The residual mechanical properties and microstructure of UHPC mixed with 6, 8, 12 mm copolymer formaldehyde fiber and steel fiber after high temperature were studied. The test results show that at 400 ℃, only plain concrete bursts. At 500 ℃, the steel fiber UHPC specimen burst, while the UHPC specimen with single copolymer formaldehyde fiber and mixed with two kinds of fiber can still maintain relatively integrity, and the latter has higher residual strength at high temperature. SEM and pore structure show that the copolymer formaldehyde fiber in UHPC can be closely bonded to the matrix after steam curing at high temperature. The pore formed by fiber melting at 165 ℃ can effectively relieve and release steam pressure, keep the concrete matrix intact and prevent it from cracking at 500 ℃. The research results reveal the mechanism of the copolymer formaldehyde fiber on the high temperature performance of concrete, which has great reference value for its application in UHPC.

BaZrO₃/Al₂O₃ composite molds were prepared via sintering at 1 600 ℃ for 8 h with BaZrO₃ as a surface coating material and Al₂O₃ as a backup coating material. The phase composition and microstructure of the interfacial bonding layer between the face and back layers before and after hydration were investigated by optical microscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. The hydration process and damage mechanism of the interfacial bonding layer in the mold were analyzed. The effect of mold damage on the directional solidification of TiAl alloy was also investigated via directional solidification tests. The results show that BaZrO₃ and Al₂O₃ generate BaAl₂O₄ at BaZrO₃/Al₂O₃ interface during the high-temperature sintering process; and BaAl₂O₄ generates Ba(AlO(OH)₂)₂, Ba₂Al₄(OH)₁₆ and Ba₃(Al(OH)₆)₂ after hydration, leading to the grain volume change to destroy the intergranular bonding force, the generation of cracks in the mold and the failure of the mold. In the directional solidification process, the generated cracks become a channel for melt penetration of TiAl alloy, resulting in a melt leakage from the mold and the appearance of heterogeneous crystals in the directionally solidified TiAl alloy castings.

The micro-displacement actuators based on the electrostriction are widely used in precision positioning and machining technology due to the merits of high accuracy, high sensitivity, low hysteresis and easy realization of the micro displacement in a submicron order. The electrostriction refers to a phenomenon that the strain is proportional to the square of electric field (or polarization) in dielectrics, which plays a crucial role in the electromechanical behavior of piezoelectric and ferroelectric materials. With particular emphasis on the sustainable development of environment, the electrostriction in lead-free perovskite ceramics has attracted a lot of attentions. In this review, recent development on the electrostriction was represented, and the design idea of materials with a low strain hysteresis and a large electrostrictive strain was discussed. Several kinds of lead-free electrostrictive ceramics were described, and their advantages and disadvantages were pointed out. Besides, the relationships among the electrostriction, piezoelectric effect and electrocaloric effect were discussed, providing an opportunity for further enhancing the piezoelectric and electrocaloric properties for piezoelectric and ferroelectric ceramics. In addition, the existing problems, challenges, and prospects were put forward to promote the development and practical application of electrostrictive ceramics and relative devices.

In addition to incandescent lamps, white light-emitting diode and nonlinear supercontinuum white light, recent studies focus on the production of continuum broadband white light by irradiating different active materials with near-infrared constant-wave lasers. In this review, we introduced and categorized different materials that exhibit NIR laser driven white light emission, i.e., inorganic phosphors, hybrid nanostructures, carbon-based materials, organometallic compounds and rare-earth complexes. The intrinsic photophysical behavior of this process in terms of spectral characteristics, temperature evolution and photoelectric response was discussed. In addition, the different mechanisms of while light generation and highlight potential applications of this process were also represented. Finally, the past results and point future research direction for this optical process were summaried.

Porous ceramics were prepared by a high-temperature melting foaming method with red mud and high-aluminum fly ash as main raw materials. The effects of raw material composition and foaming process on the cellular structure and properties were investigated. The results show that the cellular structure of porous ceramic obtained after melt foaming at 1 200 ℃ for 1 h changes from closed to open, eventually forming a composite cellular structure. Also, the average pore size and porosity increase, while the bulk density and thermal conductivity decrease with increasing the mass ratio of SiO₂/Al₂O₃ from 1.2 to 1.9 in the raw material composition. At the blowing agent of 5% (in mass fraction) SiC and the melting agent of albite and microcline of 35%, a composite cellular structure porous ceramic with the bulk density of 0.63 g/cm³, average pore size of 0.98 mm and bulk porosity of 70% is obtained, and its flexural strength and thermal conductivity are 7.17 MPa and 0.34 W/(m·K), respectively.

A ratiometric fluorescent probe was constructed with carbon quantum dots (CQDs) and europium ions (Eu³⁺) as a fluorophore for the visual detection of teracycline (TC). In this ratiometric probe, CQDs/Eu³⁺ has an intense blue fluorescence peak at 439 nm and a weak red fluorescence peak at 616 nm under the excitation of 380 nm wavelength. The fluorescence peak intensity of CQDs at 439 nm gradually decreases based on the inner filter effect. The fluorescence intensity of Eu³⁺ at 616 nm increases due to an antenna effect with the addition of TC. The experimental factors, such as CQDs and Eu³⁺ ratio, response time, stability, etc., were optimized. The results show that the ratio fluorescent probe has a specific recognition ability for TC. A linear relationship between the fluorescence intensity ratio(F₆₁₆/F₄₃₉) and different concentrations of TC (0-50 μM) was established with a detection limit of 0.68 µM. With the addition of TC, the color of the ratio fluorescent probe solution under ultraviolet light gradually changes from blue to red and is used for the detection of TC in milk with the recoveries ranging from 92.5% to 1 14.8%. In addition, a TC test paper was also prepared, which can be quickly used for a visual test paper detection of TC.

Rare-earth calcium oxyborate crystals (i.e., RECa₄O(BO₃)₃, RECOB, RE∶Y and rare-earth elements) are promising piezoelectric materials for high-temperature sensing application due to their high melting point, highs electrical resistivity, low dielectric loss and moderate piezoelectric activity. Single crystal growth of RECOB crystals was introduced, the characterization of electro-elastic properties and the research progress of RECOB piezoelectric crystals in the high-temperature sensing field were represented. High-temperature surface acoustic wave sensor for temperature sensing, high-temperature piezoelectric transducers and vibration sensors were described. The potential applications and technical advantages of RECOB crystals and related sensors were introduced.

Near net size preparation of porous mullite ceramics with controllable shrinkage was achieved via gel casting and pore-forming agent process With Al₂O₃ and kyanite as raw materials, PMMA microspheres as a pore-forming agent, and isobutylene/maleic anhydride copolymer (Isobam104) as a gelling/dispersing agent. The effect of sintering temperature on the phase composition and the effect of solid loading on the microstructure, phase composition, shrinkage, porosity, and compressive strength of samples were investigated. The results show that the shrinkage of samples sintered at 1 500 ℃ firstly decreases and then increases as the solid loading increases. At the solid loading of 30%(in volume fraction) and the content of pore forming agent of 30%(in mass fraction), the total shrinkage of the samples is close to zero, realizing the near net size preparation of porous mullite ceramics. The prepared porous mullite ceramics exhibite a higher porosity (i.e., 60.4%), a smaller average pore size (i.e., 3.75 μm) and a higher compressive strength (i.e., 8.3 MPa). The shrinkage of porous ceramics can be effectively controlled by the volume expansion effect in the preparation process, and the near net size preparation of porous mullite ceramics is of great significance for the preparation of large-size and complex porous ceramic parts and the reduction of processing cost.

1-3 piezoelectric single crystal composites with relaxor ferroelectric single crystals and composites as ideal piezoelectric elements in high-frequency transmitting transducers possess the superior characteristics including high piezoelectric constants, ultrahigh electromechanical coupling factors, and low acoustic impedance. A high-frequency wideband transmitting transducer based on 1-3 piezoelectric single crystal composite was designed and manufactured. The properties of piezoelectric single crystal composites were analyzed theoretically, and the transducer structure was optimized via simulation by finite element method. The 1-3 piezoelectric single crystal composite transducer produced has a bandwidth of 160 kHz, while the ripple of the transmitting voltage response does not exceed 3 dB in the frequency range from 250 kHz to 410 kHz. The maximum transmitting voltage response is 178.4 dB. The underwater transmitting performances of the single crystal composite transducer are superior to those of the ceramic composite transducer with the same structure and size. Fabricating high-frequency transmitting transducers using 1-3 piezoelectric single crystal composites can broaden the operating bandwith effectively, and improve the ability of acoustic emission underwater.

In order to solve the problem for high initial frequency of unilateral lightweight phononic crystals, a phononic crystal structure of bilateral hollow asymmetric scatterers was proposed based on the local resonance mechanism. The energy band structure, transmission loss spectrum and intrinsic displacement field of phononic crystals with bilateral hollow asymmetric scatterers were calculated by the finite element method. The ultra-wide first complete band gap with an initial frequency of 79.4 Hz and a bandwidth of 1 065.2 Hz was obtained. Combined with an equivalent spring mass system, the vibration modes of the intrinsic displacement field of the marked points were analyzed, and the mechanism of band gap formation in phononic crystals of bilateral hollow asymmetric scatterers was revealed. Furthermore, effects of the geometric parameters such as notch angle of cladding, width of connecting short plate and height of hollow cylindrical scatterer on the first complete band gap were analyzed, and the geometric parameters of the phononic crystal were adjusted to control the band gap frequency. The results show that the initial frequency of the first complete band gap of the proposed bilateral asymmetric two-dimensional hollow scatterer phononic crystal effectively reduces to less than 80 Hz, and the bandwidth exceeds 1 000 Hz. Adjusting the structural parameters of phononic crystals can realize the coexistence of local resonance and the Bragg scattering band gap in a phononic crystal, which makes it possible for a single phononic crystal to regulate the low-frequency and high-frequency band gaps simultaneously.