Al Bridges Research Articles

Speciation in Size and Density Fractionated Fly Ash III. The influence of HCL Leaching on the Glassy Constituents of a High-Ca Fly Ash

ABSTRACTAsh density fractions, separated from a high-Ca fly ash, were leached with 6M HCl at 105°C. The density fractions (<0.79 and >2.85 g.cm−3) selected for leaching have been shown in previous work to consist largely of two different glass types, designated Glass I and Glass II. It was shown that both Glass I and Glass II are leachable to yield solutions containing Al and modifier cations. Acid attack on Glass I appears to involve hydrolysis of Si–O–Al (silalane) bridges along with ion exchange at available non-bridging oxygen sites. Attack on Glass II is more extensive, with both silalane and siloxane bridges being hydrolysed, and ion-exchange occurring at non-bridging oxygens. The products of leaching are aluminosilicates. In the case of Glass I, these remain as pseudomorphic, hollow spheres; whereas, for Glass II, substantial reprecipitation of silica (alumina) gel was found.

Crystal structures of the hydro-sodalite Na 6[AlSiO 4] 6 8H 2O and of the anhydrous sodalite Na 6[AlSiO 4] 6

The most hydrate water rich form of the hydro-sodalites Na 6+ x [AlSiO 4] 6(OH) x nH 2O with x = O and n = 8 and the corresponding dehydrated form with x = O and n = O have studied by X-ray Rietveld analyses at 295 K and 675 K, respectively. The crystal structure of Na 6[AlSiO 4] 6. 8H 2O is strongly determined by hydrogen bonding between the non-framework hydrate water oxygens (donators) and the framework oxygens (acceptors). The hydrogen bonding scheme is destroyed during a two-step dehydratation reaction at 400–500 K, which yields a substantial relaxation of the aluminosilicate framework. The 9% volume expansion of the anhydrous sodalite Na 6[AlSiO 4] 6 is reflected by the increase of the SiOAl bridging angle from 136.2(3)° in the octahydrate to 156.3(6)° in the structure of the anhydrous high temperature product. The antagonistic effect of hydrogen bonding or hydroxo-configuration of the non-framework constituents in hydro-sodalites is discussed.

The effect of fluorine on viscosities in the system Na2O–Al2O3–SiO2: implications for phonolites, trachytes and rhyolites

The effect of fluorine on melt viscosities of five compositions in the system Na2O-Al2O3- SiO2h as been investigateda t one atmospherea nd 1000-1600'Cb y concentric-cylinder viscometry. The compositions chosen were albite, jadeite and nepheline on the join NaAlOlSiO2 and two others of the join at 75 mole percent SiO2, one peralkaline and one peraluminous. All melt viscosities were independent of shear rate over two orders of magnitude, indicating Newtonian behavior. All viscosity-temperature relationships were Arrhenian within error. Fluorine reduces the viscosities and activation energies of all melts investigated. The viscosity-reducing power of fluorine increases with the SiO2 content of melts on the join NaAlO2-SiO2 and is a maximum at Na/Al (molar) = I for melts containing 75 mole percent SiO2. Fluorine and water have similar effects on aluminosilicate melt viscosities, probably due to depolymerization of these melts by replacement of Si-O-(Si, Al) bridges with Si-OH and Si-F bonds, respectively. Evidence from slag systems shows that fluorine also reduces the viscosity of depolymerized silicate melts. The viscous flow of phonolites, trachytes and rhyolites will be strongly afected by fluorine. It appears that fluorine contents of igneous rocks may be combined with water in calculation schemes for determining the viscosity of natural melts.

On the Interaction of CrO2Cl2 Vapor with the Surface of γ-Al2O3 and the Formation of a Chromium Oxide Covering

Abstract Samples of γ-Al2O3 containing different amounts of residual hydroxyl groups were obtained by thermal treatment. The possibility of interaction of the surface hydroxyl groups of γ-Al2O3 with chromyl chloride vapor was studied by IR spectroscopy. The hydrogen chloride evolved as a result of the reaction interacts with both strained Al–O–Al bridges and the surface OH groups. Different types of OH groups show different reactivities with respect to the interaction with CrO2Cl2. Bands at 3780 and 3700 cm−1 are due to OH groups which have a much higher reactivity than the OH groups responsible for bands at 3744 and 3733 cm−1. Not all of the OH groups participate in the surface reaction. Decrease in their surface density results in increase in the reactivity. Modification of the γ-Al2O3 surface is achieved by reaction cycles consisting of treatment with CrO2Cl2 vapor and hydrolysis of the compounds obtained by water vapor. As a result, an increase in the chromium oxide amount on the surface of γ-Al2O3 is observed. This is ascribed to the “secondary” OH groups formed after the hydrolysis.

Organic matter-phosphorus associations as a sink in P-fixation processes in allophanic soils of Chile

In fertilized and unfertilized plots of ten Chilean allophanic soils the fraction of total-P associated with organic matter and the organic carbon content were determined. Cultivation with P fertilization for 40 yr or more increased the organic C and organic P in most of the soils. It is hypothesized that these effects are related to the high biochemical activity of these soil environments which are dominated by actinomycetes and fungal species as well as to the chemical and physical properties of the soils. It appears that, following its fast adsorption onto active allophanic surfaces, added-P is subjected to reactions resulting in the formation of organic matter-P associations or complexes possibly through Al bridges. The humus-P complexes compose the major portion of total-P in these soils and may be viewed as a P sink in the overall P-cycling process. There is a need for further research on the specific mechanisms by which plant roots utilize P-sinks as sources of P. Based on microbial activity a model of the P-cycle operating in these soils is hypothesized.

Temperature Dependence of Critical Current in Granular Al Bridges with Different Thicknesses and Widths

Critical currents of granular Al bridges with different thicknesses and widths have been measured as a function of temperature. The experimental values of critical current were somewhat smaller than the pair-breaking current in the Ginzburg-Landau theory, being proportional to ( T c - T ) 3/2 near the critical temperature T c . In the lower temperature region they became to be proportional to ( T c - T ). It was found from the temperature and thickness dependences that critical current seems to be governed by the mechanism, different from the pair-breaking one. Slightly below T c , appearance of electrical resistance was observed, depending on the bridge thickness, but not on its width. It is suggested that vortices are thermally activated and their flow generates a voltage.

Mixed-metal hydride complexes containing ZrHA1 bridges. synthesis and relation to transition-metal-catalyzed reactions of aluminum hydrides

Dialkylaluminum hydrides and Cp 2ZrX 2 (Cp = π 5-C 5H 5; X = Cl, H, alkyl) were found to react by aggregation to give mixed ZrAl trihydride complexes containing ZrHAl bridges. Reactions of these mixed-metal hydrides are discussed and structural parallels between them and known aluminum hydride complexes are drawn.

A model for the surface of a silica-alumina catalyst

A semiquantitative model is proposed for the surface of a silica-alumina catalyst, based on a previous model for the surface of silica gel. “Acid” sites of various types are assumed to be created by the attachment and subsequent bridging reactions of AlOH groups on a silica surface resembling a cristobalite 100 face partially covered with randomly distributed paired hydroxyl groups. Three types of “strained” AlOAl bridges and three possible types of ▪ bridges are considered. The strong “acid-base” sites (α sites) previously shown to exist on silica-alumina surfaces at about 5 × 10 12 sites/cm 2 are identified with one type of strained AlOAl link expected at a maximum surface concentration of 6.6 × 10 12/cm 2. Features of the model are discussed and related to experimental observations.

The chemistry and the stereochemistry of poly( N-alkyliminoalanes) : IV. The preparation and crystal structure of [H(HAlN-i-Pr) 5AlH 2]·LiH/Et 2O

The compound [H(HAlN-i-Pr) 5AlH 2]·LiH/Et 2O has been prepared, and its crystal and molecular structure has been determined from single-crystal, three-dimensional X-ray diffractometer data. The molecular structure is a pseudohexameric cage, consisting of a five-membered fragment, AlNAlNAl, crosslinked to a six-membered cyclohexane type ring, (AlN) 3. The hydrogen atom of LiH is indistinguishable from the other hydridic hydrogens, so that the N-isopropyliminoalane part of the molecule may be considered as an anion with a formal charge of −1. The lithium cation is linked to two adjacent molecules through three LiHAl bridges, the fourth position of its tetrahedral coordination being occupied by the oxygen of diethyl ether. Large distortions of the tetrahedral valence angles occur, both on the aluminum atoms and on the nitrogen atoms, together with a noticeable spread of the AlN bond lengths, averaging 1.919(4) Å. Colourless crystals of the compound have the following crystal data: orthorhombic space group Pna2 1; a = 19.76(2), b = 10.38(1), c = 16.60(2) Å; Z = 4; calculated density 1.048 g/cm 3. The structure has been refined by block-matrix least-squares methods, using 2487 independent reflections, to an usual R factor of 5.9%.

The chemistry and the stereochemistry of poly( n-alkyliminoalanes) : III. The crystal and molecular structure of the adduct (HalN-i-Pr) 6AlH 3

The crystal and molecular structure of the adduct (HAlN-i-Pr) 6AlH 3 has been determined from single-crystal and three dimensional X-ray diffraction data collected by counter methods. The cage-type molecular structure consists of two six-membered rings, (AlN) 3, joined together by four adjacent transverse AlN bonds; the loss of two of these bonds allows the complexation of one alane molecule, with five-coordination of the aluminum (trigonal bipyramidal geometry), through two AlN bonds and two AlHAl bridge bonds. The AlN bond lengths range from 1.873 to 1.959 Å; the average AlH bond length is 1.50(1) Å for the four-coordinated aluminum atoms; the average distance of the two apical hydrogens from the five-coordinated aluminum atom is 1.92(5) Å. Colourless prismatic crystals of the compound have the following crystal data: triclinic space group P 1 ; a = 17.13(2); b = 10.78(2); c = 10.20(2) Å; α = 124.3(4), β = 92.0(4), γ = 92.1(5); Z = 2; calculated density 1.157 g/cm 3. The structure has been refined by block-matrix, least-squares methods using 4358 independent reflections to a standard unweighted R factor of 4.9%.

Recent developments in the chemistry of polyhedral complexes derived from metals and carboranes

The formation of icosahedral carboranes, their degradation to dicarbollide ions, and formation of metallocarboranes from these ions are briefly reviewed. The bis(dicarbollyl) cobalt(ni) anion reacts with cobalt hydroxide to produce biand tn-metallic polyhedral complexes incorporating the (3o)-l.2-B8C2H ion and possessing novel structures. The strong acid (3)-1,2-B9C2H,, reacts with R3M(R alkyl, M = Al or Ga) in two steps, first to give a dialkylmetalsubstituted carborane, (3)-1,2-B9C2H1 2M R2. X-Ray diffraction and variable temperature n.m.r. (250 MHz 'H and 80 MHz B) show this carborane is bonded by B—H—Al bridge bonds and undergoes rapid tautomeric rearrangement at room temperature. It reacts further to form a monoalkylmetalsubstituted carborane, (3)-1,2-B9C2H11MR. This compound rearranges at 400°C to afford (3)-1,7-B9C2H,,MR. Thermal rearrangement also occurs in (ir-C5H,) Co[ir-(3)-1,2-B9C2H,,] ; six new isomers which result from migration of carbon atoms over the polyhedron have been isolated and characterized. Products from the thermal rearrangement of (ir-C5H5)Co[ir-(3)-1,2-B9C2H9 (CH,)2] and (it-C5H5)Co[it-(3)-1,2-B9C2119(CI-12)3] are also reported. Structural elucidation and mechanistic implications of these rearrangements are discussed. Several closed polyhedral carboranes undergo an apparent reductive opening to afford dianions which, upon subsequent reaction with CoCl2 and C5H, form new closed polyhedra which incorporate the metal; these derivatives have the overall geometry of the next highest homologue of the known polyhedral species. Complexes formed in this manner from 1,6-B6C2H8, 1,6-B8C2H,0, and 12-B,0C2H12 are reported. The red 13-atom polyhedral complex (it-C5H 5)Co(7,8 ,0C2H 2) undergoes thermal rearrangement to two new isomers, orange and red-orange, which probably differ only in positions of the carbons in the polyhedron. In 1965' the first examples of bonding between a transition metal and the two isomeric dicarbollide ions, B9C2H j were reported. The latter ions are eleven-particle icosahedral fragments which accept the transition metal in such a manner as to complete the icosahedron. The interaction of the metal with the carborane fragment may be described as similar to the it-bonding found in ferrocene2 and re'ated species. The early work in this area has been 547

Crystal structure of di-µ-phenyl-bis(dimethylaluminium)

Crystals of the title compound are triclinic, space group P, with three dimeric molecules in the reduced cell of dimensions a= 12·313, b= 12·755, c= 9·352 A, α= 102·8, β= 91·6, γ= 61·3°. The structure was determined by Patterson and Fourier methods from 3126 visually estimated photographic data, and refined by least-squares to R 10·6%. One third of the molecules lie on centres of symmetry with the [graphic omitted] ring necessarily planar, and the remainder are in general positions, with the central ring ‘folded’ by 14° about the Al ⋯ Al line. Al ⋯ Al is 2·687, Al–C(bridge) 2·144, and Al–C(terminal) 1·977 A; the Al–C–Al bridge angle is 77·6°.

Crystal structure of di-µ-phenyl-bis(diphenylaluminium)(triphenylaluminium dimer)

Crystals of the title compound are triclinic, space group P, with one centrosymmetric dimer in the reduced cell of dimensions a= 9·565, b= 10·813, c= 8·328 A, α= 106·2, β= 111·8, γ= 102·3°. The structure was determined by Patterson methods from 1636 observed data, visually estimated from Weissenberg photographs, and refined by least-squares methods to R 9·1%. The Al ⋯ Al vector (2·702 A) is almost normal (84·4°) to the planes of the bridging phenyl groups; Al–C distances are 2·182 (bridge) and 1·958 A(terminal), and the Al–C–Al bridge angle is 76·5°.

Metal Oxide Trialkylsilyloxide Polymers. Part VI. Aluminum Oxide Trimethylsilyloxides

Tris(trimethylsilyloxy)aluminum, [Al(OSiMe3)3]2, was hydrolyzed under controlled conditions in dioxane at 25 °C. The soluble initial products [AlOx(OH)z(OSiMe3)3−2x−z]n, with x = 0.03–0.65, underwent disproportionation when heated at 120–150 °C under vacuum to give final products with x = 0.8–1.1. Molecular weights were determined by cryoscopy in cyclohexane, and the linear dependence of 1/n on x was combined with an extension of the theory of regular polymer series to show that the number of OH groups, z, was small compared to the number of bridging oxygen atoms, x, per Al atom. The initial products consist of dimeric units, each linked to an adjacent unit by one or two oxygen bridges between aluminum atoms. The degree of polymerization is 1 to 4, based on the dimer unit. The final products have much higher degrees of polymerization (10–40, based on the dimer), and appear to contain a higher proportion of Al—O—Al bridges.

Pedological Problems concerning Volcanic Ash in Japan

The authors tried to review scientific works on volcanic ash soils in Japan from the pedogenetical point of view.Morphology: The soils consist of the thick humified loose A horizon and brownish structural B to BC horizon, though in younger soils A-C sequence is common, lacking B horizon. Neither any sign of podzolization nor laterization is recognized. Such a normal profile is often disturbed by denudation, accumulation of surface humic soil materials or by successive addition of recent pyroclastic fall.Mechanical, chemical and mineralogical composition: Though younger soils mainly consist of sand and gravel in texture, most of matured soils are so highly weathered that the clay content often amounts to about one-half of the total soil mass. Chemical analysis reveals that matured soils have been suffered from severe weathering which results in marked loss of silica and bases leaving clay complex rich in hydrous sesquioxides. The principal mineral of the clay fraction in volcanic ash soils is allophane with some quantity of various layer silicates, gibbsite and other sesquioxide minerals. Allophane is considered to be formed by co-precipitation of hydrous silica and alumina gels both of which are regarded as end products of severe weathering of volcanic glass and plagioclase dominant in original volcanic ash. The genesis of allophane is mainly conditoned by such peculiar physical properties of the parent material as homogeneous fine grain size, extraordinally broad specific surface area and rapid permeability. And it seems that the genesis is accelerated by the warm and superhumid climate in Japan.Accumulation of humus: The characteristic thick humus layer of volcanic ash soils contains very high amounts of organic carbon (8-30%), and its almost real black colour looks just like as in Chernozem. The raw material must be derived from grass vegetation seeing from the predominace of the phytolith or plantopal in the very fine sand fraction of the humus layer. The chernozemic black colour may be due to highly condensed and polimerized humic acid, which may have been formed in the rather aerobic soil condition of porous volcanic ash materials persisting even under humid monsoon climate. Nevertheless, judging from the fact that more content of the fulvic acid is determined than that of the humic acid in most cases, and that both acids are combined with sesquioxides or allophane and not with Ca, the humus of the soils should have also podzolic character which may be related to superhumid climate and aerobic soil condition. And allophane must be responsible for such a marked accumulation of humus in the volcanic ash soils.Physical and chemical characteristics: The volume of the solid phase of the soils occupies only 20-30% of the whole soil mass, in other words, the porosity and water holding capacity are extremely high and apparent density is very low. It is the main reason why the volcanic ash soils are not only subjected from rapid weathering and specific humification, but also suffered from wind and sheet erosion, as well as frost damage. Clods of the soils are apt to be broken down into water-stable micro-aggregate (0.05-0.02mm in dia.), which is thought to be bound by loose hydrogen bond in the swelling water with Fe or Al bridge. The soils contain a lot of swelling and hygroscopic water, both of which may be mostly combined with allophane. Besides, such structural OH is released continuously by heating or an ion exchange treatments.The reaction of surface horizon of the soils is generally acid based on humic acid, but very weakly acid to nearly neutral in subsoil in which allophane is dominant component in the clay fraction, in spite of extremely low degree of base saturation caused by severe leaching under the superhumid climate. The cation exchange capacity of the soils is rather high, though the determination tends to be ill-reproducible