Studies on the Reactions between Oxides in Solid State at Higher Temperatures. II. The Reaction between Calcium Oxide and Titanium Oxide and the Photo-sensitivity of Calcium Titanate

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Abstract
(1) It has been ascertained that there exists only one addition compound, perovskite (CaO·TiO2), in the system CaO and TiO2. As for the unit cell size of pure perovskite, a=7.615Å should be given as correct, which is twice as great as the value hitherto given. (2) CaO·TiO2 has been proved to form a solid solution with the two components, the range of which spreads approximately from a slight excess of TiO2 to CaO:TiO2=3:2, and in which the lattice constant is enlarged and the crystal form deviates from cubic with the increase of the content of CaO. (3) At the early stage of the solid reaction of this system, the product is richest in TiO2 within the possible range of the solid solution; the solid solution rich in CaO may be formed gradually when an excess of CaO is present. (4) It has been concluded that, although there exists a rapid initial reaction, a further reaction is controlled by the diffusion of the two components through the reaction product. The energy of activation of the diffusion process has been calculated as 30.3 kilocalories per mole. (5) It has been found that the reaction products turn light red by the action of light; some observations thereon have been made.

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