Biaxial Flexural Strength of Different Monolithic Zirconia upon Post-Sintering Processes

Objective Different post-sintering processes are expected to be a reason for alteration in the strength of zirconia. This study evaluated the effect of post-sintering processes on the flexural strength of different types of monolithic zirconia. Materials and Methods A total of 120 classical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness and 14 mm in Ø) were prepared, sintered, and randomly divided into four groups to be surface-treated with (1) as-glazed (AG); (2) finished and polished (FP); (3) finished, polished, and overglazed (FPOG); and (4) finished, polished, and heat-treated (FPHT) technique (n = 15). Biaxial flexural strength (σ) was determined on a piston-on-three ball in a universal testing machine at a speed of 0.5 mm/min. Statistical Analysis Analysis of variance, and post hoc Bonferroni multiple comparisons were determined for significant differences (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic strength (σ0). The microstructures were examined with a scanning electron microscope and X-ray diffraction. Results The mean ± standard deviation value of σ (MPa), m, and σ0 were 1,626.43 ± 184.38, 9.51, and 1,709.79 for CzAG; 1,734.98 ± 136.15, 12.83, and 1,799.17 for CzFP; 1,636.92 ± 130.11, 14.66, and 1,697.63 for CzFPOG; and 1,590.78 ± 161.74, 10.13, and 1,663.82 for CzFPHT; 643.30 ± 118.59, 5.59, and 695.55 for HzAG; 671.52 ± 96.77, 3.28, and 782.61 for HzFP; 556.33 ± 122.85, 4.76, and 607.01 for HzFPOG; and 598.36 ± 57.96, 11.22, and 624.89 for HzFPHT. The σ was significantly affected by the post-sintering process and type of zirconia (p < 0.05), but not by their interactions (p > 0.05). The Cz indicated a significantly higher σ than Hz. The FP process significantly enhanced σ more than other treatment procedures. Conclusion Post-sintering processes enabled an alteration in σ of zirconia. FP enhanced σ, while FPOG and FPHT resulted in a reduction of σ. Glazing tends to induce defects at the glazing interface, while heat treatment induces a phase change to tetragonal, both resulted in reducing σ. Finishing and polishing for both Cz and Hz monolithic zirconia is recommended, while overglazed or heat-treated is not suggested.

Investigation of laser and thermal sintering processes of silver nanoparticles agglomerates synthesized by spark discharge

Changes in the shape and size of silver nanoparticles (NPs) during their laser and thermal sintering have been studied experimentally and theoretically. Aerosol silver NPs forming dendrid-like agglomerates 180 nm in size were synthesized by spark discharge and exposed to laser radiation and high temperature of 750 °C. The shape and size of the NPs were investigated depending on the power of the laser radiation and the temperature of the gas. It is estimated that, at a power density of laser radiation of the order of 103-104 W/cm2, the formation of spherical NPs with an average size of 140 nm is expected. Such particles turn out to be similar to NPs thermally heated in a gas flow at 750 °C for 6 seconds.

Densification of Amorphous Calcium Phosphate: A Comparison of Cold Sintering Processes

The recent surge in interest in the densification of calcium phosphate powders needs consideration of all the influencing factors. Spark plasma sintering with the primary contribution from the spark plasma and cold compaction that densifies from the large compaction pressures were considered. X-ray diffraction and Fourier transform infra-red spectroscopy characterized the powder and tablet to confirm the retention of the amorphous phase. Density was measured using the Archimedes method and the microstructure was viewed by scanning electron microscopy. The densified tablets were indented by nanoindentation to determine the hardness and elastic modulus. Reports on the density showed that the smallest contribution to density arose from vacuum, a marginally higher densification from the spark plasma effect, but the largest densification arose from the use of significantly higher pressures. Nanoindentation showed a small difference in elastic modulus between tablets densified at 25 °C and 200 °C, but a larger difference in the hardness.

The Effect of Red Mud on Sintering Processes and Minerals of Portland Cement for Roads

As a solid waste generated in the alumina industry, red mud poses a significant environmental hazard and a storage problem. In this study, red mud was added to road cement clinker in order to utilize it. The sintering red mud was first de-alkalized, and then mixed with fly ash, clay, limestone, and sandstone, among other materials, to make Portland cement for road clinker. The effect of the addition of red mud on the thermal decomposition characteristics of Portland cement for roads was studied. The existent states of alkali and radioactive elements in Portland cement for road clinker were investigated by XRD and SEM analysis. The research results showed that the addition of red mud in Portland cement for road raw material significantly promoted the decomposition of carbonates in raw material. The major mineral phases of Portland cement for road clinker were C3S with a polyhedral morphology, quasi-sphericalC2S, and tubular C4AF. A small part of the alkali combined with the silicate phase to form a solid solution, and most of the alkali combined with S to form vermiform sulfate in the intermediate phase. The radionuclide 226Ra was mainly distributed in the silicate phase.232Th was mainly distributed in interstitial phases and then silicate phases, while 40Kwasmainly distributed in the interstitial phases.

Thermoelectric Properties of Sr1-3x/2Lax/2Smx/2TiO3-δ (0.05 ≤ x ≤ 0.30) Ceramics

Influence of strongly reducing processing atmosphere on Sr-vacancy Sr1-3x/2Lax/2Smx/2TiO3-δ (x = 0.05, 0.10, 0.15, 0.20, 0.30) ceramics was investigated. The ceramic powders were prepared by the solid-state reaction (SSR) method, and heat treated in 5 % H2/N2 reducing gas at 1573 K for 6 h and 1773 K for 8 h for calcination and sintering processes, respectively. Thermoelectric properties of Sr1-3x/2Lax/2Smx/2TiO3-δ ceramics were evaluated from 573 to 973 K. Their electrical conductivities increased with carrier concentration and also decreased with temperature, indicating metallic behaviour. The Seebeck coefficients showed n-type behaviour and increased with temperature. Additionally, the total thermal conductivities exhibited low values, with a minimum value, 2.67 W/m. K for x = 0.20 ceramics at 973 K. A maximum thermoelectric figure of merit, ZT = 0.30 at 973 K was reached for Sr0.7La0.1Sm0.1TiO3-δ ceramics, which is 20 % higher than the maximum value reported previously for La-Sm electron doped SrTiO3 ceramics.

Capacitor Electrical Discharge Consolidation of Metallic Powders—A Review

Manufacturing metallic materials from elemental or alloyed powders is an option in many industrial processes. Nevertheless, the traditional powder metallurgy processing including furnace sintering is at times detrimental for the microstructure attained in the powders. Alternative sintering processes based on the use of electricity and the energy obtained by the Joule effect in powder particles can be quick enough to avoid microstructural changes. In particular, when the energy is stored in a capacitor and then discharged, the heating process is extremely quick, lasting milliseconds or even microseconds. This process, generally known as electrical discharge consolidation, has been applied to a wide variety of metallic materials, easily preserving the original microstructure of the powders. Both porous or homogeneous and highly densified material can be obtained, and without losing the desired properties of the consolidated material. A general overview of the process and applications, as well as the results obtained by different research groups around the world, have been reviewed in this manuscript.