Influences of Al and Si Powders on Microstructure and Hot Mechanical Properties of Al2O3-C Slide Plates

The basic formulation of Al2O3- C slide plates was65%( in mass,the same hereinafter) white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, and additional 4% phenolic resin.Based on this formulation,3% Al powder,3% Si powder,and 3% Al + 3% Si powder were used to substitute equivalent white corundum fines to improve the hot mechanical properties of Al2O3- C slide plates. The specimens with dimensions of 140 mm × 25 mm × 25 mm were pressed at 150 MPa,dried at 200 ℃ for 24 h,and hot treated at 1 400 ℃ for 3 h in carbon embedded condition. Then hot modulus of rupture and thermal shock resistance of the specimens were tested and the phase compositions and microstructure were analyzed. The results show that specimen with 3% Al powder has the higher hot modulus of rupture but lower residual modulus of rupture after thermal shock than the specimen with3% Si powder; the specimen with 3% Al + 3% Si powders exhibits the highest hot modulus of rupture and the best thermal shock resistance; the change of mechanical property is closely related with the in-situ formed nonoxides: AlN in the form of bars is formed in specimens with Al powder; fibrous SiC whiskers are formed in specimens with Si powder; in the specimens with both Al and Sipowders,besides AlN and SiC whiskers,hexagonal tabular SiAlON is in-situ synthesized,which interlocks with each other.     

Replacement of Flake Graphite in Aluminacarbon Refractories by Hexagonal Boron Nitride

Three kinds of composite alumina refractories were prepared with tabular alumina （3-1 and 1-0 mm） as aggregates,tabular alumina powder,α-Al2 O3 micropowder,and Si powder as matrix,adding 3 mass％ hexagonal boron nitride （h-BN）,3 mass％ flake graphite and 10 mass％ flake graphite,respectively.Cold physical properties,hot modulus of rupture,oxidation resistance,thermal shock resistance and slag corrosion resistance of the specimens were compared.The results show that：（1） physical properties and hot modulus of rupture of Al2 O3-h-BN refractories are slightly different from those of low carbon Al2 O3-C refractories,but better than those of traditional Al2 O3-C refractories with 10 mass％ graphite ; （2） Al2 O3-h-BN refractories have better thermal shock resistance and oxidation resistance than the carbon containing refractories,while similar slag resistance with low carbon Al2 O3-C refractories ; （3） h-BN can replace flake graphite as a starting material for the preparation of composite alumina refractories,considering the overall properties of the material.     

Properties and Microstructure Evolution of Al_2O_3-Si Material Fired in Different Atmospheres

Al2O3- Si composite specimens were prepared using fused corundum,ultra-fine α-Al2O3and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties,phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that:( 1) after firing in oxidizing or weak oxidizing atmosphere,there is some Si in the specimens and some glass phases containing mullite form on specimen surface,the density and strength at room temperature are relatively high,but hot modulus of rupture and thermal shock resistance are relatively poor;( 2) after firing in weak reducing or reducing atmosphere,Si reacts completely with CO or N2forming whisker-like SiC,granular Si2N2O or O'-SiAlON,and the thermo-mechanical properties of specimens are enhanced;( 3) after firing in nitrogen atmosphere,Si reacts completely with N2,CO or C forming whisker-like SiC and columnar β-SiAlON crystals,the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.     

Properties and Microstructure Evolution of Al203-Si Material Fired in Different Atmospheres

A1203-Si composite specimens were prepared using fused corundum, ultra-fine α-A1203 and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties, phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that： （ 1 ） after .firing in oxidizing or weak oxidizing atmosphere, there is some Si in the specimens and some glass phases containing mullite form on specimen surface, the density and strength at room temperature are relatively high, but hot modulus of rupture and thermal shock resistance are relatively poor; （2） after firing in, weak reducing or reducing atmosphere, Si reacts completely with CO or N2forming whisk-phere, Si reacts completely with CO or N2forming whisk-er-like SiC, granular Si2N20 or 0＇-SiAION, and the er-like SiC, granular Si2N20 or O＇-SiMON, and the thermo-mechanical properties of specimens are enhanced;（3） after firing in nitrogen atmosphere, Si reacts completely with N2, CO or G forming wbisker-like SiC and columnar β-SiA10N crystals, the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.     

Effects of Dispersive Agent and Alumina Micropowder on Workability of Al_2O_3-MgO Castables for Steel Ladles

This work aims at enhancing the workability of Al2 O3-Mg O castables. Al2 O3-Mg O castables were prepared using tabular alumina particles( 5-3,3-1,≤1 mm),tabular alumina fines( ≤0. 088 mm),fused magnesia( ≤1 mm),reactive alumina micropowder( PFR40,PBR,and CL) and calcined alumina micropowder( AC34 B5 and CT) as the main starting materials,calcium aluminate cement( Secar71) as the binder,and polycarboxylic acid water reducer WS,FS,and AD as the dispersive agent,respectively. Effects of three dispersive agents addition( 0. 4 mass% WS,0. 2 mass% FS and 1 mass% AD),two kinds of reactive alumina micropowder addition( PFR40 and PBR),composite alumina micropowder addition( PFR40-AC34 B5 and CL-CT,the mass ratio from 9/0 to 3/6)on the flow value,apparent porosity,bulk density,cold crushing strength and cold modulus of rupture of Al2 O3-MgO castables were investigated. The results show that:( 1) with PBR or PFR40,the castables with0. 4 mass% WS own better performance than those with0. 2 mass% FS or 1 mass% AD;( 2) compared with the castables with CL-CT composite powder, the castables with PFR40-AC34 B5 composite powder have slightly higher flow value; with the decreasing ratio of PFR40 and AC34 B5,or the decreasing ratio of CL andCT,the castables have declined flow value and the dried castable specimens have decreased density but the mildly changed strength; in consideration of the high price of reactive alumina,a proper compositing ratio shall be selected.     

Abstracts from Naihuo Cailiao（Refractories）——A Chinese-Language Bimonthly

Volume 40,Number 6,2006 Effects of nano-Al2O3 on microstructure and properties of corundum refractories.Zhang Haixia,Li Hongxia,Yang Bin.(401-405).-Nano-Al2O3,Refractories,Mechanical properties,Microstructure-Corundum refractories were prepared with tabular alumina,white fused alumina and calcined alumina micropowder as main starting materials.Different contents of nano-Al2O3 powder (0,0.5%,1.0%,1.5%,2.0%) were added to the mixture by mechanical mixing and sol method respectively.The mixture was mixed for 5 min,and formed to 125 mm×25 mm×25 mm specimens under 180 MPa.The specimens were dried at 120 ℃ for 12 h and fired at 1 400 ℃,1 500 ℃,1 600 ℃,1 650 ℃ for 4 h in electric furnace with Molybdenum Disilicide Heating Elements.The bulk density(BD),apparent porosity(AP),cold modulus of rupture(CMOR) and hot modulus of rupture(HMOR) were measured and the microstructure was analyzed by SEM.The results show that:compared with mechanical mixing,adding nano-Al2O3 powder by so-gel method leads to better optimization.Proper amount of nano powder (1.5%) could improve BD,CMOR and HMOR of the specimens obviously under the same firing condition;If the addition of nano-Al2O3 in the composites was excessive (>1.5%),the strength of the specimens decreases sharply.     

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.     

Effect of Nano-ZnO or Nano-Y2O3 on Sintering Property of Fused Quartz Ceramics

Fused quartz ceramic was prepared using high purity fused quartz powder as starting material,separately introducing 1%,2% and 3%( in mass,the same hereinafter) nano-ZnO or nano-Y2O3as additive,molding at 50 MPa, firing in reduction atmosphere at1 300,1 350 and 1 400 ℃ for 1 h,respectively. Apparent porosity and cold modulus of rupture were tested and fracture morphology was analyzed by SEM. The results show that adding nano-ZnO or nano-Y2O3obviously improves sintering of fused quartz; adding nano-ZnO enhances modulus of rupture and decreases apparent porosity; the optimum addition of nano-Y2O3as sintering aid of fused quartz is 2%.     

Application Research of Dense Sintered Alumina in Iron Runner Castables

Three different kinds of corundum aggregates—tabular sintered alumina, dense sintered alumina, and fused dense corundum—were introduced into the silica fume free or silica fume containing Al_2O_3-SiC-C iron runner castables to investigate their influences on the flow ability,linear change on heating,bulk density,apparent porosity, cold strength, hot modulus of rupture,thermal shock resistance,slag resistance,oxidation resistance as well as wear resistance of Al_2O_3-SiC-C iron runner castables. The results show that( 1) compared with the specimens with fused dense corundum,the specimens with dense sintered alumina have equivalent installation property,slag resistance and oxidation resistance,equivalent or even higher cold modulus of rupture,cold crushing strength and hot modulus of rupture,exhibiting better thermal shock resistance and cold wear resistance;( 2) adopting bimodal alumina micropowder LISAL22 RABL as well as water reducers ZX2 and ZD2 can well reduce the water requirement of silica fume free castables,solving the problem of deteriorated flow ability resulted from the lack of silica fume; since the lack of silica fume avoids the formation of low melting point liquid,the hot modulus of rupture and the thermal shock resistance of the silica fume free castables are both better than those of the silica fume containing castables;( 3)the density of the castable specimens with dense sintered alumina is 4%-6% lower than that of the castable specimens with fused dense corundum so the refractories consumption of one iron runner reduces by 5% by usingthe castable with dense sintered alumina,which obviously reduces the cost of refractories.     

Thermo-mechanical Properties of In-situ Formed Al_2O_3-SiC-SiAION Composites

Al_2O_3-SiC-SiAlON composite specimens have been prepared using fused alumina,ultra fine α-Al_2O_3,Si and Al powders as starting materials and liquid phenol formaldehyde resin as binder and firing at 1 500 ℃ for3 h in carbon embedded condition. Thermo-mechanical properties of Cr_2O_3-Al_2O_3-Zr O2 composites have been studied. The results show:( 1) Cr_2O_3-Al_2O_3-Zr O2 composites can be prepared and sintered at 1 500 ℃ under carbon embedded condition. When Si / Al ratio is 8 /0and 7 /1, the prepared composite is Al_2O_3-SiC-O'-Si Al ON; when Si / Al ratio is 5/3 and 3 /5,the prepared composite is Al_2O_3- SiC-β-Si Al ON.( 2) The composites possess high temperature strength properties.Hot modulus of rupture at 1 400 ℃ is 10- 30 MPa.They are in elastic range up to 1 000 ℃,after which plastic deformation is observed; even at 1 400 ℃,amount of deformation is relatively low.( 3) The composites possess good thermal shock resistance,their residual strength ratio( ΔT = 1 100 ℃) is 65%- 80%.( 4) The marked improvement in thermo-mechanical properties of Cr_2O_3-Al_2O_3-Zr O2 composites may be attributed to the in-situ formation of Si C,Si Al ON and Al N,the fibrous Si C,columnar Si Al ON and tabular-like Al N fill in the corundum skeleton structure creating strengthening and toughening effects.     

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.     

Effect of Zircon Addition on Properties of Low Carbon Al2O3-C Refractories

Using tabular alumina as aggregate,tabular alumina fines, reactive alumina ultra-fines, aluminum powders,silicon powders,carbon black,flake graphite,B4C and zircon fines as matrix,low carbon Al2O3- C refractories were prepared. Influences of zircon powders additions( 0,3%,5% and 7%,in mass,the same hereinafter) on properties,phase composition and microstructure were investigated. The results show that the ZrO2- nitride can be in-situ formed through carbothermal reduction and nitridation in Al2O3- C refractories.With the increase of zircon powder,the oxidation resistance of the Al2O3- C refractories improves obviously,the oxidized layer thickness decreases from 7. 94 mm without zircon to 2. 71 mm with 5% zircon. HMOR at 1 400 ℃of the Al2O3- C refractories reaches the maximum 14. 9MPa when zircon addition is 5%. With the increase of zircon powder,the apparent porosity and bulk density change a little,CMOR and CCS increase.     

Relationship Between Electric Properties and Temperature of ZrB,-SiC Composite Ceramic Heating Element

ZrB2 -SiC composite ceramic has been successfully introduced as heating element in super high temperature .field. This paper further investigated the microstructure of ZrB2 - SiC composite ceramic heating element and the relationship between electric properties and temperature. SEM photos show that the heating element consists of SiC grains and ZrBz grains smaller than 10 μm. The voltage and current gradually increase and the furnace tempera- ture rises lineally with heating time prolonging. The electric resistance increases linearly with the temperature rising. The service temperatltre of the heating element can reach 1 800 ℃ and 2 150 ℃ in air and argon at- mosphere, respectively.     

Effect of ZnO on Oxidation Resistance of Low Carbon MgO-C Refractories

Al-containing low carbon MgO- C refractories were prepared using 70%( in mass,the same hereinafter)fused magnesia( ≤3 mm),24% fused magnesia powder( 0. 074 mm),3% flake graphite,3% Al powder and 4% phenolic resin( extra-added) as the basic formulation. Influence of ZnO addition on oxidation resistance of the materials was investigated by adding 1%ZnO to substitute fused magnesia powder. The relationship between in-situ formed spinel and ZnO in the matrix was discussed by comparing apparent porosity, cold crushing strength,and phase evolution of the materials matrix. The oxidation resistances of the two materials were compared by observing the formed dense MgO layer between the decarburized layer and the original layer.The result shows that adding ZnO in MgO- C refractories accelerates the in-situ formation of ZnAl2O4spinel and the formation of dense MgO layer,thus improves the oxidation resistance of the low carbon MgO- C refractories.     

Effect of Nano-Al2O3 on Mechanical Properties and Microstructure of Si3N4 Ceramics

Si3N4ceramics were prepared by pressureless sintering at 1 650 ℃ in nitrogen atmosphere using Si3N4powder as main starting material and adding nanoAl2O3powder( 3%,6%,9%,12%,and 15% in mass,the same hereinafter). The bending strength and fracture toughness( KIC) of the specimens were detected.The microstructure and phase compositions of the specimens were analyzed. The results show that Si3N4ceramics can be prepared by pressureless sintering when adding9%- 12% nano-Al2O3as active reactant,which dissolves in Si3N4,in-situ forming non-oxide SiAlON. The obtained Si3N4ceramics have the maximum bending strength of 710. 86 MPa and KICof 8. 61 MPa·m1 /2.The excellent properties come from many interwoven structures distributed uniformly in the ceramics matrix,which is composed of big and firm plate-like β-Si3N4,hexagonal SiAlON and sheet Si2N2O.     

腐植酸对发展绿色低碳经济意义重大

<正>两百多年来,人类被"高碳"长烤。今天你"低碳"了吗?已成为人类共同的问候。哥本哈根世界气候大会刚结束,我们就迎来了以"腐植酸绿色产业与低碳经济发展"为主题的"第八     

Abstracts Selected from Naihuo Cailiao （Refractories）——A Chinese Language Bimonthly

Development and prospect of China＇ s refrac- tory industry equipment/Liu Junguang, WeiTong//Naihuo Cailiao. - 2013,47 （5） ：321 Alasttact： China＇ s refractory equipment including me- chanical equipment and kilns developed rapidly in the past two decades by technological innovation, advanced products introduction and independent research and de- velopment based on the former Soviet Union＇ s aid. In recent years, some high efficient equipment was devel- oped covering fields of fine grinding, burdening, mix- ing,shaping and firing,etc. In the new developing peri- od of refractory industry from big to strong, the ad- vanced refractory equipment shall be well researched and developed ,and be well spread taking the opportu- nity of raw materials homogenization and purification, capacity large scale, quality and pollutants reduction. improvement, energy saving     

Influences of Polyvinyl Alcohol on Synthesis of A95 Polycrystalline Alumina Fibers

In order to improve the spinnabilities of A95 alumi- na silica sols, the influences of addition and polymeriza- tion degree of polyvinyl alcohol on spinnabilities of alu- mina silica sols were researched. The viscosity and rheo- logical properties of the sols, mierostructure, infrared spectra, average diameter and diameter distribution oJ the gel fibers, BET specific surface area and distribution of pore diameters were measured. The results show that iJ there is no spinning agent, the A95 sols have no spinna- bility ; when PVA 2099 addition is in the range of l. 0% -2.0% （in mass, the same hereinafter） , the prepared sols have good spinnability, the gel fibers produced are thin and uniform, and the shot content is low ; BET spe- cific surface area and gas absorption amount of A95 polycrystalline alumina fibers are the largest when PVA 2099 addition is 2. 0% ; the gel fibers are thick and non-uniform, and the shot content is high when PVA 2099 addition is 4. 0% ; with polymerization degree oJ PVA increasing, the average diameter and diameter dis- tribution range of the gel fibers increase gradually; when using PVA 1799 and PVA 1899, respectively, the spun gel fibers are thin and uniform.