Effect of Ultrafine Spinel Sources on Slag Resistance and Microstructure of Alumina-spinel Castables

In order to clarify the effect of ultrafine spinel sources on slag resistance and microstructure of alumina -spinel castables,using tabular alumina and spinel as coarse aggregates,tabular alumina powders,spinel powders,calcium aluminate cement,spinel containing cement,spinel micro-powder and reactive alumina ultrafines as matrix,alumina-spinel castables used for RH snorkels were prepared by changing the particle size and sources of preformed spinel.The effects of different ultrafine spinel sources (CMA72,spinel micro-powder) on the properties of alumina-spinel castables were investigated.Thermal shock resistance and slag resistance of specimens were compared by the residual strength rate (1 100 ℃,air cooling 1 cycle) and static crucible method.The microstructure and the slag corrosion resistance mechanism of the specimens were analyzed by SEM and EDS.The result shows that slag resistance of alumina-spinel castables can be improved by adding ultrafine preformed spinel,such as CMA72,and spinel micro-powder.The introduction of ultra-fine preformed spinel has little effect on HMOR of alumina-spinel castables,but has negative effect on TSR.ultra-fine and dispersive preformed spinel in the matrix and fine microstructure are the main reasons for the improvement of slag resistance of 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.

Comparative Study of Lightweight Corundum with Different Microstructures and Its Effect on Slag Resistance of Al2O3-MgO Castables

Corundum -spinel castables containing lightweight aggregates have drawn many attentions due to their po- tential for energy-saving, especially when applied in the high-temperature region, such as the work lining of refi- ning ladle. One main aspect that restricts their applica- tion is the slag corrosion performance. In this study, one dense tabular corundum and three kinds of lightweight corundum were chosen as aggregates to prepare four dif- ferent corundum - spinel castables. The slag resistance was compared through the induction furnace corrosion test. SEM - EDS, XRD, and thermodynamic and kinet- ics analysis were adopted for the discussion of the corro- sion mechanism. Results show that the crystal grain size and shape of aggregates are important for the slag corro- sion resistance of lightweight corundum -spinel castables under dynamic condition （enforced convection） , yet the effects of pore characteristics are not dominated. Aggre- gates with large flake-like crystal grains show a thicker dissolution diffusion boundary layer and a lower dissolution rate, resulting in a favorable corrosion resist- ance of the castable. The poor microstructure of the ag- gregates, namely, larger pores and small and spherical grains, would cause deterioration of castables＇ slag resistance.

Anisotropy of Expansion Coefficient and Slag Resistance of Spinel Carbon Bricks

Effects of the pressure direction on the thermal expansion and slag corrosion resistance were investigated and anisotropic microstructures of flaky graphite in spinel carbon bricks were examined. The experimental results show that slag corrosion velocities in the direction parallel to the pressure direction display a decrease of 34% compared to those in the vertical direction. Meantime, the linear expansion coefficient in the direction parallel to the pressure direction is 2.45 times as large as that in the vertical pressure direction. Slag corrosion velocities of spinel carbon bricks soaked in the AOD melting slag display a 46%-47% decrease compared to those of magnesia carbon bricks. The microstructure observation shows that spinel carbon bricks have a high degree of preferred orientation.

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 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.

Slag-Resistance of MgAlON Spinel

The slag-resistance and microstructural changes after the slag tests of MgAlON spinel containing different amount of nitrogenwere studied by means of crucible slag-resistant experiment, SEM and EDS in the work. The results show that the slag-resistance ofMgAlON is dependent on the nitrogen content, and the optimum amount is 2.88%. The strUcture is not changed although the grains havebeen permeated by some silicon, calcium and iron. A glass phase which contained nitrogen formed in the metaInorphic layeL The glasscan driprove the ability of the slag-resistance of MgAlON because of its higher viscosity.

Effect of Si_3N_4 on Resistance of Magnesia Based Castable

The magnesia based curable specimens with different Si3N4 contents were casted using sintered magnesite （w（MgO）=95%） as starting material, SiO2 micro-powder as binder, 0.3%, 4% and 5% β-Si3N4 powder replacing the equal addition of magnesia powder respectively. The slag resistance test was carried out at 1550℃ for 3h using Baosteel tundish slag and static crucible method. The result indicates that： introducing Si3N4 could obviously improve the slag resistance of MgO based castable, which increased with increasing Si3N4. Dense SiO2 sintered layer formed on the surface of magnesia based castable because of the oxidation of Si3N4 addition, which can prevent the further slag penetration. In the deep inner of castable, the partial-pressure of oxygen was very low, so Si3N4 can exist stably. Meanwhile in reducing atmosphere, Si3N4 was hard to be sintered, which resulted in the loose interior structure of MgO based castable.

Corrosion Behavior of Slags with Different Basicities to Alumina Magnesia Castables

Alumina magnesia castable crucible specimens were prepared using tabular corundum （ ≤ 5 mm ）, fused magnesia powder （ ≤0. 088 mm ） , fused spinel powder （ ≤0. 044 mm ） , and α-Al2O3. micropowder （d50 ≤0. 7 μm ） as main starting materials, batching, mixing, shaping, and drying. Slag resistance was determined by static crucible method at 1 600℃ for 3 h adopting two ladle slags with different basicities （3. 40 and 1.03 ）. The corrosion and penetration indexes and microstructure characteristics of the specimens after slag resistance test were analyzed to study the corrosion behaviors of the two slags to alumina magnesia castables. The results show that the corrosion of the low basicity slag to alumina magnesia custables is much more serious than that of the high basicity slag for that their reactions with castables form different products;for the low basicity slab,, the multi-phase coexistence of CA6 and compounds of CaO - Al2O3 -SiO2 in the materials together with volume expansion caused by the formation of CA6 intensify the slag corrosion and penetration ; for the high basicity slag, the reaction between slag and castables generates a CA2 dense layer and a large amount of in-situ MA in the interface, reducing the slag corrosion to the materials effectively.

Enhanced slag resistance and mechanical properties of magnesia castables with strontium carbonate addition

Magnesia castables have been widely used in metallurgical industries with the advantages of high refractoriness,non-polluting steel,and resistance to alkaline slag.Magnesia castables were prepared using strontium carbonate(SrCO_(3))as additive to enhance slag resistance and mechanical properties,and the influence of SrCO_(3) on the evolution of phases,microstructure and properties of magnesia castables sintered at different temperatures was clarified.The results show that,with the introduction of SrCO_(3)(lower than 3 wt.%),elastic modulus,mechanical strength,thermal shock resistance and densification of magnesia castables were significantly enhanced owing to the formation of needle-like Ca_(0.9)Sr_(0.1)MgSi_(2)O_(6) phase and liquid phase when sintering at high temperatures,and the introduced SrCO_(3) presented minor effects on the mechanical properties of castables for its highly structural stability below 1100℃.During the slag corrosion process,SrCO_(3) and SiO_(2) in castables reacted with Al^(3+)in molten slag to form SrAl_(2)SiO_(8) phase,resulting in the increased slag viscosity and suppressed continuing penetration.

Binder Effect on Properties of Cr_(2)O_(3)-bearing Corundum-based Refractory Castables

Cr_(2)O_(3)-bearing castables bonded with reactive MgO(RM)or calcium aluminate cement(CAC)were studied to evaluate the binder effect on their performance in corrosive environments.The properties of the as-prepared castables were compared with respect to the differences in phase composition and microstructure.The corrosion behavior of the as-prepared castables by CaO-Al_(2)O_(3)-Fe_(2)O_(3)-SiO_(2)-based slag was systematically compared viarefractory cup testing at 1600℃with respect to the differences in phase composition and microstructure.The analysis indicates that RM bonded castables show higher apparent porosity,lower bulk density and strengths after drying at 110℃and firing at 1300℃,and higher permanent linear change after firing at 1300℃,but better slag corrosion and infiltration resistance compared with CAC bonded castables.

Influence of Microporous Magnesia-rich Spinel Aggregates on Properties of Low Carbon MgO-C Refractories

Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, fused magnesia （ ≤1 mm） as fine aggregate, magnesia powder （≤ 0. 088 mm ） , flake graphite powder （ ≤0. 088 mm）, metal Al powder （ 〈0. 074 mm） as matrix, and phenol resin as binder. After curing at 220 ℃ and coke-embedded firing at 1 500 ℃ , the apparent porosity, cold crushing strength, cold modulus of rupture, permanent linear change on heating, thermal shock resistance and slag resistance of the specimens were studied comparatively. The results indicate that： （ 1 ） after curing at 220 ℃ and coke-embedded firing at 1 500 ℃, the specimen with microporous magnesia-rich spinel replacing fused magnesia has lower bulk density and higher apparent porosity than the common low car- bon MgO - C specimen. After curing at 220 ℃, the specimen with microporous aggregate has lower strength than common low carbon MgO - C specimen, but after coke-embedded firing at 1 500℃, it has higher strength and lower permanent linear change on heating; （2） low carbon MgO - C specimen using microporous magnesia-rich spinel to replace fused magnesia aggregate has better thermal shock resistance but worse slag resistance.

Effect of Different Silica Fumes on Properties of Al_(2)O_(3)-SiC-C Castables for Iron Trough

In order to improve the performance of Al_(2)O_(3)-SiC-C castables for iron trough,samples were prepared using brown corundum,dense corundum,activated alumina micropowder,ball pitch,and silicon as main raw materials,calcium aluminate cement as the binder.Several kinds of silica fumes(93SiO_(2),96SiO_(2),and 99SiO_(2))with different particle size distributions and chemical composition were added to research the effects on the properties of castables.The results show that the sample with 99SiO_(2) fume has high water requirement for molding,but the bulk density is the lowest,the apparent porosity is the highest,the oxidation resistance is the worst,and the permanent linear change on heating is low after firing at 1 450 ℃ for 3 h.The bulk density and the apparent porosity of the sample with 93SiO_(2) fume or 96SiO_(2) fume are equivalent,the hot modulus of rupture of the sample with 93SiO_(2) fume is the lowest,and the slag resistance of the sample with 96SiO_(2) fume is the best.The comprehensive performance of the sample with 96SiO_(2) fume is the best.

Effect of Treated Graphite on Properties of Al_2O_3-SiC-C Castables

Al2O3 - SiC - C castables with 2% pitch or 2%, 4% and 6% treated graphite, respectively, were prepared based on the basic formulation of traditional Al2O3 - SiC - C castables. The flowability of castables, and bulk density, volume stability, strength, oxidation resistance and slag resistance of specimens fired at 110 ℃, 1 100 ℃, and 1 500 9Z respectively were comparatively studied. The results showed that： （1） With carbon source changing from pitch to treated graphite and the increase of treated graphite addition, water addition of castables increased, bulk density of specimens fired at different temperatures increased firstly and then decreased, strength after drying decreased obviously, strength after firing and oxidation resistance changed slightly, hot modulus of rupture increased obviously; （2） Slag resistance of specimen with treated graphite was worse than that of specimen with the same amount of pitch, but the former was obviously improved with the increase of treated graphite addition.

Effect of Andalusite Aggregate Pre-fired at Different Temperatures on Properties of Al2O3-SiC-C Castables

This work investigates the effect of the pre-firing temperature of andalusite aggregate(5-3 mm)on the conversion of andalusite,the volume stability,the thermal shock resistance and the slag resistance of Al2O3-SiC-C castables.The results show that the volume stability and the thermal shock resistance of the castables could be adjusted at different pre-firing temperatures of andalusite aggregates.There was no noticeable difference in the slag resistance between the specimens without andalusite and those with andalusite aggregate pre-fired at different temperatures.

Effect of ferrotitanium slag on microstructure and properties of Al_(2)O_(3)-SiC-C castables for iron runner

Ferrotitanium slag(FS)is a waste slag produced during the smelting of ferrotitanium alloys by thermite reduction.Its alumina content is high and can be used as alumina raw material.Iron runner castables containing different amounts of FS were prepared and characterized.The results show that the introduction of FS is beneficial to the sintering of the castables sample.When the FS concentration is 11.2 wt.%,the aggregate and matrix of the castables sample have a good combination,and the mechanical strength of the Al_(2)O_(3)–SiC–C castable reaches a maximum at room temperature.However,excessive introduction of FS generates a large amount of anorthite phase,which reduces the mechanical strength of the Al_(2)O_(3)–SiC–C castable at room temperature.In addition,the high-melting phase CaTiO_(3)is formed in FS,which has good mechanical properties.Meanwhile,the cracks of FS are reduced,and the combination between phases is closer,thus significantly improving the hot modulus of rupture of the castable.When the FS concentration is not above 33.6 wt.%,the castables show good slag resistance.The TiO_(2)in FS is transformed into TiC by carbothermal reaction,which is enriched at the boundary and prevents further reaction of the slag.

不同碱度渣对刚玉-尖晶石浇注料的侵蚀行为研究

浇注料的抗渣侵蚀性能与钢渣的碱度密切相关。以烧结刚玉、缺陷尖晶石微粉、活性α-Al_(2)O_(3)微粉、电熔镁砂细粉和铝酸钙水泥(Secar71)为主要原料,制备了刚玉-尖晶石浇注料,采用静态坩埚法于1600℃保温3 h进行抗渣试验,并用热力学模拟计算了液相量和液相组成,研究了刚玉-尖晶石浇注料对3种不同碱度渣(1.6、2.3和7.6)的抗渣侵蚀性能。结果表明:刚玉-尖晶石浇注料在高碱度渣中溶解能力有限,在熔渣-耐火材料界面极易形成尖晶石固溶体和六铝酸钙等高熔点物相,形成致密层阻挡熔渣渗透和侵蚀。而其在低碱度渣中溶解度较高,在浇注料-熔渣达到较高反应程度时,才开始形成尖晶石固溶体和六铝酸钙等高温相,无法形成有效的致密层阻止熔渣对浇注料的侵蚀和渗透。因此,刚玉-尖晶石浇注料对高碱度渣抗渣侵蚀能力较强,对低碱度渣抗渣侵蚀能力较弱。

活性氧化铝加入量对活性氧化镁结合刚玉-尖晶石浇注料性能的影响

为改善活性氧化镁结合刚玉-尖晶石浇注料的性能,以板状刚玉、活性氧化铝微粉、活性氧化镁微粉和乳酸铝为原料,制备了活性氧化镁结合刚玉-尖晶石浇注料,研究了活性氧化铝微粉加入量(加入质量分数分别为0、8%、13%和18%)对浇注料显微结构、物相组成、物理性能及抗渣侵蚀和渗透性能的影响。结果表明:1)活性氧化铝微粉的加入促进了活性氧化镁结合刚玉-尖晶石浇注料的烧结,提高了骨料和基质的结合程度,使浇注料显微结构更加致密;2)随着活性氧化铝微粉加入量的增加,试样体积稳定性提高,显气孔率降低,体积密度增加,常温抗折强度和耐压强度及抗渣性提高;3)当活性氧化铝微粉加入量为18%(w)时,活性氧化镁结合刚玉-尖晶石浇注料的综合性能最好(考虑到颗粒级配和原料成本的问题,没有必要再进一步增加活性氧化铝微粉),其体积密度为3.05 g·cm^(-3),显气孔率为18.5%,加热永久线变化为0.31%,常温抗折强度和耐压强度分别为13.5和73.8 MPa,抗渣性最佳。

Al_(2) O_(3)-MgAl_(2) O_(4)复相骨料对刚玉-尖晶石浇注料抗渣性能的影响

为研究Al_(2)O_(3)-MgAl_(2)O_(4)复相骨料对刚玉-尖晶石浇注料抗渣性能的影响,在基质中添加与不添加尖晶石细粉的2种情况下,分别以板状刚玉骨料和Al_(2)O_(3)-MgAl_(2)O_(4)复相骨料制备了刚玉-尖晶石浇注料。先利用FactSage反应热力学软件计算了1600℃时板状刚玉和Al_(2)O_(3)-MgAl_(2)O_(4)复相骨料与熔渣之间的反应热力学,并采用浸泡法研究了2种骨料的抗渣性能,再采用静态坩埚法研究了2种骨料对浇注料抗渣性能的影响。结果表明:与板状刚玉骨料相比,Al_(2)O_(3)-MgAl_(2)O_(4)复相骨料侵蚀层中的裂纹细而少,遭受熔渣侵蚀后不易剥落,其过渡层中既有CA 6相也有尖晶石相,而且尖晶石相中固溶有Fe、Mn元素,该骨料不仅通过形成CA 6层来阻挡熔渣侵蚀,而且通过尖晶石吸收熔渣中FeO、MnO等物质而降低熔渣的黏度,进而起到抵抗熔渣侵蚀的作用。由Al_(2)O_(3)-MgAl_(2)O_(4)复相骨料替代板状刚玉骨料,浇注料试样的侵蚀和渗透面积百分率均有所降低,尤其在基质和骨料中同时引入尖晶石可更加有效地提高刚玉-尖晶石浇注料的抗渣性能。

添加AMC复相材料的刚玉质浇注料的性能改善及应用效果

在刚玉质浇注料中添加AMC复相材料,利用AMC复相材料的CA6和MA抗渣性好、热震稳定性好的特点来改善刚玉质浇注料的使用性能,同时AMC复相材料作为资源再利用的新产品,在价格方面具有明显的优势,它能够降低耐材的生产成本。试验表明,在刚玉质浇注料中加入30%的AMC复相材料取得了较为理想的实验数据,其应用在钢包座砖上取得了良好的效果,既降低了生产成本,又有效地提高了钢包座砖的使用寿命。