Synthesis of needle-like aragonite from limestone in the presence of magnesium chloride

Needle-like aragonite was synthesized with a reversible solution reaction from limestone without calcinations. Scan Electron Microscope (SEM) and X-ray Diffraction (XRD) were used to characterize the morphology and the crystal structure of aragonite. The synthesis of aragonite whisker involves two steps. At first GCC (Ground Calcium Carbonate) was dissolved in an aqueous solution of magnesium chloride with reflux and air flush. Then CO₂ was bubbled into the suspension at a low temperature to produce aragonite whisker. An in-house designed reactor and acid–base titration analysis were used to measure the remaining GCC content in the reaction mixture. A kinetics equation of GCC dissolution was developed, which showed a first-order kinetic feature to magnesium chloride concentration. A reaction rate constant of 0.04234 h^?1 was obtained. The dissolution rate of GCC in magnesium chloride is much higher than that in the magnesium sulfate solution. Some aragonite whiskers with a length of ca. 20 μm and an aspect ratio of 8–12 can be synthesized.     

二氧化碳腐蚀缓蚀剂及其缓蚀机理的研究进展

首先分别论述了单组分缓蚀剂和复配型缓蚀剂的缓蚀机理,即不同类型的缓蚀剂在金属表面所具有的不同吸附过程。单组分缓蚀剂中特殊的分子基团在金属表面通过物理吸附、化学吸附或混合吸附过程起到缓蚀作用,复配型缓蚀剂在金属表面通过各组分间协同吸附或竞争吸附过程起到缓蚀作用,并指出了缓蚀机理的研究所存在的问题。然后,主要综述了近几年来国内外对用于二氧化碳腐蚀缓蚀剂的研究进展,包括咪唑啉衍生物、表面活性剂、季铵盐、有机胺和复配型缓蚀剂,结合缓蚀剂的分子结构和缓蚀效率等对其进行了阐述。介绍了几种用于二氧化碳腐蚀的新型缓蚀剂,如多活性位点有机化合物、硫醇、席夫碱和聚合物等。最后针对二氧化碳腐蚀环境的复杂性,对未来缓蚀剂及其缓蚀机理的研究方向进行了展望。     

Accumulation of Contaminant Metals in the Amphipod Diporeia spp. in Western Lake Ontario

Sediment and amphipods (Diporeia spp.) were collected in areas in western Lake Ontario suspected of containing a range of sediment metal contents. The total metal contents (Al, As, Cd, Cr, Cu, Ni, Fe, V, and Zn) of depurated Diporeia tissues were measured and compared to the total metal contents of the surrounding sediment. The fractional bioavailability of As, Cu, Fe, and Zn was determined in those same sediments using a sequential chemical extraction (SCE) procedure and correlated with depurated Diporeia tissue metal contents. Results of these analyses were then used to assess the ability of Diporeia to accumulate sediment metal contamination. A comparison of metal biota-sediment accumulation factors (BSAFs) and sediment metal enrichment factors (EFs) for each metal yielded separate metal groups showing different behavior for tissue accumulation. Aluminum, Cr, Fe, Ni, and V were not enriched in the sediments and were not accumulated in Diporeia tissues, while As, Cd, Cu, and Zn were enriched in the sediments and accumulated in Diporeia tissues. SCE results showed that Cu (3.2 to 8.4 %) and Zn (13 to 19 %) contents in the easily extractable sediment fractions (MgCl₂ and Na-acetate) were significantly correlated with Cu (r = 0.86; P<0.01) and Zn (r = 0.69; P<0.05) contents in depurated Diporeia tissue. In addition, Cu and Zn in Diporeia tissues are also correlated to the total sediment metal content for each respective metal (Cu: r = 0.67, P < 0.05; Zn: r = 0.66, P < 0.05). The high BSAFs for Cu and Zn, in combination with the association of tissue metal contents with easily extracted sediment metal fractions, suggest that Diporeia may be a potential bioindicator for Cu and Zn contamination in sediments.     

Feature extraction for identification of drug and explosive concealed by body packing based on positive matrix factorization

In the analysis towards the energy dispersive X-ray diffraction (EDXRD) spectra of drug and explosive concealed by body packing, positive matrix factorization (PMF) was introduced to extract features from EDXRD spectra of samples in a set of drugs and explosive concealed in the anthropomorphic phantom, because PMF prevents the negative factors from occurring, avoids contradicting physical reality, and makes factors more easily interpretable. In order to compare with the features extracted by PMF, Principal Component Analysis (PCA) and robust PCA were investigated. Then, K-nearest neighbour (KNN) and support vector machine (SVM) were introduced to classify the samples according to the features extracted by PMF, PCA and robust PCA. It is shown that the recognition rates obtained by PMF are highest (above 99.5%) and insensitive to classifiers. This work demonstrates that PMF is effective in feature extraction for identification of drug and explosive concealed by body packing.     

Synthesis,morphology, microstructure and magnetic properties of hematite submicron particles

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe₂O₃) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ～500 nm whereas thickness is ～100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe₂O₃ particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H_C = 1140 Oe, remanent magnetization M_r = 0.125 emu/g and saturation magnetization M_S = 2.15 emu/g as well as the Morin transition at T_M ～ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample.     

Initial atmospheric corrosion of zinc in presence of Na2SO4 and （NH4）2S04

Initial atmospheric corrosion of zinc in the presence of Na₂SO₄ and (NH₄)₂SO₄ was investigated via quartz crystal microbalance(QCM) in laboratory at relative humidity(RH) of 80% and 25 °C. The results show that both Na₂SO₄ and (NH₄)₂SO₄ can accelerate the initial atmospheric corrosion of zinc. The combined effect of Na₂SO₄ and (NH₄)₂SO₄ on the corrosion of zinc is greater than that caused by (NH₄)₂SO₄ and less than that caused by Na₂SO₄. Fourier transform infrared spectroscopy(FTIR), X-ray diffractometry(XRD) and scanning electron microscopy(SEM) were used to characterize the corrosion products of zinc. (NH₄)₂Zn(SO₄)₂, Zn₄SO₄(OH)₆·5H₂O and ZnO present on zinc surface in the presence of (NH₄)₂SO₄ while Zn₄SO₄(OH)₆·5H₂O and ZnO are the dominant corrosion products on Na₂SO₄-treated zinc surface. Probable mechanisms are presented to explain the experimental results.     

Porous silicate cement membranes generated by the novel method combining freeze casting and heat-dry curing

Porous silicate cement membranes (PSCMs) fabricated by the freeze casting method show great potential to be utilized in seawater pretreatment, fermentation broth separation, and industrial wastewater treatment due to its merit of high-temperature resistance, low-cost, and hierarchically ordered porous structures, while the freeze casting method is complex and time-consuming. In this work, a combination of freeze casting and heat-dry curing was initially applied to generate PSCMs. The preparation periods of PSCMs could be shortened by simplifying preparation processes and reducing curing time. The resulting membranes presented double-layer structures, containing a nucleation zone (N-zone) with dense structures and a stability zone (S-zone) with lamellar pore structures. The X-ray diffraction pattern of membranes displayed the mixed hexagonal and rhombohedral structures. This novel method could save more than half of energy consumption compared with the traditional preparation technology of silicate cement samples. The membranes with a mesopore size of 3.794 nm showed high permeation performance with pure water flux reaching 207.23 L m⁻² h⁻¹ under 0.15 MPa and room temperature. The separation efficiency of oil-water was 78.05% under operating pressure of 0.05 MPa. Molecular dynamics simulation was applied to narrate the microscopic process of transformation during heat-dry curing, and obtained a good similarity of consequences between the computational method simulation and experimental operation.     

A defect structure model for the ab intermetallic compounds with reference to CoGa and NiGa

General expressions for the composition and temperature dependence of the defect concentrations in intermetallic compounds are obtained by minimizing the free enthalpy of the crystal written in the usual Bragg-Williams pairwise interaction approximation. Expressions are derived for the thermodynamical potential of the A and B components as well as for the composition of the most stable compound, in terms of the defect energies. The case of the NiAl-type defect structure is treated as an example. Experimental data available on the defect structure of CoGa and NiGa are analyzed. The model is found to describe adequately the experimental results, and the analysis yields reasonable values of the defect energies and formation volumes in both materials.     

Nanostructure,porosity and electrochemical performance of chromium carbide derived carbons

This paper presents the results from the investigation of the influence of the chlorination temperature, the carbide crystal structure, the Cr/C ratio and physicochemical properties of CrCl₃ on the morphology, nanostructure, textural properties and electrochemical performance of CDCs. Electron microscopy and its analytical associated techniques reveal that these carbons, mainly composed by disordered graphene layers, evolve into graphitic nanostructures as a result of increasing the Cr/C content, the reaction temperature and the template effect of the etched CrCl₃ halide. Their textural analysis indicates the formation of micro/mesoporous carbons with a pore width below 1.5 nm, surface area as high as 835 m²/g and exhibit capacitive behavior in aqueous electrolyte.