Differential pulse voltammetric determination of P(V) following adsorptive accumulation of alpha-[PMo(12)O(40)](3-) on a polypyrrole-modified glassy carbon electrode.
On the basis of the formation and pre-concentration of an alpha-Keggin-type [PMo(12)O(40)](3-) complex, a novel voltammetric method was developed for the determination of trace levels of P(V). The alpha-[PMo(12)O(40)](3-) complex was formed by heating a 5x10(-4) M Mo(VI)-0.2 M HCl-40% (v/v) CH(3)CN system containing a trace amount of P(V) at 70 degrees C for 30 min. During the electrochemical polymerization of pyrrole in the alpha-[PMo(12)O(40)](3-) solution, the alpha-[PMo(12)O(40)](3-) complex was accumulated into the polypyrrole film on a glassy carbon electrode. The differential pulse voltammetric peak current due to the alpha-[PMo(12)O(40)](3-) complex incorporated in the polypyrrole film was linearly dependent on the P(V) concentration in the range of 5x10(-9)-5x10(-7) M; a detection limit of 2x10(-9) M was achieved.
Corrosion protection of steel by bi-layered polypyrrole doped with molybdophosphate and naphthalenedisulfonate anions
Abstract Bi-layered polypyrrole (PPy) coating was investigated for corrosion prevention of steels. The PPy coating consisted of the inner layer doped with PMo12 O 40 3 - (PMo12) and HPO 4 2 - ions and the outer layer doped with naphthalenedisulfonate (NDS) ions. PMo12 ions doped in the inner layer make the passive oxide film on steel stabilized and the outer layer doped with large organic ions of NDS restricts decomposition and release of PMo12 ions in the inner layer. Corrosion tests were made in 3.5% NaCl aqueous solution for the steels covered by the single PPy–PMo12, single PPy–NDS, and bi-layered PPy–PMo12/PPy–NDS coatings. The single PPy–PMo12 and PPy–NDS coatings maintained the steel in passive state for 34 h and 24 h, respectively. The bi-layered coating kept the steel in passive state and prevented corrosion of the steels for the longer time period.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.