Synthesis of Thermally Stable MCM-41 at Ambient Temperature

A new process to synthesize thermally stable mesoporous molecular sieves of MCM-41 structure based on delayed neutralization at ambient temperature was investigated. All samples synthesized by this new method have BET surface areas of about 1100m²/g and possess high thermal stability up to 900°C. Higher crystallinity and less lattice constriction after calcination were observed for samples with a longer aging period. Those samples with aging time longer than 10 days exhibited four characteristic XRD peaks of MCM-41 both before and after calcination at 560°C. The N₂ adsorption-desorption isotherms of the calcined samples showed larger average pore size and more homogenous pore size distribution. The method was also successfully applied to the synthesis of MCM-41 with different surfactants of hydrocarbon length with 10–18 carbons and proves to be a simple route for obtaining thermally stable MCM-41 at room temperature.     

Heat release during the hydration of calcinated α-C<Subscript>2</Subscript>SH and its mixture with killalaite

In this work, the influence of the mineral composition of the synthesized calcium silicate hydrates on their hydraulic activity after thermal treatment was determined. Primary mixture, consisting of quartz sand and burnt limestone (CaO/SiO₂ = 2), was treated hydrothermally with NaOH additive at 200 °C. It was determined that α-C₂SH prevailed in the product after 4 h of the synthesis. The results of DSC and XRD analysis revealed that α-C₂SH was partially decomposed after 12 h of the synthesis and newly formed compounds were identified—killalaite, portlandite and C–S–H. The products of 4 and 12 h synthesis were treated thermally at temperatures between 450 and 1000 °C. It was determined that dellaite and x-C₂S formed already at 450 °C, β-C₂S at 600 °C and α′_L-C₂S at 800 °C when the 4 h synthesis product, in which α-C₂SH prevailed, was treated thermally. On the other hand, killalaite remained stable up to 600 °C, and the temperature values, at which mentioned calcium silicates formed, increased in case of a 12 h synthesis product. Heat flow values of the main hydration reaction and total heat release exceeded 3.1 mW g^?1 and 140 J g^?1 accordingly in case of the samples in which α-C₂SH prevailed. However, increase in the thermal treatment temperature resulted in a decrease in the mixtures hydraulic activity. It was proved that killalaite formation in the product of the 12 h hydrothermal synthesis vividly decreases its hydraulic activity after the thermal treatment in the temperature range of 450–1000 °C. No increment in the heat flow values that could be attributed to the main hydration reaction (acceleration period) was witnessed in all the curves of the heat flow analysis in this case.     

Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO₂, tlm, after a thermal treatment (1250°C). The structure of samples in the system Al₂O₃-ZrO₂ is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO₂ sol particles in decomposition of urea. The coating of ZrO₂ sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO₂ sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al₂O₃-ZrO₂ was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorption isotherms.     

Preparation of zinc sodium polyphosphates glasses from coacervates precursors. Characterisation of the obtained glasses, and their applications

A soft chemistry route is described to obtain glasses in the P₂O₅–Na₂O–ZnO–H₂O. It is based on the addition of zinc salts to coacervates prepared from sodium polyphosphate. The processing of these coacervates leads to polyphosphate glasses with the same properties as those of glasses prepared in the classical way. So far, little work has been implemented in this system using ‘coacervate route’. However, it makes an attractive method for coating and joining processes on the industrial scale. As the anion associated to zinc may take part in the adhesion mechanism, coacervate formation has been studied using zinc chloride, nitrate and sulphate as starting materials. The physical properties of the glasses obtained by this method are reported and potential applications of zinc and silver coacervate are described.     

Water-stable biphasic nanocolloids with potential use as anisotropic imaging probes

Electrified co-jetting of two aqueous polymer solutions followed by a thermal cross-linking step was used to create water-stable biphasic nanocolloids. For this purpose, aqueous solution mixtures of poly(acrylamide-co-acrylic acid) and poly(acrylic acid) were employed as jetting solutions. When the biphasic nanocolloids created by side-by-side electrified co-jetting were thermally treated, a cross-linking reaction occurred between amide groups and carboxylic groups to form stable imide groups. Infrared spectroscopy was employed to monitor the reaction. The quality and the integrity of the resulting biphasic nanocolloids were confirmed by confocal laser scanning microscopy, flow cytometry analysis, and dynamic light scattering. Selective encapsulation of two biomolecules in each phase of the biphasic colloids was maintained even after thermal reaction and suspension in aqueous environment. Well-dispersed spherical colloids with stable dye loadings in each hemisphere were kept intact without aggregation or dissolution for several weeks. Finally, biphasic nanocolloids were selectively surface-modified with a biotin-dextran resulting in water-stable particles to ensure binding of proteins only to a single hemisphere.     

Effects of inorganic nanofillers on the thermal degradation and UV-absorbance properties of polyvinyl acetate

The effects of calcium carbonate (CaCO₃) and calcium sulfate (CaSO₄) nanoparticles on the thermal and UV-absorbing properties of polyvinyl acetate (PVAc) were analyzed in this study. Nanoparticles of CaCO₃ and CaSO₄ were synthesized by in situ deposition technique. The size and shape of nanoparticles were recognized by X-ray diffraction and scanning electron microscope (SEM) analyses which confirmed that the particle was having a diameter of 25–33 nm. In this technique, the surface modification of nanoparticles was done by non-ionic polymeric surfactant. PVAc/CaCO₃ and PVAc/CaSO₄ nanocomposites film samples with an average thickness of 30 µm and in the mass ratio of nanoparticles (0–4% (w/w)) were prepared by solution mixing technique. Chemical, structural, and elemental characterizations of nanocomposites were done by, fourier transform infrared, SEM, and energy dispersive X-ray spectroscopy analyses, respectively. Thermal properties of pure polymer and nanocomposites were characterized through differential scanning calorimetric, thermogravimetric, and differential thermogravimetry techniques. The glass transition temperature of nanocomposites increases with increase in content of nanoparticles. It may be due to the interaction between inorganic and organic components. The thermogravimetric analysis results indicate that the thermal degradation temperatures of nanocomposites were enhanced upon the addition of nanosized inorganic fillers. The thermal results show that PVAc/CaSO₄ nanocomposites were more thermally stable than PVAc/CaCO₃ nanocomposites. The addition of nanoparticles affects degradation mechanism and consequently improves thermal stability of PVAc. The reduction of polymer chain mobility and the tendency of nanoparticles to eliminate free radicals were the principal effects responsible for these enhancements. The ultraviolet–visible (UV–Vis) absorbance spectra of PVAc and its nanocomposites films show that the intensity of absorbance increases with increasing filling content, suggesting that nanocomposites films have greater UV-shielding property.     

Starved Water Hydrolysis of Different Precursors and its Influence on the Properties of Precipitated Zirconia

The chemical composition of zirconia gels precipitated from methanol solutions with excess, stoichiometric or deficient amounts of water as well, as the phase composition of fine ZrO₂ powders obtained by thermal treatment of gels prepared by this method, were investigated. It was observed that both the stoichiometry and crystalline phase formation during thermal treatment of zirconia gels are strongly influenced by the amount of water added to the initial reaction mixture. Heating the hydrated zirconia gels in an inert oxygen-free atmosphere produced a black nonstoichiometric oxide. The degree of nonstoichiometry of zirconia and its microstructure are influenced by the initial conditions in the reaction mixture. The X-ray patterns of thermally treated samples prepared with a substoichiometric amount of water show power lines of monoclinic and tetragonal zirconia, while after the same thermal treatment to 700°C, those prepared with excess water in the initial methanol solution, show mainly tetragonal diffraction lines.     

Synthesis of Alumina Gels in Amphiphilic Media

This work deals with the synthesis of alumina gels from aqueous solutions of aluminum chloride in the presence of cationic surfactant molecules. The effect on the sol-gel transition of the reagent concentrations and of the synthesis temperature are first studied. The structure of the resulting wet and dried gels and the formation of liquid crystal mesophases are studied by X-ray diffraction. The thermal and structural evolutions of the gels are then characterized by thermogravimetric and X-ray diffraction measurements. Finally, nitrogen adsorption isotherms are used to investigate the porous texture of the thermally treated materials up to the transformation into -Al₂O₃.     

Amorphous manganese polyphosphates: preparation,characterization and incorporation of azo dyes

Amorphous Mn²⁺ polyphosphate materials were prepared at room temperature through the coacervation of polyphosphate solutions. These new materials display the typical Mn²⁺ red emission with a broad band centered at 15,290 cm⁻¹ (bandwidth—1,320 cm⁻¹). Excitation spectra display typical Mn²⁺ (d⁵) absorption bands assigned to transitions from the ⁶A_1g ground state to the ⁴T_2g, (⁴A_1g, ⁴E_g), ⁴T_2g, and ⁴T_1g Mn²⁺ excited states. Transition energies allow estimating the Mn²⁺ ligand field strength as intermediate between the one observed in Mn²⁺ aqueous solutions and the one observed in Mn²⁺ phosphate glasses. Azo dyes, methyl red and methyl orange, were incorporated into the manganese polyphosphate coacervates structure. Raman scattering and visible light reflectance results show azo dyes acid forms inside the hydrated polyphosphate structure and sensitivity to the atmosphere pH. Release of azo dyes species was observed from these new solid hybrid materials in aqueous medium.     

High Tg polyimide nanofoams derived from pyromellitic dianhydride and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane

New routes for the synthesis of high T_g thermally stable polymer foams with pore sizes in the nanometer regime have been developed. Foams were prepared by casting well-defined microphase-separated block copolymers comprised of a thermally stable block and a thermally labile material. At properly designed volume fractions the morphology provides a matrix of the thermally stable material with the thermally labile material as the dispersed phase. Upon thermal treatment, the thermally unstable block undergoes thermolysis generating pores, the size and shape of which are dictated by the initial copolymer morphology. Triblock copolymers comprised of a high T_g, amorphous polyimide matrix with poly(propylene oxide) as the thermally decomposable coblock, were prepared. The copolymer synthesis was conducted through the poly(amic acid) precursor and subsequent cyclodehydration to the polyimide by either thermal or chemical means. Dynamic mechanical analysis confirmed microphase separated morphologies for all copolymers, irrespective of the propylene oxide block lengths investigated. Upon decomposition of the thermally labile coblock, a 9–18% reduction in density was observed, consistent with the generation of a foam which was stable to 400°C. © 1996 John Wiley & Sons, Inc.     

Efficiency of wollastonite and ammonium polyphosphate combinations on flame retardancy of polystyrene

The thermal and fire properties of polystyrene (PS) flame retarded by a system composed of ammonium polyphosphate (APP) and wollastonite (W) were investigated by thermogravimetric analysis, pyrolysis‐combustion flow calorimeter, pyrolysis gas chromatography mass spectrometry, cone calorimetry and epiradiator. The combustion residues were observed by scanning electron microscopy/energy dispersive X‐ray spectroscopy and analyzed by X‐ray diffraction. The combination of both additives enables increasing the thermal stability of PS while increasing simultaneously the high temperature residue. The peak of HRR was also significantly reduced while time to ignition varied depending on the composition. It was shown that the degradation pathway of PS was affected by the presence of the additives implying a reduction of the effective heat of combustion. In the condensed phase, APP decomposition promotes char formation and favors the reactivity between phosphorus and silicate. A layer composed of char, W and a mixture of calcium and silicon phosphate is formed at the sample surface during combustion. This layer is cohesive enough to limit the release of combustible gases to the gas phase. Moreover, the thermally stable protective layer reaches high temperature enabling the re‐irradiation of a part of the incident heat flux. The flame retardancy of PS is thus enhanced. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural and thermal characterization of Zn2−xCoxTiO4

In this work, spinels with the general formula Zn_2?xCo_xTiO₄ were synthesized by the polymeric precursor method and thermally treated at 1,000 °C. The powder precursors were characterized by TG/DTA. A decrease in the DTA peak temperature with the amount of zinc was observed. After the thermal treatment, the characterizations were performed by XRD, IR, colorimetry and UV/VIS spectroscopy. The XRD patterns of all the samples showed the presence of the spinel phase. Infrared spectroscopy showed the presence of ester complexes for Zn₂TiO₄ after thermal treatment at 500 °C, which disappeared after cobalt addition, indicating that organic material elimination was favored.     

Zum Aufbau schlecht geordneter Calciumhydrogensilicate. I. Bildung und Eigenschaften einer schlecht geordneten Calciumhydrogendisilicatphase

On the Structure of Ill-crystallized Calcium Hydrogen Silicates. I. Formation and Properties of an Ill-crystallized Calcium Hydrogen Disilicate Phase Investigations on ill-crystallized calcium hydrogen silicates (C? S? H phases) prepared by precipitation from sodium silicate solutions with calcium chloride have shown that at temperatures 0°C primarily hydrogen silicates with such an anion composition will be formed, which had been present before in the sodium silicate solution. They are not stable. On storing the precipitate in the mother liquid at 0°C they are converted into disilicate with a composition of 1.1–1.5 CaO/SiO₂, if the concentration of Ca(OH)₂ is more than 0.8 g/l. After drying the thermally very instable solid at ?10°C the calcium hydrogen disilicate phase can be isolated. A structure proposal for this phase is given.     

Thermal characterization of bacterial cellulose–phosphate composite membranes

Cellulose–phosphate composite membranes have been prepared from bacterial cellulose membranes (BC) and sodium polyphosphate solution. The structure and thermal behavior of the new composites were evaluated by X-ray diffraction (XRD), ³¹P-nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical analysis (TMA). From XRD analyses the Iα and Iβ cellulose crystalline phases were identified together with crystalline sodium phosphate that covers the cellulose microfibrils as revealed by SEM. ³¹P NMR spectra show peaks assigned to Q⁰ and Q¹ phosphate structures to be compared to the Q² units that characterize the precursor polyphosphate. Glass transition temperature, T _g, obtained from TMA curves and thermal stability obtained from TG and DSC measurements, were observed to be dependent on the phosphate content.     

Iron oxide pigmenting powders produced by thermal treatment of iron solid wastes from steel mill pickling lines

Phase changes of iron containing solid wastes from steel mill pickling lines after thermal treatments were investigated aiming the determination of the appropriate conditions for its transformation to be useful for industrial raw materials. Above 275°C, the thermally treated wastes contain a mixture of α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite) in different proportions, depending on the maximum heating temperature of the thermal treatment. Increasing the maximum temperature the maghemite participation is decreased through its transformation to hematite. Above 850°C hematite is the main constituent, suggesting that thermal treatment of the wastes in this temperature will give a product that could be used as red iron pigment.     

Structure and Electron Spin Resonance of Annealed Sol-Gel Glasses Containing Ag

In this work, SiO₂ samples with silver, prepared using the sol-gel method, were analyzed after being thermally treated in air in the range of 100 to 800°C. The sol-gel starting solutions were prepared by mixing tetra-ethyl-orthosilicate (TEOS), water and ethanol. Samples with 4 different H₂O/TEOS molar ratios (3.3, 5, 7.5 and 11.7 respectively) and with different nominal Ag concentrations were prepared (1, 2 and 4%vol. of Ag). It was found that upon annealing, different silver spices were formed, such as Ag₂ ⁺, Ag⁺, Ag°, and metallic silver aggregates. The identification of these spices was carried out by means of X-ray diffraction, Electron Paramagnetic Resonance (EPR), optical emission and optical absorption. It was also found that the specific type of silver spices observed depends on the structure of the SiO₂ matrix and on the annealing temperatures. It was found that samples prepared from precursor solutions with a low H₂O/TEOS ratio have a more open structure, and therefore silver diffuses faster and forms agglomerates at lower temperatures. Samples prepared from solutions with larger H₂O/TEOS ratios have a more dense structure, which allows the formation of atomic or molecular spices in addition to silver particles. A systematic study of this system was carried out using EPR on samples prepared from solutions having different H₂O/TEOS molar ratios, various Ag concentrations and subjected to different thermal treatments.     

Crystallization kinetics of Ag-doped Se–Bi–Te chalcogenide glasses

Effect of Ag doping on the crystallization kinetics of amorphous Se_80.5Bi_1.5Te_18?yAg_y (for y = 0, 1.0, 1.5, and 2.0 at.%) glassy alloys has been studied by differential scanning calorimetry (DSC). The DSC curves recorded at four different heating rates are analyzed to determine the transition temperature, activation energy, thermal stability, glass forming ability, and dimensionality of growth during phase transformation. Present study shows that the thermal stability and the glass-forming ability increase with an increase in the Ag content which is in agreement with the earlier studies. Our results show that Se_80.5Bi_1.5Te₁₆Ag₂ composition is thermally more stable and has a little tendency to crystallize in comparison to other compositions under study. The increase in thermal stability with increasing Ag concentration is attributed to an increase in the cohesive energy.     

Porosity, structural and fractal study of sol-gel TiO2-CeO2 mixed oxides

Sol-gel TiO₂-CeO₂ materials were synthesized at pH=3 employing HNO₃ as hydrolysis agent. Gels were thermally treated at 473, 673, 873, and 1073 K, respectively. Morphologies of the final substrates were studied via N₂ sorption, XRD and TEM. N₂ isotherms indicated a steady porosity in TiO₂-CeO₂ samples treated up to 873 K. Adsorption-desorption isotherms and TEM micrographs were used to perform fractal analyses of annealed samples. A dominant anatase phase was detected by XRD between 473 and 873 K while a rutile phase was evident at 1073 K. The presence of cerium conferred an increased thermal stability to the TiO₂ materials against particle sintering and pore collapse. The structure of cerium-doped anatase lattice was visualized through crystal simulation to investigate the possible substitution of Ti⁴⁺ by Ce⁺⁴ ions. This effect and the progressive segregation of CeO₂ crystals with temperature on the surface of TiO₂ grains lead to substrates of assorted morphologies.     

Structural characterization of silica modified polyimide membranes

Polyimide and hybrid polyimide‐siloxane were synthesized by polycondensation, imidization, and sol‐gel reaction. The polyimides were prepared from pyromellitic dianhydride (PMDA) and 4,4‐oxydianiline (ODA) in N‐methyl‐2‐pyrollidone (NMP). Trimethoxyvinyl silane (TMVS) was used as a source of silica. Their surface morphologies, structures and thermal performances were determined using scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the silica particles were finely and rather homogeneously dispersed in polymers. The glass transition temperature (T_g) of hybrid membrane materials increased with the increasing silica content. TGA analysis showed that polyimides were thermally stable with silica. Modified polyimide‐siloxane films, thermal characteristics were found to be better than the polyimide films without silica. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and Properties of Poly(4,8-dialkoxy-1,5-naphthalenevinylene)s

Novel conjugated materials, poly(4,8-dialkoxy-1,5-naphthalenevinylene)s (OC_n-PNV, n = 4, 6, 8, and 12), have been prepared by a method similar to the Gilch procedure. The structure, optical and thermal properties of these polymers with various alkoxy side chain lengths have been evaluated by IR, UV-Vis absorption, fluorescence emission and thermogravimetric analysis. The band gap of OC_n-PNV increases with increasing side chain length. Moreover, wavelengths of the photoluminescence (PL) emission peaks (λ_max) of OC_n-PNV solutions decrease with increasing alkoxy side chain length. This is probably due to the entanglement of long side chains that causes distortion of the conjugated main chains and thereby raises band gap of the polymer. PL λ_max's of these polymers in film state are red-shifted by 14–59 nm than those in solution state. The red-shift is due to the more chain aggregations after spin coating from solution into film state and consequently the lower band gap in the film state. Besides, the polymer with shorter side chains is more thermally stable than that with longer side chains.