Phase transformations and structure characterization of calcium polyphosphate during sintering process

Abstract

Calcium polyphosphate (CPP) may be a promising bone substitute with controllably degraded ability. In this investigation, the effects of sintering temperatures on CPP's phase transformations and microstructure parameters, such as the distribution of crystallite size and micro-strain, were investigated by X-ray diffraction (XRD). The qualitative phase analysis and quantitative phase analysis based on reference intensity ratio (RIR) method were conducted for the CPP sintered at 585, 600, 650, 700, 750, 800 and 900°C. The distribution of crystallite size and micro-strain were calculated with the Warren-Averbach Fourier Transfer method. The results demonstrated that the transformation of amorphous CPP to semi-crystalline CPP occurred below 585°C, and semi-crystalline CPP to γ-CPP at temperature of 585–600°C; γ-CPP to β-CPP at 585–700°C. CPP sintered between 600–700°C were composed of both γ-CPP and β-CPP, and the mass fraction of β-CPP increased with rising of temperature. Above 700°C, the sintered CPP only contained β-CPP. At different ranges of the sintering temperature, the average crystallite size (D) and micro-strain (e) showed significant difference, for example, D and e is about 2.9 nm and 1.68% at 585°C, but D and e was 8.0 to 8.7 nm and 0.159 to 0.134% at 600 and 700°C, respectively. The results of the phase transformations and the variations of microstructure parameters in the present study may be able to provide some fundamental data for explaining CPP degradation phenomena.