. I did, however, learn a lot. Most of all I learned from my fellow students, and particularly from John Seely Brown, a graduate student in mathematics who lived in an apartment down the hall in a small house off campus (he is currently Director of Xerox's Palo Alto Research Center, PARC). John displayed an audacity of thought and intellectual ambition that I have rarely seen in any individual. My fellow housemates and I were infected with the notion that we could master any subject, and at times we did manage to at least feel that we got close.
By the time of my graduation in 1965, the job market for scientists in the United States was at an all-time high, and even chemistry graduates with just a BS degree were in great demand. Rather than proceeding directly to graduate school, I decided to take a job in the chemical industry in order to buy a bit of time to see what I really wanted to do in science, and to live a little in the "real" world. It turned out to be a terrific decision.
In the fall of 1965 I began work full time in Woodbury, New Jersey at a large polypropylene manufacturing plant owned by the Shell Chemical Company. I began as a chemist working in the quality control laboratory for the plant, a 24 hour a day operation that in the mid 60's was quite a wonderland of high technology. My first boss was a chemist named Donald S. Brath. He taught his young professionals that "chemists can do anything", and the time I worked under him was a wonderfully broadening experience. I was teamed up with chemical engineers at the plant to study problems with the quality of the polymer product. The Ziegler-Natta catalyst system then in use by Shell to produce isotactic polypropylene was no where near as efficient as those currently in use, and the level of inorganics remaining in the polymer was high. Much of what we were concerned with in those days revolved around this problem of high "ash" content and how it affected the downstream applications. These were fascinating days, involving huge volumes of material, serious real-world problems, with large financial consequences. I loved it.
After two years I moved up to the Plastics Technical Center at the same site in Woodbury, and devoted myself to developing analytical methods for various aspects of polyolefins, and of the materials involved in their manufacture, modification, and processing. Although I found my work at Shell highly enjoyable, I realized it was time to get on to graduate school, so I began to study seriously and to send out applications. At the time I was most interested in quantum chemistry, and received several offers for graduate assistantships in excellent schools. I was close to accepting an offer from the Theoretical Chemistry Institute at the University of Wisconsin when the automatic graduate student deferments from the Draft into the US military were eliminated. This was in early 1968, during a major buildup phase in the Vietnam War, and I decided it would be more prudent to remain at Shell for a while since my industrial deferment was still in effect.
In my off hours over the past few years I had met Judith Grace Sampieri who was a wonderful young secretary at Shell. We were married on May 4 of 1968. Soon thereafter even the industrial deferment was lost, and we decided that I might as well reapply for graduate school. Since Judy's family lived in New Jersey, I decided to apply to Princeton University, and was accepted. In the late fall of 1968 I was reclassified 1A for the draft and reported to the processing center in Newark for my physical. At the end of the day I ended up in the group who had passed. We were told to put our affairs in order since we would soon be called up. However, in a great stroke of luck, within a week, my wife told me she was pregnant, and within a just a few more weeks my draft board reclassified me to some status I do not remember, save that it meant I would not be drafted. On June 9, 1969 Judy and I were blessed with the birth of a beautiful child, Chad Richard. Later that summer, I held him in my lap as Neil Armstrong first stepped out onto the Moon.
In the fall of 1969 I moved my new family up to Princeton to begin studies and research for the Ph.D. in the Department of Chemistry. I was lucky enough to be in the first group of graduate students to work with Elliot R. Bernstein who was just starting as an Assistant Professor at Princeton, after having spent a few years postdoctoral work at the University of Chicago with Clyde A. Hutchison III, following doctoral training with G. Wilse Robinson at Cal. Tech. Elliot's research at the time involved detailed optical and microwave spectral probes of pure and mixed molecular single crystals cooled in liquid helium. I knew nothing about it at the time I joined the group. I was certain that it was going to be both experimentally and theoretically complex and challenging, but it seemed likely to be worth the effort. My research project was the detailed study of sym-triazine, a heterocyclic benzene analog that we expected would provide a poignant testing ground for theories of the Jahn-Teller effect. In the end we found that the crystal field surrounding each molecule was insufficiently symmetrical to provide the tests we originally sought, but much was learned. Most importantly from my standpoint, I learned from Elliot Bernstein a penetrating, intense style of research that I had never known before, and I learned a great deal about the chemical physics of condensed phase and molecular systems.
In the summer of 1973 we moved to the south side of Chicago so I could begin a postdoctoral period with Donald H. Levy at the University of Chicago. Levy had studied gas phase magnetic resonance with Alan Carrington, and had been doing some of the most impressive research anywhere in the world with microwave/optical double resonance and the Hanle effect on NO2 and other open-shell small molecules. These were the earliest days when tunable dye lasers were beginning to transform molecular spectroscopy, and Levy's group was in the lead. The optical spectrum of NO2 was the most troublesome problem for molecular spectroscopists. Even though it had only three atoms, the visible spectrum had far more structure than anyone could understand. But since NO2 was readily available and it displayed an extensive absorption spectrum just where the new lasers could readily operate (500 – 640 nm), it was a favorite object for study. Don Levy and one of his students, Richard Solarz, had made some major advances with NO2 earlier that summer, so after I arrived in Chicago I began to consider what I could do next. My biggest problem was that my training at Princeton had been in condensed mater spectroscopy, and the ultrahigh resolution gas phase spectral techniques being used by the Levy group were going to take months to understand. The detailed physics of rotating polyatomic molecules with spin is extremely complex. I was familiar only with the physics of molecules frozen still in a crystal lattice near absolute zero.
When we first arrived in Chicago, Don Levy was in Germany for a several month-long visit, so I had an opportunity to do some extended reading and to prepare for the final oral exam for the Ph.D. degree back in Princeton. At that time in the Chemistry Department at Princeton, the final oral exam consisted of a defense of three original research proposals. I spent many hours in the U. Chicago chemistry department library reading recent journal articles, searching for possible topics for these research proposals. On one day I read a new paper by Yuan Lee and Stuart Rice on the crossed beam reaction of fluorine with benzene [J. Chem. Phys. 59, 1427 (1973)] in one of Yuan's "universal" molecular beam apparatuses. It was the sort of experiment that was to lead to Yuan Lee sharing the Nobel Prize in 1986 with John Polyani and Dudley Herschbach. I was deeply struck by a passage in the paper which said that the supersonic expansion used to make the benzene molecular beam was strong enough to cool out essentially all rotational degrees of freedom. That was just what I needed. Since I didn't understand rotating molecules yet, perhaps I could just stop them from rotating in the first place!
As a result of this exciting day in the Chicago library, one of the proposals I presented to the Princeton Ph.D. committee later that fall was to use a supersonic expansion to cool NO2 to the point that only a single rotational state was populated, and then to use a tunable dye laser to study the now greatly simplified spectrum. I had found in further reading that the current supersonic expansion techniques actually would not get cold enough, so I added the further use of an electric resonance "state-selector" to do a final sorting out of just a single rotational state for study. I recommended, in fact, that the 10 meter state-selector beam machine of Lennard Wharton at Chicago could be used.
When Levy returned from Germany, I told him of this proposal, and we discussed it in some depth. He was intrigued, but was concerned that too much of the NO2 would dimerize to N2O4 before sufficient cooling was obtained. A few weeks later we discussed it again, and became sufficiently excited to walk down the hall and ask Lennard Wharton what he thought. Len lit up like a light bulb.
Wharton argued that we should first do the experiment on NO2 expanded in a supersonic free jet, and leave the much more elaborate state-selected experiment for later. I told him that wouldn't be cold enough – the lowest rotational temperature reported for a polyatomic molecule in a supersonic beam that I was aware of at that time was 30K, still way to hot to achieve the simplification we needed. Wharton smiled wryly and swiveled in his chair to reach a research notebook from the shelf behind him. After reading a few pages he looked up and asked "would 3K be cool enough?". He had already built a liquid hydrogen cryopumped supersonic beam source with argon, and in the research notebook had measured data for the velocity distribution showing the translational temperature was cooled to 3K. That, I knew from my Ph.D. proposal, would be quite cool enough in the case of NO2 to collapse the rotational population to just a few levels. We would simply mix in a percent or so of NO2 into the argon and make a "seeded" supersonic beam. This would avoid the N2O4 formation that concerned Don Levy, and may just possibly cool the rotational degrees of freedom to near the translational temperature of the argon carrier gas. Thus began the collaboration that led to supersonic beam laser spectroscopy.
On the night of August 8, 1974 (the night Nixon resigned from the US Presidency) we recorded the first jet cooled spectrum of NO2. The next morning Don Levy saw the spectrum for the first time, and immediately recognized its significance. Molecular physics had changed. Now we could study at least small polyatomic molecules with at the same penetrating level of detail previously attained only for atoms and diatomics.
A year later, Lennard Wharton came back from a trip to France where he had visited with Roger Campargue and learned of the concept of the "zone of silence" that exists in an expanding gas at sufficiently high densities. While this zone is surrounded by shock waves where the gas is heated to very high temperatures, within the zone the expanding gas is exactly as cold and unperturbed as it would be if the gas expanded into a perfect vacuum, forming no shock waves at all. Campargue had learned to fabricate a ultrasharp edged "skimmer" that could penetrate the "Mach disc" at end of the zone and transmit the gas streaming along the center line of the zone of silence to form the most intense, coldest supersonic beams ever produced. Wharton told Don Levy and I that using helium in such an apparatus we could easily get down to 1 K and perhaps even lower. I was stunned. I knew that 1 K was low enough to freeze out the rotational motion of even medium sized molecules such as benzene and naphthalene, and all such molecules could now be studied without rotational congestion.
Later that same day in a hallway conversation Len Wharton and I realized we didn't need the skimmer. The probe laser beam could easily penetrate the shock waves without perturbation, and we could image just the fluorescence from the laser-excited ultracold molecules in the zone of silence. We quickly built a new apparatus that incorporated these ideas. With the spectroscopic insight of Don Levy and with a series of graduate students we published the pioneering papers on not only jet cooled spectra of ordinary molecules such as NO2, and tetrazine, but also on the first van der Waals complexes with helium (e.g. HeI2 ), and with the vital collaboration of Daniel Auerbach the first supersonic beam study of a metal atom -- rare gas complex, NaAr.
In the summer of 1976 my family and I moved to Houston, Texas where I had accepted a position as assistant professor in the chemistry department at Rice University. I knew of Rice principally because of the beautiful laser spectroscopy that was being done there by Robert F. Curl, and I wanted to collaborate with him much the same as I had with Don Levy. The first supersonic beam apparatus I set up was a free jet machine similar to that I had used in Chicago, but adapted to use pulsed dye lasers in the ultraviolet so that we could study more ordinary molecules such as benzene. My first proposal to the National Science Foundation was for a much larger, more ambitious apparatus that would for the first time use pulsed supersonic nozzles. With these pulsed devices mounted in a large chamber I expected we could attain a 10-100 fold increase in beam intensity and cooling, and by synchronizing with the pulsed lasers in both the visible and ultraviolet be able to study a vast array of large molecules, radicals, and clusters. Being the second apparatus we constructed, it was called "AP2".
With AP2 we quickly succeeded in setting the world's record for rotational cooling of a polyatomic molecule (0.17 K). We invented resonant two-photon ionization (R2PI) with time of flight mass spectrometric detection as a means of probing the spectrum of molecules in the supersonic beam. We used this to probe the structure and molecular dynamics of large aromatic molecules, particularly focussing on the question of intramolecular vibrational redistribution. We also developed a means of producing fragments of polyatomic molecules (free radicals such as benzyl and methoxy) by directing a pulsed laser into a specially designed pulsed supersonic nozzle, and studying these cooled in the supersonic beam.
In the late 1970s In collaboration with Andrew Kaldor and his group at Exxon we had extended the capabilities of AP2 so that we could study a large uranium containing molecule ( a hexafluoro acetoacetonate-, tetahydrofuran-complexed form of UO2). These were the days of the oil crisis, when there was wide-spread belief that nuclear fission using uranium was going to be the only long term alternative. Exxon was working intensely on laser-based isotope separation schemes, and Kaldor was heading up a group to pursue the molecular route. Our experiment on AP2 ultimately revealed a beautiful sharpening of the infrared multiphoton dissociation spectrum of this volatile UO2 complex cooled in the supersonic beam, just what Exxon was looking for. Unfortunately, we began to succeed with these experiments only after the nuclear release "event" at Three Mile Island on, March 28, 1979. Within a year, Exxon made a corporate level decision to get out of the isotope separation business. But Kaldor had become so impressed with the capabilities of AP2 that he wanted his own at the corporate laboratories in Linden in any event. Under contract to Exxon, we developed a smaller version of the apparatus, and built two versions. One was kept at Rice and lived on for many years with a very productive science history. Logically, it was called AP3. The clone of AP3 was shipped to Exxon in late 1982.
After a few years of intensive research we found a way to use a pulsed laser directed into a nozzle to vaporize any material, allowing for the first time the atoms of any element in the periodic table to be produced cold in a supersonic beam. Most importantly, we developed a way to control the clustering of these atoms to small aggregates, which then were cooled in the supersonic expansion. Now for the first time it was possible to roam the periodic table and make detailed study of the properties of nanometer-scale particles consisting of a precise number of atoms. The field of metal and semiconductor cluster beams was born. We shipped Exxon this new accessory to their AP3 clone, and both groups then rapidly began to develop the new field.
As is now well known, the Kaldor group was the first to put carbon in a laser vaporization cluster beam apparatus, and see the amazing even-numbered distribution of carbon clusters that we now know to be the fullerenes. Within a year we repeated the same experiment, but now on an improved version of AP2 that had been modified for the study of semiconductor clusters. The story of what we discovered on this apparatus in September of 1985 has been told many times.
The subsequent development of my research in metal and semiconductor clusters, and the fullerenes is too involved to recount here. Increasingly, the tubular variant of the fullerenes has dominated our activities. Now our motto is "if it ain't tubes, we don't do it". We are convinced that major new technologies will be developed over the coming decades from fullerene tubes, fibers, and cables, and we are moving as fast as possible to bring this all to life.
Several years ago AP2 was dismantled and sold off in pieces to other research groups, and the main chamber where the first pulsed nozzle experiments were performed was sold off to a scrap metal dealer along the Houston Ship Canal. Now there are no supersonic beam machines of any type in the laboratory. Times change.
But science and life goes on.
Autobiography
Richard Errett Smalley
Biographical Sketch
I was born in Akron, Ohio on June 6, 1943, one year to the day before D-Day, the allied invasion at Normandy. The youngest of four children, I was brought up in a wonderfully stable, loving family of strong Midwestern values. When I was three my family moved to Kansas City, Missouri where we lived in a beautiful large home in a lovely upper-middle class neighborhood. I grew up there -- at least to the extent one can be considered to be grown up on leaving for college at age 18 -- and was convinced that Kansas City, Missouri was the exact center of the known universe.
My mother, Esther Virginia Rhoads, was the third of six children of Charlotte Kraft and Errett Stanley Rhoads, a wealthy manufacturer of furniture in the Kansas City area. She liked the unusual name Errett so much that she gave it to me as my middle name. She picked the name Richard after the crusading English king (the Lion-Hearted), but being a good American and suitably suspicious of royalty, she was fond of calling me "Mr. President" instead. She had big plans for me, and loved me beyond all reason.
My father, Frank Dudley Smalley, Jr., was the second of four children born to Mary Rice Burkholder and Frank Dudley Smalley (Sr.), a railroad mail clerk in Kansas City. Although my father went by the name of June (short for Junior), he never quite forgave his father for not having given him a name of his own, and for not having aspired to more in life. My father started work as a carpenter, and then as a printer's devil, working for the local newspaper, The Kansas City Star, and later for a farm implement trade journal, Implement and Tractor. By the time he retired in 1963 he had long since risen to be CEO of this company, and a group of several others that published trade journals in the booming agriculture industry throughout the Western Hemisphere. He was incredibly industrious, talented, and fascinated with both business and technology. He had a wonderfully analytic mind, and loved argument, open discussion, and homespun philosophy. During the depression in the early 1930's he married my mother (who fell in love with his blue eyes) and was promptly laid off from work. The story of his career is one of total dedication to both his work and his family, a dedication that held steady through a series of tribulatons, many of which I am only now beginning to appreciate. He loved me too, but he could see himself in me, and knew my failings through and through. Until late in life I was never quite good enough for my father, and I suppose that is part of what drives me even now, well after his death in 1992.
My interest in Science had many roots. Some came from my mother as she finished her B.A. Degree studies in college while I was in my early teens. She fell in love with science, particularly as a result of classes on the Foundations of Physical Science taught by a magnificent mathematics professor at the University of Kansas City, Dr. Norman N. Royall, Jr. I was infected by this professor second hand, through hundreds of hours of conversations at my mother's knees. It was from my mother that I first learned of Archimedes, Leonardo da Vinci, Galileo, Kepler, Newton, and Darwin. We spent hours together collecting single-celled organisms from a local pond and watching them with a microscope she had received as a gift from my father. Mostly we talked and read together. From her I learned the wonder of ideas and the beauty of Nature (and music, painting, sculpture, and architecture). From my father I learned to build things, to take them apart, and to fix mechanical and electrical equipment in general. I spent vast hours in a woodworking shop he maintained in the basement of our house, building gadgets, working both with my father and alone, often late into the night. My mother taught me mechanical drawing so that I could be more systematic in my design work, and I continued in drafting classes throughout my 4 years in high school. This play with building, fixing, and designing was my favorite activity throughout my childhood, and was a wonderful preparation for my later career as an experimentalist working on the frontiers of chemistry and physics.
The principal impetus for my entering a career in science, however, was the successful launching of Sputnik in 1957, and the then-current belief that science and technology was going to be where the action was in the coming decades. While I had been a rather erratic student for many years, I suddenly became very serious with my education at the beginning of my Junior year in the fall of 1959. I set up a private study in the partly furnished, unheated attic of our home, and began to spend long hours in solitude studying and reading (and smoking cigarettes). This happened to be the year when I began to study chemistry for the first time. Luckily, these years were some of the best ever for the public school system in Kansas City, and my local high school, Southwest High, was one of the most effective anywhere in the US as measured by scores on standard achievement tests, and the fraction of students going on to college. My teacher, Victor E. Gustafson, was a great inspiration. He had just begun to teach the preceding year, and was full of love for his subject and for teaching, and had an as yet unblunted ambition to reach even the slowest of students. In addition, this was the first class I had ever taken with my sister, Linda, who was a year older than I, and was a far better student than I had ever been. The result was that by the end of the year, my sister and I finished with the top two grades in the class. We hardly ever missed a question on an exam. It was an exhilarating experience for me, and still ranks as the single most important turning point in my life, even from my current perspective of nearly four decades later. It was the proof of an existence theorem. After my junior year, I knew I could be successful at science. The next year I did equally well in physics with a wonderful professor, J. C. Edwards, but my soul had already been imprinted by my exposure to chemistry the year before.
My mother's youngest sibling, Dr. Sara Jane Rhoads, was one of the first women in the United States to ever reach the rank of full Professor of Chemistry. After earning her Ph.D. in 1949 with William von Eggars Doering, who was then at Columbia University, she devoted her life to teaching and research in the Department of Chemistry of the University of Wyoming. She received the Garvan Medal of the American Chemical Society in 1982 for her contributions to physical organic chemistry, particularly in the study of the Cope and Claisen rearrangements. She was the only scientist in our extended family and was one of the brightest and, in general, one of the most impressive human beings I have ever met. She was my hero. I used to call her, lovingly, "The Colossus of Rhoads". Her example was a major factor that led me to go into chemistry, rather than physics or engineering. One of the most enjoyable memories of my early life was the summer (1961) I spent working in her organic chemistry laboratory at the University of Wyoming. It was at her suggestion that I decided to attend Hope College that fall in Holland, Michigan. Hope had then (and still has now) one of the finest undergraduate programs in chemistry in the United States.
At Hope College I spent two years in fruitful study, but decided to transfer to the University of Michigan in Ann Arbor after my favorite professor, Dr. J. Harvey Kleinheksel, died of a heart attack, and the organic chemistry professor with whom I had hoped to do research, Dr. Gerrit Van Zyl, announced his retirement. While the next two years in Ann Arbor were successful, I had become so entangled in a stormy love affair with a lovely girl back at Hope College, that I was not able to concentrate as much on science as I should have. I did, however, learn a lot. Most of all I learned from my fellow students, and particularly from John Seely Brown, a graduate student in mathematics who lived in an apartment down the hall in a small house off campus (he is currently Director of Xerox's Palo Alto Research Center, PARC). John displayed an audacity of thought and intellectual ambition that I have rarely seen in any individual. My fellow housemates and I were infected with the notion that we could master any subject, and at times we did manage to at least feel that we got close.
By the time of my graduation in 1965, the job market for scientists in the United States was at an all-time high, and even chemistry graduates with just a BS degree were in great demand. Rather than proceeding directly to graduate school, I decided to take a job in the chemical industry in order to buy a bit of time to see what I really wanted to do in science, and to live a little in the "real" world. It turned out to be a terrific decision.
In the fall of 1965 I began work full time in Woodbury, New Jersey at a large polypropylene manufacturing plant owned by the Shell Chemical Company. I began as a chemist working in the quality control laboratory for the plant, a 24 hour a day operation that in the mid 60's was quite a wonderland of high technology. My first boss was a chemist named Donald S. Brath. He taught his young professionals that "chemists can do anything", and the time I worked under him was a wonderfully broadening experience. I was teamed up with chemical engineers at the plant to study problems with the quality of the polymer product. The Ziegler-Natta catalyst system then in use by Shell to produce isotactic polypropylene was no where near as efficient as those currently in use, and the level of inorganics remaining in the polymer was high. Much of what we were concerned with in those days revolved around this problem of high "ash" content and how it affected the downstream applications. These were fascinating days, involving huge volumes of material, serious real-world problems, with large financial consequences. I loved it.
After two years I moved up to the Plastics Technical Center at the same site in Woodbury, and devoted myself to developing analytical methods for various aspects of polyolefins, and of the materials involved in their manufacture, modification, and processing. Although I found my work at Shell highly enjoyable, I realized it was time to get on to graduate school, so I began to study seriously and to send out applications. At the time I was most interested in quantum chemistry, and received several offers for graduate assistantships in excellent schools. I was close to accepting an offer from the Theoretical Chemistry Institute at the University of Wisconsin when the automatic graduate student deferments from the Draft into the US military were eliminated. This was in early 1968, during a major buildup phase in the Vietnam War, and I decided it would be more prudent to remain at Shell for a while since my industrial deferment was still in effect.
In my off hours over the past few years I had met Judith Grace Sampieri who was a wonderful young secretary at Shell. We were married on May 4 of 1968. Soon thereafter even the industrial deferment was lost, and we decided that I might as well reapply for graduate school. Since Judy's family lived in New Jersey, I decided to apply to Princeton University, and was accepted. In the late fall of 1968 I was reclassified 1A for the draft and reported to the processing center in Newark for my physical. At the end of the day I ended up in the group who had passed. We were told to put our affairs in order since we would soon be called up. However, in a great stroke of luck, within a week, my wife told me she was pregnant, and within a just a few more weeks my draft board reclassified me to some status I do not remember, save that it meant I would not be drafted. On June 9, 1969 Judy and I were blessed with the birth of a beautiful child, Chad Richard. Later that summer, I held him in my lap as Neil Armstrong first stepped out onto the Moon.
In the fall of 1969 I moved my new family up to Princeton to begin studies and research for the Ph.D. in the Department of Chemistry. I was lucky enough to be in the first group of graduate students to work with Elliot R. Bernstein who was just starting as an Assistant Professor at Princeton, after having spent a few years postdoctoral work at the University of Chicago with Clyde A. Hutchison III, following doctoral training with G. Wilse Robinson at Cal. Tech. Elliot's research at the time involved detailed optical and microwave spectral probes of pure and mixed molecular single crystals cooled in liquid helium. I knew nothing about it at the time I joined the group. I was certain that it was going to be both experimentally and theoretically complex and challenging, but it seemed likely to be worth the effort. My research project was the detailed study of sym-triazine, a heterocyclic benzene analog that we expected would provide a poignant testing ground for theories of the Jahn-Teller effect. In the end we found that the crystal field surrounding each molecule was insufficiently symmetrical to provide the tests we originally sought, but much was learned. Most importantly from my standpoint, I learned from Elliot Bernstein a penetrating, intense style of research that I had never known before, and I learned a great deal about the chemical physics of condensed phase and molecular systems.
In the summer of 1973 we moved to the south side of Chicago so I could begin a postdoctoral period with Donald H. Levy at the University of Chicago. Levy had studied gas phase magnetic resonance with Alan Carrington, and had been doing some of the most impressive research anywhere in the world with microwave/optical double resonance and the Hanle effect on NO2 and other open-shell small molecules. These were the earliest days when tunable dye lasers were beginning to transform molecular spectroscopy, and Levy's group was in the lead. The optical spectrum of NO2 was the most troublesome problem for molecular spectroscopists. Even though it had only three atoms, the visible spectrum had far more structure than anyone could understand. But since NO2 was readily available and it displayed an extensive absorption spectrum just where the new lasers could readily operate (500 – 640 nm), it was a favorite object for study. Don Levy and one of his students, Richard Solarz, had made some major advances with NO2 earlier that summer, so after I arrived in Chicago I began to consider what I could do next. My biggest problem was that my training at Princeton had been in condensed mater spectroscopy, and the ultrahigh resolution gas phase spectral techniques being used by the Levy group were going to take months to understand. The detailed physics of rotating polyatomic molecules with spin is extremely complex. I was familiar only with the physics of molecules frozen still in a crystal lattice near absolute zero.
When we first arrived in Chicago, Don Levy was in Germany for a several month-long visit, so I had an opportunity to do some extended reading and to prepare for the final oral exam for the Ph.D. degree back in Princeton. At that time in the Chemistry Department at Princeton, the final oral exam consisted of a defense of three original research proposals. I spent many hours in the U. Chicago chemistry department library reading recent journal articles, searching for possible topics for these research proposals. On one day I read a new paper by Yuan Lee and Stuart Rice on the crossed beam reaction of fluorine with benzene [J. Chem. Phys. 59, 1427 (1973)] in one of Yuan's "universal" molecular beam apparatuses. It was the sort of experiment that was to lead to Yuan Lee sharing the Nobel Prize in 1986 with John Polyani and Dudley Herschbach. I was deeply struck by a passage in the paper which said that the supersonic expansion used to make the benzene molecular beam was strong enough to cool out essentially all rotational degrees of freedom. That was just what I needed. Since I didn't understand rotating molecules yet, perhaps I could just stop them from rotating in the first place!
As a result of this exciting day in the Chicago library, one of the proposals I presented to the Princeton Ph.D. committee later that fall was to use a supersonic expansion to cool NO2 to the point that only a single rotational state was populated, and then to use a tunable dye laser to study the now greatly simplified spectrum. I had found in further reading that the current supersonic expansion techniques actually would not get cold enough, so I added the further use of an electric resonance "state-selector" to do a final sorting out of just a single rotational state for study. I recommended, in fact, that the 10 meter state-selector beam machine of Lennard Wharton at Chicago could be used.
When Levy returned from Germany, I told him of this proposal, and we discussed it in some depth. He was intrigued, but was concerned that too much of the NO2 would dimerize to N2O4 before sufficient cooling was obtained. A few weeks later we discussed it again, and became sufficiently excited to walk down the hall and ask Lennard Wharton what he thought. Len lit up like a light bulb.
Wharton argued that we should first do the experiment on NO2 expanded in a supersonic free jet, and leave the much more elaborate state-selected experiment for later. I told him that wouldn't be cold enough – the lowest rotational temperature reported for a polyatomic molecule in a supersonic beam that I was aware of at that time was 30K, still way to hot to achieve the simplification we needed. Wharton smiled wryly and swiveled in his chair to reach a research notebook from the shelf behind him. After reading a few pages he looked up and asked "would 3K be cool enough?". He had already built a liquid hydrogen cryopumped supersonic beam source with argon, and in the research notebook had measured data for the velocity distribution showing the translational temperature was cooled to 3K. That, I knew from my Ph.D. proposal, would be quite cool enough in the case of NO2 to collapse the rotational population to just a few levels. We would simply mix in a percent or so of NO2 into the argon and make a "seeded" supersonic beam. This would avoid the N2O4 formation that concerned Don Levy, and may just possibly cool the rotational degrees of freedom to near the translational temperature of the argon carrier gas. Thus began the collaboration that led to supersonic beam laser spectroscopy.
On the night of August 8, 1974 (the night Nixon resigned from the US Presidency) we recorded the first jet cooled spectrum of NO2. The next morning Don Levy saw the spectrum for the first time, and immediately recognized its significance. Molecular physics had changed. Now we could study at least small polyatomic molecules with at the same penetrating level of detail previously attained only for atoms and diatomics.
A year later, Lennard Wharton came back from a trip to France where he had visited with Roger Campargue and learned of the concept of the "zone of silence" that exists in an expanding gas at sufficiently high densities. While this zone is surrounded by shock waves where the gas is heated to very high temperatures, within the zone the expanding gas is exactly as cold and unperturbed as it would be if the gas expanded into a perfect vacuum, forming no shock waves at all. Campargue had learned to fabricate a ultrasharp edged "skimmer" that could penetrate the "Mach disc" at end of the zone and transmit the gas streaming along the center line of the zone of silence to form the most intense, coldest supersonic beams ever produced. Wharton told Don Levy and I that using helium in such an apparatus we could easily get down to 1 K and perhaps even lower. I was stunned. I knew that 1 K was low enough to freeze out the rotational motion of even medium sized molecules such as benzene and naphthalene, and all such molecules could now be studied without rotational congestion.
Later that same day in a hallway conversation Len Wharton and I realized we didn't need the skimmer. The probe laser beam could easily penetrate the shock waves without perturbation, and we could image just the fluorescence from the laser-excited ultracold molecules in the zone of silence. We quickly built a new apparatus that incorporated these ideas. With the spectroscopic insight of Don Levy and with a series of graduate students we published the pioneering papers on not only jet cooled spectra of ordinary molecules such as NO2, and tetrazine, but also on the first van der Waals complexes with helium (e.g. HeI2 ), and with the vital collaboration of Daniel Auerbach the first supersonic beam study of a metal atom -- rare gas complex, NaAr.
In the summer of 1976 my family and I moved to Houston, Texas where I had accepted a position as assistant professor in the chemistry department at Rice University. I knew of Rice principally because of the beautiful laser spectroscopy that was being done there by Robert F. Curl, and I wanted to collaborate with him much the same as I had with Don Levy. The first supersonic beam apparatus I set up was a free jet machine similar to that I had used in Chicago, but adapted to use pulsed dye lasers in the ultraviolet so that we could study more ordinary molecules such as benzene. My first proposal to the National Science Foundation was for a much larger, more ambitious apparatus that would for the first time use pulsed supersonic nozzles. With these pulsed devices mounted in a large chamber I expected we could attain a 10-100 fold increase in beam intensity and cooling, and by synchronizing with the pulsed lasers in both the visible and ultraviolet be able to study a vast array of large molecules, radicals, and clusters. Being the second apparatus we constructed, it was called "AP2".
With AP2 we quickly succeeded in setting the world's record for rotational cooling of a polyatomic molecule (0.17 K). We invented resonant two-photon ionization (R2PI) with time of flight mass spectrometric detection as a means of probing the spectrum of molecules in the supersonic beam. We used this to probe the structure and molecular dynamics of large aromatic molecules, particularly focussing on the question of intramolecular vibrational redistribution. We also developed a means of producing fragments of polyatomic molecules (free radicals such as benzyl and methoxy) by directing a pulsed laser into a specially designed pulsed supersonic nozzle, and studying these cooled in the supersonic beam.
In the late 1970s In collaboration with Andrew Kaldor and his group at Exxon we had extended the capabilities of AP2 so that we could study a large uranium containing molecule ( a hexafluoro acetoacetonate-, tetahydrofuran-complexed form of UO2). These were the days of the oil crisis, when there was wide-spread belief that nuclear fission using uranium was going to be the only long term alternative. Exxon was working intensely on laser-based isotope separation schemes, and Kaldor was heading up a group to pursue the molecular route. Our experiment on AP2 ultimately revealed a beautiful sharpening of the infrared multiphoton dissociation spectrum of this volatile UO2 complex cooled in the supersonic beam, just what Exxon was looking for. Unfortunately, we began to succeed with these experiments only after the nuclear release "event" at Three Mile Island on, March 28, 1979. Within a year, Exxon made a corporate level decision to get out of the isotope separation business. But Kaldor had become so impressed with the capabilities of AP2 that he wanted his own at the corporate laboratories in Linden in any event. Under contract to Exxon, we developed a smaller version of the apparatus, and built two versions. One was kept at Rice and lived on for many years with a very productive science history. Logically, it was called AP3. The clone of AP3 was shipped to Exxon in late 1982.
After a few years of intensive research we found a way to use a pulsed laser directed into a nozzle to vaporize any material, allowing for the first time the atoms of any element in the periodic table to be produced cold in a supersonic beam. Most importantly, we developed a way to control the clustering of these atoms to small aggregates, which then were cooled in the supersonic expansion. Now for the first time it was possible to roam the periodic table and make detailed study of the properties of nanometer-scale particles consisting of a precise number of atoms. The field of metal and semiconductor cluster beams was born. We shipped Exxon this new accessory to their AP3 clone, and both groups then rapidly began to develop the new field.
As is now well known, the Kaldor group was the first to put carbon in a laser vaporization cluster beam apparatus, and see the amazing even-numbered distribution of carbon clusters that we now know to be the fullerenes. Within a year we repeated the same experiment, but now on an improved version of AP2 that had been modified for the study of semiconductor clusters. The story of what we discovered on this apparatus in September of 1985 has been told many times.
The subsequent development of my research in metal and semiconductor clusters, and the fullerenes is too involved to recount here. Increasingly, the tubular variant of the fullerenes has dominated our activities. Now our motto is "if it ain't tubes, we don't do it". We are convinced that major new technologies will be developed over the coming decades from fullerene tubes, fibers, and cables, and we are moving as fast as possible to bring this all to life.
Several years ago AP2 was dismantled and sold off in pieces to other research groups, and the main chamber where the first pulsed nozzle experiments were performed was sold off to a scrap metal dealer along the Houston Ship Canal. Now there are no supersonic beam machines of any type in the laboratory. Times change.
But science and life goes on.
Saturday, June 21, 2008
hard yet tough nanocomposite coatings
In this review, the different approaches and future directions will be outlined.
pls comment on it. thank a lot.
Sam Zhang, Huili Wang, Soon Eng Ong, Deen Sun and Bui Xuan Lam, Hard Yet Tough Nanocomposite coatings – Present Status and Future Trend, Plasma Processes and Polymers, 4 : 219-228 (2007)
To download, pls go to the below link.
http://www3.ntu.edu.sg/mae/Research/Programmes/Thinfilms/publication.asp
pls comment on it. thank a lot.
Sam Zhang, Huili Wang, Soon Eng Ong, Deen Sun and Bui Xuan Lam, Hard Yet Tough Nanocomposite coatings – Present Status and Future Trend, Plasma Processes and Polymers, 4 : 219-228 (2007)
To download, pls go to the below link.
http://www3.ntu.edu.sg/mae/Research/Programmes/Thinfilms/publication.asp
Materials — Silicon Nitride (Si3N4) Properties - Sent Using Google Toolbar
Materials — Silicon Nitride (Si3N4) Properties
Silicon Nitride, Si3N4
Silicon nitride is a man made compound synthesized through several different chemical reaction methods. Parts are pressed and sintered by well developed methods to produce a ceramic with a unique set of outstanding properties. The material is dark gray to black in color and can be polished to a very smooth reflective surface, giving parts with a striking appearance. High performance silicon nitride materials were developed for automotive engine wear parts, such as valves and cam followers and proven effective. The cost of the ceramic parts never dropped enough to make the ceramics feasible in engines and turbochargers. The very high quality bodies developed for these demanding high reliability applications are available today and can be used in many severe mechanical, thermal and wear applications.
| .Key Properties | |
 | High strength over a wide temperature range |
| High fracture toughness |
| High hardness |
| Outstanding wear resistance, both impingement and frictional modes |
| Good thermal shock resistance |
| Good chemical resistance |
| . Typical Uses | |
| Rotating bearing balls and rollers |
| Cutting tools |
| | Engine moving parts — valves, turbocharger rotors |
| Engine wear parts — cam followers, tappet shims |
| Turbine blades, vanes, buckets |
| Metal tube forming rolls and dies |
| Precision shafts and axles in high wear environments |
| Weld positioners |
General Information
The material is an electrical insulator and is not wet by nonferrous alloys. Silicon nitride is a rather expensive material, but it's performance to cost benefit ratio is excellent in the applications where it can outperform the normally utilized materials with long life and very reliable low maintenance operation.
Engineering Properties*
| Silicon Nitride, Hot Pressed | |||
| Mechanical | SI/Metric (Imperial) | SI/Metric | (Imperial) |
| Density | gm/cc (lb/ft3) | 3.29 | (205.4) |
| Porosity | % (%) | 0 | (0) |
| Color | — | black | — |
| Flexural Strength | MPa (lb/in2x103) | 830 | (120.4) |
| Elastic Modulus | GPa (lb/in2x106) | 310 | (45) |
| Shear Modulus | GPa (lb/in2x106) | — | — |
| Bulk Modulus | GPa (lb/in2x106) | — | — |
| Poisson's Ratio | — | 0.27 | (0.27) |
| Compressive Strength | MPa (lb/in2x103) | — | — |
| Hardness | Kg/mm2 | 1580 | — |
| Fracture Toughness KIC | MPa•m1/2 | 6.1 | — |
| Maximum Use Temperature (no load) | °C (°F) | 1000 | (1830) |
| Thermal | | ||
| Thermal Conductivity | W/m•°K (BTU•in/ft2•hr•°F) | 30 | (208) |
| Coefficient of Thermal Expansion | 10–6/°C (10–6/°F) | 3.3 | (1.8) |
| Specific Heat | J/Kg•°K (Btu/lb•°F) | — | — |
| Electrical | |||
| Dielectric Strength | ac-kv/mm (volts/mil) | — | — |
| Dielectric Constant | — | — | — |
| Dissipation Factor | — | — | — |
| Loss Tangent | — | — | — |
| Volume Resistivity | ohm•cm | — | — |
| Silicon Nitride, Pressureless Sintered | |||
| Mechanical | SI/Metric (Imperial) | SI/Metric | (Imperial) |
| Density | gm/cc (lb/ft3) | 3.27 | (204) |
| Porosity | % (%) | 0 | (0) |
| Color | — | black | — |
| Flexural Strength | MPa (lb/in2x103) | 689 | (100) |
| Elastic Modulus | GPa (lb/in2x106) | 310 | (45) |
| Shear Modulus | GPa (lb/in2x106) | — | — |
| Bulk Modulus | GPa (lb/in2x106) | — | — |
| Poisson's Ratio | — | 0.24 | (0.24) |
| Compressive Strength | MPa (lb/in2x103) | — | — |
| Hardness | Kg/mm2 | 1450 | — |
| Fracture Toughness KIC | MPa•m1/2 | 5.7 | — |
| Maximum Use Temperature (no load) | °C (°F) | 1000 | (1830) |
| Thermal | | ||
| Thermal Conductivity | W/m•°K (BTU•in/ft2•hr•°F) | 29 | (201) |
| Coefficient of Thermal Expansion | 10–6/°C (10–6/°F) | 3.3 | (1.8) |
| Specific Heat | J/Kg•°K (Btu/lb•°F) | — | — |
| Electrical | |||
| Dielectric Strength | ac-kv/mm (volts/mil) | — | — |
| Dielectric Constant | — | — | — |
| Dissipation Factor | — | — | — |
| Loss Tangent | — | — | — |
| Volume Resistivity | ohm•cm | — | — |
*All properties are room temperature values except as noted.
The data presented is typical of commercially available material and is offered for comparative purposes only. The information is not to be interpreted as absolute material properties nor does it constitute a representation or warranty for which we assume legal liability. User shall determine suitability of the material for the intended use and assumes all risk and liability whatsoever in connection therewith.
Silicon nitride - Wikipedia, the free encyclopedia - Sent Using Google Toolbar
Silicon nitride - Wikipedia, the free encyclopedia
Silicon nitride
From Wikipedia, the free encyclopedia
Jump to: navigation, search
| Silicon nitride | |
|---|---|
| Identifiers | |
| CAS number | [12033-89-5] |
| Properties | |
| Molecular formula | N4Si3 |
| Molar mass | 140.28 g mol-1 |
| Appearance | grey, odorless powder |
| Density | 3.44 g/cm3, solid |
| Melting point | 1900 °C, 2173 K, 3452 °F (decomposes) |
| Hazards | |
| EU classification | not listed |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
Silicon nitride (Si3N4) is a hard, solid substance, that can be obtained by direct reaction between silicon and nitrogen at high temperatures. Silicon nitride is the main component in silicon nitride ceramics, which have relatively good shock resistance compared to other ceramics.
Rollers made of silicon nitride ceramic are sometimes used in high-end skateboard bearings, due to the material's shock and heat-resistant characteristics. It is also used as an ignition source for domestic gas appliances, hot surface ignition.
In microelectronics, silicon nitride is usually formed using chemical vapor deposition (CVD) method, or one of its variants, such as plasma-enhanced chemical vapor deposition (PECVD). It is usually used either as an insulator layer to electrically isolate different structures or as an etch mask in bulk micromachining. As a passivation layer for microchips, it is superior to silicon dioxide, as it is a significantly better diffusion barrier against water molecules and sodium ions, two major sources of corrosion and instability in microelectronics. It is also used as a dielectric between polysilicon layers in capacitors in analog chips.
Bulk, monolithic silicon nitride is used as a material for cutting tools, due to its hardness, thermal stability, and resistance to wear. It is especially recommended for high speed machining of cast iron. For machining of steel, it is usually coated by titanium nitride (usually by CVD) for increased chemical resistance.
[edit] Crystal Structure
There exist 3 crystallographic structures of silicon nitride (Si3N4), designated as α, β and γ phases. The α and β phases are the most common forms of Si3N4, and can be produced under normal pressure condition. The γ phase can only be synthesized under high pressures and temperatures and has a hardness of 35 GPa[1].
See crystallographic structure of the α- and β- Si3N4 in [1] and γ phase Si3N4 in [2].
α- and β-Si3N4 have hexagonal structures, which are built up by corner-sharing SiN4 tetrahedra. They can be regarded as consisting of layers of silicon and nitrogen atoms in the sequence ABAB... or ABCDABCD... in β-Si3N4 and α-Si3N4, respectively. The AB layer is the same in the α and β phases, and the CD layer in the α phase is related to AB by a c-glide plane. The Si3N4 tetrahedra in β-Si3N4 are interconnected in such a way that tunnels are formed, running parallel! with the c axis of the unit cell. Due to the c-glide plane that relates AB to CD, the α structure contains cavities instead of tunnels. The cubic γ-Si3N4 is often designated as c modification in the literature, in analogy with the cubic modification of boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms each coordinate six nitrogen atoms octahedrally, and one silicon atom coordinates four nitrogen atoms tetrahedrally. [3]
[edit] References
- ^ "Hardness and thermal stability of cubic silicon nitride". J. Phys.: Condens. Matter 13 No. 22 (4 June 2001)
[edit] External links
Retrieved from "http://en.wikipedia.org/wiki/Silicon_nitride"
Chemical vapor infiltration - Wikipedia, the free encyclopedia
Chemical vapor infiltration - Wikipedia, the free encyclopedia: "Chemical vapor infiltration
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Chemical vapor infiltration (CVI) is a variant on Chemical Vapor Deposition (CVD). CVD implies deposition onto a surface, whereas CVI implies deposition within a body. Chemical vapor infiltration is widely used as a means of fabricating Ceramic Matrix Composites (CMC) such as alumina-alumina, in which a chemical vapor consisting of AlCl3-H2-CO2 is deposited onto porous alumina fibers or preforms. This process was designed and first experimented by Professor Roger Naslain from the University of Bordeaux 1 on SiC composites for aerospace applications."
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Chemical vapor infiltration (CVI) is a variant on Chemical Vapor Deposition (CVD). CVD implies deposition onto a surface, whereas CVI implies deposition within a body. Chemical vapor infiltration is widely used as a means of fabricating Ceramic Matrix Composites (CMC) such as alumina-alumina, in which a chemical vapor consisting of AlCl3-H2-CO2 is deposited onto porous alumina fibers or preforms. This process was designed and first experimented by Professor Roger Naslain from the University of Bordeaux 1 on SiC composites for aerospace applications."
Thursday, June 19, 2008
Hardness
Hardness
The hardness of ceramic materials is a property which is of high significance as it relates to the ability of the material to withstand penetration of the surface through a combination of brittle fracture and plastic flow.
Often, hardness is directly equated to wear resistance. This is a mistaken concept with many metallic components and is definitely an incorrect selection criterion with regards to engineering ceramic materials.
Wear behaviour of ceramic materials is complex and is dependent upon many variables, of which hardness is an important variable but not the only significant variable.
For example, in many wear environments, such as the erosive wear behaviour of oxide engineering ceramics, it is the ratio of fracture toughness to hardness which is found to be of most significance in determining the wear performance.
In many wear environments, a much “softer” material such as a zirconia can outperform “harder” materials such as aluminas or silicon carbide.
Hardness measurements in engineering ceramics are generally measured using a Vickers hardness test. In this test a pyramidal diamond indenter is pressed into a polished surface under known loading conditions and the size of the indentation is related to the hardness of the material.
It should also be noted that the hardness value quoted for any material is a function of the type of test conducted and the loading conditions employed. Lighter loads typically provide higher hardness values.
Typically in a Vickers Hardness test, the notation HV10 or HV20 relates to the applied load in Kg (in this case 10 or 20 kg respectively).
Other factors that need to be taken into account when interpreting hardness data for ceramic materials are the amount of porosity in the surface, the grain size of the microstructure and the effects of grain boundary phases.
Some typical hardness values for ceramic materials are provided below:
Material Class Vickers Hardness (HV) GPa
Glasses 5 – 10
Zirconias, Aluminium Nitrides 10 - 14
Aluminas, Silicon Nitrides 15 - 20
Silicon Carbides, Boron Carbides 20 - 30
Cubic Boron Nitride CBN 40 - 50
Diamond 60 – 70 >
Please contact our sales engineers for further advice on the hardness properties of our engineering ceramic materials and how such properties may relate to your application.
The hardness of ceramic materials is a property which is of high significance as it relates to the ability of the material to withstand penetration of the surface through a combination of brittle fracture and plastic flow.
Often, hardness is directly equated to wear resistance. This is a mistaken concept with many metallic components and is definitely an incorrect selection criterion with regards to engineering ceramic materials.
Wear behaviour of ceramic materials is complex and is dependent upon many variables, of which hardness is an important variable but not the only significant variable.
For example, in many wear environments, such as the erosive wear behaviour of oxide engineering ceramics, it is the ratio of fracture toughness to hardness which is found to be of most significance in determining the wear performance.
In many wear environments, a much “softer” material such as a zirconia can outperform “harder” materials such as aluminas or silicon carbide.
Hardness measurements in engineering ceramics are generally measured using a Vickers hardness test. In this test a pyramidal diamond indenter is pressed into a polished surface under known loading conditions and the size of the indentation is related to the hardness of the material.
It should also be noted that the hardness value quoted for any material is a function of the type of test conducted and the loading conditions employed. Lighter loads typically provide higher hardness values.
Typically in a Vickers Hardness test, the notation HV10 or HV20 relates to the applied load in Kg (in this case 10 or 20 kg respectively).
Other factors that need to be taken into account when interpreting hardness data for ceramic materials are the amount of porosity in the surface, the grain size of the microstructure and the effects of grain boundary phases.
Some typical hardness values for ceramic materials are provided below:
Material Class Vickers Hardness (HV) GPa
Glasses 5 – 10
Zirconias, Aluminium Nitrides 10 - 14
Aluminas, Silicon Nitrides 15 - 20
Silicon Carbides, Boron Carbides 20 - 30
Cubic Boron Nitride CBN 40 - 50
Diamond 60 – 70 >
Please contact our sales engineers for further advice on the hardness properties of our engineering ceramic materials and how such properties may relate to your application.
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