Ultrasonic assisted hot metal powder compaction

Hot pressing of metal powders is used in production of parts with similar properties to wrought materials. During hot pressing processes, particle rearrangement, plastic deformation, creep, and diffusion are of the most effective powder densification mechanisms. Applying ultrasonic vibration is thought to result in great rates of densification and therefore higher efficiency of the process is expected. This paper deals with the effects of power ultrasonic on the densification of AA1100 aluminum powder under constant applied stress. The effects of particle size and process temperature on the densification behavior are discussed. The results show that applying ultrasonic vibration leads to an improved homogeneity and a higher relative density. Also, it is found that the effect of ultrasonic vibration is greater for finer particles.     

Solubilization of arsenic from gallium arsenide using aqueous suspensions of organic halides

The solubilization of arsenic in solid gallium arsenide by aqueous solutions/suspensions of organic halides is described. Although arsenic is removed from gallium arsenide surfaces, excess quantities of gallium are not found in the solution. The abilities of the organic halide to solubilize arsenic decreases as follows: C₂H₅Br> CH₃I> 2-C₃H₇I> 1-C₃H₇I> 2-C₄H₉Br> CH₂?CHCH₂I> 2-C₃H₇Br? 1-C₄H₉Br. The results correlate with a combination of organic halide solubility, bond enthalpy and carbonium ion stability factors. Other parameters investigated using gallium arsenide and iodomethane include concentration, physical state of the arsenide, pH, role of oxygen and role of light.     

Improved Determination of Aluminum in Serum by Electrothermal Atomic Absorption Spectrometry and Zeeman Background Correction

Abstract

A simple but reliable method for the determination of aluminum in serum by flameless atomic absorption spectrometry is described. By use of the Zeeman background correction, the interferences are eliminated. However, considering the numerous possible sources of contamination, extreme precautions are necessary both when taking and storing the serum. The procedures preceding the dosage per se must be minimized. The within-day and clay-to-day precision data (CV %) was 3.28 and 3.82 respectively. The average recovery for aluminum was 97.5 %. We used this method on serum from 30 healthy subjects and from 300 patients on hemodialysis. The mean aluminum concentration for the healthy subjects was 5.35 μg/l (SD ± 0.53) while the values for the hemodialyzed patients ranged from 20 to 220 μg/l.     

Sensing colorimetric approaches based on gold and silver nanoparticles aggregation: Chemical creativity behind the assay. A review

Localized surface plasmon resonance (LSPR) is one of the most remarkable features of gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs). Due to these inherent optical properties, colloidal solutions of Au and Ag NPs have high extinction coefficients and different colour in the visible region of the spectrum when they are well-spaced in comparison with when they are aggregated. Therefore, a well-designed chemical interaction between the analyte and NPs surroundings leads to a change of colour (red to blue for Au NPs and yellow to brown for Ag NPs from well-spaced to aggregated ones, respectively) allowing the visual detection of the target analyte.     

Highly Selective and Sensitive Detection of Dopamine in the Presence of Excessive Ascorbic Acid Using Electrodes Modified with C60‐Functionalized Multiwalled Carbon Nanotube Films

Electrochemical detection of dopamine (DA) in the presence of a large excess of ascorbic acid (AA) was investigated with a novel all‐carbon nanocomposite film of C₆₀‐MWCNTs (C₆₀‐functionalized multi‐walled carbon nanotubes) using a bare MWCNTs film as control. Although both films can selectively detect DA from AA by separating their oxidation potentials, the C₆₀‐MWCNTs film shows special selectivity and good sensitivity for detecting DA. On one hand, the C₆₀‐MWCNTs composite film shows a higher activity for DA oxidation with enhanced peak current. On the other hand, the C₆₀‐MWCNTs composite film effectively suppresses the oxidation of AA. Remarkably, it is found that the oxidation current of DA is over 2 times higher than that of AA even when the concentration of AA is about 3 to 4 orders of magnitude higher than that of DA. This offers a tremendous advantage for the simple and clean detection of DA free of the interfering AA signal in a real assay. Cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectrometry are used to characterize the C₆₀‐MWCNTs composite film. These novel properties are interpreted to arise from the facile electron transfer between C₆₀ and MWCNTs in the C₆₀‐MWCNTs nanocomposite film.     

The determination of tetra-alkyllead and ionic alkyllead compounds in seafood

Extraction methodologies were developed for tetra-alkyllead and ionic alkyllead compounds in seafood. Tetra-alkylleads were extracted with n-hexane after the samples had been enzymatically hydrolyzed. The ionic alkylleads were complexed with diphenylthiocarbazone (dithizone) at pH 8 and 9 from enzymatically hydrolyzed samples to optimize recovery. The dithizone extracts were butylated prior to analysis by gas chromatography–atomic absorption spectrometry (GC AA). Instrumental detection limits ranged between 1.6 and 2.3 pg lead. Application to a limited number of seafood samples indicated the possible presence of trace amounts (ca 1 ng g^?1) of trimethyllead in some samples. No other alkylleads were detected.     

几种反应型相容剂及其在聚合物共混改性中的应用

反应型增容已经成为提高聚合物相容的一个重要手段。甲基丙烯酸缩水甘油配(GMA)、马来酸酐(MAH)和丙烯酸(AA)作为主要的接枝单体己得到广泛应用。本文从GMA、MAH和AA官能化聚合物的作用机理，以及他们作为反应型相容剂，通过“原位”反应增容聚合物共混体系，提高聚合物合金的相容性两个方面，介绍了国内外在反应型增容这一领域内所取得的进展。     

Microchip-based electrochromatography: designs and applications

Different techniques and methods of electrochromatography on “lab on a chip” devices are reviewed. Described approaches include open-channel microchip electrochromatography relying on C₈, C₁₈ and novel gold nanoparticle (GNP) coating of microchannel wall; packed-channel microchip electrochromatography with new ways of automated loading and unloading of conventional octadecylsilica beads; monolith-based microchip electrochromatography with tailored casting of stationary phase at the specific places of microfluidic network and novel photolitographically fabricated collocated monolithic structures. Specific issues related to the microchip electrochromatography, i.e. importance of high aspect ratio of the microchannels in the open-channel electrochromatography or approaches eliminating the wall effect in the monolith-based electrochromatography, are discussed. Various applications for environmental, pharmacological, genomic and proteomic analysis are described. The operation parameters of reviewed microsystems are summarized in easy-to-read tables.     

Electrocatalytic Oxidation and Determination of Dopamine in the Presence of Ascorbic Acid and Uric Acid at a Poly (4‐(2‐Pyridylazo)‐Resorcinol) Modified Glassy Carbon Electrode

A sensitive and selective electrochemical method for the determination of dopamine (DA) was developed using a 4‐(2‐Pyridylazo)‐Resorcinol (PAR) polymer film modified glassy carbon electrode (GCE). The PAR polymer film modified electrode shows excellent electrocatalytic activity toward the oxidation of DA in a phosphate buffer solution (PBS) (pH 4.0). The linear range of 5.0×10^?6–3.0×10^?5 M and detection limit of 2.0×10^?7 M were observed. Simultaneous detection of AA, DA and UA has also been demonstrated on the modified electrode. This work provides a simple and easy approach to selective detection of DA in the presence of AA and UA.     

二乙基二烯丙基氯化铵与丙烯酰胺、丙烯酸共聚竞聚率

二乙基二烯丙基氯化铵;丙烯酰胺;丙烯酸;共聚合;竞聚率