Fabrication of high-purity silica glass through the WSPA-sol-gel process

High-purity and large-size silica glass was prepared by a wet process silica and pH adjustment (WSPA)-sol-gel process which involved the following steps: (1) colloidal silica synthesis through the hydrolysis reaction of TEOS catalysed by ammonia solution; (2) sol preparation through the hydrolysis reaction of TEOS by hydrochloric acid; (3) mixing the colloidal silica and sol solution; (4) adjusting the pH values of the mixed solution to 4–6; (5) gelling; (6) drying to a dry gel; (7) heat treatment of the gel to collapse the pores, finally to become a silica glass. The purity of the derived silica glass was examined in relation to the metallic impurities and -OH impurities. The relation between ultraviolet absorption of silica glass and metallic impurities was investigated. Ti addition to the silica glass gave a strong absorption at 200 m, for which the ultraviolet absorption coefficient, , was found to be 1.57×10⁴ l mol^–1 cm^–1. The effects of the properties of colloidal silica on the -OH concentration and also the relations between the sintering conditions and residual -OH concentration in silica glass were examined. Using colloidal silica with a large particle size and heat treatment in vacuum resulted in a silica glass with a low concentration of residual -OH.     

含Si-O-P键的减反膜结构及性能影响因素研究

采用SiO₂水溶胶(ACS)为硅源, H₃PO₄为桥联剂, H₂O₂为活化剂在玻璃表面成功制备了一种性能优异的新型减反膜。利用FTIR、XRD、FESEM、TEM、AFM对薄膜结构、形成机理及性能进行了研究, 结果表明, 在成胶过程中, H₂O₂的导入有效修复了SiO₂胶粒的表面羟基, 提高了SiO₂的反应活性; 而在焙烧过程中, H₃PO₄通过其自身脱水形成的偏磷酸链状体分别与SiO₂胶粒及玻璃基底表面的Si-OH进行了脱羟基缩聚, 构架了坚固的Si-O-P网络交联, 最终形成了稳定的磷硅酸盐凝胶网络结构, 提高了成膜质量。当n(H₃PO₄) : n(H₂O₂) : n(EtOH) : n(SiO₂)= 0.49: 0.52: 30: 1时, 制备的SiO₂减反膜在可见光区平均透光率高达98%, 硬度可达6H。     

Effect of colloidal silica on the mechanical properties of fiber–cement reinforced with cellulosic fibers

The effect of colloidal silica on the hydration reaction of the Portland cement system and its effect on the resulting mechanical properties are not completely understood. Silica nanoparticles can affect the behavior and performance of fiber–cement, such as the calcium–silicate–hydrate gel of the matrix and the fiber–matrix interface bonding. The main objective of this study is to evaluate the effects of various contents of colloidal silica (0, 1.5, 3, 5, and 10 % w/w) on the microstructure and mechanical performance of cement composites reinforced with cellulosic pulp. Fiber–cement composites with unbleached eucalyptus Kraft pulp as the micro-fiber reinforcement were produced by the slurry dewatering technique followed by pressing. The average values of the modulus of rupture of the fiber–cement decreased with increasing colloidal silica content. However, the pullout of the fibers increased significantly in the fiber–cement composites with additions between 3 and 10 % w/w of colloidal silica suspension, as indicated in the scanning electron microscopy images and by the improvement in the energy of fracture values.     

Silica gel functionalized with 4-phenylacetophynone 4-aminobenzoylhydrazone: Synthesis of a new chelating matrix and its application as metal ion collector

The silica gel surface immobilized with 4-phenylacetophynone 4-aminobenzoylhydrazone (PAAH) after surface modification by 3-chloropropyltrimethoxysilane (CPTS). The modified silica gel was used for sorption of Cu(II), Ni(II) and Co(II) in aqueous solution. The effect of solution pH, sorption time, temperature and initial metal ion concentration onto metal ions sorption was investigated. The characteristics of the sorption process were evaluated by using the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) adsorption isotherms. The sorption of metal ions onto modified silica gel correlated well with the Langmuir type adsorption isotherm and adsorption capacities were found to be 0.012, 0.014 and 0.018 mmol g⁻¹ for Cu(II), Ni(II) and Co(II) metal ions, respectively. From the D–R adsorption isotherms, it was concluded that chemical interactions and chelating effects were playing an important role in the sorption of metal ions onto modified silica gel.

Thermodynamic parameters such as the standard free energy change (ΔG)°, enthalpy change (ΔH°) and entrophy change (ΔS°) were calculated to determine the nature of sorption process. From these parameters, ΔH° were found to be endothermic values: 38.39, 18.0, and 14.7 kJ mol⁻¹ for the same sequence of divalent cations and ΔS° values were calculated to be positive for the sorption of each metal ion onto the modified silica gel. Negative ΔG° values indicated that sorption process for all metal ions were spontaneous in nature although they presented an endothermic enthalpy for the interaction, resulting in an entropically favoured process.     

Dielectric and piezoelectric properties of sol–gel derived Ca doped PbTiO3

Synthesis of Ca doped PbTiO₃ powder by a chemically derived sol–gel process is described. Crystallization characteristics of different compositions Pb_1−xCa_xTiO₃ (PCT) with varying calcium (Ca) content in the range x = 0–0.45 has been investigated by DTA/TGA, X-ray diffraction and scanning electron microscopy. The crystallization temperature is found to decrease with increasing calcium content. X-ray diffraction reveals a tetragonal structure for PCT compositions with x ≤ 0.35, and a cubic structure for x = 0.45. Dielectric properties on sintered ceramics prepared with fine sol–gel derived powders have been measured. The dielectric constant is found to increase with increasing Ca content, and the dielectric loss decreases continuously. Sol–gel derived Pb_1−xCa_xTiO₃ ceramics with x = 0.45 after poling exhibit infinite electromechanical anisotropy (k_t/k_p) with a high d₃₃ = 80 pC/N, ′ = 298 and low dielectric loss (tan δ = 0.0041).     

Evolution of ettringite in presence of carbonate, and silicate ions

The main objective of this work was to study the evolution of ettringite when in contact with a solution containing carbonate and silicate ions.

Ettringite was synthesised and put in contact with three types of saturated solutions: (a) CaCO₃ and silica gel saturated solution; (b) MgCO₃ and silica gel saturated solution and (c) C–S–H gel plus portlandite and CaCO₃ saturated solution. The temperature of the experiment was 4 ± 2 °C. At different ages the samples were studied by: FTIR, XRD, NMR, and SEM/EDX.

Ettringite evolves with time, reacting with carbonates and silicates and decomposing to poorly crystallised products when it is in contact with solutions (a) and (b). Ettringite decomposition rate is much higher when it is in contact with saturated magnesium carbonate solution (b) than when in contact with the solution (a). After 90 days of exposure in solution (b) ettringite decomposition starts, followed by reorganization of the atoms giving place to a semi-stable poorly crystallised compound. However 130 days are necessary for ettringite decomposition in solution (a). Ettringite in contact with solution (c) evolves more slowly and it almost remains unchanged after 380 days of treatment. Ca(OH)₂ formed in the C₃S and C₂S hydration retards ettringite decomposition.     

Optical properties of Er-doped SiO2-GeO2-Al2O3 planar waveguide fabricated by sol–gel processes

In this paper, we report silica based planar waveguides doped with Er³⁺, and co-doped with GeO₂ and Al₂O₃. These sol–gel derived planar waveguides were fabricated on SOS (silica on silicon) using multiple spin-coating and rapid thermal processing (RTP). Investigation has been made on their characteristics in terms of their application in optical amplification and lasing, including photoluminescence (PL), fluorescence lifetime, refractive index, propagation loss, surface roughness, Fourier transform infrared (FTIR) spectrum and X-ray diffraction (XRD) analysis. The propagation loss of a 20-layer planar waveguide was measured to be about 1.6 dB/cm for TE₀ and 2.2 dB/cm for TM₀ mode. A strong emission transition (⁴I_13/2→⁴I_15/2) at 1.536 μm with a lifetime of 3.6 ms has been obtained for an optimized molar composition of 90SiO₂: 10GeO₂: 20AlO_1.5: 1ErO_1.5.     

Photoluminescence characteristics of Ti2S3 nanoparticles embedded in sol–gel derived silica xerogel

Ti₂S₃ nanocrystallites embedded in sol–gel derived silica xerogel have been prepared. Their photoluminescence (PL) characteristics have been evaluated and compared with those of pure silica xerogel. UV–vis absorption spectra, transmission electron micrograph, excitation spectra and PL spectra of the doped and undoped samples have all been investigated. Two emission peaks have been observed from the doped samples, one at 440 nm (λ_ex=380 nm) while the other at 600 nm (λ_ex=550 nm). The latter has been assigned to the Ti₂S₃ nanocrystallites in the silica xerogel. Therefore, a novel luminescence property can be observed by introducing the semiconductor nanoparticles into the silica xerogel.     

Multiscale characterization of carbonated wollastonite paste and application of homogenization schemes to predict its effective elastic modulus

This paper describes the multiscale characterization of the carbonated wollastonite paste using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), and statistical nanoindentation (SNI, also known as ‘grid indentation’) methods as well as micromechanical homogenization models. Wollastonite (CaSiO₃) fibers are commonly used as filler in ceramics or plastics. However, wollastonite can also be regarded as non-hydraulic binder material since upon carbonation it forms a heterogeneous matrix with mechanical properties similar to those of the conventional hydrated cement pastes. Carbonation reaction of wollastonite results in the formation of two main products: calcium carbonate (CaCO₃) and amorphous silica gel (SiO₂). The SEM/EDS microanalysis performed on this system revealed that the average calcium to silica (Ca/Si) atomic ratio of the silica gel phase was around 0.40. Three individual carbonated wollastonite paste samples, each representing a different degree of carbonation were selected for nanoindentation tests. The obtained elastic moduli for silica gel, calcium carbonate, and unreacted wollastonite grains were, respectively, 41.7 GPa, 67.3 GPa, and 134.7 GPa. The micromechanical homogenization models were then utilized to predict the effective (also referred to as ‘homogenized’) elastic moduli of the carbonated wollastonite paste. The predicted values of the effective elastic moduli of carbonated wollastonite pastes were found to be in the range of corresponding values for hydrated high to ultra-high performance cement pastes. Additionally, the values of the effective elastic moduli of the carbonated wollastonite pastes were observed to increase with the increase in the degree of carbonation.     

Luminescence of composites based on oxide aerogels incorporated in silica glass host matrix

This paper deals with the elaboration and photoluminescence (PL) examination of oxide powder (OP = ZnO, Al₂O₃, SnO₂, TiO₂) incorporated in silica host matrix. OP, in the first step, was prepared by a sol–gel method using supercritical drying of ethyl alcohol. The obtained powder, in a second step, was incorporated in silica aerogel monolith using tetraethylorthosilicate as SiO₂ precursor and ethyl alcohol supercritical conditions for drying. In the third step, silica aerogel containing oxide powders were heated under natural atmosphere at 1200 °C for 2 h to form the composites that exhibited a strong PL bands at Vis–IR range. Photoluminescence excitation (PLE) measurements show different origins of the emission. It was suggested that OH-related radiative centres and non-bridging oxygen hole centres (NBOHCs) defects resulting from thermal treatment and crystallization at the interfaces between OP and silica host matrix, were responsible for the bands at 400–600 and 700–900 nm respectively.     

Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled‐Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, in situ mechanical compression on the transmission electron microscope and aberration‐corrected scanning transmission microscope are unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the calcium carbonate (CaCO₃)‐decorated silica (SiO₂) colloidal capsule. The stiff and brittle nature of the colloidal capsule is due to the interfacial chemical bonding between the CaCO₃ nanoparticles and SiO₂ inner shell. Such bonding strengthens the mechanical strength of the SiO₂ shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO₂ shell (310 ± 70 nm) from the silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat‐treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.     

A study of internal friction in polypropylene (PP) filled with nanometer-scale CaCO3 particles

The internal friction and relative elastic modulus of polypropylene (PP) filled with nanometer-scale calcium carbonate (nm-CaCO₃) particles in different contents (0, 4, 7, and 15 vol.%) are measured in the temperature range 150–400 K with a torsion pendulum. The peak associated with the glass transition and a small peak (′ peak) associated with the pre-melting process in crystalline parts of PP was observed around 290 and 370 K, respectively. At temperatures lower than 270 K, no peaks were observed. With increasing content of nm-CaCO₃ particles, the apparent activation energy of the peak decreases, and after passing a minimum of 4.7 eV at 4 vol.% of nm-CaCO₃, it increases. In contrary to this behavior, the peak temperature has a maximum of 289 K at the same filler fraction. Correspondingly, the highest tensile and flexural strength of PP were obtained around this content. These observations may be understood through the influences of fillers on the degree of crystallization of PP and on the mobility of molecules of PP.     

Controllable formation of Er–Yb codoped Al2O3 films by the non-aqueous sol–gel method

1 mol%Er³⁺–10 mol%Yb³⁺ codoped Al₂O₃ thin films have been prepared on thermally oxidized SiO₂/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC₃H₇)₃] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er³⁺–Yb³⁺ codoped Al₂O₃ thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC₃H₇)₃. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films, which is unrelated to the addition of DMF. Controllable formation of the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films may be explained by the fact that the DMF assisted the deprotonation process of Al–OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films.     

Using phenol–formaldehyde resin as carbon source to synthesize mesoporous carbons of different pore structures

In this research communication, we performed the phenol–formaldehyde (PF) resin as an alternative carbon source and various mesostructured silicas as the nano-templates to conveniently prepare the mesoporous carbons of high surface area (850–1500 m² g⁻¹), large pore size (2.0–22.0 nm) and great pore volume (0.65–1.15 cm³ g⁻¹). It was reasonably supposed that there exist interaction matching between the negative-charged silica surface of the silica template and PF resin. Therefore, the PF oligomers could be homogeneously adsorbed into the nanochannels or cages of the mesoporous silicas via an impregnation process. Because the thermosetting PF resin only requires a simple heat treatment process at 100 °C to form the cross-linked polymeric structure, the replication of the mesostructure of the mesoporous silica template could be readily achieved without adding any polymerization catalysts.     

Sol–gel synthesis and luminescence of unexpected microrod crystalline Ca5La5(SiO4)3(PO4)3O2:Dy phosphors employing different silicate sources

Ca₅La₅(SiO₄)₃(PO₄)₃O₂ doped with Dy³⁺ were synthesized by sol–gel technology with hybrid precursor employed four different silicate sources, 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM diagraphs show that there exist some novel unexpected morphological structures of microrod owing to the crosslinking reagents than TEOS as silicate source for their amphipathy template effect. X-ray pictures confirm that Ca₅La₅(SiO₄)₃(PO₄)₃O₂:Dy³⁺ compound is formed by a pure apatitic phase. The Dy³⁺ ions could emit white light in Ca₅La₅(SiO₄)₃(PO₄)₃O₂ compound, and the ratio of Y/B is 1.1, when the Dy³⁺ doped concentration is 1.0 mol%.     

Atomic layer deposition of calcium oxide and calcium hafnium oxide films using calcium cyclopentadienyl precursor

Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al₂O₃ capping layer occurred hygroscopic and converted to Ca(OH)₂ after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al₂O₃ capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO₂ growth cycles at 230 and 300 °C. HfCl₄ was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca₂Hf₇O₁₆ or Ca₆Hf₁₉O₄₄. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca₂Hf₇O₁₆. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2.     

Preparation and antibacterial behavior of Fe-doped nanostructured TiO2 thin films

Fe³⁺-doped nanostructured TiO₂ thin films with antibacterial activity were prepared on soda–lime–silica glass slides by using sol–gel technology. Water containing Escherichia coli K-12 with TiO₂ thin films in was exposed to low intensity fluorescent light and antibacterial efficiency was evaluated with spread plate techniques. The films are porous and have anatase phase. Iron ions increased luminous energy utilization as the absorption edge of the Fe³⁺-doped film has a red shift compared to that of the pure TiO₂ film in the UV–VIS absorption spectrum. The bacterial removal efficiency reached 95% at the optimum concentration of iron ion (about 0.5% (mol)) after 120 min irradiation. The antibacterial behavior of the doped TiO₂ films was explicitly observed using scanning electron microscopy and cell wall damage was found.     

Synthesis and optical properties of photosensitive polyimide/silica hybrid thin films

In this study, the photopatternable fluorinated polyimide/silica hybrid materials were synthesized by 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA), oxydianiline (ODA), aminopropyltriethoxysilane (APrTEOS), and 12 nm colloidal silica with a coupling agent. The monodispersed colloidal silica was used to form a silica domain instead of alkoxysilanes in the conventional process. The coupling agents used were 3-methacryloxypropyl trimethoxysilane (MPTMS) or (4-vinylphenethyl)trimethoxysilane (VPTMS). The coupling agent and the silica domain were designed to reduce the volume shrinkage and enhance the thermal properties, respectively. The retention of 2-methyl acrylic acid 2-dimethylamino-ethyl ester (MDAE) in the prepared hybrid films was supported by X-ray photoelectron spectroscopy (XPS) and thickness variation during the curing process. The particle size of silica in the hybrid materials based on SEM analysis was in the range of 10–25 nm. The prepared hybrid materials also exhibited a reduced refractive index after increasing the silica content. The SEM diagram suggested the prepared photosensitive hybrid materials could obtain lithographical patterns with a good resolution. These results indicate that the newly prepared photosensitive polyimide/silica hybrid materials may have potential applications for optical devices.     

Characterization of Ni–Pd alloy as anode for methanol oxidative fuel cell

Electrochemical deposition of Ni–Pd alloy films of various compositions from bath solution containing ethylenediamine (EDA) was carried out to use as anode material for methanol oxidative fuel cell in H₂SO₄ medium. Electronic absorption spectrum of bath solution containing Ni²⁺, Pd²⁺ ions and EDA indicated the formation of a four coordinate square planar metal–ligand complex of both the metal ions. X-ray diffraction (XRD) patterns of the deposited alloy films show an increase in Pd–Ni alloy lattice parameter with increase in Pd content, and indicate the substitution of Pd in the lattice. A nano/ultrafine kind of crystal growth was observed in the alloy film deposited at low current density (2.5 mA cm⁻²). X-ray photoelectron spectroscopic (XPS) studies on the successively sputtered films showed the presence of Ni and Pd in pure metallic states and the surface concentration ratio of Ni to Pd is less than bulk indicating the segregation of Pd on the surface. Electro-catalytic oxidation of methanol in H₂SO₄ medium is found to be promoted on Ni–Pd electrodeposits. The anodic peak current characteristics to oxidation reaction on Ni–Pd was found typically high when compared to pure nickel and the relative increase in surface area by alloying the Ni by Pd was found to be as much as 300 times.     

SiO2对掺钕铝酸盐玻璃结构及光谱性质的影响

实验通过高温熔融法制备了不同SiO₂ 浓度的掺钕钙铝酸盐玻璃。采用拉曼光谱法分析玻璃结构变化, 发现随着SiO₂含量的增加, [AlO₄]网格中非桥氧逐渐转移至Si⁴⁺离子周围, 玻璃主体Al-O网络中非桥氧减少, 聚合度提高。实验测试了玻璃的吸收光谱和荧光光谱, 并运用Judd-Ofelt理论计算Nd³⁺离子⁴F_3/2→⁴I_11/2跃迁的J-O参数Ω, 自发辐射几率A_rad, 荧光分支比β, 受激发射截面σ_e, 辐射寿命τ_rad等。结果显示: 随着SiO₂浓度的增加, 钕离子周围环境结构对称性提高, 荧光发射峰半高宽变窄, 同时受激发射截面逐渐增大。研究结果表明含有低浓度SiO₂的掺钕钙铝酸盐激光玻璃有望用于超短脉冲激光领域。