Pore Size Distribution Of Aerogel Research Articles

Low density and high strength nanofibrillated cellulose aerogel for thermal insulation application

Low density and high strength nanofibrillated cellulose aerogel based on pinewood were prepared by the freeze-drying method. The study was focused to reduce the thermal conductivity of the prepared aerogel along with the improvement in mechanical strength. Synthesized nanofibrillated cellulose aerogel had demonstrated high porosity (99.4%) and ultra low density (8.1 kg/m3). Morphological analysis of aerogel by FESEM (Field emission scanning electron microscope) confirmed nano-dimensional diameter of cellulosic fibres and pore size distribution of aerogel in the range of 2–50 nm. X-ray microtomography confirmed the three-dimensional, monolithic and porous structure. The mechanical and thermal transport properties of aerogel have been tailored via controlling the concentration of nanofibrillated cellulose in the hydrogel. The synthesized aerogel act as a thermal insulator with the thermal conductivity of 25.5 mW/m K at 1.00 wt% of aerogel, which is near to the thermal conductivity of air in ambient condition. Cyclic compression strength of aerogel was investigated at 25%, 50% and 75% strain for 50 cycles. 1.00 wt% aerogel was 70% recoverable at 25% strain but reflecting strain-hardening behaviour at 75% strain. 1.00–1.50 wt% aerogels have shown ductile, flexible and compressible behaviour. Nanofibrillated cellulose aerogel would be a candidate in practical applications such as heat insulator, kinetic energy absorber and energy efficiency building.

Large size and low density SiOC aerogel monolith prepared from triethoxyvinylsilane/tetraethoxysilane

Crack-free silicon oxycarbide (SiOC) aerogel monolith was fabricated by pyrolysis of precursor aerogel prepared from triethoxyvinylsilane/tetraethoxysilane (VTES/TEOS) using sol-gel process and ambient drying. Effects of different precursors, the amount of base catalyst (NH4OH) and the heating rate during pyrolysis on the properties such as monolithicity, bulk density, surface area and pore size distribution of aerogels were investigated. The results show that the crack-free SiOC aerogel can be easily obtained from VTES/TEOS as compared to that of methyltriethoxysilanes/tetraethoxysilane (MTES/TEOS) and phenyltriethoxysilanes/tetraethoxysilane (PhTES/TEOS) precursors. The influence of heating rate during pyrolysis process on shrinkage rate, ceramic yield and surface area of the SiOC aerogels could be ignored, while the variation in the amount of NH4OH exerted a strong impact on the properties of SiOC aerogels. Increasing the amount of NH4OH resulted in the decrease of bulk density and surface area of SiOC aerogels from 0.335g/cm3 and 488m2/g to 0.265g/cm3 and 365m2/g. The resultant SiOC aerogels exhibit high compressive strength (1.45–3.17MPa). 29Si MAS NMR spectra revealed the retention of Si-C bond in the SiOC aerogels after pyrolysis at 1000°C. The present work demonstrates VTES/TEOS is a promising co-precursors to easily and low cost synthesize large size SiOC aerogel monolith.

Monolithic germanium oxide aerogel with the building block of nano-crystals

In the present paper, we have prepared germanium oxide aerogel using the sol–gel method followed by CO2 supercritical drying. Scanning electron microscopy showed a fine microstructure of the as-prepared aerogel. Results from the nitrogen adsorption and desorption data exhibited that the aerogel had attractive specific surface area and typical pore size distribution of aerogel. X-ray diffraction indicated that the aerogel was composed of nano-crystals with hexagonal structure. X-ray photoelectron spectroscopy confirmed the existence of oxygen vacancies. At room temperature, interesting strong blue luminescence was observed at 425nm under excitation wavelength at 280nm. We proposed an explanation for the phenomenon.

Preparation of AgI ‐ Al2 O 3 Composites with High Ionic Conductivity Using Al2 O 3 Aerogel and Xerogel

composites were prepared using sol‐gel‐derived aerogels and xerogels. The addition of aerogel or xerogel to AgI enhanced the ionic conductivity. The conductivity at room temperature showed a maximum at the composition in both aerogel‐containing and xerogel‐containing composites and was for the aerogel composite. The conductivity of aerogel‐containing composites was larger than that of xerogel‐containing composites for all compositions, suggesting that the pore size distribution of aerogels was more effective than that of xerogels for enhancing the ionic conductivity. © 2000 The Electrochemical Society. All rights reserved.

Influence of temperature on the physical properties of citric acid catalyze TEOS silica aerogels

In the present paper, the experimental results on the influence of temperature on such physical properties as bulk density,percentage of porosity, pore size distribution and optical transmission of silica aerogels are reported. The aerogels were heated at different temperatures ranging from room temperature up to 1000 °C. It was found that highly transparent (> 90%), monolithic and pure silica glasses were obtained at temperatures as low as 1000 °C with a heating rate of 1.5 °C min −1. It has been observed that initially within the temperature range 25–250 °C, the bulk density decreased from 0.21 to 0.19 g cm −3 owing to weight loss without any volume and porosity changes of the aerogels, while above 250 °C the bulk density, percentage of volume shrinkage and weight loss increased with increase in temperature and at the same time the porosity of the aerogels decreased. The optical transmission of the aerogel increased (up to ≈ 70%) with an increase in temperature up to around 400 °C and then the transparency decreased (to ≈ 20%) up to a temperature of 950 °C before increasing further to ≈ 90% at 1000 °C. A sudden change of pore size distribution of the aerogels was observed in the temperature range of 800 to 975 °C, The pore size distribution and the radii of pores increased up to a temperature of 800 °C and above this temperature the size distribution narrowed with decrease in pore radii. The results have been supported and discussed by considering the particle and pore sizes observed by scanning electron microscopy.