Characteristics and Sinterability of Ceria Stabilized Zirconia Nanoparticles Prepared by Chemical Methods

Microwave assisted and molten salts synthesis were extended for preparation of ceria (10 mol%; 15 mol%) stabilized zirconia and their parameters and sinterability were compared with that of particles prepared by the sol-gel combustion method. As-prepared powders by using microwave assisted and sol-gel combustion synthesis contained single tetragonal ZrO2 phase but powders prepared by molten salts combustion method contained two ceria-stabilized tetragonal phases with different content of ceria. The crystallite size of the as-prepared zirconia phases was in the range of 3.2 – 9.4 nm and the average particles size is in the range of 7.6 – 24.6 nm depending on the synthesis method. Additional calcination of the powders up to 1000 °C led to increase of crystallite size in the range of 19 – 25 nm and decrease of specific surface area in the range of 18 – 21 m2/g and partial formation of monoclinic phase of ZrO2. Bulk materials with fine-grained microstructure (0.8 – 1.6 µm) and density in the range of 95.2 – 97.2 % were obtained by spark plasma sintering at 1280 – 1310 °C during 3 min. Nanoparticles prepared by microwave assisted synthesis showed better sinterability and higher density.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18288</p

The Effect of Raw Components on the Densification and Properties of Nanostructured Sialon Materials

Two sialon compositions (Y0,33Si10,5Al1,5O0,5N15,5 and Y0,5Si9,5Al2,5O1,0N15,0) were used to determine the effect of starting components on densification and properties of sialon materials. Plasma synthesized nanopowders (Si3N4, AlN, Al2O3, Y2O3 and 73 wt% Si3N4-27 wt%AlN nanocomposite) were used for the investigation. Materials were sintered using traditional or spark plasma sintering methods. Sintering temperature was reduced significantly, if Si3N4-AlN nanocomposite was used as one of the components. The increased amount of sialon phase and higher hardness were characteristic to materials obtained from individual Si3N4, AlN, Al2O3, Y2O3 components

Characterisation of Mullite – ZrO2 Ceramics Prepared by Various Methods

Mullite - ZrO2 ceramics was sintered from variously prepared powder mixtures - different time milled and hydrothermal synthesized. As sintering aid 8 wt. % illite clay for one part of starting mixtures was added. Two sintering routes was applied for consolidation of powder – spark plasma sintering (SPS) technique and conventional sintering reactions in air. It is shown that the structure of sintered samples for SPS was completed at at 1250C and by conventional - at 1300C. The developed microstructure both conventional and SPS can be characterized by mullite matrix with evenly distributed ZrO2 grains. For conventually prepared and sintered samples corundum and ZrO2 tetragonal grains are observed, but for SPS dominates ZrO2 cubic The microstructure of ceramic samples from hydrothermal synthesized powders and consolidated by SPS is amorphous like with xenomorfic crystals of mullite and inclusions of grains of ZrO2 cubic. It is stated that additive of illite clay promotes the densification and at conventional sintering prevents the transformation of ZrO2 tetragonal to ZrO2 monoclinic by cooling of samples, but for SPS promotes formation of ZrO2 cubic. Sintered samples are characterized by pressure strength by value for SPS sintered samples processed from conventionally milled powder mixture

Effect of Mineral Raw Material Addition on the Properties of Cordierite Based Ceramics

The main purpose of the present study is to produce cordierite ceramics using different (traditional ceramic or pressureless and spark plasma sintering) obtaining processes and mineral raw materials of Latvia (dolomites and clays) as the cheap additives. Starting mixtures were composed of synthetic reagents (MgO and Al(OH)3) with the addition of different dolomites, clay and quartz sand. Powder mixtures were sintered at different temperatures both using pressureless and spark plasma sintering methods. It was stated that secondary crystalline phases like anorthite, spinel, corundum are often present together with a glassy phase and final mixtures determine the properties of the obtained ceramics. Suitable densification levels of investigated compositions were attained using different obtaining methods. Mineralogical composition, microstructure and physical properties were detected using XRD, SEM, water immersion and mechanical strength tests. It was stated that properties of cordierite based ceramics are greatly dependent both on the nature of starting materials and sintering method

Microstructure and Properties of Mullite-Zro2 Ceramics with Silicon Nitride Additive Prepared by Spark Plasma Sintering

The process of densification and development of the microstructure of mullite-ZrO2/Y2O3 ceramics from mixture of Al2O3, SiO2, ZrO2 and Y2O3 by gradually adding α-β Si3N4 nanopowder from 1–5 wt.% by traditional and spark plasma sintering were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and some ceramic and mechanical properties. The processes of DTA for all samples are characterised by a low-pitched endo-effect, when gradual mullite formation and noticeable densification at temperatures of 1200–1400 °C is started. It is testified by shrinkage and density both for traditionally and by SPS-sintered samples. The influence of the Si3N4 additive on the density characteristics is insignificant for both sintering cases. For SPS samples, the density reaches up to 3.33 g/cm3, while for traditionally sintered samples, the value is 2.55 g/cm3, and the compressive strength for SPS grows with Si3N4 additives, reaching 600 N/mm2. In the case of traditional sintering, it decreases to approximately 100 N/mm2. The basic microstructure of ceramic samples sintered in a traditional way and by SPS is created from mullite (or pseudo-mullite) crystalline formations with the incorporation of ZrO2 grains. The microstructure of ceramic samples sintered by SPS shows that mullite crystals are very densely arranged and do not have the characteristic prismatic shape. The traditional sintering process causes the creation of voids in the microstructure, which, with an increasing amount of Si3N4 additive, are filled with mullite crystalline formations

The Study of the Synthesis of Nanosized Refractory Carbides by Carbothermal Reduction of Precursor Gels and their Characteristics

In the present study, four refractory carbides – TiC, NbC, TaC and SiC – have been produced by carbothermal reduction of a precursor prepared by sol-gel and coat-mix (SiC) process. Binary hydrogels, in which the oxide gel and a pyrolysable organic compound are combined, were prepared as precursors for synthesis of corresponding carbides. The phase structure, crystallite size, morphology and specific surface area of the synthesized powders are investigated by XRD, SEM and BET respectively. Spark plasma sintering (SPS) method (up to 1850 °C, heating rate of 100 °C/min and dwelling time of 5 min.) was used for investigation of compacting of these carbides

Spark Plasma Sintering (SPS) to the Mullite-Zirconia Ceramics Development

This research is devoted to the investigation comparison of effect of SPS (spark plasma sintering) and conventional sintering for the mullite-ZrO2 ceramics development. Mullite-ZrO2 ceramics were produced from different time ball-milled powders. The effect of illite nanoparticles on the powder sintering promotion process was investigated and evaluated. The density and compressive strength as well as microstructure and crystalline phase development of ceramics were investigated in order to show the impact of SPS by comparing with conventional sintering. It is shown that SPS at 1250 °C produces samples with densities that are to 1.6 – 2.2 times higher than densities of samples obtained with conventional sintering at 1300 °C. Both compressive strength and Vicker's microhardness increase correlate well with the increase of density. The microstructure of the SPS samples is dense and consists of well-textured mullite and cubic ZrO2 particles, but conventionally sintered samples form mullite-corundum crystals with tetragonal ZrO2 inclusion. It is shown that illite clay additive is effective to increase density and compressive strength only when using conventional sintering

Effect of Sintering Process and Additives on the Properties of Cordierite Based Ceramics

Cordierite (2MgO∙2Al2O3∙5SiO2) is a magnesium aluminium silicate possessing an extremely low thermal expansion, low thermal conductivity and high thermal shock resistance. Properties of cordierite based ceramics are greatly dependent on the composition and nature of starting materials, additives and sintering method. The main purpose of the present study is to produce cordierite ceramics using different (traditional ceramic or pressureless and spark plasma sintering) obtaining processes and mineral raw materials of Latvia (dolomites and clays) as the cheap additives