To obtain Al₂O₃-based low-temperature co-fired ceramic (LTCC) materials with low dielectric loss and high breakdown strength, glass/ceramics of x(La2O3-CaO-B2O3-SiO2)(LCBS)+(1-x)Al₂O₃ were synthesized by a solid-state method. The structure and properties of the sintered samples were characterized by X-ray diffractometer, scanning electron microscope, vector network analyzer, high voltage breakdown instrument, and high-temperature dielectric spectrometer. The results show that adding an appropriate amount of LCBS glass powder can increase the density, reduce the dielectric loss and improve the breakdown strength of the composites. Moreover, based on the complex impedance spectrum analysis, the addition of LCBS can significantly increase the resistivity and activation energy of glass/ceramics. When Al₂O₃ ceramic with 44 %(mole fraction) LCBS glass (abbreviated G44) is sintered at 850 ℃ for 0.5 h, a LTCC ceramic material with the superior properties (i.e., ε_r=7.14, Q×f =5 769 GHz at f =13 GHz, and E_b=57.44 kV/mm) can be obtained.

It is important to utilize fly ash (FA) as a resource due to its increasing amount. In this paper, a no-sintered fly ash-based zeolitised ceramsite (FACZ) was prepared by a high-temperature steaming method with FA as a main raw material, silica fume (SF) as a reinforcing agent and additional silicon source to achieve the high-value utilization of fly ash. The pore structure, crystal structure, microscopic morphology and functional group characteristics of the samples at each stage were characterized by specific surface area and pore size analyzer (BET), X-ray diffractometer (XRD), scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FTIR). The effects of alkali concentration, SF mass fraction, temperature and steaming time on FACZ were investigated. The results show that analcime with a good crystallinity can be synthesized in FACZ under the optimized conditions (i.e., 8 mol/L NaOH, 15% SF and steaming at 190 ℃ for 48 h). The specific surface area of FACZ can reach 14.4 m²/g and the strength is 27.25 MPa after steaming. The removal efficiency of FACZ can reach 99.9%, and the maximum removal amount is 31.934 mg/g under the optimal removal conditions. The removal mechanism is a combined action of silanol and zeolite ion exchange, in which the ion exchange is the main cause.

Microwave dielectric ceramics are key materials for manufacturing 5G communication components. The microwave dielectric ceramics of BaSn(Si_1-xGe_x)₃O₉(0≤x≤1.0) were prepared via conventional solid-state reactions, and the effect of substituting Ge⁴⁺ for Si⁴⁺ of BaSnSi₃O₉ ceramic on the sintering behavior, crystal structure, and microwave dielectric properties was investigated. The results show that the BaSnSi₃O₉ ceramic exhibits the porous microstructure and poor microwave dielectric properties (i.e., ε_r=6.61, Q×f=7 977 GHz at 15.03 GHz, and τ_f=-37.8×10^-6/℃). The BaSn (Si_1-xGe_x)₃O₉(0≤x≤1.0) solid solutions are obtained with Ge⁴⁺ substitution for Si⁴⁺, the crystal structure is a hexagonal structure with P-6c2 space group. The Ge⁴⁺ substitution for Si⁴⁺ can improve the microwave dielectric properties of BaSn(Si_1-xGe_x)₃O₉(0≤x≤1.0) ceramics by optimising the sintering behavior and changing the crystal structural parameters. The Q×f values of BaSn(Si_1-xGe_x)₃O₉(0≤x≤1.0) ceramics are mainly controlled by the relative covalency of Si/Ge—O and Sn—O bonds. As x=1.0, the BaSn(Si_1-xGe_x)₃O₉ ceramic exhibits the optimal microwave dielectric properties (i.e., ε_r=8.53, Q×f=15 829 GHz at 14.41 GHz, and τ_f= -34.2×10^-6 ℃^-1).

Low-dielectric-constant (ε_r) microwave dielectric ceramics are one of the key materials for future mobile communication technology, and the accurate characterization for their basic performance parameters of ε_r, Qf value and temperature-dependent coefficient of resonant frequency (τ_f) is one of the most fundamental issues. Parallel plate method and metal resonant cavity method with TE₀₁₁ mode are commonly used for measuring the microwave dielectric properties. However, the corresponding problems are neglected, which are especially important for the research and applications of low-ε_r microwave dielectric ceramics. In this review, the key problems of the identification of TE₀₁₁ resonant mode, measurement reliability of Qf value and measurement reliability of τ_f were discussed for the characterization of low-ε_r microwave dielectric ceramics, and the corresponding solutions to the problems were given.

With the development of a high-speed wireless technology, low-temperature co-fired ceramics (LTCC) technology becomes popular. The high-speed, low-delay and high-reliable wireless transmission could be achieved by using LTCC substrates with a low-permittivity (K), a low-loss and a stable-temperature of resonant frequency, as one of functional materials. This review introduced the current situation of commercial substrate materials and alternative LTCCs reported, i.e., ceramic/glass, oxide-assisted sintering, fluoride-assisted sintering and intrinsic low-sintering ceramic systems. The composition, structural characteristics, dielectric properties, coefficient of thermal expansion of low-K LTCCs, as well as the advantages and disadvantages, were also discussed. Some studies of commercial substrates were further described, and their performances in millimeter-wave application were represented. In addition, the development trend of low-K LTCCs was also proposed.

Developing some thermal insulating composite materials based on perlite is a subject to expand the application of mineral materials. In this paper, the vinyl silicone oil or room-temperature vulcanized silicone rubber was mixed with two kinds of perlite with different sizes and fumed silica as fillers through a kneading process and a direct mixing process, respectively. Some composite silicone rubber insulation boards were prepared and evaluated by the thermal conductivity and insulation performance. The results show that the product prepared by the kneading process has resulted in a reduced heat preservation ability of perlite, probably due to the broken hollow particles. The insulation board prepared with fumed silica as a main filler is difficult to form their shape, and the minimum thermal conductivity is 0.172 8 W·m^-1·K^-1 for the formed sample. When a mass ratio of perlite and fumed silica in silicone rubber is 37.5% and the product thickness is 2.5 cm, the minimum thermal conductivity is 0.034 9 W·m^-1·K^-1, and the back-side temperature is 67 ℃ after heating at 250 ℃ for 4 min, which basically meets the application requirements of thermal insulation materials for tobacco facility.

Microwave dielectric ceramics prepared via a conventional method usually require a high sintering temperature (i.e., >1 000 ℃) and long sintering time, leading to a high energy consumption and a difficulty to realize the integration and co-firing of multiple material system. Continuous innovation and development of wireless communication technology put forward higher requirements for the miniaturization and integration of microwave devices, so that some technologies for preparing low-temperature co-fired ceramic (LTCC) and ultralow-temperature co-fired ceramic (ULTCC) are developed. Developing green sintering technologies with lower sintering temperatures and higher sintering efficiencies becomes one of the research hotspots. Novel sintering technologies (i.e., liquid-phase sintering, hot press sintering, microwave sintering, spark plasma sintering, and flash sintering) promote the development of microwave dielectric ceramics. A novel ultra-low temperature sintering technology called cold sintering process is proposed. The sintering temperature of cold sintering process is rather low (≤300 ℃), which can densify ceramics in a short time, and has some advantages in the phase stability, co-firing of multiple materials and grain boundary manipulation, thus providing an opportunity for the development of ultra-low temperature sintering technology and microwave dielectric material system.

A novel phosphate binder was prepared with homemade aluminum dihydrogen phosphate as a matrix and nano-Al₂O₃, Si powder and low-temperature fused glass powder (Zn-B-Si-Al-R) as fillers to enhance the high-temperature resistance of phosphate adhesives. The interface reaction mechanism was analyzed. The results show that the high-temperature tensile strength of the adhesive is 5.28 MPa at 500 ℃, and the mass loss is only 7.8% when the additions of Fe₂O₃, ZrO₂ and CuO are 5% (in mass), 10% and 15%, respectively. From room temperature to 500 ℃, the coefficient of thermal expansion of the adhesive matches well with the stainless steel substrate, and the difference is less than 1.5×10^-6 K^-1. Meanwhile, the discrepancy of electric potentials promotes the ions exchange of Fe and Cu, forming the composition gradient layer at the interface, which effectively relieves the thermal stress caused by thermal mismatch and improves the bond strength of the adhesive at a high temperature.

Coated catalysts have attracted much attention due to the urgent need of low-resistance technology for large-flow industrial flue gas purification. However, the complex characteristics of coating slurry and the factors influencing the loading for the catalyst preparation become a challenge. For the preparation of Cu-Mn based catalyst by vacuum coating on cordierite substrate, the influence of slurry characteristics (i.e., solid content, binder type, pH value and particle size) on the loading mass and adhesivity of catalyst was investigated. The results show that the increase of solid content makes the catalyst particles more closely bound to the network structure formed by thickener and silica sol, and improves the loading mass and adhesivity of the catalyst. Silica sol can effectively increase the electronegativity on the surfaces of the particles in the slurry, thus leading to the dispersion of the catalyst particles in the slurry. The increase of pH value reduces the zeta potential on the particle surface, reduces the slurry viscosity and improves the slurry stability. Grinding can destroy the uniform and stable network structure of the slurry, affecting the catalyst adhesivity negatively. A coated catalyst with a loading mass of 216 kg·m^-3, a shedding rate of 0.6%, and a catalytic CO efficiency of greater than 98% (7 200 h^-1, 120 ℃, 8% H₂O) is obtained when an unground slurry with a silica sol content of 30% (in mass fraction), pH value of 7.3 and solid content of 30% (in mass fraction) is used.

In order to improve the serious polarization problem of zinc negative electrode in zinc-nickel secondary batteries and to improve the electrochemical performance and cycling stability of zinc negative electrode, a hydrothermal-coprecipitation method was used to prepare CaSn(OH)₆ deposited on the surface of calcium zincate and used as a negative active substance of zinc-nickel batteries. The results show that the hydrothermal-coprecipitation method can be used to deposit CaSn(OH)₆ on the surface of calcium zincate, and the prepared calcium zincate has a high crystallinity. Based on the cyclic voltammetry test, the addition of CaSn(OH)₆ reduces the charge transfer resistance of calcium zincate and is beneficial to accelerating the electrochemical reaction rate of calcium zincate in alkaline electrolyte, thus improving the discharge rate in the reaction process. The results of electrochemical impedance spectroscopy confirm that calcium zincate with CaSn(OH)₆ deposited on the surface electrode charge transfers impedance less rather than that of pure calcium zincate. The capacity retention rate of the battery is 85.34% after 70 charge discharge cycles at 0.2 C when calcium zincate with CaSn(OH)₆ deposited on the surface is used as a negative active material of Zn-Ni battery.