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Abstract: Humidity sensor based on thin micro-arc oxidation alumina (MOA) film was fabricated by a transient self-feedback control (TSFC) technique for the first time. The MOA film consisted of a polycrystalline nature of α and γ-Al2O3 phases, while high surface/volume ratio led to remarkable adsorption of the MOA film. Moreover, the humidity performance of the MOA sensor indicated good sensitivity of 8045.55 at 98% RH. Fast response and recovery times of the MOA sensor were 90s and 30s, respectively, at 20°C and 1000Hz. Exposing the MOA sensor to different humidities for longer durations indicated an excellent stability due to the α-Al2O3 phase in the MOA film. The mechanism in the sensor, to humidity, was explained by using equivalent circuits of (RC) and (C(RZ)). In the low RH range, the process was mainly dominated by the migration of protons through the adsorbed water molecule layer on the surface of the MOA film; while, in the high RH range, the process was due to the faster diffusion of protons in the single or multiple layers that were formed on the materials surface. [Copyright &y& Elsevier]

Abstract: This work for the first time reports a monolayer plasma electrolytic oxidation (PEO) coating on 2024 Al alloy substrate by transient self-feedback control (TSFC) mode. The monolayer coating without outer porous layer exhibits rather excellent compactness and corrosion protection attributed to extensive distribution of scattered ceramic particles with small size and less porosity. A possible mechanism is proposed to explain the formation of TSFC coating. Due to uniform surface distribution of the filming-formative particles and the discharge energy under high frequency square voltage (HFSV) waveform, the formation of the outer porous layer has been prevented effectively. [Copyright &y& Elsevier]

Abstract: A Si-incorporated bioactive ceramic film was prepared on pure titanium by plasma electrolytic oxidation (PEO) in a new bath containing Ca2+, H2PO4 − and SiO3 2−. The film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The apatite-induced ability of PEO film was evaluated by soaking in a simulated body fluid (SBF) for various periods. The results showed that Si-incorporated PEO film present a porous microstructure, the pore size is around 1–5μm. The film mainly consists of anatase and rutile and a small amount of CaHPO4 and CaO, besides, bioactive compounds such as CaSiO3 and SiO2, also exist in the Si-incorporated PEO film. After immersion in SBF for 28 days, not only the surface layer but also the pores inside the Si-incorporated PEO film were completely filled by apatite crystals, whereas on the surface of a benchmark PEO film free of Si just present small piles of apatite crystals. Silicon incorporated into the PEO film provided more heterogeneous nucleation sites for apatite deposition and hence increased remarkably bioactivity of the PEO film. [Copyright &y& Elsevier]