Effect of H_(2)O_(2) Addition on Anti-explosion Performance of p-Al_(2)O_(3) Bonded Corundum Castables

In order to improve the anti-explosion performance ofρ-Al_(2)O_(3) bonded corundum castables,H_(2)O_(2) was added(0,0.025%,0.050%,0.075%,0.100%and 0.125%,by mass)as the anti-explosion agent.After mixing and casting,specimens were prepared.Some specimens were cured at room temperature for 12 h and demoulded for the anti-explosion performance test at different temperatures(450,500,550,600,650,700,750 and 800℃);the other specimens were cured,dried and fired,and tested in terms of the apparent porosity,the density,the cold mechanical properties,the air permeability and the pore size distribution.The results show that:(1)with the increase of the H_(2)O_(2) addition,the anti-explosion performance of castables increases gradually,the average pore size increases gradually,and the density and the strength decrease gradually;(2)by comprehensive consideration,the appropriate addition of H_(2)O_(2) shall be within 0.075%.

Effect of Zirconia Corundum Addition on Properties of Chrome Corundum Castables

In order to investigate the effect of zirconia corundum on the preparation of chrome corundum castables,samples were prepared using tabular corundum,white fused corundum,active alumina micropowder,chromium oxide micropowder and fused ziconia corundum particles as the main raw materials,and pure calcium aluminate cement as the binder.The effects of the fused zirconia corundum particles addition(1-0.5 mm,0,4.5%,9%,and 18%,by mass)on the linear change rate,the apparent porosity,the cold modulus of rupture,and the thermal shock resistance of chrome corundum castables were studied,and the microstructure of the samples was analyzed.The results show that:(1)with the zirconia corundum addition increasing,the permanent linear change on heating of the samples gradually increases,the apparent porosity gradually increases,the cold modulus of rupture gradually decreases,and the thermal shock resistance gradually increases;(2)according to SEM,it can be found that the phase transformation of ZrO2 after heat treatment leads to a large number of microcracks in the material.On one hand,the cold modulus of rupture of the material is reduced;on the other hand,the thermal shock resistance of the material is improved.

Development of Dense Corundum-mullite Bricks for Blast Furnace Ceramic Pad

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 ofα-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 1560℃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.

Effects of Tabular Corundum Types on Properties of Corundum-spinel Castables

The corundum - spinel castables were prepared by six kinds of tabular corundum, as aggregates, respective- ly, and their linear change rate on heating, apparent porosity, bulk density, cold modulus of rupture, coht crushing strength, hot modulus of rupture and thermal shock resistance were compared and studied. The results show that： 1） the six tabular corundum materials have similar main chemical composition but their physical properties vary for the different technical procedures which result in different properties of castables ; 2 ） the optimal properties of corundum - spinel castables corre- spotut to different tabular corundum types, so the corundum type shall be selected according to the application of the castables.

Effect of Matrix Composition on Physical Properties of Al_3CON In-situ Reaction Reinforced Corundum Composite

60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder and pressed under pressure of 315 ton forging press, then dried at 200℃ for 24 h. Effects of various additives on 1500 ℃×2 h creep properties of Al3CON reinforced corundum composite were researched. The experimenal results show that creep coefficients of specimens 1#,2#,3# at 1500 ℃×2 h are 1.4×10^- 4, -9.4×10^-4, -22.6×10^-4, respectively. Crushing strength of the slide plate added with suitable additive A after fired at 1500 ℃ ×3 h reaches to 225 MPa, the creep rate is positive all the time from 0% to 0.014% at 1500 ℃ for 2 h. The microstructure result analysis shows that reinforced phases of Al3CON fiber composite have been formed after fired with Al powder in coke at high temperatures for specimen 1#, and the strength of the composite is increased. The hot modulus of rupture is up to 59 MPa at 1400 ℃ and the RUL is obviously higher than that at 1700 ℃. Its service life is two times as that of Al2O3-C slide plate when used in the process of pouring steel. The mechanism of creep rate resistance of the composites can be discovered by means of SEM and EDAX analysis. It is concluded that the active Al3CON and Al2O3 multiphases that were formed by N2 in gas, C, Al and Al2O3 inside the matrix of the composites during in-situ reaction,which gives the composites outstanding creep rate resistance for the dense zone resuiting from Al3CON oxidation that inhibits contraction at the high temperature. Besides, the matrix will turn into the multiphase with high refractoriness, N content and its Al3CON reinforced fiber will further increase accordingly. In addition, Al3CON formed by Al2O3 and C, Al in the matrix with N2 in gas will inhibit the creep rate and also greatly improve the creep rate resistance of the composites.

Kinetics of decomposition of mullite and corundum in coal fly ash under highly alkaline condition

Decomposition kinetics of mullite and corundum in coal fly ash with highly alkaline solution was studied.The effects of the reaction temperature and reaction time on decomposition rates of mullite and corundum and alumina extraction efficiency were investigated.The results show that increasing reaction temperature and reaction time increases the decomposition rates of mullite and corundum and alumina extraction efficiency,with the decomposition temperature of mullite lower than that of corundum.After 90 min reaction at 220℃,more than 100 g alumina was extracted when recycling 1 L of alkaline solution.The decomposition processes of mullite and corundum corresponded with the shrinking unreacted core model,and the reaction rate was under chemical reaction control,with the activation energies of mullite and corundum being 67.46 and 161.82 kJ/mol,respectively.

Preparation of sol-gel derived microcrystalline corundum abrasives with hexagonal platelets

The effects of different additives on the mechanical properties, microstructures, and wear behavior of corundum abra- sives were investigated. When the number of additive phases increases, the sintering temperature and wear rate decrease, while the densification and mechanical properties increase. The additive SiO2 is responsible for the development of equiaxed grains, whereas both CaO and MgO promote the development of platelike grains. By controlling the molar ratio of additives, it is pos- sible to obtain different microstructures. With SiO2-MgO-CaO （molar ratio, 2：1：1） as the additives and nano a-Al203 powders as the seed, microcrystalline corundum abrasives with hexagonal platelets were obtained using sol-gel process by sintering at 1300℃ for 0.5 h. The average diameter and thickness of hexagonal platelets are 1.38 μm and 360 nm respectively, the sin- gle-particle compressive strength is 26.44 N, and the wear rate is （3.06±=0.21）× 10^-7 mm^3/（N.m）.

Preparation of β-Sialon/ZrN bonded corundum composites from zircon by nitridation reaction sintering process

β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum,alumina micro powder,zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the synthesized composites were investigated by X-ray powder diffraction and scanning electronic microscope,and the formation process of the composites was discussed. The results show that the composites with different compositions can be obtained by controlling the heating temperature and contents of zircon and carbon black. The proper temperature to synthesize the composites is 1773 K.

Leaching of gallium from corundum flue dust using mixed acid solution

In order to extract gallium from a high-silica-content flue dust generated in corundum production,a mixed acid solution of H2SO4 and HF was used for leaching,and test parameters of the leaching process were optimized.Experimental results show that the leaching rate of gallium was only 38%when H2SO4 was used as leaching agent.Composition analysis results of micro areas in this corundum flue dust indicate that the content of gallium in silica-enriched phases was high;this portion of gallium was insoluble in H2SO4 solution.The leaching rate of gallium increased significantly with addition of HF due to corrosion of silica.Effects of reaction time,temperature,and concentrations of HF and H2SO4 on leaching rates of gallium were investigated.The leaching rate of gallium reached 91%when this corundum flue dust was leached in a mixed acid solution of H2SO4 and HF for 4 h,at a temperature of 80°C,with a liquid-to-solid ratio of 5:1(mL/g).The optimal concentrations of H2SO4 and HF in the mixed acid solution were 1.5 and 6.4 mol/L,respectively.

Effects of Nano Calcium Carbonate on Strength and Microstructure of Corundum-based Castables

The castables specimens were prepared using white fused alumina particle and powder, α-Al2O3 micropowder, hydrated alumina, nano calcium carbonate or calcium aluminate cement as starting materials. Effects of nano calcium carbonate addition on phase compositions, strength and microstructure of corundum based castables were studied. The calcium aluminate cement-containing corundum based castables with the same CaO amount was also tested for comparison. The results show that, when temperature is higher than 900 ℃ , the phase compositions of nano CaCO3-containing mixture and the calcium aluminate cement containing mixture are the same, but the forming mechanism, modality and distribution of new phases in the castables are different. With temperature rising, the hydration cement dehydrates and reacts inside cement forming calcium aluminate until the alumina in cement is not enough for the reaction （ternperature is 91 400 ℃ ） , then reacts with the surrounding alumina forming cluster CA6 in the castables. The change process of nano CaCO3 in corundum based enstables is that nano calcium carbonate decomposes to CaO after firing at 800℃ which reacts with Al2O3 forming amorphous calcium aluminate that causes an in-situ bonding. With temperature rising, the formed calcium aluminate reacts with Al2O3 in matrix and wholly forms tabular CA6 at 1 600 ℃ , which distributes uniformly in the castables. The cold and hot strength of the castables with nano calcium carbonate are obviously higher than those of the castables without nano calcium carbonate, especially at 800 -1 000 ℃ due to smaller size and higher dispersion of the nano calcium carbonate and its different reaction mechanism with Al2O3.

SiAlON Bonded Corundum or SiC Composites Synthesized in Different Atmospheres

Using corundum powder, SiC powder, Si3N4 powder, α-Al2O3 micropowder and metal Al powder as starting materials, PVA as binder, after ball milling, mixing, aging, moulding and drying, SiA10N bonded corundum or SiC composites were synthesized at 1 600 ℃ for 6 h in air, graphite embedded condition and （ graphite ＋ SiC ） embedded condition, respectively. Effects of corundum or SiC powder additions （the mass percent was 7. 5% -90% ） and sintering atmosphere on forming amount and appearance of SiA10N phase, phase composition, microstructure and properties of the composites were studied. The results show that ： （ 1 ） with corundum powder addition increasing, density and sintering property of SiA10N bonded corundum composites fired in three different conditions all improve, but the sintering property of the specimens fired in oxidation atmosphere is better than that in reduction atmosphere; （2） the main phases of SiAlON bonded corundum composites fired in two reduction atmospheres are corundum, SiAlON and SiC. The specimens fired in oxidation atmosphere have lamination phenomenon, the main phases of non-oxidation layer are SiAION, corundum and a little mullite; （3） column-like or fiber-like SiAlON forms in SiA10N bonded corundum composites fired in two dif- ferent atmospheres. Column-like SiAlON forms in oxidation atmosphere grows better than in reduction atmosphere ; （4） with SiC powder addition increasing, density and sintering property of SiAlON bonded SiC composites fired in two reduction atmospheres both reduce. The specimens fired in oxidation atmosphere are oxidized and thicker glaze layer forms.

Effect of Curing Temperature on Intermediate Temperature Properties of Calcium Aluminate Cement Bonded Corundum Castables

In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.

Influence of Dispersants on Flow Ability of Colloidal Alumina Bonded Corundum Castables

In order to make corundum castables satisfy more severe service conditions in high temperature industries,colloidal alumina due to the same main component with corundum castables was introduced for a pure binding system.The influence of three dispersants(citric acid,FS10 and urea)on the flow ability of colloidal alumina bonded corundum castables was researched to choose a suitable dispersant for solving the shaping problem.In order to further understand the influence of dispersants on the flow ability and the mechanism,the rheological property and Zeta potential value of the colloidal aluminadispersant system and the matrix-colloidal alumina-urea-water system were tested.The results show the castables added with the urea have the best flow ability,and the appropriate addition of the urea is 0.5%.

Effects of Specific Surface Area and Impurities of Reactive Alumina on Properties of Corundum Based Castables

Effects of specific surface area and tiny amount of impurities of reactive alumina on the workability, sinte- ring and high temperature mechanical strength of corun- dum based castables were investigated. The results show that the presence of reactive alumina with high specific surface area leads to accelerating of the hydration of calcium aluminate cement, thus shortening the working time and setting time of the castables, which can be as- cribed that the critical energy barrier for stable nuclei of hydration products of cement can be reduced by the high specific surface area of reactive alumina. The sintering of the corundum based castables can be accelerated by the reactive alumina with high specific surface area and high amount of impurities, however, the reactive alumina with too high specific surface area and impurities can al- so lead to noticeable shrinkage of castables. In addition, high temperature mechanical strength of corundum based castables can be decreased by the higher amount of trace impurities of reactive alumina due to formation of low- melting phase at high temperatures.

Effect of Microsilica on Chemical Bond of Calcium Aluminate Cement Bonded Corundum Castable at Low and Intermediate Temperatures

Calcium aluminate cement bonded corundum castable specimens were prepared using brown fused corundum （8 - 5, 5 - 3, 3 - 1 mm ） , white fused corundum （ ≤ 1, ≤0. 045 mm）, micro-sized α-Al2O3 and microsilica as starting materials. This work focused on investigating the relationship between the bond change in the castable matrix and the strength of the castable with 5 mass% microsilica or without microsilica after heat treatment at 110, 800 and 1 000 ℃, respectively. Chemical bond changes between the microsilica and hy- drates of calcium aluminate cement after drying at 110 ℃ or firing at 800 ℃ were investigated by XPS and FTIR. The results show that Si-O-Al bonds form be- tween the microsilica and hydrates of calcium aluminate cement after drying at 110 ℃ or firing at 800 ℃. Therefore, the increased strength of castable specimens is attributed to the formation of Si-O-Al bonds from 110 ℃ to 800 ℃.

Preparation and Properties of Sintered Corundum at Low Temperatures with Nano-η-Al2O3 Powder

In order to reduce the sintering temperature and improve the properties of sintered corundum,corundum specimens were prepared by granulation and sintering with nano-η-A l203 as the raw material and polyvinyl alcohol as the binder.The effects of different sintering temperatures(1550,1600,1650 and 1700℃)and holding time(2,4 and 6 h)on the properties and microstructures of the specimens were studied,and the transformation mechanism ofη-Al203 was analyzed.The results show that dense sintered corundum with bulk density of 3.74 g/cm^3 and apparent porosity of 1.77%is obtained by calcinating at 1650℃for 6 h;the phase transition fromη-Al203 toα-Al203 occurs first on the surface of alumina particles and then diffuses rapidly to the interior;at lower sintering temperatures there is no abnormal growth of crystals,the bonding between the grains is tight,transgranular fracture is the main fracture mode,there are fewer intergranular pores,and the grain size is in the range of 3.5-7.5μm.

Effect of Calcium Chloride Addition on Properties of Corundum Spinel Castable

Corundum spinel castable was prepared using tabular corundum as aggregates,white fused corundum powder,spinel powder and alumina powder as the matrix,pure calcium aluminate cement as a binder,and extra adding calcium chloride(0,1%,2%,and 3%,by mass).The effects of the CaCl2 addition on the cold physical properties,the hot strength,the thermal shock resistance and the microstructure of the castable were studied.The results show that,for the corundum spinel castable fired at 1550℃,with the increase of the CaCl2 addition from 0 to 3%,the cold strengthes first increase,then decrease,the apparent porosity increases,the volume density decreases,and the linear change rate first decreases and then increases,while the overall change is not significant;however,the hot modulus of rupture and the thermal shock resistance are obviously improved.This is mainly due to that,CaCl2 is evenly distributed in the castable in the form of solution,and reacts with Al2O3 to form small flake CA6 crystals,which evenly distributed in the sample matrix strengthening and toughening the material.

Effect of ZnO Precursor on Properties of Calcium Aluminate Cement Bonded Corundum Castables

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(d_(50)=1.26μm)is prone to agglomerate during sample preparation and generates ZnAl_(2)O_(4) spinel grains after firing,hindering the growth of CA_(6),thus decreasing the mechanical strength of the castables.BZC with a larger particle size(d_(50)=2.91μm),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 CA_(2) and CA_(6),thereby enhancing the hot properties of the CAC-bonded corundum based castables.

Relation Between Sintering Reactivity of Matrix and Thermal Shock Resistance of Ultra-low Cement Bonded Corundum-spinel Castables for Fired Purging Plugs

Purging plugs installed in the bottom of steel ladles are widely used for the secondary refining of high quality steel grades.The dynamic service conditions and temperature gradients caused by the cold inert gas blown through the plug during stirring create a strong thermal shock impact on the materials.This can affect its service life and restrict the safety and efficiency of steel making if the plug fails during use.In this work,the influence of the particle size distribution (PSD) and amount of reactive alumina on the sintering behavior of ultra-low cement bonded corundum-spinel based castables was investigated on lab scale.The relationship between sintering reactivity of matrix and thermal shock resistance of castables was evaluated in detail.Results show that the sintering of castables can be intensified by using finer reactive alumina.However,excessive sintering of the castable through finer reactive alumina is negative for thermal shock resistance.The microstructure characterization reveals that castables with more intense sintering show denser matrix structure,which is less effective in hampering crack propagation and therefore results in decline of their thermal shock resistance.

Effect of Nano Calcium Carbonate on Properties of Corundum-spinel Castables

Using sintered corundum as aggregate, white fused corundum powder, fused spinel powder, ultra-fine a-A12 0 3, nano calcium carbonate and hydrated alumina as matrix, effects of nano calcium carbonate additions （0. 4%, O. 8%, 1.2%, 1.6% and 2. 0% in mass, the same hereinafter） on modulus of rupture, thermal shock resi.~tanee and slag resistance of corundum -spinel castables after treating at different temperatures were studied. The results show that nano calcium carbonate decomposes at high temperatures and in-situ forms ealci- ant aluminates, which can significantly increase the CMOR and HMOR of the castables after treating at 800 -1 400 ℃ ; adding nano calcium carbonate obviously improves the thermal shock resistance of the castables, and has little influence on the high basicity slag resist- ance, however, significantly decreases the corrosion and penetration resistance to low basicity slag.