Portugaliae
Electrochimica Acta

The rate of copper dissolution in presence of phosphoric acid tert-butanol electropolishing mixtures was studied by measuring the limiting current which represents the rate of electropolishing. The rate of dissolution decreases by increasing phosphoric acid concentration, electrode height and the mole fraction of alcohol. The data show that addition of tert-butanol to phosphoric acid decreases the rate of dissolution of copper by an amount ranging from 68 % to 90 % depending on the dielectric constant of mixtures. Thermodynamic parameters are given.

A solid of Fe2O3 based carbon-epoxy composite electrode was investigated for use as a potentiometric pH sensor. The electrode was constructed with a mixture of sulfated iron(III) oxide, carbon power and epoxy resin that was deposited directly onto a glass tube. The effect of composition (Fe2O3, carbon and epoxy resin) on the electrode response and its calibration curve (mV/pH) were investigated. The analytical behaviour of the electrode in acid-base titrations was compared with that of a glass electrode. A linear response from pH 1.7 to 12.2 with a slope of -39.7 ± 0.6 mV/pH (at 25 ºC) was observed.

The formation and stability of alkali metal complexes with crown ethers containing an anthraquinone unit has been investigated in methanol and acetonitrile solutions by potentiometric methods. Complexes of 1:1 stoichiometry were observed for all the studied systems; 2:1 complexes were only detected for the larger alkali cations (Rb+ and Cs+) and with the ligand with the larger macrocyclic cavity (AQ21C7). The 1:1 complexes with the highest stability are formed by K+ ion with the AQ18C6 ligand and by Cs+ ion with the AQ21C7 ligand. In the alkali cation group and in both solvents, the stability of the 1:1 complexes was found to vary in the following order, Li+ < Na+ < K+ > Rb+ > Cs+ with AQ18C6 ligand and Li+ < Na+ < K+ < Rb+ < Cs+ with AQ21C7 ligand. The stability of the complexes of AQ21C7 is smaller than those of their AQ18C6 analogues. The stability of the silver complexes of AQ18C6 and AQ21C7 was found to be smaller than that of the alkali metal complexes of comparable size. The incorporation of an anthraquinone unit in crown ethers induces some loss of complexation stability for all cations, but the cation selectivity is not changed. The results obtained are analysed and discussed regarding the effects of the relative sizes of the cations and macrocyclic cavity of the ligands, solvating ability of the solvents towards the cation and influence of the anthraquinone unit.

The electrochemical behavior of Pt(IV) ions in the presence of dimethylglyoxime has been investigated using adsorptive stripping voltammetric method. The results indicated that the platinum is reduced from its adsorbed state as bis-dimethylglyoxi-mate platinum(IV) complex. The peak current is linearly proportional to the Pt(IV) concentration in the solution, thus representing the basis for a quantitative analysis. Various experimental parameters affecting the stripping response, indicating pH, the ligand concentration or the accumulation time and potential, and the scan rate, were studied to obtain a highly linear response. From the results the scheme for the reduction process of the platinum dimethylglyoximate complex in acidic media is presented.

In liquid ammonia, the anodic behavior of n- and p-type III-V semiconductors are strongly different from those observed in aqueous media. For both types, the anodic process in liquid ammonia involves the formation of an adsorbed film, onto the semiconductor surface just before its dissolution. This film results from the chemisorption of N atoms, issued from the oxidation of the solvent.

The cathodic electrochemical behavior of InSb was studied in liquid ammonia. In neutral unbuffered media, in spite of strong negative polarization no electrochemical modification of the interface was observed. However, in acidic media, a cathodic decomposition was detected after scanning InSb in the potential range of hydrogen evolution. Hydrogen embrittlement results from a strong interaction of hydrogen radical (H.) and indium surface. A coated film of indium results from this cathodic decomposition.