Amount Of Hemihydrate Research Articles

The influence of calcium sulfate form on the initial hydration of clinkers containing different alkali combinations

Three sets of clinkers produced under different pyroprocessing conditions in a commercial dry-process cement kiln yielded alkalis in different combinations: one set was rich in alkali sulfate compounds, alkali-stabilized orthorhombic C 3A was predominant in the second, whereas potassium rich α-C 2S and alkali oxide-aluminate mixture were noted in the third set. Using different techniques, early hydration analysis was carried out on these clinkers with no addition of calcium sulfate, with a predetermined amount of gypsum, and a corresponding amount of hemihydrate. The results of a study which focused on the identification of the early hydration products, and the interrelationship of calcium sulfate form and different alkali combinations on the hydration kinetics are presented.

Study of gypsum‐bonded casting investments. Part 2

The simultaneous differential thermal analysis--thermogravimetry (DTA-TG) method used in Part 1 of this two-part study was extended to analyse two gypsum-bonded dental casting investments, Kerr Cristobalite Inlay and GC Cristobalite Micro. Both investments had a similar cristobalite content of about 70 per cent. The remaining 30 per cent was dental stone in GCM, and a mixture of plaster and dental stone in KCl. Inclusion of plaster in KCl appeared responsible for the greater amount of water required for mixing this investment. The DTA-TG method used in the present study can be applied to identify the type and amount of hemihydrate, and the type of silica, in currently available gypsum-bonded investments.

Redistribution of impurities in commercial wet-process acid

Fifty-four commercial wet-process phosphoric acid (WPA) products were characterized to determine the redistribution of each chemical component between the solid and liquid fractions. The acid samples ranged in concentration from 24–70% P2O5 and represent production from the major U.S. phosphate rock fields (western United States, North Carolina, and Florida). The liquid and solid phases were separated and analyzed within two to three days of production and thus do not reflect long-term storage. The type and distribution of the compounds in the solid phase were dependent upon both the P2O5 concentration and that of 10 impurity components (Fe, Al, Mg, Na, K, Ca, Si, F, NH3-N, and S). The precipitates between 24 and 41% P2O5 are primarily gypsum, (Fe, Al)3(K, Na, NH4)H8(PO4)6·6H2O, and the AlF 6 3- and SiF 6 2- compounds of sodium, potassium, calcium, and magnesium. From 42–58% P2O5, the precipitates include greatly reduced amounts of most of the fluorides from the 28–41% P2O5 region and significant quantities of (Fe, Al)3(K, Na, NH4)H14(PO4)8·4H2O. Between 58 and 70% P2O5, the precipitates are primarily acid ferric phosphates and alkaline earth and ferrous pyrophosphates admixed with minor amounts of hemihydrate. Model equations were developed to estimate the concentration of a specific impurity in terms of overall solution composition. These equations exhibited correlation coefficients in the 60–80% range and allow prediction of trends for sludge formation.