Analysis of the Quality of Sulfomolybdenum Coatings Obtained by Electrospark Alloying Methods

The authors of this paper have attempted to improve the quality of surface layers applied to steel elements of machine parts constituting friction couples. The main goal of the research was to investigate an electrospark alloying method process for obtaining abrasion-resistant tribological coatings containing molybdenum disulfide on a steel surface. A substance in the form of sulfur ointment with a sulfur content of 33.3% was applied on the surfaces of C22 and C40 steel specimens. In order to determine the influence of the energy parameters of ESA equipment on the quality parameters of coatings, the ESA process was carried out using a molybdenum electrode with discharge energies Wp = 0.13; Wp = 0.55; Wp = 3.4 J. The following tests were carried out on specimens with such coatings: metallographic analysis, microhardness tests, surface roughness, and local X-ray diffraction microanalysis. The experiments revealed that sulfomolybdenum coatings consist of four zones with different mechanical properties. Depending on the discharge energy and the substrate material, the hardness of these zones varies from approx. 1100 to over 10,000 MPa. Differences in the distribution of, among others, sulfur and molybdenum in the obtained coatings, as well as differences in the microstructure of the observed coatings, were observed.

A Study on the Manufacturing of Molybdenum Pins for Electrodes

The molybdenum cup and molybdenum pin, which are the main materials of the molybdenum electrode used for the LCD BLU CCFL electrode, have not been developed in Korea and imported from Japan. In this paper, especially, research on prototype manufacturing and CAE analysis is performed to develop a molybdenum pin. In this research, to develop the manufacturing technology of molybdenum pin used for CCFL electrode of LCD BLU, development of linear processing technology, development of molybdenum wire surface treatment technology, development of wire cutting technology, production of molybdenum pin, design and fabrication of JIG and Fixture for inspection, molybdenum pin prototyping and analysis, and development of 100% molybdenum pin inspection technology. The development of molybdenum pins developed through this research can overcome Japan's technological level, which depends entirely on imports from Japan, and it is thought that the development will have a significant impact on the overall industry using molybdenum pins.

High-Efficiency Skutterudite Modules at a Low Temperature Gradient

Thermoelectric skutterudite materials have been widely investigated for their potential application in mid-temperature waste heat recovery that has not been efficiently utilized A large amount of research has focused on developing materials with a high thermoelectric figure of merit (zT). However, the translation of material properties to device performance has limited success. Here, we demonstrate single-filling n-type Yb0.25Fe0.25Co3.75Sb12 and multi-filling La0.7Ti0.1Ga0.1Fe2.7Co1.3Sb12 skutterudites with a maximum zT of ~1.3 at 740 K and ~0.97 at 760 K. The peak zT of skutterudites usually occurs above 800 K, but, as shown here, the shift in peak zT to lower temperatures is beneficial for enhancing conversion efficiency at a lower hot-side temperature. In this work, we have demonstrated that the Fe-substitution significantly reduces the thermal conductivity of n-type skutterudite, closer to p-type skutterudite thermal conductivity, resulting in a module that is more compatible to operate at elevated temperatures. A uni-couple skutterudite module was fabricated using a molybdenum electrode and Ga–Sn liquid metal as the thermal interface material. A conversion efficiency of 7.27% at a low temperature gradient of 366 K was achieved, which is among the highest efficiencies reported in the literature at this temperature gradient. These results highlight that peak zT shift and optimized module design can improve conversion efficiency of thermoelectric modules at a low temperature gradient.

Studies on Cerium Electrochemistry in High Temperature Ionic Liquids

The cathodic behavior of Ce3+ ions in LiF-NaF-BaF2, LiF-NaF-NaCl and NaCl-KCl molten salts at 730� C has been studied using different electrochemical techniques. The decomposition potential (Ed) and the cathodic overvoltage were determined by introducing NaCeF4 as electrochemical active species using steady-state potential-current curves recorded under galvanostatic conditions. The values of |Ed| were 1.85 V in LiF-NaF-BaF2, 2.114 V in LiF-NaF-NaCl and 2.538 V in NaCl-KCl, respectively. It was also found that the ohmic drop potential in melt is not dependent on NaCeF4 concentration and it rises as the current intensity increases. The Tafel slopes and other kinetic parameters were calculated on the assumption that the cathodic process consisted of direct discharge of Ce3+, with no solvent-solute interaction. In order to elucidate the mechanisn of cathodic process the cyclic voltammetry technique was finally used. From the evolution of the voltammograms we conclude that the electrochemical reduction of Ce3+ ion is actually a reversible process on the molybdenum electrode and cathodic reduction of Ce3+ takes place in one single step involving three electron exchange. Our study adds to the accumulating data and confirms available results of electrodeposition of metalic cerium from molten salts using NaCeF4 as solute.

Electrochemical behavior of B(iii) on a molybdenum electrode in NaCl–KCl eutectic molten salt

An individual spheroidal aggregate boron coating with an average size of 200 nm is obtained on a stainless steel substrate, where the reduction of B(iii) to B(0) at 1023 K is a diffusion-controlled single-step three-electron transfer reaction.