反应烧结碳化硅材料的抗热震性能研究

通过对比不同温差热震后材料的残余强度 ,对反应烧结碳化硅材料的抗热震性能进行了研究。结果表明 :反应烧结碳化硅材料的抗热震性能与显微组织密切相关 ,低游离硅含量与小粒径的反应烧结碳化硅材料具有较好的抗热震断裂性能 ,而高游离硅含量或大碳化硅粒径的材料具有相对优异的抗热震损伤性。对反应烧结碳化硅材料的抗热震性与显微组织的关系进行了探讨。     

再生SiC制造的新型耐火材料

评估了陶瓷工业用后的、硅酸盐结合SiC板重复使用于陶瓷工业和钢工业的情况。准备了几批含不同量矾土和硅灰的、使用过的SiC质板作试验料，加热到1400℃。通过检测体积密度和显气孔率来测试料的致密性。研究了这些烧结材料的矿物性能和显微结构，这些性能与30次热震实验后耐压强度同热震实验前的耐压强度比值有关。莫来石的形成、莫来石代替碳化硅和假碳化硅的生成、碳化硅的紧密结构和良好分布等都被记录。随着不断增加的莫来石含量直至40％，热震实验后强度同实验前强度相比有所增大。将料加热到950℃再用水冷处理，如此循环30次后观测发现，所有批次的料抗热震性能良好，没有剥落出现。     

多孔SiC基耐火材料的热震损伤

本文从抗热震性是材料的力学和热学性能的综合反映这观点出发,研究了SiC基耐火材料的组分-显微结构-力学性能之间的关系,从而剖析材料的抗热震能力。首先,探讨了粘土结合剂含量不同的三种SiC基材料的强度随热震温差△T的增大而下降的趋势;多次热震导致的强度衰减规律;分析了材料的热震裂纹扩展行为;确定了该系列材料具有“准静态热震裂纹扩展”的属性,亦即其抗热震能力主要由“裂纹稳定性系数”R_(at)-[γf/Eα~2]~(1/2)来表征;从而说明断裂功rf的提高,是改善该系列材料抗热震性的最重要的力学因素。在系统实验的基础上得出:在600℃≤△T≤1000℃的热震温差范围内,材料的强度不仅随着温差△T的增大而下降,亦随着热震次数的增多而衰减。因此,这是热震损伤问题较为突出的阶段,当△T≥1000℃,由于SiC颗粒间界的铝硅酸盐在高温下出现了粘滞态的玻璃相,在淬冷瞬间吸收了部分能量,削弱了热震裂纹的扩展趋势,相应缓和了材料的热震损伤倾向。     

Al_2O_3质厚膜电路基片的抗热震机理

本文研究了四种Al_2O_3瓷的力学、热学性能与其显微结构间的关系。文中从热弹性理论出发,讨论了Al_2O_3瓷的抗热震断裂特性并用断裂力学的能量平衡观点,分析了材料的抗热震损伤行为。指出:在四种材料中,高强度和低韧性、低模量的钙镁系Ⅳ-Al_2O_3瓷具有较好的抗热震断裂特性;强度较低而韧性较好的钙系Ⅰ-Al_2O_3瓷具有较高的抵抗热震诱发微裂纹进一步扩展的能力,亦即有较好的抗热震损伤特性。钙镁系Ⅱ-Al_2O_3和Ⅲ-Al_2O_3瓷的抗热震性处于上述两者之间。显然,陶瓷材料的抗热震行为是其力学和热学性能的综合表现。温差热应力是材料破坏的动力,材料固有的力学性能往往是抵抗裂纹的萌生或扩展的阻力因素。     

含锆莫来石-刚玉质陶瓷的抗热震性与断裂参数

研究了MZ-3、MZ-6和MZ-8三种含锆莫来石-刚玉质陶瓷的断裂参数(断裂韧性K_(10)、断裂功γ_f和固有强度σ_f)与其组分和组成相之间的关系,分析了三种材料热震后强度的衰减趋势。 实验表明,MZ-3材料的抗热震临界温差△T_o为200℃左右,而斜锆石含量较高的MZ-6和MZ—8材料的抗热震临界温差△T_o比MZ-3材料提高了约100℃;经过温差△T=300℃的热震处理后,MZ-6材料在强度与热震温差的关系曲线上出现极大值。热震后三种材料的强度衰减均随热震温差的增加而加剧。当温差从1000℃增大到1200℃时,粘滞态的玻璃相在淬冷瞬间吸收了部分能量,缓和了热震裂纹的扩展,除MZ-3材料因严重开裂造成强度继续衰减外,其它两种材料的强度有所提高。三种材料的断裂韧性K_(10)和断裂功γ_f随温度变化的情况与强度σ_f随温度变化的情况相同。 在实验的基础上,根据热弹性理论,讨论了三种含锆莫来石-刚玉质陶瓷的抗热震断裂特征,根据断裂力学的能量平衡观点,分析了材料的抗热震损伤能力。     

铝镁质钢包透气砖热震损毁研究

研究了w(Al2O3)为91.2%,w(MgO)为7.0%,高温抗折强度为33.4 MPa,弹性模量为146.1 GPa,热膨胀系数为7.97×10-6K-1的铝镁质钢包透气砖的热震损毁现象。采用脉冲激振法、三点弯曲法测量铝镁质钢包透气砖热震前后的热震参数、弹性模量、常温和高温抗折强度,并计算了弹性模量和抗折强度保持率。结果表明:铝镁质材料热震过程中产生大量微裂纹,裂纹扩展慢,并且铝镁质材料的细晶和网络穿插结构有助于提高其抗热震性能。     

刚玉骨料种类与粒度对刚玉-莫来石材料抗热震性的影响

以莫来石和电熔白刚玉或板状刚玉为骨料,氧化铝粉、氧化硅粉、红柱石粉为基质料,纸浆为结合剂,同时以≤0.15 mm(100目)的刚玉细骨料取代较粗(1～0.15 mm或0.5～0.15 mm)的刚玉骨料,制备了2个系列、不同粒度级配的刚玉-莫来石试样,并分别以抗折强度保持率和弹性模量保持率为评价指标,研究了刚玉骨料种类和粒度对刚玉-莫来石材料性能的影响。结果表明:1)分别以白刚玉和板状刚玉为骨料时,刚玉-莫来石材料热震后的弹性模量保持率与抗折强度保持率并不完全一致;2)以≤0.15 mm骨料代替较粗骨料,虽能提高材料强度,但可能会降低其抗热震性能。分析认为:刚玉-莫来石材料抗临界危险裂纹扩展能力与材料热震强度保持率一致,相对于弹性模量保持率,以强度保持率作为此类材料抗热震性的评价标准更为合适;由于板状刚玉骨料周围残余应力的存在,热震实验后以板状刚玉为骨料的刚玉-莫来石材料具有更高的抗折强度保持率。     

炭素材料的弹性模量、强度和破坏变形率

本文讨论了炭素材料的杨氏弹性模量、强度和破坏变形率，以及生产工艺因素对这些性质的影响。文章论证了破坏变形率是描述炭素材料，特别是石墨电极性能的重要指标，因为抗热震准数与它成正比。     

连续纤维增韧碳化硅陶瓷基复合材料研究

采用化学气相浸渗法制造了连续碳纤维和碳化硅纤维增韧碳化硅陶瓷基复合材料，并对复合材料的显微结构和力学性能进行了研究，C/SiC／SiC复合材料的密度分别为2．1g/cm^3和2．5g/cm63，在断理解过程中表现出明显的非线性和非灾难性的断裂行为和规律，C／SiC和SiC／SiC弯曲强度分别为450MPa和850MPa，从室温至1600℃强度不发生降低；断裂韧性为20MPa.m^1/2和41．5MPa.m^1/2，断裂功为10kJ.m^-2和28．1kJ.m^-2，冲击韧性为62．0kJ.m^-2和36．0kJ.m^-2，C/SiC和SiC/SiC复合材料具有优异的抗热震性能，经1300℃→←3000℃，50次热震后，强度保持率高达96．4％，热震不是材料性能损伤的控制因素，而SiC/SiC复合材料优异的抗氧化性能，对温度梯度不敏感，得合材料喷管在液体火箭发动机上成功地通过了地面实验。     

碳化硅质陶瓷膜材料评价方法的选择及材料评价

国内评价高温下碳化硅质陶瓷膜材料的标准和方法较少,本文基于碳化硅陶瓷膜材料具体实际应用工况条件,就材料的强度,耐高温、高压性能,孔结构及透气性能等方面,提出了系列测试标准和方法,并进行了测试。实验测得山东工陶院生产的碳化硅质陶瓷膜材料的抗弯曲强度能够达到18MPa,支撑体气孔率和孔径分别为34%和60μm,分离膜平均孔径为17μm,材料的线胀系数在5×10-6/k,热震性能能够满足1000℃下10次不裂,在1m/min风速下材料的初始压降为750Pa。碳化硅陶瓷膜材料具有良好强度、高温热性能和较好的孔梯度结构。     

Thermal shock damage evaluation of refractory castables via hot elastic modulus measurements

When refractory castables are submitted to continuous thermal changes, crack nucleation and/or propagation can take place resulting in a loss of mechanical strength and overall degradation of such materials. This work evaluates the thermal shock damage cycling of high-alumina and mullite refractory castables designed for petrochemical application. Hot elastic modulus analyses were carried out after 0, 2, 4, 6, 8 and 10 thermal cycles (ΔT=800 °C) in order to investigate the microcracking evolution due to the temperature changes. Additionally, apparent porosity, hot modulus of rupture, erosion and work of fracture measurements were also performed. According to the attained results, it was detected at which temperature range the stiffening or embrittlement took place in the mullite-based refractory (M-SA) microstructure. Nevertheless, the damage induced by the thermal shock tests was not permanent, as further increase of the elastic modulus results was observed for all evaluated samples after annealing. On the other hand, the alumina-based composition containing a sintering additive (TA-SA) presented enhanced mechanical strength, high thermal stability and E values. Simulations indicated that refractories with high E values (∼140 GPa, such as those attained for alumina-based castable) showed a reduced amount of stored elastic strain energy even under severe thermal stresses, which seems to be a key aspect for the engineered design of thermal shock resistance materials.     

Thermal interaction between polymer‐based composite friction materials and counterfaces

Attempts have been made to improve the performance of polymeric composite friction materials for eliminating undesirable mechanical and thermal effects on the opposing surfaces. Elastic compression modulus and thermal conductivity of the moulded friction materials were found to be the most effective parameters upon the thermal interaction between the disc and brake pad. Effects of elastic modulus on temperature accumulation of the interface have also been studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 364–369, 2001     

Elasticity and Anelasticity of Uranium Oxides at Room Temperature: I, Stoichiometric Oxide

The elastic modulus and internal friction of stoichiometric uranium oxide at room temperature were studied using a dynamic method. The elastic modulus of stoichiometric urania at room temperature increases with increasing density. When the volume fraction porosity is less than 0.1, either linear or exponential equations can he used to calculate the elastic modulus as a function of density. When the volume fraction porosity is more than 0.1, a linear equation seems to be more suitable. The elastic modulus of stoichiometric nonporous uranium oxide at room temperature was found, by extrapolation, to be 2243.56 ± 22.1 kbars when the exponential equation was used, and 2233.85 ± 22.05 kbars when the linear expression was used. The internal friction of stoichiometric urania decreases sharply as the grains become larger. The number, size, and position of pores may also affect the internal friction values.     

Behavior of silicon carbide/cordierite composite material after cyclic thermal shock

In the present work Mg-exchanged zeolite and silicon carbide were used as starting materials for obtaining cordierite/SiC composite ceramics with weight ratio 30:70. Samples were exposed to the water quench test from 950 °C, applying various number of thermal cycles (shocks). Level of surface deterioration before and during quenching was monitored by image analysis. Ultrasonic measurements were used as non-destructive quantification of thermal shock damage in refractory specimens. When refractory samples are subjected to the rapid temperature changes crack nucleation and propagation occurs resulting in loss of strength and materials degradation. The formation of cracks decreases the density and elastic properties of material. Therefore by measuring these properties one can directly monitor the development of thermal shock damage level. Dynamic Young's modulus of elasticity and strength degradation were calculated using measured values. Level of degradation of the samples was monitored before and during testing using Image Pro Plus program for image analysis. The capability of non-destructive test methods such as: ultrasonic velocity technique and image analysis for simple, and reliable non-destructive characterization are presented.     

Thermal-Shock Damage in SiC

Two silicon carbides with different fracture surface energies were subjected to increasingly severe thermal shock; the damage was monitored by changes in the specific damping capacity, elastic modulus, and fracture strength. The fracture strength followed predicted trends, but the strength losses did not correlate with the changes observed in damping and modulus. The differences in thermal-shock resistance of the materials were related to the fracture surface energy; the body with the higher fracture energy had superior resistance to thermal-shock damage.     

Mechanical Properties of Mullite–Corundum Composites Prepared from Bauxite

Mullite–corundum composites have been prepared by reaction sintering of Indian bauxite having considerable amount of impurities and silica sol. The effect of changing mullite phase proportion on the mechanical properties (i.e., flexural strength, elastic modulus, hot modulus of rupture, thermal shock resistance) of prepared composites has been studied. Flexural strength and elastic modulus increase with increasing free corundum phase content in the composites. Hot modulus of rupture for the sample containing only mullite phase increases with increasing test temperature over entire temperature range. Theoretical thermal shock resistance parameters R and R? are well supported by experimental thermal shock data.     

Thermal Shock Behavior of Open-Cell Ceramic Foams

Specimens of heated, open-cell ceramics were thermally shocked by immersion in water or oil. It was found the strength retained after thermal shock underwent a gradual decrease with increasing quench temperature, indicative of a cumulative damage mechanism which manifests itself with increasing thermal stress. This damage could also be monitored using measurements of the elastic constants before and after quenching. The thermal shock resistance of the open-cell materials was found to be strongly dependent on cell size (increased with increasing cell size) and weakly dependent on density (increased with increasing density). Two possible sources of thermal stress were considered; one was associated with the temperature gradient across the microscopic struts and the other with the heating of the quenching medium as it infiltrates the cellular structure. Such heating was confirmed and it was concluded that this was the dominant source of thermal stress in this particular study, controlling the thermal stress in this particular study, controlling the thermal shock resistance of the open-cell ceramics.     

Influence of firing temperature on correlation between thermal shock and mechanical impact resistance of refractory castables

Abstract

Three refractory castables used in the aluminium industry were investigated to establish correlations, which can be applied in practice, among the relevant properties important for performance in service. To determine the influence of firing temperature on the correlations, samples were fired at 1200 and 1450°C followed by mechanical impact (at 900°C) and thermal shock tests (quenched from 950°C into water). The relevant properties were evaluated including modulus of rupture, elastic modulus, work of fracture, and thermal expansion coefficient. The results show that there is a positive correlation between thermal shock and the mechanical impact resistance as well as with the σ_o R_st parameter at 1200°C. Two other positive correlations were established at 1450°C, the first involving mechanical impact resistance, modulus of rupture, and σ_o R_st , and the second between thermal shock resistance and the R′′′′ and R_st parameters.     

膏体充填材料变形性能的研究

经试验研究寻找出膏体充填材料力学参数单轴抗压强度、弹性模量、内摩擦角、内聚力与养护龄期、胶结料用量、粉煤灰用量等因素之间的影响规律以及抗压强度与弹性模量之间的关系.研究成果对不同煤矿工艺要求设计合理材料配比具有一定参考.该研究成果在河南煤化集团朱村煤矿充填项目中得以应用验证.     

Elevated temperature strength and thermal shock behavior of hot-pressed carbon fiber reinforced TiC composites

In order to improve the elevated strength and thermal shock resistance of TiC materials, 20vol% short carbon fiber-reinforced TiC composite (C_f/TiC) was produced by hot pressing. With carbon fiber addition, the strength and fracture toughness of TiC is increased remarkably, and the elastic modulus and thermal expansion coefficient are decreased. The strength value of C_f/TiC composite is 593 MPa at room temperature and 439 MPa at 1400°C, and the fracture toughness value at room temperature is 6.87 MPa m^1/2. The thermal stress fracture resistance parameter, R, thermal stress damage resistance parameter, R^IV, and thermal stress crack stability parameter, R_st, are all increased. The residual strength decreases significantly when the thermal shock temperature difference, ΔT, is higher than 900°C, and the residual strength is 252 MPa when ΔT is 1400°C. Carbon fiber reinforced-TiC composite exhibits superior resistance to thermal shock damage compared with monolithic TiC. The catastrophic failure induced by severe thermal stresses can be prevented in C_f/TiC composite.