Corrosion of synthetic metals

Intrinsically conducting polymers as polypyrrole or polythiophene are new materials which have found widespread interest in the last ten years. Acceptor type doping leads to a solid, which is well comparable to graphite salts. For any kind of practical application of these polymers, the problem of adequate long term stability under environmental conditions must be solved. There are only a few measurements of conductivity vs. time in the air to derive conclusions in this direction, e.g. for polypyrrole. For the first time we present results of a systematic research into the understanding of corrosion phenomena, which occur in aqueous eletrolytes at different pH. Polypyrrole is selected as a well established candidate for a synthetic metal. Layers at a nominal thickness of 10μm on platinum, doped with BF₄^? anions, were investigated in aqueous buffers in the pH-range of 1–13. Corrosion was determined via the measurement of the residual redox capacities. The material corroded after a rapid electrochemical mechanism and a relatively slow chemical mechanism. Both processes involve the radical cationic centers (polarons) in the solid. The time constants varied from 10² to > 10⁸ s. Our findings allow for a better understanding of corrosion and selfdischarge of polypyrrole. Other conducting polymers were found to corrode after the same mechanism.     

Development and cross-validation of a short form for the WISC-R.

Multiple linear regression was used to derive a short form for the WISC-R in 300 6–17 yr olds receiving treatment and/or evaluation at a university-affiliated community mental health center. The predictive validity of this approach was examined via a cross validation that included 300 additional Ss from the same population; 2 short-form regression equations were taken from the work of L. P. Kennedy and S. T. Elder (see record 1982-08867-001), and a short form was derived from the Wechsler normative sample (D. Wechsler, 1974). Correlations and standard errors of the estimates are reported for both the original and cross-validational samples. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Solubility characteristics of poly(etheretherketone) and poly(phenylene sulfide)

The crystalline high-performance polymers poly(etheretherketone) (PEEK) and poly(phenylene sulfide) (PPS) are generally considered to be highly resistant to dissolution in most common solvents. This article reveals numerous compounds that dissolve in excess of 25 wt % of each polymer at elevated temperatures. Typical binary-phase diagrams depicting the minimum solubility temperature vs. concentration are also presented for several representative polymer–solvent mixtures for both PEEK and PPS. The phenomenon of the solvent-induced crystallization of PEEK is presented. The importance of these polymer–solvent systems for the preparation of permselective membranes is discussed.     

Basic characteristics of spinel type manganese mixed oxide/titanium composite anodes for electroorganic redox catalysis

Manganese mixed oxide composite layers of about 1 μm thickness on titanium sheet as substrate were fabricated by firing of the corresponding nitrates at a typical temperature of 400°C in air. The activity of these anodes was evaluated by cyclic voltammetry (10 mV/s) and the stability was determined by chronopotentiometry (2.5 mA/cm²) in 1M H₂SO₄. The oxidation of 2-propanol was examined as a simple electroorganic model reaction. The quality of a first category of mixed oxides with general composition MnMe₂O₄ decresed in the order Me = Co, Ni, Fe. In a second group with the general formula MeMn₂O₄ a decrease in the order Me = Co, Cu, Fe, Ni, Ti, Zn, Cd, Ca, Mg, (Zn, Ge), Li was observed. The corresponding candidates of the second group were superior to those of the first. The anode service life τ of the optimum spinel anode CoMn₂O₄/Ti is dependent on the current density, according to j^λ τ = const. (λ = 1.7). Thus high current densities are precluded. The mechanism has been discussed in terms of a heterogeneous redox catalysis: surface Mn(VII) states are formed in a slow electrochemical step. In a subsequent fast chemical oxidation of the organic molecule the original reduced state is regenerated. This also explains the comparatively good service life of these anodes.     

Identification of soapstocks by gas chromatographic techniques

The stock of a given soap may be estimated when the ratios of the fatty acids present are known. A new gas chromatographic procedure utilizing a novel automatic attenuator is presented. The samples are prepared by refluxing the soap with a methanolic solution of boron trifluoride and separating the esters so formed by standard gas-liquid chromatographic procedures. Soapstock compositions are determined by comparison with reference curves.