Reactions between oxides and phosphoric acid solutions

3 Reactions between oxides and phosphoric acid solutions 

In a classic study, Kingery (1950b) examined a large number of oxides for cement formation with orthophosphoric acid. He observed three types of reaction no reaction, violent reaction with crystallization, and controlled reaction with cement formation. 

Lastly, there was the cementitous reaction which Kingery (1959b) reported with BeO, Be(OH)2, CuO, CujO, CdO, SnO and PbjO. In addition, calcined ZnO and MgO formed cements. 

Kingery himself used XRD, but except in one case failed to positively identify crystalline hydrogen phosphates in any of the cements he examined. He found either the neutral orthophosphate or unidentified crystalline species and then the lines were weak. 

Although an acid phosphate matrix cannot be excluded it is not essential for cement formation. In fact, it must be remembered that when these cements are prepared the oxide or silicate powder is normally in excess of that required for the reaction. Under these conditions most oxides (MgO 

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