不同粒度红柱石对矾土基喷涂料性能的影响

以矾土为主要原料,铝酸钙水泥、硅微粉为结合系统,分别研究了不同粒度的红柱石对矾土基喷涂料性能的影响。试样自然干燥24h脱模,再经110℃烘干24h,分别于1000℃、1300℃和1500℃热处理3h。检测各温度热处理后试样的线变化率、体积密度、常温抗折强度、常温耐压强度以及试样的热膨胀系数、耐磨性能和抗热震性能。结果表明,添加粗粒度的红柱石并不能有效弥补矾土基喷涂料经高温热处理产生的收缩。矾土基喷涂料的体积密度随着红柱石粒度的增大而增大。不同粒度的红柱石未对矾土基喷涂料的中温强度产生明显影响,粗粒度的红柱石可以提高矾土基喷涂料的高温强度。矾土基喷涂料的耐磨性能随着红柱石粒度的增大而提高。细粒度的红柱石有利于改善矾土基喷涂料的抗热震性能。     

水泥窑用低水泥浇注料性能的研究

以矾土为主要原料,铝酸钙水泥和硅微粉为结合系统,研究了不同热处理温度对水泥窑用低水泥浇注料性能的影响。试样自然干燥24h脱模后,再经110℃烘干24h,分别于300℃、500℃、700℃、900℃、1100℃、1300℃和1500℃热处理3h。检测各温度热处理后试样的体积密度(B.D)、线变化率(P.L.C)、常温抗折强度(M.O.R)、常温耐压强度(C.C.S)、常温耐磨性能以及试样的热膨胀系数和抗热震性能。结果表明,随着热处理温度的提高,水泥窑用低水泥浇注料的体积密度呈现先减小后不变再增大的变化规律;线变化率呈现收缩先增大后减小再增大的变化规律;常温抗折强度和常温耐压强度呈现先增大后减小再增大的变化规律。水泥窑用低水泥浇注料经过1500℃热处理后的磨损量小于经过1300℃热处理后的磨损量。水泥窑用低水泥浇注料具有相对优良的抗热震性能。     

堇青石对莫来石-铝矾土浇注料性能的影响

以莫来石、铝矾土为主要原料,铝酸钙水泥为结合系统,分别研究了不同堇青石含量经过不同热处理温度后对莫来石-铝矾土浇注料性能的影响.试样自然干燥24 h脱模后,再经110 ℃烘干24 h,分别于1000 ℃、1300 ℃和1500 ℃热处理3 h.检测各温度热处理后试样的线变化率(P.L.C)、体积密度(B.D)、抗折强度(M.O.R)、耐压强度(C.C.S)以及试样的热膨胀系数和抗热震性能.结果表明,莫来石-铝矾土浇注料的体积密度随着堇青石含量的增加而减小.经过1000 ℃和1300 ℃热处理后,莫来石-铝矾土浇注料的抗折强度随着堇青石含量的增加而下降.莫来石-铝矾土浇注料随着堇青石含量的增加,有助于改善材料的抗热震性,材料的强度保持率逐渐增大,且较低的体积密度有利于材料获得较高的热震后的强度保持率.     

Repeated thermal shock behavior of ZrB2-SiC-graphite composite under prestress

The thermal shock resistance of ZrB₂-SiC-graphite composite under nominal prestress of 0, 20, 30, 40 or 50 MPa after subjected to 10 and 30 cycles of thermal shock was evaluated by measuring the residual flexural strength of the tested specimen. In each test the applied prestress kept constant and in each cycle the specimen center was heated to 2000 °C within 5 s through electrical resistance heating method and cooled down naturally to room temperature. A lot of broken SiO₂ bubbles in the tested specimens were observed with a SEM. For the specimen subjected to 10 cycles of thermal shock, the residual flexural strength does not show big change under different levels of prestress, although the thickness of oxide layer increases at larger prestress, which is presumably attributed to the effect of the oxide layer that heals the cracks and the pores and enhances the strength. For the specimen subjected to 30 cycles of thermal shock, the residual strength decreases, in general, with the increase of prestress level. The thermal shock fatigue under different levels of prestress was also tested, and it was found that the increase of prestress may speed the failure of the specimen, indicating that the level of prestress may fatally affect the failure of the material.     

Cr2O3对矾土基喷涂料性能的影响

以铝矾土为主要原料,铝酸钙水泥、硅微粉为结合系统,分别研究了不同添加量的Cr2O3对矾土基喷涂料性能的影响。试样自然干燥24h脱模后,再经110℃烘干24h,分别于1000℃、1300℃和1500℃热处理3h。检测各温度热处理后试样的线变化率、体积密度、抗折强度、耐压强度以及试样的热膨胀系数、耐磨性能和抗热震性能。结果表明,在矾土基喷涂料中添加Cr2O3不利于提高材料的低温和中温强度,但利于提高材料的高温强度;在矾土基喷涂料中添加Cr2O3不能提高材料的耐磨性能;试样中添加Cr2O3后增大了试样的热膨胀系数。添加适量的Cr2O3可提高试样的抗热震性能;过量的添加Cr2O3会对试样的抗热震性产生负面的影响。     

热处理工艺对纳米氧化锆粉体微观结构与涂层性能的影响

研究了高温煅烧、等离子炬和等离子流场3种热处理工艺对ZrO2-8%(mol)Y2O3 (8YSZ)球形颗粒及其等离子喷涂涂层微观组织结构的影响. 结果表明,由等离子炬处理后的8YSZ颗粒制备的等离子喷涂涂层的结合强度最高,平均为25 MPa,抗热震性能最好,1200℃恒温5 min,水冷、热循环达41次;而采用等离子流场处理的颗粒所制涂层结合强度最差,平均为11 MPa,热震时涂层易开裂,热循环次数为17次;高温煅烧的颗粒所制涂层性能依赖于煅烧温度和时间,其中1200℃下煅烧2 h的颗粒所制涂层力学性能最优,平均结合强度为21 MPa,热循环次数为38次.     

Sintering behavior and thermal shock resistance of aluminum titanate (Al2TiO5)-toughened MgO-based ceramics

In order to improve the thermal shock resistance of MgO-based ceramics, aluminum titanate (Al₂TiO₅)-toughened MgO-based ceramics were successfully prepared by solid state sintering at 1450 °C and 1550 °C for 3 h starting from MgO and as-synthesized Al₂TiO₅ powders. The effects of various contents of Al₂TiO₅ second phase on the sintering behavior and thermal shock resistance of MgO-based ceramics were investigated. The sintering behavior of sintered samples was evaluated by comparing the relative density, apparent porosity, bending strength, phase composition as well as microstructure. The thermal shock resistance of sintered samples was characterized by using the residual bending strength after three thermal cycles and thermal expansion coefficient. The obtained samples with 10 wt% Al₂TiO₅, which were sintered at 1550 °C for 3 h, showed the highest relative density, lowest apparent porosity as well as optimum bending strength. In addition, the samples added 15 wt% Al₂TiO₅ at 1550 °C with a dwell time of 3 h were the highest residual bending strength and lowest thermal expansion coefficient. It revealed that the enhancement in thermal shock resistance was ascribed to the reduction of thermal expansion coefficient.     

Thermal shock resistance and hoop strength of triplex silicon carbide composite tubes

Multi‐layered SiC composites have been considered as a nuclear fuel cladding material of light water reactors, LWRs, because of their excellent high temperature strength and corrosion resistance under accident conditions. During a design basis accident of a LWR such as a loss‐of‐coolant accident, the peak temperature of the fuel clad rapidly increases as the production of decay heat continues. The emergency core cooling systems then automatically supply the reactor core with emergency cooling water. The fuel clad consequently suffers from thermal shock. In this study, the structural integrity of multi‐layered SiC composite tubes after thermal shock was investigated. Several kinds of multi‐layered SiC composite tubes consisting of CVD SiC and CVI SiC_f/SiC were water‐quenched from 1200°C to room temperature. The triplex SiC composite tube retained its tubular geometry during quenching. The strength degradation after thermal shock was <13% for the specimens with a PyC interphase. The residual stress distribution within the tubes during thermal shock was evaluated by a finite element method.     

Strength and thermal shock resistance of fiber-bonded Si-Al-C-O and Si-Ti-C-O ceramics

Silicon carbide-based fiber-bonded ceramics, obtained from hot pressing of woven silicon carbide fibers, are a cost-effective alternative to ceramic-matrix composites due to their ease of fabrication, involving few processing steps, and competitive thermomechanical properties. In this work, we studied the high-temperature strength and thermal shock resistance of Si-Al-C-O and Si-Ti-C-O fiber-bonded SiC ceramics obtained from hot pressing of two types of ceramic fibers, by mechanical testing in four-point bending. The bending strength of Si-Al-C-O-based fiber-bonded ceramics at room temperature is ∼250–260 MPa and remains constant with temperature, while the bending strength of Si-Ti-C-O increases slightly from the initial 220 to ∼250 MPa for the highest temperature. Both materials retain up to 90% of their room temperature strength after thermal shocks of 1400°C and show no reduction in elastic moduli. After thermal shock, failure mode is the same as in the case of as-received materials.     

Mechanism for abnormal thermal shock behavior of Cr2AlC

Some MAX phases exhibit abnormal thermal shock behavior, i.e. the residual strength of as-quenched MAX phases decreases gradually with increasing quenching temperatures and then unbelievably increases after quenching from even higher temperatures. To date, the abnormal thermal shock behavior has been found in some MAX ceramics for about 17 years and has resisted interpretation. Herein Cr₂AlC as a representative member of the MAX phases is chosen to investigate such unique behavior. Thermal shock tests show that the abnormal thermal shock phenomenon for Cr₂AlC occurs at above 1200 °C. The main mechanism for this phenomenon is that the thermal shock induced cracks are instantly healed by the formation of reactants well adhering to the crack faces during quenching. The mechanism demonstrated here can be applied to other materials with the abnormal thermal shock behavior. Such materials may find applications in environments where temperature changes abruptly.     

Effect of Crystallites on Thermal Shock Resistance of Cordierite Glass-Ceramics

Thermal shock behavior was compared for a cordierite glass and glass-ceramics subjected to a water quench. Crystallization significantly increases the critical quenching temperature difference (ΔT_c); this effect was attributed to enhanced strength and thermal conductivity offset by a corresponding increase in Young's modulus. The strength retained following thermal shock also increased significantly on crystallization for ΔT>ΔTC, probably as the result of stepwise increases in fracture toughness with increasing crack size of the glass-ceramic.     

热震条件下Al2O3-O’-SiAlON-SiC复合材料氧化行为研究

以板状刚玉(骨料和细粉)、α-Al₂O₃微粉和硅粉等为原料,在1 500 ℃下埋炭保温3 h烧结制备了Al₂O₃-O’-SiAlON-SiC复合材料。研究了热震及不同热震次数对复合材料氧化行为的影响。研究结果表明:在无热震和热震条件下,试样氧化增重率在900~1 300 ℃均随温度升高而增加;热震氧化条件下的增重率大于无热震条件,且随热震次数增加,氧化增重率略有增加。无热震条件下,试样恒温氧化曲线类似于抛物线型,而热震条件下,试样氧化曲线接近直线型。因此,热震明显促进了复合材料的氧化,其原因在于热震使试样表面的氧化保护膜破裂,试样产生微裂纹,为氧气进入试样内部提供通道,进而加速材料氧化。     

粉煤灰细粉添加量对多孔莫来石材料的影响

为了提高粉煤灰的资源化利用,在m(漂珠):m(氢氧化铝):m(V2O5):m(AlF3)=45:55:4:3的混合料中分别添加不同量(每100 g混合料分别添加0、5、10、20、30 g)的粉煤灰细粉,以PVA溶液为结合剂,经干料混匀、泥料搅拌、泥料陈腐、挤制成型、1100℃保温2 h烧成制备莫来石试样,然后检测其致...     

ZrO2-AlN复相材料的制备与性能研究

试样以部分稳定氧化锆（PSZ）和金属Al粉为原料。在N5气氛下经1600℃×4h烧结可制备出以AIN为结合相的ZrO2-AlN复相材料（ZAN）。试验研究了金属Al的氮化反应过程。以及金属Al的加入量对复相材料性能的影响。结果显示：Al粉反应生成AIN的全过程,主要由界面反应和内扩散反应交替完成．且整个反应过程应为扩散机制控制。随金属Al粉引入量的增加、ZAN试样的热膨胀系数减小,抗折强度增大,抗热震性及抗氧化性提高。ZAN-3试样的综合性能优良,其常温抗折强度为73．61MPa,热膨胀系数为6．06×10^-6/℃。室温～1100℃水冷残余抗折强度为4．64MPa。     

Effects of Damage on Thermal Shock Strength Behavior of Ceramics

When subjected to severe thermal shock, ceramics suffer strength degradation due to the damage caused by the shock. A fracture-damage analysis is presented to study the effects of damage on the thermal shock behavior of ceramics. It is assumed that a narrow strip damage zone is developed at the tip of a preexisting crack after a critical thermal shock and the damage behavior can be described by a linear strain-softening constitutive relation. Damage growth and strength degradation are determined based on fracture and damage mechanics. Numerical calculations are carried out for two ceramic materials, and the strength degradation agrees quite well with experimental results. The effects of bridging/damage stress, the fracture energy of the bridging/damage zone, and specimen size on thermal shock strength behavior are studied. A higher fracture energy can enhance the residual strength of thermally shocked ceramics and, for a given fracture energy, a higher bridging stress is needed to reduce the strength degradation. It is also shown that the thermal shock strength behavior is size-dependent, and a high value of ( K _IC/O_b)², where K _IC is the intrinsic fracture toughness and O_b is the bending strength, can improve significantly the residual strength.     

Preparation and Properties of Zirconia-Toughened Mullite Ceramics

Compacts formed from high-purity fused submicrometer mullite powders, both pure and with the additions of 5 to 25 vol% ZrO₂ of particle size 1, 2, or 4 μm (average), were sintered in air at 1610°C for 6 h to form dense ceramic bodies. Mechanical properties (flexural strength, K _ic, and Young's modulus) were measured both before and after thermal shock. The strength after thermal shock increased considerably in systems containing additions of 10 to 20 vol% ZrO₂; K _ic also increased, but not so markedly. The low fraction of tetragonal ZrO₂ (0.1 to 0.2) in the as-fired samples and the increase in Young's modulus after thermal shock for some strengthened samples supported the view that the interaction of residual internal stresses induced by quenching and the accompanying martensitic transformation of ZrO₂ result in potential nucleation sites for microcracking. Thus, microcracking may be the predominant energy-absorbing mechanism responsible for strengthening and toughening the quenched ceramic bodies.     

玄武岩纤维对高强灌浆料耐高温性能的影响

本文研究了不同掺量、不同长度短切玄武岩纤维对高强灌浆料耐高温性能的影响,主要对玄武岩纤维对高强灌浆料在不同受火温度及300℃热震处理后的强度损失、体积变化和质量变化等的影响进行了评价。结果表明:玄武岩纤维能够提高灌浆料不同温度受火处理后的强度比,特别是抗折强度比,并且能够减小受火后灌浆料的收缩和质量损失。在300℃热震处理的条件下,玄武岩纤维能够提高灌浆料的抗压强度比,并且大幅度减少因热震造成的膨胀。     

Effect of magnesium aluminum silicate glass on the thermal shock resistance of BN matrix composite ceramics

The effects of magnesium aluminum silicate (MAS) glass on the thermal shock resistance and the oxidation behavior of h‐BN matrix composites were systematically investigated at temperature differences from 600°C up to 1400°C. The retained strength rate of the composites rose with the increasing content of MAS showing a maximum value at the 60 wt% MAS. Compared with the original strength, the retained strength of the specimen after thermal shock increased to 77% (ΔT=1000°C). The strengthening effect of MAS and the surface microstructural evolution of composites are responsible for the improved thermal shock resistance. Surface oxidation of the composites during the thermal shock process plays a positive role in enhancing the retained strength by self‐healing cracks and the appearance of the compressive stress. The oxide layer also acted as a thermal barrier to decelerate the actual thermal stress. Furthermore, this dense layer also improved the oxidation resistance of h‐BN matrix composites by prevent diffusion of oxygen. These results indicated that short‐term surface oxidation during thermal shock process is favorable to the enhancement of the thermal shock resistance of BN‐MAS composite ceramics.     

Effect of MgO on thermal shock resistance of CaZrO3 ceramic

In order to improve the thermal shock resistance of CaZrO_3, CaZrO₃ was synthesized by a solid-state reaction method with analytical ZrO₂ and CaCO₃ as raw materials, and MgO as additive. The effects of MgO on Flexural strength at room temperature, thermal shock resistance, XRD and microstructure of CaZrO₃ were characterized. The results show that the grain growth of CaZrO₃ is inhibited and the thermal shock resistance of CaZrO₃ is improved by adding MgO. With the increasing of MgO, the flexural strength at room temperature of samples are improved due to the grain refinement. When the addition of MgO is 8%, the flexural strength at room temperature increases to 270.15?MPa. The thermal shock resistance of samples are improved by MgO deflecting and bridging cracks. When the addition of MgO is 4%, the residual flexural strength of samples is the maximum (26.94?MPa).     

Statistical Study of Thermal Shock Damage of a Borosilicate Glass

The statistical aspects of thermal shock damage were addressed by examining the strength distributions of quenched specimens. It was observed that slow crack growth effects were minor, and that severe damage commenced near K _Ic. The increased range of retained strengths observed after thermal shock occurs because the low-strength portion of the distribution experiences the initial thermal shock damage. Crack arrest in the damaged specimens, examined by an energy balance, indicated that a large number of surface flaws actively extend during the initial stages of thermal shock damage.