Synthesis of silica aerogel blanket by ambient drying method using water glass based precursor and glass wool modified by alumina sol

Silica aerogel blankets have been synthesized by ambient drying technique using cheap water glass as the silica source and glass wool modified by alumina sol. One step solvent exchange and surface modification were simultaneously conducted by immersing the wet hydrogel blanket in EtOH/TMCS/hexane solution. The synthesized silica aerogel blanket was light with the density of 0.143-0.104 g/cm³ and 89.4-95% porosity. The microstructure of silica aerogel blanket exhibits a porous structure consisting of glass fibers of diameter ∼2.5 μm interconnected with solid silica clusters (5-20 μm).     

Sulfated silica-titania aerogel as a bifunctional oxidative and acidic catalyst in the synthesis of diols

Sulfated silica-titania aerogel (SO₄/ST) catalyst was prepared by direct synthesis and modified with H₂SO₄ by wet impregnation method. Brønsted acid sites were generated after sulfation of the silica-titania aerogel with a pKa of −14.52. Consecutive transformation of 1-octene, catalyzed by sulfated silica-titania aerogel using aqueous hydrogen peroxide as oxidant shows high activity towards 1,2-octanediol through the formation of 1,2-epoxyoctane. The formation of 1,2-octanediol is enabled by the co-existence of sulfated Ti species with Brønsted acid sites in the SO₄/ST system. Sulfated silica-titania aerogel catalyst produced 1,2-octanediol (326 μmol) with selectivity of 63%. In contrast, no diol was produced when silica-titania aerogel was used.     

Synthesis of sodium silicate-based hydrophilic silica aerogel beads with superior properties: Effect of heat-treatment

This work demonstrates the synthesis of hydrophilic and hydrophobic high surface area silica aerogel beads with a large pore volume. Wet gel silica beads were modified and heat-treated under atmospheric pressure after modification of the surface by trimethychlorosilane (TMCS). The effects of heat treatment on the physical (hydrophobicity) and textural properties (specific surface area, pore volume, and pore size) of silica aerogel beads were investigated. The results indicated that hydrophobicity of the silica aerogel beads can be maintained up to 400 °C. The hydrophobicity of the silica aerogel beads decreased with increasing temperature in the range of 200-500 °C, and the beads became completely hydrophilic after heat treatment at 500 °C. The specific surface area, cumulative pore volume, and pore size of the silica aerogel beads increased with increasing temperature. Heating the TMCS modified bead gel at 400 °C for 1 h resulted in silica aerogel beads with high surface area (769 m²/g), and large cumulative pore volume (3.10 cm³/g). The effects of heat treatment on the physical and textural properties of silica aerogel beads were investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric and differential analysis (TG-DTA), Fourier-transform infrared spectroscopy (FT-IR), and Brunauer, Emmett and Teller (BET) and BJH nitrogen gas adsorption and desorption methods.     

Synthesis of window glazing coated with silica aerogel films via ambient drying

An ambient drying process (1 atm, 270 °C) has been developed in order to synthesize window glazing coated with silica aerogel films. The aerogel film could be manufactured by this process of wet gel films obtained via a dip-/spin-coating of the silica sol on a glass slide. Before drying, the isoproponol solvent in wet gels was exchanged with n-heptane to minimize the drying shrinkage. The thickness, refractive index, and porosity of silica films were 0.16–10 μm, 1.08–1.09, and 80–84%, respectively. The transmittance of window glazing was over 90% and we could predict that the optimal thermal conductivity (0.2 W/(m K)) of the window glazing would be obtained at the aerogel thickness of 100 μm (0.016 W/(m K)).     

The effect of chemical distribution on the magnetocaloric effect: A case study in second-order phase transition manganites

Ferromagnetic manganites of general formula ${\text{ABMnO}}_3$ (where A is a trivalent rare-earth ion and B is a divalent dopant) are candidates for magnetic cooling applications, since they can present either second- or first-order magnetic phase transitions, and the perovskite structure allows for substantial chemical substitution and tuning of the magnetocaloric properties. The consequent chemical distribution from substitution affects the magnetic and magnetocaloric properties of the compound. The change of relative cooling power with chemical disorder is discussed by the use of the molecular mean-field model. We present experimental results of the ferromagnetic, second-order phase transition ${\text{La}}_{0.70-x}(\text{Er,}\text{Eu}{)}_x{\text{Sr}}_{0.30}{\text{MnO}}_3$ system.     

Investigation of surface treatment effect of catalyst on the lifetime for Cat-CVD method

In case of amorphous silicon (a-Si) film deposition by catalytic chemical vapor deposition (Cat-CVD) method, a metal catalyzing wire is converted to silicide and this silicidation causes shortening lifetime of the catalyzing wire. In the present work, the effect of surface carbonization of catalyzing wire against silicide formation is investigated to obtain long-life catalyzer. Characteristics of a-Si film deposited by carbonized tungsten (W) catalyzer are also investigated. Silicide layer thickness formed on carbonized catalyzing wires after 60 min a-Si film deposition decreases to half of that on uncarbonized wires. Device quality a-Si films having defect density less than 4 × 10¹⁵ cm^?3 are obtained by using carbonized W, indicating that surface carbonization of W catalyzer is effective process for industrial application of Cat-CVD method.     

Effects of metal precursor in the sol–gel synthesis on the physicochemical properties of Pd/Al2O3–CeO2 catalyst: CO oxidation

The object of this research was to investigate the effects of various precursors and different fabricating procedures of Pd/Al₂O₃–CeO₂ catalysts by the sol–gel method. The physicochemical properties and structures of catalyst were characterized with BET surface area, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The performance of the Pd/Al₂O₃–CeO₂ catalyst was also evaluated by CO oxidation tests with a continuous quartz reactor. The results indicated that the catalyst prepared with inorganometallic precursors showed a high dispersion of Pd, large surface area and pore volume, and a high activity in CO oxidation. The higher redox interaction between Pd and Ce of the support starting with inorganometallic precursors, as determined from X-ray powder diffraction, is suggested as being responsible for such a catalytic behavior.     

Silica xerogels of tailored porosity as support matrix for optical chemical sensors. Simultaneous effect of pH, ethanol:TEOS and water:TEOS molar ratios, and synthesis temperature on gelation time, and textural and structural properties

The sensing of a chemical environment is achieved mainly in the surface by interactions of the sensor material with its chemical surroundings. Therefore, porous structure control is key in developing good chemical sensors. The aim of this work was to obtain materials of tailored porosity to be used as support matrix for optical chemical sensors. We studied the simultaneous effect of pH, temperature, ethanol:TEOS, and water:TEOS molar ratios on gelation time, and textural and structural properties. We used a 2⁴ factorial design that evaluates the effect of each independent variable and their interactions. Samples were characterized by XRD, SEM, FTIR, and gas adsorption (N₂ at 77 K and CO₂ at 273 K). The gelation time decreased with increasing temperature, water:TEOS molar ratio, and pH; and with decreasing ethanol:TEOS molar ratios. Synthesis conditions also affected the xerogels porous textures. Xerogels obtained at pH 2.5 were ultramicroporous. In general, samples synthesized at pH 4.5 and ethanol:TEOS molar ratio of 2.25:1 were mesoporous, but the material is not appropriate for use as support in fiber optical sensors.     

Synthesis of Pt-containing mesoporous silica using Pt precursor as a pore-forming agent

We synthesized Pt nanoparticle-containing mesoporous silica in a one-pot process using tetraammineplatinum(II) hydroxide (TPH) precursor as a pore-forming agent and silica nanospheres as a silica source. The TPH precursor was added into as-prepared colloidal silica sol with silica nanospheres (SN) of about 8 nm in particle diameter, to obtain the SN–TPH sol. During drying process of the SN–TPH sol, an amorphous SN–TPH nanocomposite was formed via hydrogen-bonding interaction between silanol groups and amine groups of the TPH precursor. The hydrogen-bonding interaction was confirmed by thermal gravimetry and differential thermal analysis (TG–DTA) profiles and Fourier transform infrared (FTIR) spectra. Using the TPH precursor as a pore-forming agent, incorporation of the Pt nanoparticles into the mesoporous silica can be simultaneously achieved with the synthesis of the mesoporous silica in a one-pot process. In addition, Pt nanoparticle size and pore diameter of the mesoporous Pt/silica were simultaneously controlled by simply varying the concentration of the TPH precursor. The pore diameter of the mesoporous silica was easily controlled from 3.2 nm to 6.5 nm with an increase in the TPH concentration.     

Silica aerogels prepared via rapid supercritical extraction: Effect of process variables on aerogel properties

We have examined experimentally the effects of rapid supercritical extraction (RSCE) process variables and their resulting pressure and temperature characteristics on aerogel properties. We employ an RSCE process that uses a hydraulic hot press to seal and heat a contained mold until the aerogel precursors reach a supercritical state. After a short stabilization period the hot press restraining force is lowered and the supercritical fluid is allowed to escape, leaving behind an aerogel monolith. The entire process can be accomplished in fewer than 3 h. To control the process, we set the restraining force, the maximum temperature, the heating and cooling rates, the pressure release rate and the mold volume fill ratio (related to the amount of initial precursor material). To investigate the effects of these variables we made silica aerogels from a TMOS-based recipe. We varied the volume of precursor material from 10 to 15 mL (60-97% fill volume), the restraining force from 43 to 111 kN, the temperature heat rate from 0.7 to 4.2 °C/min, the maximum temperature from 288 to 371 °C and the pressure release rate from 0.23 to 0.66 MPa/min. The RSCE process is robust. We were able to make transparent, monolithic aerogels under almost all conditions with little effect on the resulting aerogel properties. Typical density measurements yielded values of approximately 0.065 g/mL (bulk) and 1.9 g/mL (skeletal). The samples were translucent and transmitted 70% of the light at 800 nm (for 5-mm thick samples). The BET surface areas ranged from 517 to 590 m²/g. Maximum temperature was the only variable found to have a significant effect on the aerogels’ properties. As the maximum temperature increased from 288 to 371 °C the surface area decreased from 560 to 395 m²/g and average pore diameter (BJH desorption) increased from 21 to 32 nm.     

The effect of acidity on the structural and textural evolution of titania in the presence of primary amine and inorganic precursor

Titania was synthesized from laurylamine hydrochloride (LAHC) and Ti(SO₄)₂ under different acidic conditions. The effect of acidity on the structural and textural evolution of titania has been investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron micrographs (TEM), FTIR spectroscopy and thermogravimetric analysis (TGA). With increasing the pH value in the initial mixture, the obtained samples transformed from nanoparticles with intra-particle mesostructures (pH 0.6 and 2.0) to nanoparticles with nonporous structure (pH 3.7), and finally to worm-like porous materials with inter-particle mesostructures (pH 4.2) resulted from the aggregates of nanoparticles. The obtained mesoporous nanoparticles (pH 0.6 and 2.0) have mean diameter of ca. 25 nm, and the pore size distributions are bimodal with fine intra-particle pores and larger inter-particle pores. The intra-particle mesostructure not only retard the growth of nanocrystallites, but also prevent phase transition of anatase to rutile at high temperature. The BET surface area of the TiO₂ calcined at 300 °C decreased from 212 to 74 m²/g with pH increasing from 0.6 to 4.2.     

Luminescence of SnO2: Eu; dependence on the oxidation state of the precursor

Preparation conditions and phase composition of polycrystalline SnO₂: Eu luminophores are investigated. The results show that the luminescence intensity of SnO₂: Eu obtained from Sn(II)-containing precursors, (hydroxide or oxide), is considerably higher than that from Sn(IV) oxide hydrate. It is considered that the creation of luminescence centers in SnO₂: Eu is connected to the formation of intermediate Sn(II)—Sn(IV) oxides during the oxidation.     

Preparation of super hydrophobic silica aerogel and study on its fractal structure

The experimental results on silica aerogels with super hydrophobic property are reported. Silica alcogels were prepared via a two-step acid/base process by keeping the molar ratio of tetraethyoxysiliane (TEOS), ethanol (EtOH), water (H₂O), hydrochloric acid (HCl) and ammonia (NH₄OH) constant at 1:6:8:1.0 × 10^?3:1.1 × 10^?2, respectively, and varying the molar ratio of N,N-dimethylformamide (DMF)/TEOS (G) from 0 to 1.2. After two aging treatment steps, they were modified by isopropyl alcohol (IPA)/trimethylchlorosilane (TMCS)/n-hexane solution at 60 °C. It was found that G value at 0.8 resulted in low density (～0.2 g cm^?3) and the minimum volume shrinkage (～6%), with the total water adsorption ratio ～5.1% when exposed to water for 3 months and the contact angle θ ≈ 178°. Besides, the aerogels (G = 0.8) had higher volume fractal dimension (～1.8), which indicted that it possessed better connectivity and more uniform particle sizes.     

Highly swellable sol–gels prepared by chemical modification of silanol groups prior to drying

Sol–gel materials that swell six times their dried volume when placed in organic solvents were prepared using the bridged silsesquioxane bis(trimethoxysilyethyl)benzene through base catalysis by tetrabutyl ammonium fluoride. Prior to drying the gels, water and catalyst were rinsed from the solvated matrix and residual silanol groups were derivatized with a chlorosilane (R–Si(CH₃)₂Cl). The swelling behavior was completely reversible when the materials are dried at elevated temperature. Swelling is highly dependent on the processing conditions, including the choice of solvent and catalyst. There is no preferential adsorption of solute molecules to swelled sol–gels despite the diversity of chlorosilanes used to derivatize the materials.     

New triclinic modification of lead iodate Pb(IO3)2: Synthesis and crystal structure

A new triclinic modification of lead iodate Pb(IO₃)₂ (space group $C\bar 1$ ) is obtained under hydrothermal conditions. The crystal structure is determined without preliminary knowledge of the chemical formula. [IO₃]^? groups, which are characteristic of pentavalent iodine, have a typical umbrella-like configuration. The new phase has a more complex structure than the known orthorhombic modification. The arrangement of heavy Pb and I atoms follows a’ = a/3 pseudoperiodicity. In the layers of two types that form sheets parallel to the ab plane, Pb and I atoms have different coordinations. A polytypic nature of the new modification is responsible for the one-dimensional disordering along the a axis as well as different variants of layer alternation. It is possible to obtain crystals of acentric and polar derivatives of the centrosymmetric phase that will be promising for application.     

Synthesis of nonstoichiometric zirconium carbide whiskers by chemical vapor deposition

Nonstoichiometric zirconium carbide crystals with various compositions were prepared by chemical vapor deposition. Two gaseous mixtures, zirconium tetrachloride and argon, toluene and hydrogen, were introduced to the reaction zone where a graphite substrate was heated between 1200 and 1400°C. The deposition rate was proportional to the partial pressure of toluene. The compositional ratio of n_C/n_Zr in the gaseous mixture from 2.0 to 6.0 was found to be optimum for producing needle-like crystals. Needle-like crystal with smaller size were formed when the ratio of n_C/n_Zr was smaller than 2.0, and less needle-like crystals accompanied with more carbon were also produced when the ratio of n_C/n_Zr was larger than 6.0. The temperature of the substrate suitable for the growth of needle crystals was in the range from 1250 to 1300°C. The lattice constants of the products varied as a function of the ratio of n_C/n_Zr in the gaseous mixtures.     

Synthesis of dense polycrystalline GaN of high purity by the chemical vapor reaction process

A process for producing high-purity, dense polycrystalline gallium nitride is proposed. Dense polycrystalline gallium nitride was produced by the reaction of ammonia, gallium metal, and a halide source in a quartz boat containing metallic gallium. The process is called the chemical vapor reaction process. The hard crust-like pieces of polycrystalline GaN obtained are of high purity, can be used as source material for single-crystal growth by the ammonothermal technique, sublimation, sputtering, and pulse laser deposition.     

Homoepitaxial growth of 6H–SiC thin films by metal-organic chemical vapor deposition using bis-trimethylsilylmethane precursor

Homoepitaxial silicon carbide (SiC) films were grown on 3.5° off-oriented (0 0 0 1) 6H–SiC by metal-organic chemical vapor deposition (MOCVD) using bis-trimethylsilylmethane (BTMSM, C₇H₂₀Si₂). A pronounced effect of the growth conditions such as source flow rate and growth temperature on the polytype formation and structural imperfection of the epilayer was observed. The growth behavior was explained by a step controlled epitaxy model. It was demonstrated by high-resolution X-ray diffractometry and transmission electron microscopy that high-quality 6H–SiC thin films were successfully grown at the optimized growth condition of substrate temperature 1440°C with the carrier gas flow rate of 10 sccm.     

1H-1,2,3-triazole,a promising precursor for chemical vapor deposition of hydrogenated carbon nitride

Well-crystallized hydrogenated carbon nitride thin films have been prepared by microwave plasma enhanced chemical vapor deposition (MWPECVD). 1H-1,2,3-triazole+N₂ and Si (1 0 0) were used as precursor and substrate, respectively. Substrate temperature during the deposition was recorded to be 850 °C. The synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photo-electron spectroscopy (XPS) analyses. The plasma compositions were checked by optical emission spectroscopy (OES). XRD observation strongly suggests that the films contain polycrystalline carbon nitride with graphitic structure of (1 0 0), (0 0 2), (2 0 0) and (0 0 4). XPS peak quantification reveals that the atomic ratio of the materials C:N:O:Si is 32:41:18:9. X-ray photo-electron peak deconvolution shows that the most dominant peak of C (1s) and N (1s) narrow scans correspond to sp² hybrid structure of C₃N₄. These observations indicate that 1H-1,2,3-triazole favors the formation of hydrogenated carbon nitride with graphitic phase by CVD method and thus is in good agreement with XRD results. SEM of surface and OES of plasma also support the formation of polycrystalline carbon nitride films from 1H-1,2,3-triazole+N₂ by CVD.     

The effect of polyacrylamide on the crystallization of calcium carbonate: Synthesis of aragonite single-crystal nanorods and hollow vatarite hexagons

CaCO₃ nanorods were synthesized via a facile solution route by polymer-controlled crystallization in the presence of polyacrylamide (PAM). The morphology, size and crystal structure were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results suggest that the as-synthesized product was CaCO₃ (aragonite) nanorods with diameter ca. 50 nm and length ca. 1 μm. Selected area electron diffraction (SAED) pattern shows the single-crystal nature of CaCO₃ nanorods. The reaction time, temperature, pH and reactant concentration were systemically investigated. With the increase in the reaction time, hollow vaterite hexagonal disks can be obtained.