Non-oxidizing Atmosphere Research Articles

Acid treatment of copper sulfide middlings and rougher concentrates in the flotation circuit of carbonate ores

The beneficial effect of leaching of carbonate gangue from flotation middlings and rougher concentrates with sulfuric acid prior their final flotation has been presented. This process was effectively applied within the existing flotation circuit in order to facilitate floatability of difficult-to-treat carbonate black shale copper ores. The leaching of flotation feed with sulfuric acid selectively decomposes the carbonate gangue and leads to selective liberation of sulfide minerals, enhancing flotation results. It was shown, that after leaching out of 50–70% of carbonates from flotation feed, both flotation recovery and concentrate grade increased considerably in relation to results observed for unleached feed. The products of acidic leaching comprise gypsum, soluble magnesium sulfate and gaseous carbon dioxide. Carbon dioxide evolving during the reaction favorably creates the non-oxidizing atmosphere in the pulp during leaching and effectively prevents the digestion of metals from sulfide minerals. The beneficial effect of acid leaching on flotation was evidently confirmed during the pilot tests performed on several feed materials. The application of sulfuric acid leaching for flotation feed resulted in pronounced enhancement of flotation results (both metal recovery and concentrate grade) and could provide a rational use of H 2SO 4, particularly if it becomes a troublesome and difficult-to-sale product of copper metallurgy. Recently, the sulphuric acid prices are rather high.

Self-organized TiO2 nanotubular arrays for photoelectrochemical hydrogen generation: effect of crystallization and defect structures

The effect of crystallization and surface chemistry of nanotubular titanium dioxide (TiO2) in connection with the photoelectrochemical process is reported in this investigation. TiO2 nanotubular arrays were synthesized by a simple anodization process in an acidified fluoride electrolyte at room temperature. The TiO2 nanotubes were amorphous in as-anodized condition; their transformation to crystalline phases was a function of annealing temperature and gaseous environment. The anatase phase was observed predominantly after annealing in non-oxidizing atmospheres, whereas annealing in an oxygen environment showed a mixture of anatase and rutile phases. X-ray photoelectron spectroscopy was used to determine the chemical environment of the surface, which revealed the presence of phosphate, oxygen vacancies and pentacoordinated Ti in hydrogen annealed samples. Diffuse reflectance photospectrometry of non-oxygen annealed samples showed long absorption tails extending in the visible region. The photoelectrochemical response of the TiO2 nanotubes annealed in different conditions was investigated. Photoelectrochemical performance under simulated solar light was improved by annealing the nanotubular TiO2 samples in non-oxidizing environment.

Structure and distribution of oxides in aluminium foam

Foaming of aluminium is investigated under oxidizing and non-oxidizing gas atmospheres. Foams were prepared by mixing and pressing Al99.95 and TiH 2 powders and foaming the pressed material in a gas-tight X-ray transparent furnace while following the process by X-ray radioscopy. The structure and distribution of the oxides present in the powders, precursors and foams were studied by light microscopy, scanning and transmission electron microscopy. Sequential focused ion beam slicing was used to obtain tomographic images of oxide and micropore distributions within the individual cell walls of the foams. A complex hierarchical structure of the oxides is found. Oxides reside in the bulk of the cell walls without a pronounced segregation to the gas/metal interfaces. The presence of air retards foaming due to oxidation of the outer surface.

Thermal treatment effects on degradation of BaMgAl 10O 17:Eu 2+ phosphor for PDP

The thermal degradation mechanism of the BaMgAl 10O 17:Eu 2+ (BAM) phosphor used in plasma display panel (PDP) is not yet fully clarified. We studied the dependency of the luminance and chromaticity y-value of BAM phosphor on baking temperature, handling time, atmosphere and thermal treating process. The luminance and chromaticity y-value increased after baking at around 400 °C but decreased at 600 °C or higher temperatures. The thermal degradation was obviously aggravated in oxidative atmosphere. The shift of y-value was reversed when thermal treated in non-oxidative atmosphere. We considered that the mechanism of thermal degradation of BAM phosphor was firstly due to the migration of Eu 2+ ions and then due to the effect of oxygen. We also proposed a post-treatment for BAM phosphor to reduce the thermal degradation during panels’ fabrication.

Correlation between the luminescence properties and the surface structures of submicron silica particles

We investigated the correlation between the luminescence properties and the surface structures of submicron silica particles prepared by the Stöber method. After annealing in a non-oxidizing atmosphere, the submicron-sized silica particles show a broad photoluminescence (PL) band at 500–540 nm by excitation at an ultraviolet wavelengths (254 and 365 nm), and the one at the 600 nm by excitation an Ar + laser (488 nm). The PL appeared to result from the removal of impurities and subsequent formation of several luminescent structures on the internal surface of the primary particles by thermal annealing.

Application of pilot technologies for energy utilization of agricultural residues in Northern Greece

The enormous potential of agro biomass can be exploited to produce sustainable bioenergy. Proper management and further exploitation of this potential could lead to economically profitable approximations and solutions for the agricultural industry and even energy production industry. Gasification in-situ with energy production or pyrolysis of the above mentioned residues, under a non-oxidizing atmosphere for alternative fuels production could be a solution to the environmental problems that land filling or conventional combustion could create. The present work focuses on combustion and pyrolysis of cotton gin residues in Greece, as an alternative way of energy production. The purpose of presentation of a case study of the two alternatives methods (combustion and gasification or pyrolysis), by using cotton ginning waste as biofuel, is to show the appropriateness of new bioenergy sources by coupling them with energy production technologies. These technologies can be applied in northern Greece as well as in other Balkan or Mediterranean countries. .

Brazing of commercial pure titanium in low oxygen atmosphere by continuous furnace

Joining technology of CP-Titanium, capable of providing precision joining, is industrially very useful; however, it still has some unsolved problems in continuous atmosphere brazing technology. In this study, commercial pure titanium was brazed with laminated brazing fillers by using a newly developed continuous type non-oxidizing atmosphere furnace. This new furnace, using inert gas without hydrogen, is capable of providing oxygen partial pressure equal to or lower than that available in a vacuum furnace at a regular atmospheric pressure. Excellent applicability and capability of the new furnace in commercial pure titanium brazing was concluded by a series of evaluations after brazing including microscopic observations of the joint interface, chemical analysis, and shear test.

PRESSURELESS SINTERING AND HOT ISOSTATIC PRESSING OF Ti3Al-Al2O3 INTERPENETRATING COMPOSITES

Interpenetrating phase Ti 3 Al - Al 2 O 3 composites have been fabricated by reaction sintering of composite powders containing Al and TiO 2 discus milled for two hours using carefully controlled heat-treatment in non-oxidizing atmospheres. Pressureless sintering has been carried out in argon at temperatures between 1330°C and 1480°C and a heating rate of 5°C/min prior to hot isostatic pressing at 200MPa for two hours at 1350°C. Densification of the composites was investigated as a function of temperature before and after hot isostatic pressing. The microstructure development and mechanical properties such as Vickers hardness of near fully dense Ti 3 Al - Al 2 O 3 composites fabricated by sinter-HIP of Al - TiO 2 composite powder were examined. An increase in Vickers hardness was observed after hot isostatic pressing, which can be attributed to the decrease of closed porosity in the composites. Vickers hardness of 11.0±1.0 GPa was achieved for the near fully dense composite produced by pressureless sintering at 1480°C, while 12.6±1.0 GPa was achieved for the near fully dense composite further subjected to hot isostatic pressing.

Microstructure development and properties of alumina–Ti aluminide interpenetrating composites

Abstract Interpenetrating phase Al 2 O 3 –Ti 3 Al composites have been fabricated by reaction sintering of 2 and 4-h discus milled composite powders containing Al and TiO 2 using controlled heat-treatment in non-oxidizing atmospheres. Pressureless sintering and hot pressing of the powders has been carried out under vacuum and argon at temperatures between 1278 °C and 1500 °C and a heating rate of 5 °C/min. Densification of the composites was investigated as a function of temperature. It was shown that lower porosity was obtained by hot pressing compared to pressureless sintering. The microstructure development and mechanical properties of dense Al 2 O 3 –Ti 3 Al composites fabricated by hot pressing of Al–TiO 2 powder blends were examined. Fully dense microstructures could be achieved by hot pressing at 1387 °C under vacuum. An increase of Vickers hardness was observed with increasing temperature, which can be attributed to the increase of density and the decrease in the level of porosity of the composites. The mechanical behaviour exhibited by the composites can be related to properties such as Al 2 O 3 particle size and porosity level. Fracture toughness of 6.3 ± 0.8 MPa m 1/2 and Vickers hardness of 13.6 ± 0.4 GPa were achieved for the fully dense composite produced by hot pressing discus milled powder.

Reaction pathways of ethane oxidative and non-oxidative dehydrogenation on γ-Al 2O 3 studied by temperature-programmed reaction (TP-reaction)

In this work, the reactions of ethane and ethene in an oxidizing and non-oxidizing atmosphere over γ-alumina were investigated under temperature-programmed conditions, in an attempt to estimate the possible contribution and functionality of the support in the reaction pathway of ethane ODH over MoO 3/Al 2O 3 catalysts. The results indicate that alumina contributes to the primary deep oxidation and dehydrogenation routes of ethane to CO x and coke respectively, which proceed effectively over the acidic OH groups and the Al 3+–O 2− acidic centers. On the contrary, the formation of ethylene seems to be coupled to the presence of redox sites on the catalytic surface and requires the presence of the molybdena phase. Moreover, the redox sites of the MoO x species were found to unselectively activate the further overoxidation of the olefin to carbon oxides. Therefore, Al 2O 3 catalyzes the unselective primary oxidation of ethane to carbon oxides, whereas the molybdena phase is involved in the selective oxidative dehydrogenation (ODH) of ethane to ethene and the secondary overoxidation of ethene to CO x .

Studies on europium separation from a middle rare earth concentrate by in situ zinc reduction technique

The present work is directed to establish the laboratory conditions for europium separation from its lanthanide neighbors, which are derived from the Egyptian monazite middle rare earth concentrate. The laboratory separation procedure is oriented to be commercialized for large industrial scale application (utilizing the commercially available reagents in Egypt). The separation process is based on a combined reduction-precipitation process, in which the europium is reduced by commercial zinc metal to its bivalent state followed by the precipitation of its sparingly soluble europous sulphate. Factors affecting the efficiency of the reduction-precipitation process which include; zinc type and its stiochiometric amount, reduction time, nature of precipitating agent and its concentration, and precipitation time were studied and evaluated in details. The best resulted reduction precipitation conditions were attained with a commercial zinc metal (2.5 times the stiochiometric amount), reduction time of 60 min, sulphuric acid as the precipitating agent (3.0 M) and finally precipitation time of 2 h in a non-oxidizing atmosphere of nitrogen. Application of the resulted optimum laboratory conditions for the separation of europium on a middle rare earth concentrate containing 2.5 wt.% Nd, 10.13 wt.% Sm, 11.35 wt.% Eu, 2.6 wt.% Gd, and 2.7 wt.% Tb gave 95% recovery of europium (II) sulphate with a purity of 92%. In the second reduction-precipitation run, the purity was increased to 97% with a final recovery of 91%.

Ni direct electroless metallization of polymers by a new palladium-free process

Ni films were electrolessly deposited on the surface of different polymer substrates without having to use the conventional palladium catalyst to initiate the redox reaction leading to metallization. With this in view, the surface to be coated was seeded with Ni(+2) species from an organo-nickel precursor. After reduction of the Ni(+2) ions to the Ni(0) oxidation state, it was possible to use the remarkable autocatalytic property of nickel to deposit a metallic film on the polymer by merely immersing in a Ni plating bath. The reduction of Ni(+2) species, less easy than that of Pd(+2) species commonly used in the authors' laboratory in the case of the tin-free process, was performed in the present work either using a chemical path or by plasma treatment in a non-oxidizing atmosphere (H 2 or Ar), then checked by XPS. This method was experimented on various polymer substrates using two different industrial Ni plating baths. Adhesion of Ni films evaluated by the Scotch® tape test mainly depends on the phosphorus content of the plating bath used, i.e. on the amount of stresses generated in the film which depends on the quantity of phosphorus present, the latter originating from the plating bath reducer. Both the nature of the polymer surface treatment and especially the route used to perform the Ni(+2) reduction play an important part in the interfacial stresses generated and therefore on film adhesion.

Thermal Decomposition of Generation-4 Polyamidoamine Dendrimer Films: Decomposition Catalyzed by Dendrimer-Encapsulated Pt Particles

The thermal decomposition of hydroxyl-terminated generation-4 polyamidoamine dendrimer (G4OH) films deposited on Au surfaces has been compared with decomposition of the same dendrimer encapsulating an approximately 40-atom Pt particle (Pt-G4OH). Infrared absorption reflection spectroscopy studies showed that, when the films were heated in air to various temperatures up to 275 degrees C, the disappearance of the amide vibrational modes occurred at lower temperature for the Pt-G4OH film. Dendrimer decomposition was also investigated by thermogravimetric analysis (TGA) in both air and argon atmospheres. For the G4OH dendrimer, complete decomposition was achieved in air at 500 degrees C, while decomposition of the Pt-G4OH dendrimer was completed at 400 degrees C, leaving only platinum metal behind. In a nonoxidizing argon atmosphere, a greater fraction of the G4OH decomposed below 300 degrees C, but all of the dendrimer fragments were not removed until heating above 550 degrees C. In contrast, Pt-G4OH decomposition in argon was similar to that in air, except that decomposition occurred at temperatures approximately 15 degrees C higher. Thermal decomposition of the dendrimer films on Au surfaces was also studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum conditions. Heating the G4OH films to 250 degrees C during the TPD experiment induced the desorption of large dendrimer fragments at 55, 72, 84, 97, 127, 146, and 261 amu. For the Pt-G4OH films, mass fragments above 98 amu were not observed at any temperature, but much greater intensities for H(2) desorption were detected compared to that of the G4OH film. XPS studies of the G4OH films demonstrated that significant bond breaking in the dendrimer did not occur until temperatures above 250 degrees C and heating to 450 degrees C caused dissociation of C=O, C-O, and C-N bonds. For the Pt-G4OH dendrimer films, carbon-oxygen and carbon-nitrogen bond scission was observed at room temperature, and further decomposition to atomic species occurred after heating to 450 degrees C. All of these results are consistent with the fact that the Pt particles inside the G4OH dendrimer catalyze thermal decomposition, allowing dendrimer decomposition to occur at lower temperatures. However, the Pt particles also catalyze bond scission within the dendrimer fragments so that decomposition of the dendrimer to gaseous hydrogen is the dominant reaction pathway compared to desorption of the larger dendrimer fragments observed in the absence of Pt particles.

Large-scale synthesis of amorphous phosphorus nitride imide nanotubes with high luminescent properties

A facile solvothermal approach was successfully developed for the large-scale synthesis of amorphous phosphorus nitride imide (H3xP3N5+x) nanotubes with high luminescent properties by the reaction of 1,3,5-hexachlorotriphosphazene (P3N3Cl6) with sodium amide (NaNH2) at low temperatures. Transmission electron microscope images showed that the inner diameter of nanotubes is 120 ± 20 nm, wall thickness is 40 ± 10 nm, and length ranges from several to ten micrometers. Scanning electron microscope images revealed that the proportion of the nanotubes exceeds 90%. X-ray photoelectron spectroscopy spectra indicated that the binding energies of P2p and N1s are 133.30 and 398.40 eV, respectively, and the atomic ratio of P:N is 3:5.13. The infrared spectra of the sample are comparable to those of the reported HPN2 and HP4N7. Thermogravimetric analysis revealed that the product is very robust in a nonoxidizing atmosphere. The structure and the optical properties of the product and the annealed samples were investigated by x-ray diffraction and photoluminescence measurements, respectively.

Homogeneous and heterogeneous pathways of ethane oxidative and non-oxidative dehydrogenation studied by temperature-programmed reaction

In this work, the temperature-programmed reaction (TP-reaction) technique was employed for the study of the mechanism of ethane oxidative dehydrogenation (ODH) and the identification of primary and secondary steps of the reaction. The reactions of ethane and ethene in an oxidizing and non-oxidizing atmosphere were investigated in the presence and absence of a 20 wt.% MoO 3/Al 2O 3 catalyst, a highly active and selective catalytic material. Experiments were performed at steady flow conditions, with a 15 °C/min linear increase of temperature up to 700 °C, while the reaction effluent was monitored on-line by mass spectroscopy. Thermal reactions of ethane were found to be highly selective to ethene. Ethene seems to be primarily produced through a dehydrogenation mechanism, even in the presence of oxygen in the gas phase. However, oxygen was found to dramatically increase the overall rate of the reaction. Over the 20MoAl catalyst, ethane activation occurred at a significantly lower temperature, while the production of ethene was clearly a result of heterogeneous reactions via the oxidative dehydrogenation route. Surface pathways were found to have a significant role, even at temperatures where homogeneous reactions also occurred, indicating possible occurrence of a homogeneous–heterogeneous reaction scheme at high temperatures. In non-oxidative conditions, lattice oxygen activated ethane at the same temperature as in the presence of oxygen, leading mainly to ethene production, since lattice oxygen was found to be less reactive towards ethene. More labile forms of oxygen, resulting from adsorption of gas-phase oxygen on the surface, are probably responsible for the extensive ethene degradation observed at high conversion levels.

Relations between structure and catalytic activity of Ce–In-ZSM-5 catalysts for the selective reduction of NO by methane: II. Interplay between the CeO 2 promoter and different indium sites

The promotion of In-ZSM-5 catalysts for the selective catalytic reduction of NO by methane by CeO 2 has been investigated by a combination of physicochemical techniques (XPS, EXAFS, TPR, XRD, FTIR) and reaction studies, in particular under variation of the activation conditions. CeO 2 is a highly effective promoter for In-ZSM-5 in dry feed (e.g., X(NO)>70% at 100,000 h −1 between 723 and 773 K with 1000 ppm NO, 1000 ppm CH 4, and 2% O 2) whereas in moist feed, the promotional effect is pronounced only at high temperatures. The role of CeO 2 in the reaction mechanism is to provide a sufficient NO 2 supply on the basis of its high NO oxidation activity. Under catalytic conditions, CeO 2 undergoes interaction with the zeolite component, which stabilizes part of the Ce ions in the +3 state in an oxidative atmosphere while the majority of Ce ions remain in the CeO 2 lattice. This effect does not appear to be constitutive for the catalytic function of the CeO 2 promoter. In-ZSM-5 catalysts with different active site structures exhibit different responses to promotion by ceria. Intrazeolite indium oxo species, which are often considered the most important active sites in In-ZSM-5 SCR catalysts, are not among the most favorable cases upon promotion with CeO 2. Intense promotional effects are found with sites that catalyze unselective methane oxidation in the absence of CeO 2 (intrazeolite InO x Cl y species, extrazeolite In 2O 3 aggregates, probably active at the borderline with the zeolite). Ternary mechanical mixtures of CeO 2, In(OH) 3, and NH 4-ZSM-5 also exhibit high SCR activities provided that activation is performed in a nonoxidizing atmosphere. TPR, FTIR, XRD data, and results of experiments with separate activation of mixture components suggest that the favorable performance of these mixtures arises from extrazeolite indium sites, which are probably at the borderline between In 2O 3 aggregates and external zeolite surface and are possibly engaged in InOSi and InOAl bridges.

A solid-state potentiometric sensor for hydrogen detection in air

A solid-state potentiometric hydrogen gas sensor based on hydronium Nasicon, a hydrogen ion conducting solid electrolyte, is described. The device incorporates a patented silver-based reference electrode and a palladium working electrode. The sensor is robust, simple, fast, and capable of detecting hydrogen concentrations from at least 0.01 to 100%, a range of four orders of magnitude, in oxidizing and non-oxidizing atmospheres. The room temperature response characteristics of the sensor are reported.

Diffusion effects at the Au/p‐CuInSe2 contact studied by XPS

AbstractX‐ray excited photoelectron spectroscopy (XPS) was used to investigate the reactions at the interface between Au and CuInSe2 in case of Au/p‐CuInSe2 contacts produced by a procedure usually used to prepare low resistance ohmic contacts. Formation of an In‐Au alloy is observed after an annealing step at 300 °C in a nonoxidising atmosphere. Furthermore, it is found that some amount of gold diffuses into the CuInSe2 substrate. A tentative defect model is proposed to describe the formation mechanism of Au/ p‐CuInSe2 contacts.

A comparative study of template removal from silicalite-1 crystals in pyrolytic and oxidizing regimes

The removal of tetrapropylammonium cations (TPA +) from silicalite-1 crystals with a morphology of 90°-intergrowth and different crystal sizes was investigated. The effects of the nature of the gas (air or nitrogen) and of the hydrodynamics were examined using a stream flowing in parallel or across the crystal layer. The only process variable was the plateau temperature ( T max). Crystal domain boundaries became permeable to template degradation products when T max exceeded 300 °C. The template removal was monitored by (i) light microscopy, (ii) degree of removal of the total organics α, of nitrogen species α N and of carbon species α C and (iii) accessibility of the channel system for N 2 molecules. The sorption isotherms for N 2 exhibited two steps. The upper step started to be perceptible for a degree of organic removal higher than 55%. Its height increased with α, and its position moved to lower pressure values. The plots of the gas accessibility versus the degree of removal were modelled. For template removal in air, all plots were linear. In a non-oxidizing atmosphere, the accessibility lagged behind α N. Light microscopy showed that template degradation started along domain boundaries. Sorption kinetics of iodine into silicalite-1 crystals treated in a non-oxidizing atmosphere was considerably slower than that observed into crystals calcined in air. The tendency to crack formation increased with crystal size. The template removal efficiency was higher when using cross-flow than parallel flow calcination.

Characterization of chars from biomass-derived materials: pectin chars

The effect of pyrolysis conditions on the yield and composition of char from pectin was studied. Pectin is a component of the carbohydrate fraction of biomass-derived materials. The pyrolysis was done at atmospheric pressure under oxidative and non-oxidative (inert) atmospheres and at temperatures ranging from 150 to 550°C. The volatile product was analyzed by gas chromatography/mass spectrometry (GC/MS). The solid product, i.e. char, was characterized by solid-state 13C nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy. The char was also analyzed for its elemental composition and surface area. The surface morphology of char was studied by scanning electron microscopy (SEM). The results were compared to those from chlorogenic acid (CA), a component of the phenolic fraction of biomass-derived materials. The behavior of pectin was similar to that of CA. For both pectin and CA, the char yield decreased with increasing temperature before leveling-off at ca. 20% of the starting substrate in non-oxidative runs. In oxidative runs, the char yields from both substrates became negligible at 550°C. NMR analysis indicated that the aromatic character of char increased as the pyrolysis temperature increased. The oxygen functionality was progressively lost and the resonance bands corresponding to carbonyl groups mostly disappeared above 350°C. FTIR analysis also suggested the loss of hydroxyl and carbonyl groups from chars at high temperatures. The H/C and O/C ratios of chars decreased continuously with increasing temperature. The oxidative chars showed characteristics essentially similar to those of the non-oxidative chars. The surface area of char was negligible at low temperatures, but increased dramatically to a maximum of 70 m 2 g −1 at 450°C before decreasing at 550°C. SEM analysis indicated that the pyrolysis of pectin occurred via softening and melting of the substrate followed by bubble formation. At high temperatures, surface etching followed by the appearance of crystal deposition on the char surfaces were also observed. The results are consistent with the analysis of the evolved gases