Effect of synthesis conditions of pyrocarbon coatings on their corrosion resistance in H2SO4-HNO3 oxidizing mixture

Synthesis conditions of pyrocarbon coatings in a fluidized bed via pyrolysis of gaseous hydrocarbons from a CH₄-Ar mixture at temperatures of 1300–2000°C and from C₃H₆-Ar at 1200–1500°C were examined. The corrosion resistance of the pyrocarbon coatings in HNO₃-H₂SO₄ oxidizing mixture was studied.     

Nitration of pentaerythritol by HNO3-H2SO4-H2O system

Conclusions It was shown experimentally that the nitrating agent in the O-nitration of pentaerythritol by HNO₃-H₂SO₄-H₂O nitrating mixtures is not the nitronium cation but evidently the free unionized nitric acid molecule.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 134–140, January, 1970.     

硫氰酸盐光度法测定加压氧化钼精矿萃取液中的钼

本研究 采用硝酸-硫酸-磷酸混合酸溶解试样,建立了硫氰酸盐法测定钼精矿加压氧化萃取液中钼含量的测定方法。对试样的分解方法进行了研究,并通过还原剂选择、酸度的影响及显色条件等一系列条件试验,确定出了最佳试验方法。采用本法对试液进行多次测定,相对标准偏差RSD为<小于1％。试验结果表明,该方法有较高的精密度,测定结果准确可靠,现已成功应用于实际生产检测中。     

Activated Carbons Prepared from Chemically Modified Sapropelites

Changes in sapropelite structure at room temperature in the course of modification with HNO₃, HNO₃-Ac₂O, SO₃-H₂SO₄, and H₂SO₄ were studied. The effect of chemical modification on the development of the specific surface area at thermolysis in the presence of acid (H₃PO₄) or base (KOH) activators was analyzed.     

电解制备二氧化锰强酸性电解液中气体扩散电极的稳定性与失效行为

采用气体扩散电极(GDE)代替传统析氢阴极电解制备二氧化锰(EMD),重点研究了气体扩散电极在强酸性MnSO4-H2SO4电解液中的稳定性、寿命及失效行为.结果表明:气体扩散电极在MnSO4-H2SO4电解液中重现性好、具有一定的稳定性,寿命可达400 h;平行实验表明,阳极沉积一定厚度的EMD是槽电压第一次升高的主要原因;电流密度为100 A m-2时,气体扩散电极失效前阴极过程的速度由氧的离子化反应和氧的扩散混合控制,失效后阴极过程由氧去极化和氢去极化共同组成,主要发生析氢反应;催化层聚四氟乙烯(PTFE)网络结构的破坏和镍网层的溶解是电极失效的原因之一;Pt的团聚降低了电极的电催化活性,是电极失效的主要原因;阴极失效是槽电压再次升高的主要原因.     

Critical comparison of wet and dry digestion procedures for trace metal analysis of meat and fish tissues

The efficiency of four methods of digestion was evaluated for trace metal analysis of pork meat and carp fish tissues. Two methods of dry and two methods of wet ashing were compared in terms of calculated variances. Mixtures of HCl+HNO₃ were applied for wet ashing of the samples at 100 °C, while dry ashing with or without H₂SO₄ at 450 °C were the alternative methods. The digests were subsequently analysed for Pb, Cd, Cu and Zn by graphite furnace atomic absorption spectrometry. Analysis of variance and Student's t-test were performed separately for meat and fish analytical results. Wet digestion with a (1+1) mixture of HCl+HNO₃ has given better recovery and repeatability for almost all metals than a (9+1) mixture of HCl+HNO₃. Also between the dry ashing methods, the use of H₂SO₄ has given better results than ashing of the tissues without H₂SO₄.     

Nitration of photochromic spirophenanthroxazine

Nitration of photochromic spirophenanthrooxazine with three different reagents (cupric nitrate, NaNO₂ in acetic acid, and HNO₃-H₂SO₄) was studied. The major reaction products were specified and characterized by ¹H and ¹³C NMR and mass spectra. The mechanisms of their formation were proposed. Only the nitration with a mixture of nitric and sulfuric acids yielded a photochromic product containing the nitro group in the phenanthrene fragment. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1670–1677, July, 2005.     

Chemoselective electrolytic chlorination of methyl group of 3-methyl-3-butenoate moiety of thiazoline-azetidinone homologues

Chemoselective electrochlorination of the methyl group on the 3-methyl-3-butenoate moiety of thiazoline-azetidinone derivatives derived from penicillins G and V has been performed in a CH₂Cl₂-H₂O-NaCl-H₂SO₄-(Pt or C electrodes) system by adjusting the amount of electricity passed as well as the concentration of Cl^? in the media.     

Electrochemical oxidative modification of nanocarbon materials in aqueous electrolyte solutions

The effect exerted by electrochemical oxidative modification of carbon nanofibers and nanotubes by anodic and successive cathodic and anodic polarization in aqueous solutions of electrolytes H₂SO₄, CH₃COONH₄, HNO₃, (NH₄)₂SO₄, [H₂SO₄ + (NH₄)₂SO₄] on the structure and morphology of the fibers constituting the nanomaterials, on the composition of surface groups, on the stationary electrode potential of carbon nanofibers, and on properties of epoxy–carbon composites was studied. The results of the electrochemical modification were compared to the results of chemical modification of carbon nanofibers in a 6.0 M HNO₃ solution and of carbon nanotubes in a mixture of concentrated acids H₂SO₄ + HNO₃.     

Electrochemical behavior of [UO_2Cl_4]~(2-) in 1-ethyl-3-methylimidazolium based ionic liquids

In order to examine the chemical form of uranyl species in 1-ethyl-3-methylimidazolium(EMI) based ionic liquids,UV-visible absorption spectra of solutions prepared by dissolving [EMI] 2 [UO2Cl4] into a mixture of EMICl and EMIBF 4(50:50 mol%) were measured.As a result,it was confirmed that uranyl species in the mixture of EMICl and EMIBF 4 existed as [UO2Cl4]2-.Cyclic voltammograms(CVs) of [UO2Cl4]2-in the mixture were measured at 25 ℃ using a Pt working electrode,a Pt wire counter electrode,and an Ag/Ag + reference electrode(0.01 M AgNO 3,0.1 M tetrabutylammonium perchlorate in acetonitrile) in a glove box under an Ar atmosphere.Peaks corresponding to one redox couple were observed around-1.05 V(Epc) and-0.92 V(Epa) vs.ferrocene/ferrocenium ion(Fc/Fc +).The potential differences between two peaks(Ep) increased from 101 to 152 mV with an increase in the scan rate from 50 to 300 mV s-1,while the(Epc+Epa)/2 value was constant,-0.989 V vs.Fc/Fc + regardless of the scan rate.Furthermore,the diffusion coefficient of [UO2Cl4]2-and the standard rate constant were estimated to be 3.7 × 10-8 cm 2 s-1 and(2.7-2.8) × 10-4 cm s-1 at 25 oC.By using the diffusion coefficient and the standard rate constant,the simulation of CVs was performed based on the reaction,[UO2Cl4]2-+ e = [UO2Cl4]3-.The simulated CVs were found to be consistent with the experimental ones.From these results,it is concluded that [UO2Cl4]2-in the mixture of EMICl and EMIBF 4 is reduced to [UO2Cl4]3-quasi-reversibly at-0.989 V vs.Fc/Fc +.     

热力学模型研究KNO3-K2SO4-H2O和KNO3-KCl-H2O体系溶解度

用Pitzer-Simonson-Clegg热力学模型(PSC模型),分别拟合KCl-H2O、K2SO4-H2O、KNO3-H2O体系以及KNO3-K2SO4-H2O和KNO3-KCl-H2O体系水活度和溶解度实验数据,得到二元参数和三元离子相互作用参数,并以此计算3个二元盐水体系溶解度相图,及2个三元盐水体系在不同温度下的溶解度,结果表明计算值与实验值一致。     

Glass formation in the Al2(SO4)3-AlCl3-H2O system

Glass formation boundaries in the Al₂(SO₄)₃-AlCl₃-H₂O system were determined. The glass-formation abilities and crystallization resistance of samples were studied. A glass formation mechanism was suggested. Comparative analysis of the glass-formation abilities of samples of the Al₂(SO₄)₃-Al(NO₃)₃-H₂O and Al₂(SO₄)₃-AlCl₃-H₂O systems was carried out.     

Solvent extraction of hafnium(IV)

^{175, 181}Hafnium(IV) was extracted by HDBP in 2-ethylhexanol from 1–10M solutions of HClO₄, HCl and HNO₃, and 1–8M H₂SO₄. As with low polar organic phase diluents, the acidity dependence of the distribution ratio of Hf, D, passes through a minimum for HClO₄, HCl, and H₂SO₄ whereas only an increase of D can be observed with increasing HNO₃ concentration. From the slope analysis the following complexes were found to be extracted (HDBP=HA): HfA₄ at <4M HClO₄ and <5M HCl, lg K_extr=9, HfX₄(HA)₄ (X=ClO ₄ ⁻ , Cl⁻ or NO ₃ ⁻ ) at >5M HClO₄, >7M HCl and 1–10M HNO₃, Hf(SO₄)A₂(HA)_3–4 at <3M H₂SO₄, and Hf(SO₄)₂ (HA)₄ at >6M H₂SO₄. Coextraction of sulphate with hafnium from H₂SO₄ solutions was evidenced in experiments with macro concentrations of Hf(IV) and³⁵SO ₄ ²⁻ . Part XX: Coll. Czech. Chem. Commun., 40 (1975) 3617.     

Determination of uranium in the presence of iron and plutonium by Ti(III) reduction and biamperometric titration

A method is described for the determination of uranium in the presence of iron and plutonium. Ti(III) is used as the reductant in a mixture of H₂SO₄ and HNO₃. Fe(II) and Pu(III) are selectively oxidized by the nitrous acid generated in the reaction between Ti(III) and HNO₃. The U(IV) is determined by titration with K₂Cr₂O₇ using biamperometry to detect the end point. The method is applicable to a variety of nuclear materials encountered at different stages of the nuclear fuel cycle and has no bias. The precision of the method is evaluated at different levels from 100 microgram to 100 milligram. The method is simple, rapid and convenient.     

Glass formation in the systems Al2(SO4)3-MSO4-H2O (M = Cd2+, Zn2+, Mg2+) and Al2(SO4)3-Fe2(SO4)3-H2O

The glass formation region boundaries were found in the systems Al₂(SO₄)₃-MSO₄-H₂O, where M = Cd²⁺, Zn²⁺, and Mg²⁺, and Al₂(SO₄)₃-Fe₂(SO₄)₃-H₂O. The causes of the differences in glass-forming ability between the studied systems were analyzed. The structures and properties of glassy Al₂(SO₄)₃ · 11H₂O and Fe₂(SO₄)₃ · 11H₂O were compared.     

Heterocyclic analogs of pleiadiene XXXV. Investigation of chlorination of perimidine and its 1- and 2-methyl derivatives

The mono-, di-, tri-, and tetrachloro derivatives of perimidine and 1- and 2-methylperimidines were obtained by chlorination with sulfuryl chloride and 1-chlorobenzotriazole. Primarily the 6 and 7 positions are initially attacked by the electrophile in acidic media (SO₂Cl₂-CH₃COOH), whereas the 9 and 4 positions of the perimidine system become more active under neutral conditions (1-chlorobenzotriazole in CHCl₃).See [1] for communication XXXIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 977–984, July, 1978.     

Effects of temperature on nitration of sulfamates

Ammonium dinitramide (ADN) has attracted great interest as a potential oxidizer for next generation rocket propellants. It is a halogen-free alternative to ammonium perchlorate, which is currently in wide used as a solid propellant oxidizer. However, in ADN synthesis, N-nitration is necessary to form the N-(NO₂)₂ group. Using a reaction calorimeter, the thermal behavior of nitration of sulfamates (K, Na, and NH₄) using a mixture of acids (HNO₃/H₂SO₄ and HNO₃/AcOH) as the nitration agent was examined. The heat of decomposition of potassium sulfamate at ?10 °C was greater than that at 20 °C. The heat of decomposition decreased in the following order: K salt>Na salt>NH₄ salt in HNO₃/H₂SO₄. The dipole moments of the sulfamates were calculated, and the results revealed that the electronic states of nitrogen were different. Thus, the dipole moments of sulfamates affect the decomposition heat of sulfamates. The heat of decomposition in HNO₃/AcOH was larger than that in HNO₃/H₂SO₄.     

Synthesis of β-nitroxyalkylnitramines

β-Nitroxyalkylnitramines were obtained by nitration of β-hydroxyalkyl sulfamates, products of the condensation of derivatives of sulfamic acid with alkene oxides, by a mixture of HNO₃ and H₂SO₄. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1061–1062, May, 1997.     

Some further observations on the systems cellulose/trifluoroacetic acid/CH2Cl2 and cellulose triacetate/TFA/CH2Cl2

There is little or no trifluoroacetylation of cellulose dissolved in TFA-CH₂Cl₂ admixtures. Both cellulose and cellulose triacetate (CTA)are slowly degraded in the solvent. Cellulose forms a mesophase as low as 4%(w/w)concentration, but CTA has a much higher critical concentration, 20% (w/w), in TFA-CH₂Cl₂. The cellulose behaves as a rigid rod in TFA-CH₂Cl₂ (70/30v/v) and its persistence length calculated using the lattice model approximates its chain length, presumably due to extensive interaction with the solvent. As expected, due to low polymer-solvent interactions, the persistence length of CTA in TFA-CH₂Cl₂ is only one-fourth the chain length.     

A novel and efficient method for the synthesis of polyfluoroarenesulfonyl bromides from polyfluoroarenethiols

The first general methodology has been developed for the synthesis of polyfluoroarenesulfonyl bromides from polyfluoroarenethiols. At heating of polyfluoroarenethiols with a mixture of Br₂ and fuming HNO₃ or Br₂, HNO₃ and H₂SO₄ polyfluoroarenesulfonyl bromides were obtained in good yields.