The cold sintering process (CSP) was used to produce membranes and improve the densification of a geopolymer-zeolite matrix, fully recycling a waste geopolymer powder. The role of CSP parameters were ...studied varying temperature (25, 40 and 80°C), applied pressure (56 MPa and 168 MPa) and reactive solution (H2O, KOH or NaOH 2, 4, 6, 8 M). CSP applied on the waste geopolymer powder (molar ratio Si/Al = 2.0 and K/Al = 1.0) resulted in relative densities ranging from about 50–77%, while modal pores varied from 0.006 µm to 0.017 µm in the mesopore range. Compressive strength was up to 45 MPa. The addition of 10 wt% of the waste geopolymer powder to a geopolymer- zeolite powder containing 81% of in situ synthetized NaA phase allowed a densification approaching 70% with mechanical strength up to 7.4 MPa.
•Membranes were produced by cold sintering process (CSP).•A waste geopolymer powder was recycled to produce membranes.•Relative densities were 50–77% and modal pores 0.006–0.017 µm.•CSP on a geopolymer-NaA zeolite powder allowed a densification approaching 70%.
Dense nanocrystalline BaTiO3 ceramics are prepared in a single step by the Cold Sintering Process at 300 °C, under a uniaxial pressure of 520 MPa for 12 h using a molten hydroxide flux. Transmission ...electron microscopy reveals a dense microstructure with sharp grain boundaries. The average grain sizes are 75−150 nm depending on the flux amount. The dielectric permittivity is 700–1800 at room temperature at 106 Hz, with a dielectric loss, tan δ ∼ 0.04. The difference in permittivity and phase transition behavior are explained in terms of the intrinsic size effect of the BaTiO3. The nanocrystalline BaTiO3 ceramics still shows a macroscopic ferroelectric switching via a hysteresis loop. This work demonstrates that cold-sintering process could enable the densification of ferroelectric oxides in a single step. Futhermore, comparable dielectric properties to reported values for nanocrystalline grains are obtained, but at this time, with the lowest processing temperatures ever used.
•(1-x)Ni0.5Zn0.5Fe2O4-xK2MoO4 ceramics prepared by cold sintering method.•The composite is grain-dominated and exhibits good dielectric properties.•Multiphase ceramic comprises of grains and grain ...boundaries, with high resistivity.•The ceramic demonstrates a high dielectric contant and low loss.
In this study, (1-x)Ni0.5Zn0.5Fe2O4-xK2MoO4 ((1-x)NZO-xKMO) composite ceramics were prepared through a cold sintering process. The research aimed to investigate the effect of different cold sintering conditions on the densification, phase, and magnetic/dielectric properties of the composites. The 0.6NZO-0.4KMO composite, prepared at 180 °C for 30 min under an applied pressure of 500 MPa, and utilizing 10 wt.% deionized water as a solvent, exhibited a high dielectric constant and permeability. SEM analysis revealed that the two phases were uniformly mixed, and the microstructure was dense. The cold sintering mechanism proposed for (1-x)NZO-xKMO composites suggests that the 'dissolution-precipitation' mechanism plays a key role in driving the densification of the ceramics.
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It is difficult to get pure‐phase Mg3B2O6 (abbreviated as MBO) ceramics by the traditional high‐temperature solid‐state reaction method. In this paper, pure‐phase MBO ceramics were successfully ...densified and obtained by combining the cold sintering and post‐annealing process. The relative density of MBO ceramics was ∼80% cold sintered at 150°C/90 min/800 MPa, which was further improved to ∼91% by post‐annealing at 900°C, 400°C lower than that of the traditional high‐temperature sintering process (∼1300°C). X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman results demonstrated that the secondary phase of MgO was effectively eliminated, and dense microstructure was observed by the cold‐sintering process plus post‐annealing treatment. Finally, the microwave dielectric properties of MBO were evaluated with εr: 5.15–6.37, Q×f: 5942–16 686 GHz, τf: −48.45–69.72 ppm/°C.
Bi2Mo2O9-K2MoO4 (BMO-KMO) composite ceramics with >95% theoretical density were densified by cold sintering at 150 °C. XRD, Raman, back-scattered SEM and EDX spectroscopy indicated that the BMO and ...KMO phases coexisted in all composites without inter-diffusion and secondary phases. Temperature coefficient of resonant frequency with near-zero value ∼ -1 ppm/°C was acheived for BMO-10%KMO with pemittivity ∼ 31 and quality factor ∼ 3,000 GHz. Cold-sintered composite ceramics were directly pressed/integrated onto a printed circuit board (PCB) using the Cu metallisation as a ground plane for the design and fabrication of a circularly polarized microstrip patch antenna suitable for satellite navigation systems which achieved efficiencies 87% at 1561 MHz (BeiDou) and 88% at 1575 MHz (GPS/Galileo). The low cost, low energy integration of temperature stable, cold sintered ceramics directly onto a PCB represents a step change in substrate fabrication technology for RF devices.
Since its first introduction in 2016, cold sintering process (CSP) has gained worldwide interest from the scientific community as green and innovative fabrication route due to the dramatic reduction ...of processing time, energy, and costs. Cold sintering resembles the geological formation of rocks where a ceramic powder is densified with the aid of a liquid phase under an intense external pressure and limited heating conditions (below 350 °C). Up to date, tens of different materials, including composites, have been successfully processed through CSP and extraordinary results in terms of densification, microstructure and final properties have been achieved. In the present review, processing features and variables, possible densification mechanisms and issues also for the realization of ceramic-based composites are explored. Advantages with respect to existing techniques are analysed and current challenges are described to lay the ground for new processing opportunities to be faced in the near future.
Efficient construction of ceramic membranes can decrease the cost and ease the process of wastewater treatment. The total cost of ceramic membranes is mainly determined by the cost of raw materials ...and energy consumption during sintering process. In this work, fly ash particles recycled from electric plant and kaolin materials were respectively employed as the support and membrane layer of composite ceramic membranes. To match the sintering temperature of the kaolin material and fly ash support, rigid alumina particles were introduced into the supports (AFA supports). Also, the bending strength of the supports was improved when adding alumina particles. The kaolin/fly ash ceramic membrane was obtained by spraying the kaolin dispersion on the AFA supports and co-sintering. The mean pore diameter and water permeance of the membranes were 320 nm and 3650 Lm−2h−1 bar−1. When treating oil-water emulsions with oil content of 400 ppm, the oil removal rate was above 98.5% and the stable permeance was close to 530 Lm−2h−1 bar−1, likely due to the super-hydrophilic performance of kaolin and the electric repulsion between the membrane and oil droplets. The raw materials cost, sintering energy consumption, and fabrication time were successfully decreased. This work demonstrates the feasibility of low-cost ceramic membranes for efficient wastewater treatment in chemical industries.
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•The kaolin/fly ash composite membranes could be fabricated via one sintering process.•All the cost of materials, sintering consumption, and fabrication period are decreased.•Sintering performance of kaolin layer and fly ash supports could be balanced by alumina.•The composite membranes showed a higher water permeance compared with literatures.•The membranes show high emulsion separation performance compared with other works.
This study reports the sintering mechanisms of SiO2 and the relationship between structure, dielectric properties and processing of 1-xSiO2-xPTFE composites with volume fractions up to x = 0.25, ...prepared by the cold sintering process (270 °C, 430 MPa, 60 min). The importance of transient liquids was evaluated by using TEOS and 5 M NaOH and the densification behavior was investigated by using a semiautomated uniaxial press equipped with a dilatometer. The shrinkage behavior observed when 5 M NaOH was used highlighted the kinetics of nucleation and growth during the phase transition from amorphous silica to α-quartz. Dielectric properties (ε’ and tan δ) of cold sintered composites were studied at frequencies between 10−1 Hz and 107 Hz. For composites cold sintered with 5 M NaOH, investigations allowed to confirm the presence of PTFE polymer at the interface between two α-quartz grains by STEM EDS analysis and the presence of a dielectric relaxation at 103-104 Hz.
Corundum abrasives with good chemical stability can be fabricated into various free abrasives and bonded abrasive tools that are widely used in the precision machining of various parts. However, ...these abrasives cannot satisfy the machining requirements of difficult-to-machine materials with high hardness, high strength, and strong wearing resistance. Although superhard abrasives can machine the above-mentioned materials, their dressing and manufacturing costs are high. By contrast, ceramic corundum abrasives fabricated by sol–gel method is a cost-effective product between conventional and superhard abrasives. Ceramic corundum abrasives exhibit self-sharpening and high toughness. In this review, the optimization methods of ceramic corundum abrasive properties are introduced from three aspects: precursor synthesis, particle shaping, and sintering. Firstly, the functional mechanism of seeds and additives on the microstructural and mechanical properties of abrasives is analyzed. Specifically, seeds can reduce the phase transition temperature and improve fracture toughness. The grain size and uniformly dense structure can be controlled by applying an appropriate amount of multicomponent additives. Then, the urgent need of engineering application and machinability of special shape ceramic corundum abrasives is reviewed, and three methods of abrasive shaping are summarized. The micromold replication technique is highly advanced and can be used to prepare functional abrasives. Additionally, the influence of a new sintering method, namely, two-step sintering technique, on the microstructural and mechanical performance of ceramic corundum abrasives is summarized. Finally, the challenge and developmental trend of the optimization of ceramic corundum abrasives are prospected.
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