Nonaqueous Slurry Research Articles

S0402-1-5 窒化アルミニウムの泥しょう鋳込み成形とミリ波焼結([S0402-1]粉末成形とその評価(1))

Aluminum nitride powder is dispersed non-aqueous slurry systems and casted on plaster molds. The compacts are de-binded in vacuum at 823 K, then sintered 28GHz milli-wave sintering furnace at 2023 to 2148K for 60mim. Sintered compacts reach almost full density, but there are several defects in appearances (cracks) and microstructures (white layer parallel to casting direction, and convection mark). Cracks and convection mark may be introduced by unstable heating of the furnace and temperature gradient in the specimen during heating.

S0401-2-2 非酸化物系セラミックスの非水系泥しょう調製と鋳込み成形(粉末成形とその評価(2))

非酸化物系セラミックスには,金属材料や酸化物系セラミックスを超えた硬さや強さ,靱性,耐熱性を持つ優れた材料がある.また,窒化アルミのように,絶縁体でありながら熱伝導率が高いものなど,特殊な特性を発揮する材料もあり,その積極的な活用が期待されている.一方で,実製品に非酸化物系セラミックスが使用される割合は未だ低く,これは,原料粉末が高いことに加えて,製品形状への加工が難しく,材料本来の特性を完全に引き出せていない現状,すなわち加工能力の限界が影響しているためだと考えられる.例えば,構造部材用セラミックスは強さにばらつきが多く,信頼性に乏しい.これは組織内の欠陥による.これらの欠陥は,粉末充填組織の不均一性に起因するものが多いため,充填特性に優れた成形法が勧められるが,一方で,非酸化物系セラミックス加工の大原則である,加工中の材料酸化の抑制がおろそかにされてはいけない.そこで本研究では,安価で,しかも優れた粉末充填特性が得られる泥しょう射込み成形法を非酸化物系セラミックスに適用するための,非水系の泥しょう調製技術を中心に開発した.

Microstructure and Mechanical Properties of Mullite Composites via Pressure Molding and by Oxidation of an Al-Si Alloy Powder

A novel technique to synthesize mullite by the oxidation of Al-Si alloy powder was used for the manufacture of mullite via pressure molding. The mixed powder was consisted of powders of Al-Si alloy, Al2O3 and SiO2 and additives or powders of Al-Si alloy, Al2O3, SiO2 and ZrO2 and additives. Those mixed powders were milled in nonaqueous slurry in order to prevent the oxidation of Al-Si alloy. Then the green bodies were pressureless sintered in air at ≥1380 °C. The Oxidation caused an internal volume expansion, resulting in reducing shrinkage stresses during reaction- bonding of composites, which minimized the sensitivity to crack formation. Comparing with non zirconia reinforced mullite composites, the effect of the microstructure and mechanical properties of mullite composites were studied.

PDP 투명 유전체용 Bi계 프릿트 필름의 제조 및 특성분석

Ceramic green sheets consisting Bi-based glass frit were fabricated for an application to PDP transparent dielectric front panel. The dispersion condition of the slurry for tape casting was pre-examined, and two kinds of binder and plasticizer were used in the nonaqueous slurry system. In the fabrication process for the frit film, the properties such as dry and firing shrinkage, elongation, and transmittance were examined at the condition of various mixing ratio of plasticizers. In the mixing ratio of polyethylene glycol to dibutyl phthalate of 3:5 wt%, a good adhesion, elongation and transmittance were observed at the firing temperature of 580℃. The photograph for the cross section of the interface was also showed a dense microstructure.

Fabrication and Properties of the Tape-Cast Si<sub>3</sub>N<sub>4</sub> with Rod-Like Si<sub>3</sub>N<sub>4</sub> Seed Addition

Silicon nitride ceramics with and without β-Si3N4 seed addition were prepared via tape casting nonaqueous ceramic slurries, laminating the green ceramic tapes, and gas pressure sintering the green bodies in nitrogen atmosphere. Lu2O3 and SiO2 were used as sintering additives. The results showed that the rod-like β-Si3N4 seed was helpful to enhance β-Si3N4 grain growth unidirectionally. The elongated grains grown from seeds were preferentially oriented parallel to the casting direction, resulting in anisotropic microstructure. When a stress was applied with along the grain alignment, the bending strength of the tape-cast Si3N4 with 3 wt% β-Si3N4 seed addition measured at 1500oC was 738 MPa, which was almost the same as the room temperature bending strength 739 MPa, and the fracture energy can be improved from 301 J/m2 at room temperature to 781 J/m2 at 1500oC. The large fracture energy and bending strength at 1500oC were attributable primarily to the unidirectional alignment fibrous grains and a high melting point grain boundary phase.

Bending Strength of the Seeded and Tape Cast Si<sub>3</sub>N<sub>4</sub> before and after Oxidation Exposure in Air at 1500°C

Silicon nitride ceramics was prepared by tape casting nonaqueous ceramic slurries, laminating the green ceramic tapes, and gas pressure sintering in nitrogen atmosphere. Lu2O3 and SiO2 were used as the sintering additives, and 3 wt.% β-Si3N4 seed was added to enhance β-Si3N4 grain growth unidirectionally. The seeded and tape-cast Si3N4 showed very good high temperature bending strength at 1500oC, when the stress applied along with the grain alignment direction. This was attributable to the formation of a high melting point grain boundary phase and the fibrous Si3N4 grains alignment. After exposure in air at 1500oC for up to 100 h, the oxidation products formed on the Si3N4 surface consist of Lu2Si2O7 and SiO2. The bending strength of the oxidized and tape-cast Si3N4 was degradation, the strength decrease was associated with the formation of new defects on the surface and the interface between the oxide layer and the Si3N4 bulk.

MgO-supported Mo, CoMo and NiMo sulfide hydrotreating catalysts

The most common preparation of high surface area MgO (100–500 m 2 g −1) is calcination of Mg(OH) 2 obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO 3/MgO catalyst is complicated by the high reactivity of MgO to H 2O and MoO 3. During conventional aqueous impregnation, MgO is transformed to Mg(OH) 2, and well soluble MgMoO 4 is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO 3. Mo species of MoO 3/MgO catalyst are dissolved as MgMoO 4 during deposition of Co(Ni) by conventional aqueous impregnation. This can be avoided by using non-aqueous impregnation. Co(Ni)Mo/MgO catalysts must be calcined only at low temperature because Co(Ni)O and MgO easily form a solid solution. Literature data on hydrodesulfurization (HDS) activity of MgO-supported catalysts are often contradictory and do not reproduced well. However, some results suggest that very highly active HDS sites can be obtained using this support. Co(Ni)Mo/MgO catalysts prepared by non-aqueous impregnation and calcined at low temperature exhibited strong synergism in HDS activity. Co(Ni)Mo/MgO catalysts are much less deactivated by coking than their Al 2O 3-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al 2O 3. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al 2O 3.

Electrophoretic deposition applied to thick metal–ceramic coatings

Electrophoretic deposition was used to fabricate thick (⩾4 mm) metal–ceramic deposits from a non-aqueous slurry of nickel and alumina particles. A high solid volume in the slurry was identified as the primary parameter for depositing thick cermet coatings rather than the applied electric potential or ionic additive concentration. Ionic additives (MgCl 2, AlCl 3, etc.) were found to adequately suspend the alumina particles and provide rapid deposition rates. The nickel particles proved to be more difficult to suspend in solution, thereby sacrificing control of the deposition composition. The use of small (3.0 μm) particles and continuously pumping the slurry alleviated the suspension problems but small electric potentials (⩽100 V/cm) were required to avoid the formation of rough, columnar deposits on the depositing electrode.

Fabrication and experimental characterization of d31 telescopic piezoelectric actuators

A popular and useful piezoelectric actuator is the stack. Unfortunately with this type of actuation architecture the long lengths normally required to obtain necessary displacements can pose packaging and buckling problems. To overcome these limitations, a new architecture for piezoelectric actuators has been developed called telescopic. The basic design consists of concentric shells interconnected by end-caps which alternate in placement between the two axial ends of the shells. This leads to a linear displacement amplification at the cost of force; yet the force remains at the same magnitude as a stack and significantly higher than bender type architectures. This paper describes the fabrication and experimental characterization of three different telescopic prototypes. The actuator prototypes discussed in this paper mark a definitive step forward in fabrication techniques for complex piezoceramic structures. Materials Systems, Inc. has adapted injection molding for the fabrication of net shape piezoceramic actuators. Injection molding provides several advantages over conventional fabrication techniques, including: high production rate, uniform part dimensions, uniform piezoelectric properties, and reduced fabrication and assembly costs. Acrylate polymerization, developed at the University of Michigan, is similar to gelcasting, but uses a nonaqueous slurry which facilitates the production of large, tall, complex components such as the telescopic actuator, and is ideal for the rapid manufacture of unique or small batch structures. To demonstrate these fabrication processes a five tube telescopic actuator was injection molded along with a very tall three tube actuator that was cast using the acrylate polymerization method. As a benchmark, a third actuator was built from off-the-shelf tubes that were joined with aluminum end-caps. Each prototype's free deflection behavior was experimentally characterized and the results of the testing are presented within this paper.

Effect of sintering procedures in development of LiCoO 2-cathodes for the molten carbonate fuel cell

LiCoO 2-powder was synthesized from carbonate precursors by calcination in air. Greentapes were tape-cast using a non-aqueous slurry and 10 μm plastic spheres as pore formers. Sintering was carried out in air at 850–950°C and in argon/air at 500/750°C. The two sintering procedures led to very different sub-micron morphologies, with the primary particles being much smaller in the latter case. The electrochemical performance at 650°C, in terms of overpotential at 160 mA/cm 2, for the air- and argon/air-sintered electrodes was 57 and 81 mV, respectively. The potential drop due to contact resistance between electrode and current collector was estimated to be 100 and 70 mV, respectively. The electrode materials were characterized by scanning electron microscopy (SEM), Hg-porosimetry, the BET-method (N 2-adsorption), X-ray diffractometry (XRD), flame atomic absorption spectrometry (F-AAS), carbon analysis and a van der Pauw conductivity measurement set-up.

Ultra-Fine Particle Processing for Fine Grain Piezoelectric Ceramics

ABSTRACT Reliable fine-scale piezoelectric ceramics are essential in meeting high frequency transducer applications, offering benefits to product machinability and the increased demand for device miniaturization trends. Processing routes involving the reassessment of grinding technologies were explored in lieu of chemical synthesis routes in order to achieve ultrafine precursor powders. De-agglomeration and Theological properties of non-aqueous ceramic slurries were carefully studied to improve the colloidal pressing of dense, fine-scale Sm and Mn doped PbTiO3 ceramics.

Processing of mullite-based long-fibre composites via slurry routes and by oxidation of an AlSi alloy powder

A novel technique to synthesize mullite by the oxidation of AlSi alloy powder was used for the manufacture of Al 2O 3 long-fibre reinforced mullite composites. It included (1) slurry infiltration/fibre winding of continuous Al 2O 3 yarns (ALMAX) and (2) slurry infiltration/slip casting of sapphire fibres (Saphikon). The nonaqueous slurry used consisted of an AlSi alloy, mullite and additives. During reaction-bonding of green matrices, the AlSi alloy oxidized and was fully converted to mullite after 1 h at 1430 °C in air. The oxidation caused an internal volume expansion, resulting in reduced fibre/matrix shrinkage stresses during reaction-bonding of composites, which minimized the sensitivity to crack formations. For the ALMAX-based composites, the fracture was non-catastrophic. Regarding the sapphire-based composites, an interfacial space between the fibres and the matrix gave the desired fibre pull-out.

Influence of processing parameters on the microstructure and electrical properties of multilayer-chip ZnO varistors

Multilayer-chip varistors based on ZnO with lead zinc borosilicate glass instead of Bi2O3 were prepared by tape casting and green-sheet lamination processes using a non-aqueous slurry system. The influences of slurry composition and the degassing process on the microstructure and non-ohmic properties of multilayer-chip varistors were studied. The electrical properties of chip varistors can be influenced substantially by the pore defects resulting from an unsuitable slurry formulation for the tape-casting process. The sintering temperature of the chip varistors was lowered to 1100 ‡C and silver-palladium alloys were employed as internal electrodes. The non-linear coefficients of 27–32 and breakdown voltages of 7.6–24.5 V were achieved by controlling the green-sheet thickness and sintering temperatures in the present study. The δVbr/Vbr values for the chip varistors lie within ± 10%, indicating excellent surge-withstanding capability.

Synthesis and Performance of LiCoO2 Cathodes for the Molten Carbonate Fuel Cell

A method for fabricating electrodes has been developed. powder was synthesized from and powder by calcining in air at 650°C. Electrodes were tape cast in a nonaqueous slurry with and without a graphite poreformer. They were sintered in air at temperatures between 700 and 850°C. Powders and electrodes were characterized by using x‐ray diffraction, thermogravimetric analysis, the Brunauer, Emmett, and Teller method, Hg porosimetry, scanning electron microscopy, and a van der Pauw conductivity measurement setup. The electrodes were electrochemically characterized by polarization measurements at different temperatures. Performance of the electrodes, with and without poreformer, respectively, was also determined by measuring polarization curves at different degrees of electrolyte fill.

Separation of Colloidal Particles from Nonaqueous Media by Cross-Flow Electrofiltration

Abstract Charge characteristics of particles in aqueous or nonaqueous slurries are known to play an important role in solids-liquid separation processes. We have been conducting a fundamental study on filtration of colloidal particles suspended in nonaqueous media, such as coal and tar sand slurries based on their charge characteristics. This paper presents results of such a study involving cross-flow electrofiltration of nonaqueous slurries. Data are reported for α-Al2O3 particles suspended in tetralin. The effects of feed rate, driving pressure and electrical field strength on the filtration rate, total deposition rate on the central electrode, and the efficiency of the filter are presented. The outlet slurry concentrations were measured with a specially built X-ray densitometer. These data are analyzed by a mathematical model using a Graetz-type analysis. The rate of deposition was found to be determined mainly by the electric field. The sludge flow near the central electrode significantly affected the...

Cross-flow electrofilter for nonaqueous slurries. Reply to comments

Cross-flow electrofilter for nonaqueous slurries. Reply to comments

Cross-flow electrofilter for nonaqueous slurries. Comments

Cross-flow electrofilter for nonaqueous slurries. Comments