Papers by Keyword: Solid State Sintering

Abstract: Strontium Calcium Titanate (Sr_0.9Ca_0.1TiO₃) ceramic powders were synthesised using a solid sintering technique and were uniaxially pressed and sintered at different temperatures of 1100 °C, 1150 °C, 1200 °C, 1250 °C, and 1300 °C for three hours. Physical, phase, microstructure and dielectric properties were studied. Perovskite Cubic Strontium Calcium Titanate phase was crystallized. With an increase in sintering temperature, the density and grain size of Sr_0.9Ca_0.1TiO₃ ceramics increased. Grain boundaries were observed in the microstructure of Sr_0.9Ca_0.1TiO₃ sintered at higher temperatures. At room temperature, the dielectric constant and dielectric loss are observed to increase with the increase in sintering temperature. AC conductivity enhanced with sintering temperature.

Abstract: This study investigated the effects of sintering temperature on phase, physical properties and microstructure of calcium cobalt oxide (Ca₃Co₄O₉ or CCO) ceramic. CCO powder was prepared with using the mixed oxide method and calcined at 750°C for 24 h. The ceramics were prepared by sintering the powder at 900, 950, 1000 and 1050°C under a normal air atmosphere for 24 h. A maximum density of 4.02 g/cm³ (~92% relative density) with 12% linear shrinkage was obtained in the sample sintered at 1000°C. XRD patterns of the CCO ceramics indicated pure phase with no detected impurity. SEM images of the ceramics showed plate-like shaped grains. The average grain size value gradually increased as the sintering temperature increased, and reached a maximum value of 8.95 mm at the sintering temperature of 1000°C. The deviation from stoichiometric composition for the samples sintered at low sintering temperatures may be due to the low sample density which in turn affected the EDS analysis results.

Abstract: Solid state sintered pellets of barium hexaferrite were performed. The Curie temperature of BaFe₁₂O₁₉ pellets were measured with differential scanning colorimetry (DSC). The coefficient of thermal expansion (CTE) of pellets was defined above and below the Curie temperature. The Curie temperature calculated basedon the dilatometry is are in good agreement with the DSC measurements.

Abstract: The phase evolution of yttrium iron garnet (YIG) during reaction 3Y₂O₃-5Fe₂O₃ was investigated by modifying Fe₂O₃ particle sizes (FPS). Five different sizes of Fe₂O₃, (d₅₀) are used to prepare YIG powder. Solid state reaction (SSR) was applied at 1200 °C in order to gain insight on the effect of FPS towards the YIG formation. Rietveld refinement method was used to quantify the amount of YIG yielded (%). Larger FPS (> 50 μm) initiates only 5Fe₂O₃ + 3Y₂O₃ à 3YFeO₃ + Fe₂O₃ + Y₃Fe₅O_12.. However, when the fine FPS (5 μm) is used, the reaction pathway was changed into 5Fe₂O₃ + 3Y₂O₃ à 6YFeO₃ + 2Fe₂O₃ à 2Y₃Fe₅O_12. These behaviors is explained that the smaller FPS consumed quickly to form YIG due to the smaller particle distance between Fe₂O₃ and Y₂O₃. This shall be leading to higher reaction rates (mass-transfer kinetics).

Abstract: Sintering as a technology has been followed from ancient times. However, as science it emerged in 1940s with the seminal work of Frenkel, Huettig, Kuczynski, Lenel, Kingery and Hausner. The present paper covers the historical aspects of sintering fundamentals , right from solid state sintering to liquid phase sintering, activated sintering, electronic theory of sintering, sintering with external pressure, constrain sintering etc. Various mechanisms of sintering with their microstructural relationships have been highlighted. A generalized approach to sintering is called for, which may to great extent bridge the gap between sintering theory and practice.

Abstract: In the present work, SiC was pressureless solid state sintered with 3 wt% C and 0.6 wt% B₄C as sintering additives. The friction and wear behavior of the PSSS SiC ceramics was investigated by using a block-on-ring tribometer. The wear volume and friction coefficient was measured. It is as expected that the friction coefficient increased with the elevation of the normal load and sliding speed. The microstructure of the worn surface was observed, based on which the wear mechanism was analyzed. Different degrees of oxidation during the friction process was found and the degree of oxidation was related to the severity of wear. The normal load was found to exert great influence on the wear of the SSiC ceramics.

Abstract: Lead Zirconate Titanate (PZT) ceramics are of great technological interest because of their excellent piezoelectric and ferroelectric properties. In this research, an effort will be made to enhance the PZT properties by doping with other elements. The objective of this research is to enhance the dielectric, hence increase the efficiency and performance of piezofan. Properties that piezoelectric fan should have are high mechanical piezoelectric coupling factor, high dielectric constant, easily polarized and high piezoelectric charge constant. Soft and isovalent dopant was a very suitable candidate to fulfill this requirement. The samples will be prepared via high planetary mill and use optimum compaction pressure due to these processes can skip calcinations process, which can reduce a lot of cost. This process also can avoid PbO loss during firing process. The proposed elements are isovalent dopant which is Sr²⁺ and donor dopant which is La³⁺ to subtitude Pb²⁺ at the A-site of PZT. Dopant is beneficial to the enhancement of physical properties of PZT – based ceramics. It also effectively improved the dielectric properties of PZT ceramics due to the effect of average grain size.

Abstract: This research was carried out to fabricate and characterize Co-Cr-Mo (F-75) alloy. The samples have been prepared via solid state sintering. The lab work comprises the mixing of F-75 alloy powder with 2 wt. % of binder. The mixture was cold compacted using uniaxially press at 500 MPa. The samples were sintered at three different temperatures (1250 °C, 1300 °C and 1350 °C) in inert environment for 90 minutes of sintering time. The sintered samples were characterized by using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and optical microscope (OM) Olympus BX41M. Bulk density, apparent porosity, percentage of linear shrinkage, and microhardness of the samples were also characterized. The average of the grain sizes were measured by line intercepts method. The optical micrographs showed the difference grain size in all sintered samples after etching with Marble reagent. The result shows the percentage of linear shrinkage, bulk density value and porosity increase with increasing the sintering temperature. Beside that, higher sintering temperature yields coarser grain structure.

Abstract: In order to improve the wear resistant properties, WC ceramic particles were used to reinforce Hadfield steel. WCp/Hadfield steel composites were fabricated by optimized solid state sintering process of powder metallurgy. Interface structure, constituent phase and the forming mechanism of the composites were investigated systematically. The results show that the WCp/Hadfield steel composites have uniformly distributed particles and well bonded interface between WC particles and Hadfield steel. In the WCp/Hadfield steel composites, the interface between WC particles and Hadfield steel matrix is of shell shape, in which W, Fe and Mn elements diffuse between the two phases. The interface is of metallurgical bond, in which a new phase, namely Fe3W3C is formed. The micro-hardness of the interface layer is between those of WC and the steel matrix, which can provide a guarantee for the property transition between WC particles and Hadfield steel matrix. The diffusion reaction mechanism of the interface was also systematically studied.

Abstract: The most interesting feature in silicon carbide is the structure-property relation where the formation of different types of microstructure due to different structural modifications (polytypism) and grain-boundary/interfacial phase chemistry dictate the final properties of the monoliths. Since synthesis of SiC in last century, several methods such as hot pressing with a sintering aid (B, C), pressureless sintering with a sintering aid (B, C, Al) and reaction bonded (Si-SiC) were used to fabricate dense SiC. A newer method of fast sintering (spark plasma sintering) using pulsed current is also employed to consolidate nano/submicron size SiC with or without additives. The solid state sintered SiC materials have fine-grained equiaxed microstructure (grain size 1 to 4 µm) with thin layer of intergranular phases (amorphous film), exhibit moderate high-temperature creep and oxidation resistance, fracture toughness (3 to 4 MPam1/2) and have highly flaw-sensitive strength at room temperature. The high temperature mechanical properties are highly influenced by the presence of free C, Al and B + C containing grain-boundary phases. Moreover, during prolong processing, abnormal grain growth occurs resulting in anisotropic -SiC phase formation. The Si-SiC materials are poor candidates for high-temperature applications due to the limit set by the melting point of silicon, and the limitations of hot pressing (HPSiC) as a densification technique are well known. SPSed SiC without sintering additive revealed inferior mechanical properties attributed to poor bonding between adjacent grains. In the present survey, an overview of the new developments in silicon carbide processing and properties will be presented together with the information on structure-properties correlationship. Information on the structure of the grain-boundary/secondary phases and interfaces until now was not comprehensively analyzed.