Advanced Materials Research Vols. 105-106

Abstract: The effects of replacement of MgO by CaO, on the characterization and crystallization behavior of glas-ceramics in the CaO-MgO-SiO2 system were investigated by DTA, XRD and FTIR techniques and by density measurements. The results show that the glass transition temperature (Tg) and crystallization temperature (Tc) increase and glassy structural network becomes denser with increasing the CaO/MgO weight ratio. After certain heat-treatment procedure, the major crystal phases change from calcium magnesium silicate (diopside) to calcium silicate (parawollastonite) at the replace of MgO by CaO. Studying of density measurement shows that, the density of glass samples increase by increasing CaO content on the expense of MgO.

Abstract: In this article we present a new kind of large grain transparent glass-ceramics obtained by the method of crystal growth from a homogenous glass, the simultaneous variation of the glass matrix and crystalline compositions during the crystallization results in the high transparency of this kind of large grain, high crystalline volume glass-ceramics, which have suitable refractive indexes between respective phases. The nucleation and crystallization behaviors of this kind of glass-ceramics have been investigated. The optimum heat treatment schedule for the glass was determined by means of DSC, XRD and SEM. The desirable optical property, such as laser characteristics etc, of this new kind of glass-ceramics can be further developed by doping with transition metals or rare-earths.

Abstract: Phosphorus slag could be used to prepare wollastonite glass ceramics. With the aid of incorporated foaming agent, foam glass ceramics can be obtained via the sintering of the slag-based glass. After the glass powder reacted with graphite, macro-size pores with homogeneous distribution were formed. The level of porosity of the fabricated foams was controlled by varying heat treatment temperature and amount of foaming agent. It was found that the preferential processing parameters for producing foam glass ceramics were foaming temperature of 1000°C with holding time of 10 min and 1 wt. % of graphite. In this case, the porosity reached about 80%. The results show that dominant crystalline phase is wollastonite, and the high compression strength results from the crystallization of glass during sintering process.

Abstract: A technique for the preparation of porous ceramic materials by gelcasting mothod is studied using a water-soluble epoxy resin combined with a amine hardener. The increase in the volume and rheological behavior of slurry , TGA and DSC of the green bodies are investigated. The influence of solid content on the relative density, the cell size distribution and the compressive strenghth is studied. The experimental results show that in the measurable shear rate range the rheology of slurry exhibt a shear thinning behavior, the relative density increase with the solid content, with the decrease of the relative densities the cell size increase. The compressive strength increased exponentially with the increase relative density, and the exponent, m, is 1.094.

Abstract: Porous SiC ceramics with high porosity and high strength were fabricated by gelcasting, with tert-butyl alcohol (TBA) as solvent, acrylamide (AM) as monomer, and in-situ reaction bonding with a-Al2O3 as sintering additive. SiC suspension with 10 vol% solid loading was successfully solidified by gel-casting to form high strength green body. The results showed that the compressive strength of the porous SiC ceramics increased with sintering temperature from 1300 to 1450°C, but porosity had little change, due to formation of more volume of cristobalite and mullite phases on the surface of SiC grains, accompanied by a large volume expansion effect. Very narrow single-peak distributions with about 2 mm median pore diameter could be found for the porous SiC ceramics. The porosity and compressive strength of the porous SiC ceramics sintered at 1450°C were 71.21 % and 12.14 MPa, respectively.

Abstract: It is an effective way to decrease dielectric constant of microwave transparent materials by improving porosity rate. Network -Si3N4 porous transparent materials were prepared by gas pressure sintering (GPS) with Y2O3 additions. Porosity rate of silicon nitride using pore former with different content starch, polytetrafluoroethylene (PTEE) powder respectively and their compounded component were discussed in this paper. It is concluded that porosity rate can be improved by all the three, starch is most favorable to improve porosity but great volume rebound after cold iso-static pressing were happened and easily lead to crack of green body. Method of pore-making by step on principle of pore formers discharging in different temperature range used to get high strength and porosity green body. Series of porous silicon nitride microwave transparent materials were prepared with porosity rate from 48% to 67%, bending strength from 162MPa to 59MPa and dielectric constant from 3.41 to 2.37.

Abstract: Hydroxyapatite (HA) doped with 3%yttria-stabilized 20wt% zirconia (ZrO2) ceramic were developed in order to produce a porous composite biomaterial by integrating the gel-casting technique with polymer sponge method with improved mechanical strength and controllable porous structure. The pore morphology, size, and distribution of the scaffolds were characterized using an electron microscope. The scaffolds prepared have an open, uniform and interconnected porous structure with a pore size of 300~500m. The porosity of the open pores in the scaffold can be controlled by changing HA-ZrO2 composite concentration and it is between 87%~35%. A compressive strength of 12MPa for HA-ZrO2 porous scaffolds with HA-ZrO2 concentration of 55wt% was achieved, which is comparable to that of cortical bone.

Abstract: A foam ceramic was prepared using clay, SiC, Fe2O3, feldspar and other raw materials as main starting material in a furnace at 1140~1170oC for 15~25min. Effects of silicon carbide’s content and powder size on the bulk density, moisture absorption rate and compressive strength were studied, and the fracture surface morphology was observed and analyzed using Scanning Electron Microscope (SEM) and X-ray diffraction analysis (XRD). The results show that SiC powder reacted with Fe2O3, Fe3O4, CO2, iron, SiO2 and form foam. The sintering behavior and properties of the foam ceramics are influenced by the content and particle size of SiC, when the content of SiC is as high as 8%, and the mass ratio of grain size is 1:1, the foam ceramics with the rate of moisture absorption is 0.05%, the bulk density is 0.32g/cm3, and compressive strength is than 2.2MPa.

Abstract: The porous SiC ceramics were prepared by two methods of pore-forming. The gas permeability and flexural strength of the porous SiC ceramics prepared by different ways were investigated. The porous SiC ceramics prepared by particle stacking have evenly pore distrubution; the gas permeability was greatly increased with the particle size increasing while the porous SiC ceramics were kept a higher flexural strength. The pore-former also can be used to form large pores to increase the gas permieability. However, these unevenly distribution large pores lead to a deterioration in flexural strength.

Abstract: Zeolite-attapulgite nano-pore structure ceramisite was prepared using natural zeolite and attapulgite through compounding, granulation and calcination.After elementary characterization of this ceramisite by mercury porosimeter, batch tests were carried out to examine its removal mechanism of ammonia. The influences of pH, contact time, initial ammonia concentration and temperature on the ammonia removal were investigated. The optimum pH for adsorption of ammonia was found to be less than 7. The adsorption process followed pseudo-second order rate model. Adsorption isotherm studies showed that Freundlich model fitted the experimental data. The sorption of ammonia increased with the rise of temperature because adsorption process was endothermic. The zeolite-attapulgite composite nano- pore structure ceramisite shows very good promise for practical applicability of ammonia removal from aqueous solution.