Chlorine Impurities Research Articles

Effect of chlorine impurities on the properties of CeO2

Effect of chlorine impurities on the properties of CeO2

Effect of chlorine impurities on the properties of CeO2

The detection with ESR of radicals formed upon low temperature oxygen adsorption has been used to study the modifications introduced in the surface of CeO2 by pretreatments with nitric and hydrochloric acids. On untreated CeO2, O2 adsorption originated several types of O−2 species if the sample was previously outgassed at Tv ⩾ 473 K. The HNO3-treated sample did not show signifi signals for Tv ⩽ 573 K; for Tv ⩾ 673 K the spectra were similar to those obtained for untreated CeO2. The HCl-treated sample showed the formation of O2− interacting with Cl− for Tv ⩾ 473 K and subsequently of O−; this indicates the existence of centers, associated to chloride ions, able to activate O2 and dissociate it to give stable O−. These centers are probably present in most M/CeO2 catalysts prepared using metal chloride salts.

Comparison of two partially activated carbon fabrics for the removal of chlorine and other impurities from water

Experimental studies were undertaken at the University of Birmingham to investigate and compare the use of two partially activated carbon fabrics for the removal of chlorine and other impurities from potable water in domestic point-of-use water filters. Since the implementation of the EEC drinking water quality directive in July 1985, there has been a marketing surge in domestic water filters, generally aimed at improving taste (the taste of chlorine is frequently cited). The fabrics were observed to be very effective at removing chlorine from water; their dechlorinating powers were significantly superior to that of the granular activated carbon used for comparison. The fabrics were observed to be much less effective at removing phenol, methylene blue and colour.

Influence of the addition of an aliphatic epoxide as reactive diluent on the cure kinetics of epoxy/amine formulations

AbstractThe cure kinetics of two different diepoxy prepolymers and their mixtures with a single diamine was analyzed using size exclusion chromatography (SEC). One of the diepoxy prepolymers was based on bisphenol‐A diglycidyl ether (DGEBA), while the other one was the diglycidyl ether of 1,4‐butanediol (DGEBD), which is a typical reactive diluent. They were used either alone or as a 50% mixture (in equivalents). The cycloaliphatic diamine 4,4′‐diamino‐3,3′‐dimethyldicyclo‐hexylmethane (3DCM) was used in stoichiometric proportions in every formulation. SEC could be used to follow the conversion of each type of epoxy groups as a function of time, in the pre‐gel stage. The reaction rate followed an autocatalytic behavior (catalysis by OH groups) in every case. DGEBD was less reactive than DGEBA. Mixing of both diepoxy prepolymers led to an increase in the specific rate constant for DGEBD and a decrease of the one for DGEBA. This can be explained by the influence of the polarity of the reaction medium on the polymerization rate and the presence of chlorine impurities.

Effect of operating conditions and precursors on optoelectronic properties of OMVPE grown ZnSe

The growth of ZnSe on (100)GaAs substrates by low pressure organometallic vapor phase epitaxy (OMVPE) has been investigated in a vertical reactor. Dimethylzinc (DMZn) was used as the Zn precursor, while three selenium sources were employed: diethylselenide (DESe), methylallylselenide (MASe) and hydrogen selenide (H 2Se). Films grown at the optimal conditions, corresponding to each source combination, contain different impurities. The optically active impurities are analyzed by comparing photoluminescence spectra of as-grown films. The source combination H 2Se/DMZn produces the best quality ZnSe epilayers. The effect of operating conditions on the electrical and photoluminescence properties of films grown from H 2Se/DMZn is examined. Chlorine is determined to be the major shallow donor impurity of these films and an increase in the growth temperature is demonstrated to be a simple way to control the residual chlorine impurities. Finally, a relationship between electrical properties and photoluminescence characteristics is proposed and examined in view of data from this study as well as from previously reported OMVPE and molecular beam epitaxy (MBE) studies.

ChemInform Abstract: The Crucial Role of Halogen Atoms in the Formation of Ta2S2C.

AbstractThe successful preparation of the title compound from the elements at 1150 °C is found to be intimately linked to the presence of catalytic amounts of halogens and previous successful reactions are explained by chlorine impurities of the graphite crucibles used.

Influence of Impurities and Microstructure on the Resistivity of LPCVD Titanium Nitride Films

AbstractThe electrical resistivity of LPCVD TiN films deposited at temperatures between 450 and 700°C has been found to vary from about 900 to 150 μ Ωcm. The elemental composition (Ti:N), impurity content and the microstructure of the films have been investigated in order to explain the resistivity variation. It appears that this variation is directly related to the chlorine (impurity) content of the films. Films deposited at 700°C have both the lowest chlorine content and the lowest value of resistivity. Additionally the difference between the resistivity of this latter film and the (lower) value for bulk TiN is discussed.

Preparation and characterization of SnS 2

Single crystals of SnS 2, crystallizing with the hexagonal CdI 2 structure, were grown by vapor transport and chemical vapor transport. Electronic, optical, and infrared properties were studied, as well as thermal stability in flowing oxygen. The impact on the electrical properties of slight deviations from stoichiometry and halogen impurity were investigated. Crystals free of halogen impurity can be grown by vapor transport. The sign of the majority carriers of crystals grown by vapor transport is dependent upon the growth conditions. If higher growth temperatures are used (750-700°C), vapor-grown crystals are n-type semiconductors and exhibit low resistivities (ϱ = 4.5(5) Ω cm at 25°C). Annealing of vapor-grown crystals in sulfur at 600°C increases the resistivity to 2 × 10 5 Ω cm. When the charge-growth temperatures are lowered to 650-600°C and 5% excess sulfur is included in the charge, the crystals are p-type semiconductors with high resistivities (ϱ > 10 7 Ω cm). Crystals grown in the presence of halogen (Cl 2) contain 22(6) ppm chlorine and are n-type semiconductors, ϱ = 5 Ω cm at 25°C. The resistivity is not altered by annealing in sulfur. The chlorine impurity acts as donor states in this material.

A proposed model for the photoluminescence of ZnS : CdS : Ag : Ni : Co phosphors

Phosphors with 41% ZnS: 59% CdS: 0.009% Ag: 0.00065% Ni and containing various concentrations of Co dopant are investigated with regard to the fundamental photoluminescence processes involved. The wavelengths of maximum emission intensities in the spectral distributions of excitation and emission remain unaltered with increase in Co concentration. Thus the energy level structures with the silver impurity centres are not affected by the cobalt content. The temperature dependence of thermoluminescence has been studied over the temperature range of 77 K to 800 K. The thermoluminescence curves show peaks due to chlorine, cadmium, cobalt and nickel impurities. A new trap is identified at 0.065% concentration of cobalt which has an energy of 1.09 eV. An energy band model is proposed to explain this phenomenon. It is suggested that this peak is due to the association of cobalt and silver centres.

Lead (II) halides: A new class of acousto-optic and electro-optic materials

A novel and potentially useful class of crystals, the lead (II) halides were recognized by A.V. Zamkov et al. [Soviet Phys.-Cryst. 24 (1979) 87] for the acousto-optic and electro-optic and electro-optic devices. Lead bromide, PbBr 2, is the most highly studied of these and was tested for its acousto-optic properties. The crystal possesses certain properties which are highly desirable for signal-processing applications. For this reason, we have developed a method to purify and grow single crystals of this compound. PbBr 2 crystals up to 26 mm in diameter and several cm in length were grown by the Bridgman method. Purification is complicated by oxidation of PbBr 2 in the presence of traces of moisture. Formation of lead chlorite [ Pb( ClO 2) 2], mendipite (Pb 3O 2Cl 2), plattnerite (PbO 2) and mixed oxy halides (Pb 3O 2BrCl) were observed due to residual chlorine and oxygen impurities. Mendipite was the major constituent of dark bluish residue formed during the purification by directional freezing.

Fundamental radiation-induced defect centers in synthetic fused silicas: Atomic chlorine, delocalized E' centers, and a triplet state.

A series of synthetic fused silicas of diverse OH contents was subjected to 100-keV x irradiations at 77 K and investigated by electron-spin-resonance techniques at \ensuremath{\sim}110 K or higher temperatures. Spectra were recorded at X-band frequencies (\ensuremath{\sim}9.2--9.3 GHz) both as the first derivative of absorption and in the high-power second-harmonic mode in order to bring out features not fully accessible by using one of these methods alone. In addition to the previously known ${E}_{\ensuremath{\alpha}}^{\mathcal{'}}$, ${E}_{\ensuremath{\gamma}}^{\mathcal{'}}$, and oxygen-associated hole centers, three new defects were detected and characterized by computer line-shape simulation methods. These were atomic chlorine, a delocalized E' center (denoted ${E}_{\ensuremath{\delta}}^{\mathcal{'}}$), and the first biradical to be reported in a-${\mathrm{SiO}}_{2}$. A sample-to-sample correlation of the radiation yields of these three new centers has been noted, leading to the suggestion that all three find their origins in specific chlorine-decorated precursor sites in the unirradiated glasses. Although significant chlorine impurities (g100 ppm) may be ubiquitous in both type-III (high OH) and type-IV (low OH) fused silicas, the occurrence of chlorine-associated radiation-induced defects appears to be anticorrelated with the OH contents of the materials. Some possible technological implications of these findings are discussed.

Impurities of Epoxy Novolac Resins and their Influence on the Reliability of Encapsulated Semiconductors.

AbstractImpurities, especially chemically bonded impurities, of o-cresol novolac epoxy resins and their influence on the moisture resistance and other properties of the epoxy molding compounds have been investigated to clarify the influence of impurities of epoxy resins on the reliability of encapsulated semiconductor. As a result, the existence of hydrolyzable chlorine and hydroxyl group-containing impurities has been confirmed, and it was found that the impurity such as a hydrolyzable chlorine causes undesirable influence on both the moisture resistance and electrical properties at high temperatures. It was also found that the impurity such as a hydroxyl group causes undesirable influence on the moisture resistance, and that the lower hydroxyl content gives the higher heat resistance as a result of an increase in the epoxy content.

ChemInform Abstract: ACTIVATION AND ACTIVITY OF RUTHENIUM ON SILICA HYDROGENATION CATALYSTS

AbstractDie direkte Aktivierung von RuCl3/SiO2 mit H2 bei bis zu 700°C ist der Calcinierung des Materials an der Luft zu RuO2/SiO2 gefolgt von Hg‐Reduktion, überlegen.

X-ray emission from He-liken=2charge states produced in tokamak plasmas

Measurements of He-like x-ray line spectra for sulfur and chlorine impurity ions in the Alcator-$C$ tokamak plasma are reported. Results are presented on the relative line ratios of the resonance (w), intercombination (x and y), and forbidden (z) lines as well as dielectronic satellite lines for plasma conditions of ${T}_{e}=1.0\ensuremath{-}1.8$ keV and ${N}_{e}=(1.5\ensuremath{-}7)\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The results are compared with atomic calculations employing accurate atomic data which take into consideration effects on the line ratios due to collisional coupling between the $n=2$ states involved.

Activation and activity of ruthenium on silica hydrogenation catalysts

AbstractActivation of RuCl3‐impregnated silica by hydrogen treatment at high temperature, up to 700°C, is superior to a procedure involving air calcination of the material prior to reduction. Upon direct reduction, sintering hardly occurs, whereas the Ru metal surface, as measured by hydrogen desorption, increases at higher activation temperature, due to the removal of chlorine impurities from the Ru surface. Activity measurements of the Ru catalysts for the liquid‐phase hydrogenation of benzene and cyclohexene reflect the favourable effect of the high‐temperature reduction of RuCl3/SiO2. Similar phenomena are observed for some PdRu/SiO2 catalysts.

Titanium deposition onto copper substrates using the cold-plasma technique

Titanium coatings were deposited onto copper substrates using the r.f. cold-plasma technique. The coatings were obtained from gas mixtures of TiCl 4H 2Ar. The substrate temperature was 550°C and the total gas pressure in the reactor was 2 mbar. The plasma was sustained by an r.f. generator of 27 MHz frequency at a power of about 650 W. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy (TEM) and Auger electron spectroscopy were employed to identify and to characterize the coatings obtained. Coatings of thickness 10 μm were obtained after 5 h of deposition. The coatings were found to be slightly porous. Energy-dispersive analysis of X-rays was employed along the cross section of the coatings and the results indicate that titanium and copper compose the coating in varying concentrations. Chlorine impurities were found to constitute less than 0.5%. X-ray diffraction and TEM selected area diffraction revealed the presence of a mixture of various TiCu intermetallic compounds which compose the coating. Pure crystalline titanium was not observed.

Potassium targets from KI

Targets of potassium iodide (KI) on thin carbon backings have been prepared. Potassium isotopes are supplied as chlorides, and the chlorine is, in certain experiments, an unwanted contaminant. Target peeparation involves conversion of KCl to KI and subsequent vacuum evaporation of the iodide. Targets of both 39K and 41K in the thickness range of 60 to 100 μg/cm 2 of potassium have been prepared. These targets contain less than 0.5 μg/cm 2 of chlorine impurity and are stable in α-beams of 25 MeV.

Electron-paramagnetic-resonance study of a deep Cl-associated center in ZnTe: Cl

We describe EPR studies of ZnTe doped with chlorine. The characteristic EPR spectrum is observed under optical illumination at low temperature. A defect, which has a trigonal symmetry, is identified as ${\mathrm{Cl}}^{\ensuremath{-}}$ occupying a tellurium site associated with a positively charged ion which is tentatively assumed to be a ${\mathrm{Sn}}^{2+}$ or a ${\mathrm{Pb}}^{2+}$ ion. Under illumination, the associated defect should become paramagnetic by trapping an electron. Super-hyperfine-splitting lines are also observed and account for the Te nuclei. The Hamiltonian parameters of the center have been obtained. Luminescence, thermoluminescence, and optically detected magnetic-resonance experiments on the same crystals lead to the conclusion that part of the chlorine impurity behaves as a hydrogenic shallow donor but some of the chlorine atoms also form the ${\mathrm{Cl}}^{2\ensuremath{-}}$ associate center which is a deep center.

ChemInform Abstract: DENSIFICATION OF SILICON NITRIDE: EFFECT OF CHLORINE IMPURITIES

The effect of chlorine impurities on the densification of hot-pressed silicon nitride has been simulated by the addition of chlorine (H2PtCl6 6H2O) to the starting powders. The presence of chlorine retards the α-β phase transformation during hot-pressing. Microstructurally, it is found that the chlorine is incorporated in the inter granular noncrystalline phase. In the Y2O3 hot-pressed material, the chlorine appears to prevent the Y2Si2O7 phase from crystallizing.

Densification of Silicon Nitride: Effect of Chlorine Impurities

The effect of chlorine impurities on the densification of hot-pressed silicon nitride has been simulated by the addition of chlorine (H2PtCl6 6H2O) to the starting powders. The presence of chlorine retards the α-β phase transformation during hot-pressing. Microstructurally, it is found that the chlorine is incorporated in the inter granular noncrystalline phase. In the Y2O3 hot-pressed material, the chlorine appears to prevent the Y2Si2O7 phase from crystallizing.