The state of magnesium in silicate glasses and melts

The properties of silicate glasses and melts containing magnesium are analyzed in comparison with the properties of glasses and melts in which magnesium is replaced by aluminum. In particular, the properties of the glass and the melt of the diopside composition CaMgSi₂O₆ are analyzed in comparison with the properties of the glass and the melt of the anorthite composition CaAl₂Si₂O₈. It is demonstrated that the properties of aluminosilicate and magnesium silicate glasses and melts differ not so strongly as should be expected upon replacement of modifier ions by network-former ions. By using the parameters γ _n characterizing the cation field strength, it is shown that Mg²⁺ cations can fulfill both the function of network formers like Al³⁺ cations and the function of modifiers like Ca²⁺ cations. The degree of depolymerization of the glass and the melt of the composition CaMgSi₂O₆ is estimated to be 0.4–0.5 from the dependences of the change in the relative density (d − d ₀)/d at different pressures on the degree of depolymerization NBO/T (the ratio of the number of nonbridging oxygen atoms to the number of network-former cations) for silicate glasses and the dependence of the isothermal bulk modulus K _t on the quantity NBO/T for silicate melts.     

Effect of adding liquid glass on the compaction and reactive sintering of cermet Al2O3-Al

The salient features of the process of compaction and reactive sintering of Al₂O₃-Al cermet compacts with additions of liquid glass are studied. The introduction of 3–28 wt.% glass into the initial aluminum powder, consisting of plate-shaped particles with aluminum-oxide surface films, yields granular material with bulk mass 0.4–0.5 g/cm³. The salient features of the compaction of granular powder are studied by analyzing logarithmic diagrams. It is shown that reactive sintering of samples in air occurs in a filtration combustion regime, and the dry residue of liquid glass activates sintering, resulting in the formation of γ-Al₂O₃, θ-Al₂O₃, α-Na₂Si₂O₃, and Si nanodispersed inclusions in an aluminum matrix with a layered structure. The flexural strength of 2.40–2.45 g/cm³ cermet is 300–320 MPa. __________ Translated from Steklo i Keramika, No. 7, pp. 28–31, July, 2007.     

Explosive synthesis of ultrafine Al2O3 and effect of temperature of explosion

Synthesis of ultrafine Al₂O₃ is considered. An X-ray phase analysis indicates that ultrafine γ-Al₂O₃, (θ + α)-Al₂O₃, and α-Al₂O₃ are synthesized by explosion of water-gel explosives with a zero oxygen balance, prepared by mixing aluminum nitrate, RDX, and carbamide. All granules of ultrafine Al₂O₃ are spherical and homogeneous, and the granule size varies from 10 to 30 nm. The average crystal sizes of ultrafine Al₂O₃ are calculated by the Scherrer equation. The temperatures of explosion of water-gel explosives are found by a simplified approach. A comparison indicates that the higher the temperature of explosion, the greater the average nanocrystal size. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 127–131, September–October, 2006.     

Composite WSi<Subscript>2</Subscript>–<Emphasis Type="Italic">Me</Emphasis><Superscript>V</Superscript>B<Subscript>2</Subscript> materials in W–Si–<Emphasis Type="Italic">Me</Emphasis><Superscript>V</Superscript>–B systems

Sections are constructed for WSi₂–Me ^VB₂ of the quaternary systems W–Si–(V, Nb, Ta)–B described by eutectic diagrams of state with T _eut (1940 ± 20), (1980 ± 20) and (2020 ± 30)°C and a boride content in the eutectics of 35, 20 and 15 mol.% respectively. Translated from Novye Ogneupory, No. 3, pp. 41 – 44, March 2009.     

The transition state for metal-catalyzed dehalogenation

Substituent effects have been used to probe the nature of the transition state to catalytic carbon–halogen bond breaking. Kinetics measurements have determined the activation energies (E _act to C–Cl bond breaking on the Pd(111) surface and C–I bond breaking on the Pd(111) and Ag(111) surfaces. These barriers have been measured using alkyl halides with varying degrees of fluorine substitution. The activation energies have been correlated with the inductive or field substituent constants (σ_F) of the fluorinated alkyl groups in order to determine reaction constants (E _act=E₀+ρσ_F) for the dehalogenation reactions. In all three cases it has been found that the barriers are insensitive to inductive substituent effects and the reaction constants are all relatively small: ρ= −0.5± 1.0 kcal/mol for C–Cl cleavage on Pd(111), ρ= −0.3±0.8 kcal/mol for C–I cleavage on Pd(111), and ρ= −2.9±0.4 kcal/mol for C–I cleavage on Ag(111). This implies that the transition state for dehalogenation is homolytic and occurs early in the reaction coordinate. The implications of this result are discussed for catalytic dehalogenation processes such as hydrodechlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Friedel–Crafts catalysis using supported reagents. Synthesis, characterization and catalytic application of ZnCl2 supported on fluoride‐modified sol–gel‐derived aluminosilicates

ZnCl₂–aluminosilicate catalysts were prepared via a sol–gel route involving fluoride‐catalyzed hydrolysis of aluminum and silicon alkoxides in the presence of NaF, KF, NH₄F and ZnF₂. The catalysts were characterized by employing ²⁹Si, ²⁷Al and ¹⁹F solid‐state MAS NMR. The dependence of the activities of the catalysts on the nature and amount of fluoride present in the catalysts were investigated using Friedel–Crafts alkylation reaction of benzene with benzyl chloride. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mineral Composition and Phase Transformations in the Refractory Lining of the Bottom of Aluminum Electrolysis Cells. Part 1.

Results for specimens of the refractory lining sampled from the bottom of an aluminum electrolysis cell with a service life of 3.5 years examined by methods of petrography, chemical analysis, and electron probe x-ray microanalysis are reported. The main products of conversion are sodium aluminosilicates, sodium silicates, a glassy phase of variable composition, oxyfluoride glasses, and eutectics. Some of the specimens analyzed are high in β-alumina (20 – 50%). Fluorides are represented by NaF (about 7%), cryolite Na₃AlF₆ (2 – 5%), malladrite Na₂SiF₆ (2%), and NaF ⋅ MgF₂ (1 – 2%), and the metallic phase, by aluminum (2 – 7%) and ferrosilicon (3 – 10%). The apparent density of the used refractory material is 2.5 – 2.62 g/cm³. __________ Translated from Novye Ogneupory, No. 3, pp. 13 – 17, March, 2005.     

Equation of state for gaseous ethane determined from isotropic model potentials

A four-term virial equation of state was combined with isotropic model potentials to predict accurate volumetric and caloric thermodynamic properties of ethane in the gas phase. The parameters of the model potentials were determined from a fit to speed-of-sound data alone; no other data were used. The approximation used for the fourth virial coefficient included all interactions that contain up to two triplet potentials. Predicted ordinary second and third virial coefficients are in agreement with the data of Funke et al. [8]; we believe that predicted fourth virial coefficients are reliable and accurate. In the subcritical temperature region, the equation of state predicted compressibility factors that deviate by less than 0.04 percent at densities of up to 2.7 mol/dm³ (≈ 0.4ρ _c ). At supercritical temperatures, compressibility factors deviate by less than 0.02 percent at densities of up to 2.6 mol/dm³; also, in this region predicted isobaric heat capacity agrees with available data to within uncertainties of 0.4 percent at densities above 3 mol/dm³. We demonstrated that the four-term virial equation is more accurate than the three-term analogue.     

Condensed combustion products of aluminized propellants. IV. Effect of the nature of nitramines on aluminum agglomeration and combustion efficiency

The condensed combustion products of two model propellants consisting of ammonium perchlorate, aluminum, nitramine, and an energetic binder were studied by a sampling method. One of the propellants contained HMX with a particle size D ₁₀ ≈ 490 μm, and the other RDX with a particle size _{D 10} ≈ 380 μm. The particle-size distribution and the content of metallic aluminum in particles of condensed combustion products with a particle size of 1.2 μm to the maximum particle size in the pressure range of 0.1–6.5 MPa were determined with variation in the particle quenching distance from the burning surface to 100 mm. For agglomerates, dependences of the incompleteness of aluminum combustion on the residence time in the propellant flame were obtained. The RDX-based propellant is characterized by more severe agglomeration than the HMX-based propellant — the agglomerate size and mass are larger and the aluminum burnout proceeds more slowly. The ratio of the mass of the oxide accumulated on the agglomerates to the total mass of the oxide formed is determined. The agglomerate size is shown to be the main physical factor that governs the accumulation of the oxide on the burning agglomerate. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 78–92, July–August, 2006.     

The controlling quantity in cubic equations of state for phase equilibrium calculations

It has been demonstrated that the vapor—liquid equilibrium values calculated from the modified Martin equation and the Clausius equation are identical to those obtained from a properly modified van der Waals equation of state. The reason for this observation is explained in this work in terms of the role of Ω_a (= aP_c/r²T) at specified state conditions. It is the controlling quantity in VLE calculations when simple van der Waals-type equations of state together with the conventional mixing rules are used. Thus, equations capable of yielding identical values of Ω_a give identical equilibrium values. The evidence and the mathematical proof of the relationship required for defining such a role for Ω_a are presented.     

Wear-resistant refractories in aluminum pyrometallurgy

Service conditions for refractories and physicochemical processes at their contact with molten aluminum are provided. Thermodynamic calculations establish the relative wear resistance of a number of oxides, silicates, and oxygen-free compounds towards aluminum in the range 700–1200°C (937–1473 K). The role is revealed of contact physicochemical processes at the boundary of a refractory with molten aluminum. The high resistance towards aluminum is demonstrated for high-alumina calcium aluminates, particularly bonite CaO · 6Al₂O₃ and spinel MgO · Al₂O₃. The most practicable wear-resistant fuzed materials for preparing lining of melting furnaces are lime-aluminate slags of OAO Klyuchevsk Ferroalloy Plant. __________ Translated from Novye Ogneupory, No. 9, pp. 15–19, September 2007.     

Competing chemical transformations in the combustion wave in the Fe2O3-Cr2O3-Al mixture

Laws of combustion of a thermit-type mixture Fe₂O₃-2Al-γCr₂O₃ are considered. The limits of liquid-phase combustion and separation of the oxide and metal phases in the final products are determined. Chromium oxide is demonstrated to weakly compete with iron oxide in the oxidation-reduction reaction with aluminum and to participate mainly in oxide-phase formation. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 89–91, May–June, 2006.     

Ionothermal synthesis of FeAlPO-16 molecular sieve by microwave irradiation in eutectic mixture

FeAlPO-16 molecular sieve with AST topology has been ionothermally prepared under microwave irradiation in succinic acid-choline chloride eutectic mixture for the first time. The structure and morphology of FeAlPO-16 molecular sieve are characterized in detail by powder X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance UV–visible (UV–vis) spectroscopy, thermogravimetry–differential scanning calorimetry analysis (TG-DSC) and scanning electron microscopy (SEM). UV–vis results suggest that iron species may partially enter the framework of FeAlPO-16 molecular sieve. SEM images indicate that large spherical particles observed in the images are agglomerates of FeAlPO-16 molecular sieve nanocrystalline (ca. 100 nm in size). Effects of synthesis conditions, such as P₂O₅/Al₂O₃ ratio, pyridine/Al₂O₃ ratio, reaction temperature and crystallization time, as well as iron and aluminum source on the crystallization of FeAlPO-16 molecular sieve are systematically investigated. Experiments show that FeAlPO-16 molecular sieve can be prepared over a wide molar ratio of Al₂O₃:xP₂O₅:yPyridine:0.4Fe₂O₃:58EU (x = 1.0–3.5, y = 0.8–7.8) using aluminum isopropoxide and ferric ammonium citrate as iron and aluminum source, respectively. The synthesis of FeAlPO-16 molecular sieve is highly sensitive to iron source, but not to aluminum source, crystallization temperature and time.     

Ignition,combustion, and agglomeration of encapsulated aluminum particles in a composite solid propellant. II. Experimental studies of agglomeration

The combustion characteristics of propellants containing AP, HMX, an energetic binder, and aluminum particles with various polymer coatings are studied at pressures of 0.15 and 4.6 MPa. It is found that the coatings influence the burning rate, the particle size distribution of condensed combustion products, and the completeness of aluminum combustion. It is shown that the agglomeration can be reduced by using aluminum with fluorine-containing coatings. The application of some coatings results in a reduction in the mass of the agglomerates with an insignificant increase in their size. The greatest effect was achieved when using aluminum coated with (CH₂=CH-CH₂-O)₂Si[OCH₂(CF₂-CF₂)₂H]₂ [bis(allyloxy)-bis(2,2,3,3,4,4,5,5-octafluoropentyloxy)silane]. For this coating, a size reduction is also observed for micron-size oxide particles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 83–97, May–June, 2007.     

Electrochemical study of the codeposition of Mg–Li–Al alloys from LiCl–KCl–MgCl<Subscript>2</Subscript>–AlCl<Subscript>3</Subscript> melts

This work presents a novel electrochemical study on the codeposition of Mg, Li and Al on a molybdenum electrode in LiCl–KCl–MgCl₂–AlCl₃ melts at 943 K to form Mg–Li–Al alloys. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of magnesium on pre-deposited aluminum leads to the formation of a liquid Mg–Al solution, and the succeeding underpotential deposition of lithium on pre-deposited Mg–Al leads to the formation of a liquid Mg–Li–Al solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li and Al occurs at current densities lower than −0.47 A cm⁻² in LiCl–KCl–MgCl₂ (0.525 mol kg⁻¹) melts containing 0.075 mol kg⁻¹ AlCl₃. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Al is −2.100 V, and the codeposition of Mg, Li and Al is formed when the applied potentials are more negative than −2.100 V. The diffusion coefficient of aluminum ions in the melts was determined by different electrochemical techniques. X-ray diffraction and inductively coupled plasma analysis indicated that α, α + β and β Mg–Li–Al alloys with different lithium and aluminum contents were obtained via potentiostatic and galvanostatic electrolysis.     

Protective properties of shields of ceramic/aluminum composite for hypervelocity impact

The protective effect of thin shields of metal-composites based on a matrix of aluminum with dispersed inclusions of SiO₂ and Al₂O₃ for hypervelocity impact of spherical steel particles are examined in a one-layer protection scheme. The protective effect of shields of these materials are found to be inferior to shields of homogeneous aluminum alloy. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 126–132, May–June 1999.     

Determination of recombination and attachment rate constants from ballistic experiments

We present measurements of the electron concentration in wakes behind aluminum spherical models flying in air with velocity 3.4–5.7 km/sec at a pressure of 10–80 torr. We have calculated the heating and entrainment of aluminum from the surface of the models as they move within the flight range. We show that condensation of Al vapor may occur at distances of more than 100 diameters of the body and pressure ≳80 torr. We pose and solve the inverse problem of determining (from experimental data) the effective attachment coefficient for attachment to air molecules and the attachment rate constants for AlO+e→AlO⁻, AlO₂+e→AlO₂ ⁻. Scientific-Research Institute of Mechanics, Moscow State University, Moscow 119899. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 5, pp. 70–82, September–October, 1995.     

Sorption of copper ions by granulated chitosan

The features of sorption of Cu²⁺ ions from aqueous solutions of CuSO₄ by granulated chitosan sorbent in static conditions and the different contribution of surface and bulk amino groups in the sorbent to complexation are discussed. Sorption with freshly formed swollen and maximally amorphized granules with accessible bulk amino groups can be described by Langmuir’s equation; it attains 5.6 mmole/g of dry sorbent, which is close to the sorption calculated from the equimolar composition of the amino-copper complex. Sorption of initially dry granules with less accessible bulk amino groups does not obey Langmuir’s equation due to precipitation of copper hydroxide and hydrosulfate on the surface of the sorbent. __________ Translated from Khimicheskie Volokna, No. 2, pp. 11–14, March–April, 2006.     

Development of technology for the production of microspherical alumina support for the alkane dehydrogenation catalyst: II. The influence of hydrothermal treatment conditions on the operational characteristics of microspherical alumina support and chromium oxide/alumina catalyst for the dehydrogenation of iso-butane

For the purpose of improving the mechanical strength and reducing the abrasive activity of micro-spherical chromium oxide/alumina catalysts for the processes of alkane dehydrogenation in fluidized bed, we have developed technology for the production of new highly durable boehmite support with the use of technical aluminum trihydrate as an initial raw material. The technology includes two consecutive stages: the dehydration of aluminum trihydrate and the subsequent hydrothermal treatment of dehydration product into boehmite. Part II covers the results on the influence of conditions for the hydrothermal treatment of aluminum trihydrate dehydration products in an industrial autoclave of special construction on the phase composition, physicomechanical and structural characteristics of boehmite support, the acidic properties of its respective oxide form and chromium oxide/alumina catalyst based on this support and also on the catalytic properties of this catalyst in the reaction of iso-butane dehydrogenation into iso-butylene. It has been shown that differently sized boehmite crystallites and also gibbsite are formed in the volume of microgranule under hydrothermal conditions of χ-Al₂O₃ dehydration depending on a chosen regime (temperature, time). For the production of iso-butane dehydrogenation selective chromium oxide/alumina catalyst with the minimal content of strong acidic sites, catalyzing the cracking reactions, it is necessary to provide such hydration conditions, under which large (43–47 nm) boehmite crystals are formed. The appearance of strong acidic sites is caused by small boehmite crystals and the presence of nonhydrated χ-Al₂O₃ phase. In the absence of the impurity gibbsite phase, the highly durable microgranules of boehmite support and catalyst are formed. The conditions, providing the complete χ-Al₂O₃ hydration into macrocrystalline boehmite, have been defined. The application of the developed two-stage technology gives the iso-butylene yield of 45–49%, the selectivity of 88–90%, and the abrasivity of 0.10 g/(m² h). The given technology for the production of catalyst is realized in an industrial unit with the capacity of 100 t per month at OAO Karpov Mendeleevsk Chemical Plant (Mendeleevsk). Industrial catalyst lots are currently under operation at the Synthetic Isoprene Rubber Plant of OAO Nizhnekamskneftekhim.     

Production of nanoparticles of MgO, BAO, and A12O3 in a premixed flame and its relation to the flame structure

Formation of nanoparticles of magnesium, barium, and aluminum oxides in a fuel-lean oxy-acetylene flame is studied by means of flame sampling. The size distributions and concentrations of particles are measured in various areas of the flame. Possible reaction paths are considered. MgO and BaO nanoparticles are demonstrated to form in the reaction zone where there is a high concentration of radicals. Formation of Al₂O₃ particles is hindered by the reaction AlO + AlO₂ → Al₂O₃ being termolecular. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 25–32, November–December, 2006.