High-performance alumina-magnesia castables were developed with the addition of nano-CacO_(3) and nano-hydromagnesite.To further understand their dynamic failure mechanism,the quantitative investigation via the employ...High-performance alumina-magnesia castables were developed with the addition of nano-CacO_(3) and nano-hydromagnesite.To further understand their dynamic failure mechanism,the quantitative investigation via the employment of the Split-Hopkinson pressure bar(SHPB)method was adopted to test the dynamic failure behavior of alumina-magnesia castables under various impact velocities.The results demonstrate that the greater the impact velocity,the more intense the sample damage.The dynamic compressive stress,the ultimate strain,and the strain energy of all samples display a strain rate hardening effect,and this phenomenon is more conspicuous in the samples incorporating nano-additives.The nano-additives show a positive influence on the dynamic mechanical properties of the castables.展开更多
The penetration of ladle slag into refractory linings is an essential process in service,and the mechanical properties of the refractory castables are affected by the location and content of slag in the refractory cas...The penetration of ladle slag into refractory linings is an essential process in service,and the mechanical properties of the refractory castables are affected by the location and content of slag in the refractory castables.In this work,ladle slag was added into Al_(2)O_(3)-Mgo refractory castables and its influence on the microstructure evolution,mechanical properties and thermal shock resistance of the castables was investigated.The phase composition and contents of the castables during the corrosion process were calculated by FactSage TM(6.2)and studied.The results indicate that the residual strength decreases as the ladle slag addition increases from 0 to 6 mass%.While the hot modulus of rupture of the castable with 6%ladle slag significantly decreases by approximately 80%compared with the one without ladle slag.The elastic modulus and CMOR of the castables decrease with slag-adding,which leads to the increase of liquid phase contents inside the samples.展开更多
In order to improve the service performance of Al_(2)O_(3)-SiC-C castables,a novel Si-N-O composite micropowder was synthesized by the chemical combustion method.Using brown corundum,sintered alumina,silicon carbide,a...In order to improve the service performance of Al_(2)O_(3)-SiC-C castables,a novel Si-N-O composite micropowder was synthesized by the chemical combustion method.Using brown corundum,sintered alumina,silicon carbide,activeα-Al_(2)O_(3)micropowder,SiO_(2)micropowder,calcium aluminate cement,Si powder and spherical asphalt as the raw materials,adding additive of Si-N-O composite micropowder,Al_(2)O_(3)-SiC-Si_(3)N_(4)/Si_(2)N_(2)O-C castables were prepared.The effects of the Si-N-O composite micropowder addition on the mechanical properties and oxidation resistance of the castables were investigated,and the intrinsic mechanism of strengthening and antioxidation caused by this novel additive was discussed.Experimental results show the introduction of Si-N-O composite micropowder leads to significant improvement in the cold strength,oxidation resistance,thermal shock resistance and hot modulus of rupture of the Al_(2)O_(3)-SiC-C castables.When the Si-N-O composite micropowder addition is approximately 3 mass%,the castable possesses the best comprehensive performance.展开更多
To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia ...To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia castables for the slag dam was improved and a suitable vibration shaping method was adopted to combine it with alumina magnesia castables. The result shows： （1） workability and setting performance of magtwsia castables can be improved to match with alumina magnesia castables by adjusting setting retarder and water reducing agent, and adding proper silica fume ; （2） composite slag dam cart be prepared with alumina m,agnesia castables and the improved magnesia castables, whether by up - down composite method or right - left composite method; in order to get full vibration arrd make interface .fluctuation have proper amplitude, the vibration time oJ the two methods after two different castables contact with each other is 3 and 2.5 minutes, respectively; （3）the result of the on-site test proves that the design aims for reducing pollution to hot metal and improving corrosion resistance have been achieved.展开更多
In order to prolong the working time of calcined flint clay-bauxite castables during construction at high temperature,boric acid was added into the castables. The effect of boric acid on working time and curing cold c...In order to prolong the working time of calcined flint clay-bauxite castables during construction at high temperature,boric acid was added into the castables. The effect of boric acid on working time and curing cold crushing strength of the castables at 25 ℃ and 35 ℃ were investigated. After 24 h curing in mould and another 24 h curing at 110 ℃ after demoulding,the specimens were heat treated at 1 000 ℃,1 300 ℃,and 1 500 ℃ for 3 h,respectively. The permanent linear change,bulk density,modulus of rupture,and cold crushing strength were determined. The result shows that there is no need to add boric acid when calcined flint clay-bauxite castables works at 25 ℃; when calcined flint clay-bauxite castables works at 35 ℃,boric acid can increase the working time of the castables,but decrease the curing cold crushing strength a little. Adding boric acid into calcined flint clay-bauxite castables doesn＇t worsen performance of the castables.展开更多
Thermal behavior and physical properties of castables during curing and drying-out are associated with their binding system. In this work, five alumina based （ Al2O3 〉 87% ） castables with different combinations of...Thermal behavior and physical properties of castables during curing and drying-out are associated with their binding system. In this work, five alumina based （ Al2O3 〉 87% ） castables with different combinations of binding materials, i. e. , （ 1 ） CA cement （CA） ＋ Reactive alumina （ RA ） ＋ H2O ; （ 2 ） high level addi- tion of CA ＋ Microsilica （MS） ＋ H2O ; （ 3 ） low level addition of CA ＋ MS ＋ H2O ; （4） MS ＋ Hydratable alumina ＋ H20 and （ 5 ） MS ＋ Magnesia ＋ H2O, respectively, have been investigated on the flowability and thermal behavior during curing at room temperature, drying at 110% and heating from 200℃ to 1000℃ at an interval of 100℃ , in terms of water addition, vibration flow value, porosity, dehydration, explosion resistance, cold and hot bending strengths. Differences in dehydrating behavior and the mentioned properties have been revealed and correlated to the binding system.展开更多
Low cement (LC) and ultra low cement (ULC) bauxite SiC castables are important and high performance monolithic refractories and they have been widely used in iron making and incinerator linings. In this work, rheol...Low cement (LC) and ultra low cement (ULC) bauxite SiC castables are important and high performance monolithic refractories and they have been widely used in iron making and incinerator linings. In this work, rheological behavior of LC and ULC bauxite based SiC containing castables has been studied, including the effects of SiC content and cement content on rheological properties of the castables. The results show that with an increase of SiC and cement content, rheological properties of the castables deteriorate. On the other hand, moderate amounts of SiC (4%～8%) and of calcium aluminate cement (2%～4%) have very slight influence on rheological properties, (i.e. when the castables are sheared their torque and yield torque only slightly increase with the shearing speed). The rheological characteristics of the castables follow Bingham fluid and always show shear thinning behavior.展开更多
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 ca...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.展开更多
A series of corundum based castables with 0,2%,4%,6%,and 8% α-Al2O3 micropowders were prepared using tabular alumina aggregates （6-3,3-1 and ≤1 mm） and fines （≤0.088 and ≤0.045 mm）,calcium aluminate cement,and...A series of corundum based castables with 0,2%,4%,6%,and 8% α-Al2O3 micropowders were prepared using tabular alumina aggregates （6-3,3-1 and ≤1 mm） and fines （≤0.088 and ≤0.045 mm）,calcium aluminate cement,and α-Al2O3 micropowders （d50=1.754 μm） as starting materials. Cold mechanical strength and pore size distribution of the castables specimens after heat treatment at 110,1 100 and 1 500 ℃ were tested,respectively. The quantitative relationship between strength and apparent porosity,and that between strength and median pore diameter were verified by Atzeni equation. The correlation between interval of pore size and mechanical strength of specimens was also studied by means of gray relational theory. The results show that：（1） the pore size distribution of castables is strongly influenced by both micropowders filling and matrix sintering; the addition of micropowders decreases median pore diameter while the sintering process increases it; （2） when adding a constant correction term,Atzeni equation can substantially describe the quantitative relationship between median pore diameter and strength of castables specimens after heat treatment at the same temperature; the significant differences of the gray relational degree between the interval of pore size and castables strength are characterized; it is also found that for the same interval of pore size,the gray relational degree isaffected by the heat treatment temperature; the pore size interval 〈0.5 μm has the highest gray relational degree with the strength at 110-1 500 ℃.展开更多
In this study, the properties of self-flowing ultra-low cement castables in Al2O3-SiC-C system have been investigated and compared to vibration castables. The major physical and mechanical properties, microstructure a...In this study, the properties of self-flowing ultra-low cement castables in Al2O3-SiC-C system have been investigated and compared to vibration castables. The major physical and mechanical properties, microstructure and corrosion behavior of these castables against slag have been evaluated. The results showed that the microstructure of Al2O3-SiC-C self-flowing castable is more uniform than the vibrated structure. Also self-flowing castable has smaller pore size and more uniform pore size distribution. Hence, density, strength, oxidation and slag resistance of the self-flowing castables is higher than that of vibration castables. Therefore, besides other benefits such as noise free, easy installation, fewer mold defects and reduced installation costs, Al2O3-SiC-C self flowing ultra low cement castables will have longer service life in comparison with vibration casables.展开更多
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,s...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%.展开更多
Silicon carbide castables of different SiC contents(86%and 71%,by mass)were prepared using white fused corundum,silicon carbide particles and fines,activated alumina powder,silica fume and pure calcium aluminate cemen...Silicon carbide castables of different SiC contents(86%and 71%,by mass)were prepared using white fused corundum,silicon carbide particles and fines,activated alumina powder,silica fume and pure calcium aluminate cement as main starting materials,heat treating at 1000℃ for 3 h,and oxidizing in steam atmosphere at 1000℃ for different durations(100,200,300,400 and 500 h).The mass and volume before and after oxidation,the bulk density,the apparent porosity and the cold compressive strength were tested.The phase composition and the microstructure before and after oxidation were analyzed by XRD and SEM.The results indicate that:(1)within 300 h of oxidation duration,silicon carbide shows an increasing oxidation rate;however,the oxidation rate is low during 300-500 h of oxidation duration;2)the oxidation rate of the specimen with 71%SiC is slightly higher than the one with 86%SiC;3)with the increasing oxidation degree of silicon carbide,the apparent porosity of the specimens tends to increase,followed by the declining bulk density and cold compressive strength.展开更多
Compared with traditional aggregates,spherical aggregates with high flowability,easy control of particle size distribution and favor of dense packing and so on,are expected to replace traditional aggregates as importa...Compared with traditional aggregates,spherical aggregates with high flowability,easy control of particle size distribution and favor of dense packing and so on,are expected to replace traditional aggregates as important raw materials for future high performance refractories. Therefore,investigation of effects of spherical aggregates addition on properties of refractories becomes very meaningful. Using A70 mullite traditional aggregates and A70 mullite spherical aggregates, bauxite homogenization powder,microsilica,and calcium aluminate cement as raw materials,different AlO-SiOsystem low cement castables were prepared by replacing conventional aggregates with spherical aggregates. The effect of spherical aggregates addition on workability and mechanical properties of castables after heated at different temperatures was researched,and microstructure of the specimen was analyzed by SEM. Compared with traditional irregularly shaped aggregates,spherical aggregates endow castables with better flowability and easy pump ability. By introduction of spherical aggregates into the castables,flowability and pumpability are significantly improved,and water addition and ball completely sunk time are reduced. The introduction of spherical aggregates is favorable to density and cold crushing strength of castables,but unfavorable to CMOR. The effect of spherical aggregates addition on HMOR at1 400 ℃ can be negligible. Microstructure analysis showsthat the boundary bonding between spherical aggregates and matrix is strong,similar to the traditional aggregates.展开更多
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 c...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.展开更多
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 syst...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%.展开更多
In order to prolong the service life of castables for hot blast stove pipes,effects of SiO2 micropowder addition and aggregate kind on properties of castables for hot blast stove pipes,and properties of silica sol bon...In order to prolong the service life of castables for hot blast stove pipes,effects of SiO2 micropowder addition and aggregate kind on properties of castables for hot blast stove pipes,and properties of silica sol bonded castables were researched using homogenized bauxite,andalusite particles,andalusite fines,white fused corundum fines,α-Al2O3 micropowder,pure calcium aluminate cement,SiO2 micropowder,and silica sol as starting materials. The results show that：（1） as SiO2 micropowder addition increases,the shrinkage rate of fired specimens increases; BD increases firstly,reaches the highest at 4 mass%,and then decreases; CMOR and CCS of all specimens increase gradually; so the appropriate SiO2 micropowder addition is 4 mass%;（2） the specimens with bauxite aggregate have better CCS and volume stability,but specimens with andalusite aggregate have better thermal shock resistance;（ 3） for castables for hot blast stoves using silica sol as binder,the addition of pure calcium aluminate cement can decrease the linear change rate after treatment at 1 400℃ and can slightly enhance CCS and CMOR,but has very little influence on AP and BD; and the introduction of citric acid worsens the thermal shock resistance of specimens.展开更多
Effects of B4C additions （0,0.2%,0.4%,and 0.6%） on cold physical properties and hot modulus of rupture of Al2O3-SiC-Si3N4 castables for iron trough were investigated. The phase composition and microstructure were an...Effects of B4C additions （0,0.2%,0.4%,and 0.6%） on cold physical properties and hot modulus of rupture of Al2O3-SiC-Si3N4 castables for iron trough were investigated. The phase composition and microstructure were analyzed by XRD and SEM. The results show that bulk density,cold strength,and hot modulus of rupture of the castables first increase and then decrease while apparent porosity first drops and then increases with B4C addition increasing. The optimum addition of B4C is 0.4%. B4C mainly contributes to sintering and antioxidation. Compared with the specimens without B4C,the specimens with B4C have more fibrous O＇-SiAlON with larger length-diameter ratio. The growth mechanism of O＇-SiAlON crystals is deduced to gas-solid mechanism.展开更多
A1203-SiC-C iron trough castables were prepared using high alumina bauxite clinker GL-90 （ 〉 1 mm ） or homogenized bauxite GL-88 to replace the traditional brown corundum aggregates （ 〉 1 mm ） to reduce the cost...A1203-SiC-C iron trough castables were prepared using high alumina bauxite clinker GL-90 （ 〉 1 mm ） or homogenized bauxite GL-88 to replace the traditional brown corundum aggregates （ 〉 1 mm ） to reduce the cost of iron trough castables. Effects of the two bauxite aggregates on properties of iron trough eastables were investigated. The results show that the two kinds of bauxite affect flowability, bulk density, strength and slag corrosion resistance of trough castables differently. Compared with homogenized bauxite, high alumina bauxite clinker is more suitable to substitute brown corundum. The castables prepared from the bauxite clinker have similar performances with those prepared from brown corundum, especially used in medium or small blast furnaces with weak thermal impact and lower temperature hot metal. However, in large blast furnaces with severe thermal impact and high temperature hot metal, the performances of the two castables are significantly different. So it is suggested to use the brown corundum based castables in the front gyral zone of the slag skimmer.展开更多
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%,...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.展开更多
This work investigated the thermo-gravimetric （TG） change and explosion resistance of ultra-low cement Al2O3 - SiO2 castables added with 0, 5%, 10%, 15% and 20% of 474 μm raw bauxite powders containing 72.8% Al2O3,...This work investigated the thermo-gravimetric （TG） change and explosion resistance of ultra-low cement Al2O3 - SiO2 castables added with 0, 5%, 10%, 15% and 20% of 474 μm raw bauxite powders containing 72.8% Al2O3, respectively. The castables were prepared using white fused alumina as aggregate, powders of white fused alumina, fused mullite,α-Al2O3 ultrafines, 3% CA cement and 5% microsilica as the matrix portion. TG change of the castables was investigated by a thermo-gravimetric analyzer for large size specimen. When the raw bauxite addition is less than 10%, the mass-losing behavior of the castables is similar to that without raw bauxite, tending to reach a constant mass around 400 ℃ , before which the mass-loss is mild and producing little destructive influence. With more than 10% raw bauxite addition, however, the mass-loss increases significantly, and the temperature to reach a constant mass increases to 600 ℃ or higher, unfavorable to structural stabilization. With the raw bauxite addition up to 20% , no negative influence on explosion resistance is found.展开更多
基金National Natural Science Foundation of China(52472303 and 52304356).
文摘High-performance alumina-magnesia castables were developed with the addition of nano-CacO_(3) and nano-hydromagnesite.To further understand their dynamic failure mechanism,the quantitative investigation via the employment of the Split-Hopkinson pressure bar(SHPB)method was adopted to test the dynamic failure behavior of alumina-magnesia castables under various impact velocities.The results demonstrate that the greater the impact velocity,the more intense the sample damage.The dynamic compressive stress,the ultimate strain,and the strain energy of all samples display a strain rate hardening effect,and this phenomenon is more conspicuous in the samples incorporating nano-additives.The nano-additives show a positive influence on the dynamic mechanical properties of the castables.
基金Key Project of the National Natural Science Foundation of China(Grant No.U21A2058)China Postdoctoral Science Foundation(2023M740971)State Key Laboratory of Refractories and Metallurgy(Wuhan University of Science and Technology,G202209).
文摘The penetration of ladle slag into refractory linings is an essential process in service,and the mechanical properties of the refractory castables are affected by the location and content of slag in the refractory castables.In this work,ladle slag was added into Al_(2)O_(3)-Mgo refractory castables and its influence on the microstructure evolution,mechanical properties and thermal shock resistance of the castables was investigated.The phase composition and contents of the castables during the corrosion process were calculated by FactSage TM(6.2)and studied.The results indicate that the residual strength decreases as the ladle slag addition increases from 0 to 6 mass%.While the hot modulus of rupture of the castable with 6%ladle slag significantly decreases by approximately 80%compared with the one without ladle slag.The elastic modulus and CMOR of the castables decrease with slag-adding,which leads to the increase of liquid phase contents inside the samples.
文摘In order to improve the service performance of Al_(2)O_(3)-SiC-C castables,a novel Si-N-O composite micropowder was synthesized by the chemical combustion method.Using brown corundum,sintered alumina,silicon carbide,activeα-Al_(2)O_(3)micropowder,SiO_(2)micropowder,calcium aluminate cement,Si powder and spherical asphalt as the raw materials,adding additive of Si-N-O composite micropowder,Al_(2)O_(3)-SiC-Si_(3)N_(4)/Si_(2)N_(2)O-C castables were prepared.The effects of the Si-N-O composite micropowder addition on the mechanical properties and oxidation resistance of the castables were investigated,and the intrinsic mechanism of strengthening and antioxidation caused by this novel additive was discussed.Experimental results show the introduction of Si-N-O composite micropowder leads to significant improvement in the cold strength,oxidation resistance,thermal shock resistance and hot modulus of rupture of the Al_(2)O_(3)-SiC-C castables.When the Si-N-O composite micropowder addition is approximately 3 mass%,the castable possesses the best comprehensive performance.
文摘To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia castables for the slag dam was improved and a suitable vibration shaping method was adopted to combine it with alumina magnesia castables. The result shows： （1） workability and setting performance of magtwsia castables can be improved to match with alumina magnesia castables by adjusting setting retarder and water reducing agent, and adding proper silica fume ; （2） composite slag dam cart be prepared with alumina m,agnesia castables and the improved magnesia castables, whether by up - down composite method or right - left composite method; in order to get full vibration arrd make interface .fluctuation have proper amplitude, the vibration time oJ the two methods after two different castables contact with each other is 3 and 2.5 minutes, respectively; （3）the result of the on-site test proves that the design aims for reducing pollution to hot metal and improving corrosion resistance have been achieved.
文摘In order to prolong the working time of calcined flint clay-bauxite castables during construction at high temperature,boric acid was added into the castables. The effect of boric acid on working time and curing cold crushing strength of the castables at 25 ℃ and 35 ℃ were investigated. After 24 h curing in mould and another 24 h curing at 110 ℃ after demoulding,the specimens were heat treated at 1 000 ℃,1 300 ℃,and 1 500 ℃ for 3 h,respectively. The permanent linear change,bulk density,modulus of rupture,and cold crushing strength were determined. The result shows that there is no need to add boric acid when calcined flint clay-bauxite castables works at 25 ℃; when calcined flint clay-bauxite castables works at 35 ℃,boric acid can increase the working time of the castables,but decrease the curing cold crushing strength a little. Adding boric acid into calcined flint clay-bauxite castables doesn＇t worsen performance of the castables.
文摘Thermal behavior and physical properties of castables during curing and drying-out are associated with their binding system. In this work, five alumina based （ Al2O3 〉 87% ） castables with different combinations of binding materials, i. e. , （ 1 ） CA cement （CA） ＋ Reactive alumina （ RA ） ＋ H2O ; （ 2 ） high level addi- tion of CA ＋ Microsilica （MS） ＋ H2O ; （ 3 ） low level addition of CA ＋ MS ＋ H2O ; （4） MS ＋ Hydratable alumina ＋ H20 and （ 5 ） MS ＋ Magnesia ＋ H2O, respectively, have been investigated on the flowability and thermal behavior during curing at room temperature, drying at 110% and heating from 200℃ to 1000℃ at an interval of 100℃ , in terms of water addition, vibration flow value, porosity, dehydration, explosion resistance, cold and hot bending strengths. Differences in dehydrating behavior and the mentioned properties have been revealed and correlated to the binding system.
文摘Low cement (LC) and ultra low cement (ULC) bauxite SiC castables are important and high performance monolithic refractories and they have been widely used in iron making and incinerator linings. In this work, rheological behavior of LC and ULC bauxite based SiC containing castables has been studied, including the effects of SiC content and cement content on rheological properties of the castables. The results show that with an increase of SiC and cement content, rheological properties of the castables deteriorate. On the other hand, moderate amounts of SiC (4%～8%) and of calcium aluminate cement (2%～4%) have very slight influence on rheological properties, (i.e. when the castables are sheared their torque and yield torque only slightly increase with the shearing speed). The rheological characteristics of the castables follow Bingham fluid and always show shear thinning behavior.
文摘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.
文摘A series of corundum based castables with 0,2%,4%,6%,and 8% α-Al2O3 micropowders were prepared using tabular alumina aggregates （6-3,3-1 and ≤1 mm） and fines （≤0.088 and ≤0.045 mm）,calcium aluminate cement,and α-Al2O3 micropowders （d50=1.754 μm） as starting materials. Cold mechanical strength and pore size distribution of the castables specimens after heat treatment at 110,1 100 and 1 500 ℃ were tested,respectively. The quantitative relationship between strength and apparent porosity,and that between strength and median pore diameter were verified by Atzeni equation. The correlation between interval of pore size and mechanical strength of specimens was also studied by means of gray relational theory. The results show that：（1） the pore size distribution of castables is strongly influenced by both micropowders filling and matrix sintering; the addition of micropowders decreases median pore diameter while the sintering process increases it; （2） when adding a constant correction term,Atzeni equation can substantially describe the quantitative relationship between median pore diameter and strength of castables specimens after heat treatment at the same temperature; the significant differences of the gray relational degree between the interval of pore size and castables strength are characterized; it is also found that for the same interval of pore size,the gray relational degree isaffected by the heat treatment temperature; the pore size interval 〈0.5 μm has the highest gray relational degree with the strength at 110-1 500 ℃.
文摘In this study, the properties of self-flowing ultra-low cement castables in Al2O3-SiC-C system have been investigated and compared to vibration castables. The major physical and mechanical properties, microstructure and corrosion behavior of these castables against slag have been evaluated. The results showed that the microstructure of Al2O3-SiC-C self-flowing castable is more uniform than the vibrated structure. Also self-flowing castable has smaller pore size and more uniform pore size distribution. Hence, density, strength, oxidation and slag resistance of the self-flowing castables is higher than that of vibration castables. Therefore, besides other benefits such as noise free, easy installation, fewer mold defects and reduced installation costs, Al2O3-SiC-C self flowing ultra low cement castables will have longer service life in comparison with vibration casables.
文摘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%.
文摘Silicon carbide castables of different SiC contents(86%and 71%,by mass)were prepared using white fused corundum,silicon carbide particles and fines,activated alumina powder,silica fume and pure calcium aluminate cement as main starting materials,heat treating at 1000℃ for 3 h,and oxidizing in steam atmosphere at 1000℃ for different durations(100,200,300,400 and 500 h).The mass and volume before and after oxidation,the bulk density,the apparent porosity and the cold compressive strength were tested.The phase composition and the microstructure before and after oxidation were analyzed by XRD and SEM.The results indicate that:(1)within 300 h of oxidation duration,silicon carbide shows an increasing oxidation rate;however,the oxidation rate is low during 300-500 h of oxidation duration;2)the oxidation rate of the specimen with 71%SiC is slightly higher than the one with 86%SiC;3)with the increasing oxidation degree of silicon carbide,the apparent porosity of the specimens tends to increase,followed by the declining bulk density and cold compressive strength.
基金financial support from the National Natural Science Foundation of China ( Grant No.51402089)the Plan of Young-backbone Teachers of Colleges and Universities in Henan Province ( Project No.2015GGJS-045)
文摘Compared with traditional aggregates,spherical aggregates with high flowability,easy control of particle size distribution and favor of dense packing and so on,are expected to replace traditional aggregates as important raw materials for future high performance refractories. Therefore,investigation of effects of spherical aggregates addition on properties of refractories becomes very meaningful. Using A70 mullite traditional aggregates and A70 mullite spherical aggregates, bauxite homogenization powder,microsilica,and calcium aluminate cement as raw materials,different AlO-SiOsystem low cement castables were prepared by replacing conventional aggregates with spherical aggregates. The effect of spherical aggregates addition on workability and mechanical properties of castables after heated at different temperatures was researched,and microstructure of the specimen was analyzed by SEM. Compared with traditional irregularly shaped aggregates,spherical aggregates endow castables with better flowability and easy pump ability. By introduction of spherical aggregates into the castables,flowability and pumpability are significantly improved,and water addition and ball completely sunk time are reduced. The introduction of spherical aggregates is favorable to density and cold crushing strength of castables,but unfavorable to CMOR. The effect of spherical aggregates addition on HMOR at1 400 ℃ can be negligible. Microstructure analysis showsthat the boundary bonding between spherical aggregates and matrix is strong,similar to the traditional aggregates.
基金the National Natural Science Foundation of China (51572244 and U1604252, 51672255) for the financial supportpartly co-financed by Imerys Aluminates
文摘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.
文摘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%.
文摘In order to prolong the service life of castables for hot blast stove pipes,effects of SiO2 micropowder addition and aggregate kind on properties of castables for hot blast stove pipes,and properties of silica sol bonded castables were researched using homogenized bauxite,andalusite particles,andalusite fines,white fused corundum fines,α-Al2O3 micropowder,pure calcium aluminate cement,SiO2 micropowder,and silica sol as starting materials. The results show that：（1） as SiO2 micropowder addition increases,the shrinkage rate of fired specimens increases; BD increases firstly,reaches the highest at 4 mass%,and then decreases; CMOR and CCS of all specimens increase gradually; so the appropriate SiO2 micropowder addition is 4 mass%;（2） the specimens with bauxite aggregate have better CCS and volume stability,but specimens with andalusite aggregate have better thermal shock resistance;（ 3） for castables for hot blast stoves using silica sol as binder,the addition of pure calcium aluminate cement can decrease the linear change rate after treatment at 1 400℃ and can slightly enhance CCS and CMOR,but has very little influence on AP and BD; and the introduction of citric acid worsens the thermal shock resistance of specimens.
基金supported by the Natural Science Foundation of Hebei Province(No:E2009000784)Educational Department of Hebei Province (2008453)
文摘Effects of B4C additions （0,0.2%,0.4%,and 0.6%） on cold physical properties and hot modulus of rupture of Al2O3-SiC-Si3N4 castables for iron trough were investigated. The phase composition and microstructure were analyzed by XRD and SEM. The results show that bulk density,cold strength,and hot modulus of rupture of the castables first increase and then decrease while apparent porosity first drops and then increases with B4C addition increasing. The optimum addition of B4C is 0.4%. B4C mainly contributes to sintering and antioxidation. Compared with the specimens without B4C,the specimens with B4C have more fibrous O＇-SiAlON with larger length-diameter ratio. The growth mechanism of O＇-SiAlON crystals is deduced to gas-solid mechanism.
文摘A1203-SiC-C iron trough castables were prepared using high alumina bauxite clinker GL-90 （ 〉 1 mm ） or homogenized bauxite GL-88 to replace the traditional brown corundum aggregates （ 〉 1 mm ） to reduce the cost of iron trough castables. Effects of the two bauxite aggregates on properties of iron trough eastables were investigated. The results show that the two kinds of bauxite affect flowability, bulk density, strength and slag corrosion resistance of trough castables differently. Compared with homogenized bauxite, high alumina bauxite clinker is more suitable to substitute brown corundum. The castables prepared from the bauxite clinker have similar performances with those prepared from brown corundum, especially used in medium or small blast furnaces with weak thermal impact and lower temperature hot metal. However, in large blast furnaces with severe thermal impact and high temperature hot metal, the performances of the two castables are significantly different. So it is suggested to use the brown corundum based castables in the front gyral zone of the slag skimmer.
文摘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.
文摘This work investigated the thermo-gravimetric （TG） change and explosion resistance of ultra-low cement Al2O3 - SiO2 castables added with 0, 5%, 10%, 15% and 20% of 474 μm raw bauxite powders containing 72.8% Al2O3, respectively. The castables were prepared using white fused alumina as aggregate, powders of white fused alumina, fused mullite,α-Al2O3 ultrafines, 3% CA cement and 5% microsilica as the matrix portion. TG change of the castables was investigated by a thermo-gravimetric analyzer for large size specimen. When the raw bauxite addition is less than 10%, the mass-losing behavior of the castables is similar to that without raw bauxite, tending to reach a constant mass around 400 ℃ , before which the mass-loss is mild and producing little destructive influence. With more than 10% raw bauxite addition, however, the mass-loss increases significantly, and the temperature to reach a constant mass increases to 600 ℃ or higher, unfavorable to structural stabilization. With the raw bauxite addition up to 20% , no negative influence on explosion resistance is found.
