摘要：
Informatics analysis on inorganic compounds, surface imaging and depth profiling were carried out for PM2.5 using time-of-flight secondary ion mass spectrometry (TOF-SIMS) during different haze periods (autumn and winter). Both positive ions, such as NH4+, Si+, H+, Li+, Na+, Mg+, Al+, K+, Ca+, Ti+, Cr+, Fe+, Cu+, As+, Cs+ and Ba+, and negative ions, such as NO2-, NO3-, SO32-, SO42-, O-, Cl-, CN- and H-, were detected in the samples. Along with the increase of the depth, the signal intensity became weaker and weaker for most of the inorganic ions, however, it could be stronger for a few of them due to the variation of chemical behaviors. Moreover, the source analysis was performed, and the results indicated that PM2.5 was mainly derived from biomass combustion and fossil combustion in this area. This paper is useful to provide a tool to study the PM2.5 around the world.
摘要：
The study reported was intended to improve the leaching rate of boron-bearing tailings, using a method of sodium roasting that uses boron-bearing tailings as the raw material and Na2CO3 as the sodium agent. The effects of the roasting temperature and Na2CO3 amount on the leaching rate of boron-bearing tailings are mainly evaluated. The morphology and composition of the samples after sodium roasting are analysed by scanning electron microscopy and X-ray diffraction. The results show that sodium roasting can significantly improve the leaching rate of boron-bearing tailings. Under the optimal conditions where roasting temperature is 950°C, Na2CO3 amount is five times the theoretical amount and roasting time is 2 h, the leaching rate of boron-bearing tailings is up to 86.78%. Based on the analysis of the characterization results and the mechanism analysis of the sodium roasting process, the main reason for the increase of leaching rate is the reaction between Na2O produced by the decomposition of Na2CO3 and the boron in boron-bearing tailings resulting in soluble sodium borate. The results provide a scientific basis for the efficient comprehensive use of boron-bearing tailings.
摘要：
To prepare a new kind of electromagnetic wave absorber, and improve the processing technology and accessional value of natural microcrystalline graphite minerals (NMGMs), reduced microcrystalline graphene oxide (rGO-M), a novel absorber with high absorption, low reflection and a wide absorption band, was prepared from NMGMs using a solvent-assisted thermal reduction method. Moreover, the as-produced rGO-M with adjustable electrical resistivity can be easily transferred into well distributed bulk materials by freeze-drying technology. These unique structures and compositions make a great contribution to the impedance match, and cause strong conductive loss and various dipole polarization effects which greatly enhance the absorption. Meanwhile, the effective bandwidths below −5 dB and −10 dB are 11.7 GHz and 3.32 GHz respectively, and the reflection loss can reach −42.68 dB. The study will be beneficial to the development of carbon resources and carbon materials research. Besides, it can provide a scientific basis for the further improvement of the comprehensive utilization and the level of deep processing technology of NMGM resources.
摘要：
C/C-SiC composites were fabricated via Si-Zr reactive alloyed melt infiltration using various C/C preforms with different porosities as reinforcements. The influence of preform porosities on the microstructure, mechanical strength and ablation resistance of the as-prepared composites were investigated. The results indicated that microstructure and properties of the C/C-SiC composites seriously depended on C/C preform porosities. The composites were mainly composed of carbon, SiC and ZrSi2 phases, while some residual silicon still existed in the composites prepared with very large porosity preforms. Flexural strength of the composites firstly increased with increasing C/C preform porosities, then reached the highest value, 307 MPa, and finally turned to decrease with the further increasing of preform porosities. Densities of the composites increased with increasing preform porosities, while open porosities were generally small below 7%. Linear ablation rates of the composites firstly sharply decreased with increasing preform porosities and then slightly decreased to reach a balance value. In a word, C/C preform porosity was of great significance for reactive melt infiltration of C/C-SiC composites. Densities, microstructure, mechanical strength and ablation resistance of the resulting composites should be comprehensively taken into consideration to choose an optimal preform porosity for fabrication of C/C-SiC composites.
摘要：
We report a low-cost and effective technique for preparing borax from boron-bearing tailings, which is at a low grade of 9.98% B2O3. Well-crystallized borax is achieved by the removal of impurity, evaporation and concentration through the efficient method of sodium roasting and pressure leaching. The morphology, composition and structure of borax are investigated in this study. The result of scanning electron microscopy shows that the crystals obtained are cube-shaped with smooth surface and of good growth. The crystals are proven to be Na2B4O7·10H2O by EDS, XPS, XRD and ICP-AES. Moreover, the recovery rate of boron can reach 63.49%. This cost-effective strategy of preparing borax from boron-bearing tailings provides a guideline for the development of the boron industry and has a great potential for the commercialization of borax production.
摘要：
It is a challenge to prepare graphene-like nanosheets (GNs) with desired electrical properties from natural microcrystalline graphite minerals (NMGM) since the impurities in NMGM are always hard to eliminate and the grain size of NMGM is much smaller than that of flake graphite (FG). The morphology, structure, surface chemistry, and compositions of the GNs prepared from NMGM using a liquid oxidation–reduction approach were investigated in this study. GNs with layer number ranging from 3 to 7, thickness of 1.1 nm, and sizes up to 1 μm × 2 μm were obtained and confirmed from scanning electron microscopy, transmission electron microscopy and atomic force microscopy images. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis show that, during the whole fabrication process, the generation and elimination of oxygen-containing groups or reestablishment of the conjugated graphene network occur. The results of Raman spectroscopy and X-ray diffraction measurements show that the GNs possess an amorphous nanostructure. The as-produced GNs with adjustable electrical resistivity can be easily transferred into well distributed bulk materials by freeze-dried strategy. This cost-effective synthesis strategy of GNs from abundant NMGM provides great potential for the commercialization of GN production.
摘要：
Based on the Maxwell equation, the electromagnetic model in the coaxial fiber was described. The interaction with electromagnetic wave was analysed and the theoretical formula of axial permeability (mu(parallel to)), axial permittivity (epsilon(parallel to)), radial permeability (mu(perpendicular to)) and radial permittivity (epsilon(perpendicular to)) of Fe-C coaxial fiber were derived, and the demagnetization factor (N) of fibrous material was revised. Calculation results indicate that the composite fiber has stronger anisotropy and better EM dissipation performance than the hollow carbon fiber and solid iron fiber with the same volume content. These properties can be enhanced through increasing aspect ratio and carbon content. The mu(parallel to) is 5.18-4.46i, mu(perpendicular to) is 2.58-0.50i, epsilon(parallel to) is 7.63-6.97i, and epsilon(perpendicular to) is 1.98-0.15i when the electromagnetic wave frequency is 5 GHz with the outer diameter of 0.866 lm, inner diameter of 0.500 mu m, and length of 20 mu m. The maximum of the imaginary part of mu(parallel to) and epsilon(parallel to) are much larger than that of mu(perpendicular to) and epsilon(perpendicular to) when the structural parameters change, and the maximum of mu(parallel to) and epsilon(parallel to) can reach 6.429 and 23.59. Simulation results show that greater conductivity, larger aspect ratio, thin iron shell play important roles to improve the electromagnetic matching ability and microwave attenuation for the Fe-C coaxial fibers. (C) 2017 Elsevier B.V. All rights reserved.
关键词：
Ball milling;Graphite;Milling (machining);Particle size;Purification;Scanning electron microscopy;X ray diffraction;Electromagnetic absorbers;Energy dispersive x ray microanalysis;High frequency HF;Microcrystalline graphite;Microwave absorbing materials;Morphology and structures;Reflection loss;Reflectivity values;Electromagnetic wave absorption
作者机构：
[谢炜; 邹诚茜; 邓应军] Hunan Province Key Laboratory of Safety Design and Reliability Technology for Engineering Vehicle, Changsha University of Science and Technology, Changsha;410114, China;[唐镇宇; 匡加才] Key Laboratory of Lightweight and Reliability Technology for Engineering Vehicle, The Education Department of Hunan Province, Changsha University of Science and Technology, Changsha;[符寒光] College of Materials Science and Engineering, Beijing University of Technology, Beijing;100124, China
