Decomposition Of HA Research Articles

Plasma sprayed graded titanium hydroxyapatite coatings

A series of graded titanium-hydroxyapatite (HA) coatings have been produced by single gun plasma spray technology, and their performance was compared with that of pure HA coating. The results show that deformed HA and titanium particles exhibit an alternate distribution in respective networks formed within the coatings. In comparison with a pure HA coating, less cracks appeared on the surface of the graded coatings and the shear bond strength was increased by 50-80%. The graded coating with two interlayers and a thin outer HA layer contained crystalline HA, an amorphous phase, α-tricalcium phosphate (TCP), β-TCP, tetracalcium phosphate (TTCP), TiO2 and TiN; while no Ti-HA compounds were formed. As compared with pure HA coating, the graded coating contained more decomposed phases TCP and TTCP, resulting from titanium catalysing HA decomposition.

Degradation of humic acids by the litter-decomposing basidiomycete Collybia dryophila.

The basidiomycete Collybia dryophila K209, which colonizes forest soil, was found to decompose a natural humic acid isolated from pine-forest litter (LHA) and a synthetic (14)C-labeled humic acid ((14)C-HA) prepared from [U-(14)C]catechol in liquid culture. Degradation resulted in the formation of polar, lower-molecular-mass fulvic acid (FA) and carbon dioxide. HA decomposition was considerably enhanced in the presence of Mn(2+) (200 microM), leading to 75% conversion of LHA and 50% mineralization of (14)C-HA (compared to 60% and 20%, respectively, in the absence of Mn(2+)). There was a strong indication that manganese peroxidase (MnP), the production of which was noticeably increased in Mn(2+)-supplemented cultures, was responsible for this effect. The enzyme was produced as a single protein with a pI of 4.7 and a molecular mass of 44 kDa. During solid-state cultivation, C. dryophila released substantial amounts of water-soluble FA (predominantly of 0.9 kDa molecular mass) from insoluble litter material. The results indicate that basidiomycetes such as C. dryophila which colonize forest litter and soil are involved in humus turnover by their recycling of high-molecular-mass humic substances. Extracellular MnP seems to be a key enzyme in the conversion process.

Risk evaluation of decomposition of hydroxylamine/water solution at various concentrations

AbstractThe thermal property of HA/water solution was studied from the calorimetric data obtained using differential thermal analysis (DTA). The intensity of decomposition was studied from results of a mini closed pressure vessel test (MCPVT), and a pressure vessel test (PVT), in addition to the steel tube test.The thermal analysis was conducted to evaluate the ease of thermal decomposition using DTA. The heat‐release onset temperatures using the no‐treated stainless steel cells were more than 70° C below those measured using the gold‐coated stainless steel cells. This result implies that the heat‐release onset temperature depends on the materials of the sample cell.The intensity of the thermal decomposition was investigated using the MCPVT, the PVT, and the steel tube test. The intensity of the thermal decomposition increased as the HA concentration increased in the MCPVT. The intensity of the thermal decomposition increased greatly when the HA concentration was beyond 80% (wt.) in the MCPVT. It was determined that the thermal decomposit ion of HA 70%/water solutions was very violent in the PVT. In addition, HA/water solutions of more than 80% concentration could detonate in the steel tube test.

PHASE STABILITY AND MICROSTRUCTURAL DEVELOPMENT OF Y-TZP–DOPED HYDROXYAPATITE

Hydroxyapatite containing yttria-tetragonal zirconia polycrystals (Y-TZP) with different concentrations were prepared by using the conventional ball-milling technique. Samples prepared from these powders were compacted and sintered at three different temperatures (1250°C, 1400°C and 1600°C). The sintering behaviour of the composites were studied in terms of phase stability, densification and microstructural evolution. By X-ray diffraction, tetragonal zirconia as well as HA was identified as the major phases in the composites. In addition, small diffraction peaks corresponding to α-TCP was evident indicating sign of HA decomposition. Reaction between the zirconia and HA to form CaZrO2 was also detected in the composite system containing up to 20 wt% Y-TZP. SEM examination of the sintered composites at room temperature suggested the involvement of a reactive liquid phase during sintering. The presence of zirconia phase in hydroxyapatite matrix played an important role in the stability of the HA phase.

Synthesis of biomimetic Ca-hydroxyapatite powders at 37°C in synthetic body fluids

An important inorganic phase for synthetic bone applications, calcium hydroxyapatite (HA, Ca 10(PO 4) 6(OH) 2), was prepared as a nano-sized (∼50 nm), homogeneous and high-purity ceramic powder from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts dissolved in modified synthetic body fluid (SBF) solutions at 37°C and pH of 7.4 using a novel chemical precipitation technique. The synthesized precursors were found to easily reach a phase purity >99% after 6 h of calcination in air atmosphere at 900°C, following oven drying at 80°C. There was observed, surprisingly, no decomposition of HA into the undesired β-TCP phase even after heating at 1600°C in air for 6 h. This observation showed the superior high-temperature stability of such `biomimetic’ HA powders as compared to those reported in previous studies. The former powders were also found to contain trace amounts of Na and Mg ions, originating from the use of SBF solutions instead of pure water during their synthesis. Characterization and chemical analaysis of the synthesized powders were performed by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infra-red spectroscopy, scanning electron microscopy, and inductively coupled plasma atomic emission spectroscopy.

Glass-reinforced hydroxyapatite: a comprehensive study of the effect of glass composition on the crystallography of the composite.

Glass-reinforced HA composites were produced using phosphate-based glasses, and a structure refinement was carried out to determine the effect of the glass on the structure of the residual HA. Quantitative phase analysis showed that the glass causes some of the HA to decompose to beta-TCP and, at higher temperatures, to alpha-TCP. It also was indicated that when three phases were present, the formation of the alpha-TCP arose from decomposition of the beta-TCP and not from further decomposition of HA to alpha-TCP. The unit cell dimensions showed a decrease in the a axis and an increase in the c axis, giving an overall unit cell decrease in volume. There also was a significant effect based on the amount of glass added. The changes found in the composite containing the 4 wt% glass were attributed to the loss of carbonate and loss of hydroxyl. This was expected to cause shrinkage in the unit cell; however this was not seen, and therefore the major changes in the unit cell were attributed to the ions from the glass taking an interstitial role in the HA structure, thus not allowing the unit cell to shrink as much as expected.