Preparation of Lightweight Mullite-Anorthite Refractories by Different Routes

Mullite-anorthite as a kind of lightweight refractory combines the low thermal conductivity of anorthite and the excellent thermal properties of mullite. In this work, mullite beads and calcium aluminate cement was used as the main component and bonding agent. The lightweight mullite-anorthite refractory was prepared by difference routes including foaming method, addition of pore-forming agent and sacrificial template method. The phase composition, bulk density, apparent porosity and thermal conductivity of samples were compared. The results showed that anorthite formed as the consequence of the reaction of cement and mullite. Extra addition of foam, cornstarch and polyurethane sponge could decrease the bulk density of samples. The pore size of samples prepared by foaming method was the smallest. The apparent porosity of samples obtained by sacrificial template method was largest, but the thermal conductivity was the highest due to the open pores.

Influence of Contents of Pre-Synthesized Spinel on the Microstructures and Mechanical Properties of the Lightweight Corundum-Spinel Refractory Castables

Five kinds of lightweight refractory castables were prepared by using lightweight corundum-spinel aggregates (LCSA), pre-synthesized spinel (PSS), magnesia and corundum powders as raw materials. Effects of the PSS contents on the microstructures and mechanical properties of the refractory castables were studied by means of X-ray diffractometer (XRD), elastic modulus tester and scanning electron microscopy (SEM), etc. It is found that with the PPS content increase from 0 to 15.3 wt %, the permanent linear change (PLC) of castables sintered at 1600 °C decreases from 1.02% to -0.56%; the bulk density (BD) and apparent porosity (AP) are in the range of 29.6 %~27.8 % and 2.71~2.79 g/cm3, respectively, changing a little; the cold compressive strength (CCS) decreases from 106.0 MPa to 94.4 MPa; the thermal shock resistance improves; the hot modulus of rupture (HMOR) decreases from 6.7 MPa to 4.3 MPa. Considering these aspects, sample with 7.6 wt% PPS (LA7.6) has the best performance.

In Situ Growth of Mullite Whisker Using Different Aluminium Source and Properties of Mullite-Corundum Lightweight Refractory

In-situ growth of mullite whisker from waste coal gangue and different aluminium source mixtures by dry pressing were investigated aiming at the preparation of mullite - corundum lightweight refractory by controlling mullite whisker precursor pseudo particle size and quantity in corundum matrix. The phase composition and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Apparent porosity and bending strength were also measured. The samples exhibited characteristic alumina and mullite phases. The formation mechanism and influence factors for mullite whiskers materials were discussed. The experimental results showed that the whisker of the obtained sample changed from the accumulated short column to mesh cross acicular whisker shape, and the length to diameter ratio increases. When the aluminium source was aluminium hydroxide, the length to diameter ratio and apparent porosity reached the maximum of 17.6 and the minimum of 2.15%. The bending strength of all the samples was similar, that of the sample prepared by calcined bauxite was the largest (84 MPa), that of the sample prepared by calcined alumina was inferior, and the sample prepared by aluminum hydroxide was the lowest.

Differences in the Mechanical Properties of Lightweight Refractory Cementitious Composites Reinforced by Various Types of Fibers

Development of new composite materials is the worldwide extremely progressive branch of engineering activity. Composite materials are applied in many industries. The principle of composite materials is a combination of different materials providing an entirely new material with specific properties. Fiber-reinforced composites rank to the most frequently used composites because of their suitable mechanical properties. There were studied mechanical properties of fibre reinforced cementitious composites (FRCC) exposed to high temperatures of 600 °C and 1000 °C in the paper. For the production of refractory FRCC were used aluminous cement Secar®71 with 70 % of Al2O3. Various composites differed in the used type of fibers - basalt, carbon and ceramic fibres were applied in doses of 2 % by volume. For the experimental program were prepared prismatic specimens with the total dimensions of 40 × 40 × 160 mm3 and cured for 28 days in humid environment. Residual bulk density, flexural and compressive strength were investigated in the performed experimental program. The results showed the positive effect of the fibers used in refractory composition and the dependence on the length of the used fibers.