Synthesis of NiO-Deposited YSZ Composite Powders by Urea Hydrolysis

The urea hydrolysis method was used to prepare NiO-deposited YSZ composite powders. First, micrometer-sized YSZ particles were fabricated, and then the nanosized NiO particles were deposited on the surface of the YSZ particles. The microstructure of composite powders and the sintered bulk were further characterized with the aid of XRD, SEM, and TEM. The results indicated that the mesoporous and microsheet-like Ni(OH)₂· x H₂O ( x =0–1) crystals were deposited on the surface of YSZ particles. As the concentration of Ni²⁺ ion in the stock solution increased, the deposited NiO content and thickness of NiO layer on the YSZ particle surface also increased. In addition, the YSZ particle size showed significant influence on the microstructure and conductivity of Ni/YSZ cermet anode produced by NiO-deposited YSZ composite powders. Such NiO-deposited YSZ composite powders can be easily sintered to form a continuous NiO network.     

沉淀法制备纳米CuO及微结构控制

以Cu(NO3)2为铜源，分别用水，乙醇作为分散剂，NaOH,NaOH-Na2CO3作沉淀剂，采用液相沉淀法制备了CuO纳米晶粒，并用XRD，TEM等测试手段对产物的结构，晶粒大小和形貌等进行了表征，结果表明，产物的微结构与焙烧温度，分散剂和沉淀剂的种类有关。以水为分散剂，产物的形态是分散性良好的纺锤型，而以乙醇为分散剂，产物的形态是分散性较好的球型，同NaOH作沉淀上比，共沉淀法制备了产物粒径较小，但团聚较严重，此外，初步研究了不同微结构纳米CuO对氯酸铵（AP）的催化活性。     

Synthesis and Investigation of Solid Solutions Based on Indium Oxide in In<Subscript>2</Subscript>O<Subscript>3</Subscript>–MeO<Subscript>2</Subscript> (Me = Zr,Sn, Ti) Systems

Solid solutions in In₂O₃–MeO₂ (Me = Zr, Sn, Ti) systems based on indium oxide are synthesized by the coprecipitation method. It is found that the ultrasound treatment of the coprecipitation products reduces the degree of agglomeration of the initial particles by a factor of 3 and initiates the crystallization process of the precipitates. Nanocrystal (5–8 nm) precursor powders are obtained at 400°C. The optimal regime for sintering powders based on In₂O₃ to form a ceramic with a dense microstructure is chosen. The influence of the temperature, alloying additives, and the partial pressure of oxygen on the specific conductivity of indium oxide solid solutions is studied.     

Effect of Nano-ZrO2 on the Properties of Al-Al2O3 Nanocomposites Prepared by Mechanical Alloying

In the present work, mechanical alloying was used to prepare Al-20wt.% Al₂O₃ metal-matrix nanocomposites having up to 4wt.% ZrO₂ at the expense of Al₂O₃. The powders were milled for different time intervals. To characterize the powders after milling, x-ray diffraction and transmission electron microscopy were used to identify the phase composition, crystallite size and morphology. In order to study the sinterability, the milled powders were cold pressed and sintered in argon atmosphere at different firing temperatures up to 470 °C for 1 h. The relative density and apparent porosity of the sintered composites were determined according to Archimedes principle. Moreover, the microstructure was examined by a scanning electron microscope attached with an energy dispersive spectrometer (EDS). Microhardness and AC conductivity of sintered composites were also measured. The results pointed out that the increasing of milling time is responsible for uniform distribution of Al₂O₃-ZrO₂ particles in the Al matrix as well as remarkable increases in relative density, microhardness and AC conductivity of the sintered specimens. Also, the relative density was affected considerably by the increasing of sintering temperature. Moreover, increasing of ZrO₂ content led to a significant decrease in the crystal size of the milled powders and increase in the microhardness of the sintered compacts. No changes were observed on the conductivity after addition of ZrO₂.

     

Electromagnetic field effects in the microwave sintering of electrically conductive powders

Rapid sintering of compacted electrically conductive powders under heating by intense microwave radiation is investigated within a one-dimensional simulation model. The model accounts for the effective dielectric and magnetic properties of the powder material, electromagnetic field distribution, heat losses by thermal radiation, and densification. It is demonstrated that metal powders with insulating boundary layers on particles have low dielectric and magnetic losses, which results in a resonant character of microwave absorption. The influence of the interparticle contacts is investigated by introducing an effective electrical conductivity of the boundary layers, which can depend on the density. It is demonstrated that the losses in the boundary layers can stabilize the microwave heating process, facilitating rapid densification.     

Effects of initial α-phase content on properties of pressureless solid-state sintered SiC ceramics

α- and β-SiC starting powders of similar particle sizes were used to investigate the effect of initial α-phase content on the electrical, thermal, and mechanical properties of pressureless solid-state sintered (PSS) SiC ceramics with B₄C and C additives. For β-SiC starting powders, a coarse-grained microstructure with elongated platelet grains was formed by the transformation of 3C to 6H and finally to 4H-SiC phase. In contrast, materials prepared from α-SiC powders exhibited a fine-grained microstructure with platelet grains. This study revealed the beneficial effect of α-SiC starting powders in achieving low electrical resistivity and high thermal conductivity in PSS SiC ceramics, which was attributable to their higher sinterability, lower impurity content, and lower 6H to 4H-SiC phase transformation rate compared with β-SiC powders. The electrical resistivity decreased by an order of magnitude and the thermal conductivity increased by 32% with an increase in initial α-phase content from 0 to 100%. The flexural strength increased by approximately 16% with increasing initial α-phase content due to a decreased flaw size with decreasing grain size. However, the fracture toughness and hardness were insensitive to the change in initial α-phase content.     

Electrical and Thermal Conductivities of Nickel-Zirconia Cermets

The microstructure, electrical resistivity, and thermal diffusivity of nickel-zirconia cermets have been studied. Scanning electron microscopy of the fracture surfaces of samples shows that there are some small isolated nickel granules adhering to the surface of the zirconia particles. Considering such a microstructural feature of samples and the law of mixtures, an improved model for electrical and thermal conductivity is established. With this model, the experimental results-that electrical conductivity and thermal diffusivity increase with increasing nickel content-are interpreted. Moreover, the thermal diffusivity is observed to be almost linearly related to temperature.     

The microstructure and thermal conductivity of porous β-SiAlON ceramics fabricated by pressureless sintering with Y-α-SiAlON as the sintering additive

Porous β-SiAlON ceramics are fabricated by pressureless sintering with Y-α-SiAlON ceramic powders obtained by the combustion synthesis method as the main additives. The microstructure and composition of porous β-SiAlON ceramics are tailored by changing the addition of the synthesized Y-α-SiAlON ceramic powders. The formation mechanism of porous β-SiAlON ceramics illustrates that their bimodal grain size distributions are determined by the β-SiAlON seed crystals which are derived from the starting synthesized powders and the first precipitates in the liquid phase, respectively. A small addition of Y-α-SiAlON is conducive to the reduction of the thermal conductivity of porous β-SiAlON ceramics. Furthermore, the higher the addition of Y-α-SiAlON ceramics powders, the lower the open porosity, columnar grain size, and dielectric loss, but the larger the density, flexural strength, dielectric constant, and thermal conductivity.     

Gd2O3掺杂CeO2粉体的包覆处理

采用非均匀成核法成功地制备了Al2O3 qn stt gajftqd ffffrcd vs CeO2粉体。采用XRD分析了粉体的晶相；通过测定粉体的Zeta电位和XPS能谱。分析了Al2O3在稀土掺杂CeO2粉体表面的包覆情况。     

Ni包裹SiC对SiC(Ni)/Fe复合材料性能的影响

分别以SiC粉体和Ni包裹的SiC复合粉体为硬质相,采用热压工艺(1000°C,20°C/min,40 MPa和45 min)制备了SiC含量为1 wt%~9 wt%的SiC/Fe复合材料。采用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)等研究了复合材料的界面反应物。研究结果表明:Ni过渡层的存在有效避免了SiC颗粒与Fe基体之间的化学反应。随着Ni包裹SiC粉体含量的增加,复合材料的相对密度和抗弯强度先增加后减小,当SiC(Ni)粉体含量为5 wt%时达到最大值。     

Li3PO4 electrolyte of high conductivity for all-solid-state lithium battery prepared by plasma spray

Li₃PO₄ (LPO) deposits were prepared for the electrolytes of all-solid-state lithium batteries (ASS-LBs) by atmospheric plasma-spraying (APS) with sintered powders of three different sizes. The effect of LPO particle size on the microstructure, chemical composition, lattice structure, and ion conductivity of LPO deposits was systematically investigated. Results showed that instead of the conventional lamellar-structured splats with limited inter-splat bonding, columnar-structured grains with chemical inter-splat bonding were formed in APS LPO due to its low melting point. The porosity of the deposits decreases with the decrease in feedstock particle size and deposits with porosity less than 1% can be deposited by using powders smaller than 50 µm. The XRD presented that all deposits have the same phase compositions as that of the sintered powders. Due to more intensively vaporization of P than Li from the molten droplets during APS, the Li/P atomic ratio in the deposits was higher than the stoichiometric ratio of 3 and ranges from 3.02 to 3.17. Owning to the high-quality inter- splat bonding and the slightly deviated Li/P atomic ratio, a high room-temperature ionic conductivity of 4.65 × 10^?8 S.cm^?1 was achieved for APS LPO deposit by using the LPO particles with sizes of less than 30 µm.     

Dense TiN-Ni cermets with improved sinterability,microstructure, and mechanical properties using Ni-coated TiN powders

To solve the poor sinterability and wettability between TiN ceramic and pure metal via using coated composite powders, dense TiN-Ni cermets with uniform microstructure and fine grains were developed at a low sintering temperature of 1300℃ in this work. TiN powders were firstly activated in a strong acid solution, in order to achieve a step-like surface; Ni-coated TiN powders showed an uniform and controllable morphology. Two types of TiN-Ni cermets based on conventional milled powders and Ni-coated TiN composite powders were fabricated by spark plasma sintering (SPS), and used for the comparison concerning the sintering behavior, microstructure and related mechanical properties. Results showed that Ni-coated TiN composite powders helped to improve the sinterability between ceramic and metal, which is rather beneficial to obtain dense TiN-Ni cermets with homogeneous microstructure and high mechanical properties. Compared to those of conventional TiN-Ni, the relative density, Rockwell hardness and fracture toughness increased from 84.9% to 96.6%, 80.2 to 84.3, and 10.2 MPa·m^1/2 to 14.7 MPa·m^1/2, with a rather low sintering temperature of 1300 ℃, respectively.     

Modern high-density oxide ceramics with controlled microstructure. Part I. Effect of aggregation of oxide powders on the sintering and microstructure of ceramics

It is shown that the sintering and microstructure of oxide ceramics are determined by the properties of the powders used for its manufacture and, first of all, by the degree of aggregation of the particles and the characteristics of the aggregates. The aggregation phenomenon is considered for various technological methods. It is established that the structural features are inherited in all stages of the technological process. The highest sintering and homogeneity of the microstructure are exhibited by ceramics prepared from powders with aggregates having a size of fractions of a micrometer.Translated from Ogneupory, No. 1, pp. 5 – 14, January, 1996.     

Electrical Conductivity of Metal Powders under Shock Compression

The electrical conductivity of a series of metal powders under shock compression is measured by an electrocontact technique. Initially, the metal particles are covered by an oxide film, and the powder is non-conducting. Under shock compression, the powder acquires macroscopic conductivity. The electrical conductivity of the shock-compressed powder depends substantially on the metal, porosity, particle size, and shock-wave pressure. The macroscopic electrical conductivity behind the shock-wave front is uniform within the experimental error. The dependences for fine and coarse aluminum powders on the shock-wave pressure are found. It is demonstrated that these dependences are nonmonotonic. For high shock-wave pressures, the electrical conductivity of the substance decreases. This behavior is assumed to be related to strong temperature heating of the substance under shock compression. Estimates of temperature show that shock compression can induce melting and partial vaporization of the metal. The same is evidenced by the behavior of electrical conductivity whose value for fine particles is close to the electrical conductivity of the melt. The electrical conductivity of the coarse powder is heterogeneous because of the strong thermal nonequilibrium of the particle during shock compression. An analysis of results for different metals shows that the basic parameter responsible for electrical conductivity of the shock-compressed powder is the dimensionless density. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 128–139, September–October, 2005.     

葡萄糖为碳源合成AlN-Al2O3复合粉末及其反应机理

以葡萄糖(C6H12O6·H2O)和氢氧化铝(Al(OH)3)为起始原料,利用碳热还原法在氮气(N2)气氛下合成AlN-Al2O3复合粉末.研究了反应温度对AlN-Al2O3复合粉末的物相组成和显微形貌的影响,并探讨了AlN-Al2O3复合粉末的合成反应机理.采用X-射线衍射仪(XRD)、激光粒度分析仪(LPSA)、扫描电镜(SEM)等手段对产物进行表征.结果表明:AlN-Al2O3复合粉末适宜的合成条件为在1500℃保温2h.在1500℃下合成的AlN-Al2O3复合粉末主要有少量的片状颗粒和大量的近似球状颗粒所构成,大部分粒径在100～500nm之间的颗粒发生聚集或堆积形成0.5～1.5μm的大颗粒.在碳热还原反应过程中,Al(OH)3原料分解生成的Al2O3首先生成金属铝蒸汽和Al2O气体氧化物,然后进一步氮化生成AlN.     

Sintering behavior of a nanostructured thermal barrier coating deposited using electro-sprayed particles

During high temperature service, a series of microstructure and phase evolutions occur in thermal barrier coatings (TBCs), which result in degradation of thermal insulation and durability. In this study, the sintering behavior of an air plasma sprayed 8 wt% YSZ coating deposited using electro-sprayed nanostructured particles (ESP) as feedstock powder was investigated and compared with conventional YSZ coating deposited using hollow spherical powders (HOSP). Due to the distinct asymmetric porous structure formed by nanosized YSZ particles, the ESP powder was partially melted in the plasma jet during the deposition, which resulted in the formation of a nanostructured coating that consisted of porous nanozones and dense zones. The ESP coating not only shows a significantly lower initial thermal conductivity of 0.70 W/mK, but also exhibits a stronger sintering resistance in terms of phase stability and thermal insulation compared to the conventional coating. When subjected to prolonged sintering at 1400°C for 128 hours, the thermal conductivity of the ESP coating would gradually increase to about half that of the HOSP coating at 1.29 W/mK. These differences are ascribed to the interaction among different sintering behavior between nanozones and dense zones.     

Preparation of composite particles made from solid powders and wasted plastics by semichemical recycle method

Composite particles composed of solid powders and polymer were prepared by semichemical recycle of wasted plastics. Waste expanded polystyrene was used as raw materials of polymer matrix of composite particles. Both magnetite and silicon carbide powders were used as solid powders to give thermal and electric conductivity and magnetization, respectively. In the experiment, the oil‐phase dissolving expanded polystyrene was dispersed in fine droplets into the continuous water phase. Two kinds of powders were added at the same time or separately in the O/W dispersion. Composite particles were found to have the structure that polymer particle was covered with two kinds of solid powders. The mean diameter of composite particles and the content of each solid powder were strongly affected by the addition time when silicon carbide powder was added into the dispersion. Furthermore, it was found that the gradient adhesion layer due to two solid powders was able to be formed on the surface of polymer particle. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 483–488, 2003     

固体氧化物燃料电池CuCoNi/SDC阳极微结构与电性能的研究

本论文采用溶胶-凝胶低温燃烧合成法制作CuxCo0.5-xNi0.5O1.75-0.5x固溶体阳极粉末,并将电解质粉末和阳极合金粉末按1:1的比例制作了CuCoNi/SDC阳极片。采用热重差热仪检测粉末的处理情况,采用x射线衍射仪(XRD)检测了粉末的成相情况。并且采用四端子法检测了不同组成阳极片的电导率值。分析了固体氧化物燃料电池CuCoNi/SDC阳极的显微结构。结果显示,用上述方法合成的粉体成相很好,阳极片的电导率和组成、温度有着极强的联系,氢气还原前后微结构有明显的变化。     

Modeling the Electrical Conductive Paths within All-Solid-State Battery Electrodes

All-solid-state batteries constitute a very promising energy storage device. Two very important properties of these battery cells are the ionic and the electrical conductivity, which describe the ion and the electron transport through the electrodes, respectively. In this work, a numerical method is presented to model the electrical conductivity, considering the outcome of discrete-element method simulations and the intrinsic conductivities of both the active material particles and the conductive additive particles. The results are calibrated and validated with the help of experimental data of real manufactured electrodes. The tortuosity, which strongly influences the ionic conductivity, is also presented for the analyzed electrodes, taking their microstructure into account.     

Fabrication of Machinable Silicon Carbide-Boron Nitride Ceramic Nanocomposites

SiC/BN nanocomposite powders with the microstructure of micrometer-sized SiC particles coated with nanometer-sized BN particles were prepared via a chemical reaction, which used a mixture of boric acid (H₃BO₃) and urea (CO(NH₂)₂) as reactants coated on the surface of the SiC particles to react under a nitrogen-gas atmosphere. The results of XRD, TEM, and SAED studies showed that the coating layer (BN) was composed mostly of amorphous and nanometer-sized BN particles at the reaction temperature of 850°C. When the nanocomposite powders were hot-pressed at 1850°C, machinable SiC/BN ceramic nanocomposites with fine grain size and homogeneous microstructure were fabricated. The composite that contained 20 wt% BN exhibited high strength (the three-point bending strength was 588.4 ± 26.8 MPa) and excellent machinability.