MULTI-OBJECTIVE OPTIMIZATION OF SOLUTION’S COMPOSITION ON THE BASE OF NICKEL COMPLEXES WITH GLYCINE AND SUCCINIC ACID FOR ELECTROLESS DEPOSITION OF Ni-P ALLOY

In this paper the effect of parameters such as concentration of glycine, succinic acid and bath pH on the technological parameters of the electroless deposition of nickel-phosphorus alloy coatings (deposition rate, specific pH change during deposition), the composition of the coatings and their properties (microhardness after heat treatment) was studied. Experimental design of 23 central composite design (CCD) was used to evaluate the appearance of coating, rate, specific pH change, the chemical composition of alloys, and microhardness, as well as to optimize the electroless process of the alloy using Response Surface Methodology (RSM) associated with experimental design. The microhardness of the deposited coatings was 4.6 - 6.8 GPa and after heat treatment at 400 °C for 0.5 h increased to 9.7-11.6 GPa, which corresponds to hard chromium coatings obtained by electrodeposition from solutions of chromic acid. The Harrington desirability function was applied for optimization. The optimal composition of bath (in mol/l) and electroless conditions are proposed: NiSO4·6H2O – 0.12, NaH2PO2·H2O– 0.36, NH2CH2COOH – 0.30, (CH2)2(COOH)2 – 0.20, Pb(CH3COO)2 - 10-5; pH – 5.8. Temperature – 70 – 96 ºС. An acceptable rate deposition of 8 (70 ºС) and 34 (95 ºС) mg/(cm2∙h) was observed for an alloy obtained under optimal conditions from an solution of optimal composition. Under these conditions, the coating contained 6 wt.% of phosphorus. Therefore, the results of this work show the importance of using optimization techniques to obtain metallic coatings with controlled properties for different types of applications.

Morphological and elemental analyses of supported palladium (Pd)/silver (Ag) composite membranes

Supported palladium (Pd)/silver (Ag) composite membranes have been investigated for hydrogen separation mainly in order to avoid hydrogen embrittlement, improve hydrogen permeance and reduce membrane cost. The electroless method is recommended for the co-plating of Pd and Ag on a substrate surface. However, Ag precursor has a higher redox potential than Pd and, thus, Ag is preferentially deposited, which compromises the membrane selectivity to hydrogen. Here we investigated the morphology and elemental composition of supported palladium (Pd)/silver (Ag) composite membranes produced by different methods. The first membrane was produced from a plating solution of 80 wt% of Pd and 20 wt% of Ag. The membrane surface presented several large dendritic crystals that not grown in a direction to form a dense metallic film. According to EDS results, the membrane surface presented similar Pd and Ag composition, which confirms the preferential Ag deposition. At room temperature, this membrane presented a nitrogen flux of 0.35 mol m-2 s-1 at 200 kPa of transmembrane pressure. Thus, the formed membrane is not suitable for hydrogen separation. The second membrane was formed by adding small amounts of Ag to the plating solution during the electroless process. The final plating solution contained 75 wt% of Pd and 25 w% of Ag. The membrane thickness was 2 µm, but the membrane morphology was not totally dense. According to EDS results, the Ag composition was greater than the Pd composition, especially at the membrane top surface. This membrane also presented high nitrogen permeance probably due to the holes formed on the membrane surface. Thus, although the controlled addition of Ag is recommended to form dense membranes, the Ag was preferentially deposited over the Pd when starting with the highest rate of Ag addition. Adding lower Ag rates at the beginning could be helpful to avoid the preferential Ag deposition.

Morphological and Elemental Analyses of Supported Palladium (Pd)/Silver (Ag) Composite Membranes

Supported palladium (Pd)/silver (Ag) composite membranes have been investigated for hydrogen separation mainly in order to avoid hydrogen embrittlement, improve hydrogen permeance and reduce membrane cost. The electroless method is recommended for the co-plating of Pd and Ag on a substrate surface. However, Ag precursor has a higher redox potential than Pd and, thus, Ag is preferentially deposited, which compromises the membrane selectivity to hydrogen. Here we investigated the morphology and elemental composition of supported palladium (Pd)/silver (Ag) composite membranes produced by different methods. The first membrane was produced from a plating solution of 80 wt% of Pd and 20 wt% of Ag. The membrane surface presented several large dendritic crystals that not grown in a direction to form a dense metallic film. According to EDS results, the membrane surface presented similar Pd and Ag composition, which confirms the preferential Ag deposition. At room temperature, this membrane presented a nitrogen flux of 0.35 mol m-2 s-1 at 200 kPa of transmembrane pressure. Thus, the formed membrane is not suitable for hydrogen separation. The second membrane was formed by adding small amounts of Ag to the plating solution during the electroless process. The final plating solution contained 75 wt% of Pd and 25 w% of Ag. The membrane thickness was 2 µm, but the membrane morphology was not totally dense. According to EDS results, the Ag composition was greater than the Pd composition, especially at the membrane top surface. This membrane also presented high nitrogen permeance probably due to the holes formed on the membrane surface. Thus, although the controlled addition of Ag is recommended to form dense membranes, the Ag was preferentially deposited over the Pd when starting with the highest rate of Ag addition. Adding lower Ag rates at the beginning could be helpful to avoid the preferential Ag deposition.

Investigation of the physical and mechanical properties of Ni–P and Ni–P–PTFE nanocomposite coatings deposited on aluminum alloy 7023

In this study, various properties of Ni–P and Ni–P–PTFE coating fabricated by electroless process were investigated. These coatings were applied on aircraft-grade aluminum samples. The results showed that the addition of nano-PTFE particles decreases coating rate from 7.1 µm/h to 6.1 µm/h and hardness from 510 HV to 200 HV. Also by increasing the pH value, coating rate increases from 1 µm/h to 7 µm/h. Increasing the solution temperature from 75 ℃ to 90 ℃ also increases the hardness of coating from 125 HV to 210 HV. The results showed that the heat treatment at 300 ℃ for 4 h increases the hardness up to 375 HV due to formation of Ni3P hard phase in Ni–P–PTFE coating. Addition of PTFE particles have improved tribological properties due to its lubricating effects and simultaneously, have reduced corrosion resistance compared to Ni–P coatings, so that the corrosion current for Al, Ni–P, and Ni–P–PTFE coatings is −880, −550, and −770 μA/cm2, respectively.

EFFECT OF ETCHING AS PRE-TREATMENT FOR ELECTROLESS COPPER PLATING ON SILICON WAFER

Metallic coatings, such as copper films can be easily deposited on semiconductor materials like silicon wafer without prior surface pre-treatment using the electroless process. However, the adhesion of the copper film can be very weak and can easily peels off. In this study, the effect of etching in hydrofluoric acid solution as a surface pre-treatment prior to electroless plating on silicon wafer was studied. The etching time in hydrofluoric acid was varied at 1, 3 and 5 minutes in order to investigate the adhesion behaviour of the coating layer. The surface morphology of the electroless plated samples was observed using a field emission scanning electron microscope (FESEM) and the coating thickness was measured using cross sectional analysis. The results showed that longer etching time (5 minutes) produced thicker Cu deposits (8.5μm) than 1 minute etching time (5μm). In addition, by increasing the etching time, the mechanical bonding between the copper film and the substrate is improved.