N.R. Nik Roselina

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.

The Influence of Bath Concentration on Particle Size of Cobalt Nanoparticles

Cobalt nanoparticles have been widely used in magnetic storage media application. This study reports the characteristic and properties of Cobalt (Co) nanoparticles due to the effect of different bath concentrations. The Co nanoparticles were coated on the stainless steel substrate using different molar concentrations (M) of 0.05 M, 0.075 M and 0.1 M, respectively. The coating was done using electrodeposition method. Interestingly, the sphere particles surrounded by flakes were only found in the Co nanoparticles prepared in 0.075 M. This structure exhibited the smallest particles size, which is 83 nm. Besides, the nanoparticles also had the highest microhardness if compared to the Co nanoparticles prepared in 0.05 M and 0.1 M. The Co nanoparticles prepared in other concentrations were irregular structure without flakes. The polarization curves for all the nanoparticles showed the active behaviour without any distinctive to passivation. However, the corrosion rate of the sample prepared in 0.075 M was the lowest; 42.51 mpy compared to the other samples prepared in 0.05 M and 0.1 M, which were 176 mpy and 223.3 mpy, respectively. Hence, it was found that the bath concentrations affect the particle size of as-synthesized Co nanoparticles and finally changed the properties of final product.

Boron Dispersion Layer of Paste Boronized 304 Stainless Steel before and after Shot Blasting Process

Boronizing had been extensively used in enhancing the properties of metallic material such as steel by formation of hard casing on the surface of the substrate. This study highlighted the effect of applying surface deformation process which is shot blasting on the dispersion layer of paste boronized 304 stainless steel. Boronizing treatment was conducted using two different temperatures which are 850°C and 950°C for 6 hour holding time. Shot blasting process was conducted onto the surface of the samples before boronizing process in order to allow deeper boron dispersion layer. Microstructure and boron dispersion layer measurement were then accomplished using optical microscope. XRD analysis was performed to validate the existence of Fe2B phases and Rockwell hardness test was also conducted to obtain the hardness values. The results indicated that combinations of high boronizing temperature and shot blasting process facilitate deeper dispersion layer. Deeper dispersion layer are paramount as it will enhanced the hardness and wear properties.

Effect of Calcining Temperatures on the Morphology and Crystallinity of Strontium Doped Hydroxyapatite Nanopowders

Strontium appears to be one of the most effective substances for the treatment of osteoporosis and other bone-related conditions. Since calcium and strontium share the properties of group 2A elements, strontium can replace calcium in bone without much difficulty. Additionally, non-radioactive strontium also deposits in bones and behaves like calcium; therefore it enhances bone density and resistance to osteoporotic fractures. In this study, 10 wt% strontium doped hydroxyapatite (SrHA) nanopowders were synthesized through a sol-gel method. The obtained gel was dried and subsequently subjected to 500, 600, 700, 800 and 900 oC calcination. At 500°C calcining temperature, the SrHA nanopowders are still in amorphous state but starting to become crystalline when heated to 600°C, 700°C and 800°C. Increasing the temperature to 900 °C originates more intense and sharp peaks, corresponding to an increase in the mineral crystallinity, which is compatible with particle growth. Morphological evaluation by FESEM shows that the nanopowders calcined at 500°C and 700°C are in spherical shape and highly agglomerated. At 900°C the SrHA particles are still in globular shape with a mean diameter of 1-2 μm. The primary particles have diameter of 30-50 nm in average. No secondary phase was detected in these nanopowders, correlated to nearly 100 % presence of HA.

Influence of Ionic Substitution on the Mechanical Properties of Nanosized Biphasic Calcium Phosphates

Synthetic hydroxyapatite ceramics have been used for bone repair, implants coating and as fillers. However, hydroxyapatite ceramics have low resorption rate. In order to increase resorption rate, researchers suggested that adding another calcium phosphates phase would overcome this problem. Combining β-tricalcium phophates (β-TCP) with hydroxyapatite (HA) would increase resorption rate without compromising other properties. The mixture containing β-TCP with HA is known as biphasic calcium phosphates (BCP) ceramics and existed at various ratios depending on processing conditions. BCP is obtained by heating calcium apatite at temperature above 750 °C. Calcium apatite is influenced by preparation synthesis particularly on reaction temperature and reaction pH. The ratio of HA/β-TCP is depending on calcium phosphates ratio of synthesized apatite and heat treatment temperature. Biphasic calcium phosphate ceramic have been used as biomaterial in bone defects reconstruction applications. Furthermore, recent advancements in nanotechnology have increase investigation on nanosized BCP. By producing nanosized BCP, the material properties could be improved particularly in mechanical properties. It is known that micrometer sized calcium phosphates have poor mechanical properties. Thus cannot be used in load bearing applications. It is suggested that by reducing particles size into nanometer, better properties of calcium phosphates can be obtained particularly in sinterability, biocompatibility and mechanical properties. Furthermore, these properties can be altered by substituting various ions. In this review, the synthesis methods and characteristics of calcium phosphates were studied. Numerous properties of calcium phosphates are improved compared to micro meter sized structured by doping with various ions. Moreover, mechanical properties and phase stability of ion doped calcium phosphates after heat treatment should be investigated in more detail.

Effect of Calcination Temperature on Various Concentration of Zinc Substituted Calcium Phosphate Ceramics

In this work, nanoscale zinc substituted calcium phosphate ceramics substituted were synthesized by simple precipitation method, performed under alkaline solution of pH 10. Three different zinc concentrations (5%, 10% and 15 mol%) were incorporated into calcium phosphate ceramics with experimental ratios of (Ca+Zn)/P were all maintained at 1.67 for easier comparison. The phase composition and lattice parameters for each sample were determined by using X-ray diffraction (XRD) method. Other characterization techniques such as Fourier transform infrared (FTIR) and field emission scanning electron (FESEM) were also utilized to investigate material’s molecule internal bonds properties and powders morphology, respectively. Based on XRD results, zinc ions addition disturbed the calcium phosphate ceramics structure causing its crystallite size to become smaller as the amount of zinc increased. After the powders undergo calcination process, the bands of PO4 in its FTIR spectra increased while the H2O bands decreased. FESEM results showed that the powders are uniform but irregular in shape and tend to agglomerate with increasing zinc fraction.

Conversion of Strontium Hydroxyapatite Nanopowders to Porous Scaffolds for Bone Implant Application

The fabrication of Sr hydroxyapatite (HA) porous scaffolds was done by using polymeric sponge method. To prepare the porous samples, the synthesized SrHA nanopowders were mixed with distilled water and appropriate amount of dispersing agent followed by drying in the ambient air and sintering at 1300°C. The compressive strength of the materials was strongly influenced by the porosity, while there was almost no dependence on the crystallinity of the powders since XRD patterns showed high crystallinity of HA phase for all porous samples. Morphological evaluation by FESEM revealed that the SrHA scaffolds were characterized by macro-micro interconnected porosity, which replicates the morphology of the cancellous bone. Compression test on the porous scaffolds demonstrated that doping 10 mol% of strontium in HA has increased the compressive strength by a factor of two compared to the undoped HA with 1.81±0.26 MPa at 41% porosity.

Corrosion Behavior of Electrodeposited CoNiFe Nanoparticles Immersed in Different Environments

Replacement or repair of corrosion damaged equipment is the largest maintenance requirement for the industry. One technique for reducing the corrosion of metals is to coat them with thin layers of less reactive metals or alloys. Unfortunately, most metallic coatings are inherently porous and historically have been of little value as barriers against corrosion. Recently, with the development of new alternative material such as electrodeposited CoNiFe, these problems have largely been overcome. This paper investigated the effects of different aggressive environments on the corrosion behavior of electrodeposited CoNiFe. Interestingly, the mixed morphologies with spherical and dendritic structure were found in the neutral and alkaline environment. This morphology exhibited the smallest particle size with less percentage of oxygen elements. Besides, alkaline environment experienced the slowest corrosion rate due to the mixed morphology. It was found that spherical and dendritic refinement provides higher corrosion resistance. The corrosion rate of the sample prepared in alkaline environment was the lowest compared to the others due to the reduction of particle size.

Synthesis and Characterization of Zinc Doped Hydroxyapatite for Bone Substitute Applications

Hydroxyapatite was prepared by using precipitation method. The substitution of zinc ions in hydroxyapatite structure was studied by several characterization techniques. Several concentration of zinc ions were substituted into hydroxyapatite. Characterization technique such as X-ray diffraction method was used to study the phase changes and the lattice parameters with the addition of zinc. Field emission scanning electron microscopy was used to examine the influence of zinc on the crystal size and the morphology of the as-synthesized powders. Based on X-ray diffraction result, the addition of zinc affects the lattice parameters and phase. The result showed that zinc ions were substituted in the structure. As zinc substitution increased, the lattice parameters a and c decreased. The crystal shape of hydroxyapatite without zinc ions was regular shapes while hydroxyapatite with zinc ions was irregular and also tends to agglomerates with single particle was calculated about 28 - 34 nm .