耐高温高湿电阻用底漆的制备及性能分析

用纳米SiO2、环氧树脂、酸酐、乙二醇等在80℃下制备了耐高温、耐高湿电阻用底漆,并对底漆的电性能、结构、热稳定性、机械强度、耐湿性能及电阻耐湿失效进行了分析研究.IR分析表明,纳米SiO2的加入改变了环氧树脂固化聚合物的结构,使其交联网状结构更为致密和稳定,且聚合物分子极性变小,从而对水具有较弱的亲和力,使得这种体系的底漆具有较好的耐高温高湿性能.冲击实验SEM照片显示加纳米SiO2的固化物呈韧性断裂,这表明纳米SiO2对环氧树脂具有增韧作用.当纳米SiO2质量分数为2.79×10-2时,底漆耐高温、耐高湿性能最好,且电阻变化率均小于1‰.

Wear and corrosion resistant coatings on surface of cast A356 aluminum alloy by plasma electrolytic oxidation in moderately concentrated aluminate electrolytes

Plasma electrolytic oxidation of a cast A356 aluminum alloy was carried out in aluminate electrolytes to develop wear and corrosion resistant coatings. Different concentrations of 2, 16 and 24 g/L NaAlO2 solutions and a silicate electrolyte （for comparison） were employed for the investigation. Wear performance and corrosion resistance of the coatings were evaluated by WC （tungsten carbide） ball-on-flat dry sliding tests and electrochemical methods, respectively. The results show that the coating formed for a short duration of 480 s in 24 g/L NaAlO2 solution generated the best protection. The coating sustained 30 N load for sliding time of 1800 s, showing very low wear rate of -4.5×10^-7 mm3/（N· m）. A low corrosion current density of -8.81×10^-9 A/cm2 was also recorded. Despite low α-Al2O3 content of the coating, the compact and nearly single layer nature of the coating guaranteed the excellent performances.

Tribological and corrosion behavior of PEO coatings with graphite nanoparticles on AZ91 and AZ80 magnesium alloys

The effect of the addition of graphite nanoparticles into the electrolyte used to produce plasma electrolytic oxidation（PEO） coatings on AZ91 and AZ80 magnesium alloys was studied. The corrosion and wear resistances of the obtained coatings were investigated. A solution that contained both phosphates and silicates was used as electrolyte. Moreover, two different PEO treatment times were studied. The corrosion resistance was analyzed with potentiodynamic polarization and EIS tests; the wear resistance was investigated with a flat on ring tribometer. The results were related to the morphology, microstructure, elemental composition and thickness evaluated with SEM analysis. The presence of the graphite nanoparticles increased the thickness, produced a densification of the coating and sealed the pores on the surface, thus improving both the corrosion and wear resistance. The increase in the corrosion and wear resistances was more evident for AZ91 than for AZ80 due to the higher aluminum content.

Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy,a magnetron-sputtered Al layer with a thickness of 11μm was firstly applied on the alloy,and then treated by plasma electrolytic oxidation(PEO)in an aluminate and silicate electrolytes,respectively.The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests.The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads.The silicate coating only shows low wear rate under 10 N,but it was destroyed under 20 N.Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate.However,the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy.Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of-1.6×10^(-6) and-1.1×10^(-6) A/cm^(2),respectively,which are two orders lower than that of the un-coated AZ31 alloy.However,immersion tests and electrochemical impedance spectroscopy(EIS)show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.

Plasma electrolytic oxidation behavior and corrosion resistance of brass in aluminate electrolyte containing NaH2PO4 or Na2SiO3

Plasma electrolytic oxidation(PEO) of brass was carried out in aluminate electrolytes with the addition of NaH2PO4(S1) and Na2SiO3(S2), respectively, with the aim to investigate the effect of additives on the coating formation and corrosion resistance. For the PEO in S1 electrolyte, a mixed layer of AlPO4and Al2O3is formed at the initial stage, which leads to fast plasma discharges and formation of black coatings with the compositions of Al2O3,CuO, Cu2O and ZnO. However, in S2 electrolyte, plasma discharges are delayed and the coatings show a reddish color due to more Cu2O. Mott-Schottky tests show that the S1 coatings are p-type semiconductors;while the S2 coatings can be adjusted between n-type and p-type. Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests show that the PEO treatment can significantly improve the corrosion resistance of brass, with protection efficiency up to 91.50% and the largest charge transfer resistance of 59.95 kΩ·cm^(2) for the S1 coating.

Microstructural, corrosion and mechanical behavior of two-step plasma electrolyte oxidation ceramic coatings

Plasma electrolytic oxidation(PEO)is considered as a cost effective and environmentally friendly surface treatmentprocess for improving surface properties of light alloys.The formation of ceramic coatings on Ti6Al4V alloy was reported bytwo-step PEO process and its structural,electrochemical and mechanical properties with the coated samples were compared byone-step PEO process in an alkaline electrolyte.The structural properties were studied using field-emission scanning microscope(FESEM)and X-ray diffraction(XRD).Electrochemical studies were carried out using linear polarization method and in additionmechanical behaviors were investigated by means of Knoop microhardness and nanoindentation method.Results showed that thesecond step process resulted in an increase of both porosity percentage and average pore diameter on the surface.The two-stepprocess resulted in a small increase of thickness from about12.5to13.0μm.Electrochemical test results showed that applying thesecond step resulted in the decrease of both polarization resistance from1800.2to412.5kΩ/cm2and protection efficiency from97.8%to90.5%.Finally,the nanoindentation results indicated that the PEO coatings became softer but more ductile after applyingthe second processing step in acidic electrolyte.

Current Efficiency, Corrosion and Structural Changes in SnO2-Sb2O3-CuO Inert Anodes for Aluminium Electrolysis

A systematic study was conducted on current efficiency （CE）, corrosion and structural changes in SnO2-based inert anodes （made of 96wt%SnO2＋2wt%Sb2O3＋2wt%CuO） on a laboratory Hall-Heroult aluminium cell. The influence of operating parameters and electrolyte composition on the CE and corrosion process were evaluated. The CE was found to be more than 90% and catastrophic corrosion took place at low percent of Al2O3, high percent of LiF, low cryolite ratio and high current densities. From all the structural changes that took place in the SnO2-based inert anodes, we assumed that the most important contribution was due to the migration of CuO towards the outer limits of the constituent grains of SnO2 based ceramic. The complex process occurred during the formation of various phases and their sintering ability both directly depended on Cu/Sb molar ratio.