DTA-EGA Observations of vanadium precipitates in low alloy steel

Differential thermal analysis-evolved gas analysis (DTA-EGA) has been used, along with x-ray diffraction and microchemical techniques, to study the effect of varying the concentrations of vanadium, carbon, and nitrogen added to steels upon the composition of the second-phase compounds isolated. It was thus possible to identify and quantitatively measure vanadium carbide, nitride, and carbonitride in the presence of one another in the isolated residues. The effect of various heat treatments of the steels upon the composition of the second-phase compounds will also be presented.     

钒钛物料中钒钛化学物相分析现状及最新进展

主要概述了钒钛炉渣原料中价态钒(V2+,V3+,V4+,V5+),低价钛(Ti 2+,Ti 3+),金属钒(MV),氮化钒(VN),碳化钒(VC),碳化钛(TiC),氮化钛(TiN)及钢铁材料里固溶钒(Vsol),氮化钒(VN),碳化钒(VC),固溶钛(Tisol),碳化钛(TiC),氮化钛(TiN)等的化学物相分析的现状流程及最新进展,为从事钒钛化学物相分析方法研究者提供了参考依据。     

Colorimetric determination of carbon in titanium

A method is proposed for the colorimetric determination of carbon in titanium. In the method the sample is dissolved in a mixture of sulfuric and fluoboric acids, and nitric acid is added to dissolve the titanium carbide. The solution is boiled and filtered, and the yellow coloration from the nitrated organic complex is read with a spectrophotometer. A spectrophotometric study of the color was made. A comparison was made between the colorimetric determination of carbon in titanium and the colorimetric determination of carbon in steels. The proposed method is rapid and is readily adaptable to the determination of carbon in a large number of samples at one time. The procedure is designed for titanium containing up to 0.7 per cent. carbon. None of the elements encountered in “commercially pure” titanium metal interferes.     

Erosion-resistant metal nitride coatings and carbide and their plasmochemical synthesis

The influence of ion-plasma coatings made from high-hardness metal compounds on the erosion and corrosion resistance and mechanical properties of the alloy (substrate) + coating system is studied. The influence of the thickness, composition, and design of coatings based on metal nitrides and carbides on the relative gas-abrasive wear resistance of alloy+coating compositions in a gas-abrasive flux of quartz sand is discussed. It is shown that the zirconium nitride coating provides the best protection for compressor blades made of titanium alloys, without any decrease in fatigue resistance of the alloys, and chromium carbide coating is the most appropriate protection for steel compressor blades.     

A highly selective procedure for the spectrophotometric determination of aluminium with 8-hydroxy-quinoline and its application to the determination of

Aluminium, hydroxyquinolate can be quantitatively extracted by chloroform from an ammoniacal solution containing hydroxyquinoline, complexone and cyanide. Likewise extracted are titanium, vanadium, tantalum, niobium, uranium, zirconium, gallium, antimony, bismuth, indium and traces of beryllium. Aluminium can be separated from the first five elements by an extraction in ammoniacal solution containing hydrogen peroxide.Zirconium, gallium, bismuth and antimony can be eliminated by a cupferron extraction and indium by extraction with diethyldithiocarbamate. Beryllium is eliminated by performing an extraction with hydroxyquinoline at pH 5. The proposed method enables a practically specific photometrical determination of aluminium. Applications are given of the determination of trace and higher amounts of aluminium in steels, non-ferrous alloys and in glass.     

Determination of niobium in zirconium-niobium alloys

A rapid control determination of niobium in 50% zirconium/50% niobium master-alloy is described; it is a direct spectrophotometric procedure, based on the reaction of niobium ions with hydrogen peroxide in concentrated sulphuric acid. The procedure is suitable for the examination of zirconium alloys containing niobium in the range 0.1 to about 60%. At least 1% of chromium, cobalt, copper, manganese, nickel or tantalum, does not interfere. Interference due to optical absorption by the peroxy-complexes of titanium, tungsten, molybdenum and vanadium is not significant in the determination of niobium above about 1%, provided that these metals are not in excess of about 0.5%, 0.25%, 0.1% and 0.02%, respectively. To compensate for optical absorption due to iron(III), a solution of the sample, not treated with peroxide, is used.     

Possibilités d'obtention de dépôts dans le système céramique ti-v-c-n à partir de sources moléculaires

Monometallic and heterobtmetallic titanium and vanadium compounds were prepared and studied as precursors to the chemical vapor deposition (CVD) of carbide and nitride ceramic thin films. Their thermal properties are discussed according to the chemical environment of the metal atom and their CVD behavior is studied. Two of them, CpTiCl₂N(SiMe₃)₂ and Cp₂VMe₂, are applied to the deposition of thin films within the Ti-V-C-N quaternary system.     

Analysis of niobium alloys

An ion-exchange method was applied to the analysis of synthetic mixtures representing various niobium-base alloys. The alloying elements which were separated and determined include vanadium, zirconium, hafnium, titanium, molybdenum, tungsten and tantalum. Mixtures containing zirconium or hafnium, tungsten, tantalum and niobium were separated by means of a single short column. Coupled columns were employed for the resolution of mixtures containing vanadium, zirconium or titanium, molybdenum, tungsten and niobium. The separation procedures and the methods employed for the determination of the alloying elements in their separate fractions are described.     

过渡金属乙烯齐聚与聚合催化剂研究进展

综述了近年来过渡金属配合物催化乙烯齐聚与聚合的最新进展;介绍了乙烯齐聚或聚合的反应时间、反应温度、乙烯压力、助催化剂用量等反应条件及配体上不同取代基对前过渡金属(铬,锆,钛,钒)和后过渡金属(铁,钴,镍,铜)配合物的催化活性和齐聚或聚合产物的影响;分别以钛和镍配合物催化剂为例,介绍了前过渡金属和后过渡金属催化乙烯齐聚或聚合的机理。     

Characterization of vanadium and titanium oxide supported SBA-15

Supported vanadium and titanium oxide catalysts were prepared by adsorption and subsequent calcination of the vanadyl and titanyl acetylacetonate complexes, respectively, on mesoporous SBA-15 by the molecular designed dispersion (MDD) method. Liquid and gas phase depositions at different temperatures were carried out with vanadyl acetylacetonate, and the different results together with those of titanyl acetylacetonate in the liquid phase deposition were discussed. The bonding mechanism, the influence of the metal interaction with the support material, and differences due to the way of deposition and the temperature were investigated by TGA, chemical analysis, FTIR, and Raman spectroscopy. Elevated dissolving temperatures in the liquid phase led to higher final loadings on the SBA-15 without the formation of clusters, even at high loadings. The decomposition of the anchored vanadium and titanium complexes, their thermal stability, and the conversion to the covalently bound VO(x) and TiO(x) species on SBA-15 were studied and investigated by in situ transmission IR spectroscopy. In general, the titanium complex is more reactive than the vanadium complex toward the surface of SBA-15 and has a higher thermal stability. The MDD method of the VO(acac)2 and TiO(acac)2 enables to create a dispersed surface of supported VO(x) and TiO(x), respectively. The structure configurations of VO(x) and TiO(x) oxide catalysts obtained at different metal loadings were studied by Raman spectroscopy. Pore size distributions, XRD, and N2 sorption confirmed the structural stability of these materials after grafting. VO(x)/SBA-15 and TiO(x)/SBA-15 samples, with different metal loadings, were also catalytically tested for the selective catalytic reduction (SCR) of NO with ammonia.     

Anion-exchange separation and spectrophotometric determination of vanadium in silicate rocks

A combined anion-exchange-spectrophotometric method has been developed for the determination of vanadium in silicate rocks. A rock sample weighing about 0.1 g is decomposed with a mixture of sulphuric and hydrofluoric acids and after removal of HF the residue is taken up with dilute sulphuric acid. This solution is adjusted to be 0.05M in sulphuric acid and contain 0.3% hydrogen peroxide, and is passed through a column of Amberlite CG 400 (sulphate form). The sorbed vanadium is eluted with 30 ml of 1M hydrochloric acid. The effluent is evaporated to dryness, made 0.1M in hydrochloric acid and 3% in hydrogen peroxide content, and passed through a column of Amberlite CG 400 (chloride form) to get rid of accompanying thorium and zirconium. Vanadium is stripped by elution with 20 ml of 1M hydrochloric acid and subsequently determined spectrophotometrically with 4-(2-pyridylazo)resorcinol. The detection limit is 0.4 ppm.     

Low-temperature synthesis of nanodispersed titanium,zirconium, and hafnium carbides

Nanosized refractory titanium, zirconium, and hafnium carbides were manufactured from highly dispersed metal dioxide-carbon starting mixtures at moderate temperatures of 1200°C or lower. The products were characterized by powder X-ray diffraction, elemental analysis, and transmission electron microscopy. The average size of particles (in nanometers) manufactured at 1200°C was as follows: for TiC, 13 ± 4; for ZrC, 17 ± 3; and for HfC, 16 ± 3; the average crystallite size (in nanometers) was as follows: for TiC, 8 ± 2; for ZrC, 5 ± 2; and for HfC, 8 ± 3. Thermodynamic modeling was performed for the synthesis of Group IVB carbides via carbothermal reduction of the corresponding oxides. The results show that in the titanium dioxide-carbon system, for example, titanium monocarbide formation is possible at a temperature as low as 850°C (p = 10⁻⁴ MPa). Highly dispersed metal dioxide-carbon starting mixtures were prepared using solgel technology from metal alkoxyacetylacetonates in the presence of a polymeric carbon source.     

Problèmes spécifiques liés à la vaporisation des précurseurs organométalliques solides utilisés pour les dépôts dans le système V-C-N

The pyrolysis behaviours of titanocene dichloride and vanadocene used as a precursor for the chemical vapor deposition of titanium carbide and vanadium carbide, respectively, are studied. The influence of the gas-phase transport of these compounds on the properties of the deposits is also discussed according to the vaporization procedure.     

Étude sur le dosage colorimétrique de l'aluminium dans les aciers

Colorimetric determination of aluminium by means of a new reagent, stilbazo, is studied.The investigation leads to a method for the direct determination of aluminiumsteel alloys: nitrided steels, magnetic steels.The aluminium is determined by a technique consisting of electrolysis with mercury cathode, separation of titanium and vanadium, if present, by chloroform extraction of the complexes of these elements with cupferron, and, finally, colorimetric determination.During these experimental investigations, observations have been made concerning the influence of a number of elements on the reaction of aluminium with stilbazo. The reactions of vanadium with various reagents (dicyandiamidine, diantipyrylphenylmethane, a-benzoinoxime) and the silico-vanado-tungstic complex have been studied.     

The differentiation of submicrogram amounts of inorganic and organomercury in water by flameless atomic absorption spectrometry

The basic conditions for the determination of niobium, titanium and zirconium with an argon plasma and a Hitachi UHF Plasma Spectrascan operated at 2450 MHz and 450 W maximum output, have been established. The niobium 405.89-nm, titanium 365.35-nm and zirconium 339.19-nm lines gave detection limits of 0.5, 0.1 and 2.0 p.p.m., respectively, when pure solutions were used. Effects of gas flow rates, high-frequency output and concentration of acids were examined. In applications to steel, titanium was determined without prior chemical separation from iron at the 499.95-nm line, whereas niobium and zirconium could not be determined in the presence of large amounts of iron. When a cupferron precipitation method followed by extraction of iron with methyl isobutyl ketone was applied, satisfactory results were obtained.     

Determination of niobium, titanium and zirconium by high-frequency plasma torch emission spectrometry and its application to steel

The basic conditions for the determination of niobium, titanium and zirconium with an argon plasma and a Hitachi UHF Plasma Spectrascan operated at 2450 MHz and 450 W maximum output, have been established. The niobium 405.89-nm, titanium 365.35-nm and zirconium 339.19-nm lines gave detection limits of 0.5, 0.1 and 2.0 p.p.m., respectively, when pure solutions were used. Effects of gas flow rates, high-frequency output and concentration of acids were examined. In applications to steel, titanium was determined without prior chemical separation from iron at the 499.95-nm line, whereas niobium and zirconium could not be determined in the presence of large amounts of iron. When a cupferron precipitation method followed by extraction of iron with methyl isobutyl ketone was applied, satisfactory results were obtained.     

石墨炉原子吸收法测定钢铁及合金中微量钒

探讨了石墨炉子吸收法测定钢铁及合金中微量钒的各种实验条件及影响因素。实验表明，采用热解涂层管与光控升温相结合并在温度稳定的情况下原子化，可改善信号峰形，提高灵敏度，消除记忆效应。方法用于钢铁及合金中钒的分析，结果令人满意。     

Growth of Single-Walled Carbon Nanotubes with Controlled Structure: Floating Carbide Solid Catalysts

Single-walled carbon nanotube (SWNT) horizontal arrays with specific chirality can be enriched using solid carbide catalysts on substrates. However, scale-up production by continuous loading of the solid catalysts onto the substrates is challenging. Described here is the preparation of a floating carbide solid catalyst (FSC) for the controlled growth of SWNTs. The FSC, titanium carbide (TiC) nanoparticle, was directly obtained in the carrier gas phase by decomposition and carbonization of the titanocene dichloride precursor at high temperature. By using the TiC nanoparticle FSC, both SWNT horizontal arrays and randomly distributed networks can be obtained. The chirality of the as-grown SWNTs were thermodynamically controlled to have fourfold symmetry. Further optimization of growth condition resulted in an abundance of (16,8) tubes with about a 74 % content. This FSC chemical vapor deposition (FSCCVD) method has potential for realizing mass growth of SWNTs with controlled structures.     

Thermal effects and vibrational corrections to transition metal NMR chemical shifts

Both zero-point and classical thermal effects on the chemical shift of transition metals have been calculated at appropriate levels of density functional theory for a number of complexes of titanium, vanadium, manganese and iron. The zero-point effects were computed by applying a perturbational approach, whereas classical thermal effects were probed by Car-Parrinello molecular dynamics simulations. The systematic investigation shows that both procedures lead to a deshielding of the magnetic shielding constants evaluated at the GIAO-B3 LYP level, which in general also leads to a downfield shift in the relative chemical shifts, delta. The effect is small for the titanium and vanadium complexes, where it is typically on the order of a few dozen ppm, and is larger for the manganese and iron complexes, where it can amount to several hundred ppm. Zero-point corrections are usually smaller than the classical thermal effect. The pronounced downfield shift is due to the sensitivity of the shielding of the metal centre with regard to the metal-ligand bond length, which increase upon vibrational averaging. Both applied methods improve the accuracy of the chemical shifts in some cases, but not in general.     

Hydrogenation of CO over carbides of tungsten

CO hydrogenation on tungsten carbides has been investigated.The methanation activitiesof tungsten carbides are comparable to that of supported Group VIII metal catalysts.Temperature-programmed thermal desorption spectra of CO on tungsten carbide show that CO is adsorbed non-dissociatively,and the surface—CO bond appears to be rather weak.