Renato Alexandre Costa de Santana

Optimization of operational parameters and bath control for electrodeposion of Ni-Mo-B amorphous alloys

Optimization of operational parameters of an electrodeposition process for deposition of boron-containing amorphous metallic layer of nickel-molybdenum alloy onto a cathode from an electrolytic bath having nickel sulfate, sodium molybdate, boron phosphate, sodium citrate, sodium-1-dodecylsulfate and ammonia for pH adjustments to 9.5 has been studied. Detailed studies of the efects on bath temperature, mechanical agitation, cathode current density and anode format have led to optimum operational conditions for obtaining satisfactory alloy deposits. The highest cathode current efficiency for deposition of the alloy was about 69% for cylindrical and 64% for rectangular platinum anode while working at bath temperature 80oC, cathode rotation 15 rpm and cathode current density 100 mA cm-2. A voltammetric method for automatic monitoring and control of the process was proposed.

Otimização do banho eletrolítico da liga Fe-W-B resistente à corrosão

A study on optimization of bath parameters for electrodeposition of Fe-W-B alloys from plating baths containing ammonia and citrate is reported. A 23 full factorial design was successfully employed for experimental design analysis of the results. The corrosion resistance and amorphous character were evaluated. The bath conditions obtained for depositing the alloy with good corrosion resistance were: 0.01 M iron sulfate, 0.10 M sodium tungstate and 0.60 M ammonium citrate. The alloy was deposited at 12% current efficiency. The alloy obtained had Ecorr -0.841 V and Rp 1.463 x 104 Ohm cm2. The deposit obtained under these conditions had an amorphous character and no microcracks were observed on its surface. Besides this, the bath conditions obtained for depositing the alloy with the highest deposition efficiency were: 0.09 M iron sulfate, 0.30 M sodium tungstate and 0.50 M ammonium citrate. The alloy was deposited at 50% current efficiency, with an average composition of 34 wt% W, 66 wt% Fe and traces of boron. The alloy obtained had Ecorr -0.800 V and Rp 1.895 x 103 Ohm cm2. Electrochemical corrosion tests verified that the Fe-W-B alloy deposited under both conditions had better corrosion resistance than Fe-Mo-B.

Potentiometric and conductometric studies on the system acid-isopolytungstate and the formation of lanthanum tungstates

The stoichiometry of the polyanions formed by the action of nitric acid on sodium tungstate (≤ 0.01M) has been studied by means of electrometric techniques involving pH-potentiometric and conductometric titrations. The well defined inflections and breaks in the titration curves provide evidence for the existence of the polyanions, para-W12O41 10- and meta-W12O39 6- corresponding to the ratio of H+:WO 4 2- as 7:6 and 9:6 in the pH ranges 5.7-6.0 and 3.6-4.1, respectively. The interaction of lanthanum nitrate with sodium tungstate solutions, at specific pH levels 8.0, 5.9 and 4.0 was also studied by pH and conductometric titrations, in aqueous and alcoholic media, with each of the reagents alternatively used as titrant. The electrometric experiments provide definite evidence of the formation of normal-La2O3.3WO3, para-5La2O3.36WO3 and meta-La2O3.12WO3 tungstates in the vicinity of pH 6.3, 5.0 and 4.2, respectively. Analytical investigations on the precipitates formed confirm the results of the electrometric study.

Electrometric investigations on formation of lanthanum molybdates as a function of Ph

The precise nature of the reaction between lanthanum nitrate and sodium molybdate at specific pH levels 7.6, 5.5 and 4.1 has been studied by means of electrometric techniques involving potentiometric and conductometric titrations, in aqueous and alcoholic media using each reagent as titrant. Well-defined breaks and inflections in the titration curves provide cogent evidence for formation and precipitation of lanthanum normal-La2O3.3MoO3, para- La2O3.7MoO3 and octa-2 La2O3.24MoO3 molybdates in the vicinity of pH 5.9, 4.8 and 4.2, respectively. Analytical investigations of the precipitates of lanthanum molybdates have also been carried out, which substantiate the results of the electrometric study.

Electrometric studies on formation of cerium vanadates as a function of pH

A natureza precisa da reacao entre solucoes de acido nitrico e de ortho-vanadato de sodio foi estudada por tecnicas electrometricas envolvendo titulacoes potenciometricas e condutometricas. As inflexoes e degraus bem definidas nas curvas de titulacoes confirmaram a existencia de anions, piro-V2O74-, meta-VO3- e poli-H2V10O284- correspondendo as razoes de VO43-:H+ como 1:1, 1:2 e 1:2,6 na vizinhanca do pH 10,5; 7,4 e 3,6, respectivamente. Ainteracao entre solucoes de nitrato de cerio(III) e vanadato de sodio a especificos niveis de pH 12,4; 10,5; 7,4 e 3,6 tambem foi estudada por titulacoes potenciometricas e condutometricas entre os reagentes. Os pontos finais obtidos a partir de inflexcoes nitidas nas curvas de titulacoes forceram evidencias incontestaveis sobre a formacao e precipitacao de vanadatos orto-Ce2O3.V2O5, piro-2Ce2O3.3V2 O5 e meta-Ce2O3.3V2O5 de cerio nas proximidades dos valores de pH 7,4; 6,2 e 4,8, respectivamente. Investigacoes analiticas sobre os precipitados formados confirmam os resultados do estudo eletrometrico.

Formation of Nickel Vanadates as a Function of pH

The precise nature of the reaction between hydrochloric acid and sodium ortho-vanadate solution has been studied by means of electrometric techniques involving potentiometric and conductometric titrations. The well defined inflections and breaks in the titration curves confirm the existence of the anions, pyro-V2O74- , meta-VO3- and poly-H2V10O284- corresponding to the ratios of VO43-:H+ as 1:1, 1:2 and 1:2.6 in the neighborhood of pH 10.5, 7.4 and 3.6, respectively. The interaction of nickel chloride with sodium vanadate solutions, at specific pH levels 12.4, 10.5, 7.4 and 3.6 was also studied by potentiometric and conductometric titrations between the reactants. The end-points obtained from the sharp inflections in the titration curves provide definite evidence for the formation of ortho-3NiO.V2O5, pyro-2NiO.V2O5 and meta-NiO.V2O5 vanadates of nickel in the vicinity of pH 8.9, 8.0 and 6.8, respectively. Analytical investigations on the precipitates formed confirm the results of the electrometric study.