Papers by Keyword: Porous Ceramics

Abstract: Conventional ceramic technology is a widespread technique for synthesizing a large range of materials for household use and engineering applications. However, for advanced technical ceramics different approaches should be used in order to obtain materials with unique physical properties. Despite the well-known technology for the synthesis of alumina-based ceramics, there are a lot of challenges in optimizing manufacturing conditions or integrating the newest technologies. In particular, there are still some challenges in sintering porous bulk ceramics. In this paper, we report on synthesizing mixed-phase porous α-Al₂O₃ by modernized ceramic technology method. Precursor powders for compaction were obtained by the hydrothermal method in a Teflon vessel. X-ray diffraction and scanning electron microscopy were used to characterize the synthesized samples. It was demonstrated that hydrothermal precursors with chemical residuals make it possible to synthesize porous ceramics with an open porosity of 55–80% and an apparent density of 0.76–1.80 g/cm³. The change in microstructure of sintered samples is explained by precursor powder morphology. The developed approaches can be used in modernized ceramic technology to synthesize porous oxide materials for filters of gases and liquids or refractories.

Abstract: The aim of this study was to compare the difference in bone formation between hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) ceramics with similar porous structure. Porous HAp and β-TCP ceramics (total porosity: ~70%) with highly-interconnected structure were fabricated by firing calcium-phosphate fiber mixed with carbon beads (~150 μm). The size of highly-interconnected pores was measured by mercury intrusion technique. Each sample (ϕ4 mm × 8 mm) was implanted into the tibial bone defect (ϕ4.2 mm × 8 mm) of a pig (2 years old, male). After 6 weeks of implantation, undecalcified section was prepared and stained with hematoxylin and eosin (HE) stain. New bone area and remaining material area were evaluated.Interconnection sizes of HAp and β-TCP ceramics were 23.0 µm and 15.6 µm, respectively. New bone area of β-TCP ceramics was significantly higher compared to HAp ceramics. Remaining material ratio was 77.1 ± 3.3% for β-TCP ceramics whereas HAp ceramics remained stable. Bone formation in HAp ceramics was inhomogeneous compared to β-TCP ceramics in HE stained section. Although the β-TCP ceramics interconnection size was smaller, higher resorption may have played a positive role in homogeneous bone formation. According to the result of the study, it is suggested that highly-interconnected porous ceramics made by β-TCP could be a suitable material for bone regeneration.

Abstract: Yttrium aluminum garnet is abbreviated as YAG, which has many excellent high temperature characteristics. YAG structural materials and functional materials are promising candidates. In this paper, YAG porous ceramic materials with different mechanical properties are prepared by adjusting the parameters of the sintering process to provide reference for the preparation of high-performance porous ceramics. From the experimental results, the following conclusions can be drawn: when the sintering temperature is 1450°C and the holding time is 2h, the YAG gradient porous ceramics have no deformation and shrinkage, have a regular good shape, and have good strength after sintering. The sintering rate was 8 °C/min and carbon emission temperature is 800°C, the structure of the YAG gradient porous material is good, the pores are uniform, and the strength of the sintered sample is high, The porosity is 25.7%, the compressive strength is 8.12MPa.

Abstract: For sintering Al₂O₃ porous ceramic were used plasma-chemical synthesed powders with a specific surface area of 30 and 50 m²/g. Sintering were carried out in various conditions: sintering in nitrogen atmosphere, in air or vacuum at 1200-1700 °C. The most suitable sintering conditions are sintering in air at 1200-1500 °C using Al₂O₃ nanopowder with a specific surface area of 50 m²/g. Samples with open porosity of 35-45% and average pore size of 100-200 nm were obtained under these conditions.

Abstract: YAG materials have a number of unique properties, the application is very extensive. In order to improving the properties of YAG porous materials, the effect of forming processing on the properties of YAG porous ceramics is investigated. Through the results and analysis, the conclusions showed that the porosity of YAG porous ceramics gradually decreased with the molding pressure increases, and the compressive strength of YAG porous ceramics shows a rising trend. The size and number of pores in the microstructure are reduced with increasing the forming pressure, there are inherently many voids in the YAG porous ceramics body at low forming pressures. The porosity of YAG porous ceramic decreases with the increase of dwell time, however, the process of extending from 5 min to 10 min is much faster than the rate of descending from 10 min to 15 min. The size and number of pores in the microstructure are reduced with extending the holding pressure time, which also makes YAG porous ceramics pose the higher mechanical strength. Through the analysis of the results, when the forming pressure is 10MPa, the porosity of YAG porous ceramics is 41.11% and the compressive strength is 5.8MPa, the porosity and compressive strength of YAG porous ceramics is better.

Abstract: The sintering methods of quartz sand porous ceramics were researched with the low grade quartz sand along the Yangtze River via the vacuum sintering method in this paper, which lay technology foundation for researching new heat insulating materials. The quartz porous ceramics is obtained with the high performance cost, the quartz porous ceramics is sintered at 1050°C via the vacuum conditions, the density of ceramics is 1.267g/cm³, the porosity is 51.6%, the compressive strength is 3.184MPa, the porous ceramics show the homogeneous distribution micro-pore and good shape. The density and the compressive strength of prepared ceramics via the vacuum sintering both are higher than that of prepared ceramics via the atmosphere sintering, however, the porosity is shown the opposite results.

Abstract: The study is devoted to the study of the mechanical properties of penodiatomite ceramics. Dynamics of changes in the dynamic moduli of elasticity of highly porous (up to 70%) diatomite ceramics from the annealing time at temperatures of 800-1000 °С has been experimentally studied. The values of the activation energies of the change in the modulus of elasticity (Wa = 0.22-0.24 eV) were measured for high-temperature annealing (800-1000 °С). The change in the phase composition of the samples under the influence of annealing is demonstrated.

Abstract: Presently, there is a lack of effectiveness in the manufacturing of sensors and sensing systems, with Brazilian technologies and raw-materials, able to measure soil water content, with efficiency and practicality. On account of this, ceramics is selected as sensing elements for this application, based on relevant results obtained by researchers from the TECAMB Group of INPE, along the last 15 years. In this way, the present work tries to bring together the technologies of manufacturing, characterization and development of porous ceramics and the monitoring of soil water content in typical Brazil soils, for several applications, such as irrigation, drainage, building and environmental monitoring as well. And so, in order to improve the sensing capacity of these ceramic devices, electrical measurements were performed in different climatic conditions of controlled relative humidity and room temperature. The scanning electron microscopy technique was applied for the morphological analysis of the sintered ceramic microstructure. Results evidenced that the ceramic devices presented a very promising response to the water molecules contained in soil samples selected for tests, under established climatic conditions.

Abstract: The Starch Consolidation method of molding technique is based on the ability of starch swell and gelatinize in water, so the green bodies are formed from suspensions, generating controlled porosity after firing; however, it is strongly influenced by gelatinization temperature, starch used, content and type of dispersant, pH and viscosity. This work involves the statistical analysis of possible relations between viscosity, content of dispersant and pH. Slurries containing alumina, water and starch were prepared, settling the solids in 40% and varying the starch content of 10, 20, 30, 40 and 50%, compared to the solids at the mixture. PH and viscosity measurements were made of the slurries as a function of added dispersant. Were obtained and analyzed measures of each parameter, using the Pearson correlation, verifying the existence of an almost perfect correlation between most of the parameters studied.

Abstract: Foam-type porous silicon carbide (SiC) ceramics without cracks and hollow struts were fabricated using the polymer replica method with polycarbosilane (PCS) and polyurethane (PU) foam as the starting materials. The synthesized porous SiC was analyzed using X-ray diffraction and scanning electron microscopy. The results revealed that a porous SiC ceramic structure was formed with a dense framework at a low temperature of 1200°C. During the heat-treatment process, the PCS experienced an organic–inorganic transformation and then converted to the SiC ceramics. It was determined that the organic–inorganic transformation of PCS, which was the stage of silicon oxycarbide formation, is affected by the curing condition. In this study, the optimum curing condition was determined to be an air atmosphere at 200°C for 7 h.