Search results for "alum"
showing 10 items of 1303 documents
O Triclusters Revisited: Classical MD and Quantum Cluster Results for Glasses of Composition (Al2O3)2(SiO2)
2006
The (17)O NMR spectrum of CaAl(2)Si(2)O(8) glass shows two types of O sites that are not present in the crystalline material. One of these, with (17)O NMR parameters C(Q) = 2.3 MHz and delta = +20 ppm, has been assigned to a "tricluster" O, a local geometry in which the O is coordinated to three tetrahedrally coordinated atoms, either Al or Si. For crystalline CaAl(4)O(7), a tricluster site (with three Al linkages to O, i.e., OAl(3)) has been characterized experimentally, with a C(Q) of 2.5 MHz and a delta of about +40 ppm. Thus, a C(Q) value of 2.5 MHz or less seems to be a characteristic of such sites, although they may show a range of delta values. However, several different quantum chem…
Fatigue Crack Growth for Different Ratios of Bending to Torsion in AlCu4Mg1
2008
The paper contains the fatigue crack growth test results obtained under proportional bending with torsion in AlCu4Mg1 aluminium alloy [1]. Specimens with rectangular cross sections and dimensions: length l = 90 mm, height w = 10 mm and thickness g = 8 mm were tested [2]. Each specimen had an external unilateral notch with depth 2 mm and radius ρ = 0.2 mm. The tests were performed under the stress ratio R = −1. The notches in the specimens were cut with a milling cutter and their surfaces were polished after grinding. The tests were realized on a fatigue test stand MZGS-100 where the ratio of torsion moment to bending moment was \( M_T (t)/M_B (t) = tg\alpha = \sqrt 3 /3,1{\text{ }}and\sqrt …
Preliminary studies on the synthesis of alkaline-free large crystals of ZSM-5
1988
Single crystals of ZSM-5 were synthesized in three systems containing Na + -TPA, Li + -TPA, and NH 4 + -TPA, respectively. Applying a reaction mixture of the molar composition 8 TPA + 123(NH 4 ) 2 O + Al 2 O 3 + 59 SiO 2 + 2280 H 2 O, alkaline-free, homogeneous, and pure single crystals of ZSM-5 were prepared up to a length of 350 μm. The crystal size and yield were found to be dependent on the water content of the starting reaction mixture and on the type of aluminium source; for example, boehmite and aluminiumtriisopropylate.
Factorial Design in the Ammonia Based Synthesis of Large Uniform MFI, MEL, DOH, and DOH/DDR Type Zeolite Crystals
1989
This study reports the synthesis of large and uniform crystals of high-silica zeolite materials. Statistic factorial design was applied in order to determine significant parameters for the rapid growth of alkali-free crystals out of ammonia-based synthesis systems. For silicalite-I, high ammonia contents at low water concentrations yielded crystals up to 300 μm in size. The number of crystal nuclei in type MFI synthesis systems was found to be significantly reduced by increasing ammonia and aluminium contents. MEL-type zeolites could be prepared only with the smaller size of 15 μm. Low water concentrations improved the product yield. Aminoadamantane as a guest molecule nucleated highly unif…
Luminescence of intrinsic defects in YAG polycrystalline powder
1997
In the present work we have investigated luminescence properties of the fine, well-crystallized undoped YAG polycrystalline powders and thermochemically treated YAG polycrystalline powders. Presented work give evidence of significant role of 'antisite' defects (AD), i.e., where some portion of one type of cations (Y 3+ ) occupy another cations (Al 3+ Oh ) sites and vice versa in YAG structure, on the creation and structure of luminescence centers in complex multi-component oxides.
The essential identity of the framework structures of ZSM-8 and ZSM-5
1994
The crystal structures of TEA-ZSM-8 and its calcined template-free form have been studied by Rietveld analyses based on X-ray powder diffraction data. The results show that the aluminosilicate framework structure of ZSM-8 is essentially identical to that of ZSM-5. The tetraethylammonium molecule could be located in the difference Fourier analysis yielding positions similar to its TPA counterpart in ZSM-5. Lattice constants of ZSM-8 are in the same range as for ZSM-5. Contrary results are related to incorrectly indexed powder patterns. Optical investigations of ZSM-5 and ZSM-8 crystals showed that the zeolites studied here are both twinned exhibiting differently shaped twin individuals.
ChemInform Abstract: Ta1.09Fe2.39Te4, a New Non-Stoichiometric Ternary Tantalum Telluride.
2010
Abstract Ta1.09Fe2.39Te4 was prepared by chemical transport from the elements in sealed silica tubes in a temperature gradient from 700 to 600 °C. It crystallizes in the monoclinic space group P2/m with a = 6.162(2) A , b = 7.852(3) A , c = 7.250(3) A , β = 95.32(3)° and Z = 2 . Its structure can be derived from a hexagonal close packing of tellurium atoms with tantalum and iron atoms in octahedral voids and additional iron atoms in tetrahedral voids. The structure is closely related to the structures of MM'Te2 (MNb, Ta; M′Fe, Co, Ni) and MxFeγTe2 (MNb, x = 0.89, γ = 0.93; MTa, x = 0.77, γ = 0.90).
La circulación manuscrita de los poemas alfabéticos de Francisco de Osuna: El caso del manuscrito «MSS/74» de la Biblioteca Nacional de España
2013
International audience; A raíz del redescubrimiento en la BNE del manuscrito MSS/74 —una copiosa antología de cartas y opúsculos místicos del siglo xvi—, se pudieron identificar dos de los tres «alfabetos» anónimos al amor de Dios que cierran dicho compendio: se trata en realidad de dos poemas alfabéticos de Francisco de Osuna. Constituyendo un ejemplo inédito de versiones manuscritas de los poemas del franciscano andaluz, estos alfabetos presentan variantes significativas respecto de las versiones impresas procedentes del Segundo y del Cuarto Abecedario espiritual. El cotejo de ambas versiones, y el análisis atento de dichas variantes, evidencian la realidad de una circulación oral y manus…
A New Aluminosilicate Molecular Sieve with a System of Pores between Those of ZSM-5 and Beta Zeolite
2011
[EN] A new aluminosilicate zeolite (ITQ-39) has been synthesized. This is an extensively faulted structure with very small domains that makes the structure elucidation very difficult. However, a combination of adsorption spectroscopy and reactivity studies with selected probe molecules suggests that the pore structure of ITQ-39 is related to that of Beta zeolite, with a three-directional channel system with large pores (12-MR), but with an effective pore diameter between those of Beta and ZSM-5, or a three-directional channel system with interconnected large (12-MR) and medium pores (10-MR). The pore topology of ITQ-39 is very attractive for catalysis and shows excellent results for the pre…
Analisi numerico-sperimentale per la determinazione delle tensioni residue in un giunto saldato
2013
La durata di un componente dipende dall’interazione tra le caratteristiche meccaniche del materiale con cui è costruito e gli sforzi a cui esso è sottoposto. Per la determinazione dello stato tensionale agente, oltre agli sforzi dovuti ai carichi imposti durante l’esercizio, è necessario conoscere accuratamente gli stati tensionali residui derivanti dal processo di produzione. Generalmente, le tensioni residue sono indesiderate poiché possono essere di entità elevata e tale da ridurre la resistenza complessiva del componente meccanico. Un aspetto particolarmente insidioso delle tensioni residue è che la loro presenza viene generalmente riconosciuta solo dopo il verificarsi di un malfunziona…