The effect of calcium cyanamide (CaCN₂) addition on the sintering of AlN ceramics was investigated. Pressureless sintering was carried out with 0 to 3.0mass% CaCN₂ addition, and densified sintered specimens (relative density>97.0%) were obtained using 1.0 to 2.0mass% CaCN₂ addition depending on sintering temperature and time. All of the sintered samples exclusively belong to the same AlN phase, and no other phases were found in the X-ray diffraction (XRD) patterns. A large fraction of intergranular fracture was found in the AlN samples sintered without and with CaCN₂ additive in the scanning electron microscope (SEM) observations. The characterization of the ultrafine AlN powders sintered with CaCN₂ additive was preformed with a microstructural analysis using a transmission electron microscope (TEM) attached with an energy-dispersive X-ray analyzer (EDX) and electron diffraction (ED). Both microstructural results and sintering behavior in the AlN-CaCN₂ system arise from the interaction between the Al₂O₃ surface covering the ultrafine AlN particles and the CaCN₂ additive. Most oxygen impurity are removed from AlN as CO or CO₂ gas and the residual oxygen impurity reacts to form the 3CaO⋅Al₂O₃ phase, which is found at the grain boundaries.

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Mechanistic study of solid-state reactions occurring in a mixtured body of kaolinite and Fe₂O₃ heated in a reducing atmosphere was performed.
In the case of oxidizing firing, mullite formation started at 1300°C, whereas in the case of reducing firing, mullite, hercynite and quartz solid solution were formed at 950°C. Concentration analyses by ESCA combined with the Ar etching treatment of Al, Si and Fe in the surface layer of the mixture body fired at 1100°C in the reducing atmosphere revealed that migration of Al toward FeO grains occurred. Also taking thermodynamic calculation also into consideration, following reaction schemes for the formation of quartz solid solution and mullite were postulated.
(1) FeO reacted with Al₂O₃ in both the Al₂O₃-rich spinel phase and the SiO₂-rich amorphous phase resulting from the phase separation of metakaolin, and formed hercynite.
(2) The Al extraction ability combined with the mineralizing action of FeO caused the crystallization of quartz solid solution from the SiO₂-rich phase. Mullite formation from the spinel phase (SiO₂⋅6Al₂O₃) was also due to Al extraction by FeO.

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Bubble-containing silica glasses were fabricated by sintering amorphous silica powders with small amount of silicon nitride powders. Sintering was performed at 1800°C in N₂ gas atmosphere. It was found that the addition of Si₃N₄ is effective for forming bubbles. By controlling the Si₃N₄ content, various types of bubble-containing silica glasses, such as the so-called the opaque silica glass and the foamed silica glass, could be obtained. Addition of 0.004mol% Si₃N₄ produced highly opaque silica glasses containing a large number of small bubbles, while 0.431mol% Si₃N₄ resulted in low-density foamed silica glasses containing large 1mm-sized bubbles. Wide variations of bubble size and density were observed on these glasses. Thermal conductivities were estimated and compared with several literature values. The relation between thermal conductivity and bubble density was discussed based on a model simulation.

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The crystallographic orientations of individual grains in translucent alumina were successfully determined using polarized Raman spectroscopy. The following results were obtained.
(1) Raman tensor elements of sapphire, a and b, belonging to the A_1g mode were obtained and it was revealed that a<<b for 645cm^-1 line. Consequently, the polarized Raman intensity is given by cosφ.
(2) Projection angles of the c-axis of individual alumina grains were determined by the polarized Raman peak of 645cm^-1 line which belongs to the A_1g mode. In the special case of constant Raman intensity for sample rotation, the c-axis was perpendicular to the measured plane.
(3) Adjoining grains in translucent alumina were found to have different crystal orientations. These were experimentally determined in this study.

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Perovskite-type LaFeO₃ powders were prepared by thermal decomposition of a heteronuclear complex, La [Fe(CN)₆]⋅4H₂O at 700°C. Powders were deposited as thick films on alumina substrates with comb-type Au electrodes and then sintered in nitrogen or air atmosphere. The surface chemical analysis was performed using X-ray photoelectron spectroscopy (XPS). The O1s XPS line was separated in two peaks attributed to adsorbed oxygen (O_ad) and oxygen in the lattice (O_lattice) on the surface. The ratio [O_ad+O_lattice]/[La+Fe] was uninfluenced by the ambient during sintering. The [O_lattice]/[La+Fe] atomic ratio decreased and [O_ad]/[La+Fe] value increased upon sintering in N₂ atmosphere, as compared with samples sintered in air. It was argued that O_ad sites act as adsorption sites for nitrogen dioxide. The increase in O_ad sites is effective for enhancing electrical conductivity in nitrogen dioxide.

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The uptake of various cations by imperfectly ordered KAlSiO₄ was investigated. The KAlSiO₄ was prepared by solid-state reaction of kaolinite with K₂CO₃ at 550°C for 24h. Uptake experiments were performed at 60°C using 0.5g of the KAlSiO₄ and 50ml of solution containing 10^-3-10^-1M of each cation, with and without 0.5M NaCl buffer. The cations were alkali (Li⁺ and Na⁺), alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺) and transition metal cations (Ni²⁺, Co²⁺, Cu²⁺ and Zn²⁺). From the comparison of uptakes of various cations by KAlSiO₄ and zeolite Na-A, it was found that the ratio of uptake by both exchange materials increased with decreasing ionic radius of the exchanging cations, the KAlSiO₄ showing higher uptake of Ni²⁺ than zeolite Na-A. This trend became more distinct for the uptake of Ni²⁺ in simulated acid waste solution and groundwater because of the suppressing effects by co-existing alkali and alkaline earth cations especially for zeolite Na-A.

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This paper discusses the influences of various types of inorganic salts on the fluidity of inorganic particle suspensions with comb-type polymer. By addition of anion which form insoluble salt with Ca²⁺, the fluidity of suspension with polymer and the amounts of polymer adsorbed on CaCO₃ were remarkably reduced. It is thought that the adsorption of polymer is related to the concentration of Ca²⁺ in the liquid phase. When the concentration of Ca²⁺ in the liquid phase is reduced, the adsorbed amount of Ca²⁺ on the surface of CaCO₃ decreases. By addition of soluble Ca salts or CaO, the fluidity of suspension with polymer and inorganic electrolytes containing anions which form insoluble salt with Ca²⁺ could be greatly improved, up to almost the same value of a suspension without inorganic electrolytes. This is because almost all the anions precipitated as insoluble Ca salts or the concentration of Ca²⁺ or cations such as Al³⁺ in the liquid phase increased and, as a result, the adsorption site of polymer increased.

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The syntheses of octacalcium phospates (OCPs) containing dicarboxylic acids, Ca₈(HPO₄)_2-z(RC₂O₄)_z(PO₄)₄⋅mH₂O, were attempted. The effects of the side groups on crystal growth of these compounds were investigated. OCPs containing dicarboxylic acid were obtained from tricalcium phosphate (α-Ca₃(PO₄)₂) in acetic acid/sodium acetate buffer solution by hydrolysis. As for dicarboxylic acids, succinic acid, methyl-succinic acid, mercaptosuccinic acid, DL-malic acid and L-aspartic acid were used. OCPs containing dicarboxylic acid obtained in this process were determined by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectrometry, thermogravimetric analyses and chemical analyses. All of these identified compounds were structurally similar to octacalcium phosphate, Ca₈(HPO₄)₂(PO₄)₄⋅5H₂O, with expanded a-axis unit-cell dimensions. Phosphate ions in “hydrated layer” of OCP were replaced by succinate ions with about 94% of theoretical replacement value. The percentage of replacement for OCPs containing dicarboxylic acid having the side groups were range 24 and 59%. Namely, the polarity and the size of the side groups effected on the incorporation of dicarboxylate ions into OCP interlamellar and the crystal growth.

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Development of porous hydroxyapatite is important for organic/inorganic composite biomaterials. In developing new biomaterials, it is fundamental to design and control the porosity characteristics. This study attempted to control the pore characteristics of porous hydroxyapatite using different sintering processes and temperatures. Porous hydroxyapatite was fabricated by the pressureless-sintering method and the capsule-free hot isostatic press (HIP) sintering method using two kinds of starting hydroxyapatite powder, spherical, and whisker-like powder. The pore size distribution in porous hydroxyapatite prepared from starting spherical and whisker powders depended on the sintering temperature. The higher the sintering temperature, the larger the pore diameter. The pore diameter in hydroxyapatite prepared by capsule-free HIPing was larger than that by pressureless-sintering. According to this understanding, various porous hydroxyapatites could be designed and their porosity characteristics controlled.

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Effect of particle size of quartz and feldspar on the densification and bending strength of porcelain bodies in the quartz-feldspar-kaolin system was investigated. Measurements of bulk density, 3-point bending strength and X-ray diffraction, and the observation of microstructures were performed. Quartz powders of an average particle size in the range of 1.2-8μm and feldspar of 1.2-4μm were prepared using a dry pulverizing machine attaching an air classifier. Raw materials of quartz, feldspar and kaolin were mixed in a mass ratio of 30:31:39 and the slip-cast specimens were fired at temperatures from 1100 to 1350°C. Densification temperature lowered with decreasing the particle size of quartz and feldspar powders. When quartz and feldspar powders of 1.2μm in particle size were used, porcelain bodies fully sintered at about 1175°C. Bending strength of the bodies increased with decreasing the particle size of quartz and feldspar powders. The maximum bending strength of 176MPa was obtained when 1.2μm powder of both quartz and feldspar were used. The particle size of quartz powder has a larger effect on the bending strength than that of feldspar powder.

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The formation retes of monoclinic hydrous-zirconia particles produced by the hydrolysis of ZrOCl₂ solutions with and without an addition of aqueous ammonia or anion-exchange treatment were measured to clarify the effects of pH on the nucleation and crystal growth processes of hydrous zirconia. At pH ranges below 1.2, the crystal growth rate of primary particles of hydrous-zirconia increased monotonously with increasing pH, but the nucleation rate was independent of pH. When the pH was kept at around neutrality, amorphous hydroxide formed. The tendency of crystal growth rate of primary particles to increase at low pH can be explained by the blocking action for crystal growth of Cl^- ions attracted on the particle surface, through the formation of an electric double layer.

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Substrates for polycrystalline silicon thin film solar cells are primarily required to match the thermal expansion of silicon. Ceramics with the same thermal expansion as silicon were synthesized from zircon, which has a higher thermal expansion than silicon, cordierite, which has a lower thermal expansion than silicon, and a glass phase. Zircon, SiO₂, Al₂O₃, MgO and CaO were used as raw materials to synthesize these ceramics. The sintered ceramics had a thermal expansion matching that of silicon and contained no alkali metal oxides. The surface of the sintered bodies was self-glazed using one of the formulations.

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Adhesion and crack formation of coating films prepared from methyltriethoxysilane (MTES) on stainless steel sheets (SUS) after a thermal shock test were studied and their relation to a structure change of the films was discussed. Peeling-off caused by crack formation of the coating films prepared from MTES was observed after the thermal shock test at temperatures higher than 450°C. It was found that these damages were brought about by densification with the thermal decomposition of CH₃ groups in the MTES-derived films and also by difference in thermal expansion coefficient between coating film and SUS substrate. For the purpose of the improvement of the above properties, composite coatings containing various oxide powders, such as SiO₂, Al₂O₃, ZrSiO₄, MnO₂ and Fe₂O₃, were made. Adhesion after the thermal shock test in the composite films with any of these powders was considerably improved due to the reinforcement by the added powders, the expansion coefficient of which was close to that of SUS.

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Cavities in the sintered zinc oxide is caused by silicon and aluminum carbides which were included as impurities in the zinc oxide powder. The frequency of cavity occurrence is linearly correlated with the X-ray fluorescence intensity of silicon and/or aluminum in the residue after dissolving the raw powder with hydrochloric acid. Therefore, by analyzing these elements in raw material powder, it is possible to predict cavity formation rate before sintering.

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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, D_a, 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; D_a=(2W_MgO+W_SiO2)/{2(W_MgO/d_MgO)+(W_SiO2/d_SiO2)}. D_a is approximated to be the density of the compound, D_c. The deviation, (D_c-D_a)/D_a(=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 D_c leads to the following approximations; D_c=D_a {1+0.33(D_a-3.1)} for silicates, and D_c=D_a {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.

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The crack growth behavior in the high crack velocity region (region III) for binary sodium silicate glasses was investigated by using a DCDC (double cleavage drilled compression) specimen under compressive stress. For 15mol% Na₂O glass, despite the anomalous characteristic of the bulk modulus, subcritical crack growth in region III was detected. The slope of stress intensity factor (K_I)-crack velocity (v) curve for silicate glass depended on the number of non-bridging oxygen per SiO₄ tetrahedron rather than on the alkali content in the glass. This compositional dependence of the slope of K_I-v curve for silicate glasses could not be explained in terms of thermally activated crack growth process where the crack-tip shape would vary with the pressure derivative of bulk modulus. The smaller K_I-v slope and the higher K_IC value of 35mol% Na₂O glass may be related to the structural change from a three-dimensional network to a two-dimensional network because of the introduction of many non-bridging oxygens into the silica network.

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X-ray photoemission spectroscopy (XPS) measurements were performed on SrTiO₃ and BaTiO₃ single crystals with monochromated Al Kα radiation. Valence band (VB) spectra of as-fractured SrTiO₃ and BaTiO₃ crystals exhibit two peaks arising from the O 2pπ and O 2pσ bonding orbitals. From a partial density of states (PDOS) calculation, it is found that O 2p orbitals fairly hybridize with Ba 5p orbitals, while do not almost hybridize with atomic orbitals of Sr atom. This indicates that the nature of the chemical bonding of Ba-O in BaTiO₃ is more covalent than that of Sr-O in SrTiO₃.

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Vickers hardness of TiB₂, VB₂ and CrB₂ crystals was measured in the range of room temperature to 1100°C. The anisotropy in hardness was related to the morphology of crystals prepared from the aluminum flux. That is, the crystal plane with the highest hardness at the growth temperature became large in the flux growth.

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Dr. Katsutoshi Komeya joined Toshiba Corporation after graduating from the Faculty of Engineering, Yokohama National University, in March 1962 and in the following year, 1963, he started research on synthesizing and sintering aluminum nitride (AlN) and silicon nitride (Si₃N₄), an area in which there were very few examples of research. After several years of basic research, he and his colleagues discoverd those sintering auxiliaries that represent a creative sintering principle applicable to both nitrides, and became the first person in the world to establish a starting point for creating new functional materials. Thereafter, materials were developed on a worldwide scale based on this principle. AlN is now used for semiconductor substrates, packing materials, and parts for semiconductor manufacturing processes as a high-thermal conductive material. Furthermore, Si₃N₄ is now employed for engine parts and bearings as a high-temperature, high-strength and excellent wear resistant material.
This paper dealing with sintering of AlN was the first paper to discuss the influences of various additives on the sintering of AlN. Examination of the roles of 30 types of additives clarified that rare-earth oxides, such as Y₂O₃, La₂O₃, and Sm₂O₃, and alkaline earth compounds, such as CaCO₃ and BaCO₃, form aluminates under high-temperature sintering and that densification is promoted by liquid phase sintering. It has also been shown that, when SiO₂ is added to AlN, a sintered body of plate-like texture can be obtained by generating AlN polytypoid but densification is prevented by the generation of this phase. In addition to the above, this paper clarified the following two points, which are now deemed as important findings for the implementation of AlN. First, it was found that a black-gray color was created when compounds that contain transition elements, such as Ti, Zr, and Hf, áre added. Currently, these compounds are used as important additives to give a black color to AlN packages. Second, measurement of the bending strength of various sintered bodies consisting of AlN and additives revealed that, among those materials where densification is achieved, Y₂O₃ and CaCO₃, which are now employed in practical applications, exhibit only low strength, but La₂O₃ and Sm₂O₃ are effective for providing high strength. As the achievement of high strength is now considered the most important subject in the field of AlN ceramics, this paper provides important findings for the solution of this problem as well.
As described above, this pioneering paper was the first to clarify those sintering auxiliaries that are now basic components of ceramics and their effects in the initial stage of the development of AlN ceramics. Furthermore, this paper also suggests those additives that are effective for achieving high strength as well as for coloring and is very frequently referred even though it is written in Japanese. I therefore recommend it as “a paper that leads the studies of ceramics in the 20th century”, as I judge that it is really worthy of that honor.

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