| Budget Amount *help |
¥8,900,000 (Direct Cost: ¥8,900,000)
Fiscal Year 1987: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 1986: ¥7,400,000 (Direct Cost: ¥7,400,000)
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| Research Abstract |
The phase boundary reaction that takes place in a near-surface of the powder plays an important role in the reactivity of fine powder. In this study, the thermal behaviour of the surface layer of polycrystalline powders was followed by emanation thermal analysis (ETA) using Ra-226 parent isotope. The results obtained are as follows.
1. Experimental conditions of ETA. The ETA experiments were carried out by a Nerzsch simultaneous ETA-TG-DTA (ETA 403 - STA 409 type), using N_2 carrier gas, 50 m1/min; heating rate, 10 ゜c/min ; sample, 0.1g; time constant, 100s. Samples were labelled by a surface impregnation method using aqueous Ra-226 solution (4-10 <micrn>Ci/ml). An information from the ETA studies can be correlated th the behaviour of the near-surface of powders (<50 nm thick) during a temperature rise.
2. Preparation of samples. Various powder samples, A1_20_3, Fe_20_3, Tio_2 and Zno were pre pared from the different starting materials by changing the calcining temperatures. Then the gr
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inding and sieving treatments of these powders were carried out by a Fritsch Planetary-Micro-Pulveriser (P-7 type) and five Micro-Mesh-Sieves (Shodex MS) in the range of 5-45 <micrn>m size, respectively.
3. Characterization of the surface layer of powder. For all the samples, the characteristic ETA peaks were grouped into two peaks I and II, depending on whether are located at lower or higher temperatures than the remperatures T_s=(0.4-05)T_m at which the self-diffusion of matrix atoms and the bulk diffusion of radon start simultaneously. T_m is the absolute melting remperature. Peak II was sprit into two peaks IIa and IIB. The peak located at T_s was denoted by peak I'. Peaks I and II are due to the diffusion in the intergranular space, open micropores, etc., and the bulk diffusion of radon in the solid matrix, respectively. Peak IIa corresponds to the thernal behaviout of the defect structures such as grain boundaries. Mechanochemical effects of the grinding on the peaks appeared on the peaks I, I' and IIa, resulting in a deterioration of the texture and crystalline structure. These mechanochemical effects were annealed and eliminated by the heating treatment. ETA was an interesting technique for the thermal characterization of the near-surface of powders, and provided useful information on the thermal behaviour of grain boundaries od policrystalline metal oxides. Less
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