The apparent solubility product of cerous fluoride

The apparent solubility product of cerous fluoride has been determined to be 8.1 ± 1.1·10^-16 und 1.1 ± 0.5·10^-15 by radiometric and conductometric methods respectively. Hydrolysis of cerous fluoride is thought to be negligble. The effect of hydrogen-ion concentration on the solubility of cerous fluoride has been measured in solutions of perchloric acid of varying acidity. The solubility Was found to decrease slightly as the pH decreased from 5 to 2 and then to increase rapidly as the pH further decreased from 2 to 0.     

水分散性硫化镉纳米粒子的制备研究进展

表面修饰的硫化镉纳米粒子荧光性能优异而稳定,激发光谱宽,发射光谱窄而对称且发射波长可通过改变材料的粒径大小和组成来调控,因而在生物样本尤其是活组织的多色成像中极为有用,能有效避免因样本自身发光和光散射导致的信号干扰。硫化镉纳米粒子的研究已被许多科研工作者所青睐,是目前热点研究领域之一。近年来,水分散性硫化镉纳米粒子作生物荧光标记物的研究取得了长足的进展。本文综述了水分散性硫化镉纳米粒子的制备方法研究进展,分析了各种制备方法的优点与不足之处。     

The mechanism of electrodeposition of cadmium sulphide on inert metals from dimethylsulphoxide solution

The mechanism, of electrodeposition of CdS on Hg, and Pt electrodes has been studied in dimethylsulphoxide solutions by performing cyclic voltammetry at stationary electrodes and pulse polarography at dropping Hg electrodes in solutions containing both Cd(II) ions and elemental sulphur. Evidence is presented to demonstrate that sulphur is chemisorbed at these electrodes and that formation of at least a monolayer of metal sulphide is probable. As a result, formation of the initial layer of CdS involves reaction of Cd(II) ions with chemisorbed sulphur or with a pre-existing layer of metal sulphide. Data for the formation of CdS are compared with those obtained for the formation of PbS and ZnS.     

Ternary cadmium zinc sulphide films with high charge mobilities

Cadmium zinc sulphide thin films with high charge mobilities are obtained from acidic chemical baths employing the corresponding metal chlorides, urea and thioacetamide. The films are characterized by powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, inductively coupled plasma mass spectrometry, absorption spectroscopy and charge transport measurements. The compositional control afforded by the technique and the resultant changes in the structural, optical and electronic properties of the films are critically examined. We find good correlation between structure and properties at extremes of the composition range.     

Properties of cadmium sulphide thin films deposited from a chemical solution

Cadmium sulphide thin films have been deposited chemically at different temperatures from 50 °C to 100 °C. The composition of the solution was [CdCl₂] = 0.01 M, [Thiourea] = 0.17 M, [NH₄Cl] = 0.036 M and [NH₃] = 0.36 M. Structural, electrical and optical properties were investigated as a function of deposition parameters. The films showed strongly oriented structures and were highly transmitting in the infrared region. Their absorption coefficient was in the range 10⁴ to 10⁵ cm⁻¹ in the visible region. The direct forbidden band had an energy gap of 2.48 eV and the refractive index for high wavelengths was equal to 2.116. The dark resistivities of as-deposited films thicker than 0.5 μm had values from 10³ to 10⁵ Ωcm. These resistivities decreased to about 10 Ωcm after annealing in vaccum or in argon atmosphere at 200 °C for one hour.     

Liberation of excess energy and retransformation of mechanically activated cadmium sulphide

On heating vibro-milled CdS containing the strained high-pressure rock salt phase, the excess energy was gradually liberated accompanied by the retransformation into more stable phases and the restoration of their crystallinity. Profiles of DSC curves, inter-relationships between thermal and crystallographical properties, the stability of each phase and the mechanism of the mechanochemical activation are discussed. A direct retransformation of the strained high-pressure phase was found to accompany the liberation of the excess energy.     

Potentiometric determination of sulphate in fertilisers with cadmium sulphide membrane electrode

Summary A method is described for the determination of sulphur in fertilisers using reduction and evolution of hydrogen sulphide followed by a potentiometric titration with lead nitrate. Several procedures are tested for the destruction of the samples. The most accurate results are obtained after dissolution of the fertiliser in hydrochloric acid.

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Potentiometrische Bestimmung von Sulfat in Düngemitteln mit Hilfe der Cadmiumsulfid-Membranelektrode

Zusammenfassung Die vorgeschlagene Methode beruht auf Reduktion und Entwicklung von H₂S, gefolgt von einer potentiometrischen Titration mit Bleinitrat. Zum Aufschluß der Probe wurden verschiedene Verfahren getestet, wobei die Auflösung in verdünnter Salzsäure die besten Ergebnisse brachte.

     

Radiometric,potentiometric and conductometric measurements of the solubility and solubility product of europium trifluoride

The solubility and solubility product of europium trifluoride were measured by radiometric, potentiometric and conductometric methods. There are significant differences in the values of both solubility and solubility product obtained by the three different techniques. Due to reasons discussed in the text, radiometric values seem to be more acceptable than the others. The thermodynamic functions such as ΔH⁰, ΔG⁰ and ΔS⁰ for the dissolution process were also measured. The positive values of ΔH⁰ and ΔG⁰ and the negative value of ΔS⁰ are indicative of the slight solubility of EuF₃. The dependence of solubility on pH and also on the fluoride concentration has also been studied. It was confirmed that europium forms a monofoluoride complex in aqueous solution. The stability constant of this complex was estimated.     

Thermogravimetric characterisation of poly(methyl methacrylate) photopolymerised by colloidal cadmium sulphide

The thermal stability of poly(methyl methacrylate) (PMMA) photopolymerised using colloidal cadmium sulphide as the photoinitiator was studied by thermogravimetry (TG) and differential TG (DTG).The thermal stability of the CdS initiated PMMA was greater than that of conventional radically polymerised PMMA and approached that of anionically prepared PMMA. The DTG curve of the CdS initiated PMMA was a composite of four peaks, three of which correspond to the three peaks observed in the DTG curve of standard radically prepared PMMA. It is suggested that the additional peak arises from a new mode of depolymerisation initiation, that is, from chain end unsaturation introduced into the polymer chain during polymerisation initiation with the colloidal CdS.     

Ultrafast dynamics of transient bleaching of surface modified cadmium sulphide nano-particles in Nafion films

Ultrafast dynamics of transient photobleaching and recovery of cadmium sulphide (CdS) nanoparticles in Nafion films before and after treatment with excess cadmium ions have been studied upon excitation at 400 nm with a femtosecond laser system. Both samples gave transient bleaching in less than 1 ps and a multi-exponential recovery in the wavelength region between ca. 410 and 500 nm. Cd²⁺ treatment of the nanoparticles resulted in several dramatic changes to the fluorescence and transient bleaching spectra from the films: (1) A new fluorescence band at higher energy appeared in addition to an increase in the ‘defect’ fluorescence band at longer wavelengths. (2) A remarkable increase in the extent of transient bleaching was observed below about 440 nm, which recovered faster than that at longer wavelengths. (3) The recovery rate of the transient bleaching became faster, relative to the untreated nanoparticles, over the whole wavelength region of the bleaching. These results have been interpreted in terms of the recombination of photogenerated electrons and holes from traps or defects in/on the nanoparticles.     

Solubility and solubility product of crystalline Ni(OH)2

The solubility of crystalline Ni(OH)₂ was studied in solutions of 0.01M NaC10₄ with pH ranging from 7 to near 14. Equilibrium was approached both from over-and undersaturation, and the equilibration times extended from 3 to 90 days. The solubility of Ni(OH)₂(c) in the pH range of approximately 7 to 11.3 was effectively modeled by including aqueous Ni²⁺ and NiOH⁺ species. Values of the logarithm of the thermodynamic equilibrium constants for the reactions [Ni(OH)₂(c) ⇌ Ni²⁺ + 2OH^-] and [Ni²⁺ + OH^- ⇌ Ni(OH)⁺] were determined to be -16.1±0.1 and 5.65 ± 0.10, respectively. These data, in conjunction with Pitzer ion interaction parameters given in the literature, were used to model the reported solubilities of Ni(OH)₂(c) in chloride, sodium acetate, and potassium chloride solutions. The model predictions for these systems were in excellent agreement with the experimental data from the literature.     

The oxidation of sulphide minerals

The literature associated with the thermal behaviour of mineral sulphides has been selectively and critically reviewed. Particular attention has been paid to:

• • the importance of characterising the starting material, as well as intermediate products

• • the effect of experimental variables on the thermal analysis results

The various reactions that sulphides can undergo in inert and oxidising atmospheres are presented. Under mild oxidising conditions, such as an air atmosphere and heating rates of 10–20°C min⁻¹, the oxidation occurs as a sequence of reactions usually controlled by oxygen diffusion, although in some situations decomposition of the sulphide with evolution of sulphur can occur. Besides the formation of oxides and sulphates, and the subsequent decomposition of the latter, solid-solid reactions can occur between sulphates and unreacted sulphides. In ternary systems, such as the iron-nickel sulphides, considerable ion diffusion can take place.

Under more vigorous oxidising conditions, such as an oxygen atmosphere with a heating rate in excess of 40°C min⁻¹, some sulphides can be ignited. Under these conditions the relative ignition temperatures of sulphides can be measured, and the effects of variables such as particle size and stoichiometry on the ignition temperature examined.

The oxidation of pyrite is presented as a case study of the effects of experimental variables on the results of thermal analysis. The application of the results of studies to the industrial processing of sulphides of economic importance has been discussed.     

The solubility product of crystalline ferric selenite hexahydrate and the complexation constant of FeSeO 3 +

The aqueous solubility of Fe₂(SeO₃)₃·6H₂O(c) was studied in deionized water adjusted to a range in pH values from 0.77 to 5.1 and in Na₂SeO₃ solutions ranging in concentrations from 0.0002 to 0.02 mol-dm^?3. The studies were conducted from both the undersaturation and oversaturation directions, with equilibration periods ranging from 7 to 1725 days. Stoichiometric dissolution of the solid was observed in solutions with pH values up to nearly 4. In general, concentrations of both Se and Fe decreased as pH increased from 1 to 4. Analyses of the equilibrated suspensions confirmed the equilibrium solid to be Fe₂(SeO₃)₃·6H₂O(c) and the aqueous Se to be selenite. Pitzer's ion-interaction model was used with selected ion pairs to interpret the solubility data. The logarithm of the solubility product of ferric selenite $$Fe_2 (SeO_3 )_3 .6H_2 O(c) \begin{array}{*{20}c} \to \\ \leftarrow \\ \end{array} 2Fe^{3 + } + 3SeO_3^{2 - } + 6H_2 O$$ was found to be ?41.58±0.11. This value is less than any reported in the literature for a ferric selenite by more than 10 orders of magnitude. The solubility data and calculations show an extremely strong interaction between aqueous Fe³⁺ and SeO ₃ ^2? ; interpretation of these data requires the inclusion of FeSeO ₃ ⁺ i.e. $$Fe^{3 + } + SeO_3^{2 - } \begin{array}{*{20}c} \to \\ \leftarrow \\ \end{array} FeSeO_3^ + , log K = 11.15 \pm 0.11$$      

Studies on nanocrystalline cadmium sulphide (CdS) thin films deposited by spray pyrolysis

Cadmium chalcogenides with appropriate band gap energy have been attracting a great deal of attention because of their potential applications in optoelectronic devices. CdS in the form of thin film is prepared at different substrate temperatures by a simple and inexpensive chemical spray pyrolysis technique. The as-deposited thin films have been characterized by XRD, SEM, EDAX and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of substrate temperature. SEM studies reveal that the grains are uniform with uneven spherically shaped, distributed over the entire surface of the substrates. Compositional analysis reveals that the material formed is stoichiometric at the optimized substrate temperature. The optical band gap energy is found to be 2.44 eV with direct allowed band-to-band transition for film deposited at 300°C. The electrical resistivity measurement shows that the films are semiconducting with a minimum resistivity for film deposited at 300°C. The thermoelectric power measurement shows that films exhibit n-type of conductivity.     

Radiochemical measurement of solubility product and thermodynamic functions for erbium trifluoride-water system

The solubility and solubility product of erbium trifluoride in aqueous solution were measured using three different techniques. The more acceptable radiometric values for the solubility and solubility product are 1.98×10^–5M and 3.5×10^–18, respectively. The values for the thermodynamic functions, H ₂₉₈ ^o , G ₂₉₈ ^o and S ₂₉₈ ^o for the dissolution of ErF₃ and the stability constant for ErF²⁺ have also been measured.     

The reaction of copper(I) sulphide with a product of its oxidation copper(II) sulphate

The course of the reaction between copper(I) sulphide and copper(II) sulphate in SO₂ at 710–785 K was studied by the TG method under isothermal and non-isothermal conditions, as well as by the DTA method, X-ray analysis and scanning electron microscopy. It was established that the reaction is essentially dependent upon the initial composition of the substrate mixture, Cu₂SO₂ and Cu₂SO₂ being the chief intermediates in the reaction. Copper(I) oxide appears as the permanent final product of the reaction of interest. The reaction network, with the intermediate stages depending on the initial compositions in the temperature range studied, has been demonstrated.

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Zusammenfassung Der Verlauf der Reaktion von Kupfer(I)-sulfid mit Kupfer(II)-sulfat wurde in SO₂ bei 710–785 K durch isotherme und nichtisotherme Thermogravimetrie sowie DTA, Röntgenanalyse und Scanning-Elektronenmikroskopie untersucht. Es wurde festgestellt, daß die Reaktion wesentlich von der Ausgangszusammensetzung des Substratgemisches abhängt, wobei Cu₂SO₂ und Cu₂SO₄ die vorherrschenden intermediären Produkte der Reaktion sind. Kupfer(I)-oxid tritt als Endprodukt auf. Der die intermediären, im untersuchten Temperaturbereich von der Ausgangszusammensetzung abhängigen Reaktionsschritte in sich einschließende Reaktionsverlauf wird dargelegt.

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710–785 , , . , . Cu₂SO₂ Cu₂SO₄, . , .