The elastic properties of the glasses in the systems xR₂O⋅B₂O₃⋅rSiO₂ (0<x<1.3; r=1 and 2; R=Na and K) and yNa₂O⋅(1-y)B₂O₃ have been measured by the pulse transmission method. The elastic constants of the glasses in the sodium borate systems with and without 5mol% MgO exhibited a maximum at the molar ratio (MgO+Na₂O)/B₂O₃=0.5. This composition is equivalent to that at which the fraction N₄ of the four-coordinated boron atoms in those glasses deviates from the relation N₄=(MgO+Na₂O)/B₂O₃. Therefore the elastic constant is expected to play a role indicating the composition with the maximum value of N₄ and the formation of non-bridging oxygens. The results in the alkali borate glasses have been applied to the borosilicate glasses in order to estimate the composition at which the N₄ becomes maximum and also to assure if the potassium oxide plays the same role as the sodium oxide. The log-log plot of the bulk modulus vs, the mean atom-pair volume verifies the previous model of the borosilicate glasses (Takahashi et al., J. Non-Cryst. Solids, in print). The effect of SiO₂ content on the elastic properties of the borosilicate glasses has been discussed also.

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Sapphire-to-niobium and -tantalum metal seals were formed by using a crystalline oxide solder, and the interfaces between the materials were examined by optical microscopy and electron probe microanalysis. The results are summarized as follows:
(1) Vacuum tight seals were formed by the technique.
(2) The oxide solder composed of crystals of CaO, Al₂O₃, MgO and B₂O₃ turned into glass-ceramic composites by sealing operation. The solder of niobium metal seal showed optical microscopic appearances different from those of tantalum, but their major crystalline constituent phases were similarly 3CaO⋅Al₂O₃, CaO⋅Al₂O₃ and MgO⋅Al₂O₃ for niobium and tantalum metal seal.
(3). Diffusion of Nb into the solder was different from that of Ta. Ta concentration was relatively higher than Nb concentration up to 10μm from the interface. This is reflected by dissimilar microscopic appearances in the vicinity of interfaces.
The presumption that this difference could be explained by difference in oxidation between niobium and tantalum metal during sealing was confirmed by thermochemical calculations.
(4) B₂O₃ in the solder was very effective in improving adhesion and yield.
(5) At the solder-sapphire interface, a transition layer was formed by the diffusion of sapphire into the melted solder.
(6) At the solder-metal (niobium or tantalum metal) interface, the metal surface was oxidized by oxygen which was presumed to have originated from the ambient atmosphere and other sources. These metal oxides thus formed diffused into the melted solder to form transition layers.
(7) The transition layers at the interfaces are believed to be useful in reducing sealing stress and in improving adhesion.

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The crystallization process of Li₂O-SiO₂ glass and lithium silicate gel powders has been investigated by means of differential thermal analysis, X-ray diffraction and infrared spectroscopy. The former was prepared by melting and contained 0.004-0.177wt% water and the latter, by hydrolyzing metal alkoxide solutions. It is found that with increasing water content in the glass, the glass transition temperature and the rate of nucleation decrease, whereas the rate of crystal growth increases. It is also found that gels prepared from a metal alkoxide solution show a crystallization process different from glasses prepared by conventional melting method; the crystalline phase precipitated from the former is metastable lithium metasilicate Li₂SiO₃ and that precipitated from the latter is stable lithium disilicate Li₂Si₂O₅. It is also to be noted that the glass prepared by melting the gel shows a crystallization process similar to the glasses prepared by melting crystalline powders when their water contents are similar.

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The valence and coordination of the transition element in the transition element oxide-silica coating films prepared by sol-gel method were examined by measuring the optical absorption spectra and compared with those found in the silica glass containing a transition element oxide prepared by Schultz by flame-hydrolysis at high temperatures. The following results were obtained:
(1) The maximum possible content of a transition element oxide for obtaining homogeneous film was 10mol% for Cr₂O₃, 20mol% for Mn₂O₃, 45mol% for Fe₂O₃, 45mol% for CoO, 55mol% for NiO and 45mol% for CuO. The optical transmittance at 555nm of the homogeneously colored 0.2-0.5μm thick films with strongest absorption was 81% for Cr, 68% for Mn, 63% for Fe, almost 0% for Co, 59% for Ni and 95% for Cu.
(2) The valence and coordination of a transition element in the films were similar to those found in silica glass prepared at high temperatures. However, the concentration of a transition element showing a certain valence and coordination was not equal to that found in silica glass prepared at high temperatures. It was found that chromium is present as Cr³⁺ in octahedral site, manganese as Mn³⁺ in octahedral site, iron as Fe³⁺ in octahedral site, cobalt as Co²⁺ in tetrahedral site, nickel as Ni²⁺ in octahedral site and copper as Cu²⁺ in octahedral site.

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A series of new rare earth compounds Ln₂GeBe₂O₇ (Ln=Y, La, Pr, Sm, Gd, Dy and Er) have been synthesized. With Cu Kα radiations, 1701 powder X-ray diffraction data were collected for each of these compounds by a step scan method with a step interval of 0.05° in 2θ, and the structure analysis of the compounds was carried out by the powder pattern fitting method. Atomic coordinates and isotropic temperature factors were determined by using the least-squares program PFLS-M. The crystals have tetragonal melilite structures composed of layers of GeO₄ and BeO₄ tetrahedra parallel to (001) and rare earth ions connecting the layers along the c-axis. The c-value decreased with decrease in the ionic radius of the rare earth ions between the layers, showing a typical lanthanoid contraction. The a-axis which is parallel to layers also contacted, since the size of the Be₂O₇ double pyramids became smaller with decreasing ionic radius of the rare earth ions. Comparing eight-fold coordination sites at interlayers in the present compounds with other melilites, the former was less distorted than the latter. Though the rare earth compounds usually show the magnetic transitions at low temperatures, the present compounds showed paramagnetism down to 4.8K.

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Hydrothermal reaction sintering of hafnia (HfO₂) was studied under 100MPa at temperatures up to 1300°C. HfO₂ formed from Hf and H₂O on heating was sintered above 900°C for 3h. The density and crystallite size of sintered bodies increased monotonically with temperature in the range between 900°C and 1200°C, then saturated at the maximum relative density of 98%. The hydrothermal reaction sintering of HfO₂ proceeded through three stages with the following features; (1) a large increase in crystallite size was observed, while the density did not increase appreciably, (2) a large increase in density was observed, while crystallite size increased a little, (3) a small increase in density and a small variation of crystallite size were observed. The growth of crystallite size was influenced by the presence of high-temperature high-pressure water and the temperature of heat-treatment. The densification was thought to take place on the second and third stages in the hydrothermal reaction sintering mainly by pore elimination due to the effect of hot isostatic processing. Greyish sintered bodies were sometimes obtained, having a smaller crystallite size and larger density than white sintered bodies fabricated under the same experimental conditions. The disper sion of fine Hf hydride_particles was considered to be the cause of greyish color, smaller crystallite size and denser body, which would be expected to suppress the grain growth and to be effective for the densification.

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Fracture toughness (K_Ic) for polycrystals of Ni-Zn ferrite (grain size; 22μm) and Ba hexaferrite (grain size; 3.5μm) was measured at room temperature and elevated temperatures up to 1000°C. Room-temperature K_Ic's determined by the controlled surface flaw (CSF) technique for Ni-Zn ferrite and Ba ferrite were 1.50±0.12 and 2.97±0.16MN/m^3/2, respectively. In the indentation fracture (IF) technique, different K_Ic values were obtained, depending on the equations proposed to evaluate K_Ic and indentation load for testing. There was a difference in fracture mode at room temperature between the two ferrites transgranular fracture with relatively smooth surface in Ni-Zn ferrite, and intergranular fracture or cleavage of a specific plane in each grain with rough surface on a grainsizescale in Ba ferrite. There were also differences in K_Ic value and fracture behavior at elevated temperatures between the two ferrites. K_Ic of Ba ferrite decreased linearly with increasing temperature up to 1000°C, which appeared as if temperature dependence of K_Ic reflected only that of Young's modulus. However, tip of flaw introduced by Knoop indenter blunted above 800°C as inferred from the facts that the fracture stress increased and that the fracture often initiated nott from the introduced surface flaw but from an exaggerated grain at those temperatures. For Ni-Zn ferrite, the blunting of flaw tip appeared above 600°C, with gradual increase in K_Ic to 800°C. Above 900°C, K_Ic and fracture stress decreased and the fracture initiated not at a flaw tip but at grain boundary near the flaw tip, showing intergranular fracture throughout the fracture surface. At those temperatures, fracture often initiated from an exaggerated grain as in Ba ferrite. However, it seemed that the fracture from a large grain in Ba ferrite may be due to dislocation pile-up or cleavage in the large grain rather than the decreasing strength in grain boundary with increasing temperature as in Ni-Zn ferrite. Bending strength of Ni-Zn ferrite without an introduced flaw had a maximum at -700°C and then decreased with increasing temperature from 900°C with intergranular fracture, corresponding to the K_Ic versus temperature relationship.

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The high temperature deformation of iron-doped polycrystalline aluminum and magnesium oxides was studied by stress relaxation and dead-load creep. Linear and non-linear anelastic effects, which are important in stress relaxation, can lead to significant differences in apparent creep rates and strain rate-stress relationships which are inferred from dead-load creep and stress relaxation data. In the low stress regime, the effects of the major variables, such as temperature and grain size, are similar for both modes of deformation and are consistent with diffusional creep controlled by various combinations of lattice and grain boundary diffusion. In the non-viscous deformation of magnesium oxide, dead-load creep and stress relaxation testing yielded similar results in terms of the grain size effect and activation energy for deformation. However, in the case of iron-doped aluminum oxide, the stress relaxation is apparently athermal and strongly influenced by non-linear anelasticity.

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