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... sintering temperature effect on the densification and grain growth of compacts sintered at temperature ranging between 900 and 1500 o C for 1 hour is shown in figure 2. No significant densification was observed below 1030 o C confirming the dilatometric results (figure 1). ...
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... other two-step sintering is based on works of Chen and Wang (Chen &Wang, 2000), in which samples are first heated to a higher temperature to achieve intermediate density, and then cooled down and kept at lower temperature until they are dense. A pre-requisite for successful densification during the second step of sintering is that pores become subcritical and unstable against shrinkage. ...
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... the temperature at which the two rates become equal, junction mobility is essentially reduced despite the considerable grain-boundary diffusion. Figure 2 shows that grain growth is most intense at temperatures above 1400 o C. Since samples conditions after the first stage affect the second stage of sintering, grain growth resulting from heating in the first stage must be avoided. Thus, the temperature chosen for the first stage of sintering was 1400 °C. Figure 6 shows the behavior of relative density (%TD) versus temperature for sintering at constant heating rate of alumina. ...
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Citations
... 3 The ability to be sintered of a determined compact powder depends on chemical composition, particle size, and distribution, that is, powder morphology, green body density, atmosphere, pressure application, and presence of organics. 4 Thus, the final density and microstructure evolution combine pre-sintering body features and thermal history. In some cases, the utilization of different sintering schedules and heating rates leads to inhibition of grain growth or densification processes highlighted in techniques as two-step sintering or high heating rates. ...
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... The high sintering temperature sustained the consolidation and aiding a fairly uniform microstructure, thus creating a smooth surface texture. The sintering process induced densification via the elimination of the finest particle, the pore size becomes irregular and some of pores were confined within the grains [26,27]. The presence of small pores throughout the sample represents the transformation of the amorphous phase to the nepheline phase of crystalline ceramic, confirming that sintering primes phase transformation [28]. ...
... Besides, the addition of UHMWPE also resulted in the formation of pores through the gradual decomposition process during sintering, and the results were supported by the increase of the flexural strength and decrease in the density of the samples. 26.5° were found in kaolin based geopolymer. The kaolinite (Al2SiO5(OH)4) and quartz (SiO2) were the mineralogical components of kaolin, while the zeolite is typically crystallized from the formation of amorphous aluminosilicate gel formation by the activation of kaolin with the alkali activator. ...
The primary motivation of developing ceramic materials using geopolymer method is to minimize the reliance on high sintering temperatures. The ultra-high molecular weight polyethylene (UHMWPE) was added as binder and reinforces the nepheline ceramics based geopolymer. The samples were sintered at 900 °C, 1000 °C, 1100 °C, and 1200 °C to elucidate the influence of sintering on the physical and microstructural properties. The results indicated that a maximum flexural strength of 92 MPa is attainable once the samples are used to be sintered at 1200 °C. It was also determined that the density, porosity, volumetric shrinkage, and water absorption of the samples also affected by the sintering due to the change of microstructure and crystallinity. The IR spectra reveal that the band at around 1400 cm−1 becomes weak, indicating that sodium carbonate decomposed and began to react with the silica and alumina released from gels to form nepheline phases. The sintering process influence in the development of the final microstructure thus improving the properties of the ceramic materials.
... [53,63]. Ionic resistance determinations. ...
Tannins have been used to replace chromate in wash-primers as a temporary (“in transit”) protection for metals. In the present work, the anticorrosive properties of “quebracho colorado” tannins were tested in water solution and in wash primers to protect aluminum alloy 1050. Polarization curves (linear and Tafel) and corrosion potential measurements were done on the alloy in contact with different concentrations of the tannin. A tannin wash primer was prepared and coated panels were tested in 100% humidity chamber (ASTM D 2247) and by electrochemical techniques (linear polarization curves, corrosion potentials and ionic resistances). Chromate and talc primers as well as no-coated aluminum alloy were also tested, as control, to compare the results.
... The minimum contact surface area provides maximum resistance to the flow of electric current which in turn facilitates maximum resistance heating at the inter-particle contact surface [39]. Because of all these, time required for sintering process reduces significantly in comparison with other conventional method which requires hours for sintering [40,41]. Low temperature and short period results for better densification and foreshortened grain size. ...
In this paper, the effect of sintering techniques (conventional, CS and electric resistance, ERS) and SiC content (1, 3 and 5 wt. %) on the microstructural, mechanical and tribological properties were investigated. Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were performed for microstructural investigation. Density, porosity and hardness were evaluated at different weight fractions of SiC for comparative study. Tribological behaviour was evaluated in terms of wear loss and coefficient of friction (COF). Worn-out surfaces and formed debris were also studied using SEM for understanding the wear mechanism. Results indicated that addition of SiC improved the hardness, wear resistance and COF. With addition of 5 wt. % SiC the hardness improved by 32 % for CS and 30% for ERS, wear resistance improved by 37 % for CS and 40% for ERS while COF improved by 3 % for CS (3 wt.% SiC) and 6 % for ERS (5 wt.% SiC) compared to neat Al. ERS processed composites resulted in better densification, improved hardness (12-14%) and tribological behaviour (wear resistance 36-39 % and COF 7-15 %) for 1-5 wt. % SiC compared to CS processed ones. Abrasion, adhesion and delamination were the controlling wear mechanism for Al-SiC composites with lesser adhesion wear in ERS composites.
... На практике спекание нанопорошков с получением керамики ультратонкой микроструктуры (субмикронной зернистости) осуществлялось в исследовательских работах прежде всего методами горячего прессования, электроискрового спекания (spark plasma sintering, electric current sintering). Показано, что плотная керамика субмикронной зернистости может быть получена, не прибегая к таким аппаратурно-сложным методам, путем обычного свободного спекания (без приложения давления) за счет подбора неординарного температурного режима спекания [62]. Таким способом была получена, например, корундовая керамика со средним d 0,52-0,72 мкм при относительной плотности 91,0-96,6 %. ...
Information on foreign manufacturers of alumina ceramics, mainly fine technical, is presented. The data on the mechanical, thermal, dielectric properties of products manufactured by different companies are given. With regard to the prospects of industrial production, some methods for producing ceramics based on Al 2 O 3 have been considered. Ref. 43. Tab. 10.
... На практике спекание нанопорошков с получением керамики ультратонкой микроструктуры (субмикронной зернистости) осуществлялось в исследовательских работах прежде всего методами горячего прессования, электроискрового спекания (spark plasma sintering, electric current sintering). Показано, что плотная керамика субмикронной зернистости может быть получена, не прибегая к таким аппаратурно-сложным методам, путем обычного свободного спекания (без приложения давления) за счет подбора неординарного температурного режима спекания [62]. Таким способом была получена, например, корундовая керамика со средним d 0,52-0,72 мкм при относительной плотности 91,0-96,6 %. ...
Представлена информация о западных производителях алюмооксидной керамики, преимущественно тонкой технической. Приведены данные по механическим, теплофизическим, диэлектрическим свойствам продуктов, выпускаемых разными фирмами. Применительно к перспективам промышленного выпуска рассмотрены некоторые методы получения керамики на основе Al2O3.
... A slight density increase occurred in relation to CS, but it should be noted that a nearly-fully dense microstructure (RD > 95 %TD) was not reached. Usually, a prereq-uisite in TSS for successful densification during the second step of this sintering technique is that the pores become sub-critical and unstable against shrinkage [7,[44][45][46][47][48]. This stage is reached at 75 %TD and 82 %TD for yittria [7] and alumina [44] nanopowder, respectively. ...
This work investigated the compacting and densification behaviour of TiO2 nanoparticles prepared by the simple non-aqueous sol-gel process. The synthesized nanopowder has anatase TiO2 structure with the average
crystallite size of 10 nm and agglomerated particles. The compressibility curve shows two well-defined linear
parts that intersect at ∼380 MPa which is a measure of agglomerate compressive strength. The densification
process was investigated by the dilatometric analysis using non-isothermal experiments. The apparent activation energy for the densification was calculated (88–102 kJ/mol). Grain rearrangement by grain boundary
sliding was proposed as the dominant shrinkage mechanism.
... In order to form ceramic with good varistor characteristic, a homogeneous distribution of dopant and correct concentration of oxygen is necessary, as the conductivity of zinc oxide depends on oxygen defect in the structure [11]. Methods that involve during sintering process are important to investigate in order to achieve the solids microstructure and final properties [25]. ...
... In the production of ceramic varistor, density is one of the essential component, which requires a special concern. Without a good control on the development of density, the material will not be able to achieved its desired performance [25]. If we take a look generally on the densification step occurred during sintering, the process can be considered to be divided in three stages i.e. initial, intermediate and final stage. ...
... For conventional method, minimum grain growth can be controlled by maximization the last density that determine by the heating curve. By controlling the procedure of the heating curve, high densification of grain size can be controlled [25]. ...
Conventional, free or pressure less sintering is the simplest technique which involves heating of a powder compact, previously prepared at ambient temperatures, without applying any external pressure. It can be conducted with various box furnaces or tube furnaces under different atmospheres (oxidizing, reducing, inert, and vacuum). Through the use of this method, a highly applicable varistor can be mass produced. Varistors are of a particular interest for modern surge protection of over-voltage. Nowadays, ZnO ceramic varistors are most favorable in electronic industry due to their excellent electrical characteristics and high energy handling capabilities. By optimizing the method during sintering process, the number of potential barriers formed can be controlled thus improving the capability of the low-voltage varistor.
... 3.11 ± 0.002 98.4 ± 0.006 sonication + microfluidization are smaller than the grains in pure SiAlON sample since the GNPs prevent the growth of SiAlON grains during sintering [40]. Moreover, the sizes of the SiAlON grains in the composite containing microfluidized GNPs were even smaller than that of the composite containing only sonicated GNPs. ...
SiAlON ceramics are intensively used in different areas but still there is a need to improve the mechanical and thermal properties as well as ease of machinability and reduce the weight. In this study, the effect of graphene nanoplatelets (GNPs) exfoliation and dispersion techniques on the microstructure and properties of SiAlON ceramics were investigated. For this purpose, 2, 4 and 8 wt% GNPs were dispersed by using traditional sonication and newly proposed microfluidization techniques. Then, composites were densified in spark plasma sintering (SPS) furnace. Scanning electron microscope (SEM), x-ray diffraction analyses (XRD) and property measurements were performed in through-plane and in-plane directions. The microfluidization technique found to be more effective than sonication for the exfoliation, size reduction and homogenization of GNPs. Addition of GNPs prepared by both techniques increased the fracture toughness and in-plane direction thermal conductivity whereas decreased the hardness and through-plane direction thermal conductivity of the SiAlON.
Flash sintering is a novel technique that involves the sintering of green bodies in few seconds at relatively very low furnace temperature as compared to what is required to sinter them conventionally. In the present work, we flash‐sintered composites of 3 mol.% yttria‐stabilized zirconia (3YSZ) and graphene oxide (GO). The main aim of this work was to see if the decomposition or oxidation of carbonaceous materials can be prevented by the high heating rates during flash sintering and if composites of 3YSZ and GO can be processed in air. 3YSZ with 5, 10, and 20 wt.% of GO were prepared and subjected to constant heating rate flash‐sintering experiments where electric field was applied across the sample right from room temperature. A DC electric field of 100 V/cm was applied and the current density was set to 100 mA/mm². It was observed that GO decomposed from the surface of the samples; however, in the core of samples, GO was retained but was reduced to graphite. Grain size of the 3YSZ phase increased with increase in the GO content, whereas the hardness decreased. It was observed that the composites containing carbonaceous reinforcements need to be flash sintered in inert atmosphere to realize their full potential.
