Reaction Sintering of Bioceramic Based on Substituted Calcium Phosphates CaMPO4 (M = K, Na)

• Published in: Inorganic materials : applied research 2020, Vol.11 (2), p.394-402
• Main Authors: Orlov, N. K., Kiseleva, A. K., Milkin, P. A., Evdokimov, P. V., Putlyaev, V. I.
• Format: Article
• Language: English
• Subjects: Activated sintering; Alkali metals; Bioceramics; Calcium oxide; Calcium phosphates; Chemistry; Chemistry and Materials Science; Densification; Density; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials for Human Life Support and Environmental Protection; Materials Science; Phase relationships; Phase transitions; Phosphates; Phosphorus pentoxide; Potassium; Potassium carbonate; Recrystallization; Shrinkage; Sintering; Sodium; Transition temperature
• ISSN: 2075-1133; 2075-115X
• DOI: 10.1134/S2075113320020276

The synthesis of double phosphates based on calcium and alkali metals from different two-phase mixtures was studied. The phase relationships in the CaO–K 2 O–P 2 O 5 and CaO–Na 2 O–P 2 O 5 system were clarified, especially the phase transition temperature in potassium rhenanite CaKPO 4 . It was shown that some compounds that are mentioned in the literature, in particular, CaK 2 P 2 O 7 , CaNa 2 P 2 O 7 , CaK 4 (PO 4 ) 2 , and CaNa 4 (PO 4 ) 2 , cannot be obtained at 1000–1200°C at normal pressure. The densification and recrystallization were investigated during the reaction sintering of selected two-phase mixtures. Reaction sintering of a mixture of Ca 3 (PO 4 ) 2 and CaK 4 (PO 4 ) 2 gives CaKРO 4 ceramic with a density of 78% (linear shrinkage of the sample is 5%); when sintering a mixture of K 2 CO 3 and Ca 2 P 2 O 7 , the density of ceramic was 62% with a linear shrinkage of 15%. The reaction sintering of sodium-containing mixtures made it possible to obtain dense ceramics (density above 90%, linear shrinkage more than 6.5%) from a mixture of CaNa 4 (PO 4 ) 2 and Ca 3 (PO 4 ) 2 . The experimental features of the reaction sintering of calcium and potassium/sodium double phosphates are discussed from the point of view of volume change during the course of the reaction. Another aspect that determines the density and microstructure of ceramics is the phase transformation of α → β in alkali metal rhenanites CаMPO 4 .