Absence Of Alumina Research Articles

Alumina-enhanced valorization of ferronickel slag into refractory materials under microwave irradiation

This study presents a new approach to enhance preparation of superior-quality refractory materials by microwave sintering of the mixture of ferronickel slag and sintered magnesia with addition of alumina up to 10 wt %. It was shown that in the process of microwave sintering, the proper addition of alumina could contribute to formation of forsterite with fine and relatively uniform particle size. It also promoted the generations of high melting point magnesium aluminate spinel (MgAl2O4), magnesium iron aluminate spinel (MgFe0.6Al1.4O4), and magnesium aluminum chromate spinel (MgAl0.5Cr1.5O4) which replaced magnesium chromate spinel (MgCr2O4) formed during sintering without addition of alumina, eventually improving refractoriness and other properties of the resulting refractory material. By adding 4 wt % alumina to the mixture of slag and 25 wt % sintered magnesia for sintering at 1250 °C in only 20 min, the resulting refractory material obtained refractoriness of 1790 °C. Compared with that prepared in the absence of alumina, the refractoriness was increased by 156 °C. The method proposed in this study has good potential in improving valorization of ferronickel slag into value-added materials, exhibiting both apparent economic and environmental benefits.

Multi-wall Carbon Nanotubes Decorated with Bismuth Oxide Nanocrystals Using Infrared Irradiation and Diazonium Chemistry

A simple and efficient method using infrared (IR) irradiation is presented to decorate multi-wall carbon nanotubes (MWCNTs) with bismuth oxide nanocrystals (Bi2O3 NCs) using ammonium bismuth citrate (ABC) as Bi precursor. The present methodology comprises 4 steps: purification, functionalization, impregnation and calcination. Various techniques (XPS, TEM, PXRD, EDX, Raman and TGA) are used to characterize the resulting materials. The treatment with sodium hydroxide leads to the purification of MWCNTs (p-MWCNTs) which is confirmed by the absence of alumina. The chemical functionalization of p-MWCNTs with monocarboxylic aryl diazonium salts generated in-situ (p-MWCNTs-D1) followed by impregnation in the presence of IR radiation is the crucial step in homogeneously impregnating functionalized MWCNTs with ABC (p-MWCNTs-D1/ABC). Calcining p-MWCNTs-D1/ABC at optimum temperature results in a controlled decoration of Bi2O3 NCs in their pure phase. A bimodal distribution of Bi2O3 NCs on MWCNTs with a Gaussian mean diameter of ~ 1.1 and ~ 11.21 nm is evidenced. The originality of this work is the decoration of CNTs for the first time with Bi2O3 nanocrystals. Metastable β-Bi2O3 (tetragonal) crystal phase is noticed on the surface of CNTs. Electrical conductivity of the samples was assessed on bucky papers elaborated from the various modified MWCNTs. The present methodology is applicable to large-scale preparation which opens interesting perspectives for nanotechnology applications.

Increasing the Filtration Rate of Phosphor-gypsum by Using Mineral Additives

Phosphogypsum is a by-product of processing phosphate rock for phosphoric acid production by acidulation with sulfuric acid. The size of phosphogypsum crystals is a major factor for the economics of the process as it greatly affects the filterability of the phosphoric slurry. Some minerals containing two major chemical components, silica and alumina, proved to be very effective additives for growth of phosphogypsum crystals. To analyze the effect of these components on crystal growth, many additives are tested in the industrial scale in present work. Tests were carried out in the industrial phosphoric acid production unit of PP2 in Safi site.The present paper summarizes the results of phosphoric acid production from Youssoufia Washed Floated phosphate with addition of minerals aiming at increasing the filtration rate and better understand the effects of silica and alumina on filtration rates and phosphogypsum crystal size distribution.It is shown that the addition of reactive silica for complexation of the F element, which is unfavorable to a good crystallization, is seen to be insufficient in the absence of alumina; the crystals are developed, but in a single direction and become like thin bars. Furthermore, the presence of alumina improves the crystal morphology advantage with regular development along the three axes and achievement of large and uniform crystal shape.

Low temperature in-situ reaction sintering of zircon: Alumina composites trough spark plasma sintering

Pure Zircon and Zircon: Alumina (ZrSiO4: ?-Al2O3) composite powders were subjected to densification studies employing spark plasma sintering (SPS). Physico chemical and microstructural properties of the samples were evaluated and compared with that of conventionally sintered (CRH-Constant Ramp and Hold) compacts. Density measurements and microstructural evaluation revealed a low temperature densification of Zircon: Alumina at temperatures as low as 1300?C by SPS. Increase of temperature to 1350?C had shown negligible changes in density and on further heating the sample melts at 1400?C as a result of excessive formation of liquid phase. However, pure zircon could not be densified in the absence of alumina under SPS conditions. It is evident that addition of alumina enhances partial low temperature decomposition of zircon under the influence of plasma generated during SPS. Mullite formed as a result of this insitu reaction between alumina and silica acts as a bonding phase as revealed by the X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Electron disperse scanning (EDS) analysis.

Modulating the Host Nature by Coating Alumina: A Strategy to Promote Potassium Nitrate Decomposition and Superbasicity Generation on Mesoporous Silica SBA-15

A new strategy was utilized to generate strong basicity on mesoporous silica SBA-15 by precoating alumina before modification with the base precursor, potassium nitrate. The nature of the mesoporous silica host was greatly modulated by the alumina interlayer. Such an alumina interlayer plays a double role by enhancing the guest−host interaction to promote the decomposition of potassium nitrate and by improving the alkali-resistance of the mesoporous silica host. The majority of the potassium nitrate is decomposed at 690 °C on unmodified SBA-15, while the temperature decreases to 460 °C after precoating an alumina layer. Moreover, the ordered mesoporous structure of the parent, SBA-15, is well-preserved even if the supported potassium nitrate was decomposed to strongly basic potassium oxide, which is quite different from the complete destruction of the mesostructure in the absence of alumina. As a result, materials possessing both a mesoporous structure and superbasicity with a high strength of 27.0 were s...

Influence of Ga addition on the methanol synthesis activity of Cu/ZnO catalyst in the presence and absence of alumina

The influence of Ga addition to Cu/ZnO (CZ) methanol synthesis catalyst was investigated in the presence (CZA-Ga) and absence (CZ-Ga) of alumina. The reducibility of CZA-Ga was found to be more facile than CZ-Ga. The acidic strength of CZA-Ga was considerably decreased compared to CZA and CZ-Ga. In the presence of alumina, the addition of Ga to CZ improved the textural properties, resisted agglomeration of copper and showed higher activity and stability in methanol synthesis reaction from syngas. The easy reducibility and the appropriate acidity can be ascribed to the higher activity with high yield to methanol observed on CZA-Ga.

Synthesis of Large-Pore Micelle-Templated Silico-Aluminas at Different Alumina Contents

The EPR spectra of radical surfactant probes embedded in cetyltrimethylammonium bromide (CTAB) and trimethylbenzene (TMB) stable water emulsions (TMB/CTAB = 13) were analyzed to provide information on the kinetics of formation of micelle-templated silicoaluminas (MTSA) at 343 K, obtained by means of silica and alumina, solved in alkaline solutions, at different Si/Al ratios. Textural (surface area, pore volume, pore size, surfactant content) and structural characterization of both as-synthesized and calcined MTSA were performed by means of nitrogen sorption isotherms, TEM, and chemical analysis. This analysis showed that TMB worked as a swelling agent of the CTAB micelles, providing large-pore homogeneous and stable MTSA at TMB/CTAB = 13 for Si/Al from infinity to 10. A demixing of the emulsion occurs at Si/Al < 10: at Si/Al = 7, a double wide-and-narrow pore structure was formed; then, at Si/Al = 5, an amorphous material was obtained. At Si/Al > or = 10, the computer-aided analysis of the EPR spectra as a function of the synthesis time indicated the distribution of the probes in two different environments: "micellar" probes inserted in the surfactant aggregates, whose mobility decreases over the synthesis time, thus reporting on the progressive modification of the surfactant aggregates structure and the solid condensation, and "interacting" probes due to probe-surfactant heads electrostatically interacting with the charged surface sites induced by alumina incorporation in the silica network. This last fraction increases its relative amount over the synthesis time, informing about the condensation and structuration of the MTSA. Without alumina, the "interacting" component is absent in the EPR spectra because TMB preferentially interacts with the surfactant headgroups by cation-pi interactions, thus preventing the interactions of these headgroups with silanols. When alumina is added, the negatively charged silicoaluminate at the surface promotes the interaction of the ammonium headgroups with the surface, and some Na+ cations also interact with TMB by cation-pi interaction and contribute to decreasing the interaction of the headgroups with TMB. Therefore, increasing alumina contents promote electrostatic interactions between the positively charged surfactant heads and the negatively charged silicoaluminate groups. The strong interaction of the surfactants with the silicoaluminate surface allows the formation of a monolayerlike structure of surfactant, which is not observed in the absence of alumina. The synthesis is slowed by increasing alumina contents due to a destructuration effect of alumina in the MTSA formation.

Alumina catalyzed reactions of amino acids

Thermal reactions of glycine (Gly), alanine (Ala), leucine (Leu), valine (Val) and proline (Pro) adsorbed on activated alumina were studied by means of thermal analysis. In the absence of alumina, decomposition of amino acids was detected as a sharp endotherm above 200°C, whereas no thermal effects were detectable by differential thermal analysis (DTA) and differential scanning calorimetry (DSC) for amino acid/alumina mixtures. This could be explained by a continuous amino acid condensation to peptides and simultaneous absorption of formed water by alumina, the latter being gradually released at higher temperatures. Thermogravimetry (TG) and differential thermogravimetry (DTG) measurements revealed that the reactions of the amino acids adsorbed on alumina surface were spread over a wide range of temperatures. The catalysis of peptide bond formation on alumina surface at 85°C was proven directly by the identification of the reaction products, mainly dipeptides and cyclic anhydrides.

AN EASY AND FAST METHOD FOR OXIDATIVE DEPROTECTION OF TRIMETHYLSILYL ETHERS, TETRAHYDROPYRANYL ETHERS, AND ETHYLENE ACETALS WITH KMnO4 SUPPORTED ON ALUMINA UNDER SOLVENT-FREE CONDITIONS

ABSTRACT A manipulatively simple and rapid method for oxidation deprotection of trimethylsilyl ethers, tetrahydropyranyl ethers and deprotection of ethylene acetals to afford carbonyl compounds under solvent-free conditions in the presence or absence of alumina with potassium permanganate.

The C60-Catalysed Oxidation of Hydrogen Sulphide to Sulphur

Abstract Carbon disulphide is rapidly converted into sulphur by C60 deposited on neutral alumina, through formation of hydrogen sulphide which is then oxidised. C60 is more effective than graphite in this oxidation, which also occurs (though more slowly) in the absence of alumina. It is therefore essential to remove all traces of carbon disulphide traces when purifying C60 by column chromatography of soot extract deposited from carbon disulphide solutions.

Sintering and oxidation in gel-coated SiC w /Al2O3 composites

Boehmite gel-coated SiC whiskers have been studied as discs and as dispersed in gel and commercial alumina. The coated whiskers oxidize and react to some extent in alumina-rich composite compacts when heated in vacuum. In the absence of alumina as matrix, discs of coated whiskers turned brittle on heating above 1600°C. A density of 3.7g/cc was obtained for compacts of SiC whiskers in submicron alumina when sintered pressureless for 2 h at 1600°C. A smooth interface, compatible with the matrix, has resulted in good mechanical properties.

ChemInform Abstract: Selective N‐Prop‐2‐ynylation of Heterocycles Induced by Solid‐Liquid Phase Transfer Catalysis without Solvent and Use of Solid Inorganic Supports.

AbstractUnter Phasen‐ Transfer‐Bedingungen lassen sich Heterocyclen wie (I) und (IV) N‐propinylieren, wobei das im Falle von (IV) erhaltene Nebenprodukt (VI) auch als Hauptprodukt zugänglich gemacht werden kann.

Synthesis of silica-sodalite from non-aqueous systems

The aluminosilicate sodalite has been known since antiquity1. It occurs naturally as the polysulphide-containing mineral lapis lazuli1 and as a salt-bearing feldspathoid2 and has also been synthesized as the zeolite basic sodalite with the formula Na6(Al6Si6O24) · xNaOH · (8−2x)H2o (ref. 2). The structure is an open framework of relatively large cages which are accessible, to water molecules and some ions, through relatively small windows of ∼2.1 A free diameter. Large ions or molecules may be trapped in the cages during synthesis. In aluminosilicate sodalite, the cages contain the number of cations required to compensate for the lattice charge, together with varying amounts of H2o and salts such as NaOH and NaCl. Aluminosilicate sodalites usually have an Al/Si ratio of about unity although alumina analogues of sodalite have been synthesized3 and a silica-rich sodalite (TMA sodalite) has been prepared from aqueous hydrothermal systems4,5 in the presence of tetramethylammonium ions. We report here a new method for the synthesis of sodalite, either in a silica-rich aluminosilicate form or in a novel pure-silica form. Our method of synthesis of sodalite is unusual in that the solvent system is essentially non-aqueous. In the absence of alumina, a new material is produced, namely a pure-silica form of sodalite which, following previously published suggestions6, we call silica-sodalite. If the ‘solvent’ system is ethylene glycol then the unit cell composition approximates to Si12O24 · 2C2H4(OH)2.

Selective N-prop-2-ynylation of heterocycles induced by solid–liquid phase transfer catalysis without solvent and use of solid inorganic supports

Complementary processes promote the N-prop-2-ynylation of heterocycles: solid-liquid phase transfer catalysis without added solvent in the presence or absence of alumina or titanium dioxide and alkylation on ‘basic’ alumina in ‘dry media’.

Electrochemical behaviour of the surface treated composite-electrolyte/electrode interface

The effect of surface treatment of the solid electrolyte 50 wt% (4.7 mol% Sc2O3+95.3 mol % ZrO2)+ 50 wt % Al2O3 (used in the SIRO2 low temperature oxygen sensor) on its electrochemical behaviour has been studied by complex impedance spectroscopy. Two techniques, namely, preferential etching of alumina from the surface by a suitable etchant and cosintering of a thin layer of an alumina free electrolyte composition were used. The electrode/electrolyte interfaces prepared by using surface treated electrolyte samples had much lower electrode resistance (by a factor of 3–6) compared with the untreated surfaces. The decrease in the interfacial impedance is attributed mainly to the absence of alumina at the interface (an insulator phase) at which no oxygen exchange reactions could take place.

An alumina catalyzed addition of secondary amines to exocyclic α,β-unsaturated ketones

A Michael addition of secondary amines to exocyclic α,β-unsaturated ketones has been achieved in excellent yield in the presence of alumina. In the absence of alumina, the reaction does not proceed or takes place in low yield with many side products after a long reaction time.

Stable and Metastable Equilibria in the System SiO2‐Al2O3

Concentration profiles of Al2O3 in diffusion couples made from sapphire and fused silica were used to determine the stable equilibrium phase diagram of the system SiO2‐Al2O3. The intermediate compound mullite, 3Al2O3· 2SiO2, melts incongruently at 1828°± 10°C; its stable solid‐solution region ranges from 70.5 to 74.0 wt% Al2O3 below 1753°C and from 71.6 to 74.0 wt% at 1813°C. The microstructures of diffusion zones and heat‐treated specimens also indicate the incongruency of mullite. Additional information is given for 3 metastable systems: SiO2‐Al2O3, in the absence of mullite, SiO2‐“ordered”‐mullite in the absence of alumina, and SiO2‐“disordered”‐mullite in the absence of alumina. Under metastable conditions, ordered mullite melts congruently at = 1880°C and its solid‐solution range extends up to = 77 wt% Al2O3. The solid‐solution range of disordered mullite extends to ∼ 83 wt% Al2O3 with an estimated congruent melting temperature of ∼ 1900°C. The existence of metastable systems is associated with superheating of mullite above the incongruent melting temperature and with nucleation of alumina and mullite in supercooled aluminum‐silicate liquids.

The Silica-Alumina System: Stable and Metastable Equilibria at 1.0 Atmosphere

Diffusion couples, consisting of sapphire and fused silica, which were annealed in the temperature range from 1678 degrees to 2003 degrees C and analyzed by electron beam microprobe, have provided data on the stable phase equilibrium of the silica-alumina system. Under stable equilibrium conditions, the intermediate compound of this system, mullite (3Al(2)O(3) . 2SiO(2)), melts incongruently at 1828 degrees +/- 10 degrees C and its solid solution field extends from 70.5 to 74.0 percent (by weight) alumina. The stable phase diagram is a composite of the two binary eutectic diagrams: silica-mullite in the absence of alumina and silica-alumina in the absence of mullite. Under metastable conditions, mullite melts congruently at approximately 1890 degrees +/- 10 degrees C and its solid solution field extends to approximately 83.2 percent (by weight) alumina.