Glass Formation and Physicochemical Properties of Alloys in the Cu–Te–I System

The glass formation and the physicochemical properties of alloys in the Cu–Te–I system are investigated. Consideration is given to the glass formation region in the Cu–Te–I system, the results of differential thermal and X-ray powder diffraction analyses, and the temperature dependence of the molar volume for melts. The phase diagram is constructed along the CuI–Te join passing throughout the glass formation region. The inference is drawn that the formation of the CuTeI and CuTe₂I chemical compounds favors extension of the glass formation region in the system under investigation.     

Chemical Modification of Bisphenol A Polycarbonate by Reactive Blending with Cyclic Anhydrides

Summary Reactive blending with cyclic anhydrides in the melt is a promising process to modify the chemical structure of bisphenol A polycarbonate (PC) by insertion of ester moieties leading to consistent changes in the chemical and physical properties of PC. In particular, by the reaction with succinic anhydride it is possible to insert aliphatic moieties in the polymer backbone, decreasing the melt viscosity and the glass transition temperature of PC (and thus increase its processability). The reaction, that is catalysed by Lewis acids (e. g. titanium butoxide), proceeds through the formation of carbonyl carbonate groups that undergo decarboxylation leading to ester moieties. No side reactions have been detected by NMR analysis. The addition of phosphorous acid as catalyst quencher at the end of the process gives rise to polymers with good colour and thermal stability.     

Influence of Chemical and Phase Equilibria on the Medium-Range Order and Physicochemical Properties of Chalcogenide Glasses1

The problem associated with the influence of chemical and phase equilibria in melts on the properties of formed glasses is analyzed experimentally and theoretically by the example of chalcogenide glasses prone to glass formation. It is proved that inorganic glasses should be treated as microinhomogeneous systems formed by a set of nanometer-sized pseudophases that differ in character. The equivalentometry method has revealed that, in inorganic glasses, there exist at least two types of the pseudophases which have different chemical compositions and are responsible for microinhomogeneous structure of vitreous materials. It is established that the pseudophases in glasses are fragments composed of elementary substances and are also stable and metastable compounds. The concept of a variable number of components in vitrifying melts is introduced for the first time. This concept and the eutectoidal model of the vitreous state of matter allow one to reveal the types of chemical and phase equilibria whose freezing in glasses results in the formation of a set of the pseudophases responsible for glass microinhomogeneity. The regularities revealed make it possible to put forward the principles of analysis of composition–property diagrams for vitreous systems.     

Mixed matrix membrane materials with glassy polymers. Part 2

Analysis presented in Part 1 of this paper indicated the importance of optimization of the transport properties of the interfacial region to achieve ideal mixed matrix materials. This insight is used in this paper to guide mixed matrix material formation with more conventional gas separation polymers. Conventional gas separation materials are rigid, and, as seen earlier, lead to the formation of an undesirable interphase under conventional casting techniques. We show in this study that if flexibility can be maintained during membrane formation with a polymer that interacts favorably with the sieve, successful mixed matrix materials result, even with rigid polymeric materials. Flexibility during membrane formation can be achieved by formation of films at temperatures close to the glass transition temperature of the polymer. Moreover, combination of chemical coupling and flexibility during membrane formation produces even more significant improvements in membrane performance. This approach leads to the formation of mixed matrix material with transport properties exceeding the upper bound currently achieved by conventional membrane materials. Another approach to form successful mixed matrix materials involves tailoring the interface by use of integral chemical linkages that are intrinsically part of the chain backbone. Such linkages appear to tighten the interface sufficiently to prevent “nonselective leakage” along the interface. This approach is demonstrated by directly bonding a reactive polymer onto the sieve surface under proper processing conditions.     

The Improvement of Compatibility in Glass Fiber Reinforced PA6/PP Blends

Abstract

Rheological properties (melt flow index and melt stability), mechanical properties (tensile strength, flexural strength and impact) of polyamide (PA6) polypropylene (PP) blends were investigated. Influence of potential compatibilizors: 4,4′-diphenyhnethane carbodiimide (OCDI), 4,4′-diphenylmethane bismaleimide (BMI) and 2,2′-(1,4-pheaylene)-bisoxazoline (OX) on mechanical properties and thermostability of initial and glass reinforced polymer blends was also investigated too. We tried to study the structure of glass fiber reinforced composites by mercury intrusion porosimitry. The influence of compatibilizors on molecular weight of PA6 was studied by GPC, on chemical structure of blends was investigated by NMR and IR-spectroscopy. Addition of OCDI and OX (chain extenders) preserves the product formation as the react with the active and carbonyl groups of PA6. BMI has lower reactivity. Grafting of BMI to PP chains improves compatibility in PA6/PP blend and increases PP adhesion to glass fiber.     

Kinetics and Mechanism of the Polyene Formation during Dehydrochlorination of Poly(Vinyl Chloride) in the Solid State

Abstract

In investigating the thermal, photolytical and chemical dehydrochlorination of poly(vinyl chloride) (PVC) it is shown that the formation of polyenes proceeds independently of the kind of initiation in a fast zip reaction and by the same mechanism. The sequence length distribution of the formed polyenes depends mainly on the conformation of the PVC chains. A strong correlation between this distribution and the conformation equilibrium of the polymer chains as well as the physical structure of the polymer solid is demonstrated.     

Major Ampullate Spider Silk with Indistinguishable Spidroin Dope Conformations Leads to Different Fiber Molecular Structures

To plentifully benefit from its properties (mechanical, optical, biological) and its potential to manufacture green materials, the structure of spider silk has to be known accurately. To this aim, the major ampullate (MA) silk of Araneus diadematus (AD) and Nephila clavipes (NC) has been compared quantitatively in the liquid and fiber states using Raman spectromicroscopy. The data show that the spidroin conformations of the two dopes are indistinguishable despite their specific amino acid composition. This result suggests that GlyGlyX and GlyProGlyXX amino acid motifs (X = Leu, Glu, Tyr, Ser, etc.) are conformationally equivalent due to the chain flexibility in the aqueous environment. Species-related sequence specificity is expressed more extensively in the fiber: the β-sheet content is lower and width of the orientation distribution of the carbonyl groups is broader for AD (29% and 58°, respectively) as compared to NC (37% and 51°, respectively). β-Sheet content values are close to the proportion of polyalanine segments, suggesting that β-sheet formation is mainly dictated by the spidroin sequence. The extent of molecular alignment seems to be related to the presence of proline (Pro) that may decrease conformational flexibility and inhibit chain extension and alignment upon drawing. It appears that besides the presence of Pro, secondary structure and molecular orientation contribute to the different mechanical properties of MA threads.     

Subcritical Water Treatment: A Simple Method to Prepare Porous Glass with a Core–Shell Structure

This paper presents a subcritical water treatment method for preparing porous glass with a core–shell structure from ordinary soda-lime glass beads in one step. In this method, reactive subcritical water rather than any other chemical additive was utilized to selectively corrode the glass and mainly leach the alkali ions from the glass. The core–shell structure has been characterized by scanning electron microscope observation. The mesoporous structure of the porous glass beads has been confirmed by a nitrogen adsorption–desorption measurement. The treated alkali–lime–silicate glass beads have mesopores with a narrow distribution ranging around 4 nm, and a uniform nanoflake array on the surface. The shell structure can be easily tailored by changing the treatment temperature and water flow rate. A possible mechanism of a corrosion-ion immigrating-recondensation pattern was hypothesized to explain the formation of the core–shell porous structure.     

Chemical durability and microstructural analysis of glasses soaked in water and in biological fluids

A new glass, obtained from Bioglass^® BG45S5 original composition by substituting CaO with MgO, was produced and its chemical durability and microstructural characteristics were compared with that of Bioglass^®.The two glasses (labelled as BG45 and MG45) were soaked up to 4 weeks at physiological temperature in different solutions, i.e. bi-distilled water, Hank's Buffered Salt Solution 61200 (labelled as HBSS+), Hank's Buffered Salt Solution 14170 (labelled as HBSS−), and Kokubo's SBF. Moreover, the influence of either flat or flake surfaces was analysed for both glasses. Results showed that the chemical durability of a glass in saline at 37 °C, evaluated through pH and ICP-AES chemical analysis of the leached components, depended mainly on the chemical composition of the soaking solution. Moreover, the MG45 glass never exhibited hydroxyapatite crystal formation on its surface also after soaking in calcium-containing solutions. The apatite crystallisation and deposition mechanism, typical of a bioactive glass, was induced only if the glass itself contained calcium. The contemporaneous presence of calcium in the glass and in the soaking solution improved the reactivity of the glass, as apatite crystals nucleated in a shorter time and grew more quickly. As regards the morphology of the glass surface, rougher surfaces favoured the formation of hydroxyapatite crystals on glasses containing calcium.     

The Influence of Mesomorphic State on the Durability of Polymer Coatings

Abstract

The laws governing the destruction of polymer coatings during their use are partly defined by the fact that the rate and other specific features of their destruction are influenced by internal stresses occurring as a result of incomplete relaxation processes due to peculiarities of structure formation.¹ This paper deals with an investigation carried out with the help of the NMR method of higher resolution, electron microscopy and physicochemical methods to study the effect of the oligomeric block structure, length and flexibility of a number of oligoester acrylates on peculiarities of oligomer structure formation as well as coatings structure and properties and their durability in the conditions of aging under ultraviolet radiation. It's been shown that coatings set through the intermediacy of mesomorphic structure formation have increased durability of 2-2.5 times, during aging under ultraviolet light radiation. Of all the studied systems those with a globular structure tend to have the lowest durability.     

Nanotechnology for Encapsulating Zirconium Boride upon Formation of Heat-Resistant Coatings

The reaction formation of ZrB₂- and SiO₂-based composite materials and coatings upon heat treatment of the initial components in open air is investigated. It is shown that the glass melt formed in the course of the chemical reaction encapsulates zirconium boride particles, thus imparting high-temperature strength to the composite material. The influence of the concentration and sizes (down to a nanometer scale) of silica particles on the kinetics of oxidation of the compact samples and coated materials during their formation and heat resistance tests is studied using gravimetric, differential thermal, X-ray powder diffraction, and chemical analyses, as well as electron probe X-ray microanalysis. The structure and phase composition of the surface and the bulk of the samples are determined. The compositions of coatings that ensure effective protection of graphite from oxidation in air at high temperatures are proposed.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Ban’kovskaya, Semov, Lapshin, Kostyreva.     

Electrically melted cordierite glass: Its synthesis and behavior in heating

A high-density homogeneous cordierite material suitable for the manufacture of high-quality articles and ramming mixtures has been obtained by electric-arc melting in an OKB 2126 furnace. The structural and phase transformations in cordierite glass have been investigated and the sequence of mineral formation has been determined.Translated from Ogneupory, No. 6, pp. 11 – 13, May, 1994.     

Interrelation between the Parameters of Chemical Vapor Deposition, Properties, and Structure of Borophosphosilicate Glass Films Used in the Silicon Integrated Circuit Technology

The results of investigations into the processes occurring in the course of the synthesis, the physicochemical properties, and the compositions of thin borophosphosilicate glass films with phosphorus and boron at a total content up to 30 wt % are generalized. The films are prepared using four chemical vapor deposition methods at deposition temperatures ranging from 380 to 520°C, followed by heat treatment at temperatures of 700–950°C. It is demonstrated that the substantial differences in the properties of the glass films studied can be explained by two factors. The first factor is associated with the porosity of glass films and the occurrence of boron atoms in the threefold coordination with respect to oxygen in the glass. The second factor involves the total content of phosphorus and boron oxides, the concentration of phosphorus oxide clusters embedded into the glass structure, and their sizes. A novel approach is proposed for the characterization of the chemical stability of thin glass films used in the technology of silicon integrated circuits.     

Suppressing the effect of cullet composition on the formation and properties of foamed glass

The process of foaming glass is very dependent on the chemical composition of the glass. In this study we used a foaming-agent/oxidizing-agent couple and a crystallization inhibitor to foam cullets of flat, container and CRT-panel glass. Foamed glass with a density of 110–120?kg?m^–3, a thermal conductivity of 50–52?mW?m^–1 K^–1 and a homogeneous pore structure was obtained from a mixture of panel glass, 0.33?wt% carbon and 4.45?wt% Fe₂O₃. We also showed that it is possible to fabricate foamed glass with the same density or pore structure as mentioned above by adding up to 50?wt% container cullet or 70?wt% flat glass to the mixture. In the foamed samples with a low content of panel glass, crystals form, resulting in an increased open porosity, density and inhomogeneous pore structure. The crystallization can, however, be inhibited by adding calcium phosphate, so enabling the preparation of high-quality foamed glass from flat glass or flat/container-glass mixture. The pore gas is predominantly CO₂ and the pressure inside the pores is 0.36–0.47?bar. The reduced effect of the composition on the foaming process suggests that there is a great potential for stabilizing the production of foamed glass and ensuring the product's quality.     

Refractory concretes of a new generation. Thermodynamic aspect of the technology

With allowance for the approach developed preferentially in the works of Tsimmermanis and Shtakel'berg, a set of fundamental regularities of the thermodynamics of irreversible processes (nonequilibrium thermodynamics) is used to analyze the processes of structure formation in manufacturing new refractory concretes. Structure formation and hardening of concretes is phenomenologically realized as the formation of a capillary-porous structure in the process of changes in the free surface energy of the system, which serves as a measure for the strength, elastic, and other properties of the material. In this approach to thermodynamic analysis of structure formation the watering potential of a disperse system is treated as an analog of the Gibbs chemical potential. The notions of structural affinity and the degree of completeness of structure formation are introduced by analogy with chemical affinity and the degree of completeness of a chemical reaction.Translated from Ogneupory, No. 1, pp. 2–7, January, 1995.     

Effect of aluminum-containing raw materials on the melting of borosilicate glass for fiber

Aluminum-containing raw materials for the synthesis of aluminum-borosilicate glasses for E-glass fiber should be rationally chosen to comprehensively assess their effect on the glass melting processes. The characteristic properties of the chemical, phase, and granulometric composition of the raw materials such as metallurgical alumina, non-metallurgical alumina, disthene, and kaolin were under study. It was revealed that the type of aluminum-containing raw materials significantly influenced the rate of glass formation processes and heat consumption required for these processes. The efficiency of aluminum-containing raw materials is influenced by the following factors: the phase composition, which determines the sequence and rate of phase transformations, as well as the heat-absorbing ability of the furnace batch and glass melt. The most energy-efficient material is non-metallurgical alumina of the White Alumina brand. Using it facilitates saving energy resources for glass formation processes from 2.64% to 16.30% as compared with other types of aluminum-containing raw materials. The use of kaolin proves to be the least efficient due to the additional energy consumption for the process of destruction of the crystal structure of kaolinite, the reduced thermal conductivity of the batch, and the thermal transparency of the borosilicate glass melt.     

In-Situ Coating of Zeolite Na-A on Al2O3-SiO2 Glass Fibers

In-situ coating of zeolite Na-A crystals on Al₂O₃-SiO₂ glass fibers was investigated by a low temperature chemical process. The glass fibers were reacted with various concentrations of NaOH solutions at 60–110°C for various times. The surface of glass fibers was first leached by the solution but crystals of zeolite Na-A precipitated on the glass fibers after a certain reaction time because the concentrations of Si and Al components in the solution increased by dissolution of the glass fibers. The precipitated zeolite was identified to be Na-A type but nosean-cancrinite-type phase and/or hydroxysodalite coexisted with zeolite Na-A at longer reaction times. With higher concentration of NaOH solution, the formation rate of zeolite Na-A was faster, the formation temperature was lower and the grain size was smaller ca. 2–3 m. Dense zeolite Na-A coatings were produced when the glass fibers were reacted in 4 M NaOH solution at 60°C for 18 h. The amount of zeolite Na-A formed on the fibers was about 20 mass%.     

Making the Bend: DNA Tertiary Structure and Protein-DNA Interactions

DNA structure functions as an overlapping code to the DNA sequence. Rapid progress in understanding the role of DNA structure in gene regulation, DNA damage recognition and genome stability has been made. The three dimensional structure of both proteins and DNA plays a crucial role for their specific interaction, and proteins can recognise the chemical signature of DNA sequence (“base readout”) as well as the intrinsic DNA structure (“shape recognition”). These recognition mechanisms do not exist in isolation but, depending on the individual interaction partners, are combined to various extents. Driving force for the interaction between protein and DNA remain the unique thermodynamics of each individual DNA-protein pair. In this review we focus on the structures and conformations adopted by DNA, both influenced by and influencing the specific interaction with the corresponding protein binding partner, as well as their underlying thermodynamics.     

The structure of SiO2 — Current views

Silicon dioxide or silica, one of the most important raw materials in ceramics, undergoes rather complex phase transformations under varying conditions of temperature, pressure and chemical purity. The flexibility of the silica framework, consisting of [SiO₄] tetrahedra bonded together into a giant polymeric “open molecule” by sharing oxygen atoms, is primarily due to the easy adjustment of the SiOSi angles between tetrahedra in response to changing conditions. The structure reinvestigations of silica polymorphs done in recent years allow a comprehensive review of the structure problems, including the high-pressure and amorphous states of SiO₂ and the mechanism of some of the phase transformations. The most difficult and still controversial problem of the structure of vitreous silica is rather extensively discussed in view of the technical importance of silica glass.     

Flexibility improvement of short glass fiber reinforced epoxy by using a liquid elastomer

In certain applications of fiber reinforced polymer composites flexibility is required. The aim of this study was to improve flexibility of short glass fiber reinforced epoxy composites by using a liquid elastomer. For this purpose, diglycidyl ether of bisphenol-A (DGEBA) based epoxy matrix was modified with hydroxyl terminated polybutadiene (HTPB). A silane coupling agent (SCA) was also used to improve the interfacial adhesion between glass fibers and epoxy matrix. During specimen preparation, hardener and HTPB were premixed and left at room temperature for an hour before mixing with epoxy resin to allow possible reactions to occur. In order to compare flexibility of the specimens flexural tests were conducted and the data were evaluated numerically by using a derived relation. Test data and scanning electron microscope analysis indicated that surface treatment of glass fibers with SCA, and HTPB modification of epoxy matrix improved flexural properties especially due to the strong interaction between fibers, epoxy, and rubber. It was also observed that HTPB modification resulted in formation of relatively round rubber domains in the epoxy matrix leading to increased flexibility of the specimens.