China's Refractories

To reveal the damage mechanism of high chrome bricks for opposed multi nozzle gasifier with expanded diameter, the chemical composition and the morphology of a used high chrome brick were researched using XRF, SEM and EDS, and the properties of the high chrome bricks were improved by adding ultra fine alumina, alumina-chrome-iron oxide synthetic material with spinel structure, and chromium metal. The results show that (1) the high chrome brick is seriously damaged by the chemical dissolution of chrome as well as the chemical reactions at the slag/brick interface, the slag penetration and the structural spalling; (2) FeO in the slag reacts with Cr₂O₃ in the brick to form a FeCr₂O₄ layer on the particle surface thus leading to spalling; CaO reacts with SiO₂ and Al₂O₃ in the brick forming a metamorphic layer of low melting point materials; due to the different thermal expansion coefficients of the metamorphic layer and the original brick, cracks appear and continue to expand and deepen under multiple temperature and pressure fluctuations thus leading to spalling of brick layer; (3) the improved brick has decreased apparent porosity, increased bulk density and compressive strength, and better thermal shock resistance compared with the original brick; after one cycle of on-site application, the furnace lining surface is smooth and flat with little damage, indicating that the improved high chrome bricks basically meet the working condition requirements of the opposed multi nozzle gasifier with expanded diameter, however, the final effects need to be evaluated in detail after the whole furnace service.

This work aims at solving the problems of difficult dispersion, easy oxidation and high cost of nano carbon during application, carbon/magnesium aluminate spinel (C/MgAl₂O₄) composite powders were prepared using MgC₂O₄·2H₂O, MgO₂, Al₂O₃ powder, and Al powder as raw materials by combustion synthesis. The results indicate that with the maximum MgC₂O₄·2H₂O addition of 33.34 mass%, the prepared powder contains 1.17 mass% of carbon and carbon distributes among spinel grains. The MgAl₂O₄ spinel shows both granular and rod-like morphologies. The granular MgAl₂O₄ spinel is generated from mutual diffusion between MgO and Al₂O₃; while the rod-like MgAl₂O₄ spinel is mainly formed by the vapor-solid growth mechanism from Mg vapor and Al₂O₃.

Composites place a vital role in the applications of material science, i.e. aerospace, automobile, marine, etc. Dual reinforcement composites are a trending research area in the field of metal matrix composites. In this research article dual reinforcement, i.e. zirconium silicate (ZrSiO₄) and carbon, is added to molten LM13 using the stir casting process in terms of (as cast), (3+3) mass%, (6+3) mass%, (9+3) mass% and (12+3) mass% respectively, using copper as a chill kept toward one end. The tensile, the hardness, and the microstructure of the composite specimens at the chill end and non chill end are studied. Experimental results are compared with analytical results and tabulated. It is found an increase in reinforcement and chilling effect enhances the properties of the composite. The ultimate tensile strength (UTS) and the hardness increase gradually with the increase in ZrSiO₄ addition. The maximum UTS, the hardness and the signal to noise ratio (S/N ratio) for mechanical characterizations are evaluated using Taguchi method. It is found that 9 mass% of ZrSiO₄ yields better results than the other combinations. Results are tabulated and compared using statistical tools. Microscopic studies reveal the uniform distribution of matrix and reinforcements with negligible agglomeration.

The progress of research and production of bauxite based homogenized grogs in China was summarized and the achievements of their application and modification in recent years were epitomized. In combination with the shortcomings existing in the research, production and application, the suggestions of bauxite based homogenized grogs for future development were put forward.

Dense corundum-mullite brick for blast furnace ceramic pad was prepared using white fused corundum and tabular corundum as aggregates, andalusite fine powder, sillimanite fine powder, zircon sand powder and Guangxi soil as the matrix, and phosphate as the binder, introducing different amounts of α-alumina micropowder, tabular corundum fine powder and fused corundum powder. The properties of the prepared brick were studied. The results show that, the brick with 10 mass% of tabular corundum fine powder fired at 1 560 ℃ for 3 h in a tunnel kiln has the bulk density of 3.08 g · cm ^-3, the apparent porosity of 13.2%, the cold compressive strength of 178 MPa, the molten iron corrosion rate of 0.6%, the slag corrosion rate of 6.4%, the alkali resistance strength decreasing rate of 7.5%, and the thermal shock resistance of 32 cycles, which is both dense and of good thermal shock resistance. The slag resistance simulation test was performed, which proved that the prepared corundum-mullite brick is better than those currently supplied in the market.

To improve the thermal shock resistance (TSR) of MgO-Al-C materials, three silicon-based raw materials with low expansion coefficients (Si, fused quartz, and SiC) were introduced to the materials, and their effects on the properties of the materials were studied by XRD and SEM. The results show that: (1) the conversion of Si to SiC, SiO₂ and forsterite at high temperatures improves the hot modulus of rupture (HMOR), TSR and oxidation resistance of the materials, and the optimal Si addition is 6 mass%; (2) fused quartz improves the TSR of the materials, but its high temperature softening and crystal transformation are not conducive to the HMOR and oxidation resistance of the materials, and the optimal addition is 2 mass%; (3) the SiC addition improves the TSR, HMOR and oxidation resistance of the materials; however, when the SiC addition exceeds 10 mass%, there are more micro-cracks in the materials, decreasing the TSR and oxidation resistance.

Calcium aluminate cement (CAC) bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials, CAC as the binder, zinc hydroxide (Zn(OH)₂) and basic zinc carbonate (BZC) as the ZnO precursors. The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed, and the reasons affecting the hot performance of the castables were studied. The results show that Zn(OH)₂ with a smaller particle size (d₅₀=1.26 μm) is prone to agglomerate during sample preparation and generates ZnAl₂O₄ spinel grains after firing, hindering the growth of CA₆, thus decreasing the mechanical strength of the castables. BZC with a larger particle size (d₅₀=2.91 μm), which shows a sound dispersity, in-situ generates nano-sized ZnO after firing, and ZnO or Zn ²⁺ diffuses into calcium aluminates, promoting the sintering of CA₂ and CA₆, thereby enhancing the hot properties of the CAC-bonded corundum based castables.

This work studies the fabrication and pressureless sintering of silicon carbide (SiC) refractories. SiC particles were adopted as aggregates, introducing different amounts (20%, 30%, 40%, 50%, and 60%, by mass) of submicron SiC powder, adding resin as the binder and the carbon source, and B₄C as the sintering aid. It is found that when the mass ratio of B₄C to the submicron SiC powder is 3%, the optimal sintering can be obtained. With the increase of the submicron powder addition, the sintering linear shrinkage increases and the mechanical properties enhance. The optimal sintering temperature is 2 050-2 100 ℃.