Characteristics of Hercynite and Its Application in Refractories

The characteristics of hercynite including crystal structure,chemical compositions and physical properties, R D background of hercynite,synthesis problems of hercynite,and roles of hercynite in refractories were reviewed. The application of hercynite in refractories was introduced with emphasis. The practical applications in cement rotary kiln showed the prepared magnesia hercynite brick had better performance than the original magnesia chrome brick obviously.     

水泥回转窑烧成带用耐火材料的最新研究

对水泥回转窑烧成带用耐火材料的使用条件和要求进行了分析,并对近年来水泥窑用镁铬砖、镁尖晶石砖、镁钙锆砖的应用进行了探讨,指出所存在的缺点及改进措施。认为其发展方向为镁钙锆砖及尖晶石砖,并对其应用前景进行了展望,希望实现水泥回转窑的无铬化。     

Slag Resistance of Refractories for Direct Reduction of Laterite Nickel Ores in Rotary Kilns

Aiming at prolonging the service life of refractories for direct reduction of laterite nickel ores in rotary kilns, the slag resistance of ten materials(corundum bricks, chrome corundum bricks, silicon nitride bonded silicon carbide bricks, high alumina silicon carbide bricks, high alumina bricks, magnesia chrome bricks, magnesium aluminate spinel bricks, spinel chrome corundum bricks, chrome corundum castables and magnesia alumina chrome composite spinel bricks) was evaluated by rotary slag tests, which simulate the service conditions in rotary kilns. The corroded residual bricks were analyzed by SEM and EDS. The results show that the magnesia alumina chrome composite spinel brick possesses the advantages of magnesium aluminate spinel bricks and chrome corundum bricks; MgO-rich spinel can absorb the penetrated ferric oxide, and forms a dense zeylanite layer, which prevents the penetration of the molten laterite nickel ores; therefore, it is an ideal lining of rotary kilns for direct reduction of laterite nickel ores.     

The State—of—art of Magnesia—chrome Refractories for P—S Converter in China‘s Non—ferrous Industry

The state-of-art of magnesia-chrome refractories from direct-bonded magnesia chroma brick to fused-grain rebounded magnesia chrome brick for P-S converter is discribed.The Cr2O3 conternt of the brick is continually increased with the reduction of the impurity content of brick ,the pre-synthetic raw material is applied and the operating condition of conerter is optimized so that the service life of converter is largely enhanced.     

水泥窑用镁铬砖中Cr6+化合物的化学性质和解毒

研究了K2CrO4的化学稳定性。K2CrO4中的Cr^6 不能或难于被乙醇、乙醛、柠檬酸、酒石酸、葡萄糖甚至草酸还原，仅发现FeSO4与MnSO4可将K2CrO4的Cr^6 转化成Cr^3 。镁铬残砖产生的Cr^6 物质很难在环境中被破坏，很多情况下将长期存在自然界中，持续性地危害人体的健康。因此，水泥窑应优先使用无铬耐火材料，如使用镁铬砖，须用FeSO4或MnSO4等方法将残砖解毒。     

水泥窑用高性能镁铬砖的研制及应用

分析了普通镁铬砖在水泥窑上使用存在的不足之处。在原来普通镁铬砖工艺基础上引入特制的合成料,使制品的性能得到改善。高性能镁格砖在水泥窑上使用,寿命远远超过普通镁铬砖。     

闪速炉用镁铬砖的研制与应用

简要介绍了闪速炉用耐火材料国产化工作的现状 ,阐述了闪速炉用镁铬砖的研制、使用和损毁情况。认为现在完全可以实现闪速炉用耐火材料的国产化     

Variation of Poisson's ratio of refractory materials with thermal shocks

Investigations into the changes of Poisson's ratio as well as other mechanical properties of selected types of refractories subjected to thermal shocks have been carried out. The investigations included several types of porous refractory materials e.g. magnesia, magnesia–spinel, magnesia–chrome, chrome–magnesia, mullite, silica and low cement chamotte castable. The Poisson's ratio value of the examined materials decreased after each thermal shock. Decreasing of Poisson ratio caused by a stronger drop in Young's modulus than that for shear modulus was explained.It was found that some tested materials were characterized by low values of Poisson's ratio, which after series of severe thermal shocks decreased even to negative values. In order to explain the observed phenomenon, an attempt to correlate the obtained results with the microstructure of materials before and after a series of thermal shocks was undertaken. A hypothetical model of the microstructure of a porous ceramic material with negative Poisson ratio was proposed.     

合理选择和使用耐火砖消除铬对环境的危害

水泥窑用镁铬砖的残砖中铬含量较高，对环境危害大。为降低铬盐对环境的危害，牡丹江新材料科技股份有限公司在水泥窑上进行了使用低铬砖和无铬砖的试验。试验表明，加锆改性尖晶石砖的使用情况较直接结合镁铬砖差，而加铬方镁石复合尖晶石砖(LYC砖)的使用效果好于直接结合镁铬砖。LYC砖不仅铬含量低，对环境的危害小，且其使用寿命是普通镁铬砖的5倍，是直接结合镁铬砖的1．72倍。使用LYC砖对提高窑运转率，降低生产成本有利。     

World Production of Steel and Magnesia Refractories: State of the Art and Trends of Development

The state of the art and the trends of development of the world production of steel, nonferrous metallurgy, and the cement industry -- the chief users of magnesia refractory materials -- are considered. A new generation of magnesia refractories developed for oxygen converters, electric furnaces, post-furnace and continuous steel-casting technologies, nonferrous metallurgy, and the cement industry provide conditions for environment-friendly, competitive, and effective applications in various branches of industry.     

Main Influencing Factors on Service Life of High Chrome Refractories for Coal Water Slurry Gasifiers

The main characteristics of high chrome refractories for coal water slurry gasifiers were introduced. The damage mechanism of the refractories was analyzed by observing the microstructure of the used high chrome refractories with the aid of SEM. The main influencing factors on the service life of the refractories were summarized.     

Improvement of Durability of Purging Plugs Using MgO Micropowder for Refining Ladles

To modulate the matrix of purging plugs, MgO micropowder was introduced as a replacement to magnesia powder in alumina–magnesia castables, and the effect of MgO micropowder on the properties of alumina–magnesia castables and the possibility of developing chrome‐free castables were investigated. Experimental results showed that the introduction of MgO micropowder resulted in an improvement in the volume stability, strength, and thermal shock resistance of alumina–magnesia castables due to its high surface energy and small particle size. However, excessive amounts of MgO micropowder led to a lower densification, and there was a slight degradation in the performance of the alumina–magnesia castables. The slag resistance of the prepared alumina–magnesia castables was significantly better than that of the alumina–chrome castables. Microstructure and energy spectrum analysis showed that the formation of a solidified reaction layer, mainly consisting of spinel and CaAl₁₂O₁₉, was the major cause of the observed difference in slag resistance. In addition, the alumina–magnesia castables had a lower linear thermal expansion coefficient than that of the alumina–chrome castables at each experimental temperature, which effectively decreased the thermal stress during its service period, thus exhibiting good thermal shock resistance.     

Pollution of Chrome Bearing Materials and the Solutions

This paper summarizes the pollution, situation and solutions of chrome bearing materials used in high temperature industry. Hexavalent chromium compounds are readily soluble in water and associated with carcinogen. Therefore, serious environmental problems appeal for the study and application of chrome free materials. Chrome free products include: magnesia based materials, dolomite based materials, magnesia spinel materials, magnesia hercynite or magnesia galaxite materials and zirconia containing materials,and other substitutes. Although any product has its advantages and disadvantages, the trend to development of chrome free products is inevitable.     

水泥回转窑用含ZrO2耐火材料

含ZrO2耐火材料在水泥窑上的应用不断增加,水泥窑用含ZrO2耐火材料包括含锆白云石砖、含锆镁砖、含锆镁尖晶石砖、含锆高铝砖等.本文从材料的抗化学侵蚀性、热震稳定性、导热性和力学性能等方面讨论了ZrO2的引入对耐火材料使用性能的影响.     

A Review on Some Applications of Magnesia in Current China Refractories Industry

Being rich in the magnesite resource,China hasbecome the biggest magnesia-based products manufac-turer.With nearly300magnesite mines including somenewly built magnesite processing plants,China has to-tal output of over14million tons magnesite ore peryear,…     

Evaluation of fracture behavior of lightweight magnesia-based refractories via wedge splitting test along with acoustic emission detection

The effect of spinel powder on the fracture behavior and mechanical properties of lightweight magnesia-based refractories containing microporous magnesia aggregates with high apparent porosity (37.4%) were investigated by the wedge splitting test (WST) with the digital image correlation and acoustic emission. With the addition of spinel powder, lightweight magnesia spinel refractories showed a higher cold compressive strength compared with lightweight pure magnesia refractories. From the WST, the addition of spinel powder increased the specific fracture energy and characteristic length of lightweight magnesia spinel refractories, which improved the crack propagation resistance. The increased tortuosity of main crack and a higher ratio of crack propagation along the aggregates/matrix interface were main reasons for reducing the brittleness of lightweight magnesia spinel refractories. Besides, acoustic emission (AE) signal activity indicated that the propagation of pregenerated micro-cracks by the thermal mismatch and the development of fracture progress zone were primary ways to consume energy in lightweight magnesia spinel refractories. The reduced proportion of crack propagation within aggregates was also detected by the peak frequency of AE signals in lightweight magnesia spinel refractories. For microporous magnesia aggregates with high apparent porosity (37.4%), lightweight magnesia spinel refractories also showed reduced brittleness fracture behavior than lightweight pure magnesia refractories.     

Effects of Chrome Oxide Concentrate Powder on Properties of Magnesia Composite Materials

The magnesia composite materials were prepared using fused magnesia,used magnesia chrome bricks, magnesium aluminate spinel, alumina powder and chrome oxide powder as starting materials. In order to improve the performance of magnesia composite material,the influence of chrome oxide concentrate powder on the properties of magnesia composite material was researched. The apparent porosity,bulk density,cold crushing strength,linear expansion and thermal shock resistance of the specimens were determined. The results show that adding chrome oxide concentrate promotes the formation of the composite phases of three kinds of spinel,which is beneficial to the thermal shock resistance. The magnesia chrome spinel can not be formed at high temperatures theoretically,but can dissolve in the magnesia composite material. Comprehensively,the optimal addition of chrome oxide concentrate is 10. 0 mass% for the magnesia composite materials.     

Current state of steel-melting production and the technology for and raw-materials base of magnesia refractories in Ukraine

The state of production of magnesia refractories is considered. Ukraine does not produce promising advanced magnesia refractories (periclase-carbon, dolomite-periclase-carbon, and periclase-spinel). Periclase-chromite and chromite-periclase refractories are produced on the basis of imported raw materials of various grades. The technical level of the used equipment does not meet current requirements. The raw-materials base is underdeveloped. In order to bring the production of Ukrainian magnesia refractories to a competitive level have to attain the quality of the world counterparts at a cost 20–30% lower than the world level. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 32–35, April, 1998. For the beginning of the article see No. 3 of 1998.     

Corrosion modeling of magnesia aggregates in contact with CaO–MgO–SiO2 slags

Ladle refining is an efficient process for improvement of quality of steel on secondary metallurgy under harsh conditions. Magnesia refractories with high purity are important raw materials for ladle lining in high-quality steel production. However, the penetration by CaO–MgO–SiO₂ slags damages magnesia refractories, which considerably limits their service life. Abundant grain boundaries in magnesia create channels for slag penetration and lead to the destruction of the structure. The effect of the microstructure on the slag corrosion behavior of magnesia aggregates requires further systematic investigation. In this study, a corrosion model was established to describe the slag penetration process of magnesia aggregates. The effects of the grain-boundary size and slag CaO/SiO₂ mass ratio (C/S ratio) on slag penetration were investigated, and the possibility of the microstructure optimization of magnesia aggregates was discussed. The results indicated that magnesia aggregates exhibited excellent slag resistance for slag with a C/S ratio above 1.5 or even 2.0. When the slag C/S ratio was lower than 1.5, the dissolution rate of magnesia decreased more rapidly with the increase in the slag C/S ratio. In addition, the much smaller grain-boundary size increased the slag penetration resistance by promoting the formation of a dense isolation layer and inhibiting further penetration processes. The calculation results agreed well with the experimental results, suggesting that the corrosion model is promising for predicting slag corrosion.     

Mechanical and fracture investigation of magnesia refractories with acoustic emission-based method

In this study, the fracture behaviour of magnesia, magnesia chrome and magnesia spinel (MgAl₂O₄ and FeAl₂O₄) refractories under wedge splitting test are qualitatively and quantitatively investigated with the acoustic emission (AE) and digital image correlation (DIC). First of all, the concepts of characteristic widths are proposed for estimating the brittleness of refractory materials according to the shape of load-displacement curve and validated by their good correlation with the characteristic length. Besides, the AE data are analyzed with AE parameter-based approaches and offer new insight into the fracture behaviour of refractory materials, including the classification of the cracking events in grains and in matrix, the distinction between the tensile mode and shear mode damage, and the visualization of the fracture process zone development. It confirms that the pre-existing micro-crack networks in refractories are favourable for the brittleness reduction, which enhance their nonlinear fracture behaviour and thermal shock resistance.