氧化物-非氧化物复合耐火材料高温性能的研究

对氧化物-非氧化物复合材料(如ZCM-SiC,ZCM-BN,O’-Sialon-ZrO2,β-Sialon-Al2O3等)的高温性能(强度、抗热震性、抗氧化性等)进行了研究。结果表明(1)所研究的氧化物-非氧化物复合材料的高温强度明显优于碳结合材料的高温强度。(2)在氧化物基质中引入非氧化物,可提高材料的抗热震性。(3)在非氧化物基质中引入氧化物可明显改善材料的抗氧化性。     

石墨烯增强增韧非氧化物陶瓷的研究进展

由于在非氧化物陶瓷基体中引入石墨烯可通过裂纹偏转及桥接等多种增韧机制来提高其强度和断裂韧性,因此综述了石墨烯增强增韧非氧化物陶瓷(例如:硼化物陶瓷、氮化物陶瓷、碳化物陶瓷等)的研究现状,总结了石墨烯在非氧化物陶瓷中的增韧机制,提出了该复合陶瓷存在的缺点,并指出了其发展方向。     

稀土氧化物和CaF_2对AlN陶瓷烧结性能及热导率的影响

以4%Y_2O_3、3%Y_2O_3–1%CeO_2、3%Y_2O_3–1%CaF_2和3%Y_2O_3–0.5%CeO_2–0.5%CaF_2(质量分数)为助烧剂,于1 860℃制备得到了AlN陶瓷。研究了不同助烧剂体系对AlN陶瓷物相组成、显微结构、烧结性能及热导率的影响。结果表明:所得样品的物相组成中均含有AlN与钇铝酸盐相,在含有CeO_2助烧剂的样品中还检测到少量的铈铝氧化物相;样品晶粒尺寸分布均在3~8μm之间。与添加一元及二元助烧剂相比,三元助烧剂的引入能更有效促进AlN陶瓷烧结致密化,强化其导热性能。添加三元助烧剂制备得到AlN陶瓷的体积密度为3.29 g/cm~3,气孔率为0.58%,热导率为184.8 W/(m·K)。     

纳/微异构型钙钛矿氧化物电极在固体氧化物燃料电池的研究进展

开发高效、稳定、廉价的钙钛矿氧化物电极材料是固体氧化物燃料电池(SOFC)进一步商业化发展的关键。目前,研究重点仍集中在解决阳极积碳、硫毒化以及阴极氧还原(ORR)低温性能不佳等问题。最近,有研究报道,一些易还原过渡金属元素掺杂的钙钛矿可以在还原气氛中原位析出该金属并以纳米颗粒的形式"镶嵌"在钙钛矿表面形成"纳米金属–钙钛矿"复合结构。该方法制备的材料具有性能高、抗积碳能力强、可再生性好等优点。从钙钛矿氧化物本体的选择、A/B位掺杂、缺陷调整、以及拓扑离子交换、相变诱发等方面,总结了近年来关于构建纳米(析出金属颗粒)微米(钙钛矿氧化物母体)异质结构(统称纳微异构)钙钛矿氧化物纳米纤维复合电极的研究。此外,总结了具有纳米纤维状形貌的钙钛矿氧化物电极及其结构对于SOFC性能、稳定性的影响,最后提出了该类纳微异构材料的优势、不足和展望。     

非氧化物复合耐火材料的热力学性能

为了在耐火材料中能动地应用非氧化物,系统了解非氧化物的热力学性质是非常必要的。为此,首分析了非氧化物在氧化气氛下的不稳定性及顺序,并就如何转变这个不利的性质,以实现在氧化气氛下烧结非氧化物复合材料而提出了“逆反应烧结”工艺。在深入研究Si、Al系氮化物的氧化机理后发现,当氧分压低于“转换氧分压”时,可显著生成其气态的亚氧化物。亚氧化物可以在邻近表面层沉积,形成致密层。致密层的形成使材料具有“自阻碍氧化”的性能。Si、Al的加入可增加亚氧化物的含量,从而加厚、加宽致密层,使材料的抗氧化和抗侵蚀能力得到提高。文中详述了Si3N4 -Al2O3、Si3N4 -MgO和Si3N4 -SiC三个体系的研究情况。结果表明:逆反应烧结工艺可制备出性能良好的复合物;Si、Al除可促进烧结外,还能提高致密层的密度和宽度。     

非氧化物陶瓷超细粉的制备

非氧化物陶瓷以优异的综合性能，在冶金、化工、机械、电子等领域有着广阔的应用前景．为了制备出适于烧结的非氧化物陶瓷超细粉体，人们进行了大量的研究工作，本综述了非氧化物陶瓷超细粉的研究进展，其中涉及机械粉碎法、金属元素反应法、金属氧化物碳热还原(氮化)法、聚合物热解法、气相化学反应法及溶剂热合成法等，并对金属氧化物碳热还原(氮化)法的进展进行了较为详细的描述，     

固体氧化物燃料电池阳极的制备及表征

本文介绍了固体氧化物燃料电池对阳极材料的基本要求以及各种阳极材料的优缺点及其研究进展(包括金属、金属陶瓷、混合导体氧化物等)。以Co2O3和钐掺杂氧化铈(SDC)为原料,通过粉末冶金工艺制备出用于燃料电池的Co2O3/SDC阳极烧结体和Co/SDC阳极材料,并用X射线衍射仪(XRD)对产物的微观结构进行了表征,证明在不同Co2O3含量的样品中晶体结构非常稳定,烧结后Co3O4均匀的分布在样品内。     

闪烧技术在固体氧化物燃料电池关键材料制备中的应用

闪烧技术是一种新兴的陶瓷烧结技术,因具有烧结温度低、功耗低、时间短等显著特点而受到世界范围内的广泛关注。自2010年闪烧现象被报道以来,研究人员在闪烧实验装置的搭建、不同陶瓷材料的闪烧现象、过程参数的控制及优化等方面开展了大量工作,闪烧技术得到了飞速的发展。对闪烧技术的过程参数及影响规律进行归纳和总结,重点对近年来闪烧技术在固体氧化物燃料电池领域的应用进展进行了详细介绍。     

无机氧化物

本发明的目的是提供一种粉末，即使将颗粒直径小的无机氧化物干燥后，其粉末也能易于被再分散成基本上不聚集的无机氧化物。本发明涉及通过利用硅烷偶合剂处理无机氧化物的含水分散体并且之后进行干燥而得到的粉末，所述无机氧化物的平均颗粒直径D1通过动态光散射方法测量为3～1000nm，     

柠檬酸溶胶凝胶法合成SrFeCo_(0.5)O_2氧化物的研究

利用柠檬酸溶胶凝胶法结合微波加热合成SrFeCo_(0.5)O_x混合导体氧化物。采用XRD,TEM以及DTA方法研究与分析了不同条件下粉末样品的物相组成和形貌。结果说明:在燃料剂/氧化剂摩尔比α=0.64,经550℃焙烧得到单相钙钛矿氧化物,氧化物为10 nm左右球形颗粒,尺寸分布均匀;焙烧温度升高到850℃氧化物晶体结构无变化,颗粒尺寸明显长大,但是形状不变。850℃短时间的微波焙烧可以使样品的物相组成单一化,而且粉末颗粒没有剧烈长大和团聚。     

Competition between densification and microstructure development during spark plasma sintering of B4C–Eu2O3

The densification of nonoxide ceramics has been a known challenge in the field of engineering ceramics. The amount and type of sinter‐aid together with sintering conditions significantly influence the densification behavior and microstructure in nonoxide ceramics. In this perspective, the present work reports the use of Eu₂O₃ sinter‐aid and spark plasma sintering towards the densification of B₄C. The densification is largely influenced by the solid‐state sintering reactions during heating to 1900°C. Based on the careful analysis of the heat‐treated powder mixture (B₄C–Eu₂O₃) and sintered compacts, the competitive reaction pathways are proposed to rationalize the formation of EuB₆ as dominant microstructural phase. An array of distinctive morphological features, including intragranular and intergranular EuB₆ phase as well as characteristic defect structures (asymmetric twins, stacking faults and threaded dislocations) are observed within dense B₄C matrix. An attempt has been made to explain the competition between microstructure development and densification.     

Fundamental investigations of differences in bonding mechanisms in iron ore sinter formed from magnetite concentrates and hematite ores

Whilst increasing amounts of imported hematite ores are being added with the magnetite concentrates that dominate sinter blends in the People's Republic of China, little is known about the fundamental behaviour of magnetite concentrates during sintering compared to hematite ores. Compacted tablets of fluxed magnetite, magnetite–hematite and hematite concentrates and ores were fired under simulated sintering conditions in the laboratory to establish the fundamental differences in sintering behaviour, mineralogy and bonding mechanisms between magnetite concentrates and hematite ores.

Sinter made from magnetite concentrates (<10% hematite) relies on the formation of a network of fused magnetite–magnetite grains (diffusional bonding) and high temperatures (1350–1370 °C) to obtain satisfactory sinter tumble strength. Magnetite–hematite concentrate mixtures, with <45% hematite, behave during sintering like magnetite concentrates. The large phase field for Magnetite+Liquid under typical sintering compositions and temperatures was found to prevent all but minor formation of Ca-ferrites via hematite from low-basicity (<2.0) sinter blends dominated by magnetite concentrates.

In contrast, hematite ores with high (>2.0) effective basicity are able to form a high tumble strength sinter matrix composed of a network of abundant calcium ferrites (e.g. SFCA, SFCA I) below 1300 °C.     

Effect of nano iron oxide as an additive on phase and microstructural evolution of Mag-Chrome refractory matrix

Nano iron oxide, up to 8 wt.%, was added to Mag-Chrome refractory matrix through stirring in ultrasonic bath in an alcohol media. The phase and microstructure of samples heated up to 1650 °C were studied by XRD and SEM/EDS respectively.It was found out that the formation of magnesioferrite spinel was encouraged at lower temperatures in the presence of nano iron oxide. The dissolution of iron oxide and ionic migration improved the sintering process in the matrix of the refractory. The presence of nano iron oxide also influenced the bonding structure in a way that direct bonding was enhanced while silicate bonding was hindered.     

非氧化物陶瓷连接技术的进展

非氧化物陶瓷作为高温结构材料其应用前景非常广阔，但非氧化物陶瓷自身及其与金属的连接问题制约了它的工程使用，与氧化物陶瓷连接相比，非氧化物陶瓷的连接目前基本上处于基础性研究和实验室研究阶段，本文概述了这些年用于非氧化物陶瓷连接的几种方法及其工艺特点，其中包括：活性金属钎焊法，热压扩散连接法，过渡液相连接法，反应成形连接法，自蔓延高温合成（SHS）焊接法，热压反应烧结连接法和直接敷铜（DBC）法。     

等轴晶ZrO2(Al2O3, Fe2O3)复相陶瓷的制备

讨论了以硝酸盐溶液为原料，经喷雾干燥、热解、成型、烧结或直接烧结制备等轴晶ZrO2(Al2O3, Fe2O3)复相陶瓷的过程. 研究了成型压力、烧结温度、恒温时间及Al3+, Fe3+的加入对ZrO2陶瓷的相组成、晶粒大小和形貌的影响. 结果表明：成型压力对相组成及晶粒尺寸无明显影响；无论是直接采用硝酸盐复合粉末还是采用氧化物粉末压坯作为前驱物，烧结产物的形貌、相组成不变；加入Fe2O3可克服微观结构层状堆垛，获得相对细小均匀的等轴晶粒，且随Fe2O3含量的增加，单位体积中a-(Al, Fe)2O3核心的数量增加，晶粒尺寸更加细小、均匀，Fe2O3含量相对于Al2O3在20%左右时效果最佳；各相晶粒在长时间高温烧结时生长速度较为缓慢，0.5 h为0.5 mm左右，烧结12 h才到2.0 mm左右.     

The effect of NiO addition on the grain boundary behavior and electrochemical performance of Gd-doped ceria solid electrolyte under different sintering conditions

It has been reported that some transition metal oxides are effective aids both for the densification and the grain boundary behavior of ceria-based electrolytes. In the present work, NiO which is the most popular component of the anode of solid oxide fuel cells was added directly into the electrolyte ceramic, Ce_0.8Gd_0.2O_1.9, to investigate the effects of the presence of NiO on the properties of GDC electrolyte. All of the samples possess a single phase with cubic fluorite structure. The grain size is increased by the addition of NiO when the sintering temperature is 1400 °C. This modification in chemical composition also results in a decrease in activation energy and thus a tendency to enhance grain boundary mobility. The maximum power density of the composite electrolyte single cell is higher than that of a GDC single cell. Therefore, NiO can be used as an effective aid for ceria-based electrolytes.     

Combined role of SiC whiskers and graphene nano-platelets on the microstructure of spark plasma sintered ZrB2 ceramics

This research explores the sintering behavior and microstructure of ZrB₂-based materials containing graphene nano-platelets (GNPs) and SiC whiskers (SiC_w). Spark plasma sintering (SPS) process at 1900 °C was implemented to sinter the specimen, leading to a composite with 100% relative density. High-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), field emission-electron probe microanalyzer (FE-EPMA), and high-resolution X-ray diffractometry (HRXRD) were employed to study the SPSed sample, along with the thermodynamics predictions. According to the HRXRD result and microstructural observations, the sintering process was non-reactive, which was endorsed with the XPS analysis. Furthermore, graphene presented a beneficial role for eradicating the oxide impurities in the sample during the sintering. Such oxide impurities were reduced to the original phases of SiC and ZrB₂, contributing to porosity removal. Nanostructural investigations revealed the formation of ultrathin amorphous interfaces (~10 nm) between ZrB₂/graphene phases, disordered atomic planes in graphene platelets, and dislocations in ZrB₂ grains. One reason for generating crystalline defects in the microstructure was found out to be the mismatches amongst the elastic properties of the available compounds in the system.     

Sintering and Grain Growth of Alpha-Alumina

The sintering (densification) and grain growth of alumina were studied to determine the effect of the variables raw material, particle size, grinding in acid media, molding pressure, various single additives in different amounts, and firing temperature. Fine grinding promoted sintering and the growth of large grains and caused the grains to be more elongated in habit. Sintering was facilitated by additions of iron oxide, manganese oxide, copper oxide, and titanium oxide, provided the amounts of these oxides and the temperature of firing were within certain bounds. The growth of large grains was facilitated by additions of iron oxide and manganese oxide. Nineteen other additives had no effect or retarded sintering and large-grain growth. Both magnesium oxide and silica had a marked effect in inhibiting the growth of large grains. The alkali metal oxides, added singly, were especially deleterious to the production of strong alumina bodies. The maximum density and maximum strength of the fired body were attained approximately simultaneously with the onset of large-grain growth. The habit of the large grains was markedly altered by increasing amounts of each additive; the grains lost their characteristic crystalline shape and became nearly spheroidal particles. It is suggested that two grain-growth phenomena exist which are independent of each other. One is termed "small-grain growth" and is associated with densification; the other is referred to as "large-grain growth" and occurs in certain specimens, depending on the additions to the alumina, after the sintering (densification) is substantially complete.     

Low‐Temperature Sintering of HfC/SiC Nanocomposites Using HfSi2‐C Additives

HfC/SiC nanocomposites were fabricated via the reactive spark plasma sintering (R‐SPS) of a nano‐HfC powder and HfSi₂‐C sintering additives. The densification temperature decreased to 1750°C as the additive content increased. XRD analysis indicated the formation of pure HfC–(19.3–33.8 vol%) SiC within the sintered composites without residual silicide or oxide phases or secondary nonoxide phases. Ultrafine and homogeneously distributed HfC (470 nm) and SiC (300 nm) grains were obtained in the dense composites using nano‐HfC powder through the high‐energy ball‐milling of the raw powders and R‐SPS. Grain growth was further suppressed by the low‐temperature sintering using R‐SPS. No amorphous phase was identified at the grain boundary. The maximum Vickers hardness, Young's modulus, and fracture toughness values of the HfC/SiC nanocomposites were 22 GPa, 292 GPa, and 2.44 MPa·m^1/2, respectively.