Key Engineering Materials Vols. 368-372

Abstract: The silica-alumina sol bonding agent, prepared by the sol gel route from ethyl silicate and aluminium isopropanol, was utilized in the refractory castables. The influence of structure on the heat transfer has been investigated using different sorts of refractory matrix. The results indicated that the heat conductivity of sol-gel bonded castables was considerably affected by their structure. The phase composition of matrix, porosity, pore size distribution and pore size structure were the most important factors. Thermal conductivity has been measured from the ambient temperature up to 1250 °C. The influence of crystalline phases and the glassy phase formation and the influence of the pore size distribution on the thermal conductivity were also described in this work.

Abstract: The preparation process of alumina-spinel slurries by using micro-sized alumina-spinel mixtures as raw materials was investigated. The slurries with solids content of 62 vol% and viscosity of 0.3 Pa·s were prepared by adding self-made dispersant ANSP which was a mixture of AN-2000 and STP in mass ratio of 4 to 1. The alumina-spinel refractory was fabricated from the slurries by gelcasting process. The dry parts containing micro-sized alumina-spinel powders with 3.57wt% gel have the highest bending strength of 29.8 MPa and 17.6 MPa with 15:1 AM-MBAM and 4:1 MAM-MBAM respectively. The bending strength enhanced with the increase of reaction temperature. For example, to the 15 wt% 15:1 AM-MBAM gel premix, the bending strength of the parts gelled at 25°C and 55°C were 27.3 MPa and 32.4 MPa respectively. The bending strength also increased with the rising of the amount of monomer.

Abstract: The temperature distribution of the permeable brick was modeled using CFX software. The influence of magnesia and corundum on thermal shock resistance of non-cement bonded alumina-based permeable brick was investigated. The results indicated that, in the gas blow process, the high temperature regions near the working face of the brick gradually expanded with the increase of the gas flow rate. Therefore the inner part of the brick had the complex and large change of thermal stress. Further experiments demonstrated that thermal shock resistance of alumina-magnesia based castable refractory was better than that of alumina-chrome based castable refractory. With the increase of magnesia amount, the alumina-magnesia based castable refractory had more cycles of heating and water-cooling. When different kinds of corundum were added in the raw materials, the sample with tabular corundum showed the best thermal shock resistance, the one with white fused corundum performed worse and the one with fused dense corundum performed worst.

Abstract: The resistance coefficients through which gas flow permeable refractory are important properties and have great effect on the gas blowing parameters and gas-liquid two phase flowing characteristics in the metallurgy furnace such as ladles, tundish. In this paper, the resistance coefficients were measured according to the Forchheimer’s law. The results show when the gas flow rate is fixed, the viscosity resistance coefficient and inertia resistance coefficient decrease as the apparent porosity and average pore diameter increase. The viscous resistance coefficient is more lager than the inertial resistance coefficient. The resistance coefficients were analyzed by dimensional analysis and the statistical correlations between the resistance coefficients and parameters of porous permeable refractory were got based on the experimental data. In order to get high strength at low resistance coefficients, the raw materials particle degree were adjusted.

Abstract: The effects of Y2O3, La2O3 and Nd2O3 on the sintering, microstructure and mechanical properties of magnesia refractories were investigated. Addition of rare earth oxide (ReO) to magnesia refractories increases the bulk density, decreases the porosity and improves the mechanical strength of the refractories. The improved sinterability was attributable to the vacancies generation associated with the solid-solution reactions between MgO and ReO. In the samples with ReO, rare earth silicate phases form at magnesia grain boundaries, providing additional bonding between magnesia grains and between magnesia grains and matrix. Consequently, the samples with ReO showed much higher high temperature strengths than those without ReO.

Abstract: The paper describes β-TCP/DCHA and mineral phase structural bioceramics(CHA) as well as their 3-D structures, bioactivity, degradability and introducing new bone growth. FT-IR, XRD, SEM and Micro-CT were used to evaluate β-TCP/DCHA and mineral phase structural ceramics before and after implantation. Osteoblasts were immersed in the bioceramics and implanted in the rabbit femora. The experimental results showed that new bone grown in β-TCP/DCHA, and scaffolds were degraded with new bone formation and growth. The results indicated that β-TCP/DCHA was a better tissue engineering material. A kind of biomaterial (β-TCP/CHA) can be used for in situ formation or in vitro individuation formation. The experimental results indicated that β-TCP/CHA possessed better osteoblast affinity. Osteoblasts can adhere, proliferate and grow better on the material. The experiments in vivo showed the materials bonded with osseous tissue. The implants were degraded obviously after 6 months, and new bone replaced degradation materials.

Abstract: In this work, a simple, reproducible and low-cost synthesis method for the preparation of ß-tricalcium phosphate (ß-TCP) was developed. ß-TCP was prepared via wet mechanochemical treatment using calcium oxide and calcium hydrogen phosphate as raw materials. XRD and FTIR analysis indicated that the as-treated precursor was non-stoichiometric, poorly-crystallized carbonated hydroxyapatite (CHA) resulting from the mechanochemical reaction, and the crystalline ß-TCP powder was obtained by calcining the precursor at 800°C for 2 hours. SEM observation showed that the addition of surfactants could eliminate the agglomeration of the powder and well-dispersive ß-TCP powder with a particle diameter between 0.1 and 2.0 2m can be obtained.

Abstract: In this study, biomemitic hydroxyapatite was prepared as a nano-sized powder from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts, but using the different contents of PVP modified hydroxyapatite and synthetic body fluid (SBF) solutions as synthesis medium instead of pure water at 37.4C and pH of 7.4. SBF was prepared in accord with the chemical analysis of human body fluid, with ion concentrations nearly equal to those of the inorganic constituents of human blood plasma. Characterization and chemical analaysis of the synthesized biomemitic hydroxyapatite powders and pure hydroxyapatite were investigated by X-ray powder diffraction, scanning electron microscopy, and inductively coupled plasma atomic emission spectroscopy. Rheological properties of HAP sol which reflected the interaction of hydroxyapatite particles were measured by R/S rheometer. The results showed that PVP evidently affected the stability and rheological properties of HAP sol, and PVP were based on the different mechanism at different concentrations. PVP was operating as an interparticle bridging reagent at low concentrations(0.5%), while it acted as an dispersant at high concentrations(2.0%). The biomemitic hydroxyapatite with the sizes of 10~30nm was spherical and poor crystalline, which was synthesized in synthetic body fluid (SBF) by addition of 2.0% PVP.

Abstract: Calcium polyphosphate (CPP) bioceramics with different Ca/P ratios were fabricated. It was shown that the contents of CPP in the sintered ceramics decrease with the increasing Ca/P ratios (0.5-1.0) of the precursors. The higher the Ca/P ratios of precursors were, the more complex the phases of polymerization were. The compressive strengths of ceramics sintered at the same temperature showed a linear decreasing tendency with the increasing Ca/P ratio.

Abstract: The bioactive synthetic hydrogel materials were prepared with polyethylene glycol diacrylate (PEGDA) and 2-hydroxyethyl mathacrylate (HEMA) by UV photo-polymerization. The aim of this study was to prepare a scaffold material by combining HEMA into a composite polymeric PEGDA-based hydrogel, which were used as bioactive artificial cartilage. The structure and properties of the synthetic hydrogels were investigated in details using FTIR techniques. The swelling data indicated that the equilibrium water content depended on the precursor feed ratio. It was found that adding the HEMA into the PEGDA-based hydrogels was very helpful to improve the swelling properties.