Superconducting properties of PEO coatings containing MgB2 on niobium

A study has been carried out of superconductivity in coatings formed on niobium by plasma electrolytic oxidation (PEO) in an electrolyte containing different concentrations of MgB2. From preliminary experiments, a suitable PEO condition was selected. The coatings were examined by analytical scanning electron microscopy and X-ray diffraction. Superconductivity was assessed using magnetic moment-field measurements. At 6 K, superconductivity of the niobium dominated, which revealed strong flux pinning and sudden release. The latter was more gradual following PEO, indicating pinning was a surface effect. Between the critical temperature of niobium (9.25 K) and MgB2 (about 39 K), the diamagnetic behaviour of superconducting MgB2 was present, with earlier flux penetration the closer the temperature to 39 K. The hysteresis loop indicated stronger flux pinning for lower temperatures, as expected for a superconductor

Hourly Price-Based Demand Response for Optimal Scheduling of Integrated Gas and Power Networks Considering Compressed Air Energy Storage

Gas-fired plants are becoming an optimal and practical choice for power generation in electricity grids due to high efficiency and less emissions. Such plants with fast start-up capability and high ramp rate are flexible in response to stochastic load variations. Meanwhile, gas system constraints affect the flexibility and participation of such units in the energy market. Compressed air energy storage (CAES) as a flexible source with high ramp rate can be an alternative solution to reduce the impact of gas system constraints on the operation cost of a power system. In addition, demand response (DR) programs are expressed as practical approaches to overcome peak-demand challenges. This study introduces a stochastic unit commitment scheme for coordinated operation of gas and power systems with CAES technology as well as application of an hourly price-based DR. The introduced model is performed on a six-bus system with a six-node gas system to verify the satisfactory performance of the model

Plasma electrolytic oxidation of titanium in a phosphate/silicate electrolyte and tribological performance of the coatings

AbstractPlasma electrolytic oxidation of titanium has been investigated using a phosphate/silicate electrolyte with a square waveform and a frequency of 50Hz. A range of constant rms current densities, duty cycles and negative-to-positive current ratios was employed. The resultant coatings were examined by analytical scanning and transmission electron microscopies and X-ray diffraction. The coatings, which were limited in thickness to ∼40 to 50μm, contained anatase, rutile, Ti2O5 and silicon-rich, amorphous material. The tribological behaviour was investigated using a ball-on-disc test, revealing a coefficient of friction against steel of ∼0.8, which reduced to ∼0.4 by incorporation of ptfe particles from the electrolyte. However, due to the composition and morphology of the coatings, their wear life was relatively short

Influence of coating morphology on adhesive bonding of titanium pre-treated by plasma electrolytic oxidation

AbstractThe effect of plasma electrolytic oxidation (PEO) pre-treatments on the adhesive bonding of titanium is investigated using lap-shear tests. Two pre-treatments are compared, using aluminate-phosphate and silicate-phosphate electrolytes respectively, which result in different compositions and morphologies of coatings. Specimens were joined with an epoxy adhesive. The PEO-treated specimens revealed mainly cohesive failure within the titanium-rich inner coating regions, which contrasted with the adhesive failure of untreated titanium. The silicate-phosphate pre-treatment resulted in the infiltration of a highly porous outer region of the coating by the adhesive. The fracture of the coatings occurred close to the titanium/coating interface and intersected the bases of relatively large pores, which in the case of the aluminate-phosphate coating lay beneath nodules that were evident at the coating surface. The pre-treatments did not significantly increase the lap-shear strength in comparison with untreated titanium