Crystallization of CaO–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass prepared by float process

CaO–MgO–Al₂O₃–SiO₂ (CMAS) glass was prepared by float process. The effects of TiO₂ and heat-treatment on properties and crystallization behaviors of float glasses were investigated by atomic force microscope, differential scanning calorimeter, X-ray diffraction, electron probe microanalyzer, field emission scanning electron microscope and viscosity test. The results showed that CMAS parent glasses produced by float process had a high surface flatness (Ra is less than 80.1 ± 0.1 nm) and low tin penetration (14 μm). When the concentration of TiO₂ increased from 3.51 to 5.01 wt %, the glass transition temperature was decreased, and the crystallization temperature was shifted from 913 to 887°C using differential scanning calorimeter. Field emission scanning electron microscope images showed that phase separation was discovered in CMAS parent glass (containing 3.51 wt % TiO₂) treated at 670°C. Diopside as a major crystalline phase was precipitated in CMAS glass-ceramics nucleated at 700°C for 30 min and followed by crystallization at 910°C for 30 min.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Effect of temperature on the synthesis of nanoparticles with different morphology in the system MgO–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O under hydrothermal conditions

Nanoparticles with different morphology have been obtained by hydrothermal method in the system MgO–SiO₂–TiO₂–H₂O. It has been found that in the investigated temperature–time interval the formation of nanotubes of hydrosilicate with the structure of chrysotile with a small amount of impurity phases predominantly takes place.     

Preparation and Characterization of SiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Core–Shell Microspheres as RP-HPLC Stationary Phase

Novel SiO₂/SiO₂ core–shell monodisperse silica spheres for high-performance liquid chromatography packing materials are prepared by the layer-by-layer self-assembly technique. The core–shell silica spheres consist of micrometer-sized porous silica spheres as the core and a thin mesoporous silica shell formed from multilayer nanometer-sized silica particles. In addition, a reversed-phase packing by bonding octadecyltrichlorosilane on SiO₂/SiO₂ particles through alkyl-modified method is prepared and characterized. The results show that the carbon content of the new reversed-phase stationary phase increases by approximately 45% compared with the uncoated octadecyl-bonded SiO₂ stationary phase. Eight kinds of tested aromatic compounds are well-separated on the packing and the peaks are symmetrical, which demonstrates that the packing acts as an excellent reversed-phase chromatographic stationary phase.     

Effect of Zr/Si molar ratio and sulfation on structural and catalytic properties of ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> mixed oxides

ZrO₂–SiO₂ mixed xerogel and aerogel samples with varied molar ratios were prepared by sol–gel method followed by oven drying and supercritical drying using n-propanol as a solvent, respectively. Sulfation was carried out to further enhance the acidic properties of the mixed oxides. Effect of drying, Zr/Si molar ratio and sulfation have been studied and correlated with the structural, textural and catalytic properties of ZrO₂–SiO₂ mixed oxides. Both xerogel and aerogel mixed oxides have different structural and textural features, however, the total number of acid sites per unit surface area (0.0021–0.0029 mmol NH₃ m⁻²) and thus the catalytic activity for cyclohexanol conversion (31–41%) was found in the similar range. Sulfated mixed oxide aerogel and xerogel samples showed significant enhancement of cyclohexanol conversion (91–99%).     

Synthesis of low-melting eutectic of the CaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system in a solid phase

Results are provided for a physicochemical study of processes that occur during synthesis of eutectic composition of the CaO–B₂O₃–SiO₂ system in a solid phase, and the possibility of their activation by using starting calcium-containing components with different chemical and thermal prehistory. It is established that independent of the form of starting components, in all cases there is formation of a crystalline eutectic phase, and the sequence of physicochemical processes that occur is determined by the reaction capacity of the calcium compound introduced.     

Study of the influence of extra-framework cations and organic templates on zeolite crystallization in SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Na<Subscript>2</Subscript>O–K<Subscript>2</Subscript>О (R<Subscript>2</Subscript>O,RO) systems

Crystallization of zeolites from the gels of the (3–x)К₂О–xR₂O(RO)–0.05Na₂O–Al₂O₃–5SiO₂–100H₂O composition where x was varied from 0 to 3 and R = Li, Na, Rb, Cs, Ba, tetraethylammonium, tetrapropylammonium, and tetrabutylammonium, has been performed by hydrothermal synthesis. The influence of various cationic ratios on the final product of crystallization depending on the synthesis temperature has been studied at constant SiO₂: A₂lO₃ and H₂O: SiО₂ ratios. The correlation between the cationic composition of the initial gels, their structure, and the structure of the crystallizing zeolites has been estimated.     

Mechanical,Structural and Thermal Properties of Transparent Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–TeO<Subscript>2</Subscript> Glass System

Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi₂O₃–Al₂O₃ based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi₂O₃ and Al₂O₃ compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, T_g, onset, T_x, crystallization, T_p, and melting, T_m, temperatures were obtained by using DTA scan.     

Crystallization and Luminescence Properties of Sm<Superscript>3+</Superscript>-Doped SrO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> Glass-Ceramics

Sm³⁺-doped SrO–Al₂O₃–SiO₂ glass-ceramics with excellent luminescence properties were prepared by batch melting and heat treatment. The crystallization behavior and luminescent properties of the glass-ceramics were investigated. The results indicate that the crystal phase in this system is monocelsian (SrAl₂Si₂O₈). Under the excitation with blue light (475 nm) the Sm³⁺-doped SrO–Al₂O₃–SiO₂ glass-ceramics emit green, orange and red lights centered at 565, 605, 650 and 715 nm, which can be assigned to the ⁴G_5/2 → ⁶H_J/2 (J = 5, 7, 9, 11) electron transitions in Sm³⁺ ions, respectively. With the increase of nucleation/crystallization temperature, the crystallite part rises from 66 to 79%. Besides, by increasing crystallization temperature or concentration of Sm³⁺, the samples emission located at 565, 605 and 650 nm is intensified significantly. We envision that, by fine controlling and combining of these three (green, orange and red) lights in an appropriate proportion, the Sm³⁺-doped glass-ceramics are promising luminescence materials for white light-emitting diodes devices.     

Physical–chemical properties and conductivity of Na<Subscript>2</Subscript>O–SnO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> glass systems

The effect of tin(IV) oxide on the conductivity and chemical stability of sodium–silicate glass has been studied for five different glass compositions. Dilatometry and DSC were used to investigate the thermal behavior of the glass. The research into transport characteristics of the glass has shown that its conductivity is in the range of 2 × 10^–8–5 × 10^–7 S/cm at 25°C and 10^–3 S/cm at 300°C.     

Synthesis and characterization of nanocomposites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–chitosan based on lbl technology

In this paper, the apparent chain-like core-shell structure Fe₃O₄–SiO₂–chitosan nanoparticles was synthesized by two-step method with cross-linking action of glutaraldehyde based on layer-by-layer technology, the composite particles were characterized by IR, XRD, TEM, SEM, EDS and VSM analytical methods, and the synthesis conditions of the product were studied. The results indicated that the diameter of the composite particles is about 106.5 nm, the parietal layer of chitosan is 20 nm, and after crosslinking action of glutaraldehyde, chitosan uniformaly coated the outer surface of Fe₃O₄–SiO₂.     

Effect of the relative volume of the conducting phase on the electroconductivity of glasses in the Na<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The effect of the relative volume of the conducting phase on the electroconductivity of phase-separated glasses in the ternary system Na₂O–B₂O₃–SiO₂, whose compositions are on the same glass transition isotherm at 550°C, is investigated. It is demonstrated that the electroconductivity of phase-separated sodium borosilicate glasses does not depend on the relative volume of the conducting phase (within the limits from 0.3 to 0.9) under the condition that its composition invariable.     

Effect of preparation procedure of Iro<Subscript>2</Subscript>–Nb<Subscript>2</Subscript>o<Subscript>5</Subscript> anodes on surface and electrocatalytic properties

The influence of the electrode manufacturing procedure on surface and electrocatalytic properties for oxygen and ozone evolution at electrodes of nominal composition Ti/[IrO₂–Nb₂O₅] (45:55 mol%) was investigated. Thermal decomposition at 450 °C (1 h, air stream) was adopted as standard procedure. Metal support pretreatment, solvent mixture, method of applying the precursor mixture and calcination procedure were all investigated. X-ray diffraction, scanning electronic microscopy, voltammetric and differential capacity analysis show the use of HCl 1:1 as solvent and applying the mixture by brush led to fragile rugged/porous oxide coatings. However, for the same conditions, but controlled calcination (heating/cooling rates), the coating becomes more compact. Using isopropanol as solvent results in a more homogeneous coating, presenting the lowest morphology factor. Kinetic investigation shows the rugged/porous coating presents the lowest Tafel slopes and the highest global electrocatalytic activity for OER. The more compact the coating the lower the electrochemically active surface area and the global OER activity. Ozone efficiency depends on the electrochemically active area while support pretreatment strongly influences the lifetime of the electrode. Application of a Pt interlayer between the oxide and Ti base improves the service life.     

Synthesis and physicochemical properties of a solid oxide nanocomposite based on a ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>–MgO system

A highly dispersive powder with a (ZrO₂)_0.92(Y₂O₃)_0.03(Gd₂O₃)_0.03(MgO)_0.02 composition and specific surface area of 150 m²/g has been synthesized via a method of coprecipitation of hydroxides with the subsequent cryochemical treatment of the gel. Nanoceramics based on the cubic modification of zirconium dioxide with the grain size of ~40–45 nm have been obtained. The temperature dependence of the specific electrical conductance of the nanoceramics within a temperature range of 350–870°C in air has been studied, and the ratio of the ionic and electronic parts of the conductance has been determined. Recommendations for the use of the obtained oxide nanocomposite as an electrolyte for a high-temperature fuel cell have been given.     

Structural,Textural and Acid–Base Properties of Nano-Sized NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Spinel Catalysts

Abstract  

The effect of preparation methods on the textural, structural and acid–base properties of nano-sized nickel ferrite oxides was investigated. Several physicochemical methods are used for their characterization. Isopropanol, as a probe molecule, is used to determine acid–base properties. A correlation between textural, structural and acid–base properties of nanomaterials is established.