Study on the properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO lead-free glass using in the electronic pastes

The Sb₂O₃ doping lead-free glass in Bi₂O₃-B₂O₃-BaO ternary system were prepared in the composition of several different subsystem, and the glass powder was produced through the process of water quenching. Glass transition temperatures (T _g ), glass soften temperatures(T _s ), the volume resistivity (ρ) in the temperature range of 80–200°C, and linear thermal coefficients of expansion in the temperatures range of 25–300°C (α_25–300) were measured for subsystems along with the different ratio of Bi₂O₃, B₂O₃ and BaO. For these subsystems, T _g ranged from 458 to 481°C, and T _s ranged from 490 to 512°C, both decreasing with the increasing of Bi₂O₃/B₂O₃ ratio, and increasing with the increasing of BaO/B₂O₃ ratio. The measured α_25–300 ranged from 65.3 to 76.3 × 10⁻⁷ K⁻¹, with values increasing with increasing Bi₂O₃/B₂O₃ and BaO/B₂O₃ ratio. The volume resistivity remains at a high standards, which may caused by it’s non-alkali composition, and it fluctuated from 10¹³ to 10¹¹ Ω cm with the temperature varied from 80–200°C. The structure of Bi₂O₃-B₂O₃-BaO ternary leadfree glass system was mearsured by FT-IR. The IR studies indicate that these glasses are made up of [BiO₆], [BO₃], and [BO₄] basic structural units, and it appears that Ba²⁺ acts as a glass-modifier in this ternary system, but the Bi³⁺ has entered the glass network when it is in relative high content so as to change the α_25–300, T _s and T _g .     

Refractive index and compressibility of the KAlSi<Subscript>3</Subscript>O<Subscript>8</Subscript> glass at pressures up to 6.0 GPa

The refractive index of potassium aluminosilicate glass of the KAlSi₃O₈ composition in the pressure range up to 6.0 GPa has been measured using a polarizing interference microscope and an apparatus with diamond anvils. The changes in the relative density, which characterize the compressibility of the K₂O · Al₂O₃ · 6SiO₂ glass, have been estimated in the pressure range under investigation from the measured refractive indices within the framework of the theory of photoelasticity. The results have been compared with the data previously obtained for the Na₂O · Al₂O₃ · 6SiO₂ glass. Although the molar contents of Al₂O₃ and M ₂O (where M = K or Na) are identical in these glasses, the KAlSi₃O₈ glass exhibits a higher compressibility, which agrees with the lower degree of depolymerization of this glass as compared to that observed in the NaAlSi₃O₈ glass. The pressure derivative of the bulk modulus K′ _t , which is calculated from the Birch-Murnaghan equation for the KAlSi₃O₈ glass (K′ _t = 7–9), is higher than that for the NaAlSi₃O₈ glass (K′ _t = 5.5–6.0). An increase in the pressure derivative of the bulk modulus K′ _t upon replacement of the Na⁺ cations by the K⁺ cations is explained by the inhibition of compression of the large K⁺ cations, which are located in cavities and have a considerably larger orbital radius than the Na+ cations. This manifests itself in the fact that the curves describing the dependences of the change in the relative density (d − d0)/d (compressibility) on the pressure P for the KAlSi₃O₈ and NaAlSi₃O₈ glasses converge at pressures above 4.0 GPa.     

Glass formation region and order of formation of crystalline phases in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The glass formation region in the SrO-B₂O₃-SiO₂ system has been refined. The order of formation of crystalline phases in the system has been investigated at SrO contents of 50–75 mol %. It has been demonstrated that, at low temperatures, the 2SrO · SiO₂ and 3SrO · B₂O₃ phases crystallize first irrespective of the composition. The congruent melting temperature of the 3SrO · B₂O₃ · SiO₂ compound is determined to be 1180 ± 10°C. The triangulation previously performed for the SrO-B₂O₃-SiO₂ system in the concentration range 50–75 mol % SrO has been confirmed.     

Preparation of surface-crystallized optical glass-ceramics SrO · 2B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The physicochemical features of the phase formation upon crystallization of monolithic glasses of the strontium diborate stoichiometric composition are investigated. It is demonstrated that the first phase crystallizing on the surface of the SrO · 2B₂O₃ glass is the strontium borate Sr₄B₁₄O₂₅, which plays the role of a precursor for the subsequent crystallization of the SrB₄O₇ borate. The temperature corresponding to the maximum crystal nucleation rate on the surface and the time of complete “operation” of nuclei are determined using differential thermal analysis. The optical glass-ceramics prepared by the two-stage crystallization are surface-crystallized glasses in which the filling density of the surface is approximately equal to 30% and the content of the main phase SrB₄O₇ is as high as ∼ 70%. No second harmonic generation of neodymium laser radiation in the glass-ceramics is observed because of both the absence of the preferred orientation of SrB₄O₇ nonlinear optical crystals and the small crystal sizes (considerably smaller than the coherence length of the SrB₄O₇ crystal) in the direction perpendicular to the glass surface.     

The Structure of Fusion-Cast High-Chrome Oxide Refractories in the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> - MgO - Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System

The phase composition and structure of fusion-cast refractories composed of 57.0 – 84.2% Cr₂O₃, 4.3 – 36.1% MgO, 2.0 – 9.7% Al₂O₃, and 2.4 – 6.9% SiO₂ have been studied by petrographic and x-ray spectral microprobe analysis methods. Refractories high in MgO with modulus M = (Cr₂O₃ +Al₂O₃)/MgO = 1.64 – 3.1 are shown to consist of spinel phase Mg(Cr, Al)₂O₄ and silicate glass. Refractory materials (80.8 – 84.2% Cr₂O₃, 4.3 – 4.7% MgO, 2.0 – 9.7% Al₂O₃, and 2.7 – 6.9% SiO₂ with M = 18.7 – 20.2) are three-phase systems composed of spinel, escolaite, and glass phase. These materials, owing to their high corrosion resistance, have promising potentiality for practical applications.__________Translated from Novye Ogneupory, No. 12, pp. 69 – 74, December, 2004.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Oxidative reforming of methane on structured Ni-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts

The catalytic properties of Ni/Al₂O₃ composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6% CH₄, 2–9% O₂, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH₄, 6–12% CO₂, and 0–4% O₂, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O bond, and the phase composition of the catalyst. The structured Ni-Al₂O₃ catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal (Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La₂O₃, CeO₂) enhance the activity and stability of Ni-Al₂O₃/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming of methane on the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach a high methane conversion and does not exert any significant effect on the selectivity with respect to H₂.     

Crystallization of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystallization of strontium borate glasses containing 16.7–43.0 mol % SrO is investigated. New crystalline compounds of the hypothetical compositions 2SrO · 3B₂O₃ (metastable) and SrO · 5B₂O₃ (stable below 750°C), as well as the metastable diborate modification β-SrO · 2B₂O₃, are revealed, and their X-ray powder diffraction data are obtained. It is demonstrated that, with a deficit of strontium oxide, the 4SrO · 7B₂O₃ compound forms solid solutions. Strontium triborate SrO · 3B₂O₃, which was previously prepared only through the dehydration of crystal hydrates, is produced using crystallization of glasses. The thermal stability of this compound is studied. The influence of the dispersity on the stability of different crystalline phases is discussed. Variants of the phase diagram for the SrO · B₂O₃-B₂O₃ system in the case of monolithic and dispersed samples are proposed from analyzing the experimental results and the data available in the literature.     

Oxidation resistance before and after heat treatment for compacted Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiC–C mixtures with aluminum-chromium-phosphate binder

Oxidation resistance has been examined for compacted Al₂O₃–SiC–C mixtures, which contain an aluminum-chromium-phosphate binder without firing (DTA method) and ones that have been previously fired and given isothermal heat treatment at 800°C (as indicated by the mass loss). To obtain oxidation-resistant materials, the content of silicon carbide should not exceed 10 wt.% and the recommended graphite content is not more than 20 wt.%. Translated from Novye Ogneupory, No. 2, pp. 38 – 43, February, 2009.     

The system SiC–W<Subscript>2</Subscript>B<Subscript>5</Subscript>–LaB<Subscript>6</Subscript>

Experiments and calculations have been applied to the structure of the triple eutectic system SiC–W₂B₅–LaB₆(T _eu = 1900 ± 40°C), composition in mol.%: 10 LaB₆, 44 SiC, 46 W₂B₅, error ±2–3%, which opens up prospects for making ceramic materials for various purposes.     

Structure and crystallization of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Structure and crystalline behavior of the ternary system ZnO-B₂O₃-P₂O₅ glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number of the planar [BO₃] units increases with the increase of B₂O₃ content. When the B₂O₃ content is above ≥10 mol %, the relative content of planar [BO₃] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized glasses the predominant crystal phase Zn₂P₂O₇ decreases with the increase of B₂O₃ content, while the crystal phase BPO₄ increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion.     

Properties of materials of the system Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiC-C after firing in a reducing atmosphere

A set of studies is presented for the physicomechanical properties of corundum-graphite carbide-containing refractories. The efficiency of introducing silicon carbide as an antioxidant addition to Al₂O₃-SiC2-C-materials is established. The structure and phase composition of corundum-graphite silicon carbide-containing refractories based on an ethyl silicate binder fired in a reducing atmosphere are studied. __________ Translated from Novye Ogneupory, No. 10, pp. 52–56, October 2007.     

Volumetric nucleation of crystals catalyzed by Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> in glass based on furnace slags

The features of the volumetric nucleation of crystals in glass obtained by melting furnace slags with the additive of SiO₂, chromium sesquioxide Cr₂O₃, are studied by the methods of differential thermal and Xray phase analysis and optical microscopy. Upon the introduction of Cr₂O₃ as the catalytic additive, two phases are sequentially formed in the glass: magnesiochromite (MgO · Cr₂O₃) and diopside (CaO · MgO · 2SiO₂). The characteristics of homogeneous and heterogeneous crystallization are determined: the stationary nucleation rate, nonstationary nucleation time, crystal growth rate, and their temperature dependences are obtained. Practical recommendations on the use of the obtained glass are given.     

Oxygen permeability and structural stability of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> membrane

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ oxides were synthesized by citrate method and hydrothermal method. The oxides prepared by citrate method are perovskite type structure, while the oxides by hydrothermal method have a small amount of secondary phase in the powder. Pyrex glass seal and Ag melting seal provided reliable gas-tight sealing of disk type dense membrane in the range of operation temperature, but commercial ceramic binder could not be removed from the support tube without damage to the tube or membrane. Though the degree of gas tightness increases in the order of glass>Ag>ceramic binder, in the case of glass seal, the undesired spreading of glass leads to an interfacial reaction between it and the membrane and reduction of effective permeation area. The oxygen flux of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ membrane increases with increasing temperature and decreasing thickness, and the oxygen permeation flux through 1.0 mm membrane exposed to flowing air (P _h =0.21 atm) and helium (P₁=0.037 atm) is ca. 0.33 ml/cm²·min at 950 °C. X-ray diffraction analysis for the membrane after permeation test over 160 h revealed that La₂O₃ and unknown compound were formed on the surface of membrane. The segregation compounds of surface elements formed on both surfaces of membrane irrespective of spreading of glass sealing material. This paper was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Initiation of combustion of a CH<Subscript>4</Subscript>-O<Subscript>2</Subscript> mixture in a supersonic flow with excitation of O<Subscript>2</Subscript> molecules by an electric discharge

The possibility of intensification of ignition of a methane-oxygen mixture in a supersonic flow behind the front of an oblique shock wave by means of excitation of O₂ molecules to the states a ¹Δ_g and b ¹Σ_g⁺ in an electric discharge is discussed. Through numerical simulations, activation of O₂ molecules by an electric discharge is demonstrated to speed up chain reactions in the CH₄-O₂ mixture and to reduce the induction-zone length. Even a small amount of energy input to O₂ molecules in the discharge (≈3·0⁻² J/cm³) can reduce the ignition-delay length by a factor of hundreds and initiate combustion at distances of ≈1 m from the discharge zone at comparatively low temperatures of the gas behind the front (≈1000 K) and moderate pressures (≈10⁵ Pa). Excitation of O₂ molecules by an electric discharge is much more efficient than simple heating of the mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 3–16, May–June, 2008.     

Promoting Effect of Triglyme on Lean NO<Subscript>x</Subscript> Reduction Over Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Abstract  

The highly oxygenated hydrocarbon triethylene glycol dimethyl ether or triglyme (CH₃O–(C₂H₄O–)₃CH₃) was found to efficiently reduce NO_x under lean conditions over Ag/Al₂O₃, but gave a low NO_x conversion over Cu-ZSM-5. Furthermore, triglyme showed an extraordinary promoting effect when added together with propene as reducing agent for NO_x over Ag/Al₂O₃ at low temperature. This is most likely due to that triglyme promotes the activation of propene.     

Synthesis and characterization of zeolite mazzite analogue in Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Piperazine–H<Subscript>2</Subscript>O

Zeolite Mazzite (MAZ) analogue was synthesized directly using piperazine as a structure directing agent. The reactive gel composition used was (5.0–7.0) piperazine:(6.0–7.0) Na₂O:Al₂O₃:20.0SiO₂:400H₂O. Using this composition, the reaction time was shortened greatly to 4 days and the crystallization time was reduced as well. The DTA data showed that piperazine, in as-synthesized zeolite omega decomposed easily. The decomposition of the piperazine occurred at 400–480°C. NH₃-TPD analysis proved that zeolite H-omega from piperazine had strong surface acidity with ammonia desorption temperature up to 590°C.     

Thermomechanical properties of refractory materials of AL<Subscript>2</Subscript>O<Subscript>3</Subscript>–Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–C compositions based on acpb after impregnation with a sol-gel composition

Comparative characteristics are presented for the physicomechanical properties and oxidation resistance of refractory materials of Al₂O₃–Si₃N₄–C composition based on an ACPB for the original materials (fired at 1400°C) and after impregnation with a sol-gel composition and heat treatment at 800°C. Areduction in material porosity, increase in strength and reduction in carbon burn-off are due to development of a glassy phase in the pore space and on graphite flakes due to SiO₂formation with thermal destruction of the organosilicon substance.     

Effects of adding B<Subscript>2</Subscript>O<Subscript>3</Subscript> as a flux on phosphorescent properties in synthesis of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: (Eu<Superscript>2+</Superscript>, DY<Superscript>3+</Superscript> phosphor

SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was prepared by solid state reaction. B₂O₅ as a flux was added in SrAl₂O₄:(Eu ²⁺, Dy³⁺) in order to accelerate a solid state reaction. In this paper, the effects of B₂O₃ on the crystal structure and the phosphorescent properties of the material have been evaluated. The synthesized phosphor exhibited a broad band emission spectrum peaking at 520 nm, and the spectrum peak showed little effect by the B₂O₃ contents. The maximum afterglow intensity of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was obtained at the B₂O₃ content of 5%. Adding the B₂O₃ caused uniform distortion to the crystal structure of the phosphor and resulted in reducing the lengths of a and c axes and Β angle of the SrAl₂O₄ crystal. The uniform distortion was accompanied with crystal defects which can trap the holes generated by the excitation of Eu²⁺ ions. The afterglow characteristic of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was thus enhanced.     

Properties of unsupported MoS<Subscript>2</Subscript> species produced in the preparation of MoS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> using a sonochemical method

Unsupported MoS₂ particles, which were produced in the preparation of MoS₂/Al₂O₃ using a sonochemical method, were successfully separated from the prepared sample catalyst by adding oleylamine as an agent for dispersing the unsupported particles. The fraction of the unsupported MoS₂, which was estimated based on Mo balance, varied between 0.03 and 0.4, independent of the Mo loading levels investigated (6–54 wt% of Mo). The activity of the unsupported MoS₂ for the hydrodesulfurization of dibenzothiophene was nearly the same as that of the Al₂O₃-supported MoS₂, indicating that the activity of the prepared catalyst was not affected by the presence of the unsupported MoS₂ particles.