It is important to develop high emissivity infrared radiation materials for energy saving in high-temperature furnaces. In this work, Ni2+-doped MgCr2O4 materials were prepared by a high-temperature solid-phase reaction process. The effect of Ni2+ doping content on the infrared radiation properties of MgCr2O4 materials was investigated, and the mechanism of emissivity enhancement of MgCr2O4 materials was explored. The results show that Ni2+ ions can be doped into the lattice of MgCr2O4 materials, and the prepared Mg1-xNixCr2O4 (0.1≤x≤0.5) materials produce the lattice distortion and a small amount of Ni2+ valence state transformation. Also, the concentration of oxygen vacancies increases, the forbidden band width decreases with the increase of Ni2+ doping, thus improving the emissivity of the prepared materials in the near-mid-infrared band. The material with x of 0.5 (Mg0.5Ni0.5Cr2O4) has an average emissivity of 0.88 in the near infrared ref bands (i.e., 0.8-2.5 μm), which is 167% greater than that of the undoped specimens. Ni2+ ions doping enhances the lattice vibration absorption, free carrier absorption and impurity energy level absorption, and improves the infrared emissivity of MgCr2O4 materials in the near-mid-infrared band.

Porous aggregates are a key material for the lightweight refractory. Porous magnesia based composite spinel (Mg (Fe, Al)2O4) refractory aggregates were prepared by an in-situ decomposition synthesis method with calcined magnesite, Al(OH)3 and iron oxide as raw materials. The influence of sintering temperature (i.e., 1 000-1 600 ℃) on the microstructures and strengths was investigated, and the synthesis mechanism of porous aggregates was analyzed. The results show that the pores in the samples are composed of the pores in the micron-sized particles and the pores among micron-sized particles as well as they have a few neck connections at the sintering temperatures of 1 000-1 300 ℃, and the pores in the micron-sized particles migrate to the gaps and the necks grow with a further increase of sintering temperature to 1 400-1 600 ℃, thus promoting the compressive strength of the samples. The formation of composite spinel (Mg (Fe, Al)2O4) in the samples involves that MgAl2O4 is formed on the surface of Al(OH)3 pseudomorph and reacts with Fe3+ to form the composite spinel (Mg (Fe, Al)2O4) with a ring structure, and MgFe2O4 is formed in the position of MgO and reacts with Al3+ to form the composite spinel (Mg (Fe, Al)2O4) with the granular and strip structures. The porous magnesia based composite spinel (Mg (Fe, Al)2O4) refractory aggregates have the optimum performance (i.e., an apparent porosity of 24.4%, a median pore size of 25.89 μm, a thermal conductivity of 2.79 W/(m·K) at 1 000 ℃ and a compressive strength of 74.4 MPa) at the sintering temperature of 1 550 ℃. Meanwhile, compared with the existing sintered magnesia, the thermal conductivity of porous magnesia based composite spinel (Mg (Fe, Al)2O4) refractory aggregates synthesized can be reduced by 64.7%.

Al2O3-C refractories are important for the continuous casting process. It is essential for safe and effective steel making processes to enhance the strength and oxidation resistance of Al2O3-C refractories. A compound MAB phase Cr2AlB2 has attracted recent attention due to its high fracture toughness, high damage tolerance and excellent oxidation resistance. In this work, a ternary layered compound Cr2AlB2 was introduced into the Al2O3-C refractories. The structural evolution of Cr2AlB2 in Al2O3-C refractories after treated at different temperatures and its effect on the comprehensive properties of Al2O3-C refractories were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that a gradual decomposition of Cr2AlB2 in Al2O3-C refractories generates a core-shell structure of CrB and Al2O3 covered with Al2O3, and catalyses the formation of carbon nanotubes and carbon fibers on the surface of the core-shell structure after thermal treatment at 800-1 200 ℃. Cr3C2 covered by BN structure is formed inside the core-shell structure after thermal treatment at 1 200-1 600 ℃. As a result, the densification of Al2O3-C refractories is facilitated, and the cold modulus of rupture and oxidation resistance is enhanced. The cold modulus of rupture after coking at 1 400-1 600 ℃ is increased by approximately 9%, and the oxide index after treated in air at 1 400 ℃ is reduced from 44% to 31%.

Corundum-Ti2O3 two-phase material is a by-product obtained via adjusting the smelting process of low-ferrotitanium alloy. Al2O3 and Ti2O3 exist independently in raw material, which can be used as a refractory raw material. According to the results by thermogravimetry-differential scanning calorimetry and thermodynamic analysis, the oxidation reaction of Ti2O3 in the raw material starts at 700 ℃, and the reaction between Al2O3 and TiO2 starts at 1 263 ℃. The results by X-ray diffraction and scanning electron microscopy indicate that Ti2O3 completes the oxidation reaction at 800 ℃, which is affected by the decomposition reaction of Al2TiO5 at 1 300 ℃, only part of TiO2 and Al2O3 reacts at the corundum junction to form flake Al2TiO5. As the sintering temperature is increased to 1 400 ℃ and 1 500 ℃, the reaction of Al2O3 and TiO2 to form Al2TiO5 is gradually completed, and a typical columnar aluminum titanate is formed on the basis of flakes.

Silica bricks only used the combined mineralizer of calcium hydroxide and iron scale in the early domestic production. It is feasible and necessary to explore novel mineralizers to improve the performance of silica bricks. In this paper, novel silica bricks were prepared with ferrosilicon nitride and calcium carbonate as mineralizers instead of calcium hydroxide and iron scale. The prepared silica bricks have good properties, and the content of tridymite with 2% ferrosilicon nitride and calcium carbonate added reaches 62% and 65%, respectively. The effects of ferrosilicon nitride and calcium carbonate on the formation of tridymite in silica bricks were investigated by X-ray diffraction and scanning electron microscopy. The results show that in the silica brick with ferrosilicon nitride as mineralizer, Si3N4 network formed by the intertwined columnar Si3N4 in the sea urchin-like structure ferrosilicon nitride protects Fe and Fe3Si through its oxidation reaction, thereby achieving a higher FeO/Fe2O3 ratio and a lower liquid formation temperature in the FeO-Fe2O3-SiO2 ternary phase. The FeO/Fe2O3 ratio in the liquid phase fluctuates at a high temperature, and then the constant change of the solubility of tridymite in the saturated liquid phase promotes the crystallization of tridymite due to the reducibility of Fe, Fe3Si and Si3N4. When calcium carbonate is used as a mineralizer of silicon brick, the formation temperature of the liquid phase in the brick is increased to 1 436 ℃. Before that, the reactions in the bricks are mainly the decomposition of calcium carbonate and the transformation from β-quartz to α-quartz and to metastable α-cristobalite. The increase of the formation temperature of the liquid phase does not reduce the content of tridymite in the brick, and the content of glass phase in the brick is less than that in the brick with iron mineralizer.

To improve the resistance to hydration, thermal shock and slag penetration of magnesia, a magnesia based composite was prepared via adding TiO2 powder (i.e., 1% (in mass fraction), 2% and 3%) into a light burned magnesia powder. The effect of TiO2 content on the sintering behavior, microstructure and properties of the composite was investigated. The results show that free CaO and some MgO transform into CaTiO3 and Mg2TiO4 and the size of MgO grains increases as TiO2 addition increases, leading to an improvement in the hydration resistance. The formed CaTiO3 and Mg2TiO4 phases reduce the thermal expansion coefficient and induce the crack deflection as TiO2 content increases, therefore improving the thermal shock resistance of the specimens. Besides, as 1% TiO2 is added, the slag penetration resistance of the specimens is enhanced due to the increase in MgO grain size and the formation of high stable intergranular CaTiO3 phase. However, the further increasing TiO2 content reduces the slag penetration resistance due to the formation of low stable Mg2TiO4 phase at MgO grain boundaries.

As an important raw material of magnesia based refractories, the dissolution of the fused magnesia in the CaO-Al2O3-SiO2 slags for refining a low density and high strength steel is an important factor affecting the service life of furnace lining and the quality of steel. In this paper, the dissolution behavior of fused magnesia in the slag at 1 600 ℃ was investigated by a high-temperature laser confocal microscopy system. The effects of the shape and mass of magnesia particles and the mass fraction ratio of CaO to SiO2(C/S) on the dissolution behavior were investigated. The results show that the shape of fused magnesia particles has little effect on its dissolution rate. The dissolution rate decreases linearly with the increase of mass, and it decreases firstly and then increases with the increase of C/S ratio. The dissolution curve of magnesia particles is affected by the mass, and the n values of the dissolution model can correspond to 1/2, 2/3 and 3/5, respectively. This work provides a guidance for understanding the slag corrosion behavior of magnesia based refractories, improving the quality and optimizing the performance of magnesia based refractories.

With the development of hydrogen metallurgy and hydrogen-based shaft furnace, the corresponding refractories for critical parts have higher requirements. Understanding the service environment characteristic and implementing targeted design for the performance are thus particularly important for refractories. In this paper, the temperature, pressure and gas phase concentration distribution for interior and wall surface in reduction domain of hydrogen-based shaft furnace were simulated by a software named Ansys. Also, the thermodynamic stability of typical components of traditional refractory during the process was calculated by FactSage. The results show that the high-temperature and high-pressure service area is concentrated near the gas inlet, while H2O is concentrated in the top and bottom areas of the furnace. Increasing the temperature of inlet gas has a certain effect on the temperature field, but has little effect on the pressure field and gas phase composition. Among the typical components of conventional refractory, Al2O3, ZrO2, magnesium aluminum spinel, calcium-hexaluminate and TiO2 exhibit a thermodynamic stability, which can be used as potential refractory components of furnace walls. AlN or TiC can be used as additive materials to improve the relevant properties of these refractories. In addition, some impurity components as SiO2, MgO, CaO, Cr2O3, Fe2O3, SiC, Si3N4, B4C and BN can be eliminated. This study can provide a theoretical basis and methodological support for the service environment simulation and material component selection of refractory for a hydrogen-based shaft furnace.

Crucible refractories are very important for the quality of titanium alloy smelting. In order to develop novel crucible material with high performance, in this work, Y2O3-Al2O3-MgO-CaO composite refractories were prepared with commercial yttrium oxide and Al2O3-MgO-CaO powders (AMC) as raw materials, and the effects of sintering temperature (i.e., 1 500 ℃, 1 600 ℃) and AMC contents (i.e., 0, 25%, 50%, 75% and 100%, in mass fraction) on the phase compositions, sintering properties (i.e., linear shrinkage, volumetric shrinkage, apparent porosity, and bulk density), compressive strength at room temperature, thermal shock resistance and microstructures of as-prepared refractories were investigated. The results show that the most properties of the composites are improved, compared with Y2O3 and AMC. The performance becomes better as the sintering temperature increases. Moreover, the linear shrinkage, volumetric shrinkage, bulk density and compressive strength at room temperature of the composites increase with the increase of AMC contents. At the AMC content of 75%, the composite sintered at 1 500 ℃ for 3 h has the optimum comprehensive performance (i.e., the apparent porosity of 4.37%, the compressive strength at room temperature of 274.99 MPa, the residual strength after three water-cooling and thermal shocks of 161.60 MPa, and the residual strength ratio of 58.78%).

The application of graphite flakes in refractory castables was inhibited by their poor water-wettability, and carbides modified graphite was considered as the best way to solve this problem. Aimed to solve the high cost, difficulty in scalable fabrication, and unclear synthesis mechanism in the preparation process of carbide-modified graphite, a core-shell SiC@ graphite powder was fabricated in air by a modified molten salt shielding technique in this work. Influence of encapsulation method on the phase composition and microstructure of as-obtained SiC@C powders was investigated. The results show that SiC@C powders can be fabricated via modified molten salt shielding method. The as-prepared SiC@C powders possess better water-wettability, dispersibility and oxidation resistance. The microstructural characteristic of SiC@C powders is indicated a core-shell structure, SiC layer is formed on graphite flake. The template-growth mechanism is dominant in molten salt synthesis process, i.e., a small amount of Si is dissolved in the molten salt, diffused onto the graphite surfaces via a molten salt medium, and then reacted to form in-situ SiC coating layer on graphite flake, which is controlled due to the external diffusion of element Si.

Periclase-hercynite refractories are used in the firing zone of the cement rotary kiln, which is inextricably linked to their reaction behavior with cement clinker at high temperatures. In this paper, the corrosion behavior of magnesia aggregate and hercynite aggregate as well as periclase-hercynite refractory with cement clinker at high temperatures was investigated by scanning electron microscopy, X-ray diffraction, and Factsage simulation, respectively. The results show that magnesia particles have a superior corrosion-resistance to cement clinker, and the reaction of hercynite with cement clinker produces massive high-temperature liquid phase, which is gradually corroded. The periclase phase and hercynite particles have a synergistic effect on resisting the cement clinker corrosion in periclase-hercynite bricks at high temperatures. The periclase matrix as a major crystalline phase reacts with cement to generate a high melting point phase, forming a skeletal structure in the grain boundary phase, improving the grain boundary phase’s high-temperature viscosity, and promoting the combination of clinker and refractory. Also, ion exchange between hercynite and magnesia promotes the combination of hercynite and matrix, while inhibiting the formation of low melting point feldspar phases at high temperatures. Furthermore, the high-temperature stability of hercynite is improved, which benefits the kiln coating stability when using the refractory in the firing zone.

Magnesium silicate hydrate (MgO-SiO2-H2O M-S-H) is a main bonding phase for microsilica bonded magnesium- castables used for tundish. Its content determines the mechanical properties after demolding. In this paper, M-S-H was synthesized with Na2SiO3·9H2O and MgCl2·6H2O as raw materials. The effect of M-S-H at different calcination parameters was investigated by X-ray diffraction, scanning electron microscopy, specific surface area measurement, nuclear magnetic resonance, and thermogravimetry-differential scanning calorimetry. Moreover, the synthesized M-S-H with microsilica powder (1%) was introduced into the magnesia-based castables to evaluate their influences on the properties. The results show that M-S-H has a memory effect when the calcination temperature is below 400 ℃. Increasing the calcination time can facilitate the insertion of interlayer hydroxyl groups in M-S-H gels and contribute to the formation of a lamellar structure with a higher structure stability. A certain amount of pre-synthesized M-S-H and a small amount of silica powder can assure the castable with a good workability and a sufficient early bonding strength. The reduced silica can suppress the formation of large sized defects due to the volume shrinkage of matrix, in the interface of aggregates and matrix, thus improving the mechanical properties of castables. This work provides a support for the development of magnesia-based castables with a low silica content.

Cement rotary kilns using refractories require excellent refractoriness, thermal shock stability and corrosion resistance due to the cyclic rotation and feeding-discharging of cement clinker. In this paper, a kind of magnesia-alumina spinel refractory containing coating structured aggregates were prepared by wrapping spinel fines on the surface of magnesia aggregates. The fracture behavior and corrosion resistance of prepared refractories were characterized by three-point bending test combined with digital image correlation, acoustic emission technique, and static slag resistance method. The results indicate that by changing the distribution of spinel to make coating structure aggregates, the alumina content is effectively reduced while a more uniform and extensive distribution of spinel phase is achieved. Compared with the merchant magnesia-alumina spinel refractory (10% Al2O3) with pre-synthetic spinel aggregates, the magnesia-alumina spinel refractory (5% Al2O3) with spinel coating aggregates has the improved mechanical strength and corrosion resistance, and maintains the thermal shock resistance.

Bauxite ores usually contain some iron and titanium oxides, which are difficult to remove simultaneously with conventional beneficiation processes. The oxides of iron and titanium will form low melting point phases during the preparation of mullite by sintering with bauxite, resulting in a reduction of the high-temperature properties of mullite. This review represented the solid solution behavior of iron oxides and titanium oxides in mullite based on the open spatial structure of mullite and its ability to accommodate different metal ions at different temperatures and atmospheres. The solubility of TiO2 in mullite is 1.36%-4.10% at 1 400-1 700 ℃. Fe2O3 of 10%-12% can make a solid solution in mullite microstructure at 1 300 ℃. Ti3+ and Fe2+ are poorly solidified in mullite. Moreover, the formation of solid solutions of iron and titanium with mullite provides a limited enhancement of mullite properties. In addition, the efficient use of mullite containing iron and titanium was also discussed.

The melting of refractory in slag and the penetration of slag into refractory are the main reasons for the damage of refractory. These two aspects are related to the wettability between slag and refractory at a high temperature, and the wettability can be evaluated by the surface tension, adhesion work and spreading coefficient of slag on the refractory surface. The wettability of slag and refractory can be inhibited by changing the composition and roughness of the refractory, thus resulting in the improved service life of the refractory. This review represented the factors affecting the high-temperature wettability between refractories and slag based on the aspects of slag composition, refractory composition and surface microstructure effect. In addition, the future research direction in this field was also prospected.

In large-scale blast furnaces, the use of a proper refractory material for taphole as the most severe working area of blast furnaces has attracted much attention. This review introduced the main properties of taphole clay as a refractory material for blast furnace taphole, i.e., its plasticity, corrosion resistance and sintering properties, and summarized recent relevant work on taphole clay for aggregate, matrix and binder. In addition, the future development of taphole clay was also prospected.

Sintering process directly affects the microstructure and properties of ceramics. BaTiO3 piezoelectric ceramic was sintered by an ultrafast-high temperature sintering method. The result was compared with that of BaTiO3 sintered by a conventional furnace sintering method. The effect of sintering current on the phase composition, microstructure and property of BaTiO3 sintered in ultrafast-high temperature sintering method was investigated. Ultrafast-high temperature sintering suppresses the grain growth. After ultrafast sintering at 180 A for 5 min, the superior property with the dielectric constant of 3 450, dielectric loss of 1.89% and piezoelectric constant 283 pC·N-1 is obtained. The whole sintering time is reduced by 196 times, indicating that ultrafast-high temperature sintering is a promising densification method for functional materials.

ZrB2-based composite ceramics have great potential for applications at ultra-high temperatures, but the low toughness and poor oxidation resistance of them limit their practical applications. In this work, the Zr, B4C, Al, C and Si raw powders were used to prepare ZrB2-SiC-Zr2Al4C5 composite ceramics by reactive spark plasma sintering. The reaction processes and mechanism were studied. The effects of Zr2Al4C5 content and oxidation temperature on high-temperature oxidation behavior of multiphase ceramics were investigated for revealing the anti-oxidation mechanism. The results indicated that the B4C reacted with Zr to form ZrB2 at 900 ℃, and then the SiC formed at 1 100 ℃. At 1 400 ℃, the Zr2Al4C5 formed from the reaction of Zr3Al3C5, ZrC and Al4C3 which formed at the early initial reaction stage. And the Zr2Al4C5 transformed into Zr3Al4C6 with further increasing temperature. The main phases of the composite ceramics after oxidation are ZrO2, ZrSiO4, aluminosilicate and SiO2 glass. With increasing Zr2Al4C5 content, the surface of the oxide layer of the composite ceramics became uneven, loose and porous, while obvious long strip grains and inhomogeneous distribution of glassy phases were also observed. This study not only provides a new experimental reference for in-depth understanding of the high-temperature oxidation behavior of ZrB2-SiC based multiphase ceramics, but also provides new experimental and theoretical support for developing high-performance ZrB2-SiC based high-temperature composite ceramics.

The temperature difference between the growth temperature of plate crystal and the sintering temperature of zirconia toughened alumina (ZTA) is the key to the toughening effect of Pr0.833Al11.833O19 plate crystal on ZTA. In this paper, PrAlO3 precursor was prepared by combustion method, and high active PrAlO3 was formed by pre sintering at 900 ℃. It made the difference between the growth temperature of plate crystal and the sintering temperature of ZTA reach 100 ℃, then the plate crystal with high aspect ratio was obtained, which played a synergistic role in toughening. At the same time, the hydrothermal aging process of ZrO2 is slowed down by the solid dissolution of Pr ions into ZrO2, the microcracks induced by phase transformation are reduced, and the fracture strength and Vickers hardness of ZTA are improved. The results show that, compared with ZTA, the fracture toughness of ZTA reinforced and toughened by Pr0.833Al11.833O19 plate crystal in simulated human environment (hydrothermal aging) increases from 7.13 MPa·m1/2 to 8.97 MPa·m1/2, the fracture strength increases from 654.78 MPa to 687.59 MPa, and the Vickers hardness increases from 18.95 GPa to 19.39 GPa.

The effects of B4C addition and heat treatment temperature on the microstructure, mechanical properties and oxide resistance of SiC-based composite ceramics were investigated. The results show that the addition of B4C can improve the crystallinity and graphitization of SiC. The linear change rate of SiC-based composite ceramics decreases from 1.39% to 0.58%. The flexural strength and compressive strength are increased by 1.8 times and 2 times (i.e., from 28.06 MPa to 50.25 MPa and from 48.03Pa to 98.58 MPa), respectively, after heat treatment at 1 450 ℃ at B4C addition of 6% (in mass fraction). The oxidation index of SiC-based composite ceramics decreases from 30.33% to 18.35% after oxidation at 1 400 ℃, and the thickness of the oxide layer decreases substantially from 3.52 mm to 0.23 mm with the increase of B4C addition from 0 to 6%. Therefore, adding B4C can enhance the amount of SiC whiskers and the strength and oxidation resistance of SiC-based composite ceramics as well.

Two types of porous lead zirconate titanate (PZT) with different pore morphologies and porosities were fabricated by freeze-casting and burnt-out polymer sphere techniques, respectively. The effects of porosity and pore morphology on the sensing application of porous PZT ceramics were investigated. The result shows that the decreasing rate for piezoelectric charge coefficient d33 is slower than that of relative permittivity εr for porous PZT ceramics, leading to a better piezoelectric performance for the porous PZT rather than that of the dense ceramic. Moreover, d33 of porous ceramics with random spherical pores decreases, compared to that of the porous ceramics with aligned pores. Therefore, the porous PZT ceramic with aligned pores has a higher output voltage. The maximum output voltage reaches up to 84 V, which is generated by the 55.9% porous PZT with aligned lamellar pores under 8 N external force. This work is beneficial for understanding the effect of the pore characteristic on the sensing properties of piezoelectric ceramics and provides a new idea for the preparation of sensors with high piezoelectric coefficient.

The prestressing reinforcement has been proved to be effective for ceramics, but how this surface prestressing affects other mechanical properties is still unclear. The influence of surface residual compressive stress on the mechanical properties of composite members, including bending strength, elastic modulus, fracture toughness, hardness and damage tolerance are investigated in this work. In order to achieve suitable surface compressive stress and the appropriate interface shear stress, mullite and aluminum oxide are mixed and ground into a slurry with a mass fraction ratio of 1∶1 and coated on the pre-sintered alumina substrate. The coated samples were prepared by pressureless sintering. With the temperature drop, different shrinkage rates and interface constraints of the two materials form the residual compressive stress in the surface layer. Mechanical properties of the coated alumina were tested. The experimental results show that the prestressed design can effectively improve the bending strength of alumina by 38.9%; The fracture toughness is increased by 36.5%, and the elastic modulus and hardness are slightly decreased. The damage tolerance of the prestressed ceramic is increased from 0.389 4 m1/2 to 0.452 7 m1/2, which is 16.26% higher.

With bauxite tailings as the main raw material, adding bauxite clinker and lithium chinaite to prepare the traditional mulite-corundum multiphase ceramics, adding different contents of lepidolite, to explore the influence of the properties of mulite-corundum multiphase ceramics. The phase composition and morphology of ceramics were analyzed by X-ray diffractometer and scanning electron microscope. The effects of lepidolite content and sintering temperature on the mechanical properties of ceramics were studied. The results show that: The addition of lepidolite can reduce the sintering temperature and improve the strength of ceramics. When 10% lepidolite is added and the sintering temperature is 950 ℃, the strength of mulite-corundum multiphase ceramics is the highest, and the ceramics phase composition is corundum, mullite, quartz, hematite, rutile and glass, and the volume density is 1.75 g/cm3, the thermal conductivity is 0.447 W/(m·K), the linear shrinkage is 5.47%, and the compressive strength is 74.87 MPa. It has a wide application prospect in the fields of thermal storage ceramics and refractory materials.

YAG crystal is a typical hard and brittle material with Mohs hardness of 8.5 and insoluble in any acid or base at room temperature, so it is difficult to process. A step-by-step lapping process is proposed in order to explore lapping processing of YAG crystals in this paper. Based on the method of free abrasive lapping, the particle size of boron carbide (B4C) abrasive was reduced step by step during the lapping process, and abrasive W40, abrasive W28, abrasive W14 and abrasive W7 abrasives were selected for lapping in steps, and the particle size ranges of the four abrasive abrasives were: 40-28 μm, 28-20 μm, 14-10 μm, and 7-5 μm in order. The effect of the lapping pressure, the rotational speed of the lapping disc and pendulum, and the B4C mass fraction in the lapping solution on the lapping effect in each lapping step was investigated, and the optimal lapping parameters were derived; the depth of subsurface damage after lapping of YAG crystals was measured by cross-section microscopy method to determine the amount of subsequent polishing removal, and the relationship between the depth of subsurface damage hSSD and the surface roughness Ra after lapping was investigated. The study showed that the best lapping results were obtained for each lapping step when the lapping pressure was 44.54 kPa, the rotational speed of the lapping disc and pendulum was 60 r/min, and the B4C mass fraction in the lapping solution was 15%. The material removal rates of abrasive W40, abrasive W28, abrasive W14 and abrasive W7 lapping were 83.12, 57.32, 27.54 and 9.53 μm/min, respectively, and the surface roughness after lapping was 0.763, 0.489, 0.264, and 0.142 μm, respectively. The subsurface damage of the step-by-step lapping was 3.041 μm, which were measured by cross-section microscopy method, and needed to be removed by the subsequent polishing; The relationship between subsurface damage depth and surface roughness of YAG crystals after lapping with this lapping parameter is hSSD=41.46×Ra4/3. The study can provide guidance for the actual processing and production of YAG crystal components.

Long afterglow materials are widely used, but their luminescence mechanism is difficult to be universally explained. For Sr2MgSi2O7:Eu2+,Dy3+ silicate long afterglow material with good luminescence-afterglow properties, the molecular models of Sr2MgSi2O7 substrate, Eu doped and (Eu,Dy) co-doped Sr2MgSi2O7 were constructed, and the first-principles calculations were carried out. From the perspective of electronic structure, the electron transition trapping path is revealed to explain the persistent luminescence mechanism of Sr2MgSi2O7:Eu2+,Dy3+. The results showed that the doping of Eu and Dy ions changed Sr2MgSi2O7 from an indirect band gap semiconductor to a direct band gap semiconductor. The Dy 5d state was mainly located between the Fermi level and the Eu 5d state, and it had energy overlap with the Eu 5d state, which confirmed the rationality of Dy3+ as an electron trap. The luminescence process of Sr2MgSi2O7:Eu2+,Dy3+ was revealed, which is helpful for the subsequent regulation and improvement of optical properties.

The research of high-efficiency trichromatic phosphors based on vltraviolet/near-ultraviolet (UV/n-UV) excitation is of great significance for the development of white light-emitting diode (LED) applications. A series of Ce3+, Tb3+ or Eu3+ single-doped CaxMgyAlmSinOz (i.e., Ca2Mg0.25Al1.5Si1.25O7, Ca2Mg0.5AlSi1.5O7, Ca2Mg0.75Al0.5Si1.75O7, and Ca20Al26Mg3Si3O68) trichromatic phosphors were synthesized by a high-temperature solid-phase method. The crystal structure and band gap of samples were investigated by Rietveld refinement, crystal structure simulation and density functional theory calculation, and the effect of stoichiometry-regulating crystal field on the luminescent performance was analyzed. High-quality blue, green and red trichromatic phosphors with quantum efficiencies of 28.13, 26.42 and 26.75, fluorescence lifetime of 42.23 ns, 2.88 ms and 2.21 ms, as well as a good thermal stability were selected to compare their luminescent performance. Finally, the prototypes of white LED were fabricated with the trichromatic phosphors for UV chip, and their performance parameters (i.e., luminous efficiency, correlated color temperature and color rendering index) were tested. The results show that these phosphors have a promising potential in the application of UV-excited white LEDs.

Using blue-emitting UiO-66-NH2 with red-emitting Eu-MOF as fluorescence groups, a ratio fluorescence probe (UiO-66-NH2@Eu-MOF) was constructed and successfully applied to the determination of trace PO43- ions in environmental water samples. A ratiometric fluorescent probe for the determination of trace PO43- ions in environmental water samples was constructed via combining blue-emitting UiO-66-NH2 with red-emitting Eu-MOF. As PO43- ions concentration increases, the coupling of PO43- ions with Zr4+ ions in UiO-66-NH2 leads to a weakened ligand-metal charge transfer effect, effectively restoring the luminescence of UiO-66-NH2. Also, an intense coordination of Eu3+ ions with PO43- ions can hinder the ligand-metal energy transfer, destroy the "antenna" effect, and lead to the quenching of Eu-MOF fluorescence. Under optimal conditions, a ratio of the fluorescence intensity at 445 nm to the fluorescence intensity at 633 nm is linearly related to PO43- ions concentration in the range of 1-12 μmol/L. The sensor constructed has a good selectivity and accuracy, thus providing an effective way for the rapid detection of PO43- ions.

Piezoelectric materials are an extremely important functional materials that can be used for piezoelectric sensors, transducers and actuators due to their positive/reverse piezoelectric effects. These materials are widely used in aerospace, nuclear energy and medical fields. Among them, in the fields of aerospace and nuclear energy, piezoelectric materials have a harsh service environment of high radiation, which puts higher requirements on the radiation resistance of piezoelectric materials. This review summarized the effect of radiation on the crystal structure and electrical properties of piezoelectric materials with a perovskite structure, i.e., lead zirconate titanate (Pb(Zr, Ti)O3), potassium niobate (KNbO3), and barium titanate (BaTiO3) as well as bismuth layered structure piezoelectric materials such as Bi4Ti3O12. It is indicated that at high doses of radiation, the phase structure of piezoelectric materials is maintained in the ferroelectric phase, but the grains are damaged to some extent, while the electrical properties of piezoelectric materials generally weaken with increasing radiation doses. However, radiation can improve the fatigue resistance of piezoelectric materials, and radiation can be thus used as a promising way to modify piezoelectric materials.

The flexoelectric effect is a mechanical-electric coupling effect between strain gradient and electric polarization (i.e., positive flexoelectric effect) or electric field strength gradient and mechanical strain (i.e., converse flexoelectric effect). Unlike the piezoelectric effect, the flexoelectric effect, which is not limited by material symmetry and the Curie temperature, increases with decreasing the material size, thus attracting much attention and having a promising application. This review introduced the history of flexoelectric effect, measurement of flexoelectric coefficient, and mechanism to enhance flexoelectric effect. Recent studies on its application in the realm of sensors, actuators, mechanical memories, flexoelectric piezoelectric composites, energy harvesters, and electronic devices were highlighted. In addition, the further development of flexoelectric effect was also prospected.