Mamoru Omori

Sintering, consolidation, reaction and crystal growth by the spark plasma system (SPS)

Abstract The graphite die set in spark plasma system (SPS) is heated by a pulse direct current. Weak plasma, discharge impact, electric field and electric current, which are based on this current, induce good effects on materials in the die. The surface films of aluminum and pure WC powders are ruptured by the spark plasma. Pure AlN powder is sintered without sintering additives in the electric field. The spark plasma leaves discharge patterns on insulators. Organic fibers are etched by the spark plasma. Thermosetting polyimide is consolidated by the spark plasma. Insoluble polymonomethylsilane is rearranged into the soluble one by the spark plasma. A single crystal of CoSb3 is grown from the compound powders in the electric field by slow heating. Coupled crystals of eutectic powder are connected with each other in the electric field.

Development of a silicon carbide fibre with high tensile strength

MUCH work has been done on preparing heat-resistant silicon carbide materials in fibrous form, since plastics or metals can be reinforced with them to obtain very heat-resistant material of great mechanical strength. SiC whiskers1 are, however, impractical because of their shortness (several mm), their non-uniform diameter and high cost of production. SiC-on-W (ref. 2) and SiC-on-C (ref. 3) filaments have been produced by chemical vapour methods. These coated filaments are more expensive, and the treatment for making such composite materials requires careful control. We report here on the synthesis of continuous β-SiC fibres by a new process: the conversion of organometallic polymers to inorganic substances. We have studied the transformation process and the structure and mechanical properties of these fibres.

Preparation of pressureless-sintered SiC-Y2O3-Al2O3

Sintering additives were prepared from aluminium hydroxide and yttrium hydroxide. These additives were soluble in water and resulted in a binder. A β-SiC powder was mixed with the additive solution and sintered at 2150° C without pressure. The oxides formed from the additive promoted sintering. The sintered body contained no pores. Aluminium, silicon, and yttrium oxide were precipitated in the sintered body.

Synthesis of full-density nanocrystalline tungsten carbide by reduction of tungstic oxide at room temperature

Among the hard alloys, WC alloys find wide industrial applications as tips for cutting tools and wear-resistant parts. Their intrinsic resistance to oxidation and corrosion at high temperatures also makes them desirable as a protective coating for devices at elevated temperatures. In the industrial scale of production, WC is prepared by a direct union of the elements at a temperature of 3,273 to 3,473 K. Accordingly, the high cost of preparation is a disadvantage of this process. Here, the authors report a novel technique for preparing a large amount of WC powder using a simple method. This process is based on mechanical solid-state reduction (MSSR) followed y solid-state reaction (SSR) during room-temperature ball milling (a high energy ball mill, Fritsch P6, was used at a rotation speed of 4.2 s{sup {minus}1}) of a mixture of WO{sub 3}, Mg, and C powders.

Fabrication and characterization of SiC rod-particulate-reinforced reaction-bonded Si3N4 composites

Abstract Reaction-bonded Si 3 N 4 composites reinforced by whisker-like SiC rod particulates have been fabricated by nitriding SiC rod -containing Si powder compacts, which were presintered to a controlled density by spark plasma sintering (SPS). The effects of processing parameters, including presintered density, SiC rod content, nitriding temperature, atmosphere pressure and heating rate on the nitridation reaction were investigated. It was found that the addition of SiC rod to Si powders led to easier control of complete nitridation compared to the case of pure Si powder compacts, probably because the SiC rod not only acted as diluting filler to suppress the rapid rise in temperature resulting from an SHS-like reaction between Si and N 2 , but also provided paths for diffusion of reactant gases. The density of the reaction-bonded Si 3 N 4 –50 vol% SiC rod composites was increased up to near 90% which is quite a lot higher than that of conventional reaction-bonded Si 3 N 4 ceramics, by using SPS to improve the density prior to nitridation. The relative density increased from ∼70 to 90% after the nitridation without appreciable dimensional change, being characteristic of reaction-sintering. As the reinforcement in the reaction products, the SiC rod improved Youngs modulus and bending strength both at ambient and elevated temperatures, as well as thermal and electric conductivity.

Determination of the oxidation states of bismuth and copper in superconductor Bi-Ca-Sr-Cu-O by oxidation-reduction titration

SummaryThe oxidation state of the superconductor Bi-Ca-Sr-Cu-O was determined by two procedures. One was ferrous-chromate titration after dissolution of the sample in manganous nitrate solution. The other was the titration after dissolution in ferrous ion solution. The former procedure gives the concentration of a state like pentavalent bismuth and the latter gives the sum of concentrations of a state like pentavalent bismuth and a state like trivalent copper or peroxide. The result of the titration shows that the superconductor oxide has the state like pentavalent bismuth but not like that of trivalent copper. This is a striking contrast to YBa2Cu3O7−y having a high concentration of the latter state. Although the result was compared with X-ray photoelectron spectra, a clear relationship between them was not obtained.

Consolidation of Multi-Walled Carbon Nanotube and Hydroxyapatite Coating by the Spark Plasma System (SPS)

A multi-walled carbon nanotube (MWNT) was mixed with phenol resin a nd consolidated by the spark plasma system (SPS). Properties of the MWNT cons olidated at 1200°C at 120 MPa were as follows: bulk density was 1.74 g/cm ; apparent porosity was 16.3%; Young’s modulus was 11.1 GPa. Hydroxyapatite was coated on the consolidated MWNT at 1000°C a nd 120 MPa by SPS, using the suspension prepared from 6 moles of CaHPO 4·2H2O and 4 moles of Ca(OH) 2 . Introduction Carbon nanotubes (CNT) consist of single-walled carbon nantubes (SWNT) and multi-walled carbon nanotubes (MWNT) and have been attracting a lot of attention s ince their discovery [1]. It is said that molecular circuit devices will be fabricated from S WNT [2]. MWNTs are composed of various kinds of tube diameters and a number of carbon network layers. CNT are still expensive, but the cost of their fabrication will surely decreased in the nea r future. Low-cost CNTs will be used for fillers of composites and starting materials to produc e structural and/or functional compacts. Graphite is a hard-to-sinter material, and its powder ca n only be sintered at very high temperatures under pressing [3]. The sintering ability of CNT is the same as that of graphite, and advanced techniques are needed to consolidate it at lower temperatu res, before the transformation into graphite. The spark plasma system (SPS) has been developed for sintering of metal and ceramics in the plasma and electric field [4, 5], and it is used for consolidation of various kinds of materials such as metals, ceramics and polymers [6]. The bioac tiv ty of graphite is not excellent. The best way to increase the bioactivity of the consolidated MWN T is deposition of hydroxyapatite (HA) films on it. Plasma spraying is widely used for manufact uring HA coating on Ti or Co-Cr-based implants. However, a multitude of phase changes occur s at high temperatures of the plasma spraying process [7]. Two compounds of 6 moles of CaHPO 4·2H2 and 4 moles of Ca(OH) 2 reacted at 150°C to produce HA and H 2O by the hydrothermal hot-pressing method [8]. This reaction is able to apply to HA coating on biomaterials because t he reaction product is only HA except for H2O. In this paper, the MWNT was mixed with phenol resin in ethanol. After removing the ethanol and decomposing the phenol resin by heating, the mixture of the MWNT and the amorphous carbon was consolidated by SPS. The consolidated MWNT was dipped in the suspens ion of 6 moles of CaHPO4·2H2O and 4 moles of Ca(OH) 2. The two compounds reacted and bonded to the consolidated MWNT at 1000°C at 120 MPa by SPS. Experimental procedures Consolidation of MWNT CNT used for the consolidation was MWNT (NanoLab Inc., USA, 80% purity ). The MWNT was purified to remove a metal catalyst using a solution of 50% HNO 3. Phenol resin was dissolved in ethanol. The MWNTs were put in the ethanol solution. After evaporating e hanol, the phenol resin film on the MWNT was decomposed at about 200°C in air. The coated M WNTs were put in a graphite die and set in the spark plasma system (SPS) (Sumitom o C al Mining, Japan, SPS-1050). The consolidation was carried out between 1000°C and 1600°C at 120 MPa in a va cuum. In case of the consolidation at 1000°C, the consolidation temperature was raised as follow : heating rate from 0°C to 900°C at 100°C/min, from 900°C to 980°C at 20°C/min, from 980°C to 1000°C at 5°C/m in and holding time at 1000°C for 5 min. The microstructure of the consolidated MWNT was analyzed by a t ransmission electron Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 395-398 doi:10.4028/www.scientific.net/KEM.254-256.395

Copper and oxygen vibrations in La2CuO4 and YBa2Cu3O7

Abstract We perform eV neutron scattering experiments (neutron energy > 1 eV) on copper metal, CuO, La2CuO4 and YBa2Cu3O7, and neutron absorption experiments of HoBa2Cu3O7, and determined the mean kinetic energy of O, Cu and other atoms in these materials. The Debye temperatures of Cu atoms in La2CuO4 and YBa2Cu3O7 were estimated to be extremely large, about 1500 and 2000 K, respectively.

Polycarbosilane-derived SiC/single-walled carbon nanotube nanocomposites

One of the key issues for the development of high toughness carbon nanotube (CNT) reinforced composites is the control of the interfacial bond between the CNT and the matrix. Here, we introduce a novel technique to facilitate the homogeneous coating of single-walled carbon nanotube (SWCNT) bundles with polycarbosilane (PCS)-derived SiC nanoparticles. The PCS dissolved in n-hexane was used as a precursor for SiC nanoparticles. The results obtained from XRD, TEM and EDXS analyses confirmed the formation of β-SiC nanoparticles of about 20 nm in diameter, which possessed a relatively homogeneous distribution on the SWCNT bundles. It was shown that the number of SiC nanoparticles per unit of SWCNT surface area could be adjusted by changing the weight ratio of PCS and SWCNTs. This approach may provide a useful route for the preparation of SiC/SWCNT nanocomposites that have a tunable interface property with the matrix and potentially with an enhanced anchor effect, which may have potential applications as a reinforcing element in CNT/ceramic composites.

State of iron in glass-like carbon prepared by heat treatment of ferrocene resin

WE have investigated the conversion of organometallic polymers to inorganic materials by heat-treatment. Several of those inorganic materials are industrially useful. Earlier studies have been reported in this journal1–5. We describe here the state of iron dispersed in a glass-like carbon, which was prepared by heat-treatment of an organometallic resin containing ferrocene skeletons as the main chain. This state is unusual and strange both physically and chemically.