Factors inducing degradation of properties after long-term oxidation of Si3N4–MoSi2 electroconductive composites

2004 ◽  
Vol 19 (5) ◽  
pp. 1567-1574 ◽  
Author(s):  
V. Medri ◽  
A. Bellosi
Keyword(s):  
Electrical Conductivity ◽  
Electrical Resistivity ◽  
Flexural Strength ◽  
Room Temperature ◽  
Material Surface ◽  
Oxide Scales ◽  
Silicate Phase ◽  
Degradation Of Properties ◽  
Glassy Silicate

The effects of heat treatments on strength and electrical conductivity after 100 h in air up to 1500 °C were evaluated on hot-pressed Si3N4–35 vol% MoSi2 composite. The long-term oxidation involves microstructural changes at the material surface and subsurface, such as the formation of oxide scales and of a multilayered microstructure. At T ⩾ 1200 °C, a glassy silicate phase is formed, which embeds cristobalite grains and highly textured Y2Si2O7 crystals. At the same time, MoSi2, assisted by oxygen, reacts with Si3N4 forming Mo5Si3, Si2N2O, and SiO2. The decrease of the room temperature flexural strength reached about 25% in the samples exposed at 1000 °C for 100 h, compared to the as-produced materials. On the contrary, after treatments at higher temperatures, the strength decrease is lower at 1500 °C, the residual strength is 836 ± 62 MPa with a strength decrease of about 8%. The surface oxide scale is an insulator and, consequently, the electrical resistivity of the composite rises from 10-3 to 107–109 Ωcm.

Lanthanide Refractory Semiconductors Based on the Th3P4 Structure

1987 ◽  
Vol 97 ◽  
Author(s):  
K. A. Gschneidner ◽  
J. F. Nakahara ◽  
B. J. Beaudry ◽  
T. Takeshita ◽  
Ames Laboratory
Keyword(s):  
Electrical Resistivity ◽  
Thermal Properties ◽  
Seebeck Coefficient ◽  
Thermoelectric Properties ◽  
Room Temperature ◽  
Type Structure ◽  
Term Stability ◽  
Long Term Stability ◽  
Phase Relationships

ABSTRACTThe phase relationships and the important structural, electrical and thermal properties of the R3X4-R2X3 (where R = lanthanides and X = S, Se and Te) phases having the Th3P4 -type structure are reviewed. The room temperature electrical resistivity and Seebeck coefficient of these materials are independent of R and only slightly dependent on X, but critically dependent on the X:R ratio. The long term stability of these phases is also reviewed. Although these materials have good thermoelectric properties there are some problems which need to be solved before these phases can be utilized in thermoelectric devices. These problems include long term stability, higher than desirable thermal conductivities, and low electron mobilities.

ELECTRICAL RESISTIVITY, HALL COEFFICIENT, AND THERMOELECTRIC POWER OF AuSb2 AND Cu2Sb

1964 ◽  
Vol 42 (3) ◽  
pp. 519-525 ◽  
Author(s):  
W. B. Pearson
Keyword(s):  
Electrical Conductivity ◽  
Electrical Resistivity ◽  
Thermoelectric Power ◽  
Hall Coefficient ◽  
Low Temperatures ◽  
Room Temperature ◽  
Iron Impurity

The electrical conductivity and absolute thermoelectric power of AuSb2 and Cu2Sb have been measured between 2.5° and 300 °K. Room-temperature Hall coefficients were also determined. Iron impurity causes a giant diffusion thermoelectric power at low temperatures in the compound Cu2Sb, as it has previously been found to do in Cu, Ag, and Au.

scholarly journals The effect of room temperature pre-ageing on tensile and electrical properties of thermomechanically treated Al-Mg-Si alloy

2002 ◽  
Vol 38 (1-2) ◽  
pp. 61-73 ◽  
Author(s):  
Z. Martinova ◽  
D. Damgaliev ◽  
M. Hirsh
Keyword(s):  
Experimental Data ◽  
Electrical Conductivity ◽  
Tensile Strength ◽  
Room Temperature ◽  
Solution Treatment ◽  
Optimal Combination ◽  
Precipitation Process ◽  
Treatment Room ◽  
Alloy Properties

A commercial Al - 0.62%Mg - 0.57%Si was thermomechanically treated (TMT). The TMT process included solution treatment, room temperature preageing, drawing (e=95%) and final ageing. The experimental data were proceeded statistically and mathematical models were derived for the alloy properties such as tensile strength, electrical conductivity and elongation of the wires during TMT. The models are used to find out the area of compromise optimal combination of the alloy properties. Higher final ageing temperature and time are required to design a TMT process for production of a long-term pre-aged wires. The influence of the room temperature preageing on the precipitation process during TMT is discussed.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

scholarly journals Mechanical Properties of Cement-Treated Soil Mixed with Cellulose Nanofibre

2021 ◽  
Vol 11 (14) ◽  
pp. 6425
Author(s):  
Hidenori Takahashi ◽  
Shinya Omori ◽  
Hideyuki Asada ◽  
Hirofumi Fukawa ◽  
Yusuke Gotoh ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Flexural Strength ◽  
Geotechnical Engineering ◽  
Strength Development ◽  
Soft Ground ◽  
Wood Cellulose ◽  
Treated Soil ◽  
Made In ◽  
Cement Treatment

Cellulose nanofibre (CNF), a material composed of ultrafine fibres of wood cellulose fibrillated to nano-order level, is expected to be widely used because of its excellent properties. However, in the field of geotechnical engineering, almost no progress has been made in the development of techniques for using CNFs. The authors have focused on the use of CNF as an additive in cement treatment for soft ground, where cement is added to solidify the ground, because CNF can reduce the problems associated with cement-treated soil. This paper presents the results of a study on the method of mixing CNF, the strength and its variation obtained by adding CNF, and the change in permeability. CNF had the effect of mixing the cement evenly and reducing the variation in the strength of the treated soil. The CNF mixture increased the strength at the initial age but reduced the strength development in the long term. The addition of CNF also increased the flexural strength, although it hardly changed the permeability.

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