Masaru Yokota

Anomalous Electrical Resistivity of Bi-Sr-Ca-Cu-O System at High Temperature

The electrical resistivity of Bi-Sr-Ca-Cu-O and Bi(Pb)-Sr-Ca-Cu-O superconductors at high temperatures was studied in relation to superconducting properties. The resistivity of the samples with a low-Tc phase showed hysteresis around 300 and 650°C between the heating and cooling processes. No hysteresis was detected for nearly single phase high Tc. For the low-Tc samples, it was confirmed that the Tc, the material resistivity and the high temperature resistivity were strongly dependent on the quenching temperature. Weight loss was detected around 300°C in the heating process, but it was not detected in the cooling process.

PULSE CURRENT PRESSURE SINTERING OF AL/AL 2 O 3 FUNCTIONALLY GRADED MATERIAL

To fabricate densified Al/Al 2 O 3 functionally graded materials (FGM) on hardness and thermal expansion, a pulse current pressure sintering process was employed. This FGM consists of an aluminum layer, an α-Al 2 O 3 layer and seven intermediate layers between the two outermost layers. Aluminum and Al(OH) 3 powders were used as starting materials. Al(OH) 3 powder transformed into several types of Al 2 O 3 after the sintering process. The hardness of the intermediate layers gradually increased in proportion to the volume fraction of γ-Al 2 O 3 . The top layer, which consists of a-Al 2 O 3 , was about 1000 HV on average and 1500 HV at the surface.

Detection and Identification of the Latent Microorganisms in the Corrosion Layers of Ancient Bronze Mirrors

On an ancient bronze mirror, we carried out a scanning electron microscopic (SEM) examination of fractured corrosion layers, a biological microscopic observation of a gram-stained sample and DNA analyses of the samples removed from corroded sites. From these scientific and technical researches, we obtained the following results. Fine particles about 2 μm in length were confirmed in the corrosion layer by the SEM observation. Microorganisms of the same size were observed in the gram-stained sample removed from the corrosion layer through a biological microscope. From these results, fine particles observed under the SEM should be considered as microorganisms. A lot of fine particles were confirmed especially in the corroded sites by the SEM observation. So (certain kinds of) microorganisms may have played a role in the corrosion (deterioration) of the ancient bronze mirrors while the mirrors were buried in soil. From the base sequences obtained by DGGE analysis, two kinds of microorganisms were confirmed to exist in the corrosion layer of the ancient bronze mirror. One is 97.4% homologous to the 16S rDNA of the uncultured bacterium (Accession number: AY 053488). It was also highly homologous to the sequence derived from the 16S rDNA of the Xanthomonadaceae family such as Stenotrophomonas and Xanthomona. That is, the sequence is derived from a strain belonging to the Xanthomonadaceae family. The other base sequence is 97.4% homologous to the 16S rDNA of the Bacteroidales order such as uncultured Bacteroidales bacterium (Accession number: AY 859647). That is, the sequence is derived from a strain belonging to the Bacteroidales order. Genes of microorganisms, presumed to belong to the Acetobacter, Gluconacetobacter genuses and Fe(III)-reducing bacterium, Shewanella algae were detected from the base sequence analysis by cloning. From the results above, microbial activity is assumed to be high around the ancient bronze mirrors. The corrosion mechanism of bronze mirrors seems complicated, but a several types of microbes which possibly corrode bronze mirrors were verified.

Materials Investigation and Study on the Production Techniques of Chinese Ancient Iron Mirrors

The number of ancient iron mirrors excavated in China is far smaller than those of ancient bronze mirrors. Fortunately, we were honored to have a chance to analyze some of the rare ancient iron mirrors excavated in China. Un-corroded parts were subjected to a structural observation under an optical microscope and a chemical composition analysis with EPMA (Electron Probe Micro Analyzer). Based on the results, the production techniques of the ancient iron mirrors were discussed. The results were as follows. 1. The iron mirror produced during the later Han Period showed a mixture of ferrite and pearlite particles. The possibility that the iron mirror was made by forging small pieces of pig iron, which process accompanied decarburization, can be inferred. Traces of silicon and phosphorous were found as impurities in the uncorroded alloy. 2. The iron mirror excavated from the tomb of the Sui period showed the structure of single-phase ferrite. It is inferred to be made by forging wrought iron which had been decarburized enough. Traces of silicon, phosphorous and sulfur were found as impurities in the uncorroded alloy.

Formation and Magnetic Properties of Fe-6.5% Si-Oxides Composite Powders by Mechanical Alloying

SYNOPSIS Fe-Si-ZrO2 composite powders were prepared by mechanical alloying using vibrating ball mill under Ar atmosphere. The magnetic properties and thermal stability for Fe-Si-Zr02 composite powders were investigated by mesns of VSM, DSC and X-ray diffraction. The addition of Si increased the coercivities, He for Fe-ZrO2 composite powders as much as 130-150% of those for the powders without Si against expectation. On the other hand, X-ray diffraction patterns for annealed sample showed that the addition of Si supress the precipitation of ZrO2 from Fe matrix and the coarsening of crystallite size. These results are thought to be due to the lameller structure of Si in Fe matrix.

Effect of Heat Treatments on Superconductivity and Electrical Resistivity at High Temperature of Bi-Sr-Ca-Cu-O System

Two peaks in the resistivity of the Bi2Sr2CaCu2Oy were detected at 300 and 650°C on heating process, but no peak was detected at 300°C on cooling process in spite of holding at 300°C for 100hr. In order to elucidate the cause of the peak at 300°C, the measurments of high temperature resistivity, Tc, thermogravimetry and X-ray diffraction were carried out for the Bi2Sr2CaCu2Oy quenched for various temperatures. Tc and normal-state resistivity as a function of a quenching temperature, Tq, had a steep minimum at Tq=300°C. The high temperature resistivity was also strongly dependent on Tq, but had a peak or a slope change at about 300°C on heating. X-ray diffraction showed that no change was found before and after quenching or high temperature resistivity measurement up to 400°C. The weight decrease was detected at 350°C during heating in air, but little change during cooling process. From these results, it may be considered that the peak in the resistivi-ty at 300°C is due to the decrease in the electrical hole concentration compensating the increase in the oxygen vacancy concentration. Further detailed research is in progress.

Influence of Cold Rolling and Annealing on the Damping Capacity of Iron Sintered Compacts, Infiltrated with Lead

In fluence of cold rolling and annealing on the damping capacity of Fe sintered compacts, infiltrated with Pb was investigated by measuring internal friction. Infiltration volume ratio of Pb in sintered Fe compacts and draft of the specimens were up to 31.6% and 40%, respectively, and annealing temperatures were mainly 473 K. Results obtained were as follows:(1) Internal friction of Fe sintered compacts, infiltrated with Pb increased with the increase of infiltration volume ratio of Pb. Work of cold rolling enhanced the internal friction of specimens remarkably, but in the case of low volume ratio of infiltrated Pb in Fe sintered compacts, the internal friction tended to saturate at a certain draft.(2) Ultimate tensile strength of the specimens increased with the increase of draft, showed a maximum value, and then decreased with the increase of draft. Maximum value of ultimate tensile strength of the specimen tend-ed to shift to higher draft with the increase of Pb infiltration volume ratio.(3) Internal friction of cold rolled Fe sintered compacts fell down to that before cold rolling with annealing time at 473 K. On the contrary, in the case of cold rolled Fe sintered compacts, infiltrated with Pb, higher inter-nal friction was retained to prolonged annealing time. The origin of decrease of internal friction by annealing is thought to be the recovery of internal stress in Fe matrix by cold rolling.(4) Internal friction of Fe sintered compact, infiltrated with 30 vol%Pb and cold rolled at 40% of draft was approximately the same as that of flaky graphite cast iron. Whereas, ultimate tensile strength of this specimen was comparatively lower value of approximately 13 kgf/mm2.

Grain Orientation Controlling of Superconductive YBa2Cu3Oy Ceramics by Thermal Diffusion Treatment

Possibility of grain orientation controlling by thermal diffusion treatment at various temperature gradient was studied for the superconductive YBa2Cu3Oy ceramics by means of X-ray diffraction analysis and SEM observations: The degree of orientation estimated by X-ray diffraction analysis was unexpectedly low, but local structures in SEM images was observed to be fairly oriented along heat flow derections. For obtaining highly oriented structures, one-directional temperature gradient during sintering should be elevated as possible.

Damping Characteristics of Fe-C-Sn-Pb System Infiltrated Alloys

Damping characteristics of sintered Fe-0.030 mass%C and Fe-0.014%C-2%Sn compacts which were infiltrated with pure Pb or Pb-2%Sn were investigated by using the magnetic driving resonant vibrating method. The purpose of C and Sn additions to Fe base skeletons was in improving the strengthening of skeletons, and Sn addition to Pb was in improving the wettability of infiltrants to Fe base skeletons. Infiltrated compacts were produced by sintering at 1273 K for 7.2 ks and then infiltrating at 1123 K for 600 s in purified H2 atmosphere.Results obtained were summarized as follows:(1) The ratio of infiltration (volume of infiltrants/total volume of porosity in the skeleton) for Fe-C-2%Sn compacts was a little inferior to that for Fe-C compacts, because of the formation of closed pores by melting out of Sn.(2) Typical Snoek peaks were observed for Fe-0.030%C/Pb (A/B: A; skeleton, B; infiltrant) and for Fe- 0.030%C/Pb-2%Sn compacts in the temperature dependent internal friction (Q-1) curves. Sn addition to Fe base skeletons markedly enhanced the value of Q-1 at the temperature of the appearance of Snoek peak, o.iginating in the relaxation of grain boundary diffusion of Sn. Sn addition to Pb infiltrant generally tended to lower the value of Q-1.(3) Q-1 for Fe-0.030%C/Pb or /Pb-2%Sn at 433 K appearing Snoek peak did not show the strain amplitude dependency up to emax=5-8×10-8, and over that, increased with the increase of emax- On the other hand, Q-1 for Fe-0.014%C-2%Sn/Pb or /Pb-2%Sn did not show the strain amplitude dependency up to smax??1×10-5. Q-1 of all specimens described above at room temperature showed the strain amplitude dependency above emax??1×10-5.(4) Damping index of Fe-0.030%C/Pb or /Pb-2%Sn was about 9%, rather higher than that of Fe-0.014%C-2%Sn/Pb or /Pb-2%Sn. On the other hand, mechanical properties such as tensile strength and hardness of Fe-0.014%C-2%Sn/Pb or /Pb-2%Sn was inversely a little higher than that of Fe-0.030%C/Pb or /Pb-2%Sn.

influence of Long Time Sintering on Superconductivity of Y Ba2Cu3Oy

Y Ba 2Cu3Oy powders obtained by pulverizing the mixed powder aggregate fired at 1173K for 86.4ks were cold pressed at 98MPa and sintered at various temperatures for 86.4-1036.8ks, and the relation between the sintering behavior and superconducting properties was investigated.The abrupt increment of sintered density ratio was observed by the sintering at 1198K after gradual increment with rising sintering temperature up to 1173K, and it remained constant in the higher sintering temperature range than 1198K. Though the sintered density ratio was about 72% even after sintering at 1173K for 1036.8ks, it exceeds 90% in the case of sintering at 1223K for 1036.8ks. The marked degradation of superconducting properties was recognized in the specimen sintered at 1223K for 759.6ks, where the lamella structure along the grain boundary due to the liquid phase formed during sintering was observed.