Phase Formation and the Electrical Properties of YSZ/rGO Composite Ceramics Sintered Using Silicon Carbide Powder Bed

Fully stabilized zirconia/graphene composites are very promising advanced structural materials having mixed ion–electron conductivity for energy storage and energy conversion applications. The existing methods of the composite manufacturing have a number of disadvantages that limit their practical use. Thus, the search for new sintering methods is an actively developing area. In this work, we report for the first time the application of the SiC powder bed sintering technique for fully stabilized zirconia (YSZ) composite fabrication. The reduced graphene oxide (rGO) was used as a graphene derivative. As a result, well-formed ceramics with high density and crystallinity, the maximal microhardness of 13 GPa and the values of the ionic conductivity up to 10−2 S/cm at 650 °C was obtained. The effects of the sintering conditions and rGO concentration on the microstructure and conductivities of ceramics are discussed in detail. The suggested powder bed sintering technique in a layered graphite/SiC/graphite powder bed allowed well-formed dense YSZ/rGO ceramics fabrication and can become a suitable alternative to existing methods for various oxide ceramic matrix composite fabrication: both conventional sintering and non-equilibrium (SPS, flash sintering) approaches.

Effect of graphite nanoplatelets on spark plasma sintered and conventionally sintered aluminum-based nanocomposites developed by powder metallurgy

In this work, aluminum (Al)-based nanocomposites reinforced with graphite nanoplatelets (GnPs) have been fabricated by conventional sintering as well as spark plasma sintering (SPS) techniques, and their microstructure and mechanical properties have been studied. The powder metallurgy (PM) route has been adopted to fabricate the various Al–GnP nanocomposites. Characterization of the powder mixtures and the nanocomposites has been carried out through different characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. Compressive strength, Young's modulus, density, and Vickers microhardness of the various nanocomposites have also been determined. The HRTEM results show the formation of nonstoichiometric Al4C3 nanoparticles – during both conventional sintering and SPS – at the interface of the Al grains and GnP, which worsen the mechanical properties of the nanocomposites. SPSed nanocomposites show superior mechanical properties due to higher densification, finer grain size, and homogeneous nanofiller dispersion in the Al matrix, compared to the conventionally sintered Al–GnP nanocomposites.

Grain Boundary Conductance Mechanisms of Ultra-fine Grained CeO2/BaCeO3 Based Electrolytes Fabricated by a Two-step Sintering Process

Aiming to clarify the grain boundary conductance mechanism of CeO2/BaCeO3 based electrolytes suitable for solid oxide fuel cells (SOFCs), Sm, Bi co-doping CeO2/BaCeO3 (80 wt.% Ce0.8Sm0.1Bi0.1O2-δ - 20 wt.% BaCe0.8Sm0.1Bi0.1O3-δ, BiSDC-BCSBi) electrolytes with ultra-fine grained (110-220 nm) and micron (1-1.8 μm) structures were prepared by the two step sintering and conventional sintering method, respectively. Both electrolytes have pure phases corresponding to CeO2 and BaCeO3 without other purities. In the ultra-fine grained structure, apparent grain boundary conductivities measured at 350 oC and 400 oC are 1-2 orders of magnitude higher than micron structures, thus resulting in dramatically enhanced electrical performances. This grain boundary effect can be attributed to two aspects. One is the decrease of space charge potential Δφ(0) (0.165 V for ultrafine-fine grained ones, 0.396 V for micron ones). The other is the dilution of impurities (the impurity blocking term ω/dg is 0.94 for ultrafine-fine grained ones, and 0.53 for micron ones). In the ultra-fine grained electrolytes, no extra electronic conduction is introduced, and the ion migration number of O2- is higher than that of H+. Finally, the ultra-fine grained BiSDC-BCSBi electrolytes maintain a good long-term stability in the operating condition of SOFCs at 600 oC for 100 h.

Advances in Sintering Techniques for Calcium Phosphates Ceramics

Calcium phosphate (CaP) biomaterials are extensively used to reconstruct bone defects. They resemble a chemical similarity to the inorganic mineral present in bones. Thus, they are termed as the key players in bone regeneration. Sintering is a heat treatment process applied to CaP powder compact or fabricated porous material to impart strength and integrity. Conventional sintering is the simplest sintering technique, but the processing of CaPs at a high temperature for a long time usually leads to the formation of secondary phases due to their thermal instability. Furthermore, it results in excessive grain growth that obstructs the densification process, limiting the application of CaP’s ceramics in bone regeneration. This review focuses on advanced sintering techniques used for the densification of CaPs. These techniques utilize the synergy of temperature with one or more parameters such as external pressure, electromagnetic radiation, electric current, or the incorporation of transient liquid that boosts the mass transfer while lowering the sintering temperature and time.

Simple Fabrication and Carrier Type Modification of Semi-Conductive C/Al2O3 Composites by Powder Mixtures and Pulsed Electric Current Sintering

Semi-conductive C/Al2O3 ceramic composites were successfully fabricated by a pretty simple approach, combining a powder mixture process and pulsed electric current sintering. In order to obtain homogeneous distribution of carbon contents, popular polymers were used as carbon fillers to mix with Al2O3 powder by a wet ball milling step. The sintering was conducted by pulsed electric current sintering without any special requirement of the reductive environment like in conventional sintering. Density of bulk bodies, states of carbon contents after sintering and the electrical properties were analyzed in this study. Although the density of sintered bodies and their electrical properties were not superior, those characteristics of C/Al2O3 ceramic composites in this study were still comparatively high among semi-conductive ceramics. Especially, the carrier type of semi-conductive C/Al2O3 composites could be modified easily by adding polycarboxylic acid (PCA) in the powder mixture as a dispersant.

Synthesized Nanorods Hydroxyapatite by Microwave-Assisted Technology for In Vitro Osteoporotic Bone Regeneration through Wnt/β-Catenin Pathway

This research presents an optimal and inexpensive, without any additives, method for the synthesis and sintering of hydroxyapatite (HA) by microwave-assisted technology (MAT) furnace. The target sintering temperature of the furnace (1100 ℃) was held for one and two hours for conventional sintering. With regard to the microwave hybrid sintering, it was held at 100%MW for 20 and 30 min. FTIR, XRD, TGA, SEM/EDS, and TEM were assessed to determine HA phase composition, and structural as well as thermal decomposition behavior. The in vitro effects of sintered HA discs on cultured aged mice-isolated osteoblast cells and hydrocortisone-induced osteoclast cells were assessed by measuring ALP, osteocalcin, TRAP, calcium, and Alizarin red S staining. Moreover, their effects on cell differentiation (CD90 and CD 105 and PARR- ɣ) and death markers (GSK3b, MAPK, and β-catenin) were evaluated. The results demonstrate the production of ≈35 nm crystal-sized pure hydroxyapatite nanorod-like particles with a high degree of crystallinity and no impurities as required for biomedical application. HA increased osteogenesis (ALP, osteocalcin, and calcium) markers and decreased cell resorption markers. In addition, HA nanorods reversed the effect of cortisone on cell differentiation and death markers. In conclusion, microwave hybrid sintered HA is a potential nanomaterial for osteoporotic bone regeneration as HA reversed the cortisone adverse effect on osteoblast cell death through canonical and non-canonical pathways.