The reaction between BaCO₃ and TiO₂ has been studied in air and in CO₂ at 700-1020°C. Several products (Ba₂TiO ₄, BaTiO₃, BaTi₃O₇, and BaTi₄O₉) were obtained when the mixtures of BaCO₃ and TiO₂ were heated in air, but, under the CO₂ atmosphere of 300-700mm Hg, BaTiO₃ with very small amounts of BaTi₃O₇ was observed.
The kinetics of the reaction between BaCO₃ and TiO₂ under the CO₂ atmosphere of 500mm Hg were studied. The process of the reaction is composed of two steps, i.e. a phase boundary reaction followed by a subsequent diffusion process. The kinetic data can be expressed reasonably by the first-order equation for the earlier stage, and by Tamman's equation for the later one. The activation energy for the earlier stage of rutile is about 43Kcal/mol. There is a discontinuity at about 830°C in the plotting of log k against l/T for the earlier stage of anatase. The activation energies are about 34 and l6Kcal/mol above and below 830°C respectively. The activation energy for the later stage is about 34Kcal/mol for both anatase and rutile.

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Bending strength and Young's modulus of Ni and Ni-Zn ferrite were measured as a function of porosity and grain size. Chipping resistance has been estimated from microscopic observation at the sectional surface of specimen produced by diamond wheel cutting. It was found that the resistance to the chipping increased with the increasing (1-μ)σb/E value (σb ; bending strength, E ; Young's modulus, μ; Poisson's ratio), but it was hardly affected by porosity. Furthermore, the effect of porosity on (1-μ)σb/E was too small. Hot-press technique provided specimen having large value of (1-μ)σb/E. Such specimen also had very low porosity, small grain size and high bending strength, and then actually showed very excellent chipping resistance property.

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Some experiments carried out to synthesize nickel ferrite by hydrothermal method are described and a short discussion on the mechanism.of the formation is given.
Spinel type ferrite was easily formed from either the co-precipitated hydroxide made from the solution of constituent sulphates or the wet mixture of two hydroxides-ferric hydroxide and nickel hydroxide-suspended in water at pH 11.
It was rather difficult to synthesize the ferrite from the dry mixture of the two hydroxides. Precipitating agent and pretreatment of the ferric hydroxide were found to have a large effect on the formation.

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