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A serious challenge faced by manufacturers of large-aperture aspheric optical components of glass ceramics is the long processing time. Ultrasonic vibration–assisted grinding (UVG) allows one to effectively shorten the subsequent polishing process by several times, which is essential for grinding of aspheric components. However, the surface creation mechanism of UVG-treated glass ceramics is rarely studied. Herein, rotary ultrasonic vibration–assisted vertical grinding (RUVG) and parallel grinding (RUPG) are applied to polish the aspheric glass ceramics. Particular attention is paid to the surface formation mechanism of UVG-processed ceramics. The single-grain kinematic functions are created and the contact characteristics between the grinding wheel and aspheric surface are analyzed for the two UVG methods in terms of contact area, velocity, and trajectory. In addition, aspheric grinding texture is simulated and comparative experiments are conducted correspondingly. According to the results, the rotary ultrasonic vibration mainly influences the microscopic grinding marks. Besides, the aspheric surface form accuracy of Pt and RMS value in RUVG is 2.16 and 3.71 times lower than those in RUPG, respectively, whereas the surface roughness–related parameters (mean deviation Sa and maximum height of profile Sz) in RUVG are 6.36% and 4.56% higher than those in RUPG. This indicates that RUVG is more suitable for high precision and efficiency grinding of the aspheric surface than RUPG due to the fact that the polishing depth is primarily determined by surface form accuracy rather than surface roughness. Thus, the current research enables an in-depth understanding of surface generation mechanism in rotary ultrasonic vibration–assisted grinding, pointing out its benefits in the high-efficiency aspheric surface manufacturing. [ABSTRACT FROM AUTHOR]

Lead-free medium temperature sintering BaTiO-based X8R ceramic materials were obtained by sintering with addition of nano-size BiO-TiO-ZnO-HBO(BTZB), which was synthesised successfully via a sol-gel method. and showed high activity and great dispersion properties. Moreover, the dielectric property and bulk densities was also influenced by the BTZB nanopowder content. The results indicate that BTZB nanopowders can be used as a sintering aid to reduce the sintering temperature of BaTiO from 1300 to 1150 °C without secondary phase formation. The 4 wt% BTZB-doped sample which sintered at 1150 °C showed super dielectric properties that the dielectric constant ε = 3186 at 25 °C and dielectric loss was lower than 1.5%. the temperature stability was also improved, temperature coefficient of capacitance less than ±15% from −55 to 150 °C, meeting X8R standard. [ABSTRACT FROM AUTHOR]

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3 ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε r , dielectric stability and dielectric loss ) in Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10 12 Ω cm. These features suggested that the Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment. [ABSTRACT FROM AUTHOR]

Multi-component BaTiO 3 –Bi 0.5 Na 0.5 TiO 3 –Nb 2 O 5 (BBNN) system doped with divalent metal ions (Zn 2+ , Co 2+ , Ni 2+ ) was prepared by the conventional solid–state method.The X-ray diffraction patterns revealed all samples exhibited perovskite (P4mm) single phase. The dielectric properties and micro-mechanisms were discussed and validated. Novel theories, based on the characteristics of the different kinds of dielectric polarization, are proposed to explain the dielectric anomalies in the dielectric system. The relationships between microstructure and the dielectric properties were investigated systematically for the first time. The samples doped with 15 mol% Zn 2+ /Co 2+ presented good dielectric properties of an ultra-broad temperature stable range (from −50 and >300), high dielectric constant (ε~1925 for Zn 2+ / ε~1341 for Co 2+ ) and low dielectric loss (tan δ<0.02) were obtained. These features made the ceramics system have high practical values for miniaturization and harsh environments applications. [ABSTRACT FROM AUTHOR]

The bi-layer composite ceramic armors are widely used in the protection field, and its design method is keep changing since the Florence model has been found. In this study, an analytical design method of bi-layer was proposed and examined with a new ceramic protection efficiency definition. With this definition, the protection efficiency of composite ceramic armor can be divided into two independent parts: the protection efficiency of ceramic and the protection efficiency of backing plate. By using this analytical design method, the design of the bi-layer ceramic armor can be more efficiency and the material of armor can be selected more accurately. [Display omitted] • A design method for bi-layer ceramic armors is established. • Proposed method was verified using numerical simulation and bullet impact experiments. • Analytical solution was in predicting total armor protection efficiency per unit area density. [ABSTRACT FROM AUTHOR]

The effect of interlayer materials on the damage of ceramics in the SiC/Al composite structure was analyzed through experiments and simulation. Using 0.25 mm thermoplastic polyurethane (TPU) as a reference, a 0.5 mm aramid fabric (AFRP) or a 0.5 mm carbon fiber reinforced epoxy matrix composite (CFRP) was added to the interlayer, respectively. Through the impact tests, it was discovered that the ceramic damaged area in the TPU composite structure was severe. With the addition of AFRP, the damaged area of the ceramic layer was reduced by 73% under the same impact conditions. The addition of CFRP also reduced the damage of ceramics. The evolution process of the tensile stress on the ceramic rear surface was presented by simulation. The tensile evolution process analysis can explain the experimental phenomenon well and can be used to predict the damage of the ceramics. [ABSTRACT FROM AUTHOR]

Many studies on the protection of C/C composites in oxidizing environments have been carried out. Coating technology has proven to be highly effective in improving the oxidation resistance of C/C composites. Summaries and comparisons of antioxidation coating materials for C/C composites are needed for comprehensive understanding and further researches. In this paper, recent advances in promising single-phase materials as protective coatings for C/C composites were firstly reviewed, with attention to their characteristics and antioxidation mechanisms. Then, several common mixture systems, such as carbide mixtures, boride mixtures and MoSi 2 -based ultrahigh-temperature ceramics (UHTCs), were discussed. In addition, three kinds of nanostructured materials used for doping coatings were described in detail. Finally, some typical problems and future challenges in the development of these coating materials for C/C composites were highlighted. [ABSTRACT FROM AUTHOR]

Al alloy was the optimal metal cover material for confined silicon carbide (SiC) against blunt tungsten-heavy-alloy projectiles based on a previous research. In this study, the influence of the aluminium (Al) alloy plate thickness on the ballistic performance of SiC was investigated to determine the optimal plate thickness. In addition, the ballistic responses of covered ceramic composite structures under various impact velocities were examined. The failure features of the cover plates and ceramic were elaborated based on tests and simulation analyses. The penetration weight calculated using the measured residual penetration was applied to characterise the ballistic performance of ceramic armour modules. The results showed that thin and thick cover plates could increase the loading rate of the ceramic pressure, thus attenuating their buffering effects on the ceramic. Therefore, the determination of the optimal cover plate thickness must simultaneously meet the requirements of stiffness and the reduced ceramic pressure loading rate. The optimal thickness for the Al alloy cover plate was 4 mm for lateral and back confined ceramic against blunt projectiles in this paper, which was obtained via a numerical simulation. Finally, the buffering effect of the cover plate on enhancing the structural ballistic performance varied with the impact velocities of the projectiles. This study provides insights for covered ceramic armour applications. [ABSTRACT FROM AUTHOR]

To determine the mechanism of microwave response in AZrNb 2 O 8 (A: Mn, Zn, Mg, Co, et al.) wolframites, CuZrNb 2 O 8 ceramic with low sintering temperature (920 °C) is successfully fabricated by solid-state reaction method. Meanwhile, its structural stability is synthetically evaluated, the vibration modes are also calibrated. Except for the extrinsic factor like sintering temperature, the condition of Jahn-Teller ion Cu2+ as intrinsic part is characterized for the first time in relation to the microwave dielectric properties of the system. In virtue of Raman and EPR spectra, it is predicted that the electronic structure of transition metal ions, as the less concerned factor, may be influential on the dielectric properties of ceramics at microwave range, especially in the structure with mixed ion occupancy. In addition, the CuZrNb 2 O 8 ceramic is well matched with the silver electrode, which makes it a prospective candidate for temperature compensation material of LTCC (low-temperature co-fired ceramic) passive integration technology. [ABSTRACT FROM AUTHOR]

Low-loss (Zn 1- x Ni x )ZrNbTaO 8 (0.02 ≤  x  ≤ 0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni 2+ ( x  = 0.06) in A-site with the fixed substitution of Ta 5+ in B-site can effectually raise the Q  ×  f value of ZnZrNb 2 O 8 ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn 0.94 Ni 0.06 )ZrNbTaO 8 ceramic sample sintered at 1150 °C for 3 h exhibits an outstanding combination of microwave dielectric properties: ε r = 27.88, Q × f  = 128,951 GHz, τ f = –39.9 ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency. [ABSTRACT FROM AUTHOR]