Advanced Materials Research Vols. 29-30

Abstract: Corn gluten meal (CGM) has potential as a bioderived polymer for use in composite materials. Previous work to improve the processability of CGM has focused on the use of plasticisers including water, polyethylene glycol, glycerol and octanoic acid, however, a common problem is that these leach from the material subsequent to processing [1]. It has been raised that a certain degree of denaturation must occur in order to make proteins processable [2]. The current work explores the use of aqueous urea as chemical denaturant in processing CGM into a biodegradable polymer material. Consolidated materials were obtained which showed increased resistance to cracking with higher urea concentration. FTIR analysis revealed that processing CGM with increased concentrations of aqueous urea resulted in the progressive transformation of the protein secondary structure from an ordered, clustered conformation to that of extended chains. Aqueous urea is assumed to promote protein-solvent interactions which stabilise the extended chain conformations.

Abstract: Malaysia mainly produced low quality kaolin and the paper describes the development of a chemical process to produce high purity alumina and zeolite from this mineral. Selective leaching technique was applied to remove 45% of the Al2O3 content in kaolin. The high purity alumina produced shows similar characteristic to the commercial product. An alkaline fusion stage was then carried to transform the kaolin mineral into zeolite. Identification of the crystalline phase by XRD shows that it consists of both zeolite P and hydroxysodalite.

Abstract: Silica-coating of AgI nanoparticles with a Stöber method was carried out to find out reaction conditions for control of the shell thickness. The AgI nanoparticles were prepared from AgClO4 and KI with the use of 3-mercaptopropyltrimethoxysilane (MPS) as a silane coupling agent and dimethylamine (DMA) catalyst for alkoxide hydrolysis. The silica-coating was performed at 4.5×10-6-4.5×10-5 M MPS, 11-20 M water, 0.002-0.1 M DMA and 0.005-0.04 M tetraethylorthosilicate at AgI concentrations of 0.1-1 mM. Consequently, AgI-silica core-shell particles could be prepared with the use of 4.5×10-5 M MPS, 20 M water, 0.01 M DMA and 1 mM AgI. Silica shell thickness could be varied from 15 to 28 nm with an increase in the TEOS concentration from 0.005 to 0.04 M.

Abstract: Nitrides remain a relatively unexplored class of materials primarily due to the difficulties associated with their synthesis and characterization. Several synthetic routes, including high temperature reactions, microwave assisted synthesis, and the use of plasmas, to prepare binary and ternary nitrides have been explored. Transition metal nitrides form a class of materials with unique physical properties, which give them varied applications, as high temperature ceramics, magnetic materials, superconductors or catalysts. They are commonly prepared by high temperature conventional processes, but alternative synthetic approaches have also been explored, more recently, which utilize moderate temperature condition. Transition metal nitrides particularly, molybdenum nitride, niobium nitride, and tungsten nitride have important applications as catalyst in hydrodenitridation reactions. These nitrides have been traditionally synthesized using high temperature nitridation treatments of the oxides. The nitridation temperatures are very high (> 800- 1000 oC). The aim of our work is to synthesize molybdenum nitride by a simple, low-temperature route. The method involves pyrolysis of a polymeric precursor, which was prepared from the condensation reaction between triethanolamine and molybdic acid. The melting point of the product is 180oC. The polymeric precursor and its pyrolyzed products are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). X-ray diffraction shows that molybdenum nitride (MoN) obtained from this method has hexagonal crystal structure. MoN is obtained by this method at very low temperature (~ 400 oC).

Abstract: Polycondensations (condensation polymerization) are stepwise reactions between bifunctional or polyfunctional compoents, with elimination of simple molecules such as water or alcohol and the formation of macromolecular substances. Polyborate ester , formed by this process, gives ceramic materials during pyrolysis. Polymer pyrolysis offers an attractive alternative to the typical high temperature powder processing approach in the fabrication of high-performance ceramics. This approach might also prove to be useful in the fabrication of fibers, coatings, and composites. It is within this framework that the present study was undertaken; its aim is the preparation of boron-containing oligomeric precursors which gives boron nitride after pyrolysis. The precursor was synthesized by the condensation reaction between boric acid and urea (or other N-containing reactive multifunctional compounds). The oligomeric precursor and its pyrolysed products were thoroughly characterized by elemental analysis, IR, NMR, XRD, Thermal Analysis and Transmission Electron Microscopy(TEM). The elemental analysis results of the oligomer are---- C-13.40%, H-5.97%, N-32.44% and B-17.09%. X-ray diffraction and TEM studies showed that boron nitride obtained from this system possess tetragonal structure.

Abstract: Mullite whiskers have been manufactured by firing compacts of kaolin, Al2(SO4)3 and (NH4)2SO4 powders, with a small addition of Na2SO4, in air at 1400o C for 15 h. From the batch composition of Al2O3/SiO2 = 0.7, molar ratio, alumina-deficient (Al2O3/SiO2 = 1.02, molar ratio), orthorhombic mullite whiskers with an aspect ratio of >30 (0.2-0.4 μm in diameter) were obtained. With increasing Al2O3/SiO2 molar ratio, the size and aspect ratio of the mullite whiskers decreased.

Abstract: It has been successfully demonstrated that ceramic materials can be joined in the green state without a second phase by using low pressure injection molded parts. The investigation of the joining interface revealed that a high quality interface can be achieved by carefully adjusting the different manufacturing steps. The use of monomodal particle size distribution in the used powder CT3000SG is inferior to a broader particle size distribution obtained by replacing 33% of the finer alumina powder by coarser CT1200SG. In this way the dewaxing process is significantly improved when the wall thickness of the part exceeds 3 mm. The investigation of the mechanical properties of the joined and sintered parts revealed, that the bending strength of the joined specimens achieved about 80 % of the unjoined, monolithic specimens.

Abstract: Nanotubes were produced from commercial and self-prepared anatase and rutile which were treated with 7.5 M NaOH over a temperature range of 100 – 200°C in 20°C increments. The formation of nanotubes was examined as a function of starting material type and size. Products were characterised by X-Ray Diffraction (XRD), Transmission Electron Spectroscopy (TEM), and Raman Spectroscopy. The results indicated that both phase and crystallite size affected the nanotube formation. Rutile was observed to require a greater driving force than anatase to form nanotubes, and increases in crystallite sizes appeared to impede formation slightly.

Abstract: Al-doped ZnO (AZO) thin films were grown on Corning 1737 glass by RF Magnetron Sputtering under premixed hydrogen-argon (H2/Ar) sputtering gas. It is found that the introduction of various H2 concentrations during sputtering deposition altered the properties of Al-doped ZnO films. The presence of H2 during AZO growth at low deposition temperature leads to the growth of a-axis preferential orientation crystal whereas c-axis preferential orientation occurred only at higher deposition temperature. Highly oriented c-axis (002) crystal has been successfully grown under 3% H2 concentration at 200°C deposition temperature. Film’s resistivity is appeared to be a function of H2 concentration. Additional H2 concentration in sputtering gas increased of film’s transmittance up to 85% at visible-near infra red spectra while it caused the Burstein-Moss shift toward the blue region at 350 nm wavelength.

Abstract: Silicon carbide (SiC) and alumina (Al2O3) have been synthesized on graphite and silica (SiO2) substrates, respectively, using a solid-vapor reaction (SVR). SiC and Al2O3 layers are synthesized on each substrate by reacting between SiO vapor and substrate (SiO (vapor) + 2 C (from graphite)), and between AlO vapor and substrate (2AlO (vapor) + 1/2O2 (from SiO2)). Both reaction processes were performed at 1400 °C for 9 hour at a heating rate of 5 °C/min under an Ar/H2 (160:40) flow of 200 sccm (ml/min). The pack composition for each case was adjusted with 1:1 mole ratio, which was used as precursors of the AlO and SiO vapors. The synthesized SiC layer consists of α-SiC and β-SiC, and its thickness is affected by the porosity of graphite. The Al2O3 top layer synthesized on SiO2 substrate is coarse and relatively porous, resulting in some defects.