Microstructures and strength of microporous MgO-Mg(Al,Fe)2O4 refractory aggregates

Microporous MgO-Mg(Al, Fe)₂O₄ refractory aggregates were prepared using magnesite, Al(OH)₃ and Fe₂O₃ applying an in-situ decomposition synthesis method. At 1400–1600 °C, there was a Mg(Al, Fe)₂O₄ with Fe³⁺, which had two structures. One was a ring structure formed from Al(OH)₃ pseudomorph particle as a template and a low content of Fe³⁺. The other was the dot and strip structures precipitated in magnesite pseudomorph particles with a high content of Fe³⁺. Besides, at 1550–1600 °C, microporous MgO-Mg(Al, Fe)₂O₄ refractory aggregates had an excellent compressive strength (75.8–81.5 MPa) and apparent porosity (26.8%?28.2%).     

Microstructures and properties of novel lightweight refractory aggregates with microporous MgO@MgAl2O4 core-shell structures

Microporous aggregates are the key to the lightweight design and preparation of refractories for the working linings of the high temperature furnaces. In this work, the lightweight MgO-MgAl₂O₄ refractory aggregates with core-shell structures were prepared by in-situ decomposition synthesis technology using Mg(OH)₂ and nano-size Al₂O₃ as raw materials. The influence of the nano-size Al₂O₃ content on the microstructures and properties was thoroughly studied. The results demonstrated that the microporous MgO core structures were formed after the decomposition of Mg(OH)₂, and the MgAl₂O₄ bonds between the microporous MgO core structures were formed through the reaction between the nano-size Al₂O₃ and MgO. When the nano-size Al₂O₃ contents were less than 9 wt%, the MgAl₂O₄ bonds were discontinuous. With the increase of the nano-size Al₂O₃ contents to 9–15 wt%, more continuous MgAl₂O₄ bonds (i.e. MgAl₂O₄ shell structures) were formed at the surface of the microporous MgO core structures. Overall, the optimized specimens were lightweight MgO-MgAl₂O₄ refractory aggregates with the addition of 9 wt% nano-size Al₂O₃, which exhibited the microporous MgO@MgAl₂O₄ core-shell structures, a median pore size of 268 nm, a high compressive strength of 105 MPa, and a low thermal conductivity of 4.1 W/(m·K) at 800 ℃.     

MgO-Al2O3-SiO2系统微晶玻璃的析晶及热处理工艺研究

用XRD、DTA对MgO-Al2O3-SiO2系微晶玻璃材料的析晶过程进行了研究,讨论了热处理温度及时间对微晶玻璃热膨胀系数的影响,表明了各种晶体的析出特点.     

富镁尖晶石细粉对镁铝浇注料性能的影响

含尖晶石的耐火材料广泛应用于冶金行业.本文研究了富镁尖晶石细粉加入量对镁铝浇注料显气孔率、抗折强度和抗渣性能的影响.通过对不同温度处理后试样的性能检测和试样抗渣性能的研究发现,镁铝浇注料中富镁尖晶石细粉的加入量有一个较佳的范围,在这个范围内,浇注料的相关性能较好.     

MgO-Al2O3-SiO2系统微晶玻璃的热处理工艺对其介电性能的影响

本文制备了MgO-Al2O3-SiO2系微晶玻璃,用XRD、DTA等方法对该系统微晶玻璃材料的析晶过程进行研究,通过正交试验,讨论了热处理温度及时间对微晶玻璃介电性能的影响.结果表明通过热处理工艺来控制晶相的析出,可以使样品的介电常数和介电损耗符合要求.获得较小介电常数的热处理制度为核化温度750℃,核化时间1h,晶化温度1100℃,晶化时间1.5h,所获得的微晶玻璃的介电常数为6.13,介电损耗4.22×10-3+可作为绝缘体等微波介质材料使用.     

Microstructures and properties of microporous mullite-corundum aggregates for lightweight refractories

Five microporous mullite-corundum refractory aggregates were prepared from Al(OH)₃ and kaolinite gangue through in situ decomposition synthesis technique. The effects of the sintering temperature (1400–1600°C) and the particle sizes of raw materials (20.6–94.5 μm) on the microstructures and strengths of the aggregates were investigated through X-ray diffractometer, scanning electron microscopy, and energy-dispersive spectrometer etc., to find out the technological conditions to be controlled in industrial production. The higher sintering temperature promoted the reaction between Al(OH)₃ and kaolinite gangue, leading to the development of primary-mullite as well as the generation of secondary-mullite, which promoted the formation of the neck and improved the strength. Meanwhile, the dense mullite layers were formed continuously on the surface of Al(OH)₃ pseudomorphs, making the micropores inside the pseudomorphs become closed pores, which increased the closed porosity of the aggregates. The reduction of the particle sizes of raw materials changed the particle packing behavior, accelerated the rearrangement of the Al(OH)₃ pseudomorph particles during the process of reactive sintering, and then reduced the closed porosity. To realize the industrial production of microporous mullite-corundum refractory aggregate with high strength (103 MPa) and high closed porosity (16.1%), the sintering temperature should be at about 1600°C, and the median diameter of raw materials should be at 94.5 μm.     

镁铝复合氧化物表征及催化乙醇脱水性质的研究

通过共沉淀法制备了不同Mg/Al比的MgO-Al2O3复合氧化物,运用XRD和NH3-TPD等现代表征手段对其进行表征,研究结果表明,随着Mg/Al比的降低,MgO-Al2O3复合氧化物表面酸性逐渐增强,并以乙醇脱水制乙烯反应作为优异的探针反应来表征MgO-Al2O3复合氧化物表面的酸性。反应最佳条件为:Mg∶Al=1∶1,反应温度300℃。     

镁铝硅系堇青石基微晶玻璃的制备及性能研究

采用高温熔融法制备了MgO-Al2O3-SiO2 (MAS)系堇青石基微晶玻璃.借助X射线衍射仪(XRD)、扫描电镜(SEM)及热膨胀系数仪研究了晶化热处理工艺、MgO/Al2O3质量比以及晶核剂种类(TiO2/ZrO2)与含量对MAS系堇青石基微晶玻璃理化性能和晶化特性的影响.结果表明:在核化温度750℃、保温时间1h,晶化温度1050℃、保温时间2.5h,升温速率5 ℃/min时,微晶玻璃中堇青石含量最高,析晶性能最好;当MgO/Al2O3质量比为1左右时,在30 ～ 700℃温度范围内,平均热膨胀系数最小,在4.4 ～4.8×10-6K-1范围内可调;TiO2是MAS系堇青石基微晶玻璃的有效晶核剂,而ZrO2的加入并不利于基础玻璃的晶化.     

组成对MgO-Al2O3-SiO2系统分相析晶的影响

对MgO-Al2O3-SiO2系统的分相与析晶进行了探讨,通过对不同组成点在热处理各阶段的试样进行XRD、TEM及DTA分析,研究了玻璃组成对玻璃的分相和析晶的影响.结果表明:当组成中MgO/Al2O3越大且同时SiO2含量越高,越利于该系统产生分相.当MgO/Al2O3大于3且SiO2含量大于68mol％时,水淬试样产生分相.SiO2含量较高时,分相液滴很容易聚集在一起,形成连通的蠕虫状分相粒子.随着SiO2含量的降低,玻璃的析晶放热峰温度逐渐降低,而且析晶放热峰变得尖锐,玻璃析晶趋势增强.当SiO2含量越低且MgO/Al2O3越大时,越利于该系统析晶.     

晶化时间对MgO-Al2O3-SiO2系微晶玻璃显微结构及性能的影响

通过差热分析(DTA)、X射线衍射分析(XRD)、扫描电子显微镜(SEM)等测试手段研究了不同晶化时间对MgO-Al2O3-SiO2系微晶玻璃析晶性能、微观结构及抗弯强度的影响。研究结果表明,随着晶化时间的加长,晶粒尺寸逐步增大,抗弯强度逐渐增高。     

复合晶核剂TiO2/ZrO2对MgO-Al2O3-SiO2系统微晶玻璃的影响研究

本文制备了Mg0-Al2O3-SiO2系微晶玻璃,用XRD、DTA等方法对该系统微晶玻璃材料进行了研究;讨论了复合晶核剂对材料热膨胀性能及热处理温度的影响.结果表明TiO2/ZrO2复合晶核剂中,少量ZrO2(＜0.5wt%)能够降低微晶玻璃材料的热处理温度和热膨胀系数.     

MgO-Al2O3-C材料服役状态下MgO致密层的形成机理

一种SiC含量为6.0％的MgO-Al2O3-C(MAC)材料被用于精炼钢包包壁部位,表现出优异的抗侵蚀性能,对用后MAC材料的物相组成和显微结构进行分析.结果显示,在MAC材料侵蚀界面形成MgO致密层,提高了MAC材料的抗侵蚀性能.MAC材料内的SiC,一方面与MgO反应形成更多的Mg(g);另一方面,SiC氧化后形成的部分SiO2进入侵蚀层熔渣使熔渣碱度下降,粘度大幅上升,不但提高了MgO在熔渣中的形成速率,而且同时降低了MgO的溶解速率,促进MgO再结晶和MgO致密层的形成.     

氮化硼/二硼化锆对氧化镁-氧 化铝-碳材料性能影响

以电熔镁砂、用后镁碳砖、α-氧化铝和石墨为原料,引入复合添加剂氮化硼/二硼化锆（BN/ZrB2）,经共磨、加酚醛树脂结合剂混炼、成型及热处理工艺制备氧化镁-氧化铝-碳耐火材料,研究复合添加剂BN/ZrB2及煅烧温度对烧后试样烧结性、抗氧化性、显微结构和矿物相组成的影响。结果表明： BN/ZrB2添加剂在氧化镁-氧化铝-碳耐火材料中的优先氧化顺序为二硼化锆>氮化硼>碳,添加剂BN/ZrB2氧化生成三氧化二硼,三氧化二硼与基质中电熔镁砂及用后镁碳砖中的氧化镁反应生成低熔点相Mg3B2O6,液相Mg3B2O6有利于提高氧化镁-氧化铝-碳耐火材料的烧结性和抗氧化性。烧后试样矿物相组成为方镁石、镁铝尖晶石和少量Mg3B2O6相。     

晶化时间对MgO-Al2O3-SiO2微晶玻璃相转变及热膨胀性能的影响

采用XRD、DTA、SEM等测试方法,对MgO-Al2O3-SiO2（MAS）系微晶玻璃的析晶和微观结构进行了研究,讨论了不同的晶化时间对MAS微晶玻璃析晶行为及其热膨胀性能的影响。结果表明：在1050℃保温,堇青石能快速地晶化析出。随着晶化时间的增长,堇青石相逐渐增多,当晶化2h时几乎完全析出,析出晶粒大小约为2～5um。MAS系微晶玻璃的热膨胀系数与相组成有着密切的关系,随着晶化时间的延长,热膨胀系数逐渐减小。     

MgO-Al2O3-SiO2系透明玻璃陶瓷研究进展

透明玻璃陶瓷具有热膨胀系数可调、强度高、化学稳定性好的优点,且兼具透光/发光的特性,是一种在光学信息、生物技术、激光技术、红外遥感及民用照明等领域有着广泛的应用前景的新型功能材料。本文简述了玻璃陶瓷的透光机制,对形核剂、过渡金属离子及稀土离子掺杂MgO-Al₂O₃-SiO₂(MAS)系透明玻璃陶的析晶及透光/发光性能方面的研究进展进行了介绍,并简要分析了开发具备透光/发光性质的高结晶度MAS透明玻璃陶瓷材料存在的问题,最后展望了透明玻璃陶瓷的发展趋势与前景。     

A novel Nd3+-doped MgO-Al2O3-SiO2-based transparent glass-ceramics: Toward excellent fluorescence properties

Generally, glass-ceramics have superior properties compared to their parent glasses. Here, we prepared a novel Nd³⁺-doped MgO-Al₂O₃-SiO₂-based transparent glass-ceramics with excellent fluorescence properties. The effects of Nd₂O₃ content on the structure and properties of glass-ceramics were studied, aiming to provide a key guidance for preparing this transparent glass-ceramics. The results revealed that the glass stability increased originally and then decreased with increasing Nd₂O₃ content, so did the variation of wavenumbers in infrared spectra. And these glass-ceramics are mainly composed of cordierite with residual glassy phase. The three phenomenological intensity parameters (Ω_2,4,6) and radiative properties were estimated by Judd-Ofelt theory, and the values of Ω₂ first decreased and then increased with increasing Nd₂O₃ content. Three main emission peaks ascribed to the transitions from ⁴F_3/2 to ⁴I_9/2, ⁴I_11/2, ⁴I_13/2 at 898, 1057, 1330  nm were observed, respectively. The branching ratios for ⁴F_3/2→⁴I_11/2 transition increased as the Nd₂O₃ content raised, and the fluorescence lifetimes of the ⁴F_3/2 level were found to increase first and then decrease with Nd₂O₃ content (from 181 to 726 μs). The excellent fluorescence properties indicate that this novel glass-ceramics can be used as a potential solid-state optical functional material for 1.06 μm laser emission.     

Preparation of Al2O3@CaCO3 aggregates and its effects on the thermal shock resistance of Al2O3-MgO castables

Al₂O₃@CaCO₃ aggregates were prepared by impregnating corundum aggregates (particle sizes with 3-1 and 5-3 mm) in precursor solutions (Calcium hydrogen citrate, CaHC₆H₅O₇) followed by heat treatment at 430°C. The phase composition and microstructure of the coatings were characterized via X-ray diffraction and scanning electron microscope, respectively. The novel aggregates were used in Al₂O₃-MgO castables. The effects of the Al₂O₃@CaCO₃ aggregates on the physical properties and thermal shock resistance (TSR) of castables were investigated. The results show that uniform CaCO₃ coating of aggregates (C15) with thickness about 10 µm can be attained when the concentration of Ca²⁺ in solution was 0.15 mol L⁻¹. There was a strong bonding between the aggregates and coating that was constituted by particles with size about 0.2 µm. Both improving physical and TSR properties of the castables are related with the unique layer structure, calcium hexaluminate (CA₆) layer in-situ formed at the aggregate-matrix interface, of added Al₂O₃@CaCO₃ aggregates. There is a mass of multi-deflection of cracks along with the CA₆ layer which consumes more fracture surface energy. The castables with C15 exhibit optimal TSR and the residual strength ratio after the thermal shock test is 29.5%, which is 12.8% higher than the castables with corundum aggregates.     

水泥窑用MgO-MgAl2O4-ZrO2-La2O3复合耐火材料的研究

根据耐火材料和水泥熟料的反应机理,找到一种既可阻止窑皮中C2S相变,又不损害镁铝质耐火材料的高温性能的添加物,开发了一种基于MgO-MgAl2O4-ZrO2-La2O3体系的新型复合耐火材料。该材料具有优异的耐火性能、抗热震性能、挂窑皮性能、抗侵蚀性能和较高的机械强度,是一种替代镁铬砖的理想材料,适用于水泥窑烧成带。     

镁铬砖与熔融MgO-Al2O3-SiO2-CaO-FetO炉渣之间的反应及显微结构

在1823～1923K下经不同时间的静态炉渣侵蚀后,对MgO-Cr2O3砖的接触面与熔融MgO-Al2O3-SiO2-CaO-FetO炉渣发生的反应及其显微结构进行了研究和描述.在1923K下静态炉渣侵蚀4h,XRD结果显示主晶相为方镁石MgO和MgCr2O4尖晶石,CaMgSiO4为次晶相.MgCr2O4相导致MgO在MgO-Cr2O3砖中形成不连续的相.在1923K下静态炉渣侵蚀4h后.SEM显微照片示出该砖内部的裂纹.TEM显微照片和ED图谱描述了(Mg,Fe)(Al,Cr)2O4次要相在MgCr2O4基质中沉淀.     

氧化铬加入量对出钢口填充料性能的影响

在填充料的常规配方中,分别添加质量分数为0、1％、2％、4％氧化铬,研究了不同氧化铬加入量对材料性能的影响。结果表明：氧化铬的引入明显提高了材料抗渣性能,但同时导致材料体积密度和强度略微降低,加入2％的氧化铬时,材料综合性能最好。