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The characteristics of Lu2O3-doped ZrO2 as a solid electrolyte material were investigated in terms of its oxygen ion conductivity and flexural strength to realize its electrolytic function at intermediate and high temperatures. The effect of doping Lu3+, which has a high nuclear charge electric field strength, was examined through impedance spectroscopy, open-circuit potential measurements, and bending tests. The results with Lu2O3 dopant were compared with those obtained with a widely used dopant, Y3+, having a similar ionic radius with Lu3+, as well as a dopant that provides high ionic conduction, Sc3+, having a smaller ionic radius with Zr4+. The results revealed that, at the same dopant concentration, both the ionic conductivity and the flexural strength of Lu2O3-doped ZrO2 are higher than those of the widely used Y2O3-doped ZrO2. The conductivity of 8 mol% Lu2O3-doped ZrO2 surpassed that of 8 mol% Sc2O3-doped ZrO2 in the range of 800–950 °C (0.153 S/cm vs. 0.121 S/cm at 900 °C). These results indicate the potential of Lu3+ as a dopant for enhancing the performance of ZrO2 solid electrolytes.

A three-phase system consisting of alumina (Al2O3), magnesia (MgO) and 8 mol% yttria‐stabilized zirconia (8YSZ) was reactive flash sintered to produce MgAl2O4-8YSZ composites. We show that a critical volume fraction of the ionic conductor 8YSZ is required to promote the flash phenomenon, indicating a typical percolation behavior. The easy path for conduction could be reached with a smaller critical volume fraction when using agglomerated powders for producing the green bodies. Furthermore, microstructure and X-ray diffraction analyses demonstrate that both sintering and phase transformation largely depend on the mixing level of the precursors. Although the presence of agglomerates resulted in a decrease of the flash onset temperature, poor sintering and incomplete phase transformation were verified. This behavior is attributed to inhomogeneous heat distribution within those samples during the flash state, which could be explained by the electrical current percolation.

We investigate the reactive flash sintering of Mg0.2Ni0.2Co0.2Cu0.2Zn0.2O precursor powders prepared by a polymeric synthesis route. The flash experiments were performed at a constant heating rate of 10 °C min−1 with electric fields from 15 to 60 V cm−1. The single-phase rock-salt structure was obtained in just a few seconds at furnace temperatures as low as 500 °C, under an electric field of 60 V cm−1 and a current density of 150 mA mm−2. Success at processing an entropy-driven phase in a remarkably short time and low furnace temperature demonstrates the potential of reactive flash sintering for producing entropy-stabilized materials.

We report the transformation of an amorphous mixture of Li0.5La0.5TiO3 (LLTO) directly into a single phase dense polycrystal, all within a few seconds at about 800 °C by the flash method. The starting material is a chemically-prepared precursor powder that experiences concurrent crystallization and densification to cubic LLTO during the flash event, as shown by in-situ X-ray measurements. The experiments were conducted at a constant heating rate with fields from 80 to 120 V cm−1 and a current limit of 60 mA mm–2. The resulting polycrystal yielded a bulk conductivity of 0.5 mS cm–1.

An additive manufacturing process for fabricating ceramic matrix composites has been developed based on the C/C-SiC system. Automated fiber placement of the continuous carbon fibers in a polyether ether ketone matrix was performed to consolidate the carbon fibers into a printed preform. Pyrolysis was performed to convert the polymer matrix to porous carbon, and then Si was introduced by reactive melt infiltration to convert a portion of the carbon matrix to silicon carbide. The densities and microstructures were characterized after each step during the processing, and the mechanical properties were measured. The C/C-SiC composites exhibited a porosity of 10–20%, characteristic flexural strength of 234.91 MPa, and Weibull modulus of 3.21. The composites displayed toughness via a significant displacement to failure.

Effects of polyethylene glycol (PEG) dispersant and pH on the dispersion behavior of aqueous SiC slurry were investigated. High solid loading up to 62 vol% with low viscosity (202 mPa s) was achieved using fine SiC powders prepared by mechanical alloying process with the average diameter of 152 nm. The property analysis of the slurry in terms of zeta potential, particle size, sedimentation, TG-DTA analysis, and rheological measurements indicated that the optimum pH value and dispersant content of the highly concentrated slurry were pH 9 and 0.4 wt%, respectively. A SiC green body with the relative density of 62.9% was made by drying 62 vol% SiC slurry in an drying oven at 80 °C. Crack formation did not occur during drying because of the high solid loading and consequent low shrinkage rate (0.097%). In contrast, those prepared by cold isostatic press (CIP) under 200 MPa had a lower relative density of 58.8%.

Mechanical alloying and spark plasma sintering were used to fabricate dense and nanostructured SiC at 1525 °C under 40 MPa pressure. Round-shaped nanopowder (d50: 108 nm) consisting of amorphous Si-Al-C and β-SiC crystallites was prepared using high-energy ball-milling. Aluminum was homogeneously distributed in the Si-Al-C powder. The addition of Al during the milling process caused the decrement in the 3C-SiC crystallinity and promoted the generation of stacking faults in 3C-SiC. Dense SiC with the grain size of 132 nm was fabricated after a two-step sintering at 1600–1550 °C. The Al content in the sintered SiC grain was more than 3 times higher than the reported values. Grain boundary diffusion and lattice diffusion were activated due to the high concentration of Al in the powder.

We discuss the Arrhenius behavior of electrical conductivity σ during flash sintering of 3 mol% yttria stabilized zirconia (3YSZ). In situ x-ray diffraction is used to determine sample temperature. Sintering contribution to σ is excluded by investigating the flash event on a dense ceramic. We show that total conductivity follows an Arrhenius-like equation in both dense and green samples, even during Stage II of flash. The non-linearity often verified during flash sintering of 3YSZ is therefore related to the furnace temperature instead of the sample temperature when building the ln(σ) vs. 1/T plots. Furthermore, we verified a change in the activation energy for conduction prior to the ignition of the flash event and discussed the possible mechanisms. For instance, the decrease in activation energy from Stage I to II in the dense sample is attributed to a contribution from electronic carriers.

This study investigates the low-temperature sintering of nano Si-C powder containing Al-C additives prepared by high-energy ball-milling. The synthesized powder was composed of ultra-fine β-SiC crystallites (~5 nm) and amorphous Si-C matrix. TEM-EDS analysis showed a relatively homogeneous distribution of Al in the synthesized powder (d 50 : 170 nm). The relative density of SiC containing 6.5 wt% additives was 98.1% after sintering at 1650 °C for 30 min at a pressure of 20 MPa. The SiC could be densified at 1800 °C when the additive content decreased to 3.3 wt%. The Al content in the Si-C powders changed, e.g. , from 4.11 to 2.6 wt%, after sintering at 1650 °C, which value was much higher than the solubility limit (0.26 wt% at 1800 °C) due to the homogeneous distribution of Al within the powder and the low sintering temperature. Al was segregated at the grain boundary while liquid phase formation was not identified by TEM analysis, indicating that grain boundary diffusion was the main densification mechanism. The mechanical properties of the sintered specimens were similar to those of a SiC-Al 4 SiC 4 system, which has the same chemical components but containing large amount of sintering additives (5.6 vs. 13 wt%), sintered using higher pressure (20 vs. 60 MPa) and temperature (1650 vs. 1800 °C).

High purity Si-C (99.999%) powder prepared by mechanical alloying was added to a commercial SiC powder as a sintering additive. Reaction bonded silicon carbide balls and jars with high purity (99.98%) were used for the mechanical alloying. As a result, the purity of the sintered Si-C was higher than 99.99%. When sintered at 2200℃ under 50 ㎫ pressure for 1 h, SiC containing 10 wt% of high purity Si-C showed a relative density of 95.3%, similar to the relative density of commercial SiC (95%). However, the relative density of SiC decreased to 90.6% without the additive when the applied pressure decreased to 40 ㎫. In contrast, the relative density was nearly unaffected by the decrease of the pressure when using the Si-C additive. Therefore, the addition of Si-C powder promoted the densification of SiC above 2000℃ under 40 ㎫ pressure.

Using a modified spark plasma sintering apparatus, nano-tantalum carbide powder was synthesized at 1450 °C by the carbothermal reduction of Ta2O5. The synthesized TaC powder had ultra-fine particle size of 62 nm and a low oxygen content of about 0.5 wt%. The metal basis purity of the synthesized powder was 99.94%. The particle growth during synthesis was effectively suppressed by using the modified spark plasma sintering process due to the low synthesis temperature and fast heating/cooling rate. Dense monolithic TaC ceramics were obtained by sintering the synthesized powder without sintering additives at 2200 °C for 30 min under 80 MPa pressure. The average grain size of the dense TaC ceramics was 4 μm.