Kinetics study on the dissolution of UO<Subscript>2</Subscript> particles by microwave and conventional heating in 4 mol/L nitric acid

The dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid medium at temperatures of 90–110°C by microwave heating and conventional heating has been investigated, respectively. It is found that the dissolution ratios of UO₂ particles by microwave heating were 10%–40% higher than that by conventional heating. Kinetics research shows that the dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid is controlled by the diffusion control model for microwave heating and by the surface reaction control model for conventional heating. The diffusion control model for the dissolution of UO₂ particles by microwave heating could be explained by the diffuseness on the surface of UO₂ particles.     

Boron determination in biological materials by inductively coupled plasma atomic emission and mass spectrometry: effects of sample dissolution methods

This study compares four sample dissolution methods for Boron determination in two National Institute of Standard and Technology (NIST) botanical Standard Reference Materials (SRMs) and three Agriculture Canada/NIST RMs, each having a reference (certified or best estimate) B concentration. The dissolution treatments consisted of: 1) dry ashing at 500° C, 2) wet digestion with HNO₃ + H₂O₂, 3) extraction with hot HNO₃ and 4) closed vessel microwave dissolution. The samples were spiked before and after imposing dissolution treatments to study B recovery by inductively coupled plasma mass spectrometric (ICP-MS) analysis. Microwave digests of NIST SRM 1515 and some in-house RMs were also used to compare the B values of ICP-MS and ICP-AES (atomic emission spectrometry). While all three digestion methods (dry ashing, wet ashing and microwave) dissolved botanical samples, only the microwave method worked well for animal tissues. In terms of B values in these materials, there was no significant difference among the three digestion treatments. Near 100% recovery of B spiked before and after the sample dissolution indicates that there may not be a significant loss of B during the dissolution process used in this study. Extraction with hot HNO₃ was as effective as the three digestion treatments, and B values for this method agreed well with reference values. For the botanical materials studied, the B values determined by ICP-AES were not significantly different from ICP-MS values. This study shows that a simple, time and labor efficient hot HNO₃ extraction is as effective as other digestion/dissolution methods for quantitative B recovery from biological materials. Received: 13 June 1996 / Revised: 17 September 1996 / Accepted: 19 September 1996     

Dissolution of sintered thorium dioxide in phosphoric acid using autoclave and microwave methods with detection by gamma spectrometry

A quantitative and fast method of dissolution of refractory thoria (ThO₂) was developed for the determination of thorium (Th) in a given sample. The dissolution of sintered ThO₂ powder, microspheres and pellets using 88% phosphoric acid was investigated. The conditions of quantitative dissolution of ThO₂ microspheres were optimized by conventional heating in autoclave and also by microwave heating. 100 mg of sintered ThO₂ microspheres were dissolved in 8 g of phosphoric acid in an autoclave, and heating at 170 °C for 3 h, in comparison to 5 g of phosphoric acid by microwave heating (375 W) at 220 °C for 1 h. Dissolution studies on the powder form of sintered ThO₂ were also performed. 1 g of sintered ThO₂ powder could be dissolved in 6.5 g of phosphoric acid in autoclave heating at 170 °C for 1 h. Strong complexing of (PO₄)³⁻ with Th⁴⁺ may be the influencing factor for quantitative dissolution of ThO₂.     

The Study of the Extraction of Surface-Active Component of a Binary Liquid from Model (“Cylindrical”) Droplets

The dissolution of the droplets of a chlorobenzene and isopropanol mixture in water that filled the Hele-Shaw vertical cell is experimentally studied. The choice of a cylindrical shape for droplets, thus providing only one free (lateral) surface, makes it possible to use the interference method to obtain quantitative characteristics of the studied process. Information on arising flows is obtained by examining the motion of opaque emulsion formed at the interface during the dissolution of a mixture. The interrelation between various mass transfer mechanisms in the droplet as a function of the initial concentration of a mixture and the time of dissolution is discussed.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 357–362.Original Russian Text Copyright © 2005 by Kostarev.     

Ellipsometric and microwave reflectivity studies of current oscillations during anodic dissolution of p-Si in fluoride solutions

Periodic current oscillations during anodic dissolution of monocrystalline p-Si(100) in buffered ammonium fluoride solutions (0.1 mol dm⁻³ fluoride, pH 4.5) were investigated using a flow cell in order to eliminate mass transport limitations. The flow cell was designed to permit simultaneous in-situ ellipsometry, impedance and potential modulated microwave reflectivity measurements. Analysis of the ellipsometric response showed that the current oscillations are accompanied by a synchronous variation of the overall oxide thickness with an amplitude of 4.5±0.1 nm. Analysis of the relationship between the total oxide thickness and the current during the oscillation cycle shows that to a first approximation the rate of chemical dissolution of anodic oxide remains constant. Oscillations of the electrode admittance and potential modulated microwave reflectivity were also measured. The imaginary component of the admittance is related to the oscillation in thickness of a narrow inner region of ‘dry’ oxide and to changes in the accumulation capacitance. The oscillation in the potential modulated microwave reflectivity is interpreted in terms of the changes in the density of holes accumulated at the p-Si SiO₂ interface.     

Optimized microwave preparation procedure for the elemental analysis of aquatic sediment

 This paper summarizes several key points in applying the microwave preparation technique to the elemental analysis of aquatic sediments and reports systematic experiments in searching for an optimal microwave preparation procedure for element analysis in sediment samples. The determination of the elements Cu, Pb and Cd in a standard reference aquatic sediment sample (CRM 280, COMEUR) was achieved by first digesting the samples in a microwave oven equipped with PFA advanced composite vessels, followed by AAS measurement. The influence of microwave power, digestion time, various dissolution reagents and the HF removing conditions was studied. It has been shown that for a 0.1 g sediment sample the optimal microwave preparation conditions are: 4–5ml HNO₃/HF/H₂O₂ as solvent, digesting time 30 min with 100% microwave power and evaporating the residual acid within 8 min in an open vessel at 80 °C. The element recovery rates with AAS measurement can reach up to 92.4–100.6%. Received: 23 July 1996/Revised: 23 September 1996/Accepted: 25 September 1996     

Magnetoelectrolytic Dispersion of Ferromagnetic Metals

Processes of electrolytic dispersion of ferromagnetic metals (nickel and cobalt) to give oxides or metal powders were studied. The influence of an external magnetic field and current reversal on the processes of anodic dissolution was analyzed.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 924–927.Original Russian Text Copyright © 2005 by Zaichenko.     

Microwave-Assisted Reactions of Schiff Bases with Diethyl Phosphonate in the Presence of CdI<Subscript>2</Subscript>

The reaction of diethyl phosphonate with Schiff bases derived from aldehydes and ketones in the presence of cadmium iodide is strongly accelerated by microwave irradiation, and the corresponding α-aminophosphonates are formed in high yields.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 4, 2005, pp. 517–519.Original Russian Text Copyright © 2005 by Kabachnik, Zobnina, Beletskaya.     

High-pressure microwave dissolution of ceramics prior to trace metal determinations by microwave induced plasma atomic emission spectrometry

A commercial laboratory microwave acid digestion system was evaluated for the acid dissolution of ceramic powders (Al₂O₃, AlN, BN and Si₃N₄) prior to the determination of their trace element content by microwave induced plasma atomic emission spectrometry. Newly designed vessels, capable of withstanding internal pressures of over 110 bar, provide rapid and satisfactory results for sample dissolution. Sample preparation time was approximately 30 min (including the subsequent cooling time and preparation of the final solution). Results from conventional stainless-steel acid digestion vessel (Teflon bomb) dissolution are compared with the microwave bomb results of microwave plasma atomic emission spectrometry.     

Softeners for Rubber Based on Shale Thermal Dissolution Products

The source of raw materials for manufacturing softeners for rubber is extended through applying a nonwaste process of thermal dissolution of ordinary or enriched shale in crude producer-gas tar. The resulting products are less expensive than the conventional high-melting oil asphalts and oils.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 851–855.Original Russian Text Copyright © 2005 by Syroezhko, Pankova, Korchemkin, Otchayannyi, Proskuryakov.     

基于生命周期评价技术研究全铁含量测定对环境的影响

利用生命周期评价软件Sima Pro7和环境影响评价模型IMPACT 2002+,通过对化学分析方法的清单分析及计算,评价和比较了3种测定铁矿中全铁含量的化学分析方法(酸溶法、碱熔法、微波消解法)对人类健康、生态质量、气候变化及资源消耗等的影响。发现3个方法对环境的影响主要集中于人类健康危害、气候变化和资源消耗方面。通过计算3种方法的生命周期单一环境负荷值,发现碱熔法、酸溶法和微波消解法的单一环境负荷值分别为1.97,1.81,0.07 m Pt,对环境总体的影响,碱熔法和酸溶法分别为微波消解法的28倍和26倍。单独对人类健康危害指标而言,碱熔法为1.15 m Pt,酸溶法为1.07 m Pt,微波消解法仅为0.039 6 m Pt。碱熔法、酸溶法和微波消解法的碳足迹分别为5.12,4.62,0.189 kg CO_2eq。说明微波消解法排放量最小,其环境友好性最佳,值得推荐。     

Heterometallic Nd(III) and Fe(III) Complexes with Succinic Acid and Its Derivative: Synthesis and Physicochemical Properties

Heterometallic Nd(III) and Fe(III) complexes with succinic, malic, and tartaric acids were synthesized and studied by IR spectroscopy, thermography, and dissolution calorimetry. The formation of heterometallic compounds with specific properties was confirmed by comparison of physicochemical characteristics of heteronuclear and the corresponding mononuclear carboxylates.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 5, 2005, pp. 397–400.Original Russian Text Copyright © 2005 by Shabanova, Frolov, Storozhenko, Zelenov.     

Preparation, characterization and in vivo evaluation of antihyperglycemic activity of microwave generated repaglinide solid dispersion

The influence of microwave technology on the in vitro dissolution rate and in vivo antihyperglycemic activity of a poorly water soluble drug, repaglinide (RG) was studied. Solid dispersions were prepared by conventional fusion method and microwave method using poloxamer 188. The dispersions were characterized by solubility study, dissolution study, Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Microwave generated solid dispersions exhibited remarkable improvement in solubility and dissolution rate compared to that of pure RG. Results of DSC, XRD and SEM study showed conversion of crystalline form of RG to amorphous form. In vivo studies revealed that the microwave generated solid dispersion showed significant improvements in antihyperglycemic activity as compared to RG alone, thus confirming the advantage of improved pharmacological activity of RG by microwave method. In conclusion, microwave method could be considered as simple, efficient and solvent free promising alternative method to prepare solid dispersion of poorly water soluble drug RG with significant enhancement in solubility, dissolution rate and antihyperglycemic activity.     

Rapid on-line sample dissolution assisted by focused microwave radiation for silicate analysis employing flame atomic absorption spectrometry: iron determination

An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF+HCl+HNO₃) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 μl). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 μg ml⁻¹ (which corresponds to an Fe₂O₃ content of 0.46%) and an analytical throughput of 10 h⁻¹ were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.     

Oxidative dissolution of refractory metals by chlorination in aqueous organic media

Chlorination of rhenium, tungsten, and molybdenum with gaseous chlorine in a dimethylformamide-water medium was studied. The degree to which the metals pass to the solution is higher in the presence of water. The activating effect of water is attributed to the catalytic properties of solutions of HCl in DMF. The activating effect on metal dissolution increases in the sequence W < Mo < Re.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 262–265.Original Russian Text Copyright © 2005 by N. Drobot, Trifonova, Krenev, D. Drobot.     

Kinetics and Mechanism of Reaction of Carbon Tetrachloride with Copper(0) in Dimethylformamide

Reaction of copper(0) with carbon tetrachloride in DMF was studied. In the absence of atmospheric oxygen, the oxidative dissolution of copper(0) occurs as one-electron transfer and gives rise to C₂Cl₂ and copper(I) complexes. Kinetic and thermodynamic parameters of the process are determined, and its mechanism was considered.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1194–1198.Original Russian Text Copyright © 2005 by Egorov, Matyukhova, Anisimov.     

Determination of total chromium in Marine Sediment Reference Material BCSS-1

The determination of Cr in National Research Council of Canada Marine Sediment Reference Material BCSS-1 is addressed. Mixed acid digestions utilizing HF, HClO₄ and HNO₃ were investigated. Single microwave assisted digestions in closed vessels at medium pressures (8 bar) were inappropriate (80% recovery). Double digestion at moderate pressure and digestions at high pressure (70 bar) or lengthy open-beaker hot plate dissolutions resulted in 93±5% recovery of certified Cr content. Flame atomic absorption and inductively coupled plasma atomic emission spectrometry were used for quantitation. In all cases, the method of standard additions was necessary to eliminate the approximately 10% enhancement in re- sponce relative to unmatched standards. Compared to a certified content of 123±7 g/g (mean and standard deviation), values of 116±6 were obtained using an open beaker digestion; 114±5 using a double microwave digestion at 8 bar; 113±2 for microwave digestion at high pressure and 111±4 at high pressure (81 bar) with triple microwave digestion in a Parr bomb. No acid dissolution procedure is adequate for Cr in this sample although recovery of total Cr is complete from National Institute of Standards and Technology Buffalo River Sediment (SRM 2704).     

Regeneration of a Solution for Electroless Copper Plating

The possibility of electrochemical regeneration of a solution for electroless copper plating by membrane electrolysis was studied. The conditions of anodic dissolution of copper in a spent solution for electroless copper plating, under which the concentration of copper ions increases at a rate exceeding by an order of magnitude that of their deposition in the course of electroless copper plating, were examined. A scheme for regeneration of spent solutions for electroless copper plating was suggested.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005, pp. 586–590.Original Russian Text Copyright © 2005 by Turaev, Kruglikov.     

钛铁矿中钛的测定

利用钛铁矿能显著吸收微波的介电特性,采用家用微波炉,在微波辐照下,用浓磷酸消解矿样,并用氧化还原滴定法测定钛的含量,试验结果表明,该方法能快速分解矿样,测定结果准确,与传统分析方法比较,该法具有简便、快速、低耗、适应大批量样品分析等优点。还对钛铁矿的结构作了X-射线衍射分析。     

Reply to “Comments on the paper entitled ‘The formulation and modelling of the anodic dissolution of zinc through adsorbed intermediates’ ” by C. Cachet et al.

The points raised in the paper entitled “Comments on the paper entitled ‘The formulation and modelling of the anodic dissolution of zinc through adsorbed intermediates”’ have been discussed. It has been shown that, in contrast to the statements in the “Comments”, most of the papers concerning the reaction schemes suggested for the interpretation of the dissolution or deposition of metals, which were considered as a support for the opinion of the Authors of the “Comments”, support the views expressed in our original paper [J. Electroanal. Chem. 583 (2005) 148]. On the other hand, it has been stressed again that the criticism expressed in the original paper refers to dubious conclusions drawn on the basis of transient measurements.