Aziz Azizan

Effect of copper (II) acetate pretreatment on zinc phosphate coating morphology and corrosion resistance

Zinc phosphate coating is widely used for corrosion protection of metallic materials, mainly mild steel. In the present study, the effect of pretreatment with copper acetate solution on zinc phosphate layer properties was investigated via scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The corrosion resistance of the coating was evaluated using polarization curves and electrochemical impedance spectroscopy in an aerated 3.5% NaCl solution. The pretreatment resulted in a compact and uniform phosphate coating with smaller crystal size and greater surface coverage. Electrochemical results showed better corrosion resistance for the pretreated phosphate layer compared with the untreated one.

Effects of Cobalt Addition and Temperature on Microstructure and Density of W-25Cu Composites Prepared via Liquid Infiltration

In this study, the effect of Co and sintering temperature on microstructure of W-25Cu composites prepared via copper melt infiltration has been investigated. The concentration of Co addition used ranged from 0.5 to 3wt. %. The infiltration temperatures were performed at 1150°C and 1250°C for 2 hr under vacuum. The microstructure and sintering density of W-25Cu composites are discussed. Results indicated that, the relative density (RD) and microstructure of W-25wt. % Cu were greatly affected by the addition of low Co concentration and sintering temperature. The concentration of 3 wt. % Co to tungsten-copper compact and infiltration temperature of 1250°C give high sintering density of 98.6% theoretical density (TD). The concentration of Co and infiltrating temperature have strong effects on the densification of W-Cu composite materials. The sintered compact microstructures and density were obtained using scanning electron microscope (SEM) coupled with EDX and Archimedes technique respectively.

Synthesis and characterization of Ni–Au bimetallic nanoparticles

Bimetallic structure of nanoparticles is of great interest due to their extraordinary properties, especially in combining the specialty of the core and its shell. This work reports the effect of pH on the synthesis of Ni–Au (nickel–gold) bimetallic nanoparticles. The synthesis involves a two-step process where Ni nanoparticles were first synthesized using polyol method with hydrazine as the reducing agent. This was followed by the process of reducing to Au in the solution containing pre-prepared Ni to form Ni–Au bimetallic nanoparticles using sodium citrate as the reducing agent. The results obtained from Transmission Electron Microscopy (TEM) show that the process can possibly produce either core-shell structure, or mixture of Ni and Au nanoparticles. Magnetic property of core-shell structure investigated using Vibrating Sample Magnetometer (VSM) demonstrated typical characteristic of ferromagnetic with an increased magnetization as compared to Ni nanoparticles. The saturation magnetization (Ms) and coercivity (Hc) were obtained as 19.1 emu/g and 222.3 Oe, respectively.

Synthesis Route towards Fine and Monodisperse Ni Nanoparticles via Hot-Injection Approach

Manipulation of adding sequences have been found to influence the reaction rate, thus made it easier to produced controllable Ni nanoparticles. Hot-injection approach shown capability to significantly reduce the production time of Ni nanoparticles compared to the conventional one-pot synthesis. With minor modification on conventional polyol method, narrow, monodispersed and highly yield spherical nickel (Ni) nanoparticles were successfully produced at synthesis temperature of 60°C. Three mixing methods were investigated to study its efficiency towards producing rapid and narrower size distribution of Ni nanoparticles. Reduction processes were proposed each of the method. As-synthesized Ni nanoparticles were characterized with Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR) to analyze the size, morphology and interaction of reactants. Fine particles size distribution revealed that when hydrazine was first heated, reaction rate improved tremendously.

Luminescence of SrAl2O4:Eu2+, Dy3+ Ceramics Synthesized at Different Firing Condition

The green SrAl2O4:Eu2+, Dy3+ phosphor is a well-known persistent material for a wide region of applications such as lighting, traffic signs, interior decoration and medical application. Double activated SrAl2O4:Eu2+, Dy3+ with improved properties has been synthesized through solid state route at different firing atmospheres (reduction, vacuum, oxygen and CO2 wet gas) and heating times (1 h to 8 h). At the beginning the powders were heat treated for 2 h with a heating rate of 10°C/min. The phosphor prepared at different firing atmospheres and heating times exhibited a different wavelength and intensity of PL spectra. The emission intensity becomes stronger as the heating times increases from 1 h to 4 h. The difference found from these spectra maxima is rationalized based on the presence of intermediate phases and also on the diffusion activities of activator and co-activator in the host matrices.

Investigation of Redox-Transmetallation Process for Coating of Gold(Au)-Shell on Nickel(Ni)-Core Nanoparticles

Core-shell nanoparticle has created great interest among researchers due to their various unique properties. The new properties created are combination of both the core and the shell. In this work, pre-prepared Nickel (Ni) nanoparticles were coated with Gold (Au) to produce core-shell structure. Formation mechanism of the core-shell structure is investigated via UV-Vis spectrum of the as-synthesized particles and its supernatants. Ni nanoparticles were synthesized using polyol method with hydrazine as the reducing agent. Coating of Au was conducted using sodium citrate as the reducing agent and acid citric to control the pH of the mixture. UV-Vis absorption spectra analysis of as-synthesized nanoparticles and the supernatant results revealed that the coating happened via redox-transmetallation process with a very broad peak at about 540 nm and size range of 26 - 40 nm. XPS results suggest that the coating consists of Au compound.

Comparison of Liquid Phase Sintering and Cu-Melt Infiltration Methods to Consolidate 80W-Cu Composite Using Nickel as Sintering Activator

In this article, studies were conducted to evaluate the densification of W-Cu sintered compacts produced using two methods; liquid phase sintering (LPS) and combination of liquid phase sintering and liquid infiltration technique (LPS+LI) named Cu-melt infiltration (Cu-MI). Low concentration of nickel (1wt.%) was used to activate the sintering process in both methods. Isothermal sintering was carried out in alumina tube furnace at temperatures of 1150°C for 2 hr. under H2/Ar. as protective gas. The infiltration (Cu-MI) method proved to be effective in the densification, microstructure and hardness enhancement of the 80W-Cu compact as opposed to the other conventionally liquid phase sintered compacts. The relative densities of 80W-Cu-1Ni composites prepared by using insert method (Cu-melt infiltration) achieved 96.22% of theoretical density.

The Effect of pH on Zinc Phosphate Coating Morphology and its Corrosion Resistance on Mild Steel

Zinc phosphate coating is commonly used for corrosion protection of metallic materials, mainly mild steel. In this study, influence of the pH of phosphating bath on the surface morphology and corrosion resistance of zinc phosphate coatings on mild steel was investigated. The phosphate layers were deposited on steel from phosphating bath at different pH values (1.75 ~ 2.75). The surface morphology and composition of phosphate coatings were investigated via scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The corrosion resistance of the coating was evaluated by polarization curves (anodic and cathodic) in an aerated 3.5% NaCl solution. The results showed that better surface coverage and corrosion resistance for the steel phosphated at pH 2.75.

The Influence of Deposition Temperature on the Morphology and Corrosion Resistance of Zinc Phosphate Coating on Mild Steel

The influence of phosphating temperature on the surface morphology and corrosion resistance of zinc phosphate coatings on mild steel was investigated. The phosphate layers were deposited on steel from phosphating bath at different temperatures (45 ~ 75 C). The surface morphology and composition of phosphate coatings were investigated via scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The corrosion resistance of the coatings was evaluated by polarization curves (anodic and cathodic) in an aerated 3.5% NaCl solution. The results showed that the increase in temperature of the phosphating bath up to 55 C caused an increase in surface coverage and in turn resulted in better corrosion resistance. At high temperature (65 °C and 75 °C) the deposition coverage decreased indicating that the best coverage for the phosphate layer on the metal surface was achieved at 55 °C

Properties of Multi-Walled Carbon Nanotube / Polymethyl Methacrylite Nanocomposite Prepared via a Modified Coagulation Method

The aim of this study is to produce MWCNT/PMMA nanocomposite with enhanced properties through a modified coagulation method. Samples were prepared in respect to various high filler loadings (1%, 3%, 5%, 7% and 10% wt.). Standard ASTM D790 flexural test was used to evaluate the mechanical properties of the composites. The morphology and surface fracture was observed via Scanning Electron Microscopy (SEM). Thermal stability and electrical conductivity of the composites as a function of MWCNT concentration were measured using Thermo Gravimetric Analyzer (TGA) and UHT Meter, respectively. Flexural strength and flexural modulus of MWCNT/PMMA nanocomposite showed an improvement up to 24.1% and 107.7% compared to the neat PMMA. It was found that the thermal stability and electrical conductivity of the MWCNT/PMMA nanocomposite improved as the concentration of the MWCNT filler increased. These studies therefore demonstrated that MWCNT/PMMA nanocomposite prepared via a modified coagulation method able to successfully improve thermal stability, electrical conductivity and mechanical properties of PMMA.