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Few literature had been published on the solid solubility of oxides in nitrides before 1971. Oyama and Kamigaito originally reported that Al2O3 dissolves in Si3N4 in 1971. Jack and Wilson (1972) reported on the solid solution of Si3N4 with Al2O3 (β′-Si3N4) as well as a new material having the α-Si3N4 structure formed by the reaction of LiSi2N3 with Al2O3. The term SiAlON (Si-Al-O-N) well known these days was given by Jack and Wilson and the former material is called β-SiAlON and the latter α-SiAlON.This paper reports in detail on the solid solubility of Al2O3 in Si3N4 that was reported firstly in 1971. This paper was submitted in January and published in August 1972. Jack and Wilson's paper was submitted in April and published in October 1972.In both papers, almost the same figure, which relates the lattice constants of the solid solution and Al2O3 concentration in Si3N4, was given. The following facts are reported in this paper.(1) Based from the specific gravity of Si3N4ss, the solid solution is thought to be a substitution type.(2) The solubility limit of Al2O3 in Si3N4ss is estimated to be about 67mole% at 1750°C and 78mole% at 1850°C.(3) The high-temperature oxidation resistance of Si3N4ss is excellent compared to that of Si3N4.In our opinion, this paper should be honored from the standpoint that it has contributed much to the research on SiAlON globally. Credit is due to Oyama and Kamigaito for performing pioneering work in this field.The phenomenon that nitrides dissolve oxides could not be understood at the time this paper was submitted. Incidentally, there is a story that this paper was nearly rejected by the editorial committee of Yogyo-Kyokai-Shi (Journal of the Ceramic Society of Japan).Prior to 1980, at the dawn of the research on Si3N4 ceramics, several worldwide innovative research studies were reported in the following papers; the report on the excellent mechanical properties of reaction sintered silicon nitride, densification of Si3N4 ceramics with additives by hot-pressing, discovery of solid solubility of Al2O3 in Si3N4, the report on the conventional sintering of Si3N4, gas pressure sintering of Si3N4 and the patent on effectiveness of Y2O3 as a sintering additive of Si3N4 ceramics. Finally, it is worth mentioning that Japanese researchers performed three of these six globally famous and original works.

A method of predicting the density of compound oxides was given on the basis of the density of the single oxides which can be regarded to compose the compound oxide. A compound oxide is first expressed in the form of a combination of single oxides, such as 2MgO⋅SiO2 for forsterite (Mg2SiO4), being applicable to any compound oxide. The density, Da, of the mixture of single oxides whose composition is identical to that of the compound oxide, 2MgO and SiO2, by way of example, is then calculated from the molar weight (W) and the density (d) of the component single oxides; Da=(2WMgO+WSiO2)/{2(WMgO/dMgO)+(WSiO2/dSiO2)}. Da is approximated to be the density of the compound, Dc. The deviation, (Dc-Da)/Da(=δ), was calculated for 88 popular silicates and non-silicate oxides. δ was found to be within ±0.1 for about 80% of the oxides examined. Furthermore, δ was found to be positively large for oxides with a higher density and negatively large for oxides with a lower density. The silicates having a negatively large δ have a tendency to exhibit a negative thermal expansion, and those with a positively large δ tend to have high hardness. The relationship of δ to Dc leads to the following approximations; Dc=Da {1+0.33(Da-3.1)} for silicates, and Dc=Da {1+0.11(Da-5.3)} for non-silicate oxides. Both of these empirical expressions hold within an error of less than 10% for most oxides, though a more detailed examination with much more data will be necessary. The assumed density of 2.0 for Si (F, OH)4 and Si(OH)4 results in a good approximation for the densities of (F, OH)- and (OH)-containing silicates.

We synthesized nylon 6-clay hybrid materials using four types of clay minerals, montmorillonite, saponite, hectrite, and synthetic mica. The mechanical properties of their injection molded specimens were measured according to ASTM. Nylon 6-clay hybrid using montmorillonite was superior to the other hybrids in mechanical properties. This might result from the difference in the interaction between nylon molecules and silicates in the hybrids. To clarify this hypothesis, we synthesized intercalated compounds of the clay minerals with glycine as the model of the hybrids, and analyzed the interaction using 15N cross polarization magic angle spinning (CP/MAS) NMR spectroscopy. The 15N-NMR result reveals that the positive charge density on the nitrogen of the intercalated compound based on montmorillonite was largest in all the intercalated compounds. It was suggested that montmorillonite interacted strongly with nylon 6 by ionic interaction. This ionic interaction was one of the reasons why these hybrid materials had superior mechanical properties. © 1995 John Wiley & Sons, Inc.

Nylon-6–clay hybrid (NCH) is a molecular composite of Nylon-6 and uniformly dispersed silicate monolayers of montmorillonite. In this study, orientation of montmorillonite and Nylon-6 crystallites in the NCH film was measured by x-ray diffraction and transmission electron micrography (TEM), which revealed that, the silicate layers and the Nylon-6 crystallites (γ-form) have planar orientation, independent of montmorillonite content. Based on the crystal structure model proposed by Bradbury et al., it seems that hydrogen bonded sheet plane {020} or zigzag plane of molecular backbone {110} is parallel to the film surface. In contrast, crystallites in pure Nylon-6 film are randomly oriented. The degree of orientation of Nylon-6 crystallites increases with content of montmorillonite. © 1994 John Wiley & Sons, Inc.

A polyimide hybrid with montmorillonite clay mineral has been synthesized from a dimethylacetamide (DMAC) solution of poly(amic acid) and a DMAC dispersion of montmorillonite intercalated with an ammonium salt of dodecylamine. Montmorillonite consists of stacked silicate sheets about 2000 A in length, 10 A in thickness. In this hybrid, montmorillonite is dispersed homogeneously into the polyimide matrix and oriented parallel to the film surface. Thanks to this special structure, this hybrid showed excellent gas barrier properties. Only 2 wt % addition of montmorillonite brought permeability coefficients of various gases to values less than half of those of ordinary polyimide. Furthermore, this hybrid had low thermal expansion coefficient. © 1993 John Wiley & Sons, Inc.

Various nylon 6-clay hybrids, such as molecular composites of nylon 6 and silicate layers of montmorillonite and saponite, NCHs and NCHPs, respectively, have been synthesized. Sorption of water in those hybrids was measured to estimate the resistance to water permeation. The diffusion coefficient D and the partition coefficient K were obtained from the sorption curves. The resistance to water permeation of NCH was superior to that of nylon 6 because of a decrease in D. In NCHP, saponite had a smaller effect on the increase of the resistance. The diffusion coefficients in NCH and NCHP decreased with an increase in the amount of clay minerals. It was found that those diffusion coefficients were well described by the contribution of the constrained region calculated from the storage and the loss modulus at the glass transition temperature. According to the mixing law, the following equation was obtained between the diffusion coefficient D and the fraction of the constrained region C, D = Da(1 – C)1/n, where the values of Da (diffusion coefficient in amorphous nylon 6) and n (morphology parameter) were 12.6 X 10−7cm2/s and 0.585, respectively. © 1993 John Wiley & Sons, Inc.

Nylon 6–clay hybrid is a molecular composite of nylon 6 and uniformly dispersed silicate layers of montmorillonite. One-pot synthesis of the hybrid was carried out by the following procedures. Montmorillonite was dispersed in water, and then e-caprolactam, acid (phosphoric acid, hydrochloric acid, benzenesulfonic acid, isophthalic acid, trichloroacetic acid, or acetic acid), and 6-aminocaproic acid were added to the dispersion. The mixtures were reacted at 260°C for 6 h, yielding the nylon 6–clay hybrids (1potNCHs). X-ray diffraction revealed that the silicate layers of 1potNCH by phosphoric acid were uniformly dispersed in the nylon 6 matrix. The 1potNCH had excellent mechanical properties. The strength and the modulus of the hybrid increased compared with previously reported nylon 6–clay hybrid (NCH) synthesized by montmorillonite intercalated with 12-aminolauric acid. The heat distortion temperature (HDT) of the 1potNCH was 160°C, which was 8°C higher than that of NCH. In other 1potNCHs, montmorillonite had a smaller effect on the increase of those properties, and interlayer spacing of montmorillonite was observed at ca. 20 A. © 1993 John Wiley & Sons, Inc.

Various nylon 6-clay hybrids, such as molecular composites of nylon 6 and silicate layers of montmorillonite and saponite, NCH's and NCHP's, respectively, have been synthesized. To estimate the mechanical properties of these hybrids, tensile, flexural, impact, and heat distortion tests were carried out. NCH was found superior in strength and modulus and comparable in impact strength to nylon 6. The heat distortion temperature (HDT) of NCH (montmorillonite: 4.7 wt. %) was 152 °C, which was 87 °C higher than that of nylon 6. In NCHP, saponite had a smaller effect on the increase of these mechanical properties. The modulus and HDT of NCH and NCHP increased with an increase in the amount of clay minerals. It was found that these properties were well described by the contribution of the constrained region calculated from the storage and loss modulus at the glass transition temperature. According to the mixing law on elastic modulus, the following expression was obtained between the modulus E at 120 °C and the fraction of the constrained region C, En = Ecn = C, where the values of n and Ec (modulus of the constrained region) were 0.685 and 1.02 GPa, respectively.

Natural Na-montmorillonite was cation exchanged for the ammonium cations of various ω-amino acids [H3N+(CH2)n−1 COOH, n = 2, 3, 4, 5, 6, 8, 11, 12, and 18]. X-ray diffraction (XRD) results suggested that the chain axes of ω-amino acids with a carbon number of eight or less were parallel to the silicate layers, and that the chain axes of those with a carbon number of 11 or more were slanted to the layers. The cation-exchanged montmorillonites form intercalated compounds with ∊-caprolactam at 25 °C. The montmorillonites intercalated with both ω-amino acid and ∊-caprolactam were studied by XRD measurement at room temperature and 100 °C. We propose a model where amino acid molecules were arranged perpendicular to silicate layers and ∊-caprolactam molecules filled the space between them. When the ∊-caprolactam was melted at 100 °C, the basal spacing for the montmorillonite increased, in which the carbon number exceeds 11. This phenomenon will be applicable to obtaining the nylon 6-clay hybrid, a molecular composite of nylon 6 and montmorillonite.

It was found that montmorillonite was intercalated with ϵ-caprolactam. X-ray diffraction revealed that the chain axes of the ϵ-caprolactam were parallel to the montmorillonite plates. The intercalated montmorillonite was swollen by molten ϵ-caprolactam at 200°C. ϵ-Caprolactam and 6-aminocaproic acid (accelerator) were polymerized with the intercalated montmorillonite at 260°C for 6 h, yielding a nylon 6-clay hybrid. X-ray diffraction and transmission electron micrography revealed that the silicate layers of the hybrid were uniformly dispersed in the nylon 6 matrix. Mechanical properties of the hybrid were improved. The strength and the modulus of the hybrid increased compared with the previously reported nylon 6 clay-hybrid (NCH) synthesized by montmorillonite intercalated with 12-aminolauric acid. The heat distortion temperature (HDT) of the hybrid was 164°C, which was 12°C higher than that of NCH. © 1993 John Wiley & Sons, Inc.

The understanding of the microfracture mechanism is essential for the im provement of the performance of the materials and the establishment of the quality assurance procedures. In this study, the microfracture mechanism of composite leaf springs produced from unidirectional glass fiber reinforced epoxy resin was studied using acoustic emission technique in combination with in situ failure analysis using SEM. It was found that the fracture mechanism consists of the following two steps: the breakage of in dividual fibers followed by matrix microcracking from the broken fiber tips, and the simultaneous breakage of some tens of fibers accompanied by small delamination failure from the broken tip, leading to final failure. It was found that the mechanical property of the matrix was greatly improved by modifying the epoxy resin, which results in a retarda tion of matrix microcracking from the broken fiber tips. This retardation, confirmed by the acoustic emission measurement and in situ failure analysis, can greatly improve the dura bility of the material. The microfracture mechanism of a prototype composite spring was characterized under flexural loading using the acoustic emission measurement. Based on the result, an optimum geometrical design of the spring to reduce the microfailure was ob tained. During this study, the employment of the acoustic emission technique as a quality assurance test of the spring was assessed. It was found that improperly manufactured springs generate a lot of the emission by loading to a maximum design load, while prop erly manufactured ones hardly generate the emission. It can be concluded that the acoustic emission technique is effective as a quality assurance test for the composite springs.

Compairing the literature values of fracture toughness of various materials revealed that the value of the same kind of material scatters largely, depending on the authors or measuring ways, but that the temperature dependence is very small and almost common, particularly in the range RT through 1, 200 °C, for most ceramics in spite of the large scattering in the absolute value. The temperature coefficient, (-(dKIc/dT)/KIc(RT)), is(-2. 1-1.6)10-5/K for SiC ceramics, and(0-1.3)10-4/K for Si3N4. The unexpectedly small temperature dependence was explained on the basis of the dependence of the surface free energy, rs.which was found to be approximated by the empirical formular (-(dγs/dT)/γso = 1/(2.1Tm) ; Tm is melting or sublimation point ) and that of Young's modulus, E. On this basis, the value of KIc at 1, 600 °C is expected not to be less than 70% of the value at RT, if the material is not affected by low heat resistant boundary material. Furthermore, the literature values are found to be 2 to 6 times larger than the ideal value calculated from (2γsE)1/2. This large value is related to the generation of rough fractured surface.

The microfailure behaviour of thermoplastic polyamide 6,6 composites reinforced with randomly dispersed short glass fibres was studied. Scanning electron microscopy was carried out on the surface of the composites under load to observe directly the behaviour. The microfailure proceeds following the steps (1) interfacial microfailure occurs at the fibre tips, (2) the microfailure propagates along the fibre sides, (3) plastic deformation bands of the matrix occurs from the interfacial one, (4) crack opening occurs in the band and the crack grows slowly through the band, (5) finally a catastrophic crack propagation occurs through the matrix with pulling-out fibres from the matrix. A model for the microfailure mechanism of the composites is proposed and some methods to improve the mechanical properties of the composites are discussed on the basis of the mechanism.

Iron phyllosilicates with 1:1 and 2:1 layer structures were prepared from silicic acid, ferrous sulfate and sodium hydroxide. Hydrothermal treatment at 100–200°C of a reaction mixture with an initial Fe/Si ratio of 1.5 gave the 2:1 iron phyllosilicate, whereas a Fe/Si ratio of 2.25 gave the 1:1 phyllosilicate. The 57Fe Mossbauer spectroscopy showed that 60% of the iron in the 1:1 phyllosilicate is ferrous, versus only 3% in the 2:1 phyllosilicate. The values of quadrupole coupling showed that the iron-oxygen tetrahedra and octahedra in the 2:1 phyllosilicate were more deformed than those in the 1:1 phyllosilicate.

Significance of the constitutional size in the composites having the constitution of nanometer size (Nano-Composites) was emphasized. Every Nano-Composite should have two critical values, the upper limit and the lower limit, for the dimension of the constitution to posses the distinguishable property as Nano-Composite. The critical values depend on the property expected for the composite. The values were estimated or re-viewed on various basis which are thought to be useful for each property, such as cata-lytic activity, magnetism, optical property as well as mechanical one. For examples: The range of the binding force acting across the surface of solids was estimated from the surface free energy and the ideal strength, which gives the critical value in general expression for the constitutional dimension and also for one basic aspect of catalitic activity. The values are about 7 nm(Si3N4), 4 nm(SiC), 4 nm (Al), 2 nm(Fe), 2 nm(W) and 3 nm(Pt). The value is very small for oxides, 0.5 nm(Al2O3) and 0.4 nm(MgO) probably due to screening effect on the surface. As to magnetic properties, 100 mn for super paramagnetism's occurrence and 20 nm for making the originally hard magnetic material soft one. Optically, the value is about 50 nm for reflective intex change. Mechanically, it is about 100 nm for strengthning or restricting dislocation movement. Some improved properties, which could be expected or have been realized, are described in the relation with the critical values.

Nickel and magnesium phyllosilicates with 1:1 and 2:1 layer structures were prepared from silicic acid and metal chlorides (NiCl2 or MgCl2) in water. The phyllosilicates were allowed to crystallize at room temperature or 200°C. The 1:1 and 2:1 phyllosilicates were selectively prepared by adjusting the metal ion to silicon ratio (M/Si) in the starting mixtures. The 1:1 phyllosilicate was crystallized from the starting mixture with an M/Si ratio of 1.5 and the 2:1 phyllosilicate was crystallized from the mixture with an M/Si ratio of 0.5. The increase in the OH−/M ratio in the starting mixture accelerated the crystallization to phyllosilicates. Crystallization to the phyllosilicates occurred even at room temperature, and a hydrothermal treatment at 200°C accelerated this process. The crystal size of the 1:1 phyllosilicates was larger than that of the 2:1 phyllosilicates. The nickel phyllosilicates crystallized faster than the magnesium phyllosilicates. These results can be explained by assuming successive c...

Etude theorique de la resistance a haute temperature pour des materiaux covalents (Si 3 N 4 ) ou ioniques (magnesie, alumine, zircone)

Swelling behaviour of acrylonitrile-butadiene copolymer rubber vulcanizates immersed in a nonprotonic solvent was studied by real-time pulsed nuclear magnetic resonance (n.m.r.) measurements. The temporal change of the proton spin-spin relaxation time, T 2 , during the swelling process was obtained. The T 2 signal for the rubber vulcanizates was resolved into two exponentially decaying components (short T 2 and long T 2 ). The short T 2 component is assigned to the constrained regions in the rubber matrix, which may be mainly located around the crosslinks, and the long T 2 component to the regions lying outside the constraints. It was suggested that the decreased change of the fraction of the short T 2 component by swelling is closely connected with the enhanced molecular mobility of the network chains between the adjacent crosslinks through the diffusion of the solvent. The restricted swelling behaviour of the carbon black-filled rubber vulcanizates was interpreted mainly in terms of the constrained molecular motions of the network chains through the rubber-filler interactions and spatial effects of the filler particles. It becomes clear that the real-time pulsed n.m.r. measurements complement the results of the macroscopic swelling measurements for the rubber vulcanizates with more detailed information on the molecular interactions between the rubber and solvent molecules.

Originally incompatible blends of SAN 30% and PC 70% were extruded with extremely high shear rate up to 107 s-1 as a typical example of the blends. The.blends are of binary systems microscopically in the first run of extruding, where SAN is present as small spherical particles in PC matrix. The apparent volume fraction of the spherical SAN estimated from the microscopic photographs decreases with the shear rate. The fraction is decreased also with the repeated runs. The blend appears uniform or structureless at the fifth run. Dynamic loss tangent gives two peaks corresponding to T ?? of SAN and PC, respectively. The latter shifts to lower temperatures with the number of extruding run. It is considered that some of SAN is mixed with PC in a compatible form. The pulsed NMR analysis supports the conclusion.

The critical grain size, below which the properties of the composites could be much different from those of the conventional composites, was estimated on the basis of the ideal strength and the specific surface energy. It is about 2nm-4nm for normal metal (Fe, Co), less than 1nm for oxides (Al2O3, MgO), and about 10nm for Si3N4, which suggests Si3N4 is one of the most advantageous materials for Nanometer Composites.

Ideal Strength, aid as a function of temperature was found to be approximated by the following formula:σid≥σid=∫TxT3αE/(1-2μ)dT=3αE(Tx-T)/(1-2μ)where Tx stands for the minimum value of transformation points (melting, sublimation, solid to solid, and brittle to ductile), and α, E, μ respectively for the coefficient of linear thermal expansion, Young's modulus and Poisson's ratio. The formula's error is less than 20%, expressed in the term of error compared with whisker's strength at RT. It was also compared with literature data on high temperature strength of sapphire monofilament, which proved the compatibility of the formula.σid is estimated as 9 GPa for SiC and 3.5 GPa for Si3N4 at 1, 400°C, 1 GPa at 2, 200°C for SiC, and 1 GPa at 1, 700°C for Si3N4. These values prove the usefulness of the materials as high temperature gas turbine components. The formula tells also us that the ideal strength can be well approximated by a straight line regardless of material.The Young's modulus plotted against temperature can be converted to Young's modulus plotted against strain, e, by using e=3∫α/(1-2μ)dT, which can not be given directly from experimental measurement due to the occurrence of fracture in the material. The tangent of the curve for MgO was proved to agree well with the value given by a classical solid state theory. The range of binding force acting across material surface was estimated by using the ideal strength, giving 0.5-1 nm for SiC and Si3N4 and 0.1-0.5 nm for MgO and Al2O3. The allowable atomic distance difference between neighboring layerd material in coherently multilayered films, which has no defect was also estimated to be less than 3% from the ideal fracture strain.

Bilayer films of Au (target atom)/α-SiC (substrate) were irradiated with 2MeV electrons in an ultra-high voltage electron microscope. By irradiation, gold atoms in the upper layer were implanted into the SiC substrate. Changes in the microstructures and bonding state associated with the implantation were studied by ultra-high voltage electron microscopy and scanning Auger valence electron spectroscopy, respectively. The results obtained are as follows; (1) Irradiation with 2MeV electrons first induces a crystalline-to-amorphous transition in α-SiC. (2) Gold atoms which have been knocked-off from the gold layer by the collision with 2MeV electrons are recoil-implanted into the resultant amorphous SiC. (3) The implanted gold makes preferential bonding with silicon having dangling bonds, and new bonding states are formed between them. (4) During continued irradiation, the gold atoms repeat displacement towards the beam direction, which is induced by the collision with electrons and subsequent bonding with silicon atoms having dangling bonds. The repetition results in the deep implantation of gold into the SiC substrate.

The possibility of a thermal proof test with thermal stress of ceramics was examined experimentally. For this purpose, the bending strength and the failure temperature difference for quenching soda-lime-silica-glass into water and quench-oil were measured before and after the thermal proof test by quenching the glass into water, ethyl alcohol, silicon oil and quench-oil. The thermal proof test by water, ethyl alcohol and silicon oil quenching modified the distribution of the failure temperature difference, but it did not modify the distribution of the bending strength at all. It was suggested that the thermal proof test was able to assure the minimum failure temperature difference or minimum thermal fatigue life of ceramics.

Nickel and magnesium phyllosilicates with 1:1 and 2:1 layer structures were prepared from silicic acid and metal chlorides (NiCl2 or MgCl2) in water. The phyllosilicates were allowed to crystallize at room temperature or 200°C. The 1:1 and 2:1 phyllosilicates were selectively prepared by adjusting the metal ion to silicon ratio (M/Si) in the starting mixtures. The 1:1 phyllosilicate was crystallized from the starting mixture with an M/Si ratio of 1.5 and the 2:1 phyllosilicate was crystallized from the mixture with an M/Si ratio of 0.5. The increase in the OH−/M ratio in the starting mixture accelerated the crystallization to phyllosilicates. Crystallization to the phyllosilicates occurred even at room temperature, and a hydrothermal treatment at 200°C accelerated this process. The crystal size of the 1:1 phyllosilicates was larger than that of the 2:1 phyllosilicates. The nickel phyllosilicates crystallized faster than the magnesium phyllosilicates. These results can be explained by assuming successive c...

The effects of ion implantation on microtexture of vapordeposited carbon film were studied by Raman, XRD, TEM and sheet resistivity measurements. Growth of graphitemicrocrystals in the film was found when the film was implanted at the temperature above about 500 K. while graphite-sheet in the as-deposited film was distorted when it was implanted at the temperature below 300 K. The critical temperature for the ion beam annealing was estimated to be about 350 K. Ion implantation also caused the increase of the adhesion strength of the carbon film to a substrate.

On discute de la regle empirique voulant que la resistance a la rupture d'une ceramique soit plus elevee quand le materiau a un point de fusion ou de sublimation plus eleve

The mechanism of copolymerization of silicic acid and metal ions was found to depend on the magnitude of the hydrolysis constant of the aqua-metal cations. It was also demonstrated that the pH of the solution is the major factor governing the Si/metal ion ratios in the solid phases.

C-cut sapphire was implanted with 400 keV Co+ ions to doses of 3 × 1017/cm2 and 5 × 1017/cm2 and then annealed in air sequentially at 1273, 1373, and 1473 K. Before and after the annealing, the implanted surfaces were examined by RBS and XRD methods. A nearly homogeneous layer of 350 nm thickness was formed on the surface when sapphire was implanted to a dose of 5 × 1017/cm2 and then annealed at 1473 K. For sapphire implanted to a dose of 3 × 1017/cm2 and then annealed at 1473 K, the implanted layer had a complex structure: the top surface layer of 70 nm thickness was α-alumina with Co3+ ions at the substitutional sites and the near-surface layer (70 nm–300 nm) was a mixed phase of CoAl2O4 and α-alumina.

SiC ceramics, coated with a niobium metal film (Nb-SiC) with and without subsequent Ar + ion irradiation, were subjected to a pin-on-disk friction and wear test in an ambient atmosphere with a diamond pin for 40 h. The friction coefficient between the SiC disk and a diamond pin was about 0.1. Niobium film deposition decreased the friction coefficient to about 0.04 with a normal load of 9.8 N. The wear of SiC was also reduced to one-eighth by the niobium deposition. The Ar + -ion-irradiated Nb-SiC had very high wear resistance; effectively no wear was detected in the samples irradiated to doses over 5 × 10 15 ions cm −2 .

The effects of ion implantation on the mechanical properties are reviewed for alumina, silicon carbide and fully-stabilized zirconia. It is demonstrated that by ion implantation, (a) hardness of the near surface layer is varied over a wide range, depending on ion dose and implantation temperature, (b) significant increases in the flexural strength are observed, (c) the resistivity against the crack initiation and propagation associated with Vickers indentation is increased, (d) the resistivity against lateral and radial crackings associated with scratching by a loaded diamond stylus is increased, (e) a reduction in the friction coefficient from 0.6 to 0.15 is observed for polycrystalline silicon carbide in sliding contact with a steel. These results are discussed in terms of microstructural changes, surface compression stress and amorphized surface layer of an increased plasticity.

By introduction of ionicity into Lindemann's one-phase theory on melting temperature, a semi-empirical formula for melting temperature of simple compounds, $$T_m \doteqdot {{f_i C_i } \mathord{\left/ {\vphantom {{f_i C_i } {r_{AB} }}} \right. \kern-\nulldelimiterspace} {r_{AB} }} + {{f_c C_c } \mathord{\left/ {\vphantom {{f_c C_c } {r_{AB^{2.5} } }}} \right. \kern-\nulldelimiterspace} {r_{AB^{2.5} } }}$$ has been given, whereTm,fi,fc andrAB stand for melting temperature, ionicity, covalency and bonding distance, respectively.Ci andCc are numerical factors which are common to a group of compounds of similar character (crystal structure, valency, etc). Application of Sanderson's ionicity scale to the formula shows good agreement with the observed melting temperatures of alkali halides. A good agreement is also obtained for single oxides. From application of the formula to alkali halides, it is suggested that an anion plays an important role in melting. Similarity ofCi andCc in alkali halides of NaCl structure and MO-type oxides of the same structure suggests that melting occurs at almost the same critical position in Lindemann's model for melting in both types of compound.

In the present study, we investigated deposition of diamond films on both Si substrates pre-treated with diamond powder by an ultrasonic vibrator and also further ion-implanted. The pre-treatment with diamond powders increased a density of diamond nucleation on Si substrate by five-order of magnitude against to the untreated substrate. 280keV Ar+ ion implantation at 90K to the pre-treated substrate significantly reduced the density of the diamond nucleation while the implantation at 773K scarcely affected the density. It is proposed that healing of micro-flaws, which are thought to work as the nucleation sites, is an important mechanism to reduce the diamond nucleation density by ion implantation.

Influence of fiber diameter on the mechanical properties of short fiber composite was studied by using smaller diameter fibers than conventional ones. Strength and toughness of the composite reinforced with the small diameter fibers were improved, compared to those of the composite reinforced with the conventional ones, except for extremely small diameter fibers. Thus, there exists the maximum value for the strength and toughness for the optimum fiber diameter. This result indicates that there is an optimum condition for the reinforcing effectiveness by the small diameter fibers. In order to analyze the reinforc ing mechanism by the small diameter fibers, fracture mechanism of the composite was studied by an acoustic emission analysis, in-situ SEM observation of failure process, and observation of plastic deformation of the matrix. As a result, initiation and propagation of microcracks occurring at fiber/matrix interface were found to be strongly suppressed by using the small diameter fibers, compared with those in the conventional composite. A model for explaining the reinforcing mechanism by the small diameter fibers was pro posed, which can well explain the presence of the optimum fiber diameter, resulting in the highest reinforcing effectiveness for the composite.

Masao Kohzaki, Shoji Noda. Haruo Doi and Osami Kamigaito : Improvement of The Tribological Properties of Ceramics by Si Film Deposition and Ion Irradiation.We studied the tribological properties of surface modified SiC ceramics with a pin-on-disk friction and wear tester in an ambient atmosphere without oil lubrication. The friction coefficient between Si film deposited SiC(Si/SiC) and a diamond pin was about 0.05, which was smaller than one half of that between SiC and a diamond pin. The low friction state of Si/SiC lasted for 40 hours when the Si/SiC was irradiated with Ar+ ions. Ar+ ion irradiation was also effective for reducing the wear. Effectively no wear was detected in Si/SiC irradiated to the dose over 5 × 1015 ions/cm2.

機械的応力存在下における焼結ムライトの水中急冷による熱疲労寿命及び曲げ破壊強度を測定した. これらの実験結果を基にして、 先に導いた “機械的応力存在下でのセラミックスの熱疲労寿命予測式” の妥当性について議論した.熱疲労寿命の実測値は寿命予測式によく合い、 実測値から求めたn値 (V=AKIn, V: き裂伝ぱ速度, KI: 応力拡大係数) は, 曲げ破壊強度の応力印加速度依存性から求めた値とほぼ一致した. これらから, 熱疲労寿命予測式の妥当性を確認した.熱疲労試験での破面は曲げ破壊試験での破面とは異なり滑らかであった. この理由は, き裂の伝ぱ速度の差によると考えられた.

Effets d'une irradiation par l'ion Ar + sur la durabilite du saphir revetu d'une couche mince de Zr ou Ag