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Cerium-containing tricalcium phosphate (TCP, Ca3(PO4)2) nanopowders with the whitlockite structure have been prepared via precipitation from solution. After heat treatment at 1300°C, the materials contained 0, 0.07, 0.18, and 0.39 wt % cerium, which corresponded to х = 0, 0.0025, 0.006, and 0.013 in the general formula Ca3 –хCe2х/3(PO4)2. The thermal stability of β-TCP has been shown to increase with increasing cerium content. The synthesized cerium-containing TCP powders show luminescence properties under excitation at wavelengths from 270 to 320 nm, with a peak emission wavelength from 360 to 390 nm, characteristic of Ce3+ luminescence. Varying the percentage of cerium in the materials and heat treatment temperature causes the emission spectrum to shift. [ABSTRACT FROM AUTHOR]

Abstract—Hydroxyapatite powders containing up to 2.4 mol % Cu (Cu-HA) have been synthesized via precipitation from solution. The synthesized materials have been characterized by X-ray diffraction after heat treatment in the temperature range from 900 to 1400°C and their lattice parameters and crystallite size have been determined. We have studied the bending strength and microstructure of Cu-HA-based ceramics. The results demonstrate that the addition of more than 0.8 mol % copper reduces the thermal stability of HA, leading to its partial decomposition to monoclinic tricalcium phosphate (α-TCP) and its transformation into the hexagonal phase (β-TCP), with possible concentration of the copper in it. Increasing the percentage of copper leads to a decrease in HA sintering rate in combination with an increase in crystallite size and porosity. According to in vitro biological investigations, the ceramic materials are cytocompatible and their surface has marked matrix properties. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of sintering of nanosized (20 nm) and microsized (0.7-0.9 μm) hydroxyapatite (HA) powders with continuously increasing temperature at a constant rate was studied by dilatometry. The sintering of the HA micropowders within the temperature range 1100-1300°C occurred by the mechanism of diffusion-viscous flow of crystalline particles. The kinetics of the process was described by a power-law function of time; i.e., the process rate depended on current shrinkage. The shrinkage of the nanopowders within the sintering temperature range was directly proportional to temperature, occurred by the law of viscous flow of amorphous particles, and was independent of the temperature increase rate. The apparent sintering activation energies of the studied micro- and nanopowders were 180 and 60 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The high-temperature solid-phase interaction of hydroxyapatite (HA) with magnesium, strontium, and zinc nitrates at the stage of annealing of ceramics was investigated. The phase composition and unit cell parameters of the obtained materials were studied for various metals introduced into the structure to different concentrations. The introduction of Mg led to partial decomposition of HA to tricalcium phosphate and tetracalcium phosphate, the addition of Sr caused partial formation of tetracalcium phosphate from HA, and the doping with Zn gave rise to single-phase HAs. [ABSTRACT FROM AUTHOR]

Si3N4-based ceramics have been produced by hot pressing in the temperature range 1550–1650°C using α-Si3N4 starting powder and CaO–Al2O3 (48 : 52 wt %) sintering aids. The powders and the ceramics have been characterized by dilatometry, scanning electron microscopy, and X-ray diffraction, and we have measured the microhardness and density of the ceramic samples. The results demonstrate that the sintering aid reacted with Si3N4 to form Ca-α-SiAlON. At 40 wt % sintering aids, all of the silicon nitride was converted into Ca-α-SiAlON. We have clarified general trends in the effect of the amount of sintering aids on the properties of the ceramic samples. [ABSTRACT FROM AUTHOR]

Abstract—: This paper presents dilatometric analysis data for the sintering of off-the-shelf molybdenum disilicide (MoSi2) powder prepared by magnesiothermic synthesis. We have obtained continuous shrinkage curves for MoSi2 powder compacts with an initial relative density of 70% at different heating rates: 5, 10, 20, and 30°C/min. From a quantitative analysis of densification curves for the compacts, the activation energy for the initial stage of sintering has been determined to be Q = 695 kJ/mol. It has been shown that the dominant process in the initial stage of MoSi2 powder sintering is volume diffusion from grain boundaries and surfaces. [ABSTRACT FROM AUTHOR]