NZP族磷酸盐材料研究进展

NZP族精细磷酸盐材料是一类具有相同晶体结构特征但化学组成各异的结晶化合物粉体及其陶瓷烧结体。综述了NZP族磷酸盐化合物的晶体结构特征、合成方法、NZP族陶瓷的快离子导电性、离子取代性、低热膨胀特性及其应用领域。介绍了NZP族磷酸盐材料作为抗热震催化剂载体和新型介孔分子筛催化剂的研究进展。     

基于Lattice-Boltzmann方法的填充型复合导热材料的导热性能数值分析

陶瓷被广泛用作催化燃烧的催化剂载体。为及时将反应热导出,避免催化剂烧结、失活,需提高陶瓷导热能力。针对通过填充高导热性的金属或无机填料的方法制成的陶瓷复合导热材料,引入二维九速度不可压格子多相Lattice-Boltzmann模型,对构造的5种规则填充形状(圆形、正八边形、正六边形、正四边形和正三角形)的陶瓷基复合材料进行了完整的二维导热过程的数值分析。结果表明,在相同的填料和填充体积分数下,三角形填充的复合材料有效导热系数最大,填充形状愈趋近圆形则有效导热系数越小。同时模拟了各填充形状下,填充材料与基体材料的导热系数之比kp/km对复合材料有效导热系数的影响。研究结果表明,孤立的导热填料对于复合材料导热系数的提高作用是有限的,当kp/km增大到一定程度,有效导热系数不再明显增加。     

基于SLS的高强度低密石墨陶瓷复合隔热材料快速制备

本文率先利用选择性激光烧结技术快速制备了高强度石墨陶瓷复合隔热材料,重点研究了二次固化、真空压力浸渍、碳化和高温烧结等后处理工艺以及材料配方组成对其密度、抗压强度和导热系数的影响。研究发现加入适量的硅粉和可膨胀石墨可以对石墨陶瓷复合隔热材料的密度、抗压强度和导热系数进行调控,采取合适后处理工艺路线可以改变石墨陶瓷复合隔热材料的综合性能。最终实现了低密度(<1.2 g/cm^3)、高抗压强度(>10 MPa)、低的导热系数(<2 W/(m·K))和耐高温(>1650℃)等多个性能指标的统一,满足了工业应用需求。     

闪光法测定氧化铝陶瓷导热系数的不确定度评定

按照分析测试中测量不确定度及评定的方法程序,对利用闪光导热仪测定氧化铝陶瓷导热系数时重复测量、仪器读数、样品厚度测量、样品密度测量等引入的不确定度分量进行了评定,计算出氧化铝陶瓷导热系数的扩展不确定度。     

导热相复合陶瓷微波烧结传热模式数值分析

根据微波加热的特点,采用二维稳态导热数值分析法,建立了导热相复合陶瓷微波烧结的传热模式. 研究了导热相的浓度、导热相弥散分布状况、基质类型以及保温方式对复合陶瓷内部二维稳态温度场分布的影响,并设计了导热相SiC晶须复合TZP陶瓷的微波烧结致密化实验,对建立的复合陶瓷的微波烧结传热模式进行了验证. 结果表明：导热相复合陶瓷设计时宜选取具有高导热系数的基体,保持导热相有较高的浓度,使导热相均匀分布于基体中,且微波烧结传热宜采用合适的保温设施.     

SiC泡沫陶瓷/SiCp/Al混杂复合材料的导热性能

运用挤压铸造法制备了SiC泡沫陶瓷/SiC颗粒/Al混杂复合材料,研究了温度和SiC泡沫陶瓷体积分数对复合材料热膨胀的影响.结果表明:随着温度的升高,复合材料的热容逐渐增大,热扩散系数、导热系数逐渐减小.随着增强体SiC体积分数的增大,复合材料的热容线性下降,热扩散系数和导热系数均非线性减小.由于混杂复合材料具有独特的复式双连续结构,复合材料的导热系数大于130W/(m·℃).     

制备条件对NZP族磷酸盐粉体材料物性的影响

用化学共沉淀法配合高温煅烧合成了几种不同化学组成的NZP族磷酸盐粉体材料,从实验结果和对共沉淀反应过程的理论分析两方面入手,着重研究了反应体系的pH值与形成单相NZP族晶体化合物的关系,以及煅烧温度对NZP族粉体比表面积的影响规律.结果表明:控制液相反应过程的pH值=8.5有利于形成单相的NZP族晶体化合物,结晶形态完整的NZP族化合物的比表面积＜30m2/g,在低于晶化温度下煅烧则可以制备大比表面积的NZP族粉体.此外,本研究所合成的NZP族化合物在pH=3～9的水溶液体系中表面带负电荷.     

泡沫混凝土导热系数模型及参数修正

在Cheng-Vachon模型的基础上提出了一种针对由连续相和分散相组成的两相复合材料的新导热系数模型.通过引入一个新的参数,即分散相的修正体积含量来改进Cheng-Vachon模型不适用于分散相体积含量较大的缺点.使用新的导热系数模型预测泡沫混凝土的导热系数,与实验结果的对比表明,新的模型可以准确预测泡沫混凝土的导热系数.     

导热聚合物复合材料用填料研究进展

填充型导热聚合物复合材料因具有高热导率、价格低以及易于加工等优点,得到了广泛的应用,其导热系数的提高主要依靠其中添加的导热填料,包括金属类填料、碳类填料以及陶瓷类填料等。本文综述了不同填料对导热聚合物复合材料性能的影响,并介绍了导热填料的研究进展。     

激光闪光法测定耐火材料导热系数的原理与方法

依据激光闪光法测定导热系数的理论基础和物理模型,推导了计算导热系数所需的热扩散系数和比热容两个参数的计算公式,从而阐述了该方法的原理。以美国安特公司产FLASH—LINE-5000型热扩散系数测定仪为例,介绍了激光闪光法测定导热系数设备的主要组成,并简要说明了该设备的操作步骤及导热系数的计算方法。     

Glass reactive sintering as an alternative route for the synthesis of NZP glass–ceramics

The NZP-type crystal structure allows a large number of ionic substitutions which leads to ceramics with adjustable thermal expansion properties or interesting ionic conductivity. However, NZP is difficult to fabricate into monoliths because it requires both high temperatures and long sintering times. An alternative low temperature route to obtain a tungsten (IV) and tin (IV) containing NZP crystalline phase uses a process of glass reactive sintering of a phosphate glass. Using a microwave oven, a glass with the appropriate composition in the NaPO3–Sn(II)O–W(VI)O3 ternary diagram is prepared by a conventional melting and casting technique. After crushing, the glass powder is pressed at room temperature. The green pellet is cured during various times at temperatures where glass reactive sintering takes place. From XRD and DTA experiments, we have shown that different parameters influence the achievement of NZP phase. Consequently, specific conditions, such as (i) initial glass composition, (ii) equimolar quantities of SnO and WO3, (iii) glass particle size lower than 100 μm, and (iv) curing conducted under air, are required to obtain a glass–ceramic with a single crystalline phase with the NZP-type crystal structure.     

[NZP]陶瓷零膨胀性能的设计

研究了「ＮＺＰ」材料的零膨胀性能，并尝试对零膨胀的「ＮＺＰ」陶瓷作了设计，从晶体结构、原子复合、各向异性、显微结构和复合材料等方面提出了设计思路。     

细粒级掺杂石墨材料的制备及其出气特性的研究

通过球磨分散方法制备了细粒级掺杂石墨 ,采用SEM、EDX、TEM、XRD等手段分析了材料微观结构 ,并对其性能作了初步研究。研究表明 :当原始粉粒径小于 10 0nm时 ,材料具有高的热导率和优良的物理机械性能 (抗弯强度为 116MPa) ,与粗晶石墨材料相比 ,细晶石墨材料在电子束辐照前的出气性能与其基本相同。而辐照之后 ,细晶石墨材料释放的H2 、H2 O、CO ,特别是CO2 的量远远少于粗晶石墨材料释放的量     

[NZP]结构功能材料的性能

本文介绍了［ＮＺＰ］陶瓷的各向异性、力学性能、热膨胀行为、抗热震性、离子导电、离子交换、氧化还原和光学等性能，探讨［ＮＺＰ］材料在热负荷环境下的使用和作为隔热材料、固体电解质、抗辐射、催化载体、精密尺寸控制和高温光学窗口材料的应用前景．     

Thermal expansion studies on the Sodium Zirconium Phosphate family of compounds A1/2M2 (PO4)3: effect of interstitial and framework cations

Thermal expansion of the sodium zirconium phosphate (NZP) family of compounds A_1/2M₂(PO₄)₃ (A = Ca or Sr; M = Ti, Zr, Hf or Sn) has been measured in the temperature range 298–1273 K by high-temperature X-ray powder diffractometry. Some of the compounds in the series (calcium zirconium phosphate and calcium hafnium phosphate) display the typical thermal expansion behaviour of NZP compounds, namely expansion along the hexagonal c axis and contraction along the a axis. The other compounds, depending on their interstitial and framework composition, behave differently. The observed axial thermal expansion and contraction behaviour is explained on the basis of the crystal chemistry of the compounds. Low-expansion compounds in this series are identified and their expansion anisotropy examined. Infared spectra of the compounds are reported. Differential scanning calorimetry measurements on the tin compounds indicate the occurrence of a diffuse phase transformation at high temperatures.     

Encapsulation of heterovalent ions of two simulated high-level nuclear wastes and crystallization into single-phase NZP-based wasteforms

Preliminary data were obtained on the immobilization of various heterovalent ions present in the two selected high-level nuclear waste compositions. The entire set of ions present in the waste compositions were immobilized into sodium zirconium phosphate (NZP) structure. The waste loading was in the range 5–25%. The two types of wasteforms loaded with the simulated high-level waste compositions were characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopy. The difference in the compositions of the two simulated wastes was reflected in the waste loading percentage and the crystallization of the wasteforms into NZP structure. Up to 12% waste loading, single phase isostructural with NZP was obtained as a major product in the case of the first waste composition. An increase in the waste loading led to the segregation of ZrP₂O₇ as a secondary phase. With the second waste composition, an NZP-like phase was obtained as the major product even at 25% waste loading.     

NZP: A new family of low-thermal expansion materials

A new structural family of low-expansion materials known as NZP has been recently discovered and has generated great interest for wide-ranging applications such as fast ionic conductors, devices requiring good thermal shock resistance, hosts for nuclear wastes, catalyst supports in automobiles, etc. This family is derived from the prototype composition NaZr₂P₂O₁₂ in which various ionic substitutions can be made leading to numerous new compositions. The bulk thermal expansion of these materials varies from low negative to low positive values and can be controlled and tailored to suit the needs for specific applications. In general, most of the NZP members demonstrate an anisotropy in their lattice thermal expansions, which is the main cause of the low-thermal expansion behavior of these materials. In CaZr₄P₆O₂₄ and SrZr₄P₆O₂₄ an opposite anisotropy has been observed which has led to the development of near-zero expansion crystalline solution composition. On the basis of the coupled rotations of the polyhedral network formed by ZrO₆ octahedra and PO₄ tetrahedra, a crystal structure model to interpret and explain the thermal expansion behavior has been discussed.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

The thermal conductivity surface for mixtures of methane and ethane

A correlation is presented for the extensive series of thermal conductivity measurements of binary methane-ethane mixtures. The composition dependences of the thermal conductivity in the dilute-gas region, dense-gas and liquid region, and critical region are discussed. The average absolute percentage deviation of the thermal conductivity surface as a function of temperature, density, and composition, from the experimental data, is 1.60%.     

Molybdenum Fixation in Crystalline NZP Matrices

A possibility of fixation of molybdenum present in spent nuclear fuel in ceramic matrices with the structure of the NaZr₂(PO₄)₃ (NZP) type was studied. The crystallochemical features of molybdenum incorporation into various crystallographic NZP structures depending on the synthesis conditions were considered. New molybdate-phosphates of variable composition Na _1-x ZrMo_xO₁₂ (0 x 0.6), crystallizing in the NZP crystal type, were prepared and characterized by X-ray diffraction and IR spectroscopy. The synthesis conditions and the concentration and temperature fields of stability of molybdate-phosphates in the system Na₂O-ZrO₂-MoO₂-P₂O₅ were studied. The crystallographic parameters of single-phase samples were evaluated. The results obtained suggest that the basic factors of formation of chemically stable single-phase NZP ceramics incorporating MoO₄ ^{2 -} anions are the composition of wastes and oxidative synthesis conditions.