Synthesis of New Composite Anti—Oxidants and Their Appliction to Carbon—Containing Refractories

The present paper describes the synthesis of new com-postie anti-oxidants consisting of Al4SiC4 and aluminum-oxycarbides by heating a mixture of silica ,aluminum and carbonaceous substance at relatively low temperatures of 1500℃ in a flowing argon atmosphere.The phase compo-sition of the composite powder could be controlled through adjusting the fraction of raw materials in starting materi-als ,and also through controlling the sythesizing tempera-ture.In addition, the residual amount of Al4C3,Which was an intermediate phase in rection process,could be eliminated as much a5 possible.Therefore ,the hydration of the composite owders can be avoided.The addition of the synthesized composite anti-oxidants into carbon-bearing refractories can improve oxidation resistance greatly just like aluminum does but with non-hydration and breakage after oxidation.     

Evolution of Phase Composition and Microstructure of Al_2O_3-Si-Al Composite at High Temperatures in Reducing Atmosphere

Al2 O3-Si-Al composite specimens with the size of 25 mm × 25 mm × 125 mm were prepared using fused alumina （as aggregates and fines）,ultra-fine α-Al2O3,Si and Al powders as starting materials,liquid phenol formaldehyde resin as the binder,pressing and heating at 800-1 500 ℃ for 3 h under carbon embedded condition.Evolution of phase composition and microstructure of Al2 O3-Si-Al composite during heating from 800 to 1 500 ℃ under carbon embedded condition were studied.The results show that：（1） Al4 C3,AlN and SiC are initially formed at 800-900 ℃ due to reactions of Al and Si with C or CO and N2 ; （2） at 1 000-1 300 ℃,the amounts of Al4C3,AlN and SiC increase with temperature rising and their crystals grow; （3） at 1 400-1 500 ℃,Al4 C3 and AlN disappear,and minor SiAlON crystals are observed; the nonoxide crystals develop well and they are interlaced in the corundum skeleton structure,which creates strengthening and toughening     

Effects of Admixtures on the Anti—oxidation Property of MgO／Si3N4 Composite Refractory

The effect of the admixtures of Al and Si metals and B4C and MgAlON compounds on the oxideation of MgO/Si3N4 composite refractory has been studied,which is a promising carbon free refractory for steel-making applicatlon.The four kinds of admixtures can be used as anti-oxidants for Si3N4,ut the mixture of Al and Si achieved the best result .The mixture can not only play the role as antioxidant,but also assist the sintering process and help form dense sintering layer,improving the property of the composite.     

Formation of O‘—Sialon Matrix and Microstructure Development in the Refractory of Si3N4—SiO2—ZrO2—Al2O3 System

An O‘-Sialon-Al2O3 composite refractory was prepared by in situ reaction of Si3N4-ZrSiO4-Al2O3 mixture with fused alumina aggregates.Densification,in situreaction procedure and microstructure of the material were investigated by means of X-ray diffraction,optical and scanning electronic microscopes and EDAX.     

Fe_2O_3对天然原料合成Al_4SiC_4/Al_4O_4C复合耐火材料的影响(英文)

以焦宝石、活性炭和铝粉为原料并添加Fe2O3后制备了Al4SiC4/Al4O4C复合耐火材料。利用化学分析、X射线衍射和扫描电镜研究了Fe2O3对所制备复合材料的物相组成和显微结构的影响。结果表明:在烧结过程中,从1400℃开始,Fe2O3转变为低熔点物相Fe3Si,产生液相促进Al4SiC4成核、细化晶粒,同时包裹Al4SiC4。此外,未添加Fe2O3的样品中生成的Al4O4C短纤维,Fe2O3的加入使得Al4O4C相变为细小的晶粒。     

Effect of Al_2O_3-SiC Composite Powder on Properties of Al_2O_3-SiC一C Bricks

Al2O3- SiC- C specimens were prepared using white fused corundum( 3- 1,≤1 and ≤0. 044 mm),Al2O3- SiC composite powders( d50≤5 μm),α-Al2O3micropowder( d50= 1. 2 μm),SiC powder( ≤0. 044mm),flake graphite( ≤0. 088 mm),Si powder( d50= 42. 8 μm) and B4C powder( d50≤10 μm) as main starting materials,and thermosetting phenolic resin as binder. 4%,8%,12% and 16%( in mass,the same hereinafter) of Al2O3- SiC composite powders substituted the same quantity of α-Al2O3micropowder + SiC powder.Effects of composite powder additions on apparent porosity,bulk density,cold modulus of rupture,cold crushing strength,hot modulus of rupture( 1 400 ℃),therma shock resistance( 1 100 ℃,water quenching) and oxidation resistance( 1 000 and 1 500 ℃) of Al2O3- SiC- C specimens after 180 ℃ curing,1 000 ℃ 3 h carbon-embedded firing and 1 500 ℃ 3 h carbon-embedded firing,respectively,were researched. The results indicate that:( 1) with the increase of Al2O3- SiC composite powder,cold strengths of the cured specimens decline,those of the specimens fired at 1 000 ℃ change a little,and those of the specimens fired at 1 500 ℃ change a little except for an obvious improvement of cold crushing strength;( 2) with the increase of Al2O3- SiC composite powder,hot modulus of rupture at 1 400 ℃ decreasesand thermal shock resistance enhances significantly;( 3) when Al2O3- SiC composite powder addition is4%,the oxidation resistance at 1 500 ℃ is the best,and the reason may be the composite powder is finer and more active,which is beneficial to form dense mullite protective layer to retard the O2diffusion into the specimens.     

Al4C3 Hydration Thermochemical Analysis for Burned Carbon-Containing Refractories with Al

In this paper,X-ray diffractogram analysis and SEM observation of Al4C3 formed at high temperature from carbon-containing refractories with Al have been carried out.Aluminum added to carbon-containing refractories reacts with C(s) to form Al4C3(s) gradually during heating from 600℃ to 1200℃，It is considered that the interlocked structure of Al4C3 plate crystals promotes the outstanding increase of hot modulus of rupture of carbon-containing refractories with Al.The HMOR of carbon-contatining refractories with Al.The HMOR of carbon-containing refractories added with Al additive from 0 to 5wt% increases by 2.8 times being from 6.5MPa to 18.2MPa.After a thermochemical Calculation for hydration reaction Processes of Al4C3 and H2O(g),the equilibrium partial pressure chart of H2O(2)in H2O-Al4C3-Al(OH)3 system vs various temperatures has been attained.The H2O(g) partial pressure in the air needed for the Al4C3 hydration reaction is no more than 10-18 atm at the temperature below 120℃。It is considered that the temperature below 120℃. It is considered that the burned carbon-containing refractories with Al is extremely easy to hydrate and the cracking of buurned carbon-containing refractories is generated because that the hydration expansion is 2.11 times during transforming from Al4C3 to Al(OH)3.The fundamental measure against hydration of the refractories is to insulate the refractories from H2O(g) by various means such as pitch impregnatiion or other sealing materials.     

Corrosion Resistance of AI2O3-C Materials to Oolitic-hematite Reduction Melt

Al2O3- C specimens were prepared using fused corundum and flake graphite as starting materials,SiC as antioxidant,and phenolic resin as binder to research their corrosion resistance to oolitic-hematite reduction melt. The tests of slag penetration and corrosion were carried out by static crucible method. The corrosion resistance was presented by the corrosion area and penetration depth. The corroded specimens were investigated by XRD,SEM and EDS. The results show that:(1) the corrosion resistance of Al2O3- C materials to oolitic-hematite reduction melt is improved obviously by the addition of SiC;(2) with the rising of reduction temperature and the prolonging of reduction duration,the corrosion area and penetration depth both increase rapidly;(3) the corrosion mechanism of the oolitic-hematite reduction melt can be described as that the melt reacts with Al2O3- C materials forming some low melting compounds such as CaO·Al2O3·2SiO2,CaO·2Al2O3and Fe2SiO4.     

Effect of Carbon Source on Crystal Morphology of SiC in-situ Formed in AI2O3-Si-C Matrix

Three kinds of Al2O3- Si- C matrix specimens were prepared using tabular corundum powder and Si powder as starting materials,ultrafine flake graphite,nano carbon black,and carbon nanotubes as carbon sources,respectively,to research the effect of micro or nano carbon materials on structure and morphology of formed Si C crystals. The specimens were fired at 1 000,1 200 and 1 400℃ for 3 h in carbon-embedded condition,respectively.The phase composition was studied by XRD and the crystal morphology of Si C was investigated by FESEM. The results show that:( 1) the amount of Si C increases with the firing temperature rising;( 2) the in-situ reaction mechanism and the formed Si C crystal morphology vary with carbon source: carbon nanotubes are generally converted into Si C whiskers by carbon nanotubes-confined reaction; Si and nano carbon black react to nucleate quickly,and the nucleated Si C crystals grow evenly in all directions forming Si C particles; Si C whiskers are produced from edge to internal of ultrafine flake graphite.     

Physical Properties and Hydration Resistance of CeO2—and CeO2／Fe2O3—Bearing Dolomite Refractory Products

Dolomite refractory products with excellent hydration resistance have been produced by using CeO2-and CeO2/Fe2O3-bearing dolomite clinkers,Their physical properties as well as hydration resistance have been investigated,The addition of CeO2 has little harmful effect on the high temperature properties of dolomite refractory products such as hot MOR and slag resistance,And the shelf lives of the dolomite refractory products containing CeO2 and CeO2/Fe2O3 additions at the same condition are two times that of the common dolomite refractory produt.The dolomite refractory product containing CeO2/Fe2O3 combination possesses the best hydration resistance,but gives poor slag resistance.     

莫来石结合Al2O3-SiC浇注料的显微结构特征

借助SEM和EDAX研究了莫来石结合Al2O3 -SiC浇注料的显微结构特征。结果表明 :在莫来石结合Al2 O3 -SiC浇注料中 ,莫来石相与填充在其间隙的玻璃相形成连续基质 ;刚玉颗粒与基质中SiO2 反应生成的二次莫来石与基质中的原生莫来石交错存在 ,构成网状结构 ;SiC颗粒表面高温氧化生成的SiO2 膜 ,改善了SiC颗粒与基质的润湿性 ,是其与基质直接结合的媒介。     

Ti3SiC2/Al2O3复合材料的制备与性能研究

以TiC／TiO2/Si／Al／Ti等为主要原料，采用热压法原位合成Ti2SiC2／Al2O3复合材料，分别探讨了Al掺入量和工艺制度对Ti3SiC2/Al2O3复合材料物相、显微结构以及性能的影响。结果表明：原位合成制备的Ti3SiC2/Al2O3复合材料与传统方法合成制备的纯Ti3SiC2材料相比，材料的硬度和致密度均有很大的提高。     

氮化硅铁在Al2O3-C体系中的高温行为

为了研究高温条件下Al2O3-C体系中氮化硅铁的状态,以闪速燃烧合成氮化硅铁、炭黑、刚玉粉为原料,将试样在高温炉中分别加热至1 450、1 500、1 600℃保温5 h,急速水冷后,对其进行XRD和显微结构分析。结果表明:1 450℃烧后试样的物相包含β-Si3N4、α-Si3N4、α-Al2O3和Fe3Si;1 500℃烧后试样的物相为β-Si3N4、SiC、α-Al2O3和Fe3Si;1 600℃烧后试样中Si3N4大部分转变为SiC,其他物相未发生变化。在升温过程中,氮化硅逐渐转化为碳化硅,材料结构致密。     

无压烧结Al2O3／SiC纳米复相陶瓷的研究

将粒径为30～35nm的β-SiC粉,加入亚微米尺寸的α-Al     

添加铝对机械活化辅助合成Ti_3SiC_2粉末的影响(英文)

以Ti,Si,TiC并添加Al的混合粉末为原料,采用机械活化辅助自蔓延合成法制备了Ti3SiC2粉末。研究表明,机械活化过程可将原料的粒度尺寸细化至10μm以下,反应物活性提高,并能激发自蔓延合成反应生成Ti-Si,SiC,TiCx等中间相。在上述条件下,合成单相Ti3SiC2粉末的温度可降至1350℃。反应机理为:Al作为脱氧剂通过抑制其它元素的氧化来促进主相的生成,且在反应物中优先熔化形成局部微小熔池,加速了反应物的扩散并生成TiCx和Ti5Si3中间相,从而促进Ti3SiC2粉末的生成。     

炭／炭复合材料SiC／Mo（Six，Al1-x）2涂层形成机理与抗高温氧化性能

采用高温包渗技术在炭／炭复合材料表面制备了SiC／Mo（Six,Al1-x）2复合涂层,采用两步反应法研究了复合涂层的生成机理。发现复合涂层是由Si、Al2O3、SiC、MoSi2原始粉末材料与基体炭材料经过复杂化学反应生成的SiC、Mo（SixAl1-x）2以及微量Mo4．8Si3C0．6固溶体组成。在较低温度下（〈1750℃）,单质硅与基体碳的液-固相反应,经过2小时后可以在炭／炭复合材料表面和内部孔隙表面生成致密的SiC过渡涂层;在较高温度下（≤2000℃）,SiC、Al2O3和MoSi2间的反应较为复杂,其主要过程为SiC与Al2O3间生成液体硅、液体铝和气态SiO、Al2O的多相反应,该反应生成的液体铝能够与MoSi2颗粒发生置换反应,生成熔点降低的Mo（Six,Al1-x）2转移涂层;同时,生成的液体硅与CO反应生成晶须状β—SiC,并与Mo（Six,Al1-x）2形成增强型复合涂层。本文还研究了过量单质Si和SiC对Mo（Six,Al1-x）2的还原反应,化学反应推论与实验结果相吻合。以新提出的涂层生成机理为指导,以粉末原料质量组成为Si10％,Al2O3 10％,SiC54％和MoSi226％时所制得了致密并且无粘结的复合涂层材料,并研究了封孔处理后复合材料的抗氧化性能。     

SiC/Ni3Al界面固相反应

使用扫描电子显微镜、电子能谱仪、X射线衍射仪对经1 050 ℃等温热处理10 h的SiC/Ni3Al界面固相反应层的成分分布、微结构及相组成等进行了研究.结果表明:SiC/Ni3Al界面固相反应层由Ni5.4Al1Si2、石墨态C及NiAl构成,反应物原子(Si,C,Ni和Al)在反应层中连续分布,均呈现下坡扩散的特征.反应层由随机C沉积区(random carbon precipitation zone,R-CPZ)及无碳沉积区(carbon precipitation free zone,C-PFZ)两个亚层构成.其中,R-CPZ靠近SiC侧,主要由Ni5.4Al1Si2构成,片状和颗粒状的石墨态C随机地分布其中;C-PFZ靠近Ni3Al侧,主要由Ni5.4Al1Si2及NiAl构成,不含有石墨态C.     

逆反应烧结制备铝电解槽用氮化硅-碳化硅复合材料

采用常规的反应烧结工艺制作铝电解槽侧壁材料用Si3N4／SiC时存在不足，为此，提出应用逆反应烧结工艺进行生产性试验的设想。在制备Si3N4／SiC复合材料时，常规反应烧结是以Si和SiC为原料经氮化烧结；逆反应烧结是以Si3N4和SiC为原料，首先使Si3N4反向反应生成活性氧化物后进行烧结。结果表明：该工艺特点是新生的Si2N2O或SiO2进行活性烧结；制品具有良好的物理和化学性能。制品结构紧密，新生氧化物或亚氧化物紧密地充填在Si3N4和SiC颗粒间界，新工艺制备的砖的抗冰晶石熔体侵蚀的性能优于常规工艺烧成砖，是铝电解槽侧壁的良好材料。     

高炉用氮化硅结合碳化硅制品化学分析方法的研究

确定了高氧化铝含量（０．５％－２０％）的高炉用氮化硅结合碳化硅制品中Ｓｉ３Ｎ４、ＳｉＣ、ｆＳｉ、ＳｉＯ２、Ｆｅ２Ｏ３、Ａｌ２Ｏ３六种化学成分的化学分析方法试验条件．并按条件试验选择了分析方法，进行了精密度、准确度和实际工作的考核，证明了本分析方法可靠、切实可行，能满足科研工作和生产的要求。     

AlN-Re2O3液相烧结碳化硅

采用非氧化物AlN和Re2O3作为复合烧结助剂(Re2O3-La2O3与Y2O3)进行碳化硅液相烧结得到了致密的烧结体.烧结助剂占原料粉体总质量的20%,其中:AIN与(La0.5Y0.5)2O3的摩尔比为2:1,在30MPa压力下,1850℃保温0.5h热压烧结的碳化硅陶瓷,抗弯强度>800MPa,断裂韧性>8MPa·m1/2,明显高于同组分1 950℃无压烧结0.5h的碳化硅陶瓷的抗弯强度(433.7MPa)和断裂韧性(4.8MPam·m1/2.热压烧结的陶瓷晶粒呈单向生长,断裂模式为沿晶断裂.同组分无压烧结碳化硅陶瓷的显微结构可以观察到核壳结构.