Formation mechanism of nanopores in dense films of anodic alumina

Constant-current anodization of pure aluminum was carried out in non-corrosive capacitor working electrolytes to study the formation mechanism of nanopores in the anodic oxide films.Through comparative experiments,nanopores are found in the anodic films formed in the electrolytes after high-temperature storage(HTS)at 130°C for 240 h.A comparison of the voltage-time curves suggests that the formation of nanopores results from the decrease in formation efficiency of anodic oxide films rather than the corrosion of the electrolytes.FT-IR and UV spectra analysis shows that carboxylate and ethylene glycol in electrolytes can easily react by esterification at high temperatures.Combining the electronic current theory and oxygen bubble mold effect,the change in electrolyte composition could increase the electronic current in the anodizing process.The electronic current decreases the formation efficiency of anodic oxide films,and oxygen bubbles accompanying electronic current lead to the formation of nanopores in the dense films.The continuous electronic current and oxygen bubbles are the prerequisites for the formation of porous anodic oxides rather than the traditional field-assisted dissolution model.

Electrolytic Production of NF3 Using Boron-Doped Diamond Anode in Molten NH4F·2HF

The current efficiency for NF3 formation was independent on the current density in the range of 200 to 1,000 mA·cm^2. The average values of NF3 current efficiencies on the BDD （boron-doped diamond） anode with the boron-concentration of 2,500 ppm were 32.3% at 80℃, 63.3% at 100℃ and 59.7% at 120℃. The best current efficiencies for NF3 formation on the BDD anode with boron-concentrations of 2,500, 5,000 and 7,500 ppm were obtained at 100℃ and those were 63.3%, 73.3% and 56.2%, respectively. Although anode effect occurred on the BDD electrodes covered with a part of the surface of the spiculate structure, which had the boron-concentrations higher than 7,500 ppm, it did not take place on the BDD electrodes covered with the surface of diamond structure, even if the BDD electrode had the boron-concentration of 8,000 ppm.

Peroxyacetyl nitrate measurements by thermal dissociation-chemical ionization mass spectrometry in an urban environment： performance and characterizations

Peroxyacetyl nitrate （PAN） is an important indicator of photochemical smog and has adverse effects on human health and vegetation growth. A rapid and h!ghly selective technique of thermal dissociation chemical ionization mass spectrometry （TD-CIMS） was recently developed to measure the abundance of PAN in real time; however, it may be subject to artifact in the presence of nitric oxide （NO）. In this study, we tested the interference of the PAN signal induced by NO, evaluated the performance of TD- CIMS in an urban environment, and investigated the concentration and formation of PAN in urban Hong Kong. NO caused a significant underestimation of the PAN signal in TD-CIMS, with the underestimation increasing sharply with NO concentration and decreasing slightly with PAN abundance. A formula was derived to link the loss of PAN signal with the concentrations of NO and PAN, which can be used for data correction in PAN measurements. The corrected PAN data from TD- CIMS were consistent with those from the commonly used gas chromatography with electron capture detection, which confirms the utility of TD-CIMS in an urban environment in which NO is abundant. In autumn of 2010, the hourly average PAN mixing ratio varied from 0.06 ppbv to 5.17 ppbv, indicating the occurrence of photochemical pollution in urban Hong Kong. The tbrmation efficiency of PAN during pollution episodes was as high as 3.9 to 5.9 ppbv per 100 ppbv ozone. The efficiency showed a near-linear increase with NO, concentration, suggesting a control policy of NO,. reduction for PAN pollution.