SiO2–Al2O3–CaO glass-ceramics: Effects of CaF2 on crystallization,microstructure and properties

The effects of fluorine content on the nucleation and crystallization behavior of SiO₂–Al₂O₃–CaO glass ceramics system have been investigated. The crystalline phases were determined by X-ray diffraction (XRD). The crystallization kinetics was determined by differential thermal analysis (DTA). The microstructures were examined by using scanning electron microscope (SEM). Fourier transformed infrared spectra (FTIR) analysis was used to study the glass structure. The results showed that by increasing the fluorine content, both the crystallization peak temperature (T_p) and activation energy (E) decreased. Wollastonite, anorthite and gehlenite are the main crystalline phases that exist in the glass ceramics system. The study shows that fluorine promoted initial crystallization of glass and can be used as an effective nucleating agent in the SiO₂–Al₂O₃–CaO system.     

Transamination Reactivity of Ti(NMe2)4 and Zr(NMe2)4 with 1,3,4,5,6-Pentamethyl-2-aminoborazine and Aryl Amines. Model Chemistry for the Formation of Metalloborazine Preceramic Polymers and MN/BN (M?=?Ti, Zr) Ceramic Composites

The transamination reactions between Ti(NMe₂)₄ and 1,3,4,5,6-pentamethyl-2-aminoborazine, (Me)₃N₃(Me)₂B₃(NH₂), and diphenylamine (Ph₂NH) and between [Zr(NMe₂)₄]₂ and 1,3,4,5,6-pentamethyl-2-aminoborazine, aniline (PhNH₂) and diphenylamine have been studied and the molecular product species have been isolated, spectroscopically characterized and single crystal X-ray structure analyses completed. The results of these studies have been used to interpret the outcome of reactions of Ti(NMe₂)₄ and Zr(NMe₂)₄ with borazinylamine preceramic polymers that, upon pyrolysis, produce TiN/BN, ZrN/BN and ZrH_0.6N/BN composite powders. The transamination reactivity of a two-point poly(borazinylamine) oligomer having terminal –NH₂ amino groups with Ti(NMe₂)₄ and Zr(NMe₂)₄ has been used to obtain metallated preceramic oligomers that, upon pyrolysis, give TiN/BN and ZrN/ZrH_0.6N/BN nanocomposites. Model reactions of 1,3,4,5,6-pentamethyl-2-amino borazine, aniline and Ph₂NH₂ with Ti(NMe₂)₄ and Zr(NMe₂)₄ are also described as models for the formation of the metallated oligomers. Molecular structure determinations for the metal amides are presented. We dedicate this paper to Professor Christopher W. Allen in recognition of his distinguished career and his accomplishments in inorganic ring and polymer chemistry.     

Morphology-controlling synthesis of ZnS through a hydrothermal/solvthermal method

Different morphologies of ZnS have been synthesized by a solvothermal process, through the reaction of Zn(CH₃COO)₂·2H₂O and SC(NH₂)₂ in different mixed solvents, changing the density of the surfactant (C₁₂H₂₅SO₃Na). The samples were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX) techniques. The results show that the as-prepared ZnS have different morphologies, such as lamellar ZnS, smooth microspheres, roughen microspheres, plate-like ZnS and so on. So far, to our knowledge, lamellar ZnS have not been synthesized by solvothermal route before.     

Lamellar Morphology of Poly(3-hydroxybutyrate)/Poly(ethylene oxide) Blends as Studied via Small Angle X-ray Scattering

The lamellar morphology of a melt-miscible blend consisting of two crystalline constituents, poly(3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) have been investigated by means of small angle X-ray scattering (SAXS). The blend was a crystalline/amorphous system when temperatures lay between the melting point of PEO (ca. T _m ^PEO=60C) and that of PHB (ca. T _m ^PHB=170C), while it became a crystalline/crystalline system below T _m ^PEO. The crystalline microstructures of the blends were induced by two types of crystallization history, i.e. one-step and two-step crystallizations. In the one-step crystallization, the blends were directly quenched from the melt to room temperature to allow simultaneous PHB and PEO crystallization. The two-step crystallization involved first cooling to 70C to allow PHB crystallization for 72 h followed by cooling to room temperature (ca. 19C) to allow PEO crystallization. In the crystalline/crystalline state, two scattering peaks have been observed in the Lorentz-corrected SAXS profiles, irrespective of the crystallization histories, meaning that crystallization created separate PHB and PEO lamellar stack domains. One-step crystallization yielded lamellar stack domains containing almost pure PHB and PEO lamellae. Two-step crystallization generated almost pure PHB lamellar domains and the PEO lamellar domains with inserted PHB lamellae. In the crystalline/amorphous state, the composition dependence of the amorphous layer thickness (l _a), the presence of zero-angle scattering, and the volume fraction of the PHB lamellar stack (_s) revealed that both one-step and two-step crystallizations, generated the interfibrillar segregation morphology, where the extent of interfibrillar segregation of amorphous PEO increased with increasing PEO content.     

Nonisothermal crystallization of PP/nano‐SiO2 composites

The kinetics of nonisothermal crystallization of polypropylene (PP) containing nanoparticles of silicon dioxide (SiO₂) were investigated by differential scanning calorimetry (DSC) at various cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that the Ozawa equation and Mo's treatment could describe the nonisothermal crystallization of the composites very well. The nano‐SiO₂ particles have a remarkable heterogeneous nucleation effect in the PP matrix. The rate of crystallization of PP/nano‐SiO₂ is higher than that of pure PP. By using a method proposed by Kissinger, activation energies have been evaluated to be 262.1, 226.5, 249.5, and 250.1 kJ/mol for nonisothermal crystallization of pure PP and PP/nano‐SiO₂ composites with various SiO₂ loadings of 1, 3, and 5%, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1013–1019, 2004     

Crystallization and properties of glasses based on diopside–Ca-Tschermak’s–fluorapatite system

The crystallization characteristics of glasses based on compositions in the diopside [CaMgSi₂O₆]–Ca-Tschermak’s [CaAl₂SiO₆]–fluorapatite [Ca₅(PO₄)₃F] system have been investigated. The effect of Ca-Tschermak’s/diopside replacement, at constant Ca₅(PO₄)₃F content, on the crystallization characteristics of the glasses and the solid solution phases formed, as well as the resulting microstructure, are traced by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM).Various pyroxene solid solutions together with fluorapatite phases are detected by XRD analysis. There is a preferential tendency for diopside to capture Ca-Tschermak’s in its structure forming pyroxene solid solution of diopsidic type. The maximum concentration of CaAl₂SiO₆ that could be accommodated in the diopside structure was 25%. Above this percentage, gehlenite Ca₂Al₂SiO₇ also developed. However, there was no solid solution formed between pyroxene and fluorapatite.The thermal expansion coefficients (α-values) and microhardness of the glasses and glass–ceramics were determined. The data of the glasses were correlated to the internal structure of the glasses, nature and role played by glass forming cations. However, the properties of the crystalline glasses were mainly attributed to different factors including the crystalline phases formed, residual glassy phase and the microstructures.     

Lamellar silica mesostructures assembled from a new class of Gemini surfactants: alkyloxypropyl-1,3-diaminopropanes

Abstract  

Representative members of a new class of commercially available Gemini surfactants, namely, the alkyloxypropyl-1,3-diaminopropanes, are shown to template the direct assembly of mesoporous silicas with lamellar framework structures. The hydrolysis of tetraethylorthosilicate in the presence of a derivative with a straight hydrophobic chain, C _n H_2n+1O(CH₂)₃NH(CH₂)₃NH₂ with n = 8 and 10 (Tomah3 DA1214), afforded a layered mesophase with a surface area of 464 m²/g, a pore volume of 0.39 cm³/g, a pore size of 3.6 nm and a vesicular hierarchical structure. The introduction of electrostatic forces into the assembly process through the protonation of up to 33% of the amine centers improves the quality of the lamellar framework order as evidenced by increases in X-ray diffraction and textural properties. Also, the vesicular hierarchical structure formed under electrically neutral assembly conditions is replaced by well dispersed multilamellar nanoparticles upon surfactant protonation. Chain branching in the hydrophobic segment of Gemini derivative i-C₁₀H₂₁O(CH₂)₃NH(CH₂)₃NH₂ (Tomah3 DA14) compromises the quality of the lamellar framework structure, but affords higly dispersed nanoparticles with hierarchical coiled slab to vesicular motifs depending on the degree of surfactant protonation. In addition to providing unusual lamellar framework structures, these Gemini surfactants afford hierarchical nanoparticle motifs of relatively uniform size (50–200 nm) and a very high degree of dispersion for a potential use in a variety of materials applications.     

The influence of TiO2 content on the properties of glass ceramics: Crystallization,microstructure and hardness

The effects of compositional variation, crystallization behavior, crystalline phases and microstructure formed in the SiO₂3Al₂O₃3CaO (SAC) glass system using various amounts of TiO₂ as nucleating agent were investigated by Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR) techniques. The crystallization kinetics and mechanical properties of SAC glass ceramics were studied using crystallization peak temperature (T_p) of three different glasses as obtained from DTA, the activation energy (E) and Avrami exponent (n) were also determined. The crystallization peak temperature (T_p) and activation energy (E) were found to increase with the increase in TiO₂ content. The major crystalline phases were anorthite and wollastonite along with gehlenite and titanite as the minor crystalline phases present in the glass ceramic system. The studies showed that the three dimensional crystalline structure and the microhardness increased with the increase of TiO₂ content in the glass ceramics system.     

Effects of Surfactant Hydrophilicity on the Oil Solubilization and Rheological Behavior of a Nonionic Hexagonal Phase

The effects of surfactant hydrophilicity on the phase behavior and rheology of a hexagonal phase (H₁) and related O/H₁ emulsions in a water/C₁₂EO _n /isohexadecane system (n = 7, 9) have been investigated. In this phase behavior study, a variety of surfactant aggregates (micellar, W_m; hexagonal, H₁; bicontinuous cubic, V₁; lamellar, L_α; inverse micellar, O_m) have been observed in water-C₁₂EO _n binary systems. The oil solubility of different surfactant aggregates was strongly affected by the surfactant hydrophilicity, i.e., surfactant aggregates in the C₁₂EO₇ system could solubilize a larger amount of oil than those in the C₁₂EO₉ system. It can be inferred that the surfactant with long hydrophilic head groups could be closely packed in the interface, leading to a reduction in the oil solubility in the micellar core due to the strong head group interaction. Interestingly, the rheology of the H₁ phase also exhibits behavior that is dependent on the surfactant hydrophilicity, i.e., high values of the elastic modulus G′ and complex viscosity |η*| have been observed in the C₁₂EO₉ system, possibly due to the strong neighboring head group interaction. Hexagon structure of the H₁ phase was calculated by using the Bohlin model. The viscosity of the O/H₁ emulsions decreases with increasing oil concentration, possibly due to the low volume fraction of the continuous phase (the H₁ phase).     

Structural and thermal characterization of CaO–MgO–SiO2–P2O5–CaF2 glasses

The influence of varying the CaO/MgO ratio on the structure and thermal properties of CaO–MgO–SiO₂–P₂O₅–CaF₂ glasses was studied in a series of eight glass compositions in the glass forming region of diopside (CaMgSi₂O₆)–fluorapatite [Ca₅(PO₄)₃F]–wollastonite (CaSiO₃) ternary system. The melt-quenched glasses were characterized for their structure by infrared spectroscopy (FTIR) and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy. Silicon is predominantly present as Q² (Si) species, while phosphorus tends to coordinate in orthophosphate environment. The sintering and crystallization parameters of the glasses were obtained from differential thermal analysis (DTA) while crystalline phase fractions in the sintered glass–ceramics were analyzed by X-ray diffraction adjoined with Rietveld refinement. Diopside, fluorapatite, wollastonite and pseudowollastonite crystallized as the main crystalline phases in all the glass–ceramics with their content varying with respect to variation in CaO/MgO ratio in glasses. The implications of structure and sintering behaviour of glasses on their bioactivity were discussed.     

Porous structure of crystalline polymers by exclusion effect of carbon dioxide

We investigated the morphology of high-density polyethylene (HDPE) and poly(vinylidene fluoride) (PVDF) crystallized under carbon dioxide (CO₂) by light scattering measurements and microscopic observations. The crystallization of HDPE was delayed and the ordering of the spherulite was smaller by dissolving CO₂ rather than air at ambient pressure. A fine-layered porous structure having a size of 500 nm was obtained in HDPE, while a large rod-like porous structure radiating in the spherulite was obtained in PVDF. Such a characteristic porous structure is attributed to the exclusion of CO₂ from the crystal growth front to the intercrystalline amorphous region and the growth of bubbles by the supersaturation of CO₂ in the constrained amorphous region. The exclusion effect is covered by the Keith-Padden theory through consideration of the self-diffusion in polymer-CO₂ systems; the exclusion and the growth of bubbles occur as lamellar stacks in HDPE whereas they occur as bundles of lamellar stacks in PVDF.     

Glass structure and crystallization via two distinct thermal histories: Melt crystallization and glass crystallization

This study focuses on the effect of structural inhomogeneity of 44.4CaO-33.2SiO₂-8.8Na₂O-6.2Al₂O₃-7.4B₂O₃ glass on its crystallization behavior. The crystallization behavior of the investigated lime-sodium aluminoborosilicate glass system is explored for the two thermal histories of melt crystallization and the heat treatment of quenched glass. The results show that sodium melilite (CaNaAlSi₂O₇) and larnite (β-Ca₂SiO₄) are the dominant crystalline phases during heating (glass crystallization) and cooling (melt crystallization), respectively. In the glass structure from the heat treatment at 610 °C, both Si₂O₇ and AlO₄ units (i.e., four-coordinated Al) are dominant. This may induce sodium melilite (CaNaAlSi₂O₇) crystallization, connecting Si₂O₇ and AlO₄ units with O and linking Ca and Na between interlayers. The melt structure, meanwhile, has more SiO₄ and AlO₆ units in its silicate and aluminate. Therefore, larnite (β-Ca₂SiO₄) crystallizes on cooling by combining SiO₄ units and Ca. The crystallization behavior is further discussed considering the inhomogeneity structure of supercooled liquids before nucleation.     

Comparison of crystallization kinetics in various nanoconfined geometries

Phase morphological effect on crystallization kinetics in various nanoconfined spaces in a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer with a PEO volume fraction of 37 vol% was investigated. The phase morphology was characterized by small-angle X-ray scattering and transmission electron microscopy techniques. When the sample was cast from chloroform solution and annealed at 150 °C, a double gyroid (DG) phase was obtained. After it was subjected to a large-amplitude reciprocating shear, the sample transformed to an oriented hexagonal cylinder (Hex) phase. To obtain a lamellar confined geometry, lamellar single crystals were grown from dilute solutions. The crystallization in the lamellar (Lam) phase was one-dimensionally (1D) confined, while it was two-dimensionally (2D) confined in the DG and Hex phases, although they had different structures. Differential scanning calorimetry (DSC) was employed to study the crystallization kinetics using the Avrami analysis for these three nanoconfined geometries. Heterogeneous nucleation was found in all three samples in the crystallization temperature (T_c) regions studied. DSC results indicated that the crystallization kinetics in the Lam phase was the fastest, and the PEO crystals possessed higher thermodynamic stability than in the DG and Hex phases. For the crystallization kinetics in two 2D-confined phases, at low T_c (<35 °C) the PEO crystallization rates in the DG and Hex phases were similar, while at high T_c (>35 °C) the PEO crystallization was slower in the DG phase than in the Hex phase. The Avrami exponent n-values for the DG and the Hex samples were similar (∼1.8), yet the values of lnK in the DG phase were smaller than those in the Hex phase. This suggested that the linear growth rate was slower in the DG phase than in the Hex phase due to continuous curved channels in the DG phase.     

Thermodynamic assessment within the Zr–B–C–O quaternary system

Thermodynamic modeling of Zr–B–C–O quaternary system is conducted within the CALPHAD framework by employing data obtained from first-principle calculations and literature. The lower order binary B–O is assessed in this work by estimating the thermodynamic properties of stable solid phases of B₂O₃ and B₆O and by estimating the gas and liquid phases. First-principle calculations, in conjunction with special quasirandom structure were used to predict enthalpies of mixing for the ternary solid-solution phase of FCC-Zr(C, O). The calculated results were used to optimize the model parameters pertaining to the cubic phase, which is described by a two-sublattice model. The modeled Zr–C–O ternary phase diagrams calculated at 1923 and 2273 K under ambient pressure and 4 Pa, respectively, are in agreement with experimental phase diagrams.     

THREE-PHASE EXTRACTION STUDY OF THE TOA-ALKANE / HC1 (Zn2+ or Fe3∗) SYSTEMS 1

ABSTRACT

The three-phase extraction systems TOA-n-heptane / HC1, TOA-kerosene / HC1, TOA-kerosene / HCl-ZnCl₂ and TOA-kerosene / HCl-FeCl₃ have been investigated. The volumes and compositions of the equilibrium phases for these systems have been determined at 298K at a phase ratio of one.

In the HC1 extraction system, amphiphilic molecules TOA-HC1 in heavy organic phase (i.e. the third phase or the middle phase) self-assemble into a lamellar structure, and water and alkane are solubilized in polar layers and nonpolar layers respectively. The solubilization capacities are within the saturation value of TOAHCl:H₂0:n-heptane=l:2:3 (molar ratio). The solubiiizition decreases when the ratio of initial HC1 concentration to initial TOA concentration is less than one and excess acid and water are extracted into the middle phase if initial concentration of HC1 is higher than that of TOA.

Zinc and iron are mainly extracted into the middle phase. The metal extraction systems have different phase behavior than the acid extraction system because of the different nature of the interfacial amphiphilic molecules.     

Hydrothermal transformation of a layered aluminophosphate into a mesoporous structure

A new mesoporous aluminophosphate (AlPO₄) has been synthesized through hydrothermal transformation of a lamellar mesostructured aluminophosphate prepared in the presence of a neutral surfactant dodecylamine (DDA) under mild alkaline pH conditions and using water–ethanol mixture as the synthesis medium. Post-synthesis hydrothermal treatment was carried out at 448 K for 72 h in the presence of dilute aqueous phosphoric acid, which results this phase transformation. Lamellar and mesoporous phases of these samples were revealed from powder X-ray diffraction, SEM-EDS, transmission electron microscopic image analysis, ³¹P MAS NMR a FT IR spectroscopic studies and thermal analysis. N₂ sorption studies revealed the existence of pores with dimension of small mesopores after H₃PO₄ treatment. Pillaring of the interlayers through PO₄ units during post-synthesis hydrothermal treatment could be responsible for the transformation of lamellar to mesoporous phase.     

Contribution of gallium oxide content to the crystallization characteristics and chemical stability of sodium phlogopite glasses

The effect of gallium oxide content on the crystallization characteristics and chemical durability of a sodium phlogopite based glass-ceramic of the stoichiometric phase formula NaMg₃(Si₃[Al_1−X,Ga_x]O₁₀)F₂ where X=0.0, 0.25, 0.5, 0.75 and 1.0 was investigated. The Ga₂O₃/Al₂O₃ replacement and heat treatment have an effect on the crystalline phases developed and their microstructure. Forsterite ss, enstatite, and sodium phlogopite phases were mostly detected in the crystallized glasses. There is a preferential tendency for forsterite to accommodate sodium phlogopite ions in its structure forming olivine solid solution of forsterite type. At low Ga₂O₃/Al₂O₃ replacement an increase in the crystallization temperature led to the decomposition of the sodium phlogopite phase to form forsterite ss phase, while at high Ga₂O₃ replacement increasing the heat-treatment temperature led to the development of forsterite ss at the expense of enstatite phase. The chemical stability of the crystallized materials was better in acidic than in alkaline media. The present data provides valuable information about the role played by the glass oxide constituent in determining the nature of the crystalline phases and solid solution formed in the materials especially in the field of preparation of glass-ceramic substrate used for magnetic information storage.     

Structural dependence of crystallization in glasses along the nepheline (NaAlSiO4) ‐ eucryptite (LiAlSiO4) join

Lithium and sodium aluminosilicates are important glass‐forming systems for commercial glass‐ceramics, as well as being important model systems for ion transport in battery studies. In addition, uncontrolled crystallization of LiAlSiO₄ (eucryptite) in high‐Li₂O compositions, analogous to the more well‐known problem of NaAlSiO₄ (nepheline) crystallization, can cause concerns for long‐term chemical durability in nuclear waste glasses. To study the relationships between glass structure and crystallization, nine glasses were synthesized in the Li_xNa_1‐xAlSiO₄ series, from x = 0 to x = 1. Raman spectra, nuclear magnetic resonance (NMR) spectroscopy (Li‐7, Na‐23, Al‐27, Si‐29), and X‐ray diffraction were used to study the quenched and heat‐treated glasses. It was found that different LiAlSiO₄ and NaAlSiO₄ crystal phases crystallize from the glass depending on the Li/Na ratio. Raman and NMR spectra of quenched glasses suggest similar structures regardless of alkali substitution. Li‐7 and Na‐23 NMR spectra of the glass‐ceramics near the endmember compositions show evidence of several differentiable sites distinct from known Li_xNa_1‐xAlSiO₄ crystalline phases, suggesting that these measurements can reveal subtle chemical environment differences in mixed‐alkali systems, similar to what has been observed for zeolites.     

Crystal behavior of semicrystalline polystyrene‐block‐poly(l‐lactide) diblock copolymer in thin films with various structures

The crystal behavior of a semicrystalline polystyrene‐block‐poly(l ‐lactide) diblock copolymer in phase‐separated thin films with various thicknesses at different crystal temperatures has been investigated using atomic force microscopy and transmission electronic microscopy. Parallel and perpendicular lamellae could be obtained by annealing the thin films for different periods of time as reported previously (Chen et al., Macromolecules 40:6631 (2007)). At different temperatures, crystallization in thin films with parallel lamellar structure in the melt state gives dendrite crystals with orthorhombic structure, and the ordered structure in the melt is destroyed after crystallization. When crystallization occurs in thin films with perpendicular lamellar structure, crystal morphology and structure are greatly affected by the crystallization temperature (T_c). When T_c < T_g,ps, where T_g,ps is the glass transition temperature of a polystyrene block, crystallization is hardly confined within the lamellae. The morphology is preserved but the long period of the perpendicular lamellae is increased after crystallization. When T_c > T_g,ps, rod‐like crystals dominate the final morphology, and crystallinity destroys completely the structure in the melt.© 2012 Society of Chemical Industry     

Isothermal crystallization of polyethylene oxide/silver nanoplate composites

This research was accomplished to investigate the kinetics of isothermal crystallization of polyethylene oxide (PEO)/silver nanoplate composites. It was obtained that the spherulites increased in size and numbers with time for the composites with various particle loadings. Additionally, the spherulite growth rate of composites decreased with an increase in the crystallization temperature and increased with the addition of nanoplates. The spherulite growth rate was further analyzed by the theory developed by Lauritzen and Hoffman. The product of the lateral surface free energy (σ) and the end surface free energy (σ_e) decreased with an increase in the content of nanoplates. We proposed the possible crystallization mechanisms of these PEO/nanoplate composites according to the change of σ and σ_e with the presence of nanoplates. A controlled experiment showed a minor change in PEO crystallization with the presence of a surfactant C₁₆TAB. This implied that the unique size and shape of nanoplates plays a key role on hindering the primary nucleation of PEO and increasing the spherulite growth rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011