原料及热处理制度对合成微孔轻质莫来石骨料性能的影响

研制具有优良隔热性能的耐火骨料对开发高性能轻质浇注料有重要作用。以w(α-Al2O3)=95%,w(β-Al2O3)=3%~5%的工业氧化铝A或w(γ-Al2O3)=70%~80%,w(α-Al2O3)=5%~10%,w(三水铝石)=5%~10%的工业氧化铝B,硅石粉为主要原料,采用烧烬可燃物法制备了微孔轻质莫来石骨料,研究了两种具有不同特性的工业氧化铝和不同热处理制度对合成微孔轻质莫来石骨料性能的影响。结果表明:(1)以工业氧化铝B为原料制得的轻质莫来石骨料的体积密度要普遍低于以工业氧化铝A为原料的,且以工业氧化铝B为原料得到的莫来石骨料的常温耐压强度随热处理温度升高而增加。(2)以不同工业氧化铝为原料合成骨料的莫来石的转化率在1500℃之前大致相当,均为60%(w)左右,得到的微孔轻质莫来石骨料的平均孔径约为3~5μm。(3)以γ相为主的工业氧化铝B更适合作原料,合适的热处理制度为1350℃6h。     

Y2O3对合成微孔轻质莫来石骨料性能的影响

各类工业窑炉和热工设备的隔热保温是节能的重要方面。轻质耐火材料的应用是实现节能的有效措施。开发和应用高性能轻质不定形耐火材料对实现能源节约和提高能源利用率意义重大。研制具有优良隔热性能的耐火骨料对开发高性能轻质浇注料有重要作用。本工作以工业氧化铝、硅石粉为主要原料,采用烧烬可燃物法制备微孔轻质莫来石骨料,研究了Y2O3加入量对合成微孔轻质莫来石骨料性能的影响。结果表明引入Y2O3可促进合成料的固相反应和烧结过程。随着Y2O3含量的增加,合成微孔莫来石骨料的耐压强度显著提高,自4.5MPa提高到15MPa;引入Y2O3后合成料的气孔更小,分布更均匀。     

煅烧制度对合成轻质微孔莫来石骨料性能的影响

各类工业窑炉和热工设备的隔热保温是节能的重要方面。使用轻质耐火材料是实现节能的有效方法。开发和应用高性能轻质不定形耐火材料对实现节能意义重大。研制具有优良隔热性能的耐火骨料对开发高性能轻质浇注料有重要作用。以工业氧化铝、硅石粉为主要原料,采用加入可燃物的方法制备莫来石轻质合成料。根据坯体料的DSC-TG和大试样热重分析设置了不同的煅烧制度,比较了两种煅烧制度：一为单调升温,然后保温;另一为在高低两个温度分段保温。研究了两种煅烧制度对合成轻质微孔莫来石骨料莫来石化率及体积密度、气孔率性能的影响。结果表明,无烟煤约在600℃烧失,坯体料自1200℃开始发生莫来石化反应,试样经1350℃×6h热处理后的孔径分布3-7μm左右,莫来石转化率60%。     

钒铁冶炼炉氧化铝渣用于耐火材料的性能分析

通过选取完整的氧化铝渣饼,进行物理化学性能测试,来探索钒铁冶炼炉氧化铝渣用于耐火材料的可能性。测试结果显示,氧化铝渣的主要成分为Al2O3、MgO和CaO,且以镁铝尖晶石、铝酸钙为主;耐火度大于1 790℃,体积密度大于3.0g·cm^-3,吸水率小于3.0%;氧化铝渣具有水硬性,可替代高铝水泥;其颗粒强度与焦宝石接近,可用作耐火骨料。综合各项指标,氧化铝渣可用于耐火材料。     

Fabrication and Properties of Closed-pore Al_2O_3-based Refractory Aggregates

A novel Al_2O_3-based refractory aggregate with closed-pore structure was fabricated utilizing superplasticity with submicro-sized Al_2O_3 and MgO as raw materials,and SiC as a high temperature pore-forming agent.The effect of MgO on porosity,phase composition and microstructure of the refractory aggregate has been investigated. For comparison,the common Al_2O_3-based refractory aggregates and porous ones with open-pore structure were also prepared. The results indicate that the closed porosity of Al_2O_3-based refractory aggregate increases as the content of MgO increases. When the content of MgO is 15 mass%,the closed and apparent porosities are 14. 5% and 1. 1%,respectively. The main phase compositions are Al_2O_3 and MgAl_2O_4. The formation mechanism of closed pores is that the fine-crystallinegrain Al_2O_3 ceramic possesses superplastic deformation ability after adding MgO at high temperatures. When SiC powder is added to the Al_2O_3 ceramic,the generated gases by the reaction of SiC at the sintering temperature can provide a pressure to make grain boundaries slide. Then,the gases are enclosed by crystalline grains to form the closed pores. The slag corrosion resistance of the fabricated closed-pore Al_2O_3-based refractory aggregate is better than the common refractory aggregate and porous ones.     

Experience with the use of highly refractory concrete in slit heat-treatment furnaces

Conclusions A highly refractory concrete based on Portland cement containing chromite aggregate proved to have a high resistance in heat-treatment furnaces.This type of concrete can be used in furnaces for ferrous metallurgy and the machine-building industry, mainly where chromemagnesite brick is at present in use.Wider use, in the building of heating equipment, of large blocks of highly refractory concrete should help to mechanize installation work, reduce costs and sharply reduce building time, and also prolong the furnace life.     

Porous alumina aggregates and heat-insulating refractory concretes for use in reducing atmospheres

Conclusions Investigations were carried out on the use of commercial alumina for producing porous alumina aggregates for making heat-insulating high-alumina refractory concretes. It was found that to obtain these concretes with high heat-insulating properties it was necessary to use alumina porous aggregate with a finely porous structure.The introduction into the briquetted plastic bodies, in preparing lightweight aggretate, of unground commercial alumina mixed with finely milled material, and an addition of aluminum fluoride, yields alumina aggregate of a finely porous structure.On the basis of porous alumina aggregates and high-alumina cement we obtained heat-insulating refractory concretes containing 86–89% A1₂O₃ and low concentrations of impurities, which allows us to recommend them for service in reducing atmospheres approximately at temperatures of up to 1300–1400°C.Translated from Ogneupory, No. 1, pp. 42–47, January, 1971.     

A replacement of traditional insulation refractory brick by a waste-derived lightweight refractory castable

Lightweight insulation refractories are essential for high-temperature performance to reduce energy consumption. This study investigates a new insulation material, that is, solid waste rice husk ash (RHA) derived lightweight refractory castable, replacing traditional insulation refractory brick. The RHA is generated after the burning of rice husk as biomass fuel. The RHA is used as an aggregate and alkali-extracted silica sol from RHA as a binder to fabricate the insulation castable. The nanosilica containing (~30 wt%) sol is employed to synthesize the refractory castable by varying the sol amount (2.5-12.5 wt% silica from sol). The castable specimens are cast by a vibro-caster and fired at 900-1200°C in a muffle furnace. The physic-mechanical and thermal conductivity (κ) of the castable is investigated. At 1100°C with 10 wt% dry sol retaining sample shows an excellent apparent porosity (~65%), low bulk density (~ 0.8 g/cm³), and κ (0.136 W/m k) with sustainable compressive strength (6 MPa). The acquired results are a good match with the literature (other wastes-derived insulation materials) and industrial (silica insulation brick) obtained data. These promising outcomes may inspire the refractory industries for using RHA as an aggregate and RHA extracted sol as a binder for making insulation castable.     

高铝质耐火可塑料的组成与性能关系研究

用正交设计试验和单因素试验,研究了骨料颗粒级配、矾土细粉和结合粘土用量以及粘结剂的种类和用量与高铝质耐火可塑料性能的关系。获得了主要工艺参数。对影响可塑料性能的因素进行了讨论。研究结果表明,在一定Al_2O_3含量条件下,影响可塑料性能的主要因素是矾土细粉与结合粘土的比例和加入量以及可塑料的干湿程度。     

Caky character and plasticity of refractory clays from the Troshkovo deposit

A model is developed to represent the structure of the mineral component of Troshkovo refractory clays. According to it, a refractory clay particle is an aggregate composed of a crystalline core and an amorphized film around it. Such refractory clays owe their caky character to the colloidal mineral shells that bond the particles into strong aggregates. Mechanical working breaks up the aggregates into a finely divided material and improves the plastic and bonding properties of kaolinite clays.     

Corrosion and adherence properties of cement clinker on porous periclase-spinel refractory aggregates with varying spinel content

The corrosion and adherence properties of cement clinker on porous periclase-spinel refractory aggregates with varying spinel content were examined using a static crucible test and a sandwich test, respectively. The reaction characteristics of porous periclase-spinel aggregates and cement clinker and the effects of spinel content on the adherence property were investigated through scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and FactSage^® thermo-chemical software. It was observed that the spinel content and pore characteristics strongly affected the corrosion results and thus affected the adherence ability of cement clinker on porous periclase-spinel aggregates. With an increase in the spinel content, the amount of glass phase formed from the reaction of the refractory and cement clinker increases because the rate of the spinel dissolution into the cement clinker is higher than that of periclase. The glass phase acts as a bridge between the cement clinker and the aggregate to enhance the adherence property, which depends on the amount, area distribution and viscosity of the glass phase and its penetration in aggregates. When the spinel content is 15–40 wt%, the refractory aggregate not only has a high cement clinker resistance but also a high adherence property. Once the spinel content exceeds 50 wt%, the skeletal structure of the aggregate will be destroyed, which will lead to a substantial decline in the cement clinker resistance.     

Preparation and characterisation of closed-pore Al2O3-MgAl2O4 refractory aggregate utilising superplasticity

ABSTRACT

A novel high closed porosity Al₂O₃-MgAl₂O₄ refractory aggregate has been successfully fabricated by utilising superplasticity with Al₂O₃ and MgO as raw materials, SiC as high temperature pore-forming agent. The effects of the addition amounts of MgO and SiC on porosity, sintering behaviours, phase composition, pore size distribution and microstructure of the refractory aggregate have been investigated. The formation mechanism of the closed pore in the refractory aggregate has been discussed. The results showed that the MgO can improve the superplastic deformation ability of Al₂O₃-based ceramic at high temperature. With the content of MgO and SiC increased, the closed porosity and the pore size increased. The oxidation of SiC improved the sinterability of materials at the initial stage of sintering, and then the released gases due to the further oxidation of SiC promoted the formation of closed pores by motivating the superplastic deformation ability of Al₂O₃-based materials.     

Characterization by acoustic emission pattern recognition of microstructure evolution in a fused-cast refractory during high temperature cycling

Fused-cast refractory materials are widely used in the glass industry, especially in the building of superstructures and side walls of fusion furnaces. The HZFC (High Zirconia Fused Cast) products are especially used as tank blocks for the fusion of highly corrosive glasses melted at very high temperature (such as LCD glass), due to their high corrosion resistance and their low generation of glass defects generation.The presence of this high amount of pure ZrO₂ in the refractory can be responsible for microdamage occurrence during the cooling step after melt casting (annealing), associated to the martensitic transition of zirconia.Acoustic emission (AE) analysis is well known as a reliable tool to investigate microstuctural evolution at a very small scale. In this work, a fused-cast ZrO₂ refractory has been investigated using a AE unsupervised pattern recognition procedure and a frequency-energy coupled analysis. Data gathering during thermal cycles at high temperature (typically 1500 °C) has been done thanks to an innovative self-developed testing device. The analysis of frequency and energy parameters makes it possible to detect and to characterize the occurrence and the chronology of microdamage in specific range of temperature. Hypothesis concerning different ways of microdamage formation below the temperature of the martensitic transformation of ZrO₂ during the cooling stage can be proposed related to thermo-mechanical properties and the microstructure of the material. In particular, intergranular and intragranular microcracks due to CTE mismatches occurring in the material have been also investigated.     

Solid particle impact erosion of alumina-based refractories at elevated temperatures

Solid particle erosion tests have been conducted on three different alumina-based refractories at elevated temperatures up to 1400 °C, using sharp SiC particles between 325 and 830 μm in diameter. The impact speed is 50 m/s and the impact angle is varied between 30° and 90°. The objective of this study is to ascertain the effects of temperature and impact angle on the erosion resistance of alumina refractories. The experimental results reveal that the alumina-based refractories, in general, exhibit increasing erosion resistance with increasing temperature and decreasing impact angle, with the minimum erosion rate at 1200 °C and 30° impact angle. Chrome corundum refractory brick is the most resistant to vertical erosion, due to its highest alumina content, and associated hardness and density, as well as strongly bonded aggregate and binder phase. The primary material removal mechanisms are fracture and chipping of binder phase and aggregate, as well as aggregate pull-out.     

Influence of the impurity concentrations of rocks in original magnesites on the quality of the raw materials and concentrates

Conclusions The maximum permitted total amount of impurity rocks of diabase and dolomite in unbeneficiated magnesite grade I, guaranteeing its possible use for the production of highly refractory articles and powders, in accordance with TI 200-0-45-82 equals, for TsMP-2 2.0%, and for TsMP-3 3.1%.The calculation ratios of magnesite and impurity rocks in the original raw material enables us to assess the original raw material for determining the desirability of its beneficiation and planning the quality of the ores delivered to the various departments of the Combine in relation to the qualitative composition of the ore at the face.To obtain magnesite concentrate suitable for making highly refractory articles and powders in accordance with TI 200-0-45-82, the mass proportion of CaO in the original raw material delivered for beneficiation should not exceed 5.5%, and the dolomite impurities 7.0%.Translated from Ogneupory, No. 5, pp. 20–23, May, 1988.     

Evaluation of aluminum dross waste as raw material for refractories

An aluminum dross waste from plasma processing for Al metal reclamation was tested as a replacement raw material in refractories. The main phases of the starting Al dross waste material were MgAl₂O₄ and AlN. The waste was tested to replace calcined alumina in castables and refractory clay in a molded refractory at levels below 6.5%. The results of physical and mechanical tests indicated that the waste may be applied directly, without prior calcination, as a substitute for fine structural components in refractories. The waste and water contents used in processing, however, must be optimized to avoid the formation of crack-like defects in the microstructure. The origin of these defects is related to the generation of gas from the waste at high temperatures. It is not known if these crack defects impact physical properties. The waste was also tested as a replacement for anti-oxidant elements (Al and Si powders) in a resin-bonded refractory. Oxidation tests, however, indicated a negative effect on oxidation resistance.     

Lightweight aggregate based on waste glass and its alkali-silica reactivity

The possible use of waste glass for the production of lightweight aggregate has been studied. The aggregate, in the form of highly porous granules, was produced by mixing together finely ground waste glass and an expansive agent and firing this mixture at a selected temperature. The expansive agent was chosen on the basis of the results of DTA/TGA experiments, which were carried out on some selected agents and confirmed by using a hot-stage microscope, where the temperature interval of the expansion was also determined. Pilot production of about 0.5 m³ of the aggregate was performed in a rotary kiln, and the water absorption and bulk density of the aggregate so obtained were determined. Special emphasis was placed on the determination of the alkali-silica reactivity of the aggregate, and the results of initial tests for alkali-aggregate reaction were encouraging, given the high potential reactivity of the material. However, before such aggregate can be considered safe for general use in concrete, longer-term concrete prism tests need to be carried out, which would cover the range of mixes in which the aggregate is likely to be used.     

A comparative study on the slag resistance of dense corundum-spinel refractory and lightweight corundum-spinel refractory with density gradient

Lightweight corundum-spinel refractory with a density gradient structure from exterior to interior was fabricated. Slag resistance of lightweight and dense corundum-spinel refractory is investigated by X-ray diffraction, scanning electron microscopy, energy dispersive analysis, mercury intrusion porosimetry and Factsage. The results show that lightweight corundum-spinel refractory with high apparent porosity exhibits comparable slag resistance to dense corundum-spinel refractory, especially with superior slag penetration resistance. The dense exterior with small pore size in the lightweight corundum-spinel refractory can effectively hinder slag penetration. Corrosion product phases (C₂S, CA₂, CA₆, and C₂M₂A₁₄) with high melting point and inconsistent melting temperature, most of Fe and Mn elements in steel slag solubilizing in spinel, especially strip CA₆ around corundum aggregate, prevent the refractory from further slag penetration and corrosion.     

博耐特(Bonite)--一种新型的合成致密CA6耐火原料

介绍了基于六铝酸钙(CA_6)矿物相的一种新型合成致密耐火骨料——博耐特(Bonite);讨论了博耐特原料以及由博耐特、板状刚玉或者二者复合制备的多种试验用浇注料的理化性能;并结合博耐特的相关应用领域进行了博耐特耐火材料抗铝液侵蚀、热机械性能、热导率和微气孔等较为前瞻性的试验和探索。     

Some properties of sintered ceria ceramics

Conclusions Sintering of finely dispersed ceria occurs intensely in the 1300–1500°C range.In an atmosphere of inert gas and in vacuum the sintered CeO₂ is reduced with changes in crystal structure, which is accompanied by a reduction in the refractory and thermomechanical properties of the material.Unreduced CeO₂ is a highly refractory material which in oxidizing conditions can be used at temperature above 1900°C.