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Low-cost magnesium aluminate spinel ceramics were successfully synthesized from the minerals of magnesite(M) and bauxite(B) via the one-step sintering method. The effect of the ratio of bauxite to magnesite on the phase evolution, microstructure, as well as the mechanical properties was thoroughly investigated. The phase structural analysis indicated that Mg2+ or Al3+ ions were dissolved in the spinel lattice and formed Mg-rich/Al-rich spinel MgAl2O4 (MA). The microstructure analysis revealed that the liquid phase gradually appeared with the increment of bauxite content. Appropriate but not saturated cation solution had the effects of structural densification, homogenization of crystal grains, and the enhancement of strength. Ceramics with 1.31 bauxite to magnesite stoichimetric ratio exhibited the highest density of 3.43 g/cm3 and flexural strength of 93.5 MPa.

The in-situ formed MgAl2O4–CaAl12O19 (MA–CA6) composites were fabricated in this study. To clarify the influence of the evolution of CA6 phase on the properties of MA–CA6 composites, the sintering temperature was carried out at 1200–1700 °C for 2 h. The results show that the growth and development of CA6 grains improves the densification and flexural strength of MA–CA6 composites. The formation of MA phase occurs at 1200 °C, while the CA6 phase is formed by the reaction of CaAl4O7 (CA2) and Al2O3 appears at 1400 °C. The plate-like CA6 grains intersect with each other, presenting regular hexagonal morphology with a high aspect ratio at 1500 °C. The CaO–Al2O3–SiO2 phase acts as an interface phase to regulate the growth and development of MA and CA6 grains. The CA6 phase was crystallized from the transient liquid phase CaO–Al2O3–SiO2 to significantly increase its thickness at 1600 °C. At the same time, as the sintering temperature rises, the apparent porosity of the sample decreases from 24% at 1400 °C to 4% at 1600 °C, and the flexural strength correspondingly increases from 96.6 MPa to 167 MPa. However, the suitable sintering temperature should not exceed 1600 °C for better properties of the composites.

Low-temperature photoluminescence was employed to investigate the defects of 4H–SiC crystals after high-energy electron irradiation, and the annealing characteristics and dependence of the detecting temperature and irradiation doses were investigated. Results showed that the emission, associated with carbon antisite–vacancy (VCCSi)+ defects was dominant in the electron-irradiated 4H–SiC crystal. With increase in detecting temperature, the emission decreased demonstrating red-shifted, and the full width at half-maximum broadened, which was attributed to the increase in the concentration of carriers arising from thermal activation at high temperature. The emission intensity was the highest value at an irradiation dose of 7.9 × 1018 e/cm2, and then began to decrease. This revealed the lattice damage caused by long-term high-energy irradiation, which reduced the intensity of the defect radiation in the spectrum.

MgAl2O4–CaAl12O19 (MA-CA6) composites were prepared using Al2O3, MgO and CaCO3 powders as the raw materials by solid-state reaction sintering at 1200–1600 ℃. The effects of ZnO addition on the physical and mechanical properties, microstructure, and phase composition were investigated. ZnO additive can significantly increase the amount of MA due to the formation of the (Mg1-xZnx)Al2O4 solid solution, which greatly improves the densification and the flexural strength of the composites after sintering at 1600 ℃. Flexural strength reaches a maximum of 192.1 MPa and apparent porosity is 8.5 % when 2 wt% of ZnO is added. This is resulted by the close bonding between MA and CA6 grains. However, further increasing the ZnO content results in a slight decrease in the strength of the composites due to the weakening of the plate-like CA6 bridging effect and the concentration of Zn2+ at the MA grain boundary.

Low-density and high-strength ceramic proppants were successfully prepared from bauxite and feldspar. The addition of feldspar greatly reduced the sintering temperature (below 1300℃). The effects o...

To realize the effective recycling of solid waste fly ash (FA) and reduce the preparation cost of microwave absorbent, the Fe-loaded fly ash composites (FeFA) were synthesized using FA. In this stu...

The self-toughening property of platelet calcium hexaluminate (CaAl12O19, or CA6) grains causes great interest in the in-situ CA6 in engineering ceramics. MgAl2O4–CaAl12O19 (MA-CA6) composites with SnO2 additive by solid-state reaction sintering at 1200–1600 °C were prepared. The physical and mechanical properties, microstructure, and phase composition were investigated. The results showed that the addition of SnO2 could accelerate the formation of MA and CA6 due to the appearance of the (Mg1-2xSnx)Al2O4 solid solution in the composites. The composites, with the addition of 1 wt% SnO2 and sintered at 1600 °C, presented denser microstructures, and accordingly, the flexural strength reached a maximum of 179 MPa. This was a result of the close bonding between MA and CA6 grains. However, increasing the SnO2 content further resulted in a decrease in the densification of the composites due to the bridging effect of plate-shaped CA6 and the lamellar growth of CA6. Therefore, adding the appropriate amount of SnO2 is important in improving the properties of MA-CA6 composites.

There are a few studies reported in the literature describing the conversion of intrinsic defects but the involvement of nitrogen-interstitials in diamond has not been reported so far. In this pape...

The negative differential resistance (NDR) effect was observed in a Pt/BiFeO3/TiO2/BiFeO3/Pt memory cell by using light-illumination as extra stimulation. Further, the coexistence appearances and gradually becomes obvious when the device is exposed to light-illumination, which display an excellent stability and reversibility of the coexistence of NDR and resistive switching (RS) at room temperature. Through analysis of the physical conduction mechanism, it is expected that a large number of photo-generated charge carriers are induced under light-illumination on the surface and interface of the heterojunction is responsible for the appearance of this coexistence phenomenon. Importantly, the NDR effect is strengthened by the competition transfer of charge carrier in the polarized electric field under light-illumination. This work shows that the coexistence of light-modulated NDR and RS can deeply explore the potential applications of light-controlled multifunctional devices.

High strength ceramic proppants are a significant factor during the hydraulic fracturing process. Although many system ceramic proppants have been developed, their strength remained relatively low....

To realize the resource utilization of gangue, the gangue was effectively recycled to prepare ceramic-based microwave absorbents. The synthesis process mainly involved the pelletizing of gangue, the loading of precursor solution and in situ carbothermal reduction. Furthermore, the obtained FeG composites were measured and characterized in terms of the phase composition, microstructure and performance. The results showed that FeG500 exhibited excellent electromagnetic absorbing ability, the effective absorption bandwidth remained at 4.1 GHz and the minimum reflection loss value reached −41.9 dB correspondingly when the coating thickness was 2 mm. This mainly arises from the interfacial polarization effect and the effective impedance match. The FeG composites prepared by gangue are promising candidates as light-weight and high-performance microwave absorbents in future applications. The novel method in this work may provide a new avenue for the resource utilization of gangue, turning waste into treasure, during which the economic and environmental benefit can be achieved.

Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6 wt% AlF3, and sintered at 1200 °C, exhibited the highest flexural strength of 59.1 MPa, and had a bulk density of 1.32 g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources.

The photoluminescence (PL) spectra were employed to study the optical centers generated by the B ion irradiation in Ib diamond. The luminescent spectra with zero phonon lines (ZPLs) centered at 573, 575.8, 637.9, 390.8 nm and the most of the vibronic bands in vicinity of the ZPLs were detected using 532 and 325 nm lasers. The function of spot scan, surface scan and depth scan of Renishaw micro-Raman spectrometers were performed to understand spatial distribution of the resulting high density optical centers at 80 K. Through the spatial distribution of 575.8 and 637.9 nm optical centers, it was found that it’s more advantageous to form 575.8 nm optical centers for high density nitrogen diamond irradiated by B ion and subsequent annealing. Based on the principle of electrical neutrality and the degree of lattice distortion, it was proposed that a possible defect evolution process of the B-related optical center.

Providing access to up-to-date and expensive instruments for a large classroom is challenging for courses of analytical chemistry and physical chemistry, where knowledge on analytical methods or demonstration of phenomena is associated with a specialized instrument. In this technology report, we present our solution to this challenge: a virtual reality (VR) chemical educational tool that provides in situ user experience on research equipment to a large classroom. The VR educational tool consists of a VR camera in the laboratory attached to a teaching assistant who performs the experiment and many virtual reality playing devices in a classroom watched by students. The experience of experimenting is shared with the students in the classroom. Moreover, the VR educational tool can also provide an immersive experience on laboratory demonstrations to the general audience for outreach, without the constraint from safety concerns. Further utilization of the VR educational tool is expected to remove the barrier between the lecture room and the laboratory and enable new pedagogical methods for lectures in STEM education.

Low-cost ceramic proppants were successfully prepared from natural bauxite and solid waste coal gangue via CaCO3 additive. 40 wt% of bauxite in raw materials was replaced by coal gangue, which significantly reduced the manufacturing costs. The apparent density, bulk density, acid solubility and breakage ratio of the proppant sintered at different temperatures were systematically investigated. The phase composition and morphological structure were determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the amount of liquid phase affected the solid phase reaction velocity by changing sintering mechanism. When the sintering temperature was 1350 °C, the optimum size of the mullite crystal particles and the optimum amount of the liquid phase were observed and the samples exhibited the best performance.

Pollution is a pressing problem in the context of sustainable development, a solution to which is to reutilize waste resources. Herein, coal gangue was recycled to prepare Fe3O4 /C/CG and Fe/C/CG composites for microwave absorption via a facile method. The synthesis process involves loading a precursor solution of starch and ferric nitrate onto coal gangue matrix and then conducting the in-situ carbothermal reduction. The initial starch mass and carbothermal temperature significantly affect the dielectric and magnetic properties, further affect microwave absorption performance of the composites. For the Fe 3O4/C/CG and Fe/C/CG composite, the minimum reflection loss could reach −45.1 dB and −27.8 dB, respectively. And the maximum effective absorption bandwidth of Fe/C/CG was 4.7 GHz. The strong microwave attenuation and impedance matching, which stemmed from the conductive graphitized carbon, the abundant interfaces of the highly dispersed carbon and iron species on the matrix, must account for the excellent performance.

ZnO flower-like nanostructures have been successfully synthesized by a new and facile hydrothermal method. Their crystal structures and photocatalytic performance were also investigated. The amount of surfactant cetyltrimethyl ammonium bromide (CTAB) added to the precursor had an important effect on the ultimate morphology of the ZnO flower-like nanostructures. As the CTAB amount increased, the petals of the ZnO nanoflowers architecture changed from nanorods to nanosheets. In addition, for the nanoflowers assembled by nanosheets, the thickness of nanosheet can be controlled by adjusting the CTAB amount. The plausible growth mechanisms of the ZnO flower-like nanostructures were proposed. Furthermore, the nanosheets-assembled nanoflowers exhibited better photocatalytic performance than the nanorods-assembled nanoflowers toward Rhodamine B owning to their larger specific area and more OH groups absorbed on the nanosheet surface.

In this work, the optical centers of β-Ga2O3 irradiated with 200 keV electrons were studied by photoluminescence (PL) spectroscopy. The oxygen vacancy-related center at 690 nm were enhanced after irradiation together with a new zero phonon line (ZPL) at 697 nm. The temperature dependence of these optical centers were carefully detailed and discussed. As the increase of measurement temperature, the ZPLs showed red-shift, intensity quenching and full width at half maximum (FWHM) increase. These data were fitted by the corresponding physical formula. Results showed compared with the 690 nm emission, the 697 nm emission had a similar intensity distribution, a weaker lattice relaxation strength, a weaker lattice vibration, and a lower thermal softness. These results indicated that the 697 nm emission was probably associated with the oxygen interstitials.

Diamond has the advantages of excellent thermal conductivity, and it is the material with the largest thermal conductivity currently known, which makes it the ideal heat sink. However, in the process of processing or as a heat sink for electronic devices, diamond is often exposed to a high-frequency, high-voltage, high-temperature, and high-energy environment, which has greatly affected the performance of diamonds. Therefore, in this paper, it systematically explores the influence of near threshold energy electron irradiation and annealing at different temperatures on the thermal conductivity of IIa diamond by the method of laser excited Raman spectroscopy. The results show that before 900 °C annealing, the main factor affecting thermal conductivity in IIa diamond is the large number of vacancy defects caused by near threshold energy electron irradiation. The irradiation and annealing both affect the thermal conductivity by controlling the vacancy defects concentration.

In order to realize the sustainable development of turning waste into treasure and treating pollution with waste, the feasibility of resource utilization of fly ash (FA) to solve electromagnetic pollution was investigated. In this study, FeCo/carbon-loaded FA composites (FeCo/C/FA) were successfully synthesized via a facile one-pot method using solid waste FA as the raw material. Such ingenious design endowed FA enhanced microwave absorption (MA) capacity, and the MA mechanism derived from conductivity loss, multiple interface polarization and impedance matching. As expected, the FeCo/C/FA composites exhibited the excellent MA performance, its minimum reflection loss (RLmin) reached − 32.5 dB with the coating thickness of 1.5 mm. When the coating thickness was adjusted to 2.0 mm, the maximum value of effective absorption band was measured to be 4.7 GHz. This work confirms that FA can be directly recycled to construct a low-cost microwave absorber in the treatment of electromagnetic pollution.

Low-density bauxite-based ceramic proppants were prepared at sintering temperatures below 1300°C by adding solid wastes coal gangue and magnesium slag. The addition of solid wastes greatly decreases sintering temperature and preparation cost. The density and strength of ceramic proppants were tested according to the standard, and the morphology and phase composition were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the main crystal phases are corundum and mullite, and the most suitable sintering temperature is 1250°C. At the sintering temperature apparent density is 2.84 g/cm3, and breakage ratio is 7.16% under 52 MPa closed pressure. Magnesium slag will react with some oxides of raw material at high temperature and form liquid phase, making the structure of ceramic more compact. The prepared ceramic proppants meet China industrial standard requirements SY/T5108-2014.

In this study, the mullite-quartz-based proppants were successfully prepared by using the coal gangue as the raw materials. Then, the effects of the additive and the sintering temperature on the composition, microstructure, and properties of the proppants were investigated. Results showed that the proppants sintered at 1250°C with the 10 wt% bauxite additive presented the best performance, which was very close to that of the quartz-proppant, and met the operational requirements of the 52 MPa coal bed methane wells. The viscous flow mechanism of the liquid phase formed during the sintering process also promoted the arrangement of the grains, thus benefiting the densification and the strength of the proppants.

Low-density ceramic proppants were prepared from calcined flint clay and solid waste coal gangue by pelleting, drying, screening and sintering, namely solid state sintering method. The density and ...

The second grade bauxite and feldspar were used to synthesize ceramic proppant materials. Phase structure and microstructure of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It was found that the feldspar, as a sintering aid, was beneficial to generate liquid phase during the sintering process. The formed liquid phase, not only promoted the densification of the samples, but also reduced the sintering temperature. With the content of feldspar increasing, the sintering temperature gradually decreased. When the content of feldspar was 4 wt.%, the breakage ratio of the samples was reduced to the lowest level of 2.2% at 1400°C under 52 MPa closed pressure, which met the requirement of Chinese Petroleum and Gas Industry Standard (SY/T 5108-2014). Moreover, the sintering temperature was reduced by 100°C compared with the proppants without adding feldspar.

Phase evolution, microstructure, dielectric performance, polarization, breakdown strength as well as energy-storage behaviors for the lead-free niobates glass-ceramics with Sm2O3 were systematically investigated. Two crystallographic structures of tetragonal tungsten bronze and orthorhombic perovskite complex phases were obtained and Sm3+ entered into the crystalline phases. The optimal microstructure of the glass-ceramic was obtained with Sm2O3 of 2 mol%. Both dielectric constant and polarizability were enhanced with increasing Sm2O3. The breakdown strength and energy-storage behaviors of the glass-ceramics were also improved by increased Sm2O3. The highest breakdown field of 21.2 kV/mm, the highest charged (0.74 J/cm3) and discharged energy density (0.45 J/cm3) were obtained in the glass-ceramic with 2 mol% Sm2O3. It is due to the reduced interfacial polarization in this particular composition.

Self-assembled porous In2O3/ZnO heterostructures were prepared by a low temperature solution combustion synthesis method, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The results indicate that the as-synthesized porous In2O3/ZnO heterostructures were constructed from a large number of In2O3 and ZnO nanoparticles and showed high gas sensing performance toward Cl2. Compared with pure ZnO and other heterostructure sensors, the porous In2O3/ZnO heterostructures with an appropriate molar ratio of In2O3 : ZnO exhibited highly enhanced gas sensing performances toward Cl2. An extremely high sensitivity of 6610 could be reached when exposed to 50 ppm Cl2 at 370 °C; also, In2O3/ZnO heterostructures showed high selectivity toward Cl2. Furthermore, the gas sensing mechanism was discussed.