Regulation of Pore Structure and Hightemperature Fracture Behavior of CACbonded Alumina-Spinel Castables Based on Hydration Design

The lamellar hydrates of CAC were designed with the introduction of nano CaCO_(3)or Mg-Al hydrotalcite(M-A-H),and the effects on the green strength,pore structures,and high-temperature fracture behavior of alumina-spinel castables were investigated.The results show that nano CaCO_(3)or M-A-H stimulates rapidly the hydration of CAC and the formation of lamellar C_(4)AcH_(11)or coexistence of C_(2)AH_(8)and C_(4)AcH_(11)at 25℃.The formation of lamellar hydrates can contribute to a more complicated pore structure,especially in the range of 400-2000 nm.Meanwhile,the incorporation of well-distributed CaO or MgO sources from nano CaCO_(3)or M-A-H also regulates the distribution of CA_(6)and spinel(pre-formed and in-situ).Consequently,the optimized microstructure and complicated pore structure can induce the deflection and bridging of cracks,thus facilitating the consumption of fracture energy and enhancing the resistance to thermal stress damage.

Alumina-magnesia Refractory Castables

This standard specifies the classification, techni-requirements, test methods, quality appraisal procedures, packing, marking, transportation, storage, and quality certificate of alumina - magnesia refractory.castables.

Effect of MgCl2 Solution Impregnation Process on Properties of Alumina-spinel Castables

In order to improve the properties of purging plugs and to prolong their service life,this work attempted to impregnate alumina-spinel castables for purging plugs in refining ladle with saturated magnesium chloride solution under vacuum.After being impregnated for the first time,the specimens were treated in two different ways:(1)dried at 110℃for 24 h;(2)heated at 600℃for 3 h.Then they were impregnated for the second time.All specimens were heated at 1550℃for 3 h,then the cold properties and the high temperature properties were tested according to corresponding standards.Test results were compared and analyzed.The results show that:after being impregnated,the specimen have both better cold properties and high temperature properties,the microstructure analysis result proves that it is attributed to in situ formed spinel.However,because MgO produced by MgCl2-6H20 decomposing above 527℃can hydrate and destroy specimen microstructure,which can make the properties of specimens impregnated in the second way get worse.By comprehensive consideration,the first scheme way is more suitable.

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.

Preparation of Microporous Corundum and Its Effect on Properties of Al_2O_3-MgO Castables

Based on the pore size design of microporous aggregate by numerical simulation applying porous media model,α-Al2O3 micropowder,industrial Al2 O3fine powder,α-Al2O3 micropowder ＋ CaCO3 fine powder were used as starting materials,respectively,to prepare three microporous corundum aggregates specimens,named as A1,A2 and A3.Two lightweight Al2O3-MgO castables were prepared by selecting A1 or A3 as aggregate with O.6 μm of average pore size,then performances of castables with microporous corundum aggregates and castables with tabular corundum aggregates were compared.The results show that：（1） the microporous corundum aggregates with bulk density of 3.1-3.5 g · cm-3,apparent porosity of 5％,closed porosity of 8％-13％,and smaller thermal conductivity at 800 ℃ than tabular corundum,can be prepared by sintering at above 1 800 ℃ ; （2） compared to normal Al2 O3-MgO castables,the two lightweight Al2O3-MgO castables have lower bulk density and higher apparent porosity;lower change rate in dimensions and higher strength firing at 1 500 ℃ ; and lower thermal conductivity at 600 and 800 ℃ ; （3） compared to normal Al2O3-MgO castables,Al2O3-MgO castable with A1 has higher penetration index,and that with A3 has higher corrosion index and lower penetration index.

Fabrication and Improving Properties of Lightweight Al_(2)O_(3)-MgO Castables for L adle Working Lining

Three lightweight Al_(2)O_(3)-MgO castables were fabricated with tabular alumina or microporous corundum as the aggregates,reactiveα-Al_(2)O_(3)micropowder,tabular alumina powder,and fused magnesia powder as the matrix,calcium aluminate cement as the binder,and MgO ultrafine powder(d50=5.4μm)and Al(OH)3 ultrafine powder(d50=8.2μm)as additives.The influence of aggregates and ultrafine powders on the properties,including pore size distribution,heat conductivity,thermal shock resistance,and slag resistance of lightweight refractory castables was investigated.The results show that the incorporation of microporous corundum reduces the bulk density of Al_(2)O_(3)-MgO castables,and MgO and Al(OH)3 ultrafine powders further increases the proportion of micropores in castables,which is beneficial to reducing the heat conductivity,and improving the thermal shock resistance and slag resistance of castables.Additionally,MgO ultrafine powder and Al(OH)3 ultrafine powder increase the fluidity and the strength of castables.

Study on Chrome-free Purging Plugs for Steel Ladles

Purging plug refractories in China typically contain around 3 mass% of super-fine chromium oxide in the matrix in order to improve the performance of the purging plugs, primarily, slag corrosion and wear resistance. Alternatives to chromium oxide containing refractories have gained interest due to health concerns related to the formation of soluble chromium compounds over long storage periods of refractory wastes. Super-ground reactive alumina can replace chromium oxide in purging plug refractories and this paper discussed the new reactive alumina E-SY 88 in comparison to chromium oxide in a typical purging plug castable. The mixing behaviour, wet castable properties, as well as cured, dried, and fired properties at different temperatures up to 1 600 ℃ were compared. In addition, the hot modulus of rupture, creep behaviour, thermal shock resistance and slag corrosion resistance were tested. The microstructure after slag corrosion was investigated by SEM. The results prove that E-SY 88 is an economically viable technical alternative to chromium oxide in purging plug refractories.