Advanced Materials Research Vol. 412

Abstract: The nanosized fluorhydroxyapatite (FHA) had been synthesized by aqueous precipitation method. The effects of synthesis temperature,fluoride ion concentration and pH value on the fluoride substitution were investigated.The phase composition and the change of crystal structure were characterized by X-ray diffraction and fourier transform infrared spectroscopy. The results show that crystal lattice parameters and bond energy make changes by incorporation of F in the structure.The size of FHA crystals increase as the precipitation temperature. The phase composition of FHA is mainly controlled by the pH value.

Abstract: Transition heat adjustment of CaCl₂·6H₂O added small quantity of stable additives (Ba (OH)₂ and SrCl₂·6H₂O) was investigated by means of adding excess water. The experimental investigation results showed that, the transition heat adjustment of CaCl₂·6H₂O could be realized by adding excess water. With regard to CaCl₂·6H₂O, the suitable adjustment range of transition heat was 170kJ/kg-191.2kJ/kg as the proportion of adding excess water was 0-12.5% by weight; during the suitable adjustment range of transition heat, the phase change material with a random transition heat could be prepared by adding suitable excess water according to the actual requirement, and the transition heat of CaCl₂·6H₂O with different proportion of excess water could be forecasted. It is very beneficial for temperature and heat control in greenhouse.

Abstract: In this paper, α-Si₃N₄ was mixed with Y₂O₃ and MgO by ball milling. Spray granulation was adopted to fabricate spherical powder. The influence of the sintering temperature and the holding time on the thermal conductivity of the powder was studied. The results show that α-Si₃N₄ raw powder was transformed into β-phase after sintering. Spherical powder, of which the diameter is about 20 μm, was fabricated. Some compounds such as YMgSi₂O₅N, Y₄Si₂N₂O₇ and Y₂Si₃N₄O₃ were generated in the samples. The thermal conductivity of the pressed powder first increased then decreased with the sintering temperature rising, showing a maximum at 1800°C. Also the thermal conductivity first increased then decreased as the holding time getting longer, showing a maximum at a sintering time of 2 hours.

Abstract: Porous silicon nitride with pore forming agent of starch were prepared by cold isostatic pressing, forming problem of complex shapes were solved by methods of carbonization of starch and decreasing forming pressure. Products of porous silicon nitride had the performance parameter with density 1.5g/cm³, porosity over 55%, bending strength over 100 MPa.

Abstract: The electrophoretic deposition (EPD) technique has been developed to prepare AlN ceramics and the topic of this paper was the investigation of the AlN ceramic suspensions for electrophoretic deposition. The only addition of triethylamine didn’t promote the hydrolysis of AlN powder in 95% ethanol. The absorption of the polyacrylic acid (PAA) resulted in an increased Zeta potential, indicating that PAA is a very effective dispersant for the AlN and Y₂O₃ powders. Furthermore, by adding a combination of PAA and triethylamine, an stable AlN suspension could be obtained which was necessary for realising a high packing density in the electrophoretically deposited green bodies. The conductivity measurements indicated that suspension conductivity was lower than liquid conductivity. The lower conductivities of the suspensions could be explained by the fact that in concentrated suspensions the free ionic species are hindered in their movement by the particles. The conductivity of the centrifugate was higher than that of the suspension. It can be concluded that during the EPD the current in the suspension is mainly carried by the free ionic species. The transport of positively charged ionic species to the upper electrode (cathode) was slower than their consumption by the electrode reaction, an increased concentration overvoltage caused a significant increase in total electrical resistance due to the higher potential drop at the cathode. Finally, the EPD was usually stopped according to the increase in potential drop.

Abstract: Ti₂SnC powders (Ti: Sn: C =2: 1.2: 1, mol.%) were synthesized by pressureless sintering in argon in the temperature range of 600 to 1050°C using Ti, Sn and graphite powders as the initial materials. The phase relationships during reaction in the ternary system Ti-Sn-C have been investigated. The products for identification and analysis were characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). The reaction path for the formation of Ti₂SnC can be described in the following steps. Sn melted at 230°C, which provided a favorable liquid circumstance for the reactions between Ti and Sn to form Ti-Sn intermetallic compounds. Results showed that Ti₆Sn₅ and Ti₅Sn₃ intermediate phases were formed in turn with increase of temperature. Up to 1050°C, with consumption of Ti₅Sn₃ phases completely, the amount of Ti₂SnC increased significantly. Single phase Ti₂SnC with small amount of TiC was produced. Combined with the results of differential thermal analysis (DTA) and X-ray diffraction (XRD), it is revealed that Ti₂SnC phase is formed by the reaction of Ti–Sn intermetallic compounds, Ti and graphite. In addition, the reaction equations of the process from 230 to 1050°C were given.

Abstract: Two kinds of high active coal gangue powder (ACGP) were prepared by heat treated and ball milled coal gangue. The density, fineness, Loss on ignition (LOI), activity and influence of the fineness of the two kinds of ACGP on the density and I/W (compressive strength to weight of the foam concrete specimens) of foam concrete were also studied in this paper. The results show that the density and I/W of the foam concrete were greatly affected by the fineness of ACGP. The finer of the ACGP, the lower density and higher I/W of the coal gangue foam concrete will be got. Based on the experimental results, a method to evaluate the activity of active powder used for cement admixture is proposed and the activity of the ACGP is also evaluated.

Abstract: Recycling fly ash in a way with high benifits is important to environmental conservation and sustainable development. Using bentonite as binder and coal powder as pore-forming agent, the fly ash-based porous ceramics was prepared and effects of bentonite on performances of the ceramics were researched. With the increasing of bentonite content from 3.0mass% to 5.0mass%, liquid phase sintering process was promoted and the bending strength improved from 5.46 to 6.09Mpa. Contrarily, the open porosity decreased from 48.18% to 44.39%. But more bentonite addition would result in some larger pores distributed inhomogeneously in the microstructure so that the bend strength fell down and porosity went up.

Abstract: Mesoporous alumina is usually used as adsorption material, catalyst carrier or separation media due to its high adsorption and good thermal stability. However, the nanosized powder trends to aggregation except that its size is in sub-micron scale. The best choice is that the sub-micron alumina particles with mesoporous structure are prepared. In the present work, the mesoporous alumina spheres were prepared by micro emulsion method using aluminium isopropoxide as raw material and water/dimethylbenzene emulsion as reaction media. The obtained powder was characterized by XRD, TEM and BET. The results show that the particles are global. The particles size is in the range of 100 ~ 200 nm to several micrometers. The particle owns the worm-like structure with the pore size of 5 nm. The BET surface area of the mesoporous alumina is 81.8 m²/g. The obtained powder is suit to be used as the packing material in chromatograph.

Abstract: Highly permeable porous alumina (Al₂O₃) hollow fiber membranes have been developed by a combined phase inversion and sintering technique. Ethanol substituting for water was used as the external coagulant in order to prepare Al₂O₃ hollow fiber membranes with low trans-membrane resistance. The prepared Al₂O₃ membranes show a special asymmetric structure with an outer skin layer, highly porous inner surface and sub-layer composed of long and large finger-like pores. The influences of sintering temperature on the average pore size, N₂ permeability and bending strength were investigated. Results show that Al₂O₃ hollow fiber membranes with higher permeability can be prepared using ethanol as the external coagulant. The prepared Al₂O₃ hollow fiber membranes show a N₂ permeability of 871.5 m³·m^-2·h^-1·bar^-1 and a bending strength of 91.4 MPa when sintered at 1550°C for 5h.