Calcium silicate-phosphates, preparation

Calcium silicate-phosphates can be prepared by the following procedure. Monocalcium orthophosphate, Ca(H2P04)2, is, according to the method of Hill and Hendricks (38), recrystallized from a 50% solution of orthophosphoric acid. The crystals are then washed with acetone to remove orthophosphoric acid and dried at 70°C. By melting the resulting pure monocalcium orthophosphate at 980-1000°C., calcium metaphosphate is produced. A mixture of the calcium metaphosphate and an appropriate amount of silica gel is melted in a platinum crucible and cooled to form a glass, which has a Ca0/P205 ratio of... 

Elemental phosphorus is prepared by the reduction of calcium phosphate, Ca3(P04)o, with coke in the presence of sand, SiO>. The products are phosphorus, calcium silicate, CaSiOa, and carbon monoxide. 

Finally, sol-gel processing is widely used in the exploration of methods to prepare biomaterials for example, hydroxyapatite prepared from triethyl phosphite and calcium salts.237,238 Phosphate sol-gel synthesis is more difficult than for silicates since phosphoric esters are very difficult to hydrolyze 239... 

In addition to the above, preparation in w/o microemulsions of nanoparticles of various other types of compounds, viz. silica-coated iron oxide, Fe203-Ag nanocomposite, oxides of ytrium, erbium, neodymium, vanadium and cobalt, titanates of barium and lead, ferrites of barium, strontium, manganese, cobalt and zinc, oxide superconductors, aluminates, zirconium silicate, barium tungstate, phosphates of calcium, aluminium and zinc, carbonates of calcium and barium, sulphides of molybdenum and sodium, selenides of cadmium and silver etc. have been reported. Preparative sources and related elaboration can be found in [24]. 

For the preparation of phosphate-silicates with CaO/P205 ratios smaller than 1, calcium metaphosphate, silica gel, and phosphorus pentoxide are used as starting materials. 

Mode of Preparation.—In the United States, Canada, Bussia, and on the shores of the Baltic, various kinds of wood are burned, and their ashes collected and lixiviated. By lixiviation various potassium compounds, o.y. carbonate, sulphate, chloride, phosphate, and silicate, are dissolved, while silica and certain salts of calcium, magnesium, iron,... 

The development of the dental silicate cement in its final, satisfactory form occurred slightly later than the development of the zinc phosphate, though it, too, traces its earliest history back to the later 1870s. The pioneering woik on this material was reported in 1878 and 1879 by Fletcher [15,16], and involved canents prepared from concentrated solutions of orthophosphoric acid and sintered mixtures of oxides, including silica and alumina, with inclusions of calcium oxide and zinc oxide. One of these cements showed slight translucency when set [16], but overall the cements were not a success clinically [7]. 

Several possible calcium and aluminium phosphates exist and they differ in their solubility in aqueous media and also in their resistance to acid attack. Among the factors determining which of these products are formed are powderiliquid ratio of the cement and concentration of the phosphoric acid solution. As a result, this material was easy to prepare in a soluble or acid-sensitive state. Incorrect metering of the powder to liquid components increased the solubility of the set cement, and leaving the bottle of phosphoric acid solution open to the air led to uptake of moisture from the atmosphere, with a corresponding reduction in acid concentration. This resulted in an increase in the proportion of more soluble metal salts in the set cement. These factors combined to make the dental silicate difficult to use in the clinic and gave the material a reputation for unreliability [8]. 

Constantz BR, inventor Skeletal Kinetics, LLC, assignee. Calcium phosphate cements prepared from silicate solutions. USA 2002. 

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