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.     

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。     

Corrosion Resistance Mechanism of Magnesia Zirconia Brick to RH Furnace Slag

Magnesia zirconia brick containing 11 wt% zirconia was prepared with magnesia and monoclinic zirconia as starting materials in order to replace the chrome-containing materials for RH furnace.The corrosion resistance of magnesia zirconia brick and fused rebonded magnesia chrome brick (short for magnesia chrome brick) to high and low basicity slag of RH furnace was comparatively researched by rotary slag method and their slag resistance mechanisms were analyzed.The results show that:(1) because the reaction l...     

Progress of Environment-friendly Basic Refractories for Cement Industry

The chrome pollution from cement industry was introduced briefly,the research on chrome free basic refractories for cement kilns was reviewed,the production technologies of magnesia calcia,magnesium aluminate spinel,magnesia hercynite refractories,etc. were specified,the principles to improve thermal shock resistance and coating adhesiveness of refractories were analyzed,the measures to extend service life by improving production equipment and service conditions of refractories were put forward,the future of chrome free refractories was expected and some developing suggestions were given.     

回转窑烧成带用镁铁铝尖晶石砖的研制与应用

以新理论、新工艺合成出了结晶完好、质地均匀的铁铝尖晶石,并以合成的铁铝尖晶石为原料制备了镁铁铝尖晶石砖。大量应用结果表明,研制的镁铁铝尖晶石砖具有窑皮形成迅速、稳定、导热率小及使用寿命长等优点,总体性能超过了镁铬砖,满足了大型回转窑烧成带的无铬化要求。     

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.     

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

Magnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium-free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite-ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron-size whisker network bond domination in their matrix. Such a whisker-network bond renders the material a successful eco-friendly alternative to magnesia–chrome refractory.     

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.     

高基质普通烧镁砖的研制及应用

在普通烧镁砖中,提高基质相原料纯度,可使精炼铬铁炉炉衬寿命明显提高。     

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。     

TiO_2对镁铬砖抗渣蚀性的影响

利用XRD分析和光学显微镜等测试手段 ,研究了添加TiO2 对镁铬砖抗渣蚀性的影响。结果表明 :炉渣中的CaO能分解镁铬砖中的二次尖晶石而使镁铬砖损毁 ,但加入TiO2 后 ,TiO2 能优先于尖晶石中的Cr2 O3与渣中CaO反应 ,生成高熔点的CaTiO3,从而抑制CaO对砖中镁铬尖晶石的分解 ,提高了镁铬砖的抗高钙渣渣蚀能力     

新型镁铬质耐火泥浆的研制与使用

以废镁铬砖为主要原料 ,采用国产材料作结合剂研制了镁铬质耐火泥浆。研制的三种镁铬质耐火泥浆理化性能优良 ,施工作业性好 ,已成功应用于各种高温窑炉     

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     

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。     

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.     

用铬渣生产镁橄榄石-尖晶石质耐火材料

分析了铁合金厂的铬铁渣的结构、化学成分及其物相组成,研究了以铬铁法为原料配加镁砂生产高质量耐火材料的可行性。分析了烧成制品的抗法性能及影响因素。结果表明,以铬铁渣为原料配加一定量的镁砂,在一定的工艺条件下,可生产出高质量、高性能的镍橄枝石-尖晶石质耐火材料。     

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.     

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.     

Reactions Occurring in Basic Brick

Possible reactions occurring in basic brick were first explored by studying ( a ) binary mixtures of sesquioxides or magnesia spinels and ( b ) three silicates, namely forsterite, monticellite, and di-calcium silicate. Compositions ranging from 10 to 90% of each constituent were pressed into cylinders and heated at 100°C intervals between 800°C and a maximum of 1700°C or until melting occurred. Bulk density and volume changes were recorded and X-ray diffraction was used to explore chemical reactions. Reactions between the three silicates and three chrome ores were also studied. Since the most refractory specimens were those containing magnesiochromite as the spinel constituent, the effect of free magnesia as a third component in these series was finally explored.     

Cementing mechanism of potassium phosphate based magnesium phosphate cement

Magnesium phosphate cements (MPCs) are materials that belong to chemically bonded ceramic materials. They have a wide range of potential applications, due to their superior performance. In this paper, the reaction products and cementing mechanism of magnesium phosphate bonded cement based on the dead burned magnesia and the mono-potassium phosphate (MPP) are investigated. Fine powder and grains of dead burned magnesia were used to prepare pure cement paste and bonding cluster samples, respectively. The cement reaction products and their micro-morphology in the both different samples are examined. The microstructure of specimens is analyzed by SEM, TEM, XDR, and optical microscopy. Struvite of potassium (MgKPO₄·6H₂O) is observed in the reaction products. According to the analysis, it is found that struvite exists in both crystalline and amorphous form. There is also residual magnesia in the hardened cement paste. By means of microscopy observation, it can be seen that reaction products form around the unreacted magnesia and can develop into a continuum structure, which further produces the hardened paste. Struvite can grow up to form the more perfect crystal in a long term curing age, if large enough space is available during the hydration process.