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Among the porous media, hydroxyapatite (HA) possesses good biocompatibility and bioactivity properties with respect to bone cells and tissues, due to its similarity with the hard tissues of the body. In this study, mesoporous HA was synthesized using a soft-templating technique via a selfassembly between HA and cationic surfactant ecyltrimethylammonium bromide (C10TAB), which is analogous to the synthesis of mesoporous silica MCM-41. This co-precipitation method involved formation of hexagonal-phase micelle template by the surfactant and the precipitation of HA surrounding the micelle. After ageing, calcination was carried out to remove the templates, revealing the pores as well as to produce more crystalline and more stable HA structure. This study showed that instead of hexadecyltrimethylammonium bromide (C16TAB) which was conventionally used, C10TAB could also be used to synthesize single-phase mesoporous HA with pore size ca. 3 nm. Ageing temperature of 120 °C, for 24 hours was found sufficient for the formation of mesoporous HA. The adsorption properties of mesoporous HA was able to be improved by increasing the water content of C10TAB-phosphate solution and by constant pH adjustment during the mixing of solutions.
The improvement of ceramic synthesis and processing methodology based on digital image processing and analysis of ceramic samples is in its initial stage. The main reason is that the models are based on poorly obtained data from sample’s digital image processing. The lack of a solid statistical analysis and digital-imaging setup standardization make the method less useful that it should be if set in a sound basis. Therefore the importance of setting a new methodology in digital image processing for data acquisition on ceramic morphology analysis is essential for setting new models for customized ceramic synthesis and processing. The present paper shows results based on Scanning Electron Microscopy (SEM) from Al2O3 ceramics obtained by starch consolidation method. Observation of different sample’s regions allowed a more accurate description of ceramic morphology. Plots of resistance to flexion versus porosity and its correlation with the grain size and shape allowed one to choose the best model for representing ceramic’s morphology. Correlation of starch percentage with sample’s porosity and mechanical resistance allowed the best experimental conditions for customized ceramic’s performance.
Porous ceramic materials are used in medicine as well as in industry. They can be prepared in the form of filter components, thermal insulators, or composite components. Preforms of this type can only be applied if they meet the respective structural requirements. In the present study, such a porous ceramic material was produced by the polymeric sponge method using a polyurethane sponge and a-Al2O3 Almatis. The aqueous suspension was prepared with binders of the two types: polyvinyl alcohol and a dispersion based on methacrylic acid esters and styrene. The aim of this study was to find the relationship between the composition of the weight slips, sintering conditions, and the structure of the porous ceramic obtained. The paper presents the results of studies on the rheological properties of the ceramic slurries and the results of strength tests of the ceramic material.
High performance porous structural ceramics have been widely studied. Silicon nitride is an interesting material for this application because bodies with high mechanical strength, achieved as a result of “in situ” anisotropic grain grown, can be obtained. In this study, Si3N4 bodies with different porosity related aspects (percentage, morphology, etc.) are made using the sacrificing template method, by changing the percentage (vol%) and the drying method of the mixture as well as the sintering time. The porosity, apparent density (Archimedes method), microstructure (SEM) and the mechanical strength (in compression) of these bodies were determined. It was thus possible to relate the type and amount of starch with the porosity and mechanical properties of the bodies.
The starch consolidation technique is commonly used for obtaining porous ceramics due to bonding and porous-maker starch characteristic during gelling process. The method adopted here improved the water drainage by using a plaster porous base (70 and 90 consistency values) improving the water drainage by action of gravity and the capillary effect. It used slip with 50 vol% solids and as precursors oxide A-1000SG and commercial cornstarch with a mass concentration varying from 10 to 40%. For comparison between the present method and the common one, slip was put in impermeable and permeable base moulds. The gelling occurred at 70ºC for 2 hours and the drying at 110ºC. Pre-sintering was carried out at 1000ºC and the sintering at 1600ºC with a plateau of 1 hour. Results showed that the plaster consistency of the mould bases was preponderant on ceramics porosity. Porosity and apparent density measurements using light and electron microscopy revealed variation of 5% of porosity from the top to the bottom of the samples.
The purpose of this research was to design a processing route for the conversion of hazardous Municipal Solid Waste (MSW) fly ash into a glass-ceramic material, stable and safe for further industrial, structural, or ornamental applications. The process firstly consists in the transformation of a hazardous MDW fly ash into a vitrous material. Thermal analyses information was used to design the controlled heat treatment that further transformed this vitrous material into an environmentally safe composite. The final product obtained was a glass-ceramic material with randomly oriented crystals embedded in its residual amorphous matrix. The crystalline phases were identified as Nepheline and Diopside. CLSM (Confocal Laser Scanning Microscopy) was used for real-time in-situ observation of the microstructure under simulated heat treatment conditions.
Solution–combustion is an attractive approach to synthesis of nanomaterials for a variety of applications, including catalysts, fuel cells, and biotechnology. In this paper, several novel methods based on the combustion of a reactive solution are presented. These methods include selfpropagating sol-gel combustion and combustion of impregnated inert and active supports. It was demonstrated that, based on the fundamental understanding of the considered combustion processes, a variety of extremely high surface area materials could be synthesized. The controlling process parameters are defined and discussed. Examples of materials synthesized by the above methods are presented. A continuous technology for production of nanopowders by using the solution combustion approach is also discussed.
Microwaves (MW) at the ISM frequency of 2.45 GHz have been used to ignite the Combustion Synthesis (CS) of pressed ceramic and metallic powders mixtures, using a single-mode applicator (TE103). This experimental apparatus allows to study the separate effect of prevalent electric or magnetic field on the selective heating of the reactive powders compacts, while transferring energy and not heat before and after CS. Microwave activated combustion syntheses (MACS) of TiC-40 wt%Fe and FeAl intermetallic compounds were performed in the two different field configurations (maximum of the electric field (E) and maximum of magnetic field (H)) in order to investigate any possible difference in the reaction mechanism and in the final microstructure of the products.
MACS in the maximum of E has also been applied to high temperature materials joining, with the application of a moderate pressure during the irradiation with electromagnetic waves, to promote adhesion and to reduce the newly formed compounds porosity.
Due to the lack of specialty kinetic methods and instruments, the kinetics of fast hightemperature reactions SHS-ceramic systems has not been adequately studied. Recently, we have developed a number of methods of so-called non-isothermal kinetics (NIK) and designed instruments allowing one to obtain information about reactions of ceramic systems in a wide range of practically important temperatures and rates. The use of one of the NIK-methods (called electrothermal analysis based on the phenomena of electro thermal explosion) allows one to study kinetics of SHS of some ceramic materials characterized by the total reaction time ~ 10 μs. In ETE, both samples pressed from reagents powders or cylindrical samples made from tightly rolled foils were studied. The joule heating was accompanied by high-speed scanning of the non-stationary temperature field on its surface. Description and technical characteristics of the specialty device electrothermoanalyzer ETA-100 manufactured by ALOFT are given. Kinetic parameters of fast EM reactions for the temperatures up to 3600 K can be measured by ETE method using ETA-100. New kinetic data for fast high-temperature gasless SHS yielding individual and composite materials (including refractory carbides and borides of transition metals, silicon and boron carbides, some refractory oxides and hard alloys) are presented. At high-speed impact of the samples, the reaction rate constants were found to exceed the combustion rate constants (measured by ETA-100) by many orders of magnitude. It was concluded that the kinetic mechanisms of the corresponding fast reactions in the static conditions and under the impact are dramatically different. It was shown that SHS in ETE mode has a significant potential as a modern practical method to be used for welding of refractory and dissimilar materials, production of coarse superabrasives, etc.
The direct 3D method of numerical simulation of gasless combustion of mechanically activated solid powder mixtures is developed. The method under consideration falls into three stages. On the first stage, a simulation of mixture structure is performed. An analysis of the structure obtained in simulations is carried out. On the second stage, the thermal conductivity of solid powder mixture is calculated. On the third stage of simulation, the ignition and combustion of each particle of the mixture is considered with taking into account of heat exchange between contacting particles. The results of numerical simulations are represented dynamically and compared with the experimental data, obtained by high-speed digital recording of mechanically activated SHS systems combustion.
A heterogeneous model for ignition and combustion of cylindrical free-gas samples with a gas-permeable and impermeable surface, including the description of structural and phase transformations is formulated. The effective method for numerical model research, taking into account a zonal structure of combustion wave is offered. Dynamics of porous structure forming of products from a stage of ignition up to the steady mode of exothermal reaction front propagation is considered. The calculated stationary combustion rate and elongation of a burned specimen versus its diameter, particle size of a fusible component, initial porosity and pressure of inert gas are received. Experimental data are qualitatively compared with calculated ones. The change in characteristics of combustion wave in a non-stationary mode is analyzed. The structural oscillations resulting in lamination of a porous specimen in a zone of synthesis products in a self-oscillatory combustion mode are found out. The factors, which are the reason for structural oscillations occurrence are determined. Modeling for mechanical compression of a sample shows that a stabilizing effect on the process of combustion consists of additional compensation of loosening forces.
A comprehensive review of both past and current world-wide accomplishments in the area of combustion synthesis, with special emphasis on the production of oxide and nonoxide ceramic powders, is presented. This review focuses on scale-up and production initiatives undertaken by international companies and institutions. A significant part of this review is dedicated to manufacturing of dense and porous structures involving combination of self-propagating hightemperature technique with other processing methods. Finally, new initiatives and challenges associated with this novel synthesis technique are discussed.
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