Effect of ZrC Modified Graphite on Structure and Properties of Low-carbon Al_(2)O_(3)-C Refractories

To address the issues of reduced performance and shortened lifespan during the low-carbonizating process of Al_(2)O_(3)-C refractories,nano-crystalline ZrC modified graphite was prepared using Zr powder and flake graphite as raw materials,with NaCl and NaF mixed salt serving as the medium.The flake graphite was gradually replaced by ZrC modified graphite in the preparation of Al_(2)O_(3)-C refractories,and its impact on the material’s structure and properties was investigated.The results indicate that,compared to samples with only flake graphite,the introduction of 1 mass%to 5 mass%nano-crystalline ZrC modified graphite can significantly enhance the mechanical performance of low-carbon Al_(2)O_(3)-C refractories.When 5 mass%ZrC modified graphite is added,the mechanical properties of the samples are optimal,with the cold modulus of rupture and elastic modulus reaching 22.5 MPa and 65.0 GPa,respectively.

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 Spinels on Properties of MgO-Al_(2)O_(3) Refractories for RH Snorkels

With satisfactory high temperature properties,thermal shock resistance and mechanical properties,refractories in the MgO-Al_(2)O_(3) system have become promising alternative to MgO-Cr_(2)O_(3) counterpart used as RH snorkel lining.High purity dead burned magnesia,fused magnesia and sintered spinel were used as raw materials and sulfite pulp waste as the binder,specimens of the refractories in the Mg0-Al_(2)O_(3) system were prepared for the purpose of investigating the influences in terms of the addition of three kinds of spinels,with Al_(2)O_(3) 50%,66% and 78%,by mass,respectively,and the size of MA50 spinel on properties of the specimens.Relatively superior comprehensive properties can be achieved when 16%of MA50 spinel with sizes under 1mm is adopted.

Effect of Al Powder and Si Powder Additions on Structure and Properties of Unburned Magnesium Aluminate Spinel Refractories

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.

Chinese Standards on Refractories Magnesium Aluminate Spinel

1 Scope This standard specifies the terms, definitions, classifications, technical requirements, test methods, inspection rules, packing, marking, transportation, storage, and quality certificate of magnesium aluminate spinel. This standard is applicable to the magnesium alu- minate spinel prepared by sintering method or electric mehing method with raw materials of industrial alumina or bauxite, and light burnt magnesia.

Comprehensive Utilization of Natural Magnesium-Containing Resources and the Development of MgO-Based Refractories

This paper presents the ways of comprehensive utilization of the natural magnesium containing resources and the trends of the MgO based refractories used in high temperature industries. In the first part, the uses and productions of metal Mg, sorel cement, Mg (OH) 2 fire retardant, light magnesium carbonate, light magnesia and magnesium sulphate are described. In the second part, the developments of MgO based refractories used in steelmaking process, nonferrous metallurgy, cement rotary kiln and waste melting furnace are described from some applied theories, including corrosion resistant and slaking resistant MgO CaO materials, chrome free bricks such as MgO CaO ZrO 2 , MgO MgO Al 2 O 3 , MgO MgO·Al 2 O 3 ZrO 2 , MgO MgO·Al 2 O 3 2MgO ·TiO 2 and MgO FeO·Al 2 O 3 , and MgO containing monolithic refractories etc.

Current Situation and Development of Refractories for Clean Steel Production

The low cost and high efficient clean steels metallur- gy has been focused much attention in China. Among the factors affecting the cleanliness and consequent quali- ty of steel products, refractories are one of the key fac- tors. Meanwhile the restriction of resource, energy and environment is getting stronger, thus the improvement of refractories becontes much more important. In this paper, refractories selection principle Jbr clean steel production according to their thermodynamic features was ex- plained; refractories for tundLsh and flow control in con- tinuous casting, which play important roles in prohibi- ring secondary contamination of molten steel, were intro- duced. Moreover, new development of low-carbon and carbon-free refractory materials was also described.

Sintering Complexity of Magnesia-chrome Refractories

Magnesia-chrome refractories are appropriate to work under cyclic temperatures or atmospheric conditions because some oxides of chrome ore readily release oxygen(are reduced)upon heating and pick up oxygen(are oxidized)upon cooling or upon changing the atmosphere.They have been ideal lining materials for RH degassers for many years,despite challenging of Cr^(6+) disposal issue after using.The varieties of magnesia-chrome refractories depend on their raw materials and burning temperatures,which could be well demonstrated by their microstructures.But Indian chrome concentrate cannot be directly used in the production of magnesia-chrome bricks because of reducing sintering density.Silicate bonded magnesia-chrome bricks are produced with low purity magnesia after burning at relatively lower temperatures,resulting in liquid film forming as silicate bond around chrome ore particles.Direct bonded and rebonded fused-grains magnesia-chrome refractories are made of high purity magnesia or fused magnesia-chrome grains,forming euhedral and intergranular secondary chromite spinels as the main feature.The amount of secondary spinel increases with the rising burning temperature,leading to increasing hot modulus of rupture and overall hot properties as well.It is important to burn magnesia-chrome bricks under weakly reducing atmosphere.The oxygen content of burning atmosphere from 800℃ to 1650℃ would better controlled below 0.5%to increase the burnt strength and to avoid inner cracks and loose bonding of magnesia-chrome bricks,while the atmosphere contains 3%-6%O_(2) under most economical firing condition.

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

Volume 50,Number 3,2016 Preparation and properties of infrared ceramics with high infrared emissivity/Yang Jinping,Wang Chunmei,Wei Hengyong,Chen Yang//Naihuo Cailiao.-2016,50（4）：241Abstract：This work aims at preparing ceramics with high infrared emissivity.Analytically pure Fe_2O_3,Co_2O_3,CuO,MnCO_3,Bi_2O_3,MgCO_3,talcum（≤0.1mm industrially pure）,kaolin clays,high temperature solid state synthesized spinel type ferrite.

Effect of micro-Al_(2)O_(3) powders on oxidation and corrosion behaviors of low-carbon MgO-C refractories

To solve the problem of poor high-temperature service performance caused by low carbonization of MgO-C refractories,low-carbon MgO–C refractories with excellent thermal shock,oxidation and corrosion resistances were successfully designed by using SiC whiskers as reinforcing phases and introducing micro-Al_(2)O_(3) powders as additives.The results indicated that the addition of micro-Al_(2)O_(3) powders optimized the internal structure of the material,like the columnar β-Si_(3)N_(4) with a stepped distribution and the mosaic structure formed between granular and flaky Mg_(2)SiO_(4),which synergistically strengthened and toughened the material and gave the material excellent mechanical properties and thermal shock resistance.Specifically,the cold modulus of rupture and cold crushing strength after thermal shock were increased by 4.1 and 20.3 MPa,respectively.Moreover,the addition of micro-Al_(2)O_(3) powders promoted the formation of fine particles of Mg_(2)SiO_(4),MgAl_(2)O_(4) and MgO,as well as a dense protective layer of Mg_(2)SiO_(4) in the material under high-temperature environment.Furthermore,spinel and high-temperature solid solution were formed in the corrosion environment.The oxidation and corrosion resistances were greatly improved by 41%and 15%,respectively.

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.

In-situ Formation of Spinel Fibers in MgO-C Refractory Matrixes

In-situ magnesia-rich spinel fiber was formed resulting from the addition of ferrocene into MgO-C refractory matrixes. The formation of in-situ spinel fiber was detected to start at 1300 ℃. The amount, diameter and length of the fibers increased with rising temperature. Ferrocene may have catalytic effects on the growth of the fibers in two aspects. First, the reaction between MgO and C and the decomposition of Al4C3 may be catalyzed at high temperature. Suitable concentration gaseous phase is then created for vapor-vapor reaction which could result in the in-situ formation of fibers. Second, Fe nanoparticle produced from ferrocene can act as catalytic droplets and catalyze the growth of the fibers. The fibers are formed via the vapor-liquid-solid and vapor-solid mechanisms. In terms of chemical thermodynamics, the partial pressure of CO and Mg（g） are found to play an important role in the in-situ fibers formation. Different concentration of vapors affects the size, amount and composition of the fibers at different temperatures. The mechanical properties of MgO-C brick was found to be improved by ferrocene addition.

镁铝合金添加剂对SiC-MgAl_(2)O_(4)材料显微结构和性能的影响

为探索煤气化用耐火材料的无铬化,本研究采用碳化硅颗粒和镁铝尖晶石细粉为主要原料制备SiC-MgAl_(2)O_(4)复合耐火材料,于流动氮气中500~1450℃热处理,对比未添加和添加4%(质量分数)镁铝合金粉的复合材料在热处理升温过程中的微观结构及性能变化,探究镁铝合金氮化烧成中形成的低维相对SiC-MgAl_(2)O_(4)复合材料性能的改善效果。结果表明,镁铝合金与热处理环境中的N 2、O_(2)的反应温度区间为650~800℃,主要反应产物为AlN和MgO。添加镁铝合金后的试样在700℃形成蜂窝状MgAl_(2)O_(4)尖晶石,增强了SiC骨料和MgAl_(2)O_(4)基质间的结合,此时试样的常温力学强度达到最高;900~1300℃时,MgAl_(2)O_(4)尖晶石由蜂窝状转变为棒状,1300~1500℃时,其再转变为片状、粒状的MgAlON尖晶石,这些形貌和物相的转变伴随体积膨胀,导致试样的强度小幅下降。镁铝合金的添加能使SiC-MgAl_(2)O_(4)在较低温度热处理下原位形成尖晶石,从而提高材料的力学性能。

方镁石-尖晶石质免烧耐火材料抗渣性能研究

采用烧结镁砂和电熔尖晶石为主要原料,酚醛树脂为结合剂,以单质硅粉、氧化钇等为添加剂,对比研究了添加剂及熔渣特性对方镁石-尖晶石质免烧耐火材料抗渣性能的影响.结果表明,熔渣碱度越高,黏度越小,越易于向耐火材料内部渗透.复合添加Al和Y_(2)O_(3)有利于改善材料结构与性能,一方面,Y_(2)O_(3)能够调节MgO晶粒生长、促进材料烧结。另一方面,Y_(2)O_(3)与熔渣中的CaO反应形成CaYAlO_(4),增大熔渣黏度,提高材料的抗渣侵蚀性能.

Recent progress in synthesis of composite powders and their applications in low-carbon refractories

The development of low-carbon refractories is of great significance,but it is limited by the deteriorated properties that resulted from the decreased graphite content.Incorporating composite powders has proved to be effective in improving the properties of low-carbon refractories.The recent progress in the synthesis of composite powders including modified graphite,nanocarbon-containing composite powders,oxide/non-oxide and non-oxide composite powders and their applications in low-carbon refractories were reviewed,and the future development of composite powder technology was prospected.

Enhanced oxidation resistance of low-carbon MgO-C refractories with ternary carbides:a review

The demand for low-carbon MgO–C refractories is ever growing to meet the development of advanced steelmaking technologies and efficient energy conservation.Meanwhile,to improve the oxidation resistance and inhibit the weakness of low-carbon MgO–C refractories,antioxidants are necessary.The application of ternary carbides that focused on improving the oxidation performance of MgO–C refractories has been explored,and the ternary carbides including Al_(4)O_(4)C,Al8B_(4)C_(7),Al_(4)SiC_(4),Ti_(2)AlC,Ti_(3)AlC_(2),and Ti_(3)SiC_(2)have been proved effective.The crystal structure,physical properties,oxidation behavior,and synthesis of these ternary carbides were summarized,and their oxidation mechanism in assisting antioxidation of MgO–C refractories was discussed.In addition,the potential aspects related to the usage and development of ternary carbides in low-carbon MgO–C refractories were proposed.

Challenges and Opportunities of China's Refractory Industry

This paper reviews the current development status and achievements of China's refractory industry,summarizing the significant progress made by China's refractory industry over the past 40 years in energy conservation,environmental protection,green and low-carbon development,and intelligent manufacturing.It analyzes the challenges and difficulties faced by China's refractory industry currently,focusing on how the current adjustment cycle in China's steel industry provides new opportunities for China's refractory sector.China's refractory industry must adhere to the path of innovationdriven,intelligent manufacturing,green and low-carbon.We should seek and seize new opportunities for transformation and upgrading,continuously optimize the industrial structure,enhance product and service quality,and carefully balance the domestic and international markets.This approach aims to form a new capacity management mechanism that includes market competition and constraints from both energy consumption and carbon emission,with government supervision and industry self-discipline.

镁铝尖晶石粉体的制备方法

综述了目前常用的制备镁铝尖晶石粉体的各种方法的工艺过程、特点及其产物的性能特征。经分析指出纯度和粒度是粉体最重要的两个性能指标;降低合成温度、简化工艺过程是今后制备技术发展的趋势。金属醇盐可能成为获得高纯度产物最有应用前景的前驱物;水热处理、溶剂蒸发、超临界干燥等物理手段是解决粒度最有效的途径。

镁铝尖晶石基耐火材料的最新研究进展

综述了镁铝尖晶石基耐火材料的最新研究进展 ,介绍了合成镁铝尖晶石原料的几种新方法 ,重点介绍了镁铝尖晶石原料合成的最新研究进展 ,如添加剂、气氛、原料活性等对镁铝尖晶石原料烧结性的影响 ,同时也简介了镁铝尖晶石基耐火材料的高温使用性能 ,如抗渣性、热震稳定性等。

含ZrO_2添加剂对方镁石-尖晶石耐火材料力学性能的影响

在方镁石 -尖晶石耐火材料中 ,加入三种不同类型的含ZrO2 添加剂 ,均能明显提高材料的力学性能。经XRD、偏光显微镜及电子探针分析 ,认为改善性能的机理在于 :引入ZrO2 改善了材料的显微组织结构 ,并产生了适量微裂纹 ,强化了基质 。