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Objectives: To evaluate the effects of spark plasma sintering (SPS) on the microstructure of lithium disilicate glass-ceramics., Methods: IPS e.max CAD glass-ceramic samples were processed using spark plasma sintering (SPS) and conventionally sintered (CS) as a comparison. Specimens were sintered at varying temperatures (T1: 840°C, T2: 820°C, T3: 800°C), heating rates (HR1: 150°C/min, HR2: 300°C/min, HR3: 500°C/min) and pressures (P1: 15MPa, P2: 50MPa, P3: 70MPa). IPS e.max Press glass powder samples were densified at 750 and 800°C (50 or 200MPa pressure). Samples were characterized using XRD, HTXRD, and SEM and quantitative image analysis., Results: There was a significant increase in median crystal size (MCS) between the CS and the SPS T1 groups. A statistical difference (p>0.05) in MCS between SPS T1 and SPS T2 groups was observed. The SPS HR3 sample produced a smaller MCS than the CS, SPS HR1 and HR2 groups (p<0.05). The SPS P3 sample had a reduction in MCS compared with the CS group (p<0.05). XRD of the SPS samples revealed major lithium disilicate/lithium metasilicate phases and minor lithium orthophosphate and cristobalite/quartz phases. Densified IPS e.max Press glass samples resulted in fine fibrils or graduated lithium disilicate crystals., Significance: The effects of SPS were used to refine the microstructure of IPS e.max CAD lithium disilicate glass-ceramics. Densification by SPS of IPS e.max Press glass resulted in textured and fine nano-crystalline microstructures. SPS generated glass-ceramic microstructures may have unique properties and could be useful in the production of CAD/CAM materials for dentistry., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Multi-walled carbon nanotube (MWCNT)-Bioglass (BG) matrix composite was fabricated using a facile and scalable aqueous colloidal processing method without using any surfactants followed by spark plasma sintering (SPS) consolidation. The individual MWCNTs were initially uniformly dispersed in water and then entirely immobilized on the BG particles during the colloidal processing, avoiding their common re-agglomeration during the water-removal and drying step, which guaranteed their uniform dispersion within the dense BG matrix after the consolidation process. SPS was used as a fast sintering technique to minimise any damage to the MWCNT structure during the high-temperature consolidation process. The electrical conductivity of BG increased by 8 orders of magnitude with the addition of 6.35 wt% of MWCNTs compared to pure BG. Short-duration tests were used in the present study as a preliminary evaluation to understand the effect of incorporating MWCNTs on osteoblast-like cells. The analysed cell proliferation, viability and phenotype expression of MG-63 cells showed inhibition on 45S5 Bioglass(®)-MWCNT composite surfaces.

Well dispersed 45S5 Bioglass(®) (BG)-graphene nanoplatelets (GNP) composites were prepared after optimising the processing conditions. Fully dense BG nanocomposites with GNP loading of 1, 3 and 5 vol% were consolidated using Spark plasma sintering (SPS). SPS avoided any structural damage of GNP as confirmed using Raman spectroscopy. GNP increased the viscosity of BG-GNP composites resulting in an increase in the sintering temperature by ~50 °C compared to pure BG. Electrical conductivity of BG-GNP composites increased with increasing concentration of GNP. The highest conductivity of 13 S/m was observed for BG-GNP (5 vol%) composite which is ~9 orders of magnitude higher compared to pure BG. For both BG and BG-GNP composites, in vitro bioactivity testing was done using simulated body fluid for 1 and 3 days. XRD confirmed the formation of hydroxyapatite for BG and BG-GNP composites with cauliflower structures forming on top of the nano-composites surface. GNP increased the electrical conductivity of BG-GNP composites without affecting the bioactivity thus opening the possibility to fabricate bioactive and electrically conductive scaffolds for bone tissue engineering.

Two-step pressureless sintering processing was used to prepare high density (97.6%) Ca3Co4O9 thermoelectric ceramics. A duplex structure was observed and channel paths for charge carriers were formed between the grains. Oxygen vacancies were identified by fitting of XPS spectra, and the effect of the oxygen vacancies on thermoelectric properties was investigated. The electrical resistivity of samples decreased from 17.5 to 11.7 mΩ·cm and Seebeck coefficient decreased from 197.5 to 181.4 μV/K at 1073 K with increasing of the first-step sintering temperature. Furthermore, a low thermal conductivity of 0.94 W/(m·K) and the peak ZT of 0.30, which was 1.3 times larger than previous work, were obtained at 1073 K when the first-step sintering temperature was 1373 K. [ABSTRACT FROM AUTHOR]

There is a concerted effort to develop lead-free piezoelectric ceramics. (Na0.5K0.5)NbO3-based ceramics have good electrical properties, and are a potential replacement material for lead zirconate titanate piezoelectric ceramics. In this work a commercial powder based on (Na0.5K0.5)NbO3 with an initial particle size of ~260 nm was consolidated by spark plasma sintering (SPS). To avoid volatilization, high mechanical pressures were used to minimize the densification temperature. It was found that under a uniaxial pressure of 100 MPa, fully densified compacts can be prepared at 850 °C. Ceramics densified at such a low temperature demonstrate an unusually high remanent polarization (30 µC/cm2) and high d33 (146 pC/N). The improved ferroelectric properties are ascribed to the homogeneous, dense, and submicron grained microstructure achieved. [ABSTRACT FROM AUTHOR]

Materials with colossal permittivity (CP) have attracted wide interest and have tremendous potential application in super-capacitors [1]. Many materials with the colossal permittivity have been fabricated, such as Cu 3 Ti 4 O 12 [2–6] , TiO 2 [7–10] , BaTiO 3 [11] , and SrTiO 3 [12–15] , etc. However, the exact physical mechanisms and explanations for generating CP are still unclear. In our previous publication "Point defect structure of La-doped SrTiO 3 ceramics with colossal permittivity" [16] , we investigated point defects in pure SrTiO 3 and La-doped SrTiO 3 , and reported that the origin of CP in La-doped SrTiO 3 ceramics is related to a sharp polarization increase resulting from defects dipole structure. Recently, A. Tkach et al. commented on the publication and put forward some different viewpoints. In this letter, we would like to discuss the related issues and reply to the comments. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Sr 1- x La x TiO 3 (SLTO) ceramics with colossal permittivity were fabricated by conventional solid-state reaction method. The point defects of pure STO and SLTO ceramics were analyzed by Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening (CDB). The charge compensation mechanisms and dielectric properties of ceramics were investigated. The results indicated that the intrinsic defects in pure STO ceramics were mainly V T i ″ ″ . The charge compensation mechanism of SLTO ceramics was predominantly formation of V S r ″ . With increasing La content, ε r of SLTO ceramics increased up to ∼70000 at room temperature. The results of first-principle calculations indicated that the colossal permittivity came from a sharp polarization increase caused by dipole structure of defects. tan δ of SLTO ceramics showed obvious Debye relaxation at high temperatures and the relaxation showed a multiple relaxation times derived from different kinds of polarization mechanism. The main polarization mechanism of SLTO ceramics gradually changed from ion displacement polarization to defect dipole polarization influenced by the concentration of La dopants. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract: Bi3.15Nd0.85Ti3O12 ceramic, which is a three-layer ferroelectric Aurivillius phase, was prepared by spark plasma sintering. The effect of texture on the anisotropy of dielectric, ferroelectric and piezoelectric properties was studied. X-ray diffraction showed that samples perpendicular to the hot-pressing direction had a–b-axis preferred texture, whereas, samples parallel to hot-pressing direction had c-axis preferred orientation. The dielectric constant, remanent polarization and piezoelectric constant of samples with orientation close to a-axis are larger than those of samples with orientation close to c-axis. Their Curie points are all about 410°C. [Copyright &y& Elsevier]