Calcium metaphosphate

For several years TVA produced calcium metaphosphate, Ca(POs)2, in a demonstration-scale plant. The process consisted of burning elemental phosphorus and reacting the resulting P2O5 vapor with phosphate rock. The molten product was tapped out of the ftirnace and -solidified on a watei cooled steel drum [17]. The resulting vitreous flakes were cooled further and crushed to pass a 10-mesh screen (about 1.6 mm). Development of a process for production of calcium metaphosphate involved three pilot plants and three demonstration-scale plants and a considerable amount of laboratory- and bench-scale work [IS]. The third demonstration-scale plant was technically successful and operated about 16 years, starting in 1949. A total of nearly 1 miflion tonnes was produced, including relatively small amounts from the first and second demonstration-scale plants. The process was economically competitive with TSP when both products were based on elemental phosphorus made by the electric-furnace process. 

Pure calcium metaphosphate contains 71.7% P2O5 the TVA product contained about 65% P2O5 because of impurffies the rock. TKe material was not water soluble but hydrolyzed sloviy in water or moist soil, forming water-soluble compounds [19]. About 98% or more of the P2O5 was soluble in neutral ammonium citrate. 

The main disadvantage of the process was its dependence on elemental phosphorus, which has become too expensive for fertilizer use in most situations. Also its agronomic effect depends on the rate of hydrolysis in the soil, which may be too slow for short-season crops. 

Calcium metaphosphate glass may also be produced by heating TSP to fusion crystalline structures, which are not citrate soluble, are formed at lower temperatures. 

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Calcium metaphosphate [13477-39-9] is made by reaction of P2O3 in HPO3 with rock phosphate. The insoluble, polymeric product must be hydrolyzed before it can act as a fertilizer (13) ... 

This calcium metaphosphate may be regarded as a dehydrated triple superphosphate made directly from phosphate rock. The calcium metaphosphate is quite insoluble, and it must hydrolyze to become effective. 

Figure 7.29. Two-dimensional rotor-synchronised P NMR spectra of calcium metaphosphate glass with a small amount of added Si02 to prevent crystallisation. A. Spectrum of powdered sample showing a spectrum only in the central slice. B. Spectrum of extruded glass showing additional spectral intensity outside the central slice arising from structural order induced during the extrusion process. From Braun et al. (1998), by permission of Elsevier Science.

Establishments primarily engaged in manufacturing phosphatic fertilizer materials, or mixed fertilizers from phosphatic materials produced in the same establishment. Included are phosphoric acid normal, enriched, and concentrated superphosphates ammonium phosphates nitrophosphates and calcium metaphosphates. 

Ammonium phosphates Calcium metaphosphates Defluorinated phosphates Diammonium phosphates Fertilizers, mixed made in plants producing phosphatic fertilizer materials... 

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... 

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. 

Brosheer, J. C. 1953. Development of Processes for Production of Calcium Metaphosphate, TVA Chemical Engineering Report No. 6, Tennessee Valley Authority, Muscle Shoals, AL, U.S.A. 

At 500°C, phosphoryl chloride can be obtained by heating the pentoxide with rock salt (4.57), and if calcium fluoride is added, mixed phosphoryl halides are produced together with calcium metaphosphate (4.58). With calcium fluoride alone, phosphoruspentaflnoride is obtained (4.244). Metaphosphates are also produced by heating with sodium carbonate under anhydrous conditions (4.59). 

FIGURE 10.35 Poly 3-HB calcium metaphosphate complex, (a) Concentric helices, axes perpendicular to plane of membrane and (b) section perpendicular to axis of helices. 

Fusion of a phosphate with a silicate does not easily give a condensed polymer of Si04 and PO4 (12.62). Calcium metaphosphate fused with silica gel at 980°C (Si02 < 12.5%) gives a clear glass which is slowly but completely soluble in water. If the silica content is >12.5%, the resulting glass is turbid and not completely soluble in water. 

Calcium metaphosphate can be bonded into sheets with relatively minor quantities of glass, PVC, rayon, polyester, graphite and so on [55]. Calcium polyphosphate fibres have been developed as a possible substitute for asbestos (Chapter 5.4). 

Calcium metaphosphate fibres based on p Ca(P03)2) , or NaCa(P03)3) are of potential interest because of their biocompatibility combined with relatively high strength and flexibility [46] (Section 12.15). Both phosphate glasses and fibres show great promise for tissue engineering at the present time [47]. 

Calcium metaphosphate is the most significant of the metaphosphate glass-ceramics with regard to its applications. The structure of calcium metaphosphate, which has been studied in detail by Rothammel et al. 

Figure 1-25 Structure of calcium metaphosphate, according to Rothammel et al. (1989).

A calcium metaphosphate glass rod composed of Ca0 P205 = 0.95 (molar ratio) was produced. One area of this rod was heated to the softening point in a special furnace at 600°-650°C. In the process, nucleation and controlled ciystallization of P-Ca(P03)2 needlelike crystals occurred. It was interesting to note that crystals formed along the glass rod in one direction only, from the hotter to the colder areas. As the glass rod was pushed farther into the furnace, crystallization continued in the hot areas until unidirectional Ca-metaphosphate was produced as the main crystal phase. That is, the crystals were precipitated anisotropically and with preferred orientation. 

Lin Chen. Preparation and properties of p-calcium metaphosphate whiskers/poly-L- laetide composites for internal fixation of bone fractures. Chengdu Sichuan University, 2007. 

Effective Adhesion of Dental Ceramics Development of Adhesive Monomers for Calcium Metaphosphate Ceramics... 

In view of the potential importance of ceramic materials for esthetic dentistry, we have focused our attention on the development of high-performance dental adhesives for calcium metaphosphate ceramic as a novel restoration material. The calcium metaphosphate ceramic is characterized by considerable similarities of the appearance, composition, and physical... 

Calcium metaphosphate glass (Asahi Glass Co., Japan) was cast at llOOX, and the resulting plate (10 x 10 x 3 mm) was crystallized at 700°C for 16 hr. After cooling to room temperature, the surface was polished with emery papers of up to No. 600 grit in running water, washed with water and then with acetone, and dried. 

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