Lefu Zhang

Synthesis of filled skutterudite compound La0.75Fe3CoSb12 by spark plasma sintering and effect of porosity on thermoelectric properties

Filled skutterudite compounds La0.75Fe3CoSb12 with different porosities were synthesized using spark plasma sintering (SPS) and the Archimedes method was used to measure the porosities of the specimens. Phase constitutions and compositions of the compounds were examined by XRD and EPMA, and fracture surfaces of the compounds were observed by SEM. The effect of porosity on the thermoelectric properties was studied based on the changes in the electrical resistivity, Seebeck coefficient and thermal conductivity as a function of porosity. Our results show that the Seebeck coefficient is independent of porosity and the increase of electrical resistivity is consistent with the reduction of thermal conductivity due to scattering of carriers and phonons by pores. In addition, the thermoelectric figure of merit ZT (where T is temperature and Z is a function of the Seebeck coefficient, electrical resistivity, and thermal conductivity) of specimens with high porosity is comparable to that of specimens with low porosity. This suggests that the ZT value of La0.75Fe3CoSb12 compound does not depend significantly on the porosity.

Corrosion and Stress Corrosion Cracking Susceptibility of Type 347H Stainless Steel in Supercritical Water

The corrosion resistance and stress corrosion cracking (SCC) susceptibility of Type 347H stainless steel (SS) in supercritical water (SCW) were investigated. The general corrosion behavior was inve...

Stress Corrosion Crack Growth Behavior of Type 310S Stainless Steel in Supercritical Water

Stress corrosion crack (SCC) behavior of Type 310S stainless steel (SS) in supercritical water was evaluated at 400°C to 550°C. Crack growth rates (CGR) were obtained as a function of temperature and corrosion potential. Results show that Type 310S SS exhibits 100% intergranular SCC, and creep plays an important role in the overall growth rate. The SCC CGR increases with temperature between 400°C and 550°C, and is higher at a medium-low corrosion potential (argon deaerated water) than in water with dissolved O2 or dissolved H2. A mechanism for SCC of Type 310S SS in supercritical water is proposed to explain the combined effect of SCC and creep.

Effects of Dissolved Gas and Cold Work on the Electrochemical Behaviors of 304 Stainless Steel in Simulated PWR Primary Water

The effects of dissolved gas and cold work on the electrochemical behaviors of Type 304 stainless steel were investigated in simulated pressurized water reactor primary water environment by potentiodynamic polarization and electrochemical impedance spectroscopy. Results reveal that both dissolved gas and cold work have a significant influence on anodic passivation properties and corrosion resistance of the oxide film. In Ar deaerated water and oxygenated water environments, the corrosion potential of stainless steel and Pt is controlled by the dissolved oxygen concentration, and the corrosion resistance of the inner barrier layer is much higher. However, in H2 deaerated water, the corrosion potential is depressed by the H2/H2O redox potential and the inner oxide film formed in H2 deaerated water is less stable. In addition, the passive region of polarization curves on 304 stainless steel in oxygenated and Ar deaerated water is controlled by metal dissolution instead of water oxidation, and the passive cur...

Corrosion Fatigue Crack Growth Behavior of Alloy 690 in High-Temperature Pressurized Water

Corrosion fatigue crack growth behavior of Alloy 690 was investigated in air and high-temperature pressurized water environments. The stress intensity factor amplitude threshold (ΔKth) was obtained, and the effects of stress intensity factor (ΔK), cyclic frequency (f), loading ratio (R), and material orientation on the corrosion fatigue crack growth rates were studied. The observed environmental acceleration on corrosion fatigue crack growth was quantitatively analyzed, and an empirical formula and the Ford-Andresen model were utilized to describe and explain the corrosion fatigue behavior of Alloy 690.