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Dense (Bi0.95Li0.05)(V0.9Mo0.1)O4-Na2Mo2O7 (100−x) wt.% (Bi0.95Li0.05)(V0.9Mo0.1)O4 (BLVMO)-x wt.% Na2Mo2O7 (NMO) composite ceramics were successfully fabricated through cold sintering at 150 °C under at 200 MPa for 30 min. X-ray diffraction, back-scattered scanning electron microscopy, and Raman spectroscopy not only corroborated the coexistence of BLVMO and NMO phases in all samples, but also the absence of parasitic phases and interdiffusion. With increasing NMO concentration, the relative pemittivity (εr) and the Temperature Coefficient of resonant Frequency (TCF) decreased, whereas the Microwave Quality Factor (Qf) increased. Near-zero TCF was measured for BLVMO-20wt.%NMO composites which exhibited εr ~ 40 and Qf ~ 4000 GHz. Finally, a dielectric Graded Radial INdex (GRIN) lens was simulated using the range of εr in the BLVMO-NMO system, which predicted a 70% aperture efficiency at 26 GHz, ideal for 5G applications.

Glass with high visible-light transparency is widely considered as the most important optical material, which typically requires a processing temperature higher than 1000 °C. Here, we report a translucent aluminosilicate glass that can be prepared by cold sintering process (CSP) at merely 300 °C. After eliminating structural pores in hexagonal faujasite (EMT)-type zeolite by heat treatment, the obtained highly active nanoparticles are consolidated to have nearly full density by adding NaOH solution as liquid aids. However, direct densification of EMT powder cannot remove the structural pores of zeolite completely, leading to an opaque compact after the CSP. It is proved that the chemical reaction between the NaOH- and zeolite-derived powders is highly beneficial to dissolution-precipitation process during sintering, leading to the ultra-low activation energy of 27.13 kJ/mol. Although the addition of 5 M NaOH solution greatly promotes the densification via the reaction with aluminosilicate powder, lower or higher concentration of solvent can deteriorate the transmittance of glass. Additionally, the CSP-prepared glass exhibits a Vickers hardness of 4.3 GPa, reaching 60% of the reported value for spark plasma sintering (SPS)-prepared sample.

The densified MnZn ferrite ceramics were prepared using the cold sintering process under pressure, with an acetate ethanol solution used as the transient solvent. The effects of the transient solvent, the pressure and annealing temperature on the density, and the micromorphology and magnetic properties of the sintered MnZn ferrites were studied. The densified MnZn ferrite was obtained using the cold sintering process and its relative density reached up to 85.4%. The transient solvent and high pressure are essential to the cold sintering process for MnZn ferrite. The annealing treatment is indispensable in obtaining the sample with the higher density. The relative density was further increased to 97.2% for the sample annealed at 950 °C for 6 h. The increase in the annealing temperature reduces the power loss at high frequencies.

Using melt-derived LD glass powders and 5–20 M NaOH solutions, porous lithium disilicate (Li2Si2O5, LD) glass–ceramics were prepared by the cold sintering process (CSP) associated with the post-annealing technique. In this novel technique, H2O vapor originating from condensation reactions between residual Si–OH groups in cold-sintered LD glasses played the role of a foaming agent. With the increasing concentration of NaOH solutions, many more residual Si–OH groups appeared, and then rising trends in number as well as size were found for spherical pores formed in the resultant porous LD glass–ceramics. Correspondingly, the total porosities and average pore sizes varied from 25.6 ± 1.3% to 48.6 ± 1.9% and from 1.89 ± 0.68 μm to 13.40 ± 10.27 μm, respectively. Meanwhile, both the volume fractions and average aspect ratios of precipitated LD crystals within their pore walls presented progressively increasing tendencies, ranging from 55.75% to 76.85% and from 4.18 to 6.53, respectively. Young’s modulus and the hardness of pore walls for resultant porous LD glass–ceramics presented remarkable enhancement from 56.9 ± 2.5 GPa to 79.1 ± 2.1 GPa and from 4.6 ± 0.9 GPa to 8.1 ± 0.8 GPa, whereas their biaxial flexural strengths dropped from 152.0 ± 6.8 MPa to 77.4 ± 5.4 MPa. Using H2O vapor as a foaming agent, this work reveals that CSP associated with the post-annealing technique is a feasible and eco-friendly methodology by which to prepare porous glass–ceramics.

The great prospects for introducing the cold sintering process (CSP) into industry determine the importance of finding approaches to reduce the processing time and mechanical pressure required to obtain dense ceramics using CSP. The introducing zinc acetate into the initial ZnO powder of methods, such as impregnation, thermovapor autoclave treatment (TVT), and direct injection of an aqueous solution into a die followed by cold sintering process using a spark plasma sintering unit, was studied. The effect of the introduction methods on the density and grain size of sintered ceramics was analyzed using SEM, dynamic light scattering, IR spectroscopy, and XRD. The impregnation method provides sintered samples with high relative density (over 0.90) and significant grain growth when sintered at 250 °C with a high heating rate of 100 °C/min, under a uniaxial pressure of 80 MPa in a vacuum, and a short isothermic dwell time (5 min). The TVT and aqueous solution direct injection methods showed lower relative densities (0.87 and 0.76, respectively) of CSP ZnO samples. Finally, the development of ideas about the processes occurring in an aqueous medium with CSP and TVT, which are subject to mechanical pressure, is presented.

Hydroxyapatite (HAp) is a key bioceramic for biomedical applications, but conventional pressureless sintering (PS) requires high temperatures that can promote phase degradation. Here, we compare PS (1100 °C/180 min) and cold sintering process (CSP) (150 °C/450 MPa/30 min) for pure HAp and an HAp composite containing 4 wt.% niobium–phosphate bioglass (BG), using a 2 M H3PO4 transient liquid (10 wt.%). CSP increased relative density from 73.10% to 79.92% for HAp and from 68.43% to 83.54% for HAp/BG, representing up to a 22.1% gain compared with PS. One-way ANOVA confirmed a significant effect of processing route/composition on relative density (F(3,24) = 919.69, p < 0.05), and Tukey HSD indicated that all groups differed statistically. SEM revealed a markedly more consolidated and homogeneous microstructure for CSP, particularly for HAp/BG, consistent with enhanced dissolution–reprecipitation and pore filling. XRD showed that PS at 1100 °C led to partial HAp degradation with β-TCP formation, whereas CSP preserved the HAp phase with broader peaks, smaller crystallite size, and higher specific surface area. These results demonstrate CSP as an efficient low-temperature alternative for densifying HAp-based bioceramics, with BG addition further improving consolidation.

The cold sintering process, thermal insulating performance and compressive strength of ZSM-5 zeolite ceramics were investigated. Densification of ZSM-5 zeolite ceramics could be achieved by cold sintering process at 393 K under a pressure of 450 MPa for 0–60 min by adding 3 mol/L NaOH solution. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) image, N 2 adsorption/ desorption measurements and fourier transform infrared (FT-IR) spectra demonstrated that zeolite framework was preserved without collapse of ordered microporous structure in the present ceramics. The thermal conductivity as low as 0.88 W/m·K was achieved together with a high compressive strength up to 315 MPa, which was attributed to the ordered microporous structure, amorphous phase and porosity in zeolite ceramics. The ZSM-5 zeolite ceramics prepared by cold sintering process could be expected as promising thermal insulating materials, since the low thermal conductivity was comparable with typical porous ceramics while the compressive strength was much higher than that of them.

Silver selenide (Ag 2 Se) stands out as a promising thermoelectric (TE) material, particularly for applications near room temperatures. This research presents a novel approach for the fabrication of bulk Ag 2 Se samples at a relatively low temperature (170°C) using the cold sintering process (CSP) with AgNO 3 solution as a transient liquid agent. The effect of AgNO 3 addition during CSP on the microstructure and TE properties was investigated. The results from phase, composition and microstructure analyses showed that the introduction of AgNO 3 solution induced the formation of Ag nano-precipitates within the Ag 2 Se matrix. Although the nano-precipitates do not affect the phase and crystal structure of orthorhombic β-Ag 2 Se, they suppressed crystal growth, leading to reduced crystallite sizes. The samples containing Ag nano-precipitates also exhibited high porosity and low bulk density. Consequently, these effects contributed to significantly enhanced electrical conductivity and a slight decrease in the Seebeck coefficient when small Ag concentrations were incorporated. This resulted in an improved average power factor from ∼1540 µW·m −1 ·K −2 for pure Ag 2 Se to ∼1670 µW·m −1 ·K −2 for Ag 2 Se with additional Ag precipitates. However, excessive Ag addition had a detrimental effect on the power factor. Furthermore, thermal conductivity was effectively suppressed in Ag 2 Se fabricated using AgNO 3 -assisted CSP, attributed to enhanced phonon scattering at crystal interfaces, pores, and Ag nano-precipitates. The highest figure-of-merit ( zT ) of 0.92 at 300 K was achieved for the Ag 2 Se with 0.5wt% Ag during CSP fabrication, equivalent to >20% improvement compared to the controlled Ag 2 Se without extra Ag solution. Thus, the process outlined in this study presents an effective strategy to tailor the microstructure of bulk Ag 2 Se and enhance its TE performance at room temperature.

A form stable NaCl-Al2O3 (50–50 wt-%) composite material for high temperature thermal energy storage was fabricated by cold sintering process, a process recently applied to the densification of ceramics at low temperature 300°C under uniaxial pressure in the presence of small amount of transient liquid. The fabricated composite achieved as high as 98.65% of the theoretical density. The NaCl-Al2O3 composite also retained the chloride salt without leakage after 30 heating-cooling cycles between 750°C–850°C together with a holding period of 24 h at 850°C. X-ray diffraction measurements indicated congruent solubility of the alumina in chloride salt, excellent compatibility of NaCl with Al2O3, and chemical stability at high temperature. Structural analysis by scanning electron microscope also showed limited grain growth, high density, uniform NaCl distribution and clear faceted composite structure without inter-diffusion. The latent heat storage density of 252.5 J/g was obtained from simultaneous thermal analysis. Fracture strength test showed high sintered strength around 5 GPa after 50 min. The composite was found to have fair mass losses due to volatilization. Overall, cold sintering process has the potential to be an efficient, safe and cost-effective strategy for the fabrication of high temperature thermal energy storage materials.

Cold sintering as a new technology for the fabrication of ceramic composites could overcome the shortcomings of traditional high temperature sintering approach and achieve dense structure in the composite at a relatively low temperature (<200°C). In this work, a shape stabilization phase change composite is fabricated and investigated by dint of such new fabrication approach, in which a mixed nitrate salt of NaNO 3 -KNO 3 is used as phase change material and magnesia powder is acted as structure skeleton. Using of deionized water as sintering additive, the effects of sintering agent content, sintering temperature, uniaxial pressure and time on the composite microstructure characteristics and macroscopic properties are evaluated. The results show that the liquid salt could be effectively accommodated in the magnesia skeleton, forming a dense and stable structure in the composite. There is existence of optimal cold sintering parameters at which a benign combination of mechanical strength and thermal cycling performance could be attained in the composite. Under the sintering temperature of 150°C, duration time of 8 min, uniaxial pressure of 150 MPa, and water mass content of 7%, the fabricated composite exhibits a heat storage density of 610 kJ/kg at its potential utilization temperature range of 30°C–580°C and a compressive strength over 240 MPa with a dense density higher than 98%, demonstrating that it can be a viable alternative used in thermal energy storage domains.