Peculiarities in thermal evolution of precipitated amorphous calcium phosphates with an initial Ca/P ratio of 1:1

Abstract

Thermal evolution of amorphous calcium phosphate (ACP) powder from a fast nitrate synthesis with a Ca/P ratio of 1:1 were studied in the range of 20-980 °C. The powder consisted of amorphous dicalcium phosphate anhydrate (CaHPO) after heating to 200 °C. CaHPO gradually condensed to amorphous calcium pyrophosphate CaPO (CPP) between 200 to 620 °C. Amorphous CPP crystallized at 620-740 °C to a metastable polymorph α'-CPP of the high-temperature phase α-CPP and β-CPP. The α'-CPP/ β-CPP phase ratio reached a maximum at 800 °C (60 wt% α'-CPP/40 wt% β-CPP), and α'-CPP gradually transformed to β-CPP at a higher temperature. Some β-TCP occurred at 900 °C, so that a three-phasic mixture was obtained in the powder heated to 980 °C. The occurrence of metastable α'-CPP is attributed to Ostwald's step rule, and a mechanism for β-TCP formation is proposed. The advantages of prospective biomaterials from these powders are discussed.

Phase evolution during heat treatment of amorphous calcium phosphate derived from fast nitrate synthesis

“…Formation of calcium phosphate (CP) with a higher Ca/P ratio than the given in mother solution (for Ca/P < 1) Z.Z. Zyman et al / Processing and Application of Ceramics 11 [2] (2017) 147-153 was also observed earlier [14] under the conditions similar to those in the study [13]. However, no explanation was proposed [14] for this effect.…”

“…A powder from the process consists of large particles with high crystallinity, which significantly reduces its bioactivity compared to a nanocrystalline one [9][10][11][12]. It was recently observed that fine-grained α ′ -and β-CPPs and small amount of β-TCP can be formed from ACP powder with a Ca/P ratio of 1 : 1 using a fast variation of the nitrate synthesis upon heating above 800°C [13]. β-TCP is well known due to excellent bioactivity [12], so its presence may improve the biological performance of the CPPs.…”

“…The aim of this study was to prepare fine powders based on CPP and TCP including their metastable polymorphs, and to examine thermal phase evolution in the powders. The idea was also to get more data on the mechanism of TCP formation in the powders derived from the fast nitrate syntheses under Ca/P of 1 : 1, proposed recently in literature [13].…”

Complex phase evolution of Brushite-based calcium phosphate CaHPO4·2H2O using in situ high temperature X-ray diffraction and thermal analysis

“…], as reported for many pyrophosphate materials [41,42]. The rst was attributed to the amorphous CPP and the second to crystalline CPP.…”

Iron, Copper, and Nickel Removal with Calcium Hydrogen Phosphate and Calcium Pyrophosphates in Solution

“…[11][12][13][14]. The formation of these phosphates was affected from a Ca/P mixing ratio of raw materials, heating temperature and time, additives, and so on [15][16][17]. Further, phosphate materials produce condensed phosphate in a dehydration reaction [18,19].…”