In this work, wet oxidative decomposition of (NH4)2SO4 in an air and Ar atmosphere was conducted in a lab-scale airtight glass vessel reactor by adding Na2S2O8 and H2O2 as oxidative agents to (NH4)2SO4 solution. The initial concentration of NH4+ in (NH4)2SO4 aqueous solution was set to 1,000 mg-NH4+/dm3. The experiments were conducted at temperatures of 343–363 K, keeping the initial pH at a prescribed value between 5.5 and 13.5. The mixing molar ratio of (NH4)2SO4/oxidant was set to 1/1 – 1/10. Results show that the decomposition of (NH4)2SO4 by Na2S2O8 in an alkaline region was more significant than that by H2O2 because most H2O2 disappeared by self-decomposition under the present conditions. Results further showed that (NH4)2SO4 was almost decomposed completely in about 150 min reaction time by adding Na2S2O8 at a molar ratio of (NH4)2SO4/Na2S2O8=1/3 at 363 K in an alkaline condition of pH=13.5. The rates of decomposition of Na2S2O8 and (NH4)2SO4 were expressed by the first-order kinetics with respect to the concentrations of Na2S2O8 and (NH4)2SO4 with constant initial concentrations of (NH4)2SO4 and Na2S2O8, respectively. When Na2S2O8 was added to (NH4)2SO4 solution, NH3(aq) was decomposed by reactive oxygen species such as • SO4−, • OH−, • O−, • O3−, etc. in an alkaline condition, producing the main reaction product of N2 and small amounts of NO2− and NO3− by-products. In this oxidative decomposition of (NH4)2SO4, O2 formation was suppressed by the consumption of these reactive oxygen species.
The inhibitory effect of BTA on the anodic dissolution of copper in an acid solution was studied using a channel flow double electrode. Electrochemical measurements obtained using channel flow double electrode enable the determination of dissolution currents of cuprous or cupric ions with the measurement of the potentiodynamic polarization curve. The diffusion-limiting current decreased remarkably in an acid solution containing BTA. Results show that the actions of BTA on the dissolution mechanisms of cuprous and cupric ions are different. Potential-pH diagrams were constructed and compared with the experimental data. CuCl and Cu(I)-BTA are in equilibrium at the forming potential of Cu(I)-BTA film. The decrease of the dissolution current of cuprous ions by the addition of BTA originates from the formation of Cu(I)-BTA film by reacting CuCl and BTA. Cupric ions dissolve at the noble potential in the presence of Cu(I)-BTA film on the copper surface. For the measurement of transient current at potentiostatic polarization, the time at which the initial current value becomes 1/10 was defined as the film formation time(t1/10), which was evaluated at various potentials. The competitive reactions of copper dissolution and Cu(I)-BTA film formation were investigated based on the potential dependence on t1/10.
It is well known that bulk Pd-Ni-P metallic glass with a wide range of compositions (Pd: 25–60 at%; Ni: 20–57 at%; P 16–22 at%) can be prepared. In the present study, we investigated the method of production of electrodeposited Pd-Ni-P metallic glass films whose composition range is the same as that of bulk Pd-Ni-P metallic glass. The composition of electrodeposited Pd-Ni-P films were controlled by adjusting the concentrations of PdCl2, NiSO4·6H2O and H3PO3 in the Pd-Ni-P bath. X-ray diffraction patterns and transmission electron microscopy images showed that the electrodeposited Pd-Ni-P films were amorphous. The results of differential scanning calorimetry indicated that the electrodeposited Pd-Ni-P films were metallic glass with Pd, Ni, and P compositions of 36–57 at%, 25–43 at%, and 17–20 at%, respectively, which were almost identical to those in bulk Pd-Ni-P metallic glass. Furthermore, we succeeded in producing a Pd42Ni37P21 metallic glass film by electrodeposition. The alloy composition of this film was very similar to that of Pd40Ni40P20, which is one of the best bulk metallic glasses because of its glass forming ability (GFA).