FeCr alloy coating can be sprayed on low-carbon steel to improve the corrosion resistance because of FeCr alloy’s high anti-corrosion capacity. In this paper, Fe microparticles/Cr nanoparticles coating (NFC) and FeCr microparticles coating (MFC) were prepared by atmospheric plasma spraying and NFC was heat-treated under hydrogen atmosphere at 800 °C (HNFC). EDS mapping showed no penetration of Ni in MFC and NFC while penetration of Ni occurred in HNFC. X-ray diffraction results indicated the form of the NiCrFe (bcc) solid solution in HNFC. SECM testing in 3.5 (wt.%) NaCl revealed that the anti-corrosion capacity of NFC improved compared with MFC, while HNFC improved further.

In this study, Fe-Si nanoparticle composite coating (FSN) and Fe-Si microparticle composite coating (FSM) were prepared via atmospheric plasma spraying, and FSN was thermally treated under hydrogen atmosphere at 1120 °C for holding time of 2.5 h (TFSN). Under transmission electron microscopy, many unmelted nanoscale particles were observed in FSN, while no substantial particles were found in TFSN. On scanning electron microscopy analysis, pores and cracks were observed in FSM and FSN, while no defects were found in TFSN. Scanning electrochemical microscopy testing in 3.5 wt.% NaCl for 5 h revealed that FSM underwent severe pitting corrosion, FSN showed relatively minor pitting corrosion, and TFSN had no pitting corrosion.

Mott–Schottky analysis, electrochemical impedance spectroscopy in conjunction with the Point Defect Model (PDM), were performed to characterize the semi-conductor property of passive films formed on Cu–Ni alloys in 1 mol/L NaOH solution. The acceptor density, flat potential and vacancy diffusion coefficient in the passive films formed on Cu–Ni alloys were determined. Results indicated that the passive films displayed p-type semi-conductive characteristics, where metal vacancies (over oxygen vacancies and interstitials) preponderated. With the increase of Cu, the flat potential moved towards positive, while the acceptor density and impedance of passive films decreased due to its steady oxidation-from Cu(I) to Cu(II), which increased the susceptibility to corrosion. In addition, the acceptor density and flat potential increased when the formation potential moved towards negative. The calculated value obtained for D0 was around 10−14 cm−2 s−1.Highlights► The passive films of all coatings displayed p-type semi-conductive characteristics. ► An anodic peak appeared during passive region with the increase of Cu content. ► The Rpf and Na for Cu–Ni alloys reduced with increase of Cu, while Efb became higher. ► The calculated value obtained for D0 was in the range 10−14 cm−2 s−1.

Silver in the form of AgNO3 was added to ZnO-based varistor ceramics prepared by the solid-state reaction method. The effects of AgNO3 on both the microstructure and electrical properties of the varistors were studied in detail. The optimum addition amount of AgNO3 in ZnO-based varistors was also determined. The mechanism for grain growth inhibition by silver doping was also proposed. The results indicate that the varistor threshold voltage increases substantially along with the AgNO3 content increasing from 0 to 1.5mol%. Also, the introduction of AgNO3 can depress the mean grain size of ZnO, which is mainly responsible for the threshold voltage. Furthermore, the addition of AgNO3 results in a slight decrease of donor density and a more severe fall in the density of interface states, which cause a decline in barrier height and an increase in the depletion layer.

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd2O3 in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn3(PO4)2 · 4H2O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd2O3 reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.

Deep level donor’s ionization behavior of passive film formed on the surface of stainless steel was investigated by Mott-Schottky plots. It is indicated that transformation process of deep level donors’ ionization behavior of passive film on surface of stainless steel can be divided into 4 stages with rising immersion time. At the initial immersion stage (10 min), Fe(II) located in the octahedral sites of the unit cell is not ionized and the deep level does not appear in Mott-Schottky plots. At the second stage (9–38 h), Fe(II) located in the octahedral sites starts to be ionized, which results in deep level donors’ generation and density of deep level donors almost is constant with augmenting immersion time but the thickness of space charge layer is more and more thicker with rising immersion time. At the third stage (48 h–12 d), density of deep level donors rises with increasing immersion time and the thickness of passive films space charge layer decreases. At last stage (above 23 d), both the space charge layer’s thickness and density of deep level donors are no longer changed with increasing immersion time. In the overall immersion stage, the shallow level donors’ density is invariable all the time. The mechanism of deep level donor’s ionization can be the generation of metal vacancies, which results in crystal lattice’s aberration and the aberration energy urges the ionization of Fe(II) in octahedral sites.