Physicochemical principles underlying the preparation of high-purity substances for microelectronic and optical applications

This paper presents results on liquid-vapor, solid-vapor, liquid-liquid, and crystal-melt equilibria in solvent-solute systems. The data provide a physicochemical basis for the development of processes for the ultrapurification of volatile compounds of group II to VI elements (halides, hydrides, metalorganic compounds, and elemental substances).     

Physicochemical aspects of the preparation of high-purity arsenic-containing substances from various raw materials

We have developed physicochemical principles of the preparation of high-purity arsenic-containing substances from conventional (As₂S₃, As₄S₄, and FeAsS sulfide ores) and unconventional raw materials (chemical warfare (lewisite) detoxification products, semiconductor fabrication waste, and nonferrous metals industry waste). We have identified and investigated transformations of chemical forms of impurities in the recovery, synthesis, and ultrapurification of arsenic-containing compounds. The observed fundamental aspects of the behavior of impurities, with allowance for the origin of the raw materials to be processed, were taken as a basis for designing combined, environmentally friendly processing schemes for the preparation of high-purity arsenic and arsenic compounds (AsCl₃ and AsH₃).     

Thermal decomposition of arsine,a lewisite detoxification by-product

We developed the physicochemical principles of the thermal decomposition of arsine resulting from the electrochemical reduction of the products of lewisite detoxification by alkaline hydrolysis. The thermodynamic and kinetic parameters of the thermal dissociation of arsine were calculated for the temperature range of practical interest in order to minimize the arsine concentration in the effluent gas. A process was proposed and tested for processing lewisite detoxification products which includes the thermal decomposition of arsine. The resultant arsenic is 99.9999% pure. Based on the scientific and technological foundations of arsine pyrolysis, we designed a system for the thermal decomposition of arsine, which was integrated into a lewisite detoxification process.     

Physicochemical principles of preparation of U(VI) carbonate solutions for extraction reprocessing in the Carbex process

Physicochemical principles of preparation of U(VI) carbonate solutions in the step of oxidative dissolution of U₃O₈ and UO₂ in the Carbex process are considered. Carbonate solutions with the U(VI) concentration higher than 100 g L^–1, suitable for subsequent final purification of uranium by extraction, can be prepared under the conditions of formation of U(VI) carbonate–peroxide complexes in the course of dissolution with prevention of hydrolysis of U(VI) compounds. The behavior of impurities simulating some fission products in the course of oxidative dissolution was studied, and the decontamination factors of U(VI) from the chosen simulated fission products were determined.     

Physicochemical principles of the decontamination and utilization of arsenic-containing waste

Thermodynamic computer simulation of heterogeneous multicomponent systems containing arsenic(III), arsenic(V), and calcium chlorides, hydrochloric acid, nitric acid, hydrogen peroxide, and oxygen is carried out for temperatures of 25–100‡C. The solute state of arsenic is found to influence the fugacities of arsenic trichloride and hydrogen chloride. Arsenic(III) oxidation in chloride solutions and distillation of arsenic-containing solutions in the presence of oxidants are studied experimentally to determine conditions for a rapid and virtually complete oxidation of arsenic in chloride solutions by nitric acid, ammonium nitrate, and hydrogen peroxide.     

Dissolution of high-purity lead and subsequent crystal growth during the preparation of corrosion coupons

High-purity lead discs were prepared using several combinations of polishing, rinsing and ultrasonic treatment. Physical degradation of the lead surface and the premature generation and deposition of oxides on the surface were observed for certain combinations of preparation steps. Ultrasonic treatment of the discs was found to be particularly detrimental as it induced significant crystal growth and, in several instances, deterioration of the polished surface. Simple air drying of freshly rinsed discs also led to oxide formation on the surface after as short a time as 1 min. An effective method for preparing discs from high-purity lead is described. This revised version was published online in November 2006 with corrections to the Cover Date.     

高纯金属酞菁的制备及其对TiO2光催化性能的影响研究

通过简易的溶液沉淀分离方法制得了纯度>97%的高纯金属酞菁的二甲基亚砜(DMSO)溶液。应用制得产物对TiO2 薄膜进行敏化,发现经酞菁铁(FePc)、酞菁钴(CoPc)、双核酞菁钴铁(CoFePc)敏化的TiO2 薄膜的光催化性能分别较未经敏化的TiO2薄膜提高67.3%、63.0%、16.1%,并通过一系列的对比实验解释了双核酞菁钴铁催化效率低于前两者的原因,为后继利用酞菁敏化TiO2 及其它光催化材料提供借鉴。     

Electrochemical preparation of metal cluster compounds

The electrochemical formation of low-valent cluster compounds is described. K₄Nb₆Cl₁₈ crystallizes on the cathode at 610°C, when an eutectic KiCl/KCl melt containing Nb₃Cl₈ is electrolysed with a niobium anode at 0.6 to 1.2 V cell voltage. Electrolysis of GdCl₃ at 770° yields h-GdCl both at the tantalum cathode and the gadolinium anode. Crystals of Gd₂Cl₃ form by the secondary reaction between GdCl and the GdCl₃ electrolyte upon slow cooling. The new cluster compound Gd₅Cl₉C₂ which contains interstitial C₂ units is formed, when a graphite crucible is serving as cathode.     

Preparation of high-purity gallium from semiconductor fabrication waste

This review summarizes the results of systematic studies aimed at developing processes for the preparation of high-purity gallium from semiconductor fabrication waste. A classification is proposed for Gacontaining waste materials according to the host and impurity compositions. We compare the efficiencies of different processes for the fine purification of crude gallium recovered from waste materials: wet-chemical processing, vacuum heat treatment, filtration, electrorefining, and directional solidification. Taking into account the behavior of impurities during the purification process and the nature of the waste materials, we have developed a multistep, environmentally safe process for preparing high-purity (99.9999%) gallium from unconventional raw materials. The product of this process compares well with gallium produced from conventional raw materials. We demonstrate that the use of semiconductor fabrication wastes as raw materials in large-scale-production of high-purity gallium and related microelectronic products is a commercially viable approach.     

A novel depot preparation of desferrioxamine-B: development of formulation principles

This report describes the feasibility of simple oil-based depot formulations of a novel n-decanesulfonate salt of the iron chelator desferrioxamine-B. After subcutaneous administration in rodents, desferrioxamine-B n-decanesulfonate depot induces both (a) prolonged release of drug and (b) an increase of at least threefold to fourfold in iron excretion efficiency compared with the parent compound Desferal (desferrioxamine-B mesylate). Optimization experiments probing vehicle composition, surfactant loading, drug loading, and particle size distribution of the depot preparation are described, and the physiochemical stability of an identified pilot formulation is assessed.     

Treatment of groundwater polluted by arsenic compounds by zero valent iron

Batch experiments were carried out to study the kinetics and efficiency of inorganic arsenic removal by zero valent iron (ZVI) powder, and as well as the effects of pH, anions, and humic material (HM) on this process. Moreover, column experiment was conducted for 31 days to treat arsenate solution of 500 microg As/L using waste iron chippings as filling. Batch experiments showed that both arsenate and arsenite compounds could be removed efficiently from simulated groundwater by ZVI under aerobic and relative anaerobic conditions. Aerobic condition was favorable to arsenic removal especially for arsenate, while arsenite could be removed more rapidly than arsenate in relative anaerobic condition. Oxidation of arsenite to arsenate by iron species in aerobic environment was observed, which is thought to be an important pathway of arsenite removal. In an unsealed system, the removal efficiency of both arsenate and arsenite decreased at higher pH value. In a sealed system, acidic and alkaline condition seemed to be favorable for arsenate and arsenite removal, respectively. Phosphate and low concentration sulfate caused a decrease in arsenate removal, while high concentration sulfate as well as nitrate caused slight increase in arsenate removal. Presence of HM in solution slightly inhibited arsenic removal. Arsenic removal efficiency in column study was influenced by flow rate and work period of the column. More than 98% of arsenate could be removed stably with a hydraulic resident time of 2 h at last, and the effluent meet the drinking water standard.     

Specific features of multicrystalline silicon growth from high-purity commercial silicon

The distribution of impurities in multicrystalline silicon (mc-Si) blocks grown at various velocities from refined commercial silicon by the Stochbarger method have been studied. It is established that the growth velocity V strongly influences the distribution of impurities along the block height. Growth at V > 1 cm/h leads to the breakdown of a crystallization front and the trapping of impurities. The results are explained by the concentration supercooling that arises when the growth velocity is increased above the critical level for a given type of initial material. The optimum rate for the crystallization with simultaneous effective purification of a commercial silicon from impurities has been experimentally determined.     

Synthesis and characterization of high-purity silica nanosphere from rice husk

The work reports the synthesis, characterization, and the properties of high-purity silica nanospheres from low-cost rice husk. Primarily, the rice husk was washed with distilled water (DW) and subjected to acid leaching to remove the impurities. The treated rice husk was annealed at different temperatures (620 and 900 degrees C) for varied time periods to achive the desirable silica nanospheres. The annealing temperature and time considerably affected the properties of the synthesized silica nanospheres. The morphology studies confirmed that the size of nanospheres were of approximately 50-60 nm. The photoluminesence studies revealed that the synthesized silica nanospheres showed less structural defects and good optical properties. On the basis of the formation and the characterization of silica nanospheres a possible mechanism was suggested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis confirmed that the synthesized silica nanospheres contained approximately 99.93% purity.     

An investigation of the preparation and properties of some IIIa-Vb compounds

Previous work bearing on the techniques of preparation of the IIIa-Vb compounds is reviewed and the preparative problems systematically analysed. This study has resulted in the development of a simple low temperature method for preparing these compounds from their component elements with the minimum of contamination. It has been found that these very high melting point compounds can be sublimed and that sublimation techniques offer a convenient route for their purification and fabrication in thin film form.Evidence that some of the IIIa-Vb compounds are semiconductors has been obtained from studies of the optical properties of thin films of PrAs, NdAs, SmAs, GdAs, DyAs, TmAs, YbAs, PrSb, SmSb, YbSb and SmP; their respective optical energy gaps were determined as 1, 1.04, 1.03, 0.63, 1, 1.18, 1.02, 0.66, 0.59, 1, and 1.09 eV respectively. A comparison is made between these measured values and those predicted by N. Sclar [1].     

Combined use of photocatalyst and adsorbent for the removal of inorganic arsenic(III) and organoarsenic compounds from aqueous media

A novel method for the removal of inorganic arsenic(III) (As(III)), monomethylarsonate (MMA), and dimethylarsinate (DMA) from aqueous media, was proposed and investigated. This method involves the combined use of TiO₂-photocatalyst and an adsorbent, which has a high ability of As(V) adsorption, under photo-irradiation. When an aqueous solution of As(III) was stirred and irradiated by sunlight or xenon lamp in the presence of TiO₂ suspension, the oxidation of As(III) into As(V) was effectively attained. By use of the same photocatalytic reaction, MMA and DMA were also degraded into As(V), while the total organic carbon (TOC) in the aqueous phase was decreased. When an aqueous solution of As(III) was stirred with a mixed suspension of TiO₂ and an adsorbent for As(V) (activated alumina) under sunlight irradiation, the arsenic removal reached 89% after 24 h. By use of the same photocatalyst–adsorbent system, 98% of MMA and 97% of DMA were removed. The mechanism of the removal of arsenic species by the photocatalyst–adsorbent system was discussed.     

The preparation and characterization of some skutterudite related compounds

New, skutterudite-related compounds IrGe_1.5S_1.5, IrGe_1.5Se_1.5, IrSn_1.5S_1.5, and RhGe_1.5S_1.5 were prepared by direct combination of the elements at 800°C under conditions of ambient pressure, or by heating the partially reacted elements at 40 Kbars pressure and 600°C. The single-phase products were characterized by X-ray analysis, room temperature magnetic susceptibility determinations and four-probe resistivity measurements. Observed weak superstructure reflections in the X-ray spectra suggest an ordering between the group IVa and group VIa atoms.     

Thermal decomposition products of hydrotalcite-like compounds: low-temperature metaphases

Synthetic hydrotalcite-like samples with composition [M_{1 – x} ²⁺Al_x ³⁺(OH)₂](CO₃)_x/2 ·nH₂O, where M = Mg, Ni, x = 0.25 and 0.33, n = 2x and 1.5x, are studied by XRD, DTA, TG and IR spectroscopy after heating in the temperature interval 120–260 °C and rehydration in air and water. Structural models of the two metaphases obtained are proposed. Metahydrotalcite-D (HT-D) is formed at 140–180 °C by the reversible dehydration of the interlayer. Metahydrotacite-B (HT-B) is formed at temperatures 240–260 °C as a result of the dehydroxilation of a part of OH groups of the brucite-like layer and inclusion of two oxygenes from the CO₃-group in the same layer. The HT-B has a specific crystal structure. Rehydration does not restore the initial structural state but leads to the formation of a phase (HT-B-r) characterized with increased thickness of the interlayer, high content of water and a low temperature of dehydration. The properties of HT-B depend on the ratio M²⁺: Al of the initial sample. The substitution Mg Ni does not influence the properties of the metaphases in the low temperature region.     

Evaluation of arsenic trioxide-loaded albumin nanoparticles as carriers: preparation and antitumor efficacy

Bovine serum albumin (BSA) nanoparticles containing arsenic trioxide (As(2)O(3)) were prepared by a pH-coacervation method. To investigate the properties of the As(2)O(3)-loaded BSA nanoparticles, a study on drug-to-polymer ratio was done to determine the drug loading (DL), and a H-600 transmission electron microscope (TEM) was used to examine the particle sizes. The results showed that the DL was 27.8% and the average particle size was about 734 nm. The drug release in vitro test was done, which revealed that the drug release was found to provide a slow release after an initial burst release and the cumulative percentage release reached close to 95%. In vitro cytotoxicity test was carried out using APL NB4 cell lines (acute promyelocytic leukemia), and the anticancer efficacy in vivo against mouse H22 hepatoma cells was evaluated on kungming mice. The results indicated that the anticancer efficacy of the As(2)O(3)-loaded BSA nanoparticles was very obvious.