Thermo-mechanical properties of mullite ceramics: New data

Coefficients of elastic stiffnesses and thermal expansion of hot isostatically pressed, reaction-sintered and technical fused-mullite ceramics were measured between 100 and 1673 K in comparison with single crystal mullite employing resonant ultrasound spectroscopy and dilatometry, respectively. Additionally, chemical and phase compositions and the microstructure of the ceramics were studied using X-ray diffraction techniques and scanning electron microscopy. Our studies revealed that despite polycrystallinity and slight porosity of up to 1.6%, the elastic behavior of the hot isostatically pressed ceramics is near to ideal aggregate elastic properties of mullite single crystal, for example, their bulk moduli fit within 0.7% to B = 170.0 GPa of single crystal mullite. On the other hand, with B = 155 GPa, the reaction-sintered mullite behaves significantly softer. The difference can be explained with more tight grain to grain contacts in hot isostatically pressed ceramics as compared to reaction-sintered materials. The thermal expansion of both types of ceramics almost coincides with the corresponding averaged behavior of single crystal mullite. For example, between 573 and 1273 K, the volume expansion coefficients of all these materials are (18.0 ± 0.3)·10⁻⁶ K⁻¹. Obviously, the microstructural features are less important for the macroscopic thermal expansion. Due to heterogeneous microstructure and high α-alumina and zirconia contents, the corresponding properties of fused-mullite refractory deviate strongly from those of the other mullite materials.     

钛酸铝材料研究进展及应用

钛酸铝是一种优异的高熔点、低膨胀无机非金属材料。主要阐述了钛酸铝材料的微观结构，以及热分解、热膨胀及其影响因素。简述了钛酸铝材料的制备方法。讨论了合成的工艺条件及添加剂对钛酸铝材料性能的影响，并对其应用作了简单介绍。最后提出了改善钛酸铝材料性能的技术途径。     

Effects of holding time on structure and the properties of spodumene/mullite composite ceramics

In this paper, spodumene/mullite ceramics with good thermal shock resistance were prepared from spodumene, quartz, talc, and clay when the sintering temperature was 1270℃. In the sintering process, the effect of holding time on densification, mechanical properties, phase transformation, microstructure, and thermal shock resistance of the composite ceramics were investigated. The phase transition and microstructures of the ceramics were identified via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The interaction between holding time and bulk density was studied by response surface methodology. The result show that an appropriate holding time can improve the mechanical properties of spodumene/mullite ceramics. When the holding time was kept 90 min, the spodumene/mullite ceramics with the apparent porosity was .47%, the bulk density was 2.28 g/cm³, and bending strength was 63.46 MPa. Furthermore, since no cracks formed after 20 thermal shock cycles for the composite ceramics with a bending strength decreasing rate of 12.66%, it is revealed that spodumene/mullite ceramics exhibit good thermal shock resistance. Therefore, this study can provide beneficial guidance for both industrial production and energy conservation.     

添加线胀材料对瓷器坯体抗热震性的影响

以锂辉石、堇青石、钛酸铝三种线胀系数较低的材料作为添加剂,单独或复合加入到普通瓷器坯料中,研究了加入不同比例的上述材料来降低陶瓷坯料线胀系数、提高产品抗热震性的可行性。     

Sintering and characterization of aluminum titanate ceramics with enhanced thermomechanical properties

Aluminum titanate (Al₂TiO₅) was synthesized from Al₂O₃-TiO₂ system by solid-phase reaction with additives of light magnesium carbonate and SiO₂, incorporating with silicon carbide (SiC) particle. The influence of additives on the phase composition, microstructure configuration, sintering, and thermomechanical properties of the developed materials was investigated. The experimental results illustrated that the utilization of additives with applicable contents was conducive to the development of complex microstructures. The microstructures characterized by microcracks matrix together with interlocked grains were identified. The samples incorporating SiC and SiO₂ simultaneously displayed exceptional densification properties and microstructure as a result of a SiO₂ liquid phase accelerating SiC oxidation. Meanwhile, high flexural strength (41.51 MPa) and low thermal expansion coefficient of 0.485 × 10⁻⁶ K⁻¹ (RT-1000 °C) were detected, encouraging refractory applications with high thermomechanical solicitations.     

环保型Ca/Zn复合热稳定剂的研究现状和发展方向

重点阐述了国内外PVC用环保型Ca/Zn复合稳定剂的研究现状及发展方向。     

PVC水滑石类热稳定剂研究进展

水滑石(LDHs)是一种新型的热稳定剂,其特殊的化学组成决定了其对HCl具有吸收作用,而且其特殊的层状结构可以对其进行层间有机阴离子嵌入改性。将其用于聚合物PVC中,可以起到阻止PVC热分解的作用。文中综述了水滑石稳定剂的制备﹑性能和稳定机理。     

一种Ca/Zn/Sn复合稳定剂及其性能的研究

对一种Ca/Zn/Sn复合稳定剂及其性能进行了研究。Sn和Ca/Zn复合,不仅改善了PVC树脂色泽稳定性,而且提高了其热稳定性。实验表明该稳定剂具有优良的热稳定性和加工性能。     

无毒PVC热稳定剂的研究现状与发展趋势

介绍了PVC的热分解机理及热稳定剂的作用机理。综合分析了PVC热稳定剂的种类和技术现状，指出不舍重金属的水滑石类，稀土类及复合型热稳定剂将成为未来的主导品种。     

钙/锌复合稳定剂对PVC热稳定性能与耐候性能影响的研究

研究了钙/锌复合稳定剂对PVC热稳定与耐候性能的影响。结果表明,流变仪热分解时间试验能反映PVC加工过程中的长期热稳定性能;钙/锌复合稳定剂添加量达到一定数值时,对PVC热稳定性能与耐候性能的影响较小。此研究对稳定剂添加量的确定有指导意义。     

新型复合稳定剂在PVC-U制品中的应用

研究了新型复合稳定剂(XWP)对PVC-U制品性能的影响,分别探讨了材料的填料改性、热稳定性、力学性能。试验结果表明,该助剂除具有热稳定作用外,还具有很好的润滑性和偶联性。     

Dynamic mechanical properties of polystyrene–aluminum nitride composite

A composite of aluminum nitride (AlN) particles dispersed around polystyrene matrix particles was synthesized in this study. The purpose of using this microstructure is to improve the thermal properties of a polymer at a low filler content with a minimal increase in the dielectric constant of the polymer composite to meet the material requirements for electronic packaging. The dynamic mechanical properties of this type of polystyrene–AlN composite were investigated here. The experimental results indicate that the dynamic mechanical property of the polystyrene–AlN composite is a function of the polystyrene particle size, AlN filler concentration, and temperature under this dispersion state. The addition of an AlN concentration into polystyrene increases both the storage modulus and the α‐transition temperature. The smaller polystyrene particle size gives a higher storage modulus and damping peak. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1348–1353, 2000     

复合稳定剂的种类及配方对流变性能的影响

研究了复合稳定剂的种类及配方对流变性能的影响。在聚氯乙烯硬制品加工中,改变复合稳定剂种类及生产厂家后,必须根据复合稳定剂的特点进行相应的配方调整,才能使改变前后的流变曲线重合。     

添加钾长石对镁掺杂钛酸铝陶瓷烧结及热膨胀行为和抗弯强度的影响

以镁掺杂钛酸铝固溶体粉体为原料,钾长石为烧结助剂制备了具有较高强度的低膨胀钛酸铝陶瓷.用场发射扫描电子显微镜观察了钛酸铝陶瓷断口形貌,并测量了陶瓷的烧结密度、抗弯强度和热膨胀曲线,研究了钾长石的引入量对钛酸铝陶瓷的烧结行为、微观结构、力学性能和热膨胀行为的影响.结果表明:钾长石的引入促进了镁掺杂钛酸铝陶瓷的烧结.引入8...     

不同沸石在聚氯乙烯用钙锌复合稳定剂中的应用

采用转矩流变仪和老化试验箱等设备,研究不同种类、不同沸石含量的钙锌复合热稳定剂对PVC体系静态热稳定性和流变性能的影响。结果表明:在钙锌复合热稳定剂中,3种沸石的热稳定性能为沸石A>沸石C>沸石B;当沸石A用量达到14份时,PVC体系的静态热稳定时间超过100min,动态热稳定时间超过20min,此时体系具有较好的协同稳定作用。     

Mechanical and thermal properties of h-BN based composite containing dual glass phases at elevated temperatures

High-temperature mechanical and thermal properties of h-BN based composite containing amorphous silica and Yb-riched silicate glass phases were systematically investigated in this work. Owing to anisotropic microstructure of h-BN matrix, the obtained composite demonstrates anisotropic mechanical and thermal properties. The composite possesses higher elastic modulus at 1673?K than that at room temperature and presents excellent high-temperature stiffness. Flexural strengths in parallel and perpendicular directions reach 496?±?22 and 258?±?21?MPa at?1073?K, respectively, and increases by 74 and 66% compared with the room-temperature strengths of 285?±?4?and 155?±?5?MPa. The composite containing dual glass phases shows lower coefficients of thermal expansion in the temperature range of 473–900?K, the values are ?1.4?×?10^?6 and 0.3?×?10^?6 ?K^?1 for the perpendicular and parallel directions, respectively. Thermal conductivities in the perpendicular and parallel directions at 373?K are 24.8 and 14.8?W?m^?1?K^?1, respectively, and then decrease to 14.9 and 9.3?W?m^?1?K^?1 at 1473?K.     

Thermal properties of strained thermoplastic polymers

Injection moulded tensile bars of several amorphous and semi-crystalline thermoplastic polymers have been deformed uniaxially to a macroscopic strain of 40% so that they showed necked and unnecked regions. From both the necked and unnecked regions of the tensile bars the specific heat and the thermal expansion coefficient were measured. The specific heat of the necked regions decreases about 20% with respect to unstrained samples for semi-crystalline polymers at temperatures between 40°C and 60°C and for amorphous polymers at temperatures between 50°C and 70°C. The thermal expansion coefficient becomes negative at these temperatures. A smaller negative expansion coefficient is observed even in the unnecked region although nearly no change in specific heat can be observed. There is also an increase in the heat of fusion of the semi-crystalline specimens of the necked region. Strain rate dependent effects on specific heat and thermal expansion were not observed within the accuracy of thermal analysis.     

Thermal properties of alkali‐activated aluminosilicate composite with lightweight aggregates at elevated temperatures

Thermal diffusivity, specific heat capacity and linear thermal expansion coefficient of a lightweight composite with alkali‐activated aluminosilicate binder and heat‐resistant aggregate mixture of expanded vermiculite and electrical porcelain are measured in a wide temperature range. Experimental results show that the studied material has good prerequisites for high‐temperature applications. The apparent thermal diffusivity at one‐sided heating is significantly lower than at room temperature, and decreases for temperatures higher than 400^°C. The effective specific heat capacity at elevated temperatures increases with temperature in almost the whole analyzed temperature range. The linear thermal expansion coefficient is substantially lower compared with common cement‐based composites. Copyright © 2010 John Wiley & Sons, Ltd.     

Yb2O3-Gd2O3 codoped strontium zirconate composite ceramics for potential thermal barrier coating applications

Strontium zirconate (SrZrO₃) has been considered as a promising thermal barrier coating (TBC) material for application in gas turbine engines; however, the phase transition problem limits its application. In this study, an Yb₂O₃ and Gd₂O₃ codoped SrZrO₃ system with excellent properties was reported. Yb₂O₃-Gd₂O₃ codoped SrZrO₃ ceramic powders [Sr_0.8(Zr_0.9Yb_0.05Gd_0.05)O_2.75, SZYG/YGZO], [Sr(Zr_0.9Yb_0.05Gd_0.05)O_2.95, SZYG] and pure SrZrO₃ (SZO) powders were produced by a conventional solid-state reaction method. The XRD and Raman results show that, the composite SZYG/YGZO ceramics consist of the SZO and Yb_0.5Zr_0.5O_1.75 phases with a low thermal conductivity of ~1.3 W/(m·K) at 1000°C, which is at least 40% lower than that of the SZO ceramics. The TG-DSC results show that the SZYG/YGZO ceramics have no phase transition in the temperature range of 600 to 1400°C. The thermal expansion coefficient of the SZYG/YGZO ceramics reaches 10.9 × 10⁻⁶ K⁻¹ (1250°C). In addition, the fracture toughness of the SZYG/YGZO ceramics increases by more than 30% compared with the SZO ceramics, and this can be attributed to the presence of the Yb_0.5Zr_0.5O_1.75 phase.     

The effect of boron nitride nanosheets on the mechanical and thermal properties of aluminum nitride ceramics

The boron nitride nanosheets (BNNSs)/aluminum nitride (AlN) composites were prepared by hot press sintering at 1600°C. The microstructure, mechanical properties, and thermal conductivity of the samples were measured, and the effect of adding BNNSs to AlN ceramics on the properties was studied. It is found that the addition of BNNSs can effectively improve the mechanical properties of AlN. When the additional amount is 1 wt%, the bending strength of the sample reaches the maximum value of 456.6 MPa, which is 23.1% higher than that of the AlN sample without BNNSs. The fracture toughness of the sample is 4.47 MPa m^1/2, a 68.7% improvement over the sample without BNNSs. The composites obtained in the experiment have brilliant mechanical properties.