Hydroxyapatite coatings by a polymeric route

A new polymeric route using calcium nitrate and phenyldichlorophosphine as initial compounds and acetone as solvent is described. Hydrolysis and subsequent oxidation with air led to the formation of a viscous solution which could be transformed to a solid polymer by subsequent drying. Calcining this polymer at temperatures in the range of 900 to 1100°C led to the formation of hydroxyapatite possessing a slightly distorted lattice. Dip-coating of alumina and titanium substrates using highly viscous solutions, or repeatedly carried out dipcoating, led to the formation of thick, highly porous hydroxyapatite layers.     

Facile synthesis of SiBCN powders by a carbonitriding route

SiBCN ceramic powders were facilely synthesized from the compacts of silicon, B₄C and cornstarch by a carbonitriding route. Effects of silicon content in raw materials on phase composition, chemical bond, microstructure and oxidation resistance of as-received products after heated at 1550 °C were investigated. The featured chemical bonds such as CN and BCN in as-received products were detected by X-ray photoelectron spectroscopy (XPS). The microstructure of BN(C) distributed around nano-sized α/β -SiC/SiCN grains was revealed by transmission electron microscopy (TEM). The synthesized products with the Si/B/C ratio of 1:1:1 presented better oxidation resistance than SiC because of the strengthened chemical bonds and BN(C) formation.     

碳化钨/钴热喷涂粉末和涂层的研究进展

热喷涂传统碳化钨/钴金属陶瓷作为耐磨涂层已得到广泛的应用。近几年来,纳米结构涂层的热喷涂研究成为新的发展趋势。本文总结了传统和纳米结构 WC/Co热喷涂粉末的制备方法及其性质对涂层性能的影响因素,分析了涂层的微观结构和脱碳机理,简述了热喷涂纳米结构及纳米结构 微米结构 WC/Co涂层的研究进展,并指出了其发展方向。     

Fabrication of nanosized alumina powders by a simple polymer solution route

Nanosized alumina (Al2O3) powders had been successfully fabricated by a simple polymer solution route employing polyvinyl alcohol (PVA) as an organic carrier. The fabricated alumina powders had an average particle size of 6.1 nm with a high specific surface area of 99.5 m2/g. As well, the alumina powders were fully crystallized to alpha phase at a relatively low temperature of 1000 degrees C. The PVA polymer contributed to a soft and porous microstructure of the calcined alumina powders, and ball-milling process with the porous powders was effective in making nanosized alumina powders. In addition, the content and degree of polymerization of the PVA affected the development of crystallization and powder properties. In this study, the simple polymer technique and milling process for the fabrication of nanosized alumina powders are introduced, and the effects of PVA on the property of the synthesized alumina powders are observed. For the study, the characterizations of the synthesized powders are conducted by using XRD, TEM, particle size analyzer, and nitrogen gas adsorption.     

Nanocrystalline cobalt-oxide powders by solution-combustion synthesis and their application in chemical sensors

The present study demonstrates the relationship between the combustion reaction mechanism induced by the exothermicity of the cobalt nitrate-glycine solution-combustion reactions and morphological details of the nanocrystalline Co₃O₄. The thermal decomposition pathway and the amount of the heat liberated in combustion are defined by the exothermic reaction between gaseous NH₃ and N₂O species. A direct evidence that the exothermicity of the combustion reaction plays an important role in formation of the powders with different morphology was obtained from the scanning and transmission electron microscopies. In contrast to stoichiometric reaction, where the short-string Co₃O₄ particles form hard agglomerates, the energetically softer 50% fuel lean reaction is responsible for weak bonds between Co₃O₄ particles and formation of the loose cauliflower-like agglomerates. The latter powder with the specific surface area of 64.4 m²/g and the average crystallite size of ～11 nm was used for the processing of drop-coated sensors, which showed a superior sensor response toward 20 ppm of acetone in 25% r.h. humidity and at low operating temperature of 150 °C.     

Evaluation of hard coatings on steel by particle erosion

There is a great need for better methods to characterize the mechanical properties of coated materials, especially for thin hard well-adhering films on, for example, steel. In this paper particle erosion is proposed as a potential test for the performance of coated materials.High speed steel was coated with a 1 μm TiN layer and exposed to particle erosion using various erosion parameters. The removal of the coating was monitored by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The change in intensity of the Fe Kα peak versus the particle dose was used to obtain a measure of the proportion of the substrate area revealed.A theoretical model was developed to describe the erosion process in terms of the particle dose and two characteristic film parameters. These are the mean area affected by a single impact and the mean number of consecutive impacts in one site necessary to make the coating spall.These quantities are closely related to practical adhesion, and controlled particle erosion is therefore proposed as a technique to evaluate adhesion.     

液相沉淀法制备羟基磷灰石粉体的现状及进展

评述了液相沉淀法制备羟基磷灰石(HA)粉体的最新进展,给出了各种工艺的常见反应物、工艺过程及工艺参数.比较了各种工艺之间的差异,并指出粉体制备存在的问题及发展趋势.     

Characterization of zinc carbonate hydroxides synthesized by precipitation from zinc acetate and potassium carbonate solutions

Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation of a white solid, whose composition and structure depend on the initial concentrations of the reagents. Hydrozincite, Zn₅(CO₃)₂(OH)₆, forms when the K₂CO₃ concentration is low and a new K-containing zinc carbonate hydroxide phase forms when the K₂CO₃ concentration is high. The chemical formula of the new phase has been determined to be Zn(CO₃)_0.61(OH)_0.780.233K₂CO₃ by TGA, CHNO and AA analysis. The new phase is insoluble in water and extensive water washing of the new phase does not change its composition or structure, suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified CO₂ causes disproportionation to separate phases of ZnCO₃ and K₂CO₃. Pure ZnCO₃ was synthesized for comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal synthesis of ZnCO₃.     

Preparation of nanocrystalline bredigite powders with apatite-forming ability by a simple combustion method

Nanocrystalline bredigite (Ca₇MgSi₄O₁₆) powders were synthesized by a simple solution combustion method. Phase pure bredigite powders with particle sizes ranging from 234 to 463 nm could be obtained at a relatively low temperature of 650 °C. The apatite-forming ability of the bredigite powders was examined by soaking them in a stimulated body fluid. The compositional and morphological changes of the powders before and after soaking were analyzed by X-ray diffraction and scanning electron microscopy and the results showed that hydroxyapatite was formed after soaking for 4 days.     

Preparation and dielectric properties of B-doped SiC powders by combustion synthesis

The SiC(B) solid solution powders were synthesized via combustion reaction of Si/C system in Ar atmosphere, using boron powder as the dopant and polytetrafluoroethylene as the chemical activator, which were investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and Raman spectra. Results show that the prepared powders are C-enriched SiC with C antisites and sp² carbon defects in which the sp² carbon is transformed to the sp³ carbon due to boron doping. The electric permittivities of the prepared powders were determined in the frequency range of 8.2-12.4 GHz. The dielectric real part ?′ and dielectric loss tan δ of undoped powder have maximum values (?′ = 5.5-5.3, tan δ = 0.23-0.20), and decrease with increasing boron content. The mechanism of dielectric loss by doping has been discussed.     

Pure and Gd doped LAMOX powders and thin films obtained by chemical route

Abstract

The present work deals with the preparation of pure and Gd doped LAMOX powders and thin films by a Pechini's based solution method. Gd doping proved to be efficient not only in stabilising the β form at room temperature but also in reducing the particle size and improving the film quality. Best results for both particles and films were achieved using 10 mol.-% dopant, which corresponds to the solubility limit. Concerning substrates, it was verified that they play a key role in film microstructure. Homogeneous and crack free films were obtained on glass, silicon and alumina substrates. Film density is quite dependent on the type of substrate, and glass substrates provided the densest films. The average thickness is ～150 nm for one layer film.     

Flame pyrolysis – a preparation route for ultrafine pure γ-Fe2O3 powders and the control of their particle size and properties

Highly dispersed γ-Fe2O3 powders with particle sizes down to 5 nm were directly synthesized by combustion of solutions of iron pentacarbonyl or iron(III) acetylacetonate in toluene in an oxyhydrogen flame. The particle size as well as other properties of the obtained powders can be controlled simply by varying the iron concentration in the starting solutions. Phase composition, morphological and magnetic properties of the powders were studied. The reasons for the formation of γ-Fe2O3 are discussed by means of structure–chemical/kinetic considerations. The materials are interesting as recording materials, or ferrofluids, or for colour imaging and bioprocessing. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of the mixing rate on the morphology and photocatalytic activity of ZnO powders prepared by a precipitation method

The urchin-like shape of ZnO powders was prepared by mixing of Zn²⁺ and NaOH solutions at various mixing rates. In this work, ε-Zn(OH)₂ was the first precipitant that was subsequently transformed to ZnO in the alkaline medium during heating. The size of the urchin-like shape of the ZnO powder decreased with a decrease of the mixing rate. The large urchin-like shape also had a large diameter of its hexagonal facet (0 0 0 1) and showed the highest photocatalytic degradative activity on methylene blue.     

Effect of fuel characteristics on synthesis of calcium hydroxyapatite by solution combustion route

The effect of fuel characteristics on the processing of nano sized calcium hydroxyapatite (HA) fine powders by the solution combustion technique is reported. Urea, glycine and glucose were used as fuels in this study. By using different combinations of urea and glycine fuels and occasional addition of small amounts of highly water-soluble glucose, the flame temperature (T _f) of the process as well as product characteristics could be controlled easily. The powders obtained by this modified solution combustion technique were characterized by XRD, FTIR spectroscopy, SEM, FESEM-EDX, particle size analyser (PSD) and specific surface area (SSA) measurements. The particle size of phase pure HA powder was found to be <20 nm in this investigation. The effects of glucose addition with stoichiometric (μ = 1) and fuel excess (μ > 1) urea and glycine precursor batches were investigated separately.