Lubrication of Mo, W, and their Alloys with H2S gas admixtures to room temperature air
Abstract The in situ lubrication of molybdenum and tungsten using admixtures of hydrogen sulfide to room temperature and pressure air was achieved. Raman spectroscopy confirmed the presence of molybdenum disulfide and tungsten disulfide solid lubricants on elemental molybdenum and tungsten specimens, respectively. Pin-on-disk experiments were conducted with elemental molybdenum, elemental tungsten, and alloys of molybdenum and tungsten in atmospheres containing hydrogen sulfide. Friction coefficients were continuously recorded and comparisons between the sliding friction coefficient in air and in the hydrogen sulfide atmospheres were evaluated. In general, hydrogen sulfide admixtures reduced the friction coefficient for all materials containing molybdenum or tungsten. Friction coefficients for self-mated elemental molybdenum and self-mated elemental tungsten were reduced to μ =0.15 with hydrogen sulfide admixtures to air of 5% and 15%, respectively. In some cases friction coefficients as low as μ =0.08 were recorded.
In situ analysis of the tribochemical films formed by SiC sliding against Mo in partial pressures of SO2, O2, and H2S gases
X‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to identify gas reaction layers and tribochemical films formed during reciprocating sliding tests in an ultrahigh vacuum (UHV) tribometer. Tests were performed on UHV cleaned SiC pins and Mo flats during or after exposure to SO2, O2, or H2S gas at pressures around 40 Pa. XPS identified the gas reaction layers on Mo to be chemisorbed MoS2 and/or MoO2 phases less than 1 nm thick. AES of Mo wear tracks showed tribochemical films similar in composition to, but thicker than, the reaction layers. AES of SiC wear scars in all three gases indicated tribochemical films containing Si oxide and/or Si sulfide and possibly graphite. In addition, transfer films of Mo oxysulfide and Mo oxide were found in SO2 and O2 tests, respectively, but no transfer films were detected in H2S tests. Thermochemical calculations of stable reaction products of the gas–solid reactions were in good agreement with the phases inferred from XPS and AES. An...
Effective adsorption of lead ions using fly ash obtained in the novel circulating fluidized bed combustion technology
Abstract Fly ash was examined for the separation efficiency of Pb2+ ions from water in batch experiments. Fly ash is industrial waste produced from the incineration of sewage sludge by the novel circulating fluidized bed combustion (CFBC) technology and was taken into the experiments. Physical and chemical properties of the material were characterized using several methods, such as fraction analysis, particle size distribution, bulk density, composition, morphology, surface and internal structure by elemental analysis, FT-IR, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, comprehensive thermal analysis, fly ash texture by BET adsorption isotherms, specific surface area, volume of pores, average pore diameter and pore volume distribution by the BJH method. The influence of pH values on zeta potential of the fly ash surface before and after the adsorption process was conducted. The calculated maximum adsorption capacity of Pb2+ by fly ash reached 51.98 mg/g. The kinetic analysis revealed that the adsorption process is better described by the pseudo-second order equation and it is well fitted to the Freundlich model. In conclusion, fly ash obtained in the CFBC technology is a promising low cost adsorbent for the highly effective recovery of Pb2+ from wastewater.