Zhongsheng Deng

A novel route to control refractive index of sol-gel derived nano-porous silica films used as broadband antireflective coatings

Abstract A relatively new method to adjust refractive index of nano-porous silica films rapidly and continuously is reported. The thin films were prepared with the base/acid two-step catalytic sol-gel process and the dip-coating method. The structure, reflective spectra and refractive index of the films were analyzed with TEM, AFM, SEM, spectrophotometer, and ellipsometery, respectively. The experimental results have shown that the base/acid two-step catalysis can adjust the refractive index of the nano-porous silica films from 1.18 to 1.42 rapidly and continuously. And a broadband antireflective coating made with the method has very low reflectance. The average reflectance of the coated glass in the solar energy spectrum decreases to 1.5% from ∼7% of the glass.

High strength SiO2 aerogel insulation

Silica aerogels with titanium dioxide powder and inorganic binders were made using tetraethoxysilane (TEOS), water and HF catalyst, followed by supercritical drying with ethanol leading to crack-free monolithic aerogels. Strength of the monolithic silica aerogels increased from 1.8×104 Pa to 1.2×105 Pa with doping, while the thermal conductivity of the doped silica aerogel remains below 0.02 w/m K at room temperature in air.

Properties of sol-gel derived scratch-resistant nano-porous silica films by a mixed atmosphere treatment

Abstract A strengthening mechanism for sol–gel derived nano-porous silica films was studied. The silica films were prepared with the dip method from two-step catalyzed silica sols and treated in a mixed atmosphere of ammonia and water vapor afterwards. Properties of the films were analyzed by using atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), ellipsometry and an abrasion test, respectively. The experimental results have shown that the two-step catalysis strengthens the films and the scratch resistance of the silica films is further improved after treatment in the mixed gas. The increase in strength is attributed to the cross-linking of silica particles by randomly branched or/and entangled linear chains in the sols, more Si–O–Si bonds formed by the mixed gas treatment and structural changes in the silica films.

Scratch-Resistant Improvement of Sol-Gel Derived Nano-Porous Silica Films

Scratch-resistance of sol-gel derived nano porous silica films were studied. The thin films were prepared with a dip-coating method from both one-step and two-step catalyzed silica sols, and treated in a mixture gas of ammonia and water vapour afterwards. The thin films were characterized by using Atomic Force Microscope (AFM), ellipsometer, Fourier-transform Infrared Spectroscope (FTIR), respectively. Experimental results have shown that the two-step catalysis remarkably improves strength of the films, and abrasion-resistance and adhesion of the silica films were further increased after the mixture gas treatment. It is attributed to the cross-linking of silica particles in the sols by randomly branched or/and entangled linear chains and more Si–O–Si bonds formed by the mixture gas treatment.

A new method to control nano-porous structure of sol-gel-derived silica films and their properties

Abstract To control structure of nano-porous silica films effectively, a base/acid two-step catalytic sol-gel process was investigated. The nano-porous structure and IR absorption of the thin films were characterized by means of FE-SEM, AFM, SEM, FTIR, and ellipsometry, respectively. The experimental results have shown that the base/acid two-step catalysis can adjust the refractive index of the films from 1.18 to 1.41 rapidly and continuously. With a change of the experimental conditions, the frequency shift of the ω 4 (TO 3 ) peak of FTIR absorption to a lower wave number indicates a decrease in the average Si-O-Si bridging angle. A reduction of FWHM of the ω 4 peak reveals a narrow distribution of the Si-O-Si bridging angle. These results suggest that influence of the experimental conditions on the FTIR absorption of the nano-porous silica films is attributed to a change of silica particle shape and state of aggregation of the particles in the films.

Sol-Gel Processing of Zirconia Coating for HR Mirrors with High Laser Damage Threshold

High laser-damage resistant coatings are very important in high power laser systems. In this study ZrO2 thin films are prepared by sol-gel spin-coating technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO2 at room temperature synthesized by a hydrothermal process from an inorganic precursor (ZrOCl2·8H2O). By adding a soluble organic binder PVP to the suspension prior to application, it is possible to substantially increase the coating refractive index and the abrasion-resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions are investigated. Multilayer highly reflective dielectric coatings are also elaborated by applying quarterwave-thick alternating coatings of the binder-aided zirconia and silica, which is prepared with the sol-gel process from TEOS. To achieve 99% reflectivity, 19–21 layers are required. Single shot laser damage tests are carried out using a high power laser at 1064 nm wavelength with a pulse duration of 2.5 ns. The laser damage thresholds of 18 and 15 J/cm2 are achieved for single ZrO2-PVP coating and ZrO2-PVP/SiO2 multilayers respectively.

The investigation of the adsorption character of carbon aerogels

The influence of pyrolysis temperature and density on the microstructure of carbon aerogels is studied by nitrogen adsorption analysis. Resorcinol-formaldehyde (RF) aerogel and carbon aerogels all give type II isotherms and hysteresis loops of type A. Carbon aerogel pyrolized at 600°C has the largest specific surface area (SSA). The trend of pore size distribution of RF aerogel and its pyrolized derivatives is same. Carbon aerogels with low and high density have different pore size distribution, while carbon aerogel with low density has greater SSA.

Preparation and photocatalytic activity of TiO2-SiO2 binary aerogels

Abstract The preparation, characterization and photocatalytic degradation of phenol pollutant of TiO 2 -SiO 2 aerogels were investigated. The aerogels were mostly turned to anatase microcrystalline after supercritical drying in ethanol. Photocatalytic degradation of phenol in water on aerogels shows that the binary aerogels have high efficiency than the commercial TiO 2 and pure TiO 2 aerogel. The photocatalytic activity of the aerogels increased with the SiO 2 content at first but came to a maximum at molar ratio = 1:1.

Strengthening mechanism of porous silica films derived by two-step catalysis

A scratch-resistant improvement of sol-gel derived nano-porous silica films by a base/acid two-step catalysis is reported. The silica films were prepared with the two-step catalytic sol-gel process and a dip-coating method, and then post annealed in air and a mixed gas atmosphere. The films were characterized with FE-SEM, AFM, TEM, XPS, FTIR, an ellipsometer, and an abrasion test. With the post annealing, the frequency shift of the FTIR absorption ω4(TO3) peak of the films to a lower wavenumber results from a decrease in the average Si-O-Si bridging angle. An increase in the full-width at half-maximum of the ω4 peak is ascribed to a wide distribution of the bridging angle because of formation of strained Si-O-Si bonds caused by the post annealing. XPS analysis shows that the effect of the mixed gas annealing on the binding energy and full-width at half-maximum (FWHM) for Si (2p) and O (1s) peaks is attributed to the further condensation reaction of the films resulting from the disappearance of the OH groups. The abrasion and adhesion tests indicate that the two-step catalysis obviously improves the scratch resistance and adhesion of the films, and that the mixed gas treatment further strengthens the silica network. The increase in strength is attributed to more Si-O-Si bond cross-linkages between silica particles formed by the two-step catalysis and the mixed gas treatment.

Physical Properties of Silica Aerogels Prepared with Polyethoxydisiloxanes

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by supercritical drying with ethanol. The morphology and microstructure of the silica aerogels were investigated by using specific surface area, SBET, SEM, TEM and the pore size distribution techniques. The thermal conductivity was also measured as a function of air pressure. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is 20–80 nm. The specific surface area of the silica aerogel is about 470 m2/g and the thermal conductivity of the silica aerogel prepared with E-40 is 0.014 w m−1 K−1 at room temperature and 1 atm.