Papers by Keyword: Nanosized

Abstract: Nanosized La_0.75K_0.05Ba_0.05Sr_0.15MnO₃ manganite have been synthesized using sol-gel method. Afterwards, the samples were sintered at eight different temperature ranging from 650 to 1000 °C. Phase purity, crystal structure and the morphology of the sample have been examined using X-Ray Diffractometer (XRD) and Scanning Electron Microscope. It has been found that different higher sintering temperature greatly affect the phase purity and crystallite size of the sample. Regardless of the sintering temperature, all the samples crystallized in rhombohedral structure with R-3c space group. The crystallite size of the samples is found to increase from 41.59 nm up to 73.42 nm as the sintering temperature increases. Further analysis from XRD result shows that sintering temperature also affect the average Mn-O bond length and Mn-O-Mn bond angle of the sample. The average Mn-O bond length is found to increase while the average Mn-O-Mn bond angle tends to decrease as sintering temperature increases. SEM measurement shows that various grain size ranging from ~100 nm up to ~ 350 nm exists in all the sample regardless the sintering temperature.

Abstract: In this paper, nanosized La_0.85Na_0.15MnO₃ (LNMO) has been synthesized via sol-gel method by involving two major steps, first the complexation of citric acid (CA) with metal ions (MI) and second the polyesterification between CA and ethylene glycol (EG). The effect of molar ratio CA:MI varying from 2-4 on structure, microstructure and electrical transport properties of LNMO have been investigated by constant the amount of EG. All samples show single perovskite phase with hexagonal structure and space group R3c after sintering at 800°C for 10h. Sample of molar ratio 2.5 is observed to possess smallest grain sizes which yield high resistivity value compared with others, is suggested to originate from the increase of tunneling barriers (grain boundaries). The large low field magnetoresistance (LFMR) of about ~ -16% at 0.1T and low temperature confirmed the important role of grain boundaries in the nanosized LNMO.

Abstract: We have investigated the structural, microstructure and electrical transport properties of nanosized Pr_0.85Na_0.15MnO₃ (PNMO) synthesized by sol-gel technique and sinter from 600°C to 1000°C. The grain size increases from 67 nm (S600) up to 284 nm (S1000) due to the grain growth during heat treatment. XRD showed that single phase orthorhombic crystal structure of PNMO is fully forms started at 600°C. The resistivity decreased with the increased of grain size and crystallite size due to the reduction of grain boundary effect (dead magnetic layer) which improved their grain conductivity.All samples showed semiconductor behavior where their metal insulator transition temperatures (T_MIT) were estimated to be lower than 80K.

Abstract: Nanostructured materials have attracted considerable attention in recent years because of their unique and amazing properties. With a high surface activity due to their small particle size, enormous surface area and specific mechanical properties, it has been used for various engineering purposes including chemical, mechanical and civil engineering applications. The rapid development of nanostructured materials and nanotechnology will change the traditional processes of fabrication and applications of construction materials. nanosized materials can be used in construction industry to produce lighter and stronger structural composites such as modified steel. The present work introduces a novel idea for the production of metallic alloys from nanosized nickel ferrites using powder technique routes. nanosized nickel ferrite (50 nm) is being used as starting material for the production of metallic alloy containing iron and nickel. The prepared alloys were characterized physically and chemically through X-ray diffraction and optical microscope. The composition of these alloys is often a key factor to control the mechanical, chemical and physical properties of the synthesized alloys. The reduction processes take place in a stepwise manner via the formation of a series of intermediate oxides. The microstructures of the produced alloy together with the kinetics data obtained from reduction process were used to elucidate the reduction mechanism under isothermal conditions.

Abstract: A novel process was developed to obtain high content of ceria powder directly from bastnasite mineral. The bastnasite was roasted with NaHCO₃ at 550 oC for 2 h, washed with water and dilute HCl respectively to remove impurities, and finally calcined in air. TG-DTA, XRD, XRF, SEM was used to characterize the decomposition process of bastnasite, crystalline phase, the chemical composition, and morphology of the product. The results showed that the concentration of HCl solution was the most important factor in the leaching process, and the calcining temperature of bastnasite mineral should be controlled below 600 oC. The optimal technological parameters were suggested as follows: leaching temperature at 45 oC, for 45min in 3 mol/L HCl, with the weight ratio of solid to liquid of 1:5, and the calcining of the leachate at 600 oC for 2 h. And the high content of ceria (T_REO > 80wt %, Ceria/T_REO > 85wt %) nanosized (20~100 nm) powder was obtained succeffully, which showed potential application in polishing materials.

Abstract: A novel synthesis of nanosized spinel LiMn₂O₄ cathode has been developed by a combination of high-gravity technology and microwave technology. Spinel lithium manganate precursor were prepared by co-precipitation method in a rotating bed with helix channels (RBHC). Calcination of the precursor in the microwave field produces uniformly sized, nanoparticles of spinel LiMn₂O₄ as the final product. The phase structures and morphologies were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM), transform electron microscopy (TEM). The results show that nanosized spinel LiMn₂O₄ powders with high crystallinity, uniform particle size, and the average size of about 60 nm can be synthesized by the integration of high-gravity technology and microwave technology.

Abstract: The polycrystalline nickel ferrite - NiFe₂O₄ has been obtained by ceramic route starting from a stoichiometric mixture of oxides (NiO and α-Fe₂O₃ powders). The obtained NiFe₂O₄ was subjected to high energy ball milling. The formation of NiFe₂O₄ by ceramic method and also the evolution of the powder during milling were studied by X-ray diffraction. The mean crystallite size of the NiFe₂O₄ continuously decreases with the increasing of the milling time and for all the milling time it is in nanometric range. The particles sizes are drastically reduced by milling process. For the milled samples, the particles size is ranging from tens of microns to few nanometers. The powder morphology and local chemical homogeneity were investigated by scanning electron microscopy (SEM) and respectively by energy dispersive x-ray spectrometry (EDX).

Abstract: In the present work, using nanosized rare earth oxide CeO₂ as filler and acetonitrile as organic solvent, a novel solid-state composite polymer electrolyte (CPE) films (PEO)₁₀LiClO₄-x wt.%CeO₂ (x=0,2,6,9,12,15) was prepared by solution-casting technique. The effect of CeO₂ filler concentration on morphology and electrical characteristics of CPE films has been investigated and analyzed. The AC impedance measurements show that the ionic conductivity of CPE can be efficiently enhanced by adding appropriate CeO₂. The highest room temperature (25^OC) ionic conductivity of 1.71×10^-5S•cm^-1 is achieved with the CeO₂ content of 9 wt.%. With the CeO₂ content continues to increase, CPE ionic conductivity begin to decline. This is because appropriate CeO₂ can disorder the chain structure and effectively inhibit the crystallization of PEO, which expands the amorphous region required for the lithium-ion transport.

Abstract: There has been much recent activity in the research area of nanoparticles and nanocrystalline materials, in many fields of science and technology. This is due to their outstanding and unique physical, mechanical, chemical and biological characteristics. Recent developments in biomineralization have demonstrated that nano-sized particles play an important role in the formation of the hard tissues of animals. It is well established that the basic inorganic building blocks of bones and teeth of mammals are nano-sized and nanocrystalline calcium orthophosphates (in the form of apatites) of a biological origin. In mammals, tens to hundreds of nanocrystals of biological apatite are found to combine into self-assembled structures under the control of bio-organic matrixes. It was also confirmed experimentally that the structure of both dental enamel and bones could be mimicked by an oriented aggregation of nano-sized calcium orthophosphates, determined by the biomolecules. The application and prospective use of nano-sized and nanocrystalline calcium orthophosphates for clinical repair of damaged bones and teeth are also known. For example, a greater viability and a better proliferation of various cells were detected on smaller crystals of calcium orthophosphates. Furthermore, studies revealed that the differentiation of various cells was promoted by nano-sized calcium orthophosphates. Thus, the nano-sized and nanocrystalline forms of calcium orthophosphates have the potential to revolutionize the field of hard tissue engineering, in areas ranging from bone repair and augmentation to controlled drug delivery devices. This paper reviews the current state of knowledge and recent developments of various nano-sized and nanocrystalline calcium orthophosphates, covering topics from the synthesis and characterization to biomedical and clinical applications. This review also provides possible directions of future research and development.

Abstract: Sintered stainless steel has a wide range of applications mainly in the automotive industry. Properties such as wear resistance, density and hardness can be improved by addition of nanosized particles of refractory carbides. The present study compares the behavior of the sintering and hardness of stainless steel samples reinforced with NbC or TaC (particles size less than 20 nm) synthesized at UFRN. The main aim of this work was to identify the effect of the particle size and dispersion of different refractory carbides in the hardness and sintered microstructure. The samples were sintered in a vacuum furnace. The heating rate, sintering temperature and times were 20°C/min, 1290°C and 30, 60 min respectively. We have been able to produce compacts with a relative density among 95.0%. The hardness values obtained were 140 HV for the reinforced sample and 76 HV for the sample without reinforcement.