Electrical Conductivity of Mullite Ceramics

The electrical conductivity of a lab‐produced homogeneous mullite ceramic sintered at 1625°C for 10 h with low porosity was measured by impedance spectroscopy in the 0.01 Hz to 1MHz frequency range at temperatures between 300°C and 1400°C in air. The electrical conductivity of the mullite ceramic is low at 300°C (≈0.5 × 10^?9 Scm^?1), typical for a ceramic insulator. Up to ≈ 800°C, the conductivity only slightly increases (≈0.5 × 10^?6 Scm^?1 at 800°C) corresponding to a relatively low activation energy (0.68eV) of the process. Above ≈ 800°C, the temperature‐dependent increase in the electrical conductivity is higher (≈10^?5 Scm^?1 at 1400°C), which goes along with a higher activation energy (1.14 eV). The electrical conductivity of the mullite ceramic and its temperature‐dependence are compared with prior studies. The conductivity of polycrystalline mullite is found to lie in‐between those of the strong insulator α‐alumina and the excellent ion conductor Y‐doped zirconia. The electrical conductivity of the mullite ceramic in the low‐temperature field (< ≈800°C) is approximately one order of magnitude higher than that of the mullite single crystals. This difference is essentially attributed to electronic grain‐boundary conductivity in the polycrystalline ceramic material. The electronic grain‐boundary conductivity may be triggered by defects at grain boundaries. At high temperatures, above ≈ 800°C, and up to 1400°C gradually increasing ionic oxygen conductivity dominates.     

High‐Temperature Electrical Conductivity of LaCr1−xCoxO3 Ceramics

LaCr_1?xCo_xO₃ solid‐solution ceramics (x = 0.0–0.3) were prepared by pressureless sintering of a submicrometer powder. The powder was synthesized by a modified glycine nitrate process at 800°C. The electrical conductivity of the material sintered at 1600°C was measured by AC four‐wire method from room temperature to 1200°C. While undoped (x = 0) LaCrO₃ revealed semiconductivity dominated by thermally activated mobility of small polarons over a vast temperature range, substitution of Co for Cr gave rise for a pronounced enhancement of conductivity at temperatures >200°C. XPS analysis showed that the concentration of Cr⁴⁺ on the Cr‐site and Co²⁺ at the Co‐site increased with Co substitution suggesting a thermally activated redox reaction Cr³⁺ + Co³⁺→Cr⁴⁺ + Co²⁺ to create additional charge carriers. Thus, Co doping offers a high potential for designing the electrical conductivity making LaCr_1?xCo_xO₃ an interesting resistivity material for high temperature applications.     

Electrical Conductivity in Lead Zirconate-Titanate Ceramics

Electrical conductivity was investigated in polycrystalline lead zirconate-titanate ceramics, with and without various dopants and stoichiometry, fabricated from chemical solutions and mixed-oxide powders. A multiphase packing-powder technique was used to control the stoichiometry of the system during sintering. The dc resistivity was measured by using a guard-ring method. Electrical conduction follows typical semiconductor behavior. Thermoelectric power measurements showed that hole conduction was dominant. Impurity ions which can serve as acceptors or donors significantly affect the conduction process. For undoped PZT the activation energy was 3.6 eV from 650° to 800°C and 1.4 eV at <650°C.     

Dielectric and Electrical Conductivity Properties of PMS–PZT Ceramics

The dielectric and electrical conductivity properties of x Pb(Mn_1/3Sb_2/3)O₃–(1− x )Pb(Zr_0.52Ti_0.48)O₃ (PMS–PZT) ceramics were studied. X-ray diffraction indicated that all samples exhibit a single-phase perovskite structure. Dielectric study revealed that the dielectric relaxor behavior was induced by co-doping Mn²⁺ and Sb⁵⁺ into Pb(Zr_0.52Ti_0.48)O₃ ceramics. Electrical conductivity measurements showed that the concentration of carriers are increased with the increase in PMS contents. After annealing in an oxygen atmosphere for 30 h, the direct current conductivity of PMSZ15 was much lower than that of the as-sintered sample. The reason why this phenomenon occurs may be the reduction of oxygen-vacancy concentration.     

Electrical Conductivity of Cadmium Oxide—Antimony Oxide System Ceramics

The electrical conductivity of Cd₂Sb₂O_6.8 and Cd₆Sb₂O₁₀ semiconductive ceramics was examined from −78° to 1000°C under oxygen, nitrogen, argon, air, methane, and CO /CO₂ atmospheres. The existing form of excess CdO in the crystal lattice structure, the relationship between oxygen vacancies and the atmosphere, the conduction mechanism in different temperature regions, the associated defect structure, and phase-transition properties were analyzed. The activation energy and mobility of the carriers were calculated.     

Syntheses of Spinon Thermal Conductivity Materials in Sr–Cu–O System by Glass‐Ceramics Technique

We have synthesized spinon thermal conductivity materials in Sr–Cu–O system by glass‐ceramics technique. The materials are promising for active control of thermal energy in microelectronic devices because of high and anisotropic thermal conduction, its controllability, and electric insulation. Nevertheless, research on these materials has been limited to that concerning theoretical perspectives and investigation of physical properties using large single crystals. In this study, we adopt glass‐ceramics technique to synthesize these materials: We prepared melt‐quenched multicomponent oxides including SrO and CuO, and checked its glass‐forming ability and crystallization behaviors by heating. As a result, we have found that SrCuO₂ and Sr₁₄Cu₂₄O₄₁, known as the spinon thermal conductivity materials, are synthesized using SrO–CuO–?Li₂O–?Al₂O₃?–Ga₂O₃ system. This synthesis process for the system will provide practical application of the spinon thermal conductivity materials.     

Effect of Thermal Initiator Concentrations on the Structure and Optical Band Gaps of Polyvinylsilazane‐Derived SiOCN Ceramics

SiOCN ceramics are formed by the thermal decomposition of a polyvinylsilazane precursor in the presence of a dicumyl peroxide (DP) thermal initiator with different concentrations. The SiOCN ceramics pyrolyzed at 1000°C with different concentrations of DP are characterized with X‐ray diffraction, transmission electron microscope, electron paramagnetic resonance, and UV‐visible spectroscopy. We find that the structure and optical band gap of the SiOCN ceramics can be changed by altering the concentration of DP. There is a critical concentration, at which the structural and optical behavior varied in different ways as a function of the concentration of DP. The detailed mechanism is discussed.     

Thermal Conductivity of Very Porous Kaolin‐Based Ceramics

A clay‐based material exhibiting high pore volume fraction and low thermal conductivity suitable for thermal insulation is described. Starting with a commercial clay containing >75% kaolinite, foams were made by mixing in water and methyl cellulose as a surfactant then beating. After drying at 70°C, the pore volume fraction >94% remains almost constant for treatments up to 1150°C. In contrast, the phases constituting the solid skeleton evolve strongly with removal of surfactant, dehydroxylation of kaolinite, and formation of mullite. The latter leads to greater mechanical strength but also an increase in thermal conductivity. Thermal treatment of the kaolin foam at 1100°C yields a suitable compromise between low thermal conductivity of 0.054 W.(m.K)^?1 at room temperature with a compressive yield stress of 0.04 MPa. The radiation component in the effective thermal conductivity is <10% at 20°C increasing to >50% at 500°C.     

Simple Mathematical Model for the Electrical Conductivity of Highly Porous Ceramics

A novel approach has been proposed to describe the relationship between the conductivity and relative density of highly porous materials. As a first approximation, porous material was represented by a uniaxial string of spheres along the direction of the potential gradient. Then, a string of spheres was remodeled into a rotating body of sine-wave functions, f ( x ) = (1 + r ₀)/2 + [(1 – r ₀)/2] sin (π x / c ) for 0 ≤ x < c and f (π x ) = (1 + r ₀)/2 + [(1 – r ₀)/2] sin {π( x + 1 − 2 c )/(l − c )} for c ≤ x < 1, where the former represents the shape of a sphere, the latter that of the bottleneck between neighboring spheres, and r ₀ denotes the ratio of the minimum diameter at the bottleneck to the maximum diameter of the rotating body. It was shown that the calculated relationships reproduced the reported experimental results for the relationship between the porosity and conductivity of La_0.5Sr_0.5CoO₃, BaF₂, and (ZrO₂)_0.9(Y₂O₃)_0.1. The relative conductivity to the bulk material was close to zero at 45–60% relative density, which is the density of green wares. It steeply increased with an increase in the relative density and then gradually approached that of the bulk material.     

Fracture Resistance Behavior of High‐Thermal‐Conductivity Silicon Nitride Ceramics

Silicon nitride ceramics were prepared from a high‐purity silicon powder doped with 2 mol% Y₂O₃ and 5 mol% MgO as sintering additives via a route of sintering of reaction‐bonded silicon nitride (SRBSN). The materials sintered at 1900°C for 3, 6, 12, and 24 h had thermal conductivities of 109, 125, 146, and 154 W/m/K, and four‐point bending strengths of 786, 676, 608, and 505 MPa, respectively. The fracture toughness values, determined by the single‐edge‐precracked‐beam (SEPB) method, were 8.4, 8.6, 9.7, and 10.7 MPa m^1/2 for the materials sintered for 3, 6, 12, and 24 h, respectively, which were similar to the results measured by the chevron‐notched‐beam (CNB) test method. The materials sintered for longer times (12 and 24 h) showed stronger R‐curve behaviors over longer range of crack extension, in comparison with the materials sintered for shorter times (3 and 6 h).     

煤基聚苯胺复合材料的导电性能研究

以煤为基体，不外加质子酸掺杂，制备了煤基聚苯胺复合导电材料，研究了其在不同条件下的导电性能。并对煤基聚苯胺合成反应后的废液进行了回收测试与循环利用研究。结果表明，在压力0．2～1．0MPa时，煤基聚苯胺的电导率随着压力的增大而增大；在30～120℃时，煤基聚苯胺的电导率随着温度的升高而减小；随着在环境中放置时间不同，煤基聚苯胺的电导率会有不同程度的变化；煤基聚苯胺聚合反应后的废液可以进行回收利用。     

Flue Gas Desulfurization by a Powder‐Particle Spouted Bed

The powder‐particle spouted bed process is one of the semi‐dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO₂ removal by a powder‐particle spouted bed, the reaction term is included in one‐dimensional and streamtube models that were presented previously for spouted beds. Hydrated lime is used as the sorbent in this process. The predictions of the models are compared with some published experimental data and it is found that the developed models are valid. The results of two models are compared with each other and their various properties are evaluated. The effects of different operating conditions on SO₂ removal efficiency are also investigated and preferred operating conditions are discussed.     

PS／炭黑复合材料导电性能的研究

本文通过炭黑（简称ＣＢ）用量、加工工艺、温度对ＰＳ／ＣＢ复合材料导电性能影响的探讨、复合导电材料亚微观结构的观察，研究了ＰＳ／ＣＢ复合材料的导电性能。结果表明，随着ＣＢ含量的增加，材料的电阻率呈非线性下降，当ＣＢ的质量分数在１０％～４０％的范围内时，电阻率下降明显，在此含量范围以后，体积电阻率变化不大；材料的导电性能与加工工艺有关，溶剂法的导电性能比混炼法好；电阻率随温度的升高均有上升的趋势。由复合材料的亚微观结构表明，随着ＣＢ含量的增加，ＣＢ由分散的单个颗粒逐渐连结在一起，最后与ＰＳ形成了一种相互交错式的结构     

高聚物/炭黑复合材料导电性能的研究

本文介绍了炭黑（ＣＢ）对低密度聚乙烯（ＬＤＰＥ）、高密度聚乙烯（ＨＤＰＥ）、聚苯乙烯（ＰＳ）等高分子材料导电性能的影响,研究了其导电性能和导电机理,分析了不同导电体系中基体对炭黑临界值的影响。     

多层石墨烯/钢纤维复合砂浆导电性能研究

制备了多层石墨烯(MG)/钢纤维(SF)复合砂浆.利用四电极法测试复合砂浆的电阻率,研究了测试时间、MG和SF掺量、养护龄期和含水量对砂浆电阻率的影响,并通过扫描电镜观察多层石墨烯在砂浆中的微观形貌.结果表明:砂浆外通电流后,内部产生的极化效应导致测试电阻率随导电时间增长而增大,导电填料抗氧化性越强,极化效应越小;砂浆的电阻率随MG和SF掺量的变化出现了渗流现象,运用GEM理论拟合了单掺MG和SF砂浆的电导率与其掺量的关系;MG和SF的协同作用可以增加导电链条、提高导电能力,其中复掺SM比单掺MG电阻率降低21.7％～41.8％;养护龄期越长,砂浆导电能力越差;砂浆干燥状态下的电阻率比湿润状态增加了29％～199％,复掺不同导电填料或增加导电填料含量,都能降低含水量对电阻率的影响.     

3D Printing of a Robust Polyamide‐12‐Carbon Black Composite via Selective Laser Sintering: Thermal and Electrical Conductivity

The need for big volume powder materials in building mechanically robust sintered parts via selective laser sintering (SLS) has been observed considering the direction towards the future of mass fabrication. This work presents a facile approach of combining polyamide‐12 (PA12) and carbon black (CB) powders to be used in the SLS application. The study investigates the mixing consistency, mechanical property, and thermal stability changes of the resulting 3D printed material. Bulk resistivity is correlated with the amount of CB, showing consistency of carbon content in the sintered parts produced by the effective separate grains mixing method. 3D printed parts are built with 0, 1.5, 3, 5 and 10 wt% CB via SLS. Improvements are seen at 1.5 and 3 wt% CB with the blockage of crack growth by the CB particles on applied load. For concentrations greater than 3 wt%, mechanical properties degrade due to hindering of physical contact between PA12 particles caused by CB particles, thereby reducing the effectiveness of the sintering process. The CB/PA12 sintered parts exhibit enhanced thermal stability resulting in higher degradation temperatures than the neat PA12. Therefore, in this study, thermally and mechanically enhanced 3D printed CB/PA12 build parts via SLS are successfully demonstrated.     

VGCF填充PVDF/PMMA复合材料导电性能的研究

以气相生长碳纤维（VGCF）为导电填料,聚偏氟乙烯（PVDF）、聚甲基丙烯酸甲酯（PMMA）为基体制备复合型导电高分子材料。考察了填料用量、基体种类、配比以及PVDF结晶行为对复合材料导电性能的影响。结果表明,VGCF填充PMMA、PVDF、PVDF／PMMA（50／50）体系的渗滤阔值分别为5、4、3phr的填料用量。VGCF的加入会导致PVDF／PMMA体系发生微观相分离,而且VGCF会选择性富集在PVDF的非晶相中,所以PVDF／PMMA／VGCF体系的导电性呈现双重渗滤现象,该体系的体积电阻率不仅取决于富集相中VGCF的含量,而且还与PVDF相的连续性及其结晶行为密切相关。     

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

Pyrochlore oxides of A₂Zr₂O₇, where A represents trivalent rare‐earth elements, have a high electrical conductivity, which makes them suitable for applications as high‐temperature solid electrolytes. The influence of Gd and Yb cations co‐doping at the Nd site on structure and electrical conductivity of a pyrochlore oxide Nd₂Zr₂O₇ is investigated using X‐ray diffraction and impedance spectra measurements. Different zirconate ceramics of Nd₂Zr₂O₇, Nd_1.8Gd_0.2Zr₂O₇, Nd_1.8Gd_0.1Yb_0.1Zr₂O₇, Nd_1.4Gd_0.6Zr₂O₇ and Nd_1.4Gd_0.3Yb_0.3Zr₂O₇ are prepared by pressureless‐sintering method at 1,973 K for 10 h in air. Nd₂Zr₂O₇ doped with Gd and Yb cations at the Nd site exhibit a single phase of pyrochlore‐type structure. The measured values of the total conductivity obey the Arrhenius relation. Nd₂Zr₂O₇ and its doped zirconate ceramics are oxide‐ion conductors in the oxygen partial pressure range of 1.0 × 10^–4 to 1.0 atm at all test temperature levels. The total conductivity increases with reducing average ionic radii of A‐site rare‐earth cations. The dual Yb+Gd intermix doping causes a distinctly enhanced total conductivity as compared to unmodified Nd₂Zr₂O₇ and singly Gd‐doped zirconate ceramics. The highest total conductivity value obtained in this work is 1.02 × 10^–2 S cm × ¹ at 1,173 K for Nd_1.4Gd_0.3Yb_0.3Zr₂O₇ ceramic.     

Matrimid Aerogels by Temperature‐Controlled,Solution‐Based Crosslinking

This paper reports on a temperature‐controlled, solution‐based method to prepare diamine crosslinked Matrimid aerogels. Addition of a diamine to a preheated polymer solution resulted in a well‐dispersed solution, allowing formation of a homogeneous gel upon cooling. The gels (studied by FTIR and AFM) were dried by solvent extraction with supercritical CO₂. The resulting aerogels showed surface areas of approximately 150 m² · g^?1 and porosities of 0.66–0.69 mL · g^?1 with polymer domains and pore sizes of tens of nanometers. A room temperature‐prepared, inhomogeneous aerogel gave approximately 250 m² · g^?1 and 0.31 mL · g^?1 with meso‐ and micropores. SEM images of the aerogels show similar surface features as AFM images of the Matrimid solvent gels.