Cement formation with phosphoric acid

CHEMICAL PROPERTIES noncombustible solid gradually absorbs carbon dioxide upon exposure to air reacts with hydrochloric acid to produce zinc chloride reacts with sulfuric acid to produce zinc sulfate, and it reacts with carbon monoxide or hydrogen to produce elemental zinc reacts lowly with fatty acids in oils and fats to produce lumpy masses of zinc oleate, stearate, etc. forms cement-like products when mixed with a strong solution of zinc chloride or with phosphoric acid, owing to the formation of oxy-salts hydrogen peroxide is produced when ointments containing zinc oxide and water are melted and exposed to UV light FP (NA) LFL/UFL (NA) AT (NA) HC (NA) HF (-350.5 kJ/mol crystal at 25°C) pH (6.95 American process zinc oxide, 7.37 French process zinc oxide). 

Komrska Satava (1970) showed that these accounts apply only to the reaction between pure zinc oxide and phosphoric acid. They found that the setting reaction was profoundly modified by the presence of aluminium ions. Crystallite formation was inhibited and the cement set to an amorphous mass. Only later (7 to 14 days) did XRD analysis reveal that the mass had crystallized directly to hopeite. Servais Cartz (1971) and Cartz, Servais Rossi (1972) confirmed the importance of aluminium. In its absence they found that the reaction produced a mass of hopeite crystallites with little mechanical strength. In its presence an amorphous matrix was formed. The amorphous matrix was stable, it did not crystallize in the bulk and hopeite crystals only grew from its surface under moist conditions. Thus, the picture grew of a surface matrix with some tendency for surface crystallization. 

A year-old bottled sample, containing syrupy phosphoric acid as stabiliser and which already showed signs of tar formation, exploded in storage. The pressure explosion appeared to be due to polymerisation, after occlusion of inhibitor in the tar, in a container in which the stopper had become cemented by polymer [1], A similar pressure explosion occurred when dry redistilled nitrile, stabilised with ethanol [2], polymerised after 13 days [3], The spontaneous and violent decomposition of the nitrile on standing for more than a week is usually preceded by formation of a red polymer [4],... 

For many years, the dental silicate cement was thought to set by the formation of a sihcate stracture [9]. However, studies by Wilson et al. in the 1960s showed that it was, in fact, a phosphate cement [10-12]. Reaction of the glass with aqueous phosphoric acid was shown to yield a complex matrix that consisted of a mixture of calcium and alnminium phosphates. There was also some siUca gel formed, though... 

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