Crystallite Size Effect on Lattice Strain and Crystal Structure of Ba1/4Sr3/4MnO3 Layered Perovskite Manganite

The single phase polycrystalline Ba1/4Sr3/4MnO3 layered perovskite manganite has been synthesized by combustion method having various crystallite sizes. The room temperature X-ray diffraction patterns reveal that Ba1/4Sr3/4MnO3 crystallizes into hexagonal crystal structure with space group P63/mmc as confirmed by Rietveld refinement. The scanning electron micrographs of Ba1/4Sr3/4MnO3 reveal uniform crystallite size of the samples. Effect of crystallite size on lattice strain and crystal structure has been studied using Rietveld refinement and Williamson-Hall plot, respectively. The structural lattice parameters decrease with increasing crystallite size. However, lattice strain increases with increasing crystallite-size

Studies on Aluminum – Iron ore in-situ Particulate Composite

Discontinuously reinforced aluminium matrix composites are fast emerging as engineering materials and competing with common metals and alloys. They are gaining significant acceptance because of higher specific strength, specific modulus and good wear resistance as compared to ordinary unreinforced alloys. Reinforcing particles or short fibers normally used are silicon carbide and alumina which are added externally. Recently it has been shown that alumina particles can be produced in-situ by reaction with metallic oxides reduced by aluminium. Alumina particles thus produced are dispersed in the aluminium matrix and the elementary metal gives slid solution strengthening of the matrix. In-situ particulate composites in comparison with conventional cast particulate composites produced by external addition, promote cleaner interface, eliminates interface incompatibility of the matrices with the reinforcements, help to achieve greater thermodynamic stability of reinforcement particles in the matrix at elevated temperature and also increase the possibility of developing coherency between the matrix and particles formed in-situ. The morphology and the distribution of particles strongly influence the physical and mechanical properties of composites In the present investigation, iron ore was added to molten aluminium, aluminium-magnesium and aluminium-silicon alloys by vortex method. The iron oxides present in the iron ore are observed to react with aluminium, magnesium resulting in production of Al2O3, MgO and metallic iron which dissolved in liquid aluminium. The composites thus produced were cast into cast iron die. The mechanical properties of the composites were evaluated. Strength and hardness value of the composites shows considerable improvement. The dry sliding wear behaviour of the composites in the cast condition was studied at different loads and different sliding velocities using Pin-On-Disk configuration wear testing machine. The worn surfaces and the wear debris were also analyzed using optical microscope and scanning electron microscope

RENEWABLE RESOURCE LACTIDE DERIVED MATERIALS: SCALED-UP SYNTHESIS, CHARACTERIZATION AND APPLICATIONS

Renewable resource monomer, lactide, derived copolymers and terpolymers were synthesized on a few hundred gram scale with specialty/commodity co-monomers such as perfluoropolyether and bisphenol A derivatives. The modifications resulted in improved properties such as surface energy, crystallization, and glass transition temperature of the polylactide. Ring-opening polymerizations of L-lactide were performed using different block length perfluoropolyethers as macro-initiators and tin octoate as the catalyst. The resultant polylactide-perfluoropolyether-polylactide block copolymers were characterized by various analytical and microscopic techniques such as differential scanning calorimetry, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, dynamic mechanical analysis, wide-angle x-ray diffraction spectroscopy, polarized optical microscopy, etc. The incorporation of low surface energy perfluoropolyether into the polylactide backbone modified its surface energy and the copolymers possessed a very low surface energy (16-20 mN/m) compared to that of polylactide (35-40 mN/m) even when at a very low concentration of perfluoropolyether. The copolymerization affected the thermal properties of the polylactide and the copolymers exhibited lowered glass-transition, crystallization, and melting temperatures compared to the homopolymer, polylactide. The copolymers exhibited unique crystallization behavior and higher crystallinity and faster crystallization rates of the copolymers were found in comparison to polylactide. The enhanced crystallization properties of copolymers were speculated to be due to the nucleating action of perfluoropolyether. The high density and low surface energy perfluoropolyether enables it to behave as a foreign material and as an ideal sight for nucleation. The crystallization half-time, spherulitic growth rate, Avarami\u27s parameters, etc., were studied. The hydrolytic stability of polylactide-perfluoropolyether-polylactide block copolymers was studied in acidic, alkaline and neutral conditions. Degradation parameters such as weight loss, decrease in molecular weight, and change in thermal properties, hydrolytic solution properties, and surface morphology were monitored. Films hydrolyzed in alkaline conditions showed significant weight loss whereas in acidic and neutral conditions, the weight loss was comparatively low. Initial resistance to the weight loss of the films in alkaline conditions can be seen for the copolymers due to their hydrophobic nature. Molecular weight loss was observed for both homopolymer and the copolymers in all of the hydrolytic conditions. The melting temperatures of hydrolyzed films decreased with increasing hydrolysis time as the ester cleaved chain ends acted as impurities in the crystalline phase. Melt spinning of polylactide and block copolymers were performed to obtain monofilaments. The terpolymerization of lactide and bisphenol A derivatives resulted in a moderate molecular weight (Mn ~ 12 kg/mol) and a high glass transition (ca. 100 °C) terpolymer. The terpolymer also showed better thermal stability than PLA and the surface properties were unchanged compared to the PLA. Successful electro-spinning of the terpolymer was performed from chloroform and tetrahydrofuran solutions

Study on The Effect of Different Sols on High Alumina Castable Refractory

Ever-increasing demand and application of unshaped refractories replacing shaped ones have inspired the scientists and manufacturers to investigate these materials in depth for further improving the quality and performance. Among the various unshaped refractories, castables lead in all the areas of research, development, manufacturing and application. Physical, mechanical, chemical and thermo-mechanical characteristics of various castable systems as well as their processing and bonding mechanisms are the focus of such investigations. Among the different bonding materials, calcium aluminate cement (CAC) is most common, but the introduction of CaO in the refractory castable system by the use of CAC produces low melting phases on reaction with Al2O3 and SiO2 of the refractory systems and finally resulting in poor high temperature properties. To avoid the crisis, decrease in cement content and use of alternate bonding system were widely experimented. Among alternate bonding materials, development of sol-gel technique has opened a new horizon in bonding system for refractory technologists. The principle behind sol-gel bonding is the formation of a 3-dimensional network (gel) of particles that surrounds the refractory materials and which on subsequent heating develop strength by formation of ceramic bonding through sintering. In the present work, four different precursor sol systems have been synthesized, namely alumina, boehmite, mullite, and spinel by wet chemical synthesis. The sol systems were chosen in such a way that they generate high temperature withstanding refractory oxides on firing (alumina, mullite, and spinel). These synthesized sols are used as a sole binder in high alumina castable systems, with two different particle size distributions, containing no cement. The castables were processed conventionally and evaluated at different temperatures for the various refractory properties. Phase analysis and microstructural development are also studied to investigate the reasoning for the development of the properties. These synthesized sol based castable compositions were further compared with commercially available silica sol and cement-containing compositions using similar raw materials, particle size distributions and processed under exactly similar conditions. The synthesized sol bonded castables showed well-sintered density and strength compared to traditional cement and silica sol bonded castables. The densities (3.0-3.2 g/cc) obtained signifies a well compact microstructure, as also observed in the microstructural analysis. Considerably high hot strength and higher thermal shock and corrosion resistances were observed for the developed sol containing compositions, higher than the commercial binders, mainly due to the absence of any impurity phase. Among the developed sol bonding systems, mullite and spinel sols were found to have improved hot properties and greater resistances against corrosion and thermal shock. All the developed sol containing compositions showed no deformation or any considerable shrinkage even on firing at 16500C, indicating its application at and above this temperature without any difficulty. However, conventional cement and silica containing compositions resulted in poor properties due to the formation of low melting compounds in the system

X-ray Diffraction Analysis of Cu2+ Doped Zn1-xCuxFe2O4 Spinel Nanoparticles using Williamson-Hall Plot Method

The nanoparticles (NPs) of Zn1-xCuxFe2O4 (ZCFO) spinels with x = 0, 0.2, 0.4, 0.6 and 0.8 were synthesized by a sol-gel combustion method using acetate precursor. The NPs of ZCFO were prepared by following calcination process at 600C for 8hrs. The synthesized NPs of ZCFO were characterized by X-ray diffraction (XRD) analysis using Rietveld refinement. The Rietveld refinement of the XRD patterns revealed that the ZCFO spinels crystallize into single diamond cubic structure with Fd-3m space group. The lattice constant and unit cell volume for ZCFO NPs shrink with enhancing doping concentration of Cu2+ ion. The crystalline growth in the NPs of ZCFO was examined by peak broadening present in the XRD pattern. The Williamson-Hall (W-H) plot method were used to study the individual involvements of crystallite sizes and lattice strain on the peak broadening of the NPs of ZCFO spinels. Whereas, particle size of the ZCFO sample with x = 0.40 was estimated by high-resolution scanning electron microscopy micrograph