Search

This research paper provides an illustration of how to use the Spark Plasma Sintering technology (SPS) for powder materials in order to obtain lightweight ceramics (based on alumina) and describes physical principles ensuring efficiency of high heating rates for sintering high-temperature ceramics (pure silicon carbide). Optimization of SPS modes helps to produce Al 2 O 3 /ZrO 2 ceramics with grain size of less than 400 nm, microhardness H v =24 GPa, and crack resistance K IC =4.2 MPa m 1/2 ., and ceramics of pure SiC with grain size less than 50 nm, microhardness H v =21 GPa and crack resistance coefficient K IC =3.5 MPa m 1/2 . [ABSTRACT FROM AUTHOR]

Submicron-grade Y 2.5 Nd 0.5 Al 5 O 12 oxide (YAG:Nd) powder with garnet structure was synthesised by the co-precipitation method. YAG:Nd ceramics with a relative density of ∼99 % were obtained by Spark Plasma Sintering. The ceramics had a fine-grained microstructure and low YAlO 3 impurity phase content. The radiation resistance of the ceramics was investigated with irradiation with accelerated Xe ions (E = 148 MeV) and Ar ions (E = 46 MeV), with the fluences ranging from 6 × 1011 to 1 × 1013 cm−2. The phase composition, microstructure and microhardness of the irradiated ceramics were studied. X-ray diffraction (XRD) analysis in the symmetric mode and grazing incidence XRD were used to study the irradiated layer structure. A gradient-defect structure was shown to be formed in the YAG:Nd ceramics under irradiation: amorphous phase, deformed garnet phase and non-deformed garnet phase. The dependencies of the volume fraction of the amorphous phase and of the amorphisation structure on the fluence were analysed. The calculated value of the critical fluence was 1 × 1013 cm−2, corresponding to 0.044 displacements per atom (dpa). The microhardness Hv of the surface layer decreased with increasing ion fluence. [ABSTRACT FROM AUTHOR]

Abstract Applicability of Spark Plasma Sintering has been studied for production of high-density (98.6–99.5%) composite ceramics Y 2.5 Nd 0.5 Al 5 O 12 (YAG:Nd) – x MgO (x = 5, 10, 20 vol %). Powder YAG:Nd-MgO compositions have been obtained by precipitation of the MgO phase from Mg(NO 3) 2 water solution of magnesium nitrate onto the surface of garnet nanoparticles YAG:Nd. It has been demonstrated that the intensity of sintering fine-grained YAG:Nd-MgO composites is governed by volume diffusion at low temperatures and by grain boundary diffusion at high temperatures. Faster sintering at low temperatures is caused by formation of MgAl 2 O 4 spinel particles and internal stress fields that are manifested as broadening and shifting of garnet peaks in the sintered composites. Highlights • Ultrafine-grained Y 2.5 Nd 0.5 Al 5 O 12 (YAG:Nd) powders obtained by co-precipitation. • Powder obtained by precipitation of the MgO phase from Mg(NO 3) 2 water solution. • YAG:Nd + (5, 10, 20) vol% MgO high-density ceramics obtained by SPS. • Compression fields of internal stresses form in composites during SPS. • Sintering rate is governed by the diffusion in the lattice and in grain boundary. [ABSTRACT FROM AUTHOR]

Fine-grained ceramics based on solid solutions of ZrO 2-x -Ln 2 O 3 (where Ln = Sm, Yb), which are used to simulate inert matrix fuel (IMF), were obtained by colloidal chemical synthesis of powders and their Spark Plasma Sintering (SPS). It has been established that the SPS activation energy (Q s ) for fine-grain ceramics based on ZrO 2 corresponds to the activation energy of oxygen diffusion on grain boundaries of zirconium oxide (zirconia). We have demonstrated that introducing oxides of samarium (Sm 2 O 3 ) and ytterbium (Yb 2 O 3 ) into zirconia decreases SPS activation energy and stabilizes the phase composition of zirconia. Ceramics with densities up to 100% were obtained by the following modes of SPS: sintering temperature 1000–1250 °C, sintering time 6–10 min. Hydrolysis testing in the static mode (Т = 20 °C, P = 1 atm) in distilled water revealed no leaching of lanthanide ions at detection thresholds of 5 ppm for Sm ions and 0.1 ppm for Yb ions. [ABSTRACT FROM AUTHOR]

Mineral-like matrix Na x (Ca/Sr) 1-2x Nd x WO 4 ( x = 0, 0.1 and 0.2) for radwaste is proposed. Powder samples of complex tungstates have been synthesized by coprecipitation from aqueous solutions of Na, Ca, Sr, Nd salts. Crystallographic characteristics of compounds have been calculated and a monotonous change observed in them along with some x value changes. Monophasic ceramics with high relative density (97–100%) from these powders have been obtained through Spark Plasma Sintering (SPS). SPS of tungstates has been shown to occur in multiple stages, with the sintering kinetics at the final stage of sealing controlled by diffusion both in the crystal lattice and along grain boundaries. Activation energies have been determined for sintering of tungstates at different x values. The reduced activation energy of sintering at the third heating stage (at high temperatures) could be ascribed to the grain growth. [ABSTRACT FROM AUTHOR]