Kimihiro Ozaki

p-Type Sb2Te3 and n-Type Bi2Te3 Films for Thermoelectric Modules Deposited by Thermally Assisted Sputtering Method

We developed a thermally assisted sputtering method (TASM) based on direct current magnetron sputtering to increase the rates of deposition of Sb2Te3 and Bi2Te3 films. The sputtering target was heated with the thermal energy of Ar plasma without any additional heating systems. The stoichiometric Sb2Te3 (p-type) and Bi2Te3 (n-type) films were obtained by TASM. The maximum deposition rate of the films was approximately 1.6 µm/min, which is large for a sputtering method. The differences in the composition ratio between the sputtering target and the deposited films were as small as 3.6 (p-type) and 1.5% (n-type). TASM was applied to the fabrication of a flexible thermoelectric film module. The generation properties of the film module coincided with the values that were estimated on the basis of the thermoelectric properties of films deposited on a SiO2 glass substrate. These results indicate that TASM is useful for fabricating thermoelectric film modules.

Anisotropic Sm2Fe17N3 sintered magnets without coercivity deterioration

In order to solve the problem of coercivity decrease during sintering, we developed a low-oxygen process capable of producing sintered compacts while avoiding oxidization. This study proved that Sm2Fe17N3 sintered compacts produced by the low-oxygen process maintained the coercivity of the raw powder. Scanning transmission electron microscopy observation found no obvious formation of an oxide layer at the sintered interfaces. Magnetic measurements revealed that the coercivity of the sintered magnets decreased as the oxygen concentration increased. In summary, this study demonstrated that Sm2Fe17N3 sintered magnets having the same coercivity as the raw powder can be produced by avoiding oxidization.

Properties of New TiC/TiB2/Fe-Al Cermet Alloy

Effect of TiB2 substitution on thermal conductivity and hardness in TiC / Fe-Al cermets was investigated. The (70-x)TiC / xTiB2 / 26Fe-4Al mass % cermets were fabricated by mechanical milling and subsequent pulsed current sintering method. The high relative density compacts was formed by sintering at 1423 K under 25 MPa for 60 s. The sintered materials were mainly composed of TiC, TiB2 and Fe-Al intermetallic compound. In addition, small amounts of Fe2B surrounding TiB2 were formed. The thermal conductivity of the sintered compact lineally increased with increasing TiB2 volume fraction. However, the hardness of the sintered compacts of x = 20 – 40 were higher than that of x = 0. Therefore, the substitution of TiC to TiB2 in the TiC / Fe-Al based cermet is effective to improve the thermal conductivity without the degradation of hardness.

Investigation of optimal route to fabricate submicron-sized Sm2Fe17 particles with reduction-diffusion method

Submicron-sized Sm2Fe17powder samples were fabricated by a non-pulverizing process through reduction-diffusion of precursors prepared by a wet-chemical technique. Three precursors having different morphologies, which were micron-sized porous Sm-Fe oxide-impregnated iron nitrate, acicular goethite impregnated-samarium nitrate, and a conventional Sm-Fe coprecipitate, were prepared and subjected to hydrogen reduction and reduction-diffusion treatment to clarify whether these precursors could be convert to Sm2Fe17 without impurity phases and which precursor is the most attractive for producing submicron-sized Sm2Fe17powder. As a result, all three precursors were successfully converted to Sm2Fe17powders without impurity phases, and the synthesis route using iron-oxide particle-impregnated samarium oxide was revealed to have the greatest potential among the three routes.

Improvement of magnetization of submicron-sized high coercivity Sm2Fe17N3 powder by using hydrothermally synthesized sintering-tolerant cubic hematite

We investigated the cause of forming of aggregates which decreases magnetization of a submicron-sized Sm2Fe17N3 powder. The aggregation was considered to be caused through sintering and growth of α-Fe particles in a hydrogen reduction treatment. We newly synthesized cubic hematite powder which has tolerance for the sintering of particles in a hydrogen reduction treatment. The aggregation of submicron-sized Sm2Fe17N3 particles was significantly reduced by using the cubic hematite as a precursor, and the magnetization was improved without decreasing the high coercivity.

Columnar thermoelectric elements of linked spheres for miniature electric generation modules

Thermoelectric elements that were formed from vertically aligned microspheres were fabricated from 500-µm monosized spherical particles of Fe2VAl alloys with a particle assembly that used pulsed current micro-welding. P-n pairs of the elements consisting of three particles generated relatively large temperature differences ΔT despite being 1.5 mm tall. At ΔT = 19 K, the five pairs generated a voltage of 21 mV and a maximum generation power of 40 µW, which converted to 0.21 V/cm2 voltage per unit area and 0.4 mW/cm2 power density, respectively. Moreover, we demonstrated the feasibility of building a massive array with 100 elements.

Mechanical Alloying of Ti-Nb-Si and Their Consolidation by Pulsed Current Sintering

Ti-xat%Nb-10at%Si (x=5-40) alloys were synthesized by mechanical alloying (MA) using a planetary ball mill with as starting materials of Ti, Nb and Si powders. The MA powders milled for 360ks were spherical particles of about 20μm in all the alloys studied. The characteristics of these MA powders were examined by XRD, DSC and TEM.Ti-5at%Nb-10at%Si powder milled for 360ks consisted of fine α-Ti crystals. The MA powders containing 10at%Nb to 40at%Nb showed exothermic reaction in the DSC curves. In Ti-20at%Nb-10at%Si and Ti-10at%Nb-10at%Si, the exothermic reactions were observed at higher temperature than 800K. This exothermic reaction was the crystallization from amorphous phase in MA powder to α-Ti crystalline phase. In Ti-40at%Nb-10at%Si and Ti-30at%Nb-10at%Si, the exothermic reaction was observed at about 600K. This exothermic reaction was characterized as crystallization from amorphous phase to β-Ti crystalline. The Ti-10at%Nb-10at%Si MA powder was consolidated by the pulsed current sintering with a high pressure. The obtained bulk amorphous compact contained 18vol% pores.