Spark Plasma System Research Articles

Low temperature synthesis of hydroxyapatite from CaHPO 4·2H 2O and Ca(OH) 2 based on effect of the spark plasma system (SPS)

A mixture of 6 mol of CaHPO 4·2H 2O and 4 mol of Ca(OH) 2 was reacted to produce hydroxyapatite (HA) by spark plasma system (SPS). The reaction was carried out at 300–1200 °C under pressure of 20–670 MPa for 10 min in a vacuum. HA formation started at 300 °C at 600 MPa and was completed at 500 °C at 670 MPa, the same product being obtained at 1200 °C in air using a furnace. The temperature of the HA formation increased with decreasing pressure and was 1150 °C under 20 MPa. There was a linear relationship between the reaction temperature and pressure. The crystal size of the HA prepared at 500 °C at 670 MPa and that at 600 °C at 600 MPa by SPS were less than 1 and 2 μm, respectively.

Preparation of Multi-Walled Carbon Nanotube Compact by the Spark Plasma System (SPS)

The multi-walled carbon nanotube (MWNT) was not consolidated without additives by the spark plasma system (SPS). The phenol resin of 33 wt% was added to promote the consolidation. The MWNTs were aligned perpendicular to pressing direction of SPS in the consolidated compact. Bulk density and Young's modulus were more than 1.7 g/cm3 and 10 GPa for the MWNT consolidated at 120 MPa at 1200°C and 1400°C. The fracture behavior on bending test was a kind of quasiplastic deformation and was based on pull out of the MWNTs.

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

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

601 SPS 法によるハイドロキシアパタイトの低温合成

Hydroxyapatite (Ca_<10>(PO_4_6(OH_2,HA) is a bioactive material and is synthesized by four kinds of methods. The spark plasma system (SPS) is a promising method to produce advanced materials. Sintering and some chemical reactions are enhanced by SPS. This paper is concerned about the HA synthesis from the mixture of 6CaHPO_42H_2O and 4Ca(OH)_2by SPS. These two compounds are dehydrated under 600℃ and the mixture is turned into the composition of HA. Small crystals of HA were prepared without pressure at 600℃ by heating, but they were decomposed at this temperature for extended times or at higher temperatures. On the other hand, SPS enabled to form stable HA crystals at 600℃, and this growth was based on an effect of SPS. The HA formation was performed at 1000℃ at the high pressure such as 120 MPa. The high pressure of SPS could promote the crystal growth and the stability of HA compared with the decomposition products of HA.

Consolidation of Al2O3–Y3Al5O12 (YAG) eutectic powder prepared from induction-melted solid and strength at high temperature

Abstract The eutectic composition powder of Al 2 O 3 –Y 3 Al 5 O 12 (YAG) was melted using a Mo crucible by induction heating. The melt was slowly solidified and resulted in a eutectic structure of large twinned crystals. The eutectic solid was ground and sieved into 3–44 μm and 64–124 μm powders. The powder was consolidated to reproduce eutectic composite by the spark plasma system (SPS). Mechanical properties of the consolidated eutectics were measured at room temperature. The high temperature strength was obtained from 1000 to 1400 °C. The consolidated eutectics was not plastically deformed at 1400 °C.

316 酸化物共晶複合材料の放電プラズマシステム(SPS)による作製(新技術開発レポート)

Eutectic composites consist of twined single crystals and are prepared by solidification of the melt. The properties of eutectic composites are different from those of conventional composites. The high strength of oxide eutectic composites is not lost near 1500℃, and composites such as Al_2O_3-ZrO_2 and Al_2O_3-Y_3Al_5O_<12>(YAG) can be used for ceramic turbine blade. The synthesis of a eutectic composite free from cracks is carried out by unidirectional solidification. This solidification is inadequate to produce large and near-net-shaped materials. Eutectic powders of A12O3-YAG were prepared from the eutectic composite melted by arc discharge. The powder was classified into 3 - 44, 44 - 64 and 64 -124 μm, and consolidated by the spark plasma system (SPS).

317 SPS法によって作製したAl基合金の機械的性質(新技術開発レポート)

P/M Al_<92>Fe_3Cr_2Ti_2Mm_1 alloy prepared by the powder metallurgy (P/M) process have high tensile strength exceeding 600 MPa, high-elevated temperature strength exceeding 300 MPa after holding for 100 hr at 573 K. In this work, structural and mechanical properties of the SPS Al_<93>-xFe_3Cr_2Ti_2Mmx (X=0.5, 1.0) alloys prepared by the spark plasma system (SPS) were studied. The results were as follows: compressive fracture strength of 750 MPa, plastic elongation of 4.0%, Vikers hardness of 195 at room temperature and 110 at 573 K.

Consolidation of Eutectic Powder of Al2O3–GdAlO3

A eutectic solid of Al2O3–GdAlO3 was prepared by arc discharge and crushed to a eutectic powder of 3–125 μm. The powder was consolidated by the spark plasma system (SPS). The consolidated powder duplicated the eutectic structure: Al2O3 and GdAlO3 were joined to each crystal. There were no flaws such as cracks or pores in the eutectic composite. The bending strength was half that of the eutectic composite prepared by unidirectional solidification.

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

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 CoSb 3 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.

Pure WC/Mo Functionally Graded Materials

Pure WC powders were sintered by spark plasma system (SPS). The hardness and toughness of the WC body were 24 GPa and 6 MPa.m 1/2 , respectively. Functionally graded materials (FGMs) were fabricated from WC and Mo powders using SPS by stacking layers consisting of a different ratio of WC and Mo powders. Two layers of a mixture of WC and Mo powders inserted between WC and Mo layers were sufficient to relax residual stress based on the thermal expansion mismatch of WC and Mo. At room temperature toughness of the WC layer was decreased along the periphery of disk samples near the edge but increased inside the sample.

放電焼結の基礎と応用 放電プラズマシステムにおける特異な現象

Spark plasma system (SPS) has been called spark plasma sintering (SPS) or plasma activated sintering (PAS). This system is characterized by generation of spark plasma. The plasma has not been identified directly. There are several unique phenomena which are considered to be resulted from the effect of plasma. The following examples are described. Aluminum metal is sintered. Pure tungsten carbide becomes a dense body. Discharged pattern is obtained on the surface of insulator. Organic fibers are etched. Carbon is solidified. Thermosetting polyimide is consolidated. Structure of insoluble polymonomethylsilane is rearranged into soluble one.

WC系傾斜機能材料の作製

WC powders have not been sintered by normal sintering and by hot press sintering without sintering additives. Spark plasma system (SPS) makes it possible to consolidate pure WC powders. The Vickers hardness and toughness of the dense WC were 24 GPa and 6 MPa·m1⁄2. The hardness was 50% larger than that of WC-Co hard alloys, and the toughness is half. A functionally graded material (FGM) of WC and WC-Co or Mo can afford good hard materials with high hardness and toughness. WC/WC-CoFGM was not obtained, because Co diffused rapidly at high temperatures during the densification of a WC layer. Two graded layers were enough to relax the residual stress of WC/Mo FGM and prevent cracks.