Environmental problems of finely dispersed titanium dioxide production

Finely dispersed titanium dioxide is widely used in modern technologies. Proved reserves of titanium ores in Russia are expected to meet industrial needs. However, the available facilities for the manufacture of titanium dioxide from ores are clearly insufficient, which naturally requires new plants to be put into operation. The technologies used for the production of titanium dioxide were developed as early as 1940s, when ecological aspects of the production process were almost not taken into account. The present survey analyzes environmental problems related to the titanium dioxide production according to the sulfate and chloride technologies in comparison with the fluoride process proposed for industrial implementation. The fluoride process has been examined as applied to ilmenite from the Turan deposit in Tomsk oblast, and some actions directed toward improvement of ecological parameters of this process have been proposed.     

Research of Fluorination Process of Rutile Concentrate

The brief review of industrial technologies of titanium-containing concentrates processing has been carried out. Drawbacks of the existing titanium manufacture schemes are shown and the necessity of the essentially new fluoride technologies development has been proved. The reactions proceeding during the fluorination of rutile concentrate with element fluoride are described in the given work. The thermodynamic research of the process has been carried using ASTRA software. Dependence of mass concentration change of titanium tetrafluoride has been investigated in products of reaction on the temperature of the process, and the choice of optimum excess of fluoride has been proved.     

A direct electrochemical route from ilmenite to hydrogen-storage ferrotitanium alloys

An unrecognised but predictable need for a hydrogen-supported society is tens or even hundreds of million tonnes of hydrogen-storage materials, and thus challenges existing technologies in terms of resource and economical realities. Ilmenite is an abundant mineral, and ferrotitanium alloys are among the earliest known hydrogen-storage materials. At present, industrial production of ferrotitanium alloys goes through separate extraction of individual metals, followed by a multistep arc-melting process. In particular, the extraction of titanium from ilmenite is highly energy intensive and tedious, accounting for titanium's high market price and restricted uses. This article reports the electrochemical synthesis of various ferrotitanium alloy powders directly from solid ilmenite in molten calcium chloride. More importantly, it demonstrates, for the first time, that such produced alloy powders can be used without further treatment for hydrogen storage and perform comparably with or better than similar products by means of other methods, but cost just a fraction.     

Use of Chelate Complexes of Lead(II) in Low-Temperature Technologies of Ceramic Piezoelectric Materials

Technology is suggested for fabrication of ceramic piezoelectric materials from the lead-containing ferroelectric phase. The technology includes a low-temperature synthesis of ultradispersed lead titanate and zirconate powders and also of phases of solid solutions on their basis and the low-temperature procedure for sintering of ceramic fabricated from ultradispersed powders of ferroelectric phases. As precursors used in the suggested low-temperature synthesis serve lead glycerate and tartrate. It was found that, when interacting (at temperatures of 240–330°C) with hydroxo-peroxo-aqua complexes of titanium and(or) zirconium(IV) in the course of 30–40 min, the precursors form ultradispersed powders of these phases, which are single-phase and contain particles with average size of less than 100 nm. It was shown that using the suggested technology makes it possible not only to reduce the energy expenditure for separate procedures for synthesis of ultradispersed ferroelectric phases and for synthesis of piezoelectric materials, but also to substantially diminish the discharge of lead(II) compounds into the atmosphere of industrial premises. It was also shown that the technology enables fabrication of piezoelectric materials with prescribed values of electrical parameters.

     

Application of ultrafiltration-complexation process for metal removal from pulp and paper industry wastewater

In recent years, the pulp and paper industries have been trying different technologies to reduce fresh water consumption in paper mills. This has led to a fast development of new wastewater treatment technologies for industrial reuse. Lately, water-soluble polymeric ligands have shown to be powerful substances to remove trace metals from industrial wastewater through ultrafiltration (UF). In the present study, polyethyleneimine (PEI) and polyvinylalcohol (PVA) were used as water-soluble polymeric macroligands. The UF experiments were carried out in stirred dead-end cells. The membrane used was formed from polyvinilidene fluoride (PVDF). The performance of water-soluble polymeric ligands was evaluated by determining metal removal and chemical oxygen demand (COD). In general, the complexation–ultrafiltration process was efficient for metal removal from wastewater, leading to a better effluent quality when compared to ultrafiltration without any ligands addition.     

利用偏钛酸浆料制备大比表面纳米管钛酸工艺的研究

以偏钛酸浆料为原料通过水热法合成了纳米管钛酸,并采用TEM,比表面积测定仪等分析手段观察其形貌和管径大小,测定了其比表面积和孔体积.同时运用正交实验法考察了反应温度、反应时间对纳米管钛酸比表面积和孔体积的影响.实验结果表明,所制备的纳米管钛酸平均比表面积高达 340m2 /g,最佳的制备工艺是:工业碱NaOH的质量分数为 25. 7 %、偏钛酸浆料的质量分数为 17. 1 %、后处理酸度为pH=1、反应温度为 120℃、反应时间为 20h.     

The influence of fluoride on the physicochemical properties of anodic oxide films formed on titanium surfaces

The influence of fluoride (and its concentration) on the electrochemical and semiconducting properties of anodic oxide films formed on titanium surfaces was investigated by performing electrochemical measurements (potentiodynamic/pontiostatic polarization, open circuit potential (OCP), and capacitance measurements) for a titanium/oxide film/solution interface system in fluoride-containing 1.0 M HClO(4) solution. On the basis of the Mott-Schottky analysis, and with taking into account both the surface reactions (or, say, the specifically chemical adsorption) of fluoride ions at the oxide film surface and the migration/intercalation of fluoride ions into the oxide film, the changes in the electrochemical behavior of titanium measured in this work (e.g., the blocked anodic oxygen evolution, the increased anodic steady-state current density, the positively shifted flat band potential, and the positively shifted film breakdown potential) were interpreted by the changes in the surface and the bulk physicochemical properties (e.g., the surface charges, surface state density, doping concentration, and the interfacial potential drops) of the anodic films grown on titanium. The fluoride concentrations tested in this work can be divided into three groups according to their effect on the electrochemical behavior of the oxide films: < or =0.001 M, 0.001-0.01 M, and >0.01 M. By tracing the changes of the OCP of the passivated titanium in fluoride-containing solutions, the deleterious/depassive effect of fluoride ions on the titanium oxide films was examined and evaluated with the parameter of the film breakdown time. It was also shown that the films anodically formed on titanium at higher potentials (>2.5 V) exhibited significantly higher stability against the fluoride attack than that either formed at lower potentials (<2.5 V) or formed natively in the air.     

Preparation and characterization of nitrogen-doped titanium dioxides

A type of high visible-light active titanium oxinitride(TiO2-xNx) powder was prepared by a simple proc-ess:the calcination of the hydrated titanium dioxide at the atmosphere of ammonia-argon using a tu-bular electric furnace at high temperatures. The hydrated titanium dioxide was synthesized as the precursor of TiO2-xNx using titanic acid as raw material,which came from sulfate technique of produc-ing titanium white. The effects of temperature and reaction time on the nitrogen content,grain size and crystal structure were studied. The visible-light activity and photocatalysis capability of the powder were also investigated.     

不同前驱体制备氮掺杂二氧化钛及其光催化性能比较

在氨气气氛中和不同温度下焙烧纳米管钛酸和商业Degussa-P25,得到两系列可见光响应型氮掺杂二氧化钛光催化剂.采用高分辨透射电子显微镜、紫外-可见漫反射光谱仪和X射线衍射仪对两系列样品的形貌、光谱吸收和晶体结构等物理化学性质进行了表征和比较.通过可见光光催化氧化丙烯评价系统对两系列样品的活性进行了评价.结果表明,600℃处理纳米管钛酸得到的催化剂可见光催化活性最好,是相同条件下处理Degussa-P25得到的催化剂(N-P25)活性的3.3倍.研究表明,纳米管钛酸是制备可见光响应型光催化剂较好的前驱体.     

Influence of dispersion aluminum powders on the regularities of their interaction with nitrogen

Regularities of the interaction of widely dispersed industrial powders and electroexplosive aluminum nanopowder with nitrogen under atmospheric pressure in a linearly rising temperature and isothermal conditions have been investigated. The effect of the powder’s dispersion and composition, and the structure of the oxide shell and metal core of the aluminum particles on the temperature range of reaction and its kinetic parameters is shown. The relationship between the process of dehydration of hydroxides that are part of the superficial oxide shell of Al particles and the initial temperature of interaction between the powders and nitrogen was investigated. It is shown that the staged nature of weight gain for powders in a nitrogen atmosphere that is observed under conditions of linear heating results from a change in the macrokinetic regime, due to the effect of the Al nitride layer.     

Hydrothermal synthesis and enhanced photocatalytic activity of mixed-phase TiO2 powders with controllable anatase/rutile ratio

In this study, mixed-phase TiO₂ powders were novelly synthesized via a facile and mild hydrothermal method without any post-heat treatment. TiOSO₄ and peroxide titanic acid (PTA) were used as inorganic titanium sources, while no special solvent or additive were introduced. The XRD and TEM results showed the mixed-phase TiO₂ powders were composed of anatase and rutile phases, and the PTA sol played an important role on forming the rutile nucleus. The proportion of rutile in the mixed-phase TiO₂ could be easily controlled in the range of 0%–70.5% by changing the amount of PTA sol used in the synthesis process. The UV-Visible absorption spectra indicated the prepared mixed-phase TiO₂ showed enhanced visible light absorption with the increase of rutile ratio. The photodegradation experiments revealed the mixed-phase TiO₂ exhibited the best photocatalytic activity at the rutile ratio of 41.5%, while a higher or lower rutile ratio both resulted in the decrease of photocatalytic activity.     

Solvothermal synthesis of photocatalytically active titania in acetic acid

A new solvothermal method has been developed for preparing nanocrystalline titania powders by reacting titanium isopropoxide with acetic acid. The photocatalytic activity of a sample prepared at 250°C is shown to far exceed the activity of a commercially available sample.     

Liquid membrane transportation of fluoride ions with alizarin based azacrown ether Zr-complex

A new alizarin based azacrown ether N-(alizarin-4-methylene)-4-azadibenzo-18-crown-6 (AMADCE) was synthesized, for the transportation of fluoride ions, by reacting 4-aza dibenzo 18-crown-6 with alizarin in the presence of formaldehyde. The compound forms a stable purple-red coloured complex with Zr(IV) in 0.5-1.0 M hydrochloric acid and gets quantitatively extracted into diphenyl ether. This diphenyl ether extract of the Zr(IV) complex instantaneously transfers fluoride ions from the aqueous phase, which was utilised for the sensitive determination and transportation of fluoride ions through the liquid membrane. The conditions like concentration of membrane phase, acidity of the source phase and the receiving phase, and the transportation time were optimized. The continuous transportation of fluoride ions was achieved by adding receptor ions like La³⁺ and Ca²⁺ in the receiving phase. The rate constant K and t_1/2 for the transportation were determined. The studies were extended for the removal of fluoride ions through the liquid membrane from the ground water samples and industrial effluent.     

锌掺杂TiO_2的制备及其可见光催化性能

以钛酸纳米管[H2Ti2O2(OH)2,NTA]作为钛的前驱体、ZnCl2为锌源,采用水热法制备了锌掺杂的TiO2光催化剂;采用X射线衍射仪和透射电镜分析了催化剂产物的晶体结构和微观形貌;同时以亚甲基蓝为模型反应物,研究了锌掺杂量和水热温度对催化剂可见光光催化性能的影响.结果表明,水热温度为130℃,锌掺杂量为0.5%时,所得样品的光催化性能最佳.     

Influence of chemical impurities in ammonium phosphate and ammonium sulfate on the properties of ABCE fire extinguishing dry powders

The influence of chemical impurities on hygroscopic properties, as well as on the grinding and modification efficiency of ammonium phosphate and ammonium sulfate was analyzed. It was shown that application of chemically pure ammonium sulfate and ammonium phosphate free of ammonium fluoride and magnesium phosphate impurities provides the best conditions for obtaining fire extinguishing dry powders with high fire suppression ability and properties that satisfy relevant specifications.     

Effects of Pretreatments on the Structure of Palladium-Containing Amorphous Alloys Followed by DSC

Amorphous PdZr, PdCuZr and PdCuSi alloy ribbons and powders are characterized by DSC, XRD and XPS in the as-received state and after treatments with oxygen, hydrogen or dilute hydrogen fluoride solution. Zr-containing alloys are shown to undergo substantial structural changes resulting in palladium enrichment on their surface, whereas no apparent changes in the bulk structure are found for PdCuSi. Catalytic activity and selectivity of the pretreated samples were tested in the hydrogenation of phenylacetylene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of rutile titanium dioxide from Russian raw materials

The conditions of the structure formation of rutile titanium dioxide from titanium dioxide (anatase) and titanium hydroxide isolated by thermolysis from the titanium compound (NH₄)₂TiO(SO₄)₂ · H₂O and by thermal hydrolysis of a titanium sulfate(IV) solution, respectively, were studied. It was shown that the mechanical activation of the studied powders causes, in addition to a decrease in the initial grain size, deep destructuring with the formation of the transition phase, which, in the process of the subsequent high-temperature treatment, functions as a matrix for the formation of rutile. The research results will be used for the development of a new variant of the technology for the synthesis of titanium dioxide, which is an important component of compositions for polymeric materials—in particular, the K-300-61 and K-153 adhesives.     

由工业硫酸钛液制备TiO2纳米微粉

本文首次报道了通过加入乙二醇单甲醚由工业硫酸钛液热水解制备ＴｉＯ２纳米微粉的工艺过程，并对其水解、煅烧条件进行了探讨。表征了ＴｉＯ２的晶型和颗粒度、分析了其纯度。结果表明，ＴｉＯ２为金红石型，颗粒大小为３５－４２ｎｍ，平均为３８ｎｍ，杂质含量小于０．１ｐｐｍ。     

Rapid volumetric method for the estimation of iron in presence of interfering ions

Summary It has been shown that in the photochemical reduction method for the volumetric estimation of iron, there is no interference by chromium, titanium, tungsten, molybdenum, manganese, cobalt, nickel and fluoride. This method is therefore recommended for a rapid determination of iron in alloys and ores without the elimination of these interfering ions. Vanadium, however, was found to give slightly higher values for iron.Our thanks are due to Prof. G.Gopala Rao for his kind interest in the work.     

Separation of carrier-free 48Sc tracer and its determination by isotopic dilution

An easy method for speedy and quantitative separation of carrier-free scandium tracer formed by the (48)Ti(22)(n,p)(48)Sc(21) nuclear reaction has been developed. Separation of (48)Sc (1.83 days) from the target titanium metal was carried out by co-precipitating the tracer with calcium fluoride precipitated at pH approximately 4 from the solution of irradiated titanium in hydrofluoric acid. The freshly formed fluoride precipitate was dissolved in conc. hydrochloric acid, and the tracer extracted with tributyl phosphate and then stripped into aqueous medium. The carrier-free tracer was estimated by isotopic dilution. with calcium fluoride as non-isotopic diluent.