Jia Lin Sun

Preparation and Properties of MgO-MgAl2O4-FeAl2O4 Bricks in Cement Kiln

Sintered magnesia with different particle sizes, fused MgAl2O4 and FeAl2O4 were used as the raw materials. FeAl2O4 is added in MgO-MgAl2O4 bricks at different ratios to gradually replace MgAl2O4. After the raw materials were molded and sintered at the tunnel furnace with the temperature 1 530°C for 10 hours, the MgO-MgAl2O4-FeAl2O4 bricks could be made. After the analysis of the phase composition, microstructure and routine performance of the specimens, the influence by adding FeAl2O4 to the samples on the properties such as thermal shock resistance, adhesion strength of kiln crust are discussed as the key point. The result shows that the addition of FeAl2O4 has no evidently influence on the apparent porosity and volume density. The cold compressive strength of the samples reduces gradually with the addition of FeAl2O4, and it decreases obviously when the amount of FeAl2O4 is more than 8%. When the addition of FeAl2O4 is 5% FeAl2O4 in the MgO-MgAl2O4-FeAl2O4 bricks, MgAl2O4 and FeAl2O4 can combine each other’s advantages. The thermal shock resistance not only decreased obviously but the adhesion strength to kiln crust is increased.

Effect of Silicon Addition on the Properties and Microstructure of Corundum-Mullite Refractory

The influence of silicon addition on the microstructure and properties of corundum-mullite refractory was studied. Results show that Si addition as raw material of the matrix can accelerate mullite crystal formation. The oxidation of Si leads to nucleation of mullite via liquid phase and gas phase. The network microstructure is formed by tiny mullite crystals with few glass phase. So it enhances obviously the high temperature strength of sintered corundum-mullite refractory.

Corrosion Resistance Mechanism of MgO-ZrO2 Brick in RH Degasser Slag

Slag corrosion resistance behavior of MgO-ZrO2 refractory was investigated in this work. The results indicated that in the non-oriented electric steel slag system with a high ratio of calcia to silica, the slag resistance behavior of MgO-ZrO2 composite could be described as follows: the ZrO2 reacts with CaO forming the calcium zirconate compound which is densification encapsulating periclase lay. However, in the oriented electric steel slag system with a high concentration of silica and the low ratio value of calcia to silica, the slag corrosion resistance behavior of MgO-ZrO2 composite is different. The ZrO2 would react with CaO forming the calcium zirconate and simultaneously, one more product C2S as well. C2S has double response of strength and could increase corrosion resistance performance by blinding pore and thickening slag viscosity. Therefore, it is expected to be the major reason for the enhanced corrosion resistance behavior observed for MgO-ZrO2 refractory.

Study on High Performance Fe3Si-Si3N4-SiC Composite Preparation and its Application in Blast Furnace

Excellent Fe3Si-Si3N4-SiC composites were successfully prepared with FeSi75 and SiC as main starting materials by nitridation reaction(at 1300°C for 8Hrs). The effect of ferrosilicon alloy addition amount on material properties was studied; the ferrosilicon nitridation mechanism was analyzed through chemical thermodynamics; phase composition, microstructure, alkali resistance of products were also investigated. The results show that when ferrosilicon addition amount is 12wt%, the comprehensive property of Fe3Si-Si3N4-SiC is the best. The nitridation products are fiber-like α-Si3N4 and rod-like β-Si3N4, which makes better mechanical behavior due to fiber reinforcement; a great deal of Fe3Si intermetallic compounds uniformly distribute in matrix, which is one of the products of Fe-Si nitridation and as a plastic phase forming in grain boundary optimizes the performance of products. Chemical thermodynamic analysis shows that the fiber-like α-Si3N4 is formed by SiO(g) and N2(g) reaction which also increases the rate of nitridation. Fe3Si-Si3N4-SiC material has good performance. Now it has been successfully applied to one 2000M3 domestic steel plant, the blast furnace operation goes well.

Fabrication, Structure and Properties of Porous SiC Ceramics with High Porosity and High Strength

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.

Synthesis of MgAlON-Bonded MgO Refractory

Fused magnesite, α–Al2O3 micropowder and aluminum powder were used as starting materials to form MgAlON and MgAlON-bonded MgO materials in nitrogen atmosphere. Influence of technical conditions, such as composition, on formation of MgAlON was studied. Influence of vapouring of MgO in low PO2 atmosphere at high temperature on sintering of MgAlON-bonded MgO material was also discussed, showing that vapouring of MgO makes the material porous and damages its sintering.

Effect of Premelted Calcium-Magnesium-Aluminate Flux on Magnesia Carbon Brick

The novel Calcium-Magnesium-Aluminate (CMA) based premelted fluxes with different concentrations of MgO are developed and their corrosion to MgO/C brick is compared with traditional fluxing practice based on CaF2 addition. Results show that the corrosion of the MgO/C brick can be reduced obviously with initial high content of MgO employed in CMA. Additionally, the corrosion could be decreased correspondingly with the increase of MgO content in CMA fluxes, and the working lifetime of ladle slag zone can be extended by adding CMA flux.

Study on Melting Properties of CaO-Al2O3-SiO2-MgO System Calcium Aluminate Flux

Melting properties of CaO-Al2O3-SiO2-MgO system calcium aluminate (CA) flux were investigated through orthogonal design on three levels of four factors (content of CaO, Al2O3, SiO2 and MgO, respectively) to explore a reasonable chemical composition of CA flux. Results show that the softening temperature (Ts), hemispherical temperature (Th) and flowing temperature (Tf) of CA flux are influenced by the flux components in the order of SiO2 > MgO > CaO > Al2O3. The optimal chemical composition of flux is 3 wt.% SiO2, 6~12 wt.% MgO, 45 wt.% CaO and 40 wt.% Al2O3. Additionally, mineralogy composition analysis of flux clinker shows that the CA flux is mainly composed of 12CaO•7Al2O3 (C12A7), 3CaO•Al2O3 (C3A) and 6CaO•4Al2O3•MgO•SiO2 (C6A4MS, Q phase).

Corrosion Resistance of MgO-ZrO2 Brick and MgO-Cr2O3 Brick Compared by Rotating Slag Attacking Method

An environment-friendly material MgO-ZrO2 brick which is hoped to substitute for MgO-Cr2O3 brick was investigated. The using effects of MgO-ZrO2 brick and MgO-Cr2O3 brick were compared by rotating slag attacking method whose environment is similar to the environment in RH degasser. It indicates that the corrosion resistance performance of MgO-ZrO2 brick is better than that of MgO-Cr2O3 brick. Due to the effect of molten steel, slag and oxygen, Fe being oxidized to FeO or Fe2O3 at high temperature 1900K will produce volume expansion which results in MgO-Cr2O3 brick being cracked. At the same time, Cr2O3 will be decomposed to CrO3 gas, which will be evaporated seriously by the airflow and lead to MgO-Cr2O3 brick structural loosen and deterioration, ultimately. While the activity of oxygen dissolved molten steel is extremely low and ZrO2 is stable in the rotary kiln at 1900K. Furthermore, ZrO2 will react rapidly with CaO and its product CaZrO3 will form dense layer to prevent MgO-ZrO2 brick from being corroded. Therefore, trial production of MgO-ZrO2 brick applied for RH degasser is recommended.

Effect of Brown Corundum Dust Powder on the Sintering Performance of Corundum-Silicon Nitride Castable

The sintering performance of corundum-silicon nitride castable with brown corundum dust powder added was studied in this paper to provide a theoretical basis for the reuse of this waste powder. Waste powder, corundum, silicon nitride and silicon carbide were used as raw materials in this experiment. The sintered samples were measured routine physical property, and analyzed the microstructure of samples by SEM. Results shows that the addition of dusting powder could promote the sintering performance of non-oxides and the formation of Sialon, and improve the physical properties of samples. But when dusting powder added over 6% of the total, there are too much liquid phases, which will reduce the fire resistance performance at high temperature, so the appropriate added amount of dusting powder should be less than 6%.