Influence Parameters on Properties of Dolomite Bricks Containing Different Bonding Systems

Pitch and tar bonded dolomite bricks are extensively used in ladles and converters for long time because of their superior properties such as. steel melt refining, easy production as well as low production cost. Recently, resin bonded dolomite bricks are presented for using in steel plants. Generally, quality and final cost of steels are affected by properties of refractories especially dolomite bricks. Therefore, recognition of influence parameters on dolomite refractory properties is very important. In this study, the effects of tar and resin as bonding systems, and addition of graphite （ 2wt% ） on the properties of dolomite refractory bricks have been investigated. Properties such as ： density and porosity, cold crushing strength, hydration time and depth of slag penetration have been studied. Results show that the bonding sys- tems and graphite have a great effect on the mentioned properties especially cold crushing strength and hydra- tion time. In addition to their low rate of pollution, resin bonded dolomite bricks show higher performance with proper technical specifications.     

Comparisons Between Vibration and Self-Flowing Ultra-Low Cement Castables Properties in Al2O3-SiC-C System

In this study, the properties of self-flowing ultra-low cement castables in Al2O3-SiC-C system have been investigated and compared to vibration castables. The major physical and mechanical properties, microstructure and corrosion behavior of these castables against slag have been evaluated. The results showed that the microstructure of Al2O3-SiC-C self-flowing castable is more uniform than the vibrated structure. Also self-flowing castable has smaller pore size and more uniform pore size distribution. Hence, density, strength, oxidation and slag resistance of the self-flowing castables is higher than that of vibration castables. Therefore, besides other benefits such as noise free, easy installation, fewer mold defects and reduced installation costs, Al2O3-SiC-C self flowing ultra low cement castables will have longer service life in comparison with vibration casables.     

Effects of Additives on Properties of Unburned MgO—Al2O3 Refractory

The influences of four kinds of additives added into the matrix of MgO-Al2O3 unbuned products were investigated,The results show that samples with proper MgO/Al2O3 ration and proper addition of Cr2O3(2%- 4%) have good thermal shock resistance and slag corrosion resistance as well,XRD and SEM determination results indicate that a kind of compound spinel(Mg,Al, Cr) O4 was formed and the microstucture of the samples are denser.     

Development of MA—C Refractory for Smelting—reduction Iron—Making Process

A kind of carbon-bering refractory (MA-C1) has been developed for smelting-reduction iron-making process and its physical chemistry properties were measured,Smilting-reduction slag (15 wt% FeO) resistance of the developed refractory has been compared with commercially available refractories by curcible test,static slag soaking test and fractal dimension analyses,The results show that slag resistance of the developed refractories(MA-C1) is better than those of alumina-carbon refractory (AM-C1),alumina-magnasia-carbon brick (AM0(J)) ,and Si3N4-SiC brick.     

Application Study onβ—Sialon—Al2O3 Brick in Iron Ladle

The microstructure and slag erosion fractal dimension of reaction interface of β-Sialon-Al2O3 brick used in 300 Mt iron ladle of Baosteel have been studied by SEM and XRD.The results indicated that β-Sialon-Al2O3 brick exhibited excellent slag resistance.The main wear mechanism of β-Sialon-Al2O3 brick is mainly from the spalling caused by thermal mechanical stress and attacked by slag secondly.     

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.     

Characteristics and Problem of Chrome-containing Refractory

One of characteristics of Cr2O3-containing refractory is excellent corrosion resistance. However, there is a problem of hexavalent chromium, which is noxious to the human body, and easily formed by the reactions among the refractory and CaO, Na2O and/or K2O in slag. In this article, the reason why the Cr2O3-containing refractory has excellent corrosion resistance, the forming conditions of hexavalent compounds, and the methods for suppressing generation of the compound, are described as a base of further development of excellent refractories.     

Effects of Cr2O3 on Properties of Alumina—spinel Castable

The effects Cr2O3 on properties of alumina-spinel castable has been discussed in this paper,The results show that modulus of rupture(MOR) and cold crushing strength(CCS) of the alumina-spinel castable can be improved when Cr2O is added to this material.At higher temperature,Cr2O3 moves into the melt and raises its viscosity,forming high creep resistance bonding phase,so the thermal shock resistance and slag corrosion resistance are improved.     

Application Study on β-Sialon-AI_2O_3 Brick in Iron Ladle

The microstructure and slag erosion fractal dimension of reaction interface of β-Sialon-Al2O3 brick used in 300 Mt iron ladle of Baosteel have been studied by SEM and XRD. The results indicated that β-Sialon-Al2O3 brick exhibited excellent slag resistance. The main wear mechanism of β-Sialon-Al2O3 brick is mainly from the spalling caused by thermal mechanical stress and attacked by slag secondly.     

Self-glazing SiC-andalusite Refractories for High Temperature Gasification Applications

The combination of SiC and andalusite with calcium aluminate binder for castables in high corrosive gasifying environments is a promising alternative refractory system for many different slag systems. After sintering,a glassy protective layer has been identified. Beside the interactions of the refractories with intermediate slag also the thermomechanical properties,the thermal shock performance and the microstructure have been evaluated as a function of different binder systems.     

Fundamentals of Sintering Dolomite

The difficulties in sintering of dolomite rise form the low mutual diffusibilites of Ca^2 in MgO and Mg^2 in CaO ,and from unique pore and agglomerate structures formed after calcination of dolomite.These microstructures in decompsoed dolomite play a great role in inhibition of densification during sintering.The measures ,which can destroy these stuctures,such as hydration or isostatic pressing after calcination of dolomite,result in increasing the sintered density and reducting the sintering temperature,Addition of ome oxide such as Fe2O3,ater the sintering mechanism from solid state sintering to liquid phase sintering,therefore,dense dolomite ody can be obtained at relatively low sintering temperature,Com-minution of dolomite before its calcination can lower the sintering temperature and enhance the sinterd ensity due to increasing both the quantity and homogeneity of Fe2O3 in dolomite.     

Different Approaches to Incorporating Natural Flake Graphite into Al2O3—SiC—C Castables

In this stil undergoing work,three approaches have been adopted to incorporate natural flake graphite into Al2O3-SiC-C castables by adding either micropellets of graphite or cushed briquette of alumina-graphite of finally surface modified flake graphite by TiO2 coating,Characteristics of these approaches are described,Overall properties including flowability,compactness,cold and hot stredgths ,slag resistance,anti-oxdation and thermal shock resistance of the castables have been compared in correlation with the ways of incorporating graphite,Very encouraging results have been achieved by using micropellets of graphite or crushed alumian-graphite briquete in comparison with straight natural flake graphite addition.     

Development of Semi—Graphite Carbon—Silicon Carbide Brick and Its Application in Slag Forming Zone of Large—sized Blast Furnace

Based on the damage mechanism of the lining at the slag forming zone of the blast furnace and the charactieristics of various refractory ma-terials,the methods to increase the service life of the lining at the slag forming zone have been found:(1) to improve the capacity of the blast furnace brick lining subjet to heat impact;(2) to reduce the working side temperature of the brick lining.On this basis,the semi-graphitized ,high temperature electrically calcined anthracite and silicon carbide etc ,were used as the main raw materials,Through a lot of experiments the proper raw material mix and grain size compo-sition were determined,In addition ,a suitable amount of additives and binders was added.After high pressur forming,high temperature firing and grinding ,the semi-graphitic carbon-silicon carbide bricks with close dimension tler-ances and ideal physical and chemical properties have been made.They have been applied in some blast furnaces,such as No.11(2580 m^3) and No.6(1050 m^3) blast furnaces etc.at Anshan Iron and Steel Company,and the problem of short service life at slag forming zone of blast furnace has been solved.     

Influence of Special Silica on the In—Situ Growth of Silicon Carbide Whiskers in Al2O3—C Refractories

In this paper,the influence of special silicas on the in-situ growth of silicon carbide whiskers in Al2O3-C refractories has been stud-ied.The microstructures of the products have been analyzed by means of SEM,and it is found that the whiskers grew better by adding some special silicas,Silica ② shows the best result because the VLS mechanism made the whiskers grow as long as 40μm and could be expected to greatly improve the mechnical properties of the refractories.     

Recent Progress of Carbon Nanotubes Reinforced MgO-C and Al_2O_3-C Refractories

Carbon nanotubes （CNTs） have been extensively studied over the last two decades since they possess excellent properties.CNTs have been considered as new promising reinforcements for carbon containing refractories （CCRs）.Current research progress of the CNT-reinforced MgO-C and Al2O3-C refractories was summarized in this mini-review,and the CNT-reinforced CCRs possess remarkable mechanical properties and superior thermal shock resistance compared to CCRs without CNTs.     

The Microstructure and Properties of Alumina—Rich Spinel and Its Products

The paper describes the effect of chemical composition on the microstructure and properties of spinel specimens synthesized from bauxite and magnesite,The alumina-rich spinel with higher ratio of Al2O3/MgO,with smaller spinel grain,contains more titaniferous mineral and silicate phase compared to the spinel with lower Al2O3/MgO ratio.In the products obtained from alumina-rich spinel and magnesite clinker,the ratio of Al2O3/MgO of spinel decreases,ti-taniferous mineral and silicate phase in the spinel aggregate are changed,and its content tends to degradation,contrasted with original alumina-rich spinel,The products have good high temperature properties.     

Slag Corrosion Resistace of β－Sialon－Al2O3 Composites－Part I. Thermodynamics and Mechanism

Slag corrosion resistance of β－Sialon and β－Sialon-Al2O3 composites has been studied .The effects of FeO content and temperature on corrosion rate have been investi-gated by mens of dip method(static and self-rotating).The corrosion process and microstructural analysis.It is shown that FeO preferentially attacks β-Sialon in the composite and the protruded corundum grains would gradualy fall off into the slag.     

Development of Forsterite Based Insulating Board for Alloy Steel Con—casting Tundish

To meet the operation requirement of com-casting tundish for alloy steel.a forsterite based insulating board has been developed.The effects of binder ,fiber and other additives on the properties of the properties of the products have been described;the theoretial reason of assuring containing clear steel by using inorganic binder bonded forsterite based insulating board were also discussed;the mineral composition and microstructure of the products have been analyzed by means of XRD.SEM and microscope ,The results indicate that the forsteite based insulating board with excel-lent performance and dood application results has been obtained.     

Application of Semi—rebonded Magnesite—Chrome Bricks of LRCO at RH Lower Vessl of NKK Keihin Works

The application results of Semi-rebonded Magnesite-Chrome bricks at RH lower vessl of the NKK Corporation Keihin Works have been analysed.The results indicate that the main reasons that cause the damage of the refractory bricks include chemical at-tack of slag to the Semi-rebonded Magnesite-Chrome bricks;penetration of molten steel and slagn into the bricks;and thermal spalling due to teperature fluctuation during steel making operation. The re-sulits of multiple effection of these factors lead to alternative action of erosion(chemicl attack and penetration) and spalling (thermal spalling and structure peeling) resulting in the damage of the brick,In order to improve the performance of the bricks,it is necessary to promote the resistance to ero-sion and thermal shock resistance as well as to keep the aurate dimensions of the brick .The measures to improve the resistance to erosion of magnesite-chrome bricks taken by the researchers mainly in-clude:lowering the contents of impurities in the bricks (mainly including SiO2,CaO,and next Fe2O3 and Al2O3);promoting the extent of direct bond of the brick;forming a large amount of magnesia-chrome composite spinel well-distributed in the bricks through adding a large amount of synthe-sized materials ;enhancing the resistance to erosion by adding a little amount of high-effective addi-tives,Improvement of thermal shock resistance of the bricks is mainly through introducing some addi-tive to make a certain amount of micro-cracks occur-ing in the brick so as to obtain the effect of increase toughness or through formation of second high tem-perture solid phse in the brick by adopting addi-tive,In ddition,it is needed to improve the quality of the brick appearance and ensure accurate dimen-sions of the brick ,The purpose of this paper is to describe the further improvement of the service life of refactory brick by the measures taken on the basis of the nalysis results to the used bricks.     

Compositions and Properties of Hydration-Resistant Coating of Magnesia-Calcia Materials

The complex coating on the MgO-CaO clinker was prepared by dipping method and adding the second mineral to restrain the formation and expansion of the craks.Meansohile,the microstructure and the morphology of the coating and hydration resistance of the MgO-CaO clinker were also investigated.The result shows that the coating consists mainly of Ca2P2O7,MgO and CaCO3,its thickness ranges from 5μm to 20μm,and the coating is dense and even,no micro-cracks are observed.Also,the coating adheres closely to the matrix.The hydration resistance of the MgO-CaO clinker after treatment is improved greatly,and the castables prepared with the treated MgO-CaO clinker have better physical properties than MgO castable.