Role of oxidizers in the active dissolution and passivation of metals

It was established that addition of hydrogen peroxide to a solution of sulphuric acid leads to acceleration of the active dissolution of chromium and to the shift of its passivation potential in negative direction. Similar data were obtained for Fe-28% Cr alloy in H₂SO₄ solution containing H₂O₂ and for iron in sulphuric acid with K₂Cr₂O₇ additions. The conclusion was made that depending on the potential the molecules of oxygen-containing oxidizers can undergo different transmissions on the surface of the metal, including transformations connected with the direct participation of the oxidizer in the anodic dissolution of the metal or in the building of inhibiting or passivating layers on the metallic surface.     

Mechanism of the initial stage of silicate oligomerization

The mechanism of the initial stage of silicate oligomerization from solution is still not well understood. Here we use an off-lattice kinetic Monte Carlo (kMC) approach called continuum kMC to model silicate oligomerization in water solution. The parameters required for kMC are obtained from density functional theory (DFT) calculations. The evolution of silicate oligomers and their role in the oligomerization process are investigated. Results reveal that near-neutral pH favors linear growth, while a higher pH facilitates ring closure. The silicate oligomerization rate is the fastest at pH 8. The temperature is found to increase the growth rate and alter the pathway of oligomerization. The proposed pH and temperature-dependent mechanism should lead to strategies for the synthesis of silicate-based materials.     

The mechanism of metal corrosion passivation

The main regularities of variations in the thermodynamic properties of components of cubic vanadium carbide, depending on the composition in the region of homogeneity, are investigated experimentally. It is believed that these regularities are inherent only to metal oxides. This serves as the basis for the concept that passivation during the corrosion of metals occurs due to the formation of surface metal oxide whose composition corresponds to the maximum concentration of oxygen in the region of homogeneity. The thermodynamic stimulus of corrosion is in this case reduced to almost zero.     

煤自燃初期的反应机理研究

从实验得到的可能引起煤自燃的8个活性基团入手，提出了一系列简单煤分子模型，利用密度泛函DFT/6-31G对其完成了几何优化，计算了包括反应焓变、吉布斯自由能和活化能等，从热力学和动力学角度分析了计算结果。基于理论计算获得了煤活性基团的活泼性次序，得出了煤自燃初期的反应机理主要是氧分子先进攻煤分子中的活性基团，产生活泼性很高的中间体，然后中间体进一步反应得到水或二氧化碳及其他反应产物，计算结果与实验基本符合。     

Kinetics of propylene polymerization in the initial acceleration stage

The kinetics of propylene polymerization catalyzed over a superactive and stereospecific catalyst for the initial build-up period was investigated in slurry-phase. The catalyst was prepared from Mg(OEt)₂/benzoyl chloride/TiCl₄ co-activated with AlEt₃ in the absence or presence of external donor. Despite a very fast activation of the prepared catalyst the acceleration stage of polymerization could be identified by the precise estimation of polymerization kinetics for a very short period of time after the commencement of polymerization (ca. 2 min). The initial polymerization rate, (dR_p/dt)₀ extrapolated to the beginning of the polymerization was second order with respect to monomer concentration. The dependence of initial polymerization rate on the concentration of AlEt₃ could be represented by Langmuir adsorption mechanism. The initial rate was maximum at about Al/Ti ratio of 20. The activation energy for the initiation reaction was estimated to be 14.3 kcal/mol for a short-time polymerization. The addition of a small amount of p-ethoxy ethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer, which was obtained after 120 s of polymerization, to 98% and the initial polymerization rate decreased sharply as [PEEB]/[AlEt₃] increased. © 1994 John Wiley & Sons, Inc.     

Effect of amalgamation on the passivation of transition metals in their anodic dissolution in tetrahydroadipic acid solutions

Effect of anode amalgamation on the degree of passivation of the electrodes and on the current efficiency in electrosynthesis of coordination compounds of copper(II), nickel(II), zinc(II), and cadmium(II) with galactaric acid was studied. An improvement of anodic synthesis characteristics was observed when amalgamated zinc, copper, and cadmium were used. Complex compounds of 1 : 1 composition were obtained and the structure of the coordination environment of the metal ion was determined by IR spectroscopy.     

Simultaneous achievement of defect passivation and carrier transport promotion by using emerald salt for methylammonium-free perovskite solar cells

Defect passivation along with promoted charge transport is potentially an effective but seldom exploited strategy for high-performance perovskite solar cells (PSCs). Herein, the in situ defect passivation and carrier transport improvement are simultaneously realized by introducing a conductive polymer (i.e., emerald salt, ES) into the precursor solution of methylammonium (MA)-free perovskites. The interaction between ES and uncoordinated Pb²⁺ reduces defect density to suppress the non-radiative recombination. Moreover, ES can act as a “carrier driver” to promote the carrier transport due to its conductive feature, resulting in efficient PSC devices with a decent power conversion efficiency (PCE) of 23.0%, which is among the most efficient MA-free PSCs. The ES-based unencapsulated devices show superior stability, retaining 89.1% and 83.8% of their initial PCEs when subjected to 35 ± 5% relative humidity (RH) storage and 85 °C thermal aging for 1000 h, respectively. To further assess the large-area compatibility of our strategy, 5 × 5 cm² mini modules were also fabricated, delivering an impressive efficiency of 19.3%. This work sheds light on the importance of conductive additives in boosting cell performance by playing multiple roles in passivating defects, retarding the moisture invasion, and enhancing and balancing charge transport.

A conductive polymer, emerald salt (ES), is introduced into methylammonium (MA)-free perovskite solar cells, enhancing the device performance and stability by passivating defects, promoting charge transportation, and retarding the moisture invasion.     

Preconcentration of trace metals from salt solutions using thiuram disulphide as collector

Traces of Fe, Co, Ni, Cu, Zn, Cd and Pb in salt solutions (e.g. KCl, Ca(NO₃)₂, A1₂(SO₄)₃, Cr₂(SO₄)₃, (NH₄)₂SO₄) are determined by flame AAS after preconcentration with thiuram disulphide (TDS) as collector precipitate. The preconcentration recovery is mainly influenced by pH, TDS amount and its aging in the sample solution. Conditions of an optimal preconcentration procedure were elaborated. Detection limits vary from 0.5 ng/ml (for Cd) to 8.3 ng/ml (for Pb) and the relative standard deviation is 2 to 6 %. The accuracy of the results was checked by differential pulse anodic stripping voltammetry and by electrothermal AAS.     

Molecular complexing as the initial stage of some reactions of organometallic compounds

Complexing of molecular oxygen with arylmercury compounds and phenyl derivatives of Group IV and V elements has been studied by electronic spectroscopy. The type of complexing appeared to depend on the nature of the central heteroatom in the organometallic compounds.The chemical model for the reaction of R₂Hg (R = Et, n-Pr, n-Bu, Ph) with CCl₄ indicates that the complex R₂Hg · L (L = molecular oxygen, aromatic compound) is formed in the initial stage of the interaction. By studying the influence of π-donors on this process the correlation between the yield of alkylmercuric chloride and the donor properties of the ligand has been determined.     

Positron lifetimes at the initial stage of pore formation in Vycor glass

The formation of narrow pores during leaching of Vycor glass by sulphuric acid was investigated using the positron lifetime technique. During the leaching process the pore diameter remained roughly constant (except for the case of cold leaching). The time of processing changed the total length of capillaries, but not their number; at the temperature 50°C during 20 min of leaching the average leaching depth was 24 μm.     

Investigation of the initial stage in the polycondensation of polychloronaphthalenes with sodium sulfide

Conclusions A charge-transfer complex is formed at the Initial stage of the polycondensation of polychloronaphthalenes with sodium sulfide. In polar solvents It evidently dissociates with the formation of the radical-anion of octachloronaphthalene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 549–553, March, 1985.