Polyimide film is one of the most commonly used organic film materials for spacecrafts. In the low-Earth orbit (LEO) environment, the polyimide film applied to the surface of spacecraft will be eroded by atomic oxygen. Generally, performance failure will occur in about one year due to the erosion effect, affecting the service life of spacecrafts. The siloxane coating prepared by plasma-enhanced chemical vapor deposition (PECVD) method has good atomic oxygen resistance, which can reduce the atomic oxygen erosion rate of polyimide film to less than one-thirtieth. At the same time, the coating also has good light transmittance, flexibility and bendability. In recent years, there have been many studies on the effects of electrode spacing, power, pressure and other parameters on the properties of siloxane coatings prepared by PECVD at home and abroad, but the effect of oxygen flow rate on the atomic oxygen resistance of siloxane coatings has not been reported. This work focuses on the deposition rate, cross-sectional morphology, composition and structure of siloxane coatings prepared by PECVD under different oxygen flow rates. The atomic oxygen effect test was carried out on the coatings, and the mass loss data of different samples were successfully collected. The oxygen flow rate parameters of coatings with excellent atomic oxygen resistance has been obtained, which provides support for the research of atomic oxygen resistant coatings.

The coating samples were prepared by the PECVD method using a self-developed continuous roll-to-roll PECVD coating equipment. The substrate material for coating was 50 μm thick DuPont Kapton HN polyimide film. The reactant gases were Alfa Aesar hexamethyldisiloxane monomer (HMDSO) and oxygen (O₂). With a fixed HMDSO flow rate of 25 mL/min, the O₂ flow rate was adjusted to 4, 8, 12, 16, 20, and 24 mL/min respectively, while maintaining a deposition pressure of 8 Pa and a reaction power of 400 W. This setup was used to investigate the deposition rate, structure and composition of deposited coatings under different precursor ratios. The coatings were subjected to atomic oxygen irradiation tests using a microwave atomic oxygen generator. The atomic oxygen flux was calibrated using DuPont Kapton HN polyimide film. The composition of the coatings was analyzed using the INVENIO R Fourier Transform Infrared (FTIR) spectrometer from Bruker Optics, Germany. In this test, the siloxane coating was deposited on the surface of a nearly mid-infrared transparent potassium bromide (KBr) single crystal to reduce the influence of the substrate on the test results. The surface and cross-sectional morphology of the coatings were examined using a Zeiss Sigma 500 scanning electron microscope from Germany, and the thickness of the coatings was also determined.

Under low oxygen flow rates, the deposition rate of the coating was significantly higher than that under high oxygen flow rates. This was attributed to the fact that at lower oxygen flow rates, most of the precursor reactants contribute to the formation of the coating, resulting in a higher deposition rate. Conversely, at higher oxygen flow rates, the probability of reactions between HMDSO and O₂ increases, leading to an increase in the amount of gaseous products generated and a corresponding decrease in the deposition rate. All the siloxane coating samples exhibited a fairly dense cross-sectional morphology with no observable crystallization. When the oxygen flow rate was 8, 12, or 16 mL/min, the coating cross-sections were smooth and free of texture. At 4 mL/min, however, local damage was observed in the coating cross-section, possibly related to an incomplete formation of the composite network structure. At 20 and 24 mL/min, the coating interfaces remained dense but exhibited a textured structure, indicating the formation of local atomic ordered arrangements within the coating and the generation of structural stress. The FTIR spectra of the coatings revealed that as the oxygen flow rate increased, the intensities of rocking and stretching vibration peaks (both symmetric and asymmetric)belonging to the Si-O bond increased, indicating an increase in the content of silicon oxides in the coating. Concurrently, the intensities of the methyl bending vibration peaks in Si—(CH₃)₂, Si—(CH₃)₃, and Si—CH₃, as well as the C—H stretching vibration peak, decreased with increasing oxygen flow rate, suggesting a reduction in the methyl content of the coating. The stretching vibration of the O—H bond became more pronounced, indicating that higher oxygen concentrations favored the combination of H and O elements. Atomic oxygen exposure tests on siloxane coatings prepared under different oxygen flow rates showed that as the oxygen flow rate increased from 4 mL/min to 20 mL/min, the mass loss of the coatings decreased exponentially. However, when the oxygen flow rate reached 24 mL/min, the mass loss increased sharply. Coatings prepared at lower oxygen flow rates exhibited smooth surface morphologies without cracks, holes, or other defects. In contrast, the siloxane coating prepared at 24 mL/min exhibited a large number of cracks, with the coating tilting at the crack sites. These severe cracks provided channels for atomic oxygen erosion, leading to a higher atomic oxygen erosion rate for the sample.

During the deposition process of siloxane coatings, the deposition rate is highest when the oxygen flow rate is 8 mL/min, and then it decreases as the oxygen flow rate increases. The cross-section of the siloxane coatings grown under low oxygen flow conditions does not exhibit visible grains or grain boundaries. In contrast, the cross-section of siloxane coatings grown under higher oxygen flow conditions indicates the occurance of textures, although they haven't displayed typical grain morphologies, which may be related to the stress within the coatings. The increase in oxygen flow rate can facilitate the oxidation of CH₃ in the gas phase during PECVD and the formation of siloxane coatings. As the oxygen flow rate increases, the mass loss of the coating under atomic oxygen exposure decreases at first and then increases. At lower oxygen flow rates, insufficient oxidation of HMDSO results in the presence of more methyl and hydroxyl groups in the coating. These methyl and hydroxyl groups are easily oxidized by atomic oxygen to produce volatile gases, leading to higher mass loss. However, at higher oxygen flow rates, cracks appear in the coating, causing an increase in mass loss. This study demonstrates that a suitable oxygen flow rate is crucial in optimizing the performance of siloxane coatings by promoting the reactions of HDMSO and forming a dense microstructure,

ZnO varistor ceramics have some advantages of high nonlinear coefficient, low leakage current and low production cost, which are widely used in the protection of power systems and electronic equipment. With the development of electronic devices in the direction of better performance and miniaturization, the electrical performance of ZnO varistor ceramics needs to be further improved. It is thus necessary to prepare ZnO varistor ceramics with a high breakdown voltage and a uniform fine grain size. In common ZnO-Bi₂O₃-Sb₂O₃ varistor ceramics, Bi₂O₃ and Sb₂O₃ are the two most important elements, and Bi₂O₃ and Sb₂O₃ doped in a certain proportion play an important role in the optimization of electrical properties and microstructure regulation of ZnO varistor ceramics. The melting point of Bi₂O₃ is 825 ℃ and the melting point of Sb₂O₃ is 655 ℃ in the high-temperature sintering process volatile, resulting in the loss of components and the increased porosity, structural uniformity, deterioration of electrical properties of ZnO varistor ceramics. Therefore, reducing the sintering temperature of ZnO varistor ceramics (i.e., below 1 000 ℃) is a necessity, which is expected to provide the experimental basis for the realization of pure silver internal electrode co-firing of multi-layer chip ZnO varistor elements.

ZnO-Bi₂O₃ based varistor ceramics with a Bi∶Sb molar ratio of 4∶1 were prepared by a traditional electronic ceramics process. ZnO powder was mixed with Bi₂O₃, Sb₂O₃ powder, agate ball and deionized water in a certain proportion and then the mixed slurry was ground in a planetary ball mill. The ground mixed slurry was dried at 110 ℃, then ground and passed through the 100 mesh screen. 5% polyvinyl alcohol (PVA) solution was used as a binder for granulation, and then pressed into green billets with a diameter of 13 mm and a thickness of 2 mm. The green billet was firstly discharged in a muffle furnace at a rate of 2 ℃/min to 500 ℃, and then sintered in a sintering furnace at different temperatures (i.e., 880, 900, 920, 950, and 980 ℃, respectively). The obtained sample was polished and silvered. The final sample size was φ10 mm×1 mm. The phase was analyzed by X-ray powder diffraction (XRD). The backscattering mode of field emission scanning electron microscopy (FESEM) was used to characterize the surface morphology of the samples, and the distribution of elements on the surface of the samples was analyzed by X-ray energy spectroscopy (EDS). The electrical properties of the samples were measured by a varistor tester, and the grain boundary characteristic parameters were measured by wideband dielectric impedance spectrometry.

In this experiment, 800 ℃ is selected as a turning point. When the temperature is higher than 800 ℃, the sample is heated at a lower rate and the sintering temperature is below 1 000 ℃, obtaining fully developed ZnO grains. The grain size of the two groups of samples is small and evenly distributed. The molar ratio of Bi₂O₃ and Sb₂O₃ of the two groups of samples is 4∶1. When the sintering temperature is 920 ℃ or above, the breakdown voltage of the two groups of samples is similar. At the Bi₂O₃∶Sb₂O₃ molar ratio of 4∶1, the breakdown voltage of the sample is more related to the Bi₂O₃∶Sb₂O₃ molar ratio rather than to the total doping amount of Bi₂O₃ and Sb₂O₃. This means that the breakdown voltage regulation can be achieved with less doping of Bi₂O₃ and Sb₂O₃. The high breakdown voltage ZnO varistor ceramics can be prepared by sintering at a low temperature, and the breakdown voltage of doped with the same proportion of Bi₂O₃ and Sb₂O₃ is similar in the less addition of Bi₂O₃ and Sb₂O₃, thus providing an effective way for the low-carbon preparation of ZnO varistor ceramics.

Low-temperature sintering could effectively inhibit the growth of ZnO grains. The breakdown voltage of the two groups of samples was high, ranging from 599-1 154 V/mm. ZnO grains of all the samples were fully developed, and the average size of ZnO grains of the samples was 2.7-3.6 μm. In addition, the grain size distribution and microstructure of the sample were more uniform. The optimum comprehensive electrical performance of the sample sintered at 900 ℃ was obtained (i.e., the breakdown voltage of 1 154 V/mm, the nonlinear coefficient of 13.7, and the leakage current of 39 μA).

Environmental protection and sustainable development have attracted recent attention. Especially, the lead-free reproduction of ancient ceramic glazes with rich historical and cultural values becomes a common concern for both academia and industry. Jizhou kiln is one of the well-preserved ancient kiln sites in China, and is one of the famous folk firing kilns during the Song and Yuan dynasties. Jizhou kiln green glaze is colored in addition to the chemical composition as well as coloring mechanism. The sintering temperature is also one of the key factors influencing the ceramic glaze color, microstructure, and physical properties. However, the current research on the sintering process of copper-green glaze is still insufficient. The lead-free preparation of green glaze from the Jizhou kiln was achieved using the conventional ceramic raw materials in the Jingdezhen area and Cu²⁺ coloring. The influence of sintering temperature on the formation of glaze color, microstructure, and color-presenting mechanism of lead-free green glazed ceramics, as well as the mechanism of the effect of sintering temperature on the glaze's physical properties were systematically investigated. This study provides a scientific guidance and a technical support for the lead-free reproduction of green-glazed porcelain of Jizhou kiln to further promote the protection and inheritance of traditional ceramic culture, and to provide an important reference basis for the sintering behavior of other types of glazes.

A base glaze was prepared using 23% (in mass fraction, hereinafter the same) wollastonite, 9% talc, 20% feldspar, 26% quartz, 10% kaolin, 8% smelter's ash, and 4% zinc oxide (ZnO) from mineral raw materials originating in the Jingdezhen area of Jiangxi Province, China, with 4% CuO as a coloring agent. ZnO (99% analytically pure), CuO (99% analytically pure), and glazes were applied to blanks by an impregnation method (blanks were already 900 ℃ plain firing), and the impregnation time was 20 s. Subsequently, the samples were put into a box-type resistance furnace and sintered in air. Six lead-free green glaze samples sintered at different temperatures (i.e., 1 250, 1 260, 1 270, 1 280, 1 290 ℃ and 1 300 ℃) were obtained.

The chemical composition of the mineral raw materials was analyzed by energy-dispersive X-ray fluorescence spectrometry. The phase structure of the sample glazes was analyzed by X-ray diffraction and micro-confocal laser Raman spectrometry. The optical photography of the sample surfaces was carried out using a super depth of field microscope. Scanning electron microscopy was used to observe the microstructure of the samples after etching with 5% HF solution for 20 s as well as the fractional phase structure in the glaze. The chromaticity values and reflectance spectra of the glazes were determined by benchtop spectrophotometry as well as a UV-Vis-IR reflectance spectrophotometry. The elemental valence states were analyzed by X-ray photoelectron spectroscopy.

The optical analysis indicates that the glaze surface changes from greenish blue to light green and green with the increase of sintering temperature, and reaches the optimum effect of glaze surface at 1 280 ℃, at which time the glaze surface of the samples is smooth and uniformly colored, with a strong sense of glassy feeling. The results of XRD patterns and Raman spectra show that the glaze layer is composed of a glassy phase and trace SiO₂ crystals, and the phase of glaze layer is not a main factor of color presentation. The structural analysis shows that the glaze layer is not a homogeneous material, it is composed of two kinds of phase separation structures, i.e., round and worm-like. The phase separation structure shrinks and grows further to form a large-size round phase separation droplet, and the incident light undergoes Mie scattering with the increase of sintering temperature and the gradual decrease of high-temperature viscosity of the glaze layer, which produces a white opalescence and deepens the glaze surface coloration. Lead-free green glaze is mainly due to the effect of Cu²⁺ color presentation. As the sintering temperature increases, the Cu²⁺ concentration gradually increases, and copper ions and six bridging oxygen (O^b) form a six-coordinated structure, mainly presented in green. The coloration of lead-free green glaze is a result of the synergistic coupling of the phase separation structure and the valence state of copper ions, and the lead-free green glaze with a stable coloration and a good glaze quality can be prepared via optimizing the sintering temperature.

Conclusions The viscosity of the glaze layer gradually decreased, and the glaze surface showed greenish blue, light green, and green in turn, and the optimum effect of the glaze surface reached at 1 280 ℃ as the sintering temperature increased. The glaze was mainly dominated by the green coloration of Cu²⁺, and the molar ratio of Cu⁺/Cu²⁺ gradually increased, while the glaze changed from blue-green to lime green as the sintering temperature increased The round and worm-like phase-separated structures both appeared in the samples, and the phase-separated structures contracted at higher sintering temperatures and grew further into large-sized round phase-separated droplets, with Mie scattering occurring to produce a white opalescence that deepened the glaze coloration; The color-presentation mechanism of the lead-free green glaze was a result of the synergistic coupling of copper ion valence and phase-separated structures.

Organic compound formaldehyde (HCHO) is a toxic volatile gas with an irritating odour, which is mainly derived from building materials, furniture and various adhesive coatings. Living in an environment containing formaldehyde gas for a long time can cause a series of hazards to human health, such as headaches, allergies, nausea, and even genetic mutations and leukaemia. It is thus necessary to design a gas sensor with a superior sensing performance to detect formaldehyde in real time. ABO₃ type chalcogenide metal oxides have attracted much attention in sensor research, but their application is restricted due to the drawbacks such as poor sensitivity and high operating temperature. Many studies indicate that the modification of metal oxides with two-dimensional transition metal dihalides (2D TMDs) is one of the effective strategies to improve the gas sensing performance, and among the 2D TMDs materials, WS₂ has aroused much interest in sensor research because of its high specific surface area, good thermal stability and excellent electron mobility. The gas sensor performance of metal oxides can be improved via the combination of WS₂ to form a novel nanocomposite material. Hence, in this paper, a series of WS₂-CdSnO₃ composites with different mass ratios were prepared by an ultrasonic mixing method. The microstructure, crystal structure, and valence state structure of WS₂-CdSnO₃ composite material were characterized, and the gas sensing performance of the composite material was analyzed.

CdSnO₃ was prepared with Cd(NO₃)₂·4H₂O (AR, Shanghai Sarn Chemical Technology, China) and SnCl₄·5H₂O (AR) (Shanghai Aladdin Reagent Co., China). CdSnO₃ was ultrasonically compounded with WS₂ (99.9%) to obtain WS₂-CdSnO₃ composites. The physical phase composition, surface morphology, elemental composition, valence and pore size distribution and specific surface area of the composites were characterized by a model SmartLab SE X-ray diffractometer (XRD, Rigaku Co.,), scanning electron microscope (SEM, Tescan Mira Lms), a model K-Alpha X-ray photoelectron spectrometer (XPS, Thermo Scientific Co., USA), and a model ASAP 2460 fully automated specific surface and porosity analyser (BET, Micromeritics Co., USA).

For the determination of gas sensing performance of WS₂-CdSnO₃ composite material, WS₂-CdSnO₃ composite material was put into a mortar with 1-2 drops of terpineol, and thoroughly mixed and ground. The paste was evenly applied to the outer wall of the alumina ceramic tube with a small brush, and an Ni-Cr heating wire put through the ceramic tube and welded firmly to the hexagonal base. The operating temperature was indirectly controlled via adjusting the amount of power added to the two sections of the heating wire. The sensitivity to gases is expressed as a ratio of the stable resistance value of the gas sensing material in air to a stable resistance value in the gas tested. The gas sensing performance of the composites was investigated at a relative humidity of 55% (except for humidity tests).

From the SEM images, the microcube appeared is CdSnO₃, and the cubes structure is agglomerated on the surface of layered WS₂. Based on the EDS analysis, there are five elements Cd, Sn, O, W and S in the composites. It is indicated that WS₂-CdSnO₃ can be prepared. According to the XPS analysis, there are more oxygen vacancies in the sample WSC-2, which can provide more sites for oxygen adsorption, so that more target gases participate in the reaction on the surface of the material. The introduction of WS₂ increases the specific surface area of the sample WSC-2, and the material with a larger specific surface area has more gas adsorption active sites, thus improving the gas sensing performance of the sensor. The sample WSC-2 has the maximum response value of 15.7 for 0.01% formaldehyde at 140 ℃. To check the potential practical application of the prepared WSC-2 sensor, the selectivity and sensitivity of the sensor to different gases were investigated at 140 ℃. The results show that the sample WSC-2 has the optimum selectivity for 0.01% formaldehyde, and the response value is 4.2 times higher than that of CdSnO₃.

A series of WS₂-CdSnO₃ composites with different ratios were prepared via ultrasonic dispersion mixing. WS₂-CdSnO₃ had a large specific surface area, which was beneficial for gas adsorption and diffusion. The gas sensing performance of CdSnO₃ with different ratios of WS₂-CdSnO₃ composites were investigated, and the results showed that 3.5% WS₂-CdSnO₃ had the optimum selectivity for formaldehyde and the superior gas sensing performance at 140 ℃, and the sensitivity for 0.01% formaldehyde was 4.2 times higher than that of CdSnO₃ material, and the detection limit was 0.0001%. Therefore, the 3.5% WS₂-CdSnO₃ composite had potential applications in indoor formaldehyde detection. This study indicated that the modification of metal oxides by two-dimensional TMD could be one of the effective strategies to improve the gas sensing performance.

The Si₃N₄ ceramic is an ideal substrate material for high power device, and its high thermal conductivity is essential. However, there is still a significant gap between the actual and theoretical values of the thermal conductivity of Si₃N₄ ceramics due to the influence of lattice oxygen impurity and microstructure composition. The approaches to obtain Si₃N₄ ceramics with a high thermal conductivity are to decrease the lattice oxygen content, reduce the grain boundary phase and obtain the double peak structure composed of fine grains and a high aspect ratio β-Si₃N₄ grains through improving the purity of raw materials, selecting appropriate sintering aids and forming methods and optimizing the sintering system.

To obtain high thermal conductive Si₃N₄ ceramics, a research on the raw material powder with a high purity and a low oxygen content should be strengthened. The high quality equipment for Si₃N₄ ceramics production should be developed through controlling the sintering and processing technology. The practical application research should be promoted continuously and the completed application closed loop should be formed among powder production companies, product manufacturing enterprises and users. The timely feedback and response about the problems discovered during this process should be provided quickly to improve the performance of high thermal conductive Si₃N₄ ceramic products.

The purity of the Ni-based superalloy is directly related to the alloy-crucible interaction during induction melting. It is thus of great significance to clarify the interaction mechanism for the achievement of preparing the high-purity superalloys. In this study, pure Ni and Ni-based superalloys were melted in MgO crucibles, respectively. The phase composition, microstructure of the crucible and the oxygen concentration of the metals were analyzed by scanning electron microscopy, X-ray diffractometry and O/N analyzer. The interaction between the metals and the crucibles were investigated, and the interaction mechanism was elucidated. The results indicate that after melting pure Ni in MgO crucible, pure Ni melt exhibits a good wettability to the crucible, but little interaction occurs. However, a significant interaction between the superalloy melt and MgO crucible occurs. This reaction primarily involves the dissolution and decomposition of MgO in the alloy melt. The decomposed element O reacts with element Al to form Al₂O₃ products, which can float to the surface of the superalloy. Also, some Al₂O₃ can further react with MgO crucible matrix to generate MgAl₂O₄ product, which can attach to the inner surface of the crucible, and float into the slag, respectively. A slag layer with the thickness of approximately 80 μm composed of Al₂O₃, MgAl₂O₄, and a portion of the alloy can be formed on the surface of the alloy.

In this study, an industrial grade MgO (purity>99.5%) was used as a raw material. The MgO powder was mixed and ground in ethanol in a concrete mixer with yttria stabilized zirconia (YSZ) balls at a speed of 300 r/min. The mass ratio of powders, YSZ balls and ethanol were 3.0 ∶ 5.0 ∶ 0.8. The ground powder was then dried in an oven for 12 h. The MgO crucible green body was fabricated via cold isostatic pressing at 150 MPa for 3 min. Subsequently, the green body was sintered in a high-temperature silicon molybdenum rod sintering furnace at 1 750 ℃ for 6 h. The outer diameter, inner diameter, and height of the sintered crucible are 60, 50 and 70 mm, respectively.

An electrolytic pure Ni and DD419 alloy was used as an experimental metal. Pure Ni of 100 g was ground and acid pickled. The DD419 alloy was cut into 2 cm×2 cm×4 cm block caret, and its weight was 120 g. After grinding and acid pickling, the alloy was used as an experimental metal. The sintered MgO crucible was placed in a coil of a vacuum induction melting furnace, and filled with fused MgO sand around the crucible. It could prevent the short circuit of the induction coil due to the leakage of the molten metal. The experimental metal was inserted into the crucible, and the furnace was evacuated with a mechanical pump and a molecular pump to approximately 1×10^-2 Pa. The furnace was backfilled with high-purity argon to 0.06 MPa, and repeated for three times in order to eliminate the influence of the residual oxygen. The melting experiment was conducted in high vacuum. The metal temperature was raised slowly until the appearance of the liquid at the bottom of the metal. The temperature of the molten metal rapidly increased to 1 550 ℃, and hold at this temperature for 20 min. Finally, the molten melts were cooled in the crucibles to obtain the corresponding samples. After melting, the samples were cut via wire-electrode cutting and polished for the coming use.

The surface of pure Ni after melting in the MgO crucible is smooth without the appearance of the impurities. However, the surface of the superalloy has a black slag layer with a thickness of 80 μm, indicating that the slag is formed during the interaction between the alloy and the crucible. The surface of the slag can form a wrinkled shape due to the difference in the cooling rate between the slag and the alloy melt. No corrosion phenomenon occurs on the surface of the crucible after melting pure Ni. However, some Ni melt is residual on the surface of the crucible due to the wettability. In contrast, after melting the alloy in the crucible, the grain morphology and grain boundaries on the surface of the crucible disappear, indicating that the surface of the crucible is corroded by the alloy melt, thus leading to the generation of MgAl₂O₄ products. The slag primarily consists of Al₂O₃ and MgAl₂O₄ as well as some residual alloy melt, respectively. The generation of Al₂O₃ and MgAl₂O₄ products is attributed to the reaction at the melt-crucible interface. These products can float into the surface of the alloy melts under the electromagnetic stirring because Al₂O₃ and MgAl₂O₄ products have a lower density than that of the alloy melts. The thermodynamic stability for Al₂O₃, MgO, Cr₂O₃ and NiO indicates that element Al in the alloy has an intense affinity for element O, leading to the dissolution of MgO refractory and the oxygen contamination of the alloy melt. The uneven distribution of MgAl₂O₄ in both the inner surface of the crucible and the slag exhibits that the interaction and electromagnetic stirring significantly affect the formation of the slag.

Pure Ni did not react with MgO crucible. However, DD419 alloy could exhibit a significant interaction with the crucible, resulting in the alloy contamination and the formation of a slag layer. The thickness of the slag layer was 80 μm, and it consisted of Al₂O₃, MgAl₂O₄ and some alloy. In addition, Al₂O₃ and MgAl₂O₄ were the interaction products between the alloy melt and the crucible. The dissolution of MgO refractory could result in the release of elements Mg and O, respectively. Element Al reacted with element O to generate Al₂O₃ products. A portion of the products could float, and another part could react with MgO matrix on the inner wall of the crucible to form MgAl₂O₄. Meanwhile, some of the generated MgAl₂O₄ was adhered to the inner wall of the crucible, and another portion was floated into the slag layer.

Copper is a kind of strategic resource to support low carbon transition and economic development. The main sources of raw materials for copper smelting are copper concentrate and recycled copper resources. The existing researches on the damage mechanism of refractories that are used in copper smelting mainly focus on the smelting furnace, converter, anode furnace and other furnace types for copper concentrate pyrometallurgical copper refining process. However, there is little research on the damage mechanism of refractory, used in recycled copper refining furnace. Nerin-Gutai-Lu (NGL) has a great significance for the recycled of waste copper and alleviates the shortage of copper concentrate resources. The copper smelting process is characterized by intense chemical reactions, fast speed, high heat intensity and complex furnace atmosphere (i.e., O₂ and SO₂) in the furnace, which can easily damage the furnace lining refractories. The magnesia-chrome refractories have extensive applications in coppers smelting because of its excellent slag corrosion resistance. In this study, the damage mechanism of magnesia-chrome brick used in NGL recycled copper refining furnace was investigated. The macroscopic morphology, phase composition, and microstructure of the used magnesia-chrome brick were analyzed.

The sample was selected from magnesia-chrome brick used in the NGL furnace of a copper plant in Jiangxi Province, China, and their corrosion behavior and mechanism were analyzed. The residual brick was horizontally cut and divided into different areas according to the degree of corrosion, which were the reaction layer, infiltrated zone and the similar original brick zone. The chemical and phase composition of different areas of the residual brick were characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD), and the bulk density and apparent porosity were measured based on the Archimedes principle using water as a medium. The degradation on mechanism and microstructure of the sample were analyzed by scanning electron microscopy (SEM), and the composition of the sample was identified by attached energy dispersive spectrometry (EDS).

The magnesia-chrome brick is destroyed through chemical damage by NGL slag and copper melt due to the forsterite phase and the dissolution of periclase grains. The crude copper and copper oxides exhibit an intense permeability due to the penetration of slag (containing gas) and dissolution of periclase particles. With a large number of crude copper and copper oxides melting, the direct combination of fused magnesia-chrome, and periclase is destroyed. This metal melt can penetrate into the internal structure of magnesia-chrome brick and reach over 260 mm, which distributes in the matrix around the chromite particles and the grain boundaries, and pores or cracks of magnesia aggregate. Subsequently, SO₂ and O₂ are diffused to the similar original brick layer on the cold face of the residual brick due to the dissociation of monticellite at the grain boundary. SO₂/SO₃ in gas-phase medium reacts with CaO in brick to form CaSO₄. The XRD patterns indicate that the main component of the reaction layer on the cold face of the residual brick is CaSO₄ phase. The related reaction under the gas diffusion of SO₂-O₂ can cause a volume expansion, leading to the structural looseness and exacerbating the melting corrosion of refractories.

The diffusion of metal elements in NGL refining slag, i.e., ferrum, nickel and zinc, led to the interaction between slag and periclase grains, resulting in the formation of forsterite (containing Fe) and (Mg, Fe, Ni)O solid solutions, which reacted with chromite to form (Mg, Fe, Ni)(Cr, Al, Fe)₂O₄ multiphase spinel. The reasons of chemical damage in magnesia-chrome refractories included the formation of forsterite phase and the dissolution of periclase grains. The corrosion of refractories by metal melts, such as Cu-Cu_xO, was mainly infiltrated. The gases containing SO₂-O₂ diffused into the similar original brick layer of the residual brick cold surface, generating low melting point alkaline earth metal sulfides mainly composed of MgSO₄ and CaSO₄. The relevant reactions under the action of SO₂-O₂ could cause a volume expansion, resulted in a loose structure of magnesia-chrome refractories and exacerbating the melting corrosion of refractories. The uniform microstructure of the fused magnesia-chrome block in the furnace lining was a mixture of magnesia-chrome spinel and periclase, which could effectively resist the infiltration of copper melt. In addition, the high-Fe spinel ring formed at the edge of chromite particles also enhanced the slag corrosion resistance.

These researches involve 1) the introduction of organic dispersants to increase the dispersion of C and Al₂O₃ particles, and the formation of a uniform binding interface between particles, 2) the introduction of a binder (i.e., an organic carbon source) on the uniform coating of Al₂O₃ particles and pyrolysis to form a uniform combination of cracked carbon and Al₂O₃ particles, 3) the decomposition of organic matter, combustion synthesis and sol-gel and foam-injection coagulation to obtain precursors with a porous structure and a high specific surface area and the uniform mixing of aluminium and carbon sources in a micron scale, thus reducing the conditions for complete reaction and synthesizes high-quality nanopowders of AlN and 4) increasing the substitution (flow) efficiency of the reaction atmosphere, reducing the partial pressure of CO and increasing the partial pressure of N₂ to promote the positive synthesis reaction. According to the existing research, the future industrial development can be based on the combination of key process technology and key equipment. The continuous precursor manufacturing and continuous high-temperature synthesis equipment, especially continuous high-temperature synthesis equipment to eliminate differences in temperature zones and in airflow fields, need to be developed for the enhanced performance and efficiency of AlN powder synthesized by the CRN method.

A high-nickel ternary cathode material of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) has a high energy density. However, this material suffers from interfacial/structural instability, leading to a loss of more than 10% of its capacity during cycling. Cathode materials can be surface coated to improve their overall performance, in which nano-powder of zirconium dioxide can be used as a coating material to effectively improve the structural stability of high nickel ternary materials. However, the method for zirconia preparation has some disadvantages like complicated process flow, high production cost, and easy particle agglomeration. Flame spray pyrolysis (FSP) is simple in operation, fast in reaction speed, high in product quality, and easy to scale up production. In this paper, a variety of metal-based nanomaterials with small particle sizes and well-dispersity were prepared via FSP. The effect of process parameters (i.e., precursor solution concentration, feed rate and hydrogen flow rate) on the particle size, morphology and specific surface area of the powder was investigated. The synthesis process parameters of ZrO₂ were optimized, and the effect of optimal parameters on the coating modification of high-nickel ternary cathode materials was analyzed.

A certain amount of ZrCl₄ was weighed and dissolved in ethanol, and stirred at 40 ℃ to dissolve it completely and formulate precursor solutions at different concentrations (i.e., 0.16, 0.50, and 1.00 mol/L). At different hydrogen flow rates (3.3, 6.6, and 9.9 L/min) and feed rates (3, 5, and 7 mL/min), the precursor solutions with different concentrations were injected into a flame spray pyrolysis unit by a syringe pump. Finally, ZrO₂ powder was collected through a filter. The physical and chemical properties of the powders were determined by Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), and laser particle size (DLS) analysis.

The specific surface area of ZrO₂ is inversely proportional to the feed rate, and the particle size of ZrO₂ is directly proportional to the feed rate. The specific surface area of ZrO₂ powder decreases from 54.89 m²/g to 28.99 m²/g as the feed rate of precursor increases from 3 mL/min to 7 mL/min. Also, the distribution of particle size gradually becomes wider, and the average particle size obtained from the fitting increases from 7 nm to 18 nm. The specific surface area of ZrO₂ is inversely proportional to the hydrogen flow rate, and the particle size of ZrO₂ is directly proportional to the hydrogen flow rate. The uniformity of the particle size distribution of ZrO₂ nanoparticles decreases, and the fitted average particle size gradually increases from 7 nm to 10 nm, while the specific surface area of the product decreases from 61.57 m²/g to 44.73 m²/g as the hydrogen flow rate increases from 3.3 L/min to 9.9 L/min.

The specific surface area of ZrO₂ is inversely proportional to the precursor concentration, and the particle size of ZrO₂ is proportional to the precursor concentration. The specific surface area of ZrO₂ gradually decreases from 71.58 m²/g to 45.29 m²/g, the particle size gradually increases from 6 nm to 11 nm, meanwhile, and the large-size particles increases significantly as the precursor concentration increases from 0.16 mol/L to 1.00 mol/L.

Zirconium dioxide nanoparticles with a high specific surface area, a small particle size and a good dispersibility could be prepared via flame spray pyrolysis with ZrCl₄ as a precursor, ethanol as a solvent at a feed rate of 3 mL/min, a hydrogen flow rate of 3.3 L/min, and the concentration of precursor solution of 0.16 mol/L. The feed rate, hydrogen flow rate and precursor concentration all affected the particle size and specific surface area of the product, and the effect of the feed rate was dominant. A lower feed rate was favorable for the synthesis of ZrO₂ particles with a smaller particle size and a larger specific surface area. A high hydrogen flow rate exacerbated the agglomeration of ZrO₂ particles and reduced their specific surface area. A high concentration of precursor solution induced the generation of more large-sized particles, resulting in a decrease in the specific surface area. Zirconia obtained under the optimal process conditions of 0.2% (mass fraction) coating on the surface of NCM811 cathode material could increase the capacity retention of the battery by 14% at 1 C and 2.7-4.3 V. Nano-sized powder of zirconium dioxide was prepared via flame spray pyrolysis at suitable process parameters, providing a promising method for the preparation of zirconium dioxide powder with a small particle size and a high specific surface. In addition, the application in anode capping could also improve the comprehensive performance of the battery.

This review summarizes recent research progress on the preparation of aerogels by chemical vapor deposition. The template-free chemical vapor deposition (CVD) method of the aerogel preparation can produce carbon material aerogels and multifunctional silicon carbide nanowire aerogels with superior performances for several hours. The template-assisted CVD method can customize the microstructure of the aerogel according to the template in order to achieve some special functions (i.e., superelasticity, negative Poisson's ratio, etc.). The chemical vapor deposition process for the preparation of aerogel can completely avoid the influence of surface tension during the drying process and the preparation process is more efficient due to the absence of liquid phase, compared with the traditional aerogel liquid-phase preparation process. The existing research in the related field is not sufficient due to the presence of some problems. Some possible aspects of subsequent research include:

1) To further simplify the process. The template-assisted chemical vapor deposition method in the chemical vapor deposition preparation process for aerogels usually requires the specialized preparation of templates with aerogel structures, which increases the complexity of the process and is not conducive to large-scale production. Industrially produced fumed silica or fumed alumina has a structure similar to that of an aerogel, and the use of fumed silica or fumed alumina as a template to grow the desired material on its nano-skeleton is expected to reduce the cost of preparation of partial oxide aerogels.

2) To develop a chemical vapor deposition preparation process for aerogels with milder conditions. At present, the reaction temperature is mostly more than 1 000 ℃ when using chemical vapor deposition to prepare aerogels. The reaction conditions become milder and the requirements of equipment reduce through the introduction of catalysts and other methods, which is an important research aspect for the future development of chemical vapor deposition process of aerogel.

3) To broaden the scope of application of the material type of aerogel chemical vapor deposition process. From the existing reports, the chemical vapor deposition process can be used for the preparation of some aerogel types (i.e., mainly carbon materials, carbides, borides and other aerogels). The reaction mechanism of the aerogel chemical vapor deposition preparation process needs to be further investigated. The chemical vapor deposition process can be used to prepare oxide aerogels (i.e., silica and alumina) via utilizing the advantages of the chemical vapor deposition process (i.e., short cycle time and no drying).