Noordin Mohd Yusof

Photocatalytic magnetic separable beads for chromium (VI) reduction

Magnetically separable photocatalyst beads containing nano-sized iron oxide in alginate polymer were prepared. This magnetic photocatalyst beads are used in slurry-type reactors. The magnetism of the catalyst arises from the nanostructured particles gamma-Fe(2)O(3), by which the catalyst can be easily recovered by the application of an external magnetic field. These synthesized beads are sunlight-driven photocatalyst. In the system without magnetic photocatalyst beads, no chromium reduction was observed under sunlight irradiation due to the stability of the chromium (VI). Upon the addition of magnetic photocatalyst beads, the photo-reduction of Cr(VI) was completed in just after only 50min under sunlight irradiation due to the photocatalytic activity of the beads. However when placed away from sunlight, the reduction rate of the chromium is just about 10%. These observations were explained in terms of absorption occurrence of chromium (VI) onto the catalyst surface which took place in this reaction. In addition, photo-reduction rate of chromium (VI) was more significant at lower pH. The results suggest that the use of magnetic separable photocatalyst beads is a feasible strategy for eliminating Cr(VI).

Hard Machining of Stainless Steel Using Wiper Coated Carbide: Tool Life and Surface Integrity

Carbide cutting tools, which are inexpensive and widely used by machine shops, are alternatives for performing hard machining, yet limitations due to their low strength requires performance evaluation as well as appropriate selection of cutting parameters. In this study, a carbide tool with TiAlN coating with wiper geometry at the cutting edge is proposed for performing mild range of hard machining of martensitic stainless steel (48 HRC). The tools performance was evaluated based on its tool life and the resulting surface finish when hard machining at various cutting speeds and feeds and at constant depth of cut without using cutting fluid (dry machining). Response surface methodology was used to quantify the effect of cutting speed and feed to the tool life and proposing the optimum cutting parameters. Further observation was made on the worn tool, the machined surface, and the generated chip to observe the process. Results showed that the wiper coated carbide tool are capable of performing particular hard machining.

A review of: Application of synthetic scaffold in tissue engineering heart valves

The four heart valves represented in the mammalian hearts are responsible for maintaining unidirectional, non-hinder blood flow. The heart valve leaflets synchronically open and close approximately 4 million times a year and more than 3 billion times during the life. Valvular heart dysfunction is a significant cause of morbidity and mortality around the world. When one of the valves malfunctions, the medical choice is may be to replace the original valves with an artificial one. Currently, the mechanical and biological artificial valves are clinically used with some drawbacks. Tissue engineering heart valve concept represents a new technique to enhance the current model. In tissue engineering method, a three-dimensional scaffold is fabricated as the template for neo-tissue development. Appropriate cells are seeded to the matrix in vitro. Various approaches have been investigated either in scaffold biomaterials and fabrication techniques or cell source and cultivation methods. The available results of ongoing experiments indicate a promising future in this area (particularly in combination of bone marrow stem cells with synthetic scaffold), which can eliminate the need for lifelong anti-coagulation medication, durability and reoperation problems.

Application of response surface methodology in optimization of electrospinning process to fabricate (ferrofluid/polyvinyl alcohol) magnetic nanofibers

Magnetic nanofibers are composed of good dispersion of magnetic nanoparticles along an organic material. Magnetic nanofibers are potentially useful for composite reinforcement, bio-medical and tissue engineering. Nanofibers with the thinner diameter have to result in higher rigidity and tensile strength due to better alignments of lamellae along the fiber axis. In this study, the performance of electrospinning process was explained using response surface methodology (RSM) during fabrication of magnetic nanofibers using polyvinyl alcohol (PVA) as a shelter for (γ-Fe2O3) nanoparticles where the parameters investigated were flow rate, applied voltage, distance between needle and collector and collector rotating speed. The response variable was diameter distribution. The two parameters flow rate and applied voltage in primary evaluation were distinguished as significant factors. Central composite design was applied to optimize the variable of diameter distribution. Quadratic estimated model developed for diameter distribution indicated the optimum conditions to be flow rate of 0.25 ml/h at voltage of 45 kV while the distance and rotating speed are at 8 cm and 1500 rps respectively. The obtained model was verified successfully by the confirmation experiments.

γ-Fe2O3 nanoparticles filled polyvinyl alcohol as potential biomaterial for tissue engineering scaffold

Maghemite (γ-Fe2O3) nanoparticle with its unique magnetic properties is recently known to enhance the cell growth rate. In this study, γ-Fe2O3 is mixed into polyvinyl alcohol (PVA) matrix and then electrospun to form nanofibers. Design of experiments was used to determine the optimum parameter settings for the electrospinning process so as to produce elctrospun mats with the preferred characteristics such as good morphology, Youngs modulus and porosity. The input factors of the electrospinnning process were nanoparticles content (1-5%), voltage (25-35 kV), and flow rate (1-3 ml/h) while the responses considered were Youngs modulus and porosity. Empirical models for both responses as a function of the input factors were developed and the optimum input factors setting were determined, and found to be at 5% nanoparticle content, 35 kV voltage, and 1 ml/h volume flow rate. The characteristics and performance of the optimum PVA/γ-Fe2O3 nanofiber mats were compared with those of neat PVA nanofiber mats in terms of morphology, thermal properties, and hydrophilicity. The PVA/γ-Fe2O3 nanofiber mats exhibited higher fiber diameter and surface roughness yet similar thermal properties and hydrophilicity compared to neat PVA PVA/γ-Fe2O3 nanofiber mats. Biocompatibility test by exposing the nanofiber mats with human blood cells was performed. In terms of clotting time, the PVA/γ-Fe2O3 nanofibers exhibited similar behavior with neat PVA. The PVA/γ-Fe2O3 nanofibers also showed higher cells proliferation rate when MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was done using human skin fibroblast cells. Thus, the PVA/γ-Fe2O3 electrospun nanofibers can be a promising biomaterial for tissue engineering scaffolds.

Investigation of three steps of hot corrosion process in Y2O3 stabilized ZrO2 coatings including nano zones

Abstract Phase transformation of tetragonal ZrO2 to monoclinic phase and also increment of bond coat oxidation kinetic (TGO thickening) can substantially restrict the life time of thermal barrier coating systems (TBCs). So, nanostructured and conventional Y2O3 stabilized ZrO2 coatings were evaluated in fused V2O5-Na2SO4 salts during thermal exposure in air. Microstructural characterization showed lower hot corrosion products (monoclinic zirconia, YVO4 crystals) formation and reduction of TGO thickness in thermal barrier coating system consisting of nanostructured Y2O3 stabilized ZrO2 (YSZ) top coat. It was found that inhomogeneities, pores and micro-cracks played a principal role in the molten salts infiltration into the YSZ coating during three steps of hot corrosion process. In the nanostructured YSZ coating with tri-model structure, nano zones which surrounded by fully molten parts could fill the aforementioned defects and could act as barrier for the oxygen and corrosive molten salts penetration into the TBC.

Improvement of thermally grown oxide layer in thermal barrier coating systems with nano alumina as third layer

Abstract A thermally grown oxide (TGO) layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni(Cr,Al)2O4 mixed oxides (as spinel) and NiO onto the Al2O3 (TGO) layer. The formation of detrimental mixed oxides (spinels) on the Al2O3(TGO) layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.

The Influence of Bismuth, Antimony, and Strontium on Microstructure, Thermal, and Machinability of Aluminum-Silicon Alloy

In this article, the influence of separate additions of bismuth, antimony, and strontium on microstructure, thermal, and machinability of Al-11%Si-2%Cu alloy (ADC12) has been reported. Additives depressed the aluminum-silicon eutectic growth temperature (TG) and altered the silicon morphology. Different silicon morphologies, namely flake, lamellar, and fibrous influenced the main cutting force, feed force, and surface roughness during turning. Workpieces with fibrous silicon morphology produced the highest cutting force, feed force, and surface roughness while that of bismuth-containing workpieces produced the lowest cutting force, feed force, and the best surface roughness due to the formation of bismuth compound which acts as lubricant during turning. The results showed that the highest TG is related to the best surface roughness and as such the best machinable alloy investigated.

Effect of Y2O3 stabilized ZrO2 coating with tri-model structure on bi-layered thermally grown oxide evolution in nano thermal barrier coating systems at elevated temperatures

Abstract Bi-layered thermally grown oxide (TGO) layer plays a major role in the spallation of Y2O3 stabilized ZrO2 (YSZ) layer form the bond coat in the thermal barrier coating (TBC) systems during oxidation. On the other hand, bi-layered TGO formation and growth in the TBC systems with nanostructured YSZ have not been deeply investigated during cyclic oxidation. Hence, Inconel 738/NiCrAlY/normal YSZ and Inconel 738/NiCrAlY/nano YSZ systems were pre-oxidized at 1000 °C and then subjected to cyclic oxidation at 1150 °C. According to microstructural observations, nanostructured YSZ layer over the bond coat should have less micro-cracks and pinholes, due to the compactness of the nanostructure and the presence of nano zones that resulted in lower O infiltration into the nanothermal barrier coating system, formation of thinner and nearly continuous mono-layered thermally grown oxide on the bond coat during pre-oxidation, lower spinels formation at the Al2O3/YSZ interface and finally, reduction of bi-layered thermally grown oxide thickness during cyclic oxidation. It was found that pre-heat treatment and particularly coating microstructure could influence microstructural evolution (bi-layered TGO thickness) and durability of thermal barrier coating systems during cyclic oxidation.

Development of highly porous biodegradable γ-Fe2O3/polyvinyl alcohol nanofiber mats using electrospinning process for biomedical application

The use of electrospinning process in fabricating tissue engineering scaffolds has received great attention in recent years due to its simplicity. The nanofibers produced via electrospinning possessed morphological characteristics similar to extracellular matrix of most tissue components. Porosity plays a vital role in developing tissue engineering scaffolds because it influences the biocompatibility performance of the scaffolds. In this study, maghemite (γ-Fe2O3) was mixed with polyvinyl alcohol (PVA) and subsequently electrospun to produce nanofibers. Five factors; nanoparticles content, voltage, flow rate, spinning distance, and rotating speed were varied to produce the electrospun nanofibrous mats with high porosity value. Empirical model was developed using response surface methodology to analyze the effect of these factors to the porosity. The results revealed that the optimum porosity (90.85%) was obtained using 5% w/v nanoparticle content, 35kV of voltage, 1.1ml/h volume flow rate of solution, 8cm spinning distance and 2455rpm of rotating speed. The empirical model was verified successfully by performing confirmation experiments. The properties of optimum PVA/γ-Fe2O3 nanofiber mats such as fiber diameter, mechanical properties, and contact angle were investigated. In addition, cytocompatibility test, in vitro degradation rate, and MTT assay were also performed. Results revealed that high porosity biodegradable γ-Fe2O3/polyvinyl alcohol nanofiber mats have low mechanical properties but good degradation rates and cytocompatibility properties. Thus, they are suitable for low load bearing biomedical application or soft tissue engineering scaffold.