Nano-indentation tests with a Berkovich diamond indenter are conducted for examining the gelling process of polyphenylsilsesquioxane hybrid films. A mathematical algorithm is formulated for quantitatively analyzing the indentation-generated stress-relaxation data. The viscoelastic functions of the films are, then, correlated to the microstructural evolution in the gelling process.

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Mechanical properties of thin films are, in principle, determined from nanoindentation tests. However, these quantities may be seriously affected by many factors, such as the tip shape of indenter, frame compliance of the nanoindenter used, mechanical properties of the substrate and surface roughness of the film. In this study, these factors are critically examined in the analysis of the load-displacement (P-h) curves to reveal the mechanical properties of commercial diamond-like-carbon (DLC) films about 1 micron thick. The effect of the substrate is also examined with the aid of computer calculation of indentation-induced deformations.

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The mechanical properties of thin films of ceramic materials are useful in the packaging of micro electro mechanical systems (MEMS). For example silicon nitride microclips 3 micrometer thick have been used in silicon optical benches to hold fibres in silicon v-grooves [1]. This paper describes work to enlarge the set of ceramic materials available for MEMS applications. Focused laser micromachining in combination with wet etching of the substrate is used to prototype structures such as microbeams for testing with a scanning profiler to evaluate the properties of new materials. For example 5 micrometer thick chemical vapour deposited silicon carbide has a Youngs modulus 360 +/- 50 GPa, indicating that it is a promising material for mechanical and packaging applications.[1] R. M. Bostock, et.al., J. Micromechanics Microengineering 8, 343 (1998).

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The tensile strength of insulating thin films was measured by a new tensile testing method using an electrostatic grip. Two thin film tensile testers both in the air and in vacuum were realized using this method. These testers are applied for a tensile test of plasma enhanced CVD SiO₂ thin films. The tensile strength and the fracture toughness were measured both in vacuum and in the air, and these results were compared and discussed. Tensile strength was strongly affected by the testing environment, and these effects must be mainly due to water in the air.

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Zirconia (ZrO₂) thin films were prepared at low temperature by ECR (electron cyclotron resonance) plasma MOCVD. Zr-hexafluoroacetylacetonato [Zr(Hfac)₄] was used as a CVD source. Cubic and tetragonal zirconia films were obtained cubic and monoclinic zirconia films were obtained below T_sub=473 K. Crystallized zirconia film was prepared with no heating. The ECR plasma was significantly effective to prepare crystallized zirconia films at low temperature. The deposition rate was 10 nm/min.

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Ti-Si-N nanocomposite coatings with Si content between 0 and 13.5 at% were deposited by a combined DC/RF unbalanced reactive magnetron sputtering process. Super high hardness (>40 GPa) was measured in the coatings with silicon content at about 8 at%. The RF power applied to the Si targets was found to have a significant influence on the microstructure and mechanical properties of the coatings. Ultra-high erosion resistance was observed in a micro sand-blasting test using 17 micron alumina particles, which demonstrated high potential for applications in aircraft compressor blades and other abrasive wear components.

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We proposed new oxide compounds with low thermal conductivity and layer structure as candidate materials for Thermal Barrier Coating. In order to assuage the heat stress of TBC films, we sought the possibility of controlling the preferred orientation structure of these compounds by plasma spraying.

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Polysilazane thin films were exposed to various kinds of vapors, being converted into silica thin films. The effect of the kinds of vapors on the conversion was studied, and also the properties of the resultant films were evaluated.

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A novel aluminum nitride precursor, poly(allyl iminoalane-co-ethyl iminoalane) was prepared by a reaction between lithium aluminum hydride, allylamine hydrochloride and ethylamine hydrochloride, and was characterized by infrared (IR), nuclear magnetic resonance (NMR) and thermogravimetric (TG) analyses. The IR and ²⁷Al NMR spectra of the precursor indicated that the precursor contained four-coordinated HAlN₃ environments, suggesting the presence of cage-type structures as main components. TG analysis shows that a ceramic yield of the precursor up to 1000 degree under Ar atmosphere was about 72 mass%, which exceeded the ceramic yield of poly(ethyliminoalane), about 61 mass%. The high yield could be ascribed to the presence of the carbon-carbon double bonds in the precursor.

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Polyaluminosilazane (PAS) was prepared from cage-type poly(ethyliminoalane), (HAlNEt)_n, and perhydropolysilazane (PHPS) as a precursor for SiC/AlN ceramics composite. The precursor was characterized by IR and NMR, which indicated no noticeable progress of polymerization. Solid-state NMR spectra and XRD patterns of pyrolyzed residue from PAS showed that PAS was converted into SiC/AlN ceramics composite upon heating at 1600 degree under Ar. Therefore, PAS was present as a blended polymer and was converted into a ceramic residue during pyrolysis. The ceramic yield of PAS up to 1000 degree was determined by TG operated under an Ar atmosphere to be higher than those of (HAlNEt)_n and PHPS.

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In this study, spherical carbon black in a nanometer scale diameter was dispersed in resin- silicate hybrid precursor to obtain C-SiO2 hybrids with uniquely modulated nano structures after 1273K pyrolysis. They were pyrolyzed at 1838K in an Ar gas flow to be converted to SiC-C nano sphere. 973K heat treatment is successively performed to eliminate the residual carbon. Effect of the preparation conditions on the morphology of the resulting SiC and the conversion rate were investigated.

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Bridgestone Corporation has established a unique mass production process of pure (6N) silicon carbide (SiC) powder (precursor method). We also invented a new sintering method for obtaining ultra-high purity SiC sintered body using non-metallic sintering agent. We will describe outline of the process, characteristics of the SiC products and some applications. The products has already been widely accepted by major semiconductor device makers and tool makers. We will also touch upon the development of single crystal silicon carbide wafer of extremely high purity.

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Preparation and pyrolysis of p-diethynylbenzene-modified polymethylsilane was studied. Polymethylsilane (PMS) was modified by platinum-catalyzed hydrosilylation of PMS with p-diethynylbenzene at room temperature and characterized by spectroscopic analyses (infrared (IR) and ¹H, ¹³C and ²⁹Si nuclear magnetic resonance (NMR)), and thermogravimetric(TG) analysis. IR and ¹H, ¹³C and ²⁹Si NMR suggested that Si-H groups were reacted at two terminal groups or one terminal group of p-diethynylbenzene during hydrosilylation. TG analysis up to 1000 degree under an Ar atmosphere revealed that cross-linked PMS showed a ceramic yield of 63 mass%, while PMS showed a much lower ceramic yield (28 mass%). The drastic increase in a ceramic yield could be ascribed to a crosslinking reaction, which possibly involved the C=C groups in cross-linked PMS. The ceramic residues of modified PMS were characterized by IR spectroscopy, solid-state ¹³C and ²⁹Si NMR spectroscopies with magic angle spinning technique (solid-state ¹³C and ²⁹Si MAS NMR) and X-ray diffraction (XRD). IR and solid-state ¹³C and ²⁹Si MAS NMR spectroscopies showed transformation of a polysilane skeleton into a carbosilane-type skeleton via the Kumada rearrangement in the temperature range from 400 to 600 degree. The mineralization process significantly proceeded in the temperature range from 600 to 1000 degree. Crystallization of SiC occurres above 1200 degree.

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Aiming at development of hydrogen separation membranes, optimum conditions for preparation of SiC-based membranes from polycarbosilane, and effects of a cross-linking agent (p-diethynylbenzene) and a pore-making agent (polystyrene) on the membrane performance were investigated. It was shown from derivative thermogravimetric curves that DTG peak of these starting materials agreed with the pyrolysis temperature at which highest SF6 permeance and H2 and N2 permeance was obtained, indicating that volatilization species affect the pore size distribution of membranes.

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We found that PCS fiber as a SiC precursor could be cured by EB oxidation only surface part of the fiber, and developed the hollowing process after curing of the PCS fiber by extracting of the un-crosslinked core. The SiC micro tube has high corrosion resistance in addition to high strength and heat resistance, therefore it could be applied to the ceramic filter, adsorbent, catalyst and micro-reactor.

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Ceramics are often prepared with surface layers of different composition from the bulk, in order to impart a specific functionality to the surface or to act as a protective layer for the bulk material. Here I describe a general process by which functional surface layers with a nanometer-scale compositional gradient can be readily formed during the production of bulk ceramic components. The basis of this approach is to incorporate selected low-molecular-mass additives into either the precursor polymer from which the ceramic forms, or the binder polymer used to prepare bulk components from ceramic powders. Thermal treatment of the resulting bodies leads to controlled phase separation ('bleed out') of the additives, analogous to the normally undesirable outward loss of low-molecular-mass components from some plastics; subsequent calcination stabilizes the compositionally changed surface region, generating a functional surface layer. Using this technology, we developed a strong photocatalytic fiber (TiO2-covered SiO2 fiber), which effectively decomposed many types of organic chemicals and bacteria into CO2 and water by irradiation of UV light. Furthermore, we performed some field tests using a circulation purifier with a module composed of the cone-shaped felt material of our new fiber.

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The syntheses and properties of polysilzanes as a precursor for silicon nitride was investigated by the ammonolysis of isocyanatosilanes. Highly hydrolyzable polysilazanes were synthesized by the reaction of isocyanatosilanes with ammonia with the production of ammonium cyanate as a byproduct. Silicon nitride fibers were produced by the sintering the precursor fibers, prepared by melt spinning of polysilazanes, under ammonia atmosphere.

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Atomic structures of amorphous silicon nitride based ceramics were simulated by the molecular dynamics method. Effects of carbon and/or boron addition on diffusion behavior in the amorphous state were investigated. Based on the results obtained, the observed excellent thermal stability of the amorphous state was discussed.

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The pyrolysis process of cage-type poly(ethyliminoalane) was explored by analyzing evolved gases and pyrolyzed products. Poly(ethyliminoalane) was converted into a cross-linked structure below 300 degree. One possible mechanism involves the formation of ethylene and ethylamine via heterolytic Al-N bond cleavage and attack of terminal nitrogen on an ethyl group, and the other is due to cross-linking involving cage opening without gas evolution. In the temperature range of 300 - 650 degree, the evolution of ethylene, ethane, and methane were observed. The loss of AlH groups up to 400 degree appears to result in the conversion of HAlN₃ environment into cross-linked environments, such as an AlN₄ environment.

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Most of materilas have showed generally a positive thermal expansion, but a negative thermal expansion has been observed in the limited temperature range for some materials such as Cu2O, SiO2,etc. In this lecture, crystal structure and thermal properties of cubic ZrW2O8 system having a negative thermal expansion in the wide temperature range will be focussed and discussed.

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We have recently reported that it was possible to control the coefficient of thermal expansion (CTE) in HfW₂O₈-MgWO₄ co-sintered ceramic system and a newly tungstate, (HfMg)(WO₄)₃, was synthesized in that system.
In xHfW₂O₈–(1-x) MgWO₄ ceramic system, the thermal behavior of each component was observed carefully with X-ray diffraction data under any temperature.
Furthermore, a single-phase tungstate, (HfMg)(WO₄)₃ were synthesized and the thermal expansion in (HfMg)(WO₄)₃ was measured using thermal mechanical analysis.
From these data, we determined a newly tungstate, (HfMg)(WO₄)₃ had a negative CTE, about -2ppm/degree, from room temperature to 800 degree.

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Catalytic chemical vapor deposition is one of the promising methods for thin-film formation on meter-size large-area substrate without plasma excitation at high deposition rates. It is also expected that consumption of energy for film formation is lowered since the efficiency for gas utilization is high. Although Cat-CVD method has been known to present high-quality films at temperatures below about 300C, recently, dense films are obtained at only 100C or at even room temperature. Therefore Cat-CVD method has attracted much attention as coating technique for enhancing the value of plastic films or fiber. Now Cat-CVD method is applied to not only semiconductor or flat-panel display industries but also chemical, ceramics and precise machine industries. In this talk both fundamentals and applications of Cat-CVD technologies are introduced including recent situations of industries.

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