Advanced Materials Research Vol. 748

Abstract: In order to explore effects of various processing parameters on the mechanical properties of jute fiber reinforced polyurethane foam composites, jute fiber reinforced polyurethane composites were prepared by variable fiber reinforced reaction injection technology. The influence of jute fiber contents, fiber length, mold pressure and fiber modification treatment to the impact toughness was analyzed by orthogonal test in this paper. The microstructure and fracture micrograph of impact fracture specimens were studied with scanning electron microscope (SEM). The results showed that the best impact performance was obtained while fiber content was 10%, fiber length was12.5mm, mold pressure was 80tons, and jute fibers were modified by alkali. Furthermore, the result was compared with the corresponding research of glass fiber and carbon fiber reinforced polyurethane composites, and provided a theoretical basis for the application of the fiber reinforced polyurethane foam composites.

Abstract: Near infrared (NIR) emitting LaF₃:Ln³⁺ (Ln^3+→Nd³⁺, Er³⁺, Yb³⁺ and Ho³⁺) singly doped nanoparticles (NPs), with an average size of 5 nm, have been synthesized using simple co-precipitation route. Nanoparticles were functionalized with oleic acid. FTIR spectra revealed the prescience of chemisorbed oleic acid on the surface of nanoparticles. 10 wt % of LaF₃:Nd³⁺ nanoparticles were incorporated into epoxy by solution mixing method. The LaF₃:Nd³⁺-Epoxy Nanocomposites showed good transparency along with prominent NIR emissions at 880 nm, 1053 nm and 1330 nm on excitation at 575 nm.

Abstract: The oxidation resistance of 18%Cr-oxide dispersion strengthened (ODS) ferritic steels with and without 5%Al has been investigated in air at 700900 °C for time period up to 540 h. The oxidation rate of ODS steels is significantly dependent on the oxidation time and temperature. Compared to Al-containing ODS steel, the finer grains of Al-free ODS steel are due to the formation of smaller coherent oxide particles which suppress the steel's grain growth. The grain refinement of ODS steels is expected to allow rapid segregation of Cr or Al to the steel surface, so that the continuous Fe-Cr spinel or alumina layer is formed quickly in comparison to the alloys without oxide particles dispersion. Therefore, the excellent oxidation resistance of ODS steels is owing to the formation of continuous, protective oxide layers which correlate with oxide nanoparticles and grain refinement.

Abstract: Carbon dioxide (CO₂) has been reported as an interesting substitute of banned ozone-depleting blowing agents, such as HCFC and HFC etc., for low-density polystyrene (PS) foam production, but it is difficult to industrialize due to its low solubility in PS matrix; therefore, high pressure is always needed in order to obtain the required gas concentrations for low density foam. Mixtures of blowing agents might be a practical way to make foam processing easy to control. In this paper, the foaming behaviors of PS-CO₂ by using water or ethanol as co-blowing agent were investigated. The performances of foams obtained by PS-CO₂, PS-CO₂-water and PS-CO₂-ethanol systems were tested respectively. It was found that cell size increased owing to the existence of co-blowing agent; in particular, the expansion ratio of PS foam obtained by CO₂-ethanol was 1.3 times greater than that by CO₂. At the same time, cell density as well as apparent density decreased with temperature increasing, while cell size showed the opposite. Cell size and apparent density, rather than cell density, decreased with pressure. These results were explained by the solution behavior of each of blowing agent.

Abstract: Embedding rare earth compounds and inorganic materials in polymer matrix are of great interest due to its various applications in sensors, optical batteries etc. The hydrated form of optical compounds possesses interest due to the possibility of crystal field effect on the electronic and magnetic field structure of the 4f shell. The stiochiometric cerium compounds have attracted attention due to its high temperature phase stability, high melting point, low thermal conductivity, optical fluorescence etc. In this paper we discuss the synthesis of cerrous sulphate Ce₂(SO₄)₃, Cerium fluoride CeF₃ and Cerium Phosphate doped with terbium Ce_1-xPO₄:Tb_x composites and dependence of their structural and optical behavior on particle size. Cerrous sulphate exists in several phases, mostly hydrated. In polymer composite the anhydrous phase of Ce₂(SO₄)₃ is observed. Also CePO₄ composites crystallize to monazite phase. The significant changes in Ce³⁺ emission and absorption spectra are observed due to this phase change. Cerium fluoride composites prepared with different concentration show three absorption peaks around 237, 275 and 265nm. The lower concentration of CeF₃ shows different absorption. CePO₄ composites doped with various concentrations of terbium shows intense green emission at 543 nm and maximum energy transfer for 10 mol % of Tb³⁺. The Ce³⁺ emission is shifted to 337nm. The S.E.M. photograph of the composite shows well separated particles with average size 300nm.

Abstract: The present work investigated precipitation behavior in an Al-17at%Mg alloy isothermally aged at 473K, by means of Vickers microhardness tests, DSC measurements and TEM observations. A quantitative analysis of DSC measurements revealed that the metastable β-phase precipitates mainly contribute to precipitation hardening of this alloy aged at 473K. The present STEM-EDX observations confirmed that the metastable β-phase precipitate has a layer structure with a composition similar to the stable phase (Al₃Mg₂)_.

Abstract: In this paper, the nanoporous silicon layer was formed by electrochemical etching of silicon wafer in hydrofluoric acid solution. The purpose of this research, the nanoporous silicon layer were investigated the nanostructure and photoluminescence properties. We report the investigation on nanostructure of nanoporous silicon by using SEM, the gravimetric and fourier transform Raman spectroscopy (FT-Raman) technique. It is found that increasing the constant current density between electrochemical etching have effect to increasing porosity of nanoporous silicon. And increasing porosity of nanoporous silicon is effect from decreasing average size of silicon crystallites in nanoporous silicon which can confirm with Raman spectroscopy. The Changes in the photoluminescence intensity of nanoporous silicon samples are studied during nanoporous silicon stored in various ambient gases such as air, nitrogen, oxigen and vacuum. From data of this experiment when nanoporous silicon were stored in ambient air for a long time, the photoluminescence intensity of nanoporous silicon will decrease. In addition, we found strongly decreasing in its photoluminescence intensity when nanoporous silicon were stored in ambient of oxygen which can confirm by using fourier transfrom infrared spectroscopy (FT-IR) technique.

Abstract: Waste cooking oils are problematic disposal especially in the developed countries. Management of such oil is a significant challenge due to the disposal problems and possible contamination of the water and landfills. Thus, paper presented the synthesized of polyol based on waste cooking oil as raw material to produce Bio-foam polymer. The purpose of the study is to develop the High Density solid Biopolymer (HDB) foam by using hot compression moulding technique. The tensile strength and damping characterization shows a good correlation with it density. The maximum tensile strength of HDB is 4.89 MPa with Youngs Modulus of 0.26 GPa. The Scanning Electron Microscopy (SEM) micrograph, shows two characteristic and classified as a brittle and ductile fracture of granular (shiny) texture or cleavage character with little yielding before the sample breaks. Brittle fracture was characterized by rapid crack propagation and ductile fracture by stress whitening zone meanwhile, the damping characteristics have been studied via vibration test. It is revealed that HDB foam was highly absorbed the vibration frequency up to 19.2% as compared to rigid HDB foam of only 5.7%. Furthermore, the addition of sandwich layer of the vibrational test were revealed unchanged of the amplitude values.

Abstract: Hyperduplex, as a new class of duplex stainless steels, having high Cr and Mo present excellent combination of mechanical and corrosion resistance, due to their strict composition control and ferrite/austenite phase balance. This balance may, however, be disturbed during welding in both the weld metal and the Heat Affected Zone (HAZ) due to the rapid cooling rates. Those may lead to loss of the good corrosion and mechanical properties of the weldments. The present investigation is to establish the effect of heat input and the nitrogen addition in the argon shielding gas, for controlling the microstructure of hyperduplex stainless steels welded by the Gas Tungsten Arc Welding (GTAW) technique autogeneously. Hyperduplex stainless steel in the form of tube having outside diameter of 32 mm and thickness of 2 mm, was welded using limited range of heat input to control the microstructure in the HAZ, and using the nitrogen addition of 2-5% into argon shielding gas to control the ferrite/austenite phase balance of the weld metal. The microstructure of the weldment was examined by calculating the volume fraction of ferrite and austenite phases. The result shows that the heat input of 0,6 kJ/mm gives the optimum ferrite/austenite phase balance in the HAZ. The addition of 2% nitrogen into argon shielding gas is recommended to give the optimum balance of ferrite/austenite phases in weld metal in addition to the heat input employed. The heat input higher than 0,6 kJ/mm promoted sigma phase at the HAZ as well as at the weld metal particularly when welded with addition of more than 2% nitrogen in the argon shielding gas.

Abstract: Ni coatings were successfully electrodeposited on Ti substrates using galvanostatic technique. The scanning electron micrography showed a smooth coating with a few round particles formed at current density of-1 mA/cm², whereas the Ti surface was fully covered with round particles consisting of like-worm fibrils when applying higher current densities of-5 and-10 mA/cm². The stability and electrocatalytic activity tests were conducted by cyclic voltammetry and potentiostatic techniques. The results indicate that Ni/Ti catalysts prepared at current densities of-5 and-10 mA/cm² possess high active surface area and exhibit higher electrocatalytic activity performance towards methanol oxidation as compared to Ni/Ti prepared at-1 mA/cm². It was concluded that the deposition current density has significantly influenced the formation of Ni coatings on Ti substrate which consequently affecting the performance of electro-oxidation of methanol. The Ni/Ti catalysts also have good stability for the oxidation process in alkaline solution.