轻质氧化镁含量对方镁石-镁铝尖晶石砖性能的影响

以不同粒径的烧结镁砂、电熔镁铝尖晶石、镁铝尖晶石空心球为起始原料,采用固相烧结法制备了方镁石-镁铝尖晶石砖。通过X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征试样的物相组成和微观结构,利用阿基米德排水法测试试样的体积密度和显气孔率,研究轻质氧化镁含量和烧结温度对方镁石-镁铝尖晶石砖性能的影响。结果表明,随轻质氧化镁含量的增加,方镁石-镁铝尖晶石砖显气孔率呈增加趋势,而体积密度变化不明显,试样表现出优异的力学性能。当轻质氧化镁含量为25%(质量分数)时,方镁石-镁铝尖晶石砖的抗折强度最大为9.56 MPa,热导率最低为1.92 W·m^-1·K^-1。显微结构表明骨料和基质结合良好,并能形成微孔状通道。利用其特殊的微孔结构,提高了试样的力学性能和耐腐蚀性,进一步保护方镁石-镁铝尖晶石砖免受碱侵蚀。     

TiO2加入量对固相烧结合成镁铝尖晶石致密化行为的影响

以低品位菱镁矿和工业α氧化铝微粉为主要原料固相烧结合成镁铝尖晶石,探讨TiO2添加剂对合成镁铝尖晶石致密化行为的影响.用X射线衍射(XRD),扫描电镜(SEM)及相关分析软件对烧后试样的相组成和显微结构进行研究,以揭示镁铝尖晶石烧结致密化的过程机理.研究结果表明:添加剂TiO2与形成镁铝尖晶石的置换固溶作用是促进固相合成镁铝尖晶石烧结致密化的重要机理,阳离子空位的产生以及镁铝尖晶石的晶格缺陷,高温下有利于镁铝尖晶石的晶体发育和长大,在空间位阻效应的作用下,达到排除气孔使试样致密化的目的;随着TiO2加入量的增多,镁铝尖晶石的致密化程度也逐渐升高,能够有效的改善制品的烧结性能和显微结构.     

方镁石–铁铝尖晶石材料与水泥熟料间的作用行为

方镁石–铁铝尖晶石耐火材料在水泥回转窑烧成带取得良好使用效果,这与其高温下同水泥熟料之间的反应行为密不可分。利用扫描电子显微镜、X射线衍射仪与Factsage模拟等手段研究了镁砂和铁铝尖晶石颗粒以及方镁石–铁铝尖晶石砖高温下与水泥熟料的作用行为。结果表明：镁砂具有优异的抗水泥熟料侵蚀性能,铁铝尖晶石与水泥熟料高温反应生成大量高温液相,并逐渐被蚕蚀。对于方镁石–铁铝尖晶石砖,方镁石物相和铁铝尖晶石颗粒高温下抵抗水泥熟料侵蚀表现出协同作用。以方镁石为主晶相的基质与水泥物料反应生成高熔点物相,在晶界相内形成骨架结构,提高了晶界相的高温粘度,促进了水泥熟料与耐火材料的结合。同时,铁铝尖晶石与方镁石之间的离子交换促进了铁铝尖晶石颗粒与方镁石基质的结合,抑制了高温下与水泥物料反应时长石类低熔点相的产生,提高了铁铝尖晶石的高温稳定性,有利于该类耐火砖在烧成带使用时窑皮的稳定。     

从相图解析干式捣打料

根据有关二元系与三元系相图解析了硅质、刚玉质、镁钙质、方镁石-镁铝尖晶石质以及刚玉-镁铝尖晶石质干式捣打料的化学组成、合适的烧结剂及其加入量。     

基于铝热反应的金属结合剂金刚石工具初探

文章探索了一种基于铝热反应的新型金属结合剂金刚石工具的制备方法,分析了铝热反应制备结合剂过程的反应合成机理,研究了热压烧结温度对铝热反应结合剂的相组成、微观结构、力学性能的影响。制备了铝热反应结合剂金刚石磨具,并测试了干、湿磨两种条件下磨削建筑陶瓷砖的加工性能。研究表明, Fe_2O_3-Al复合粉体在1028.8℃开始发生铝热反应,反应产物主要为Fe、Fe_3Al相以及少量Al_2O_3及FeAl_2O_4(铁铝尖晶石)相,随着热压烧结温度的升高, FeAl_2O_4含量有所增加,结合剂的硬度、致密度和抗弯强度都随之升高。初步测试显示铝热反应结合剂金刚石磨具可以对建筑陶瓷砖进行加工,但工具耐磨性还存在不足。     

微孔镁尖晶石碳耐火材料的抗渣性能研究

以方镁石-尖晶石微孔陶瓷、电熔镁砂为骨料,以电熔镁砂细粉、鳞片石墨、金属铝粉为基质材料,以酚醛树脂为结合剂制备了含微孔陶瓷骨料的镁尖晶石碳试样.采用感应炉浸渍法对试样进行了抗渣试验,并对渣蚀后的试样进行了SEM和EDAX分析.结果发现:熔渣和熔钢冲刷是损毁的主要原因,熔损并不显著.显微结构分析表明,在侵蚀层和原质层之间可以发现MgO致密层的形成,MgO致密层的形成可抑制渣对试样进一步的侵蚀和渗透.渣对MSO颗粒的侵蚀主要是FeO和MnO等在方镁石中的固溶,导致MgO颗粒出现结构剥落;方镁石-尖晶石微孔陶瓷骨料的蚀损主要是尖晶石被渣中的CaO和SiO2所侵蚀,而渣对微孔骨料渗透并不严重.     

化学组成对轻烧镁铝尖晶石结构与性能的影响

相比传统电熔镁铝尖晶石和烧结镁铝尖晶石,轻烧镁铝尖晶石晶格畸变大,反应活性高,所制备的铝镁浇注料抗渣渗透性更好。本文以工业氧化铝和轻烧镁砂细粉为原料,在1 600 ℃下烧结合成Al₂O₃质量分数在68%~76%的富镁尖晶石(68%和70%)、正尖晶石(72%)和富铝尖晶石(76%)试样,研究Al₂O₃含量对尖晶石试样常温物理性能、物相组成、晶体结构参数和显微结构的影响。结果表明:Al₂O₃含量的增加提高了试样的显气孔率;富镁尖晶石试样的物相为尖晶石和少量方镁石,其余试样只有尖晶石相;富铝尖晶石的晶格畸变大于富镁尖晶石和正尖晶石,晶粒尺寸和平均孔径小于富镁尖晶石和正尖晶石。     

尖晶石包覆骨料对镁铝质耐火材料抗热震性和抗水泥熟料侵蚀的影响

由于周期性水泥熟料回转以及进出料,水泥回转窑用耐火材料需要兼顾优异的耐火度、热震稳定性和耐侵蚀性。本研究通过将尖晶石细粉包裹于镁砂骨料表面,制备出含包覆结构骨料的方镁石–镁铝尖晶石耐火材料,并采用三点弯曲测试结合数字图像相关以及声发射技术表征其断裂行为,以及采用静态抗渣法表征其抗侵蚀性能。结果表明：通过改变尖晶石分布,形成包覆结构复合骨料,降低了氧化铝含量,尖晶石相达到更为均匀且广泛的分散。与氧化铝含量(质量分数)为10%的市售预合成尖晶石骨料耐火材料相比,采用尖晶石包覆骨料的方镁石–尖晶石耐火材料(Al₂O₃含量为5%)在保证材料抗热震性能的同时,提升了力学强度、热震稳定性能以及抗侵蚀能力。     

SiO2含量对合成铁铝尖晶石的影响

为了研究以矾土做原料合成铁铝尖晶石时其SiO2成分对合成铁铝尖晶石的影响,以氧化铁粉、α-Al2O3粉和碳粉为原料,分别加入质量分数为0、2%、5%和8%的SiO2粉,在氮气气氛中分别于1 400、1 450、1 500、1 550℃保温4 h合成铁铝尖晶石。通过对所合成铁铝尖晶石的烧结性能、物相组成及微观结构进行分析,研究了SiO2加入量对铁铝尖晶石合成及烧结性能的影响。结果表明:氮气气氛下,加入2%(w)SiO2能够促进铁铝尖晶石的合成及烧结;加入大于5%(w)SiO2时,试样的体积密度迅速下降,SiO2与氧化铁生成大量的低熔点液相,Al2O3则以刚玉相存在,反而阻碍铁铝尖晶石相的生成。采用特级矾土为原料合成铁铝尖晶石时,由于矾土中杂质SiO2和TiO2以及R2O的大量存在,导致矾土基铁铝尖晶石的体积密度更低,烧结性能更差,用其制备的方镁石-铁铝尖晶石制品的性能较差。可见,合成铁铝尖晶石以矾土为原料是不合适的。     

TiO_2对合成片状镁铝尖晶石相组成和显微结构的影响

片状镁铝尖晶石有望用于增强陶瓷基复合材料和调控浇注料的性能。为了探索片状镁铝尖晶石的低成本合成,以氧化镁和片状氧化铝为原料,分别添加3%和6%(w)TiO_2,采用固相反应法分别在1 200、1 300、1 400和1 500℃保温5 h合成镁铝尖晶石粉体,并比较了镁铝尖晶石粉体的物相和显微结构,分析TiO_2对合成片状镁铝尖晶石的影响。结果表明:TiO_2的添加能促进氧化铝与氧化镁的高温反应,并大幅度提高镁铝尖晶石的生成量,其中1 500℃下添加6%(w)TiO_2试样的合成产物中镁铝尖晶石含量为74%(w);随着合成温度的升高,更多的Al2O3固溶于镁铝尖晶石中,但在TiO_2对烧结的促进作用下,各物相结合在一起,单一片状的镁铝尖晶石逐渐减少。     

Microstructure and phase evolution of Indian magnesite‐derived MgAl2O4 as a function of stoichiometry and ZrO2 doping

To aid development of cost‐effective sintered spinel as a refractory raw material, this paper presents an extensive analysis of microstructure and complex phase evolution of Al‐rich, Mg‐rich, and stoichiometric spinel aggregates derived from Indian magnesite and calcined alumina. Pore morphology in Al‐rich spinel was transformed upon sintering at 1650°C and corundum laths embedded in porous Al‐rich spinel matrix was formed. Stoichiometric spinel sintered at 1600°C consisted of mostly direct bonded angular equiaxed spinel grains which incorporated the impurities in solid solution. Mg‐rich spinel was composed of spinel grains with reduced angularity along with intergranular amorphous phase, small round monticellite grains, and periclase. EDS line scan revealed impurity‐free joins existed between direct bonded spinel grains. Mg‐rich spinel containing 0.65 wt% ZrO₂ formed cubic ZrO₂‐CaO‐MgO solid solution located along spinel boundaries, which reduced both intergranular amorphous phase and monticellite. This increased SiO₂ and MgO content in spinel solid solution triggering exsolution of metastable cubic forsterite manifested as split spinel peaks in XRD pattern. A 14.7% reduction in slag penetration was exhibited upon doping Mg‐rich spinel with 0.21% ZrO₂. Stoichiometric and Mg‐rich spinels attained 0.35% and 0.54% apparent porosity at 1600°C, which is better than most commercial sintered refractory spinels.     

Effect of composition,quantity, and synthesis temperature of spinels,and some properties of periclase — Spinel compositions

Conclusions The incorporation of spinel (5–10%) into the composition of the solid solution leads to periclase grain growth and to its sintering. Excess spinel in combinations with periclase over this quantity prevents recrystallization sintering of the specimens.A reduction in the synthesis temperature of most the spinels from 1750 to 1450°C contributes the sintering of the compositions under investigation, and improves their technical properties.In the periclase—spinel compositions the maximum influence on the grain growth and the properties of the specimens is exerted by the temperature conditions used for synthesizing the high-alumina spinels, while the conditions used to obtain the highly chromic spinels, and especially the magnesiochromite, have little or no effect on the technical properties of the fired product.With an increase in the spinel phase concentration from 5 to 30%, and also when there is a change in its composition in the direction from magnesia-alumina spinel to magnesiochromite, such factors as strength, porosity, and spalling are impaired.In the MgO-Mg(Al_1–X, Cr_X)₂O₄ system it is possible to obtain strong, dense, and simultaneously spalling-resistant refractories by using small additions of alumina spinel, synthesized at low temperatures ensuring the completion of the spinel-forming reaction.Translated from Ogneupory, No. 3, pp. 53–57, March, 1971.     

Role of Ti and Sn ions in spinel formation and reactive sintering of magnesia-rich ceramics

The solid solubility of magnesia in magnesium aluminate spinel and magnesium aluminate spinel in magnesia does not change with temperature thus not creating bonds or precipitation over periclase grains in a single stage sintering process. In comparison, the precipitated spinels in magnesia-chromia refractories form complex spinel due to inversion in the position of bivalent and trivalent cations within the structure, making them more stable at high temperature than either normal or inverse spinel. Additives form low-temperature compounds that diffuse into the spinel structure and create defects that change the properties of spinel solid solution. In the present study, magnesia and alumina powders along with tetravalent oxide additives were analyzed for their role in reactive densification of spinel in a single stage firing process in order to achieve a better binding system for magnesia-based refractories. These tetravalent oxides on reaction with magnesia form spinel solid solution with MgAl₂O₄ as they have similar crystal structure. The spinel solid solution formed using oxide additives is expected to have higher solubility in magnesia than magnesium aluminate spinel, resulting in improvement of the bonding during sintering through increased in solid solubility at elevated temperatures followed by precipitation of secondary spinel phases, similar to the complex spinel in magnesia-chrome refractories. The formation of spinel during firing remains as a second phase that retards the grain growth of periclase. The changes in unit cell dimensions with temperature and amount of additive were analyzed using Reitveld method and correlated with the densification behaviour at different temperatures.     

Self-Propagating High-Temperature Synthesis of Ti3SiC2: I, Ultra-High-Speed Neutron Diffraction Study of the Reaction Mechanism

In situ neutron diffraction at 0.9 s time resolution was used to reveal the reaction mechanism during the self-propagating high-temperature synthesis (SHS) of Ti₃SiC₂ from furnace-ignited stoichiometric 3Ti + SiC + C mixtures. The diffraction patterns indicate that the SHS proceeded in five stages: (i) preheating of the reactants, (ii) the α→β phase transformation in Ti, (iii) preignition reactions, (iv) the formation of a single solid intermediate phase in <0.9 s, and (v) the rapid nucleation and growth of the product phase Ti₃SiC₂. No amorphous contribution to the diffraction patterns from a liquid phase was detected and, as such, it is unlikely that a liquid phase plays a major role in this SHS reaction. The intermediate phase is believed to be a solid solution of Si in TiC such that the overall stoichiometry is ∼3Ti:1Si:2C. Lattice parameters and known thermal expansion data were used to estimate the ignition temperature at 923 ± 10°C (supported by the α→β phase transformation in Ti) and the combustion temperature at 2320 ± 50°C.     

Effect of reaction of periclase and iron-chrome spinel on the properties of periclase-spinel refractories

Conclusions Using a typical composition of the type MgO-Mg(Al_1–x–yCr_xFe_y)₂O₄ a study was made of the effect of the processes involved in the processing and decomposition of solid solutions of periclase and spinels on the technical properties of the fired products.During cooling from 1600–1750°C decomposition occurs in the solid solutions of periclase and spinel; the crystals of spinel separating under these conditions are able to grow to large sizes which inevitably should lead to the development of stresses inside the periclase grains.The decomposition of the solid solution of periclase and spinel adversely affects the strength and thermal-shock resistance of the fired specimens.The best technical properties are possessed by combinations of periclase with small (up to 15%) quantities of high-alumina (x=0.16 and 0.46) spinels.The use of compositions of periclase with high-alumina spinels of the type x=0.16 and 0.46 enables us to obtain denser and more thermal-shock resistant refractories.Translated from Ogneupory, No.6, pp. 44–47, June, 1970.     

Interaction of MgAl2O4 and MgCr2O4 spinels with calcoferruginous melts

Conclusions The interaction was studied between MgAl₂O₄ and MgCr₂O₄ spinels (and their solid solutions and compositions with periclase) with calcoferruginous melts, which are the essential constituents of various slag reagents.On exposure to a highly basic calcoferruginous melt, the magnesium-aluminum spinel forms magnesio-ferrite, brownmillerite, and some calcium aluminate.On interaction of magnesiochromite with calcium ferrite, chiefly high-temperature compounds form.With the action of highly ferruginous melts on magnesiochromite, the resulting solid solution increases in volume, and a distortion is observed at the boundary of the reaction and little-change zones of the samples.The addition of granular MgO to spinels or their solid solutions improves the chemical stability of the compositions against calcoferruginous melts [4].During use in contact with highly basic calcoferruginous melts, the addition of periclase to chromium spinellide additives is recommended; for use in contact with highly ferruginous melts, periclase and aluminum spinellide compositions are recommended.Translated from Ogneupory, No. 7, pp. 44–47, July, 1969.     

Phase transformations in periclase-spinel roofs of open-hearth furnaces with blowing through of the bath by compressed air

Conclusions The crystallochemical properties of the periclase and the spinels of the periclase-spinel bricks were radically changed during service in open-hearth furncces with blowing through of the bath with compressed air; new types of ferrite spinels and their solid solutions in periclase were formed. Periclase forms magnesiowüstite and magnesioferrite with ferric oxides resulting in a lowering of the melting point from 2800 to 1600°C. This type of transformation of periclase is one of the main causes of wear of periclase-spinel roofs by fusion.Under the service conditions chrome spinel is transformed into magnesioferrite and magnetite, with a lowering of the melting point from 2100 to 1750°C.In the working zone the lattice parameters of the solid solutions in periclase (magnesiowüstite) increased from 4.204 to 4.218 Å, indicating a considerable amount of divalent iron and manganese cations in the periclase crystal lattice.In the periclase-spinel bricks we identified independent types of spinel, represented by inverted (magnetite), almost inverted (magnesioferrite), partially inverted (chrompicotite) and ordinary (magnesiospinel) structures. In the spinels the cations are variously distributed at tetrahedral and octohedral lattice sites. In the working zone ferrite spinels (up to 90%) — magnesioferrite and magnetite — predominated; they have an inverted structure and low melting points. The content of easily fusible ferrite spinels increased with increasing intensity of blowing of air through the bath. The formation of a large amount of ferrite spinels is one of the main causes of the fusion and rapid wear of periclase-spinel roofs of open-hearth furnaces.Translated from Ogneupory, No. 2, pp. 25–31, February, 1969.     

使用后铝镁炭砖的显微结构分析

对宝钢电炉盛钢桶用铝镁炭砖使用后的显微组成和结构进行了分析 ,研究了用后铝镁炭砖的相组成和显微结构变化。结果表明 ,铝镁炭砖在使用过程中组成相的烧结反应产物产生的微膨胀使制品结构进一步致密 ,尤其是越靠近工作面 ,尖晶石晶粒尺寸越大 ,最终在工作面与蚀变铝酸钙一起形成致密层 ,有效地减缓和阻止了铁水和熔渣向砖内的侵蚀与渗透。     

Densification and properties of magnesia-rich magnesium-aluminate spinel derived from natural and synthetic raw materials

Magnesia rich magnesium aluminate spinel (MgO: Al₂O₃=2:1) was developed by reaction sintering of Indian natural magnesite of Salem region as well as from synthetic caustic magnesia with calcined alumina. Dilatometric study of the green compacts was carried out to evaluate the spinelisation and sintering behaviour of both the samples. Green samples were heat treated between 1400 to 1600 °C and characterised in terms of densification behaviour, high temperature flexural strength, microstructure and phase development. Spinel and periclase are the major phases in both the samples, where as forsterite is found only in the sample developed from Indian magnesite due to presence of silica as impurities.