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The crystal growth of hydroxyapatite (HAp) using a solvothermal method was investigated under various reaction conditions. The purpose of the present study is the synthesis of HAp nanocrystals with multiple facets and the atomic arrangement for various orientations of the crystal was clarified. HAp nanorods were obtained at 200°C after 24 h using a reaction medium of water. The atomic arrangement in HAp nanorods was examined for a characteristic facet in the direction of [21−13−] and [0110−] incidences and crystal orientation along the c‐axis of HAp nanorod was confirmed using electron microscopy. The present study clarifies the HAp crystal growth mechanism, where the adsorption of cations or anions onto the crystal facet determines the HAp crystal shape. The crystals of HAp grew along the c‐axis and became rod‐shaped suggesting that cations were adsorbed predominantly over anions. [ABSTRACT FROM AUTHOR]

Magnesium whitlockite (Mg-WH, Ca18Mg2(HPO4)2(PO4)12) is a promising candidate for biomedical application in bone regeneration; however, the fabrication of Mg-WH bioceramics by conventional methods is limited. Mg-WH is known to be thermally unstable and decomposes upon heating. The mechanism of thermal decomposition and phase evolution has not comprehensively been investigated so far. In the present work, Mg-WH was synthesized by a dissolution–precipitation process under hydrothermal conditions. Thermally induced degradation of the synthesized powders was investigated in detail by combining X-ray diffraction (XRD) analysis, infrared spectroscopy (FTIR), Raman spectroscopy as well as 1H and 31P solid-state nuclear magnetic resonance (NMR). The as-prepared Mg-WH powders were annealed at different temperatures in the range from 400 to 1300 °C. It was found that thermal decomposition starts at around 700 °C with the formation of beta-tricalcium phosphate (β-TCP, Ca3(PO4)2) and a mixture of two Ca2P2O7 polymorphs. Thermal decomposition occurs gradually and the co-existence of both Mg-WH and Mg-substituted β-TCP phases was observed in a wide temperature range up to 1200 °C. Complete disappearance of the HPO42− structural unit was confirmed only after annealing at 1300 °C followed by melting at 1400 °C. [ABSTRACT FROM AUTHOR]

Octacalcium phosphate (OCP) has received considerable attention in the field of ceramic biomaterials as an advanced functional material. It exhibits a layered structure composed of apatitic and hydrated layers and can incorporate various dicarboxylate ions into the hydrated layer. Saturated dicarboxylic acids (HOOC(CH2)nCOOH) with an odd number of methylene groups (–CH2–) exhibit lower incorporation fractions than those with an even number of methylene groups, possibly owing to a compositional dependence on the synthetic method. In this study, calcium carbonate, phosphoric acid, and various amounts of glutaric acid were used to produce glutarate-ion-incorporated OCP by a wet chemical method, which is different from the conventional synthetic strategy. While utilising 1–20 mmol of glutaric acid during synthesis did not produce the desired product, using 25 mmol of glutaric acid resulted in the formation of single-phase glutarate-ion-incorporated OCP with a Ca/P molar ratio of 1.57 and a 90% incorporation fraction of glutarate ions. This glutarate-ion-incorporation fraction is significantly higher than that reported in the previous studies (35%). Thus, the synthetic procedure proposed herein was able to produce single-phase OCP containing glutarate ions with a high incorporation fraction. Our findings can contribute to development of novel functional ceramic biomaterials in the future. [ABSTRACT FROM AUTHOR]

Zinc whitlockite (Zn-WH, Ca18Zn2(HPO4)2(PO4)12) is a new synthetic analog of the second most abundant biomineral – magnesium whitlockite (Mg-WH, Ca18Mg2(HPO4)2(PO4)12), which is considered as a potential material for bone regeneration. In the present work, the formation of Zn-WH via a dissolution–precipitation process under hydrothermal conditions was investigated in detail. The influence of medium pH, reaction time, temperature and concentration of precursors on the formation of the single-phase material was studied. It was demonstrated that the phase-pure material can be obtained in the pH range from 5.6 to 6.2 in a very short period of time – 1 h. Variation of chemical composition in terms of the Ca-to-Zn ratio was determined to be possible in a narrow range. The structural properties of the synthesized Zn-WH were investigated by powder X-ray diffraction analysis along with 1H and 31P solid-state NMR spectroscopy, FTIR spectroscopy, Raman spectroscopy and XPS. Rietveld refinement confirmed that the synthesized material has a rhombohedral structure with the R3c space group. The NMR study confirmed the presence of three inequivalent phosphorus atoms in the crystal structure, whereas only one PO43− tetrahedron was determined to be protonated. The size and shape of the particles can be controlled by the concentration of the precursors as well as by the initial Ca-to-Zn ratio in the reaction mixture. [ABSTRACT FROM AUTHOR]

This work aims to enhance the fracture toughness of brittle Al2O3 ceramics and apply insulated Al2O3 ceramics with electrical conductivity by dispersing second tungsten (W) metal particles. In order to investigate the effects of W dispersion on mechanical and electrical properties, Al2O3–W composites with various amounts of W (ranging from 5 vol% to 20 vol%) were fabricated by the hot‐press sintering method at various sintering temperatures. Microstructure analysis revealed submicron Al2O3 matrix grains and W particles. The existence of three phases of Al2O3, W, and AlWO4 was confirmed by X‐ray diffraction patterns. All Al2O3–W composites showed higher fracture toughness than monolithic Al2O3. The toughening mechanism was attributed to crack deflection and crack bridging. Transgranular fracture was visible in all composites. Electrical resistivity dramatically lowered from 2.9 × 1012 Ω cm of monolithic Al2O3 to 4.1 × 102 Ω cm of the composite with 20 vol% W addition. The percolation threshold is calculated as 18.5%. With the increase in sintering temperature, the amount of W particles was decreased and Al2O3 grains became large, leading to the reduced number of conductive pathways formed by the dispersed W particles. As a result, electrical conductivity was decreased. [ABSTRACT FROM AUTHOR]

A YBaCo4O7 oxygen storage material has been synthesized by the glycine-complex decomposition method at a low temperature of 800 °C and its crystal structure and reaction kinetics were investigated. This sample showed the highest storage/release speed among all the reported YBaCo4O7+δ materials. [ABSTRACT FROM AUTHOR]