A New Form of Tricalcium Phosphate

Abstract

may be increased by the suction induced by the rapidly flowing water at the tip.Mayne 1 has shown that rapid oxidation of ferrous hy~roxide at a_pH_value greater than 5 gives goethite while slow oxidation leads to the formation of an intermediate between magnetite and ferric oxide (yFe 20 3 ). Thus the formation of goethite in the present case is readily explained. The formation of magnetite, the second constituent, is not likely to occur in the same area at the same time as goethite since slow oxidation would appear to be necessary. Therefore, the oxidation to form this compound must occur in some areas sheltered from the direct action of the water. This may occur in pockets of ferrous ion-containing water trapped in the goethite crystals or by slow oxidation of the ferrous ion during its passage through the whisker either by a small amount of oxygen contained in the water or by oxygen diffusing through the wall of the .tubule.

The revised phase diagram of the Ca3(PO4)2–YPO4 system. The temperature and concentration range of solid-solution phase fields

“…Since the highenergy barrier stabilizes the metastable a phase at room temperature, its lowering should result in rapid transition and presence of the low-temperature solid solution in samples quenched from high temperatures. At the same (8) time, the a 0 modification of Ca 3 (PO 4 ) 2 could be not obtained by quenching [4].…”

“…The phosphate was prepared in a solid state by the ceramic method according to method proposed in [42]. In this synthesis route, a stoichiometric mixture of CaCO 3 4 . The chemical composition of samples under study is shown in the Tab.…”

“…The YPO 4 phase was found in samples with x(YPO 4 ) C 20 mass%. It should be also mentioned that several of the most intensive YPO 4 reflections overlapped with these of b-Ca 3 (PO 4 ) 2 . This made the qualitative analysis of the patterns complicated.…”

“…It melts congruently at a high temperature (T m = 1,810°C) [3], and it has three polymorphic modifications: b, a, and a 0 . The a 0 form exits at temperatures above 1430°C [4] and it has a trigonal structure (S.G P " 3m) with parameters: a = b = 5.3507 (8), c = 7.684(1) Å [5]. It is not possible to overcool the polymorph, even in the course of quenching.…”

Ca3(PO4)2 - CaNaPO4 System

“…Ando1,2) identified the principal mineral of the phosphate to be a solid solution of a new compound "A" Ca 5Na2(PO4) 4, and suggested that the crystals of "A" might consist of a superlattice of hexagonal…”