Effect of pH on electroless nickel deposition on alumina substrates for chip resistor application
Alumina has been used widely in electronics industry specifically for chip resistor application. Currently, the deposition of nickel on alumina surface using electrodeposition method suffered from the insufficient bonding between the metallic coating (nickel) and the ceramic substrate (alumina). Electroless deposition method however can produce strong adhesion between the metallic coating and ceramic substrate. In this research, the effect of pH on the electroless nickel on alumina substrate was investigated. The electroless deposition of nickel on alumina substrate was conducted at pH 4.0, 5.6 and pH 10.0 for 3, 5, 10, 20 and 30 minutes at constant temperature. The crystal structure of the substrate and coating was characterized by using X-ray diffraction (XRD). The surface morphology of the coating was observed by using scanning electron microscopy (SEM) and the coating thickness was measure by X-ray fluorescence (XRF). The coating performance was tested by using Standard ASTM D3359 (Tape-Test). It was found that the optimum pH of plating solution was 10.0 with the maximum thickness was obtained at 30 minutes of deposition with thickness of 1.15 μm. These optimum coating parameters shows homogeneous and uniform nickel deposition on the alumina surface as observed by SEM. Nickel deposition by electroless method at pH 4.0, 5.6, and 10.0 have excellent bonding with alumina substrate as shown by tape test analysis.
Electroless deposited black nickel-phosphorous solar absorber coatings on carbon steel: Effect of plating bath pH
Abstract One of the challenges of solar energy collection is energy conversion efficiency, particularly the absorbent surface capability to convert solar energy to thermal energy. In this work, nickel-phosphorous (Ni-P) coating was deposited onto a carbon steel substrates using the electroless plating process containing nickel sulfate as the nickel source and sodium hypophosphite as the reducing agent. This study focuses on the study of plating bath pH effect on the light absorption properties of the black surface after blackening process and at the same time maintain the characteristic of protective coating to protect the substrate from corrosion. The electroless nickel plating was conducted at various plating bath pH (4.5, 5.0, and 6.0) for 3 h at a constant bath temperature and composition. Electroless black Ni-P surfaces were obtained through an etching process of Ni-P coating with 9 mol/L nitric acid solution. The surface morphology of Ni-P coating and black Ni-P coating were observed using scanning electron microscopy (SEM). The chemical composition of Ni-P coating deposited at various pH was measured using energy dispersive X-ray (EDX) equipped on the SEM. The SEM results show that black Ni-P coating for pH 4.5 sample has the highest porosity which is 47.1% of the surface area with highest phosphorus content shown by EDX analysis. The cross-sectional analysis showed that the depth of the etching effect occurred only up to the 33% of the coating thickness. The remaining 67% of coating thickness still uniformly attached on the substrate without the presence of any defects or flacking after the etching process. The visible near-infrared spectrophotometer, (VIS-Nir) showed that the black Ni-P coating of pH 4.5 sample had the highest absorption capability which is 92% of light absorption due to its high surface roughness.
The role of forensic epidemiology in evidence-based forensic medical practice
Objectives This thesis is based on 4 papers that were all written with the same intent, which was to describe and demonstrate how epidemiologic concepts and data can serve as a basis for improved v ...