Chapter 7. Hybrid green aerogels: processing and morphology

Hybrid bio-based aerogels exhibit enhanced synergistic properties as compared to their corresponding constituents. The technology has attracted increasing research interests, particularly as these syntheses lead to formation of various microstructures with different properties of the composite. In this chapter, the recent developments in hybrid bio-based aerogels are introduced, including the use of new precursors, doping techniques, and microstructure, as well as morphology of composites. Applications of the new precursors such as collagen, xyloglucan, pectin, lignin, aniline, polypyrrole, graphene oxide and halloysite nanotubes are discussed separately. Detailed syntheses of hybrid bio-based aerogels are elaborated in the stages of sol formation, gelation, doping and drying. Micrographic images are categorized based on the microstructures of the hybrid aerogels, where the formation of each type of microstructure is illustrated and discussed. At the end of the chapter, a new technique, called synchrotron X-ray tomography is introduced, which is able to probe the degree of anisotropy of the hybrid aerogels. © The Royal Society of Chemistry 2018

Novel cement curing technique by using controlled release of carbon dioxide coupled with nanosilica

Nanotechnology has attracted a lot of interest in the modification of building materials involving nanoparticles. Among the nanoparticles available, the incorporation of nano-silica draws intense attention due to the similarity of its chemical composition with cement and its pozzolanic properties. In this work, the potential capability to utilise CO2 in improving cement composites properties through carbonation acceleration mechanism was explored. In this study, various type of nano silica was used as a CO2 carrier and incorporated into cement mortar design with different amount of carbonated silica loading, ranging from 0.55 wt% to 2.42 wt% and cured in water and ambient air condition. The aim of this study is to examine the effects on the compressive strength of nano-silica impregnated with CO2 and incorporated into cement mortar. From the results, it was found that at 1.89% silica loading, the hydrophilic silica mortar (HSAM) samples can achieve the highest compressive strength of 34.1 MPa at 7 days and 40.7 MPa at 28 days, with a percentage gain of +38.06% and +17.29% respectively as compared to blank samples. However, the incorporation of silica for more than 1.89 wt% resulted in a negative effect on the compressive strength gain of HSAM samples. By the incorporation of 2.42 wt%, the samples showed a significant drop in compressive strength of −21.46% at 7 days and −17.29% at 28 days. The results proved that nano-silica coupled with CO2 can accelerate curing of cement mortar by means of carbonation

A friction-wear correlation for four-ball extreme pressure lubrication

A first-ever friction-wear model for Four-Ball Extreme Pressure (EP) Lubrication test (ASTM D2783) is presented in this work. The model considers the rate of entropy generation and dissipation within the lubricated tribosystem to establish the friction-wear correlations for 12 lubricating oils comprising minerals, esters and other formulated oils. The correlations can be used to calculate the probability to pass/fail in the EP lubrication. The probability has similar trend as load-wear index from ASTM D2783 method. Besides, the friction-wear correlations allows quick estimation of EP performance of an unknown lubrication, upon comparing with that of an established one. The methods demonstrated here will help researchers or lubricant technologist to characterize the EP behavior quickly without over-relying on tribotester

Synthesis and characterization of bamboo leaf based carbon-opacified silica aerogel (COSA) / Kow Kien Woh

Silica aerogel with extremely low thermal conductivity has great potential to be used as thermal insulating material. Its application is currently restricted by the expensive raw materials such as tetramethyl-orthosilicate (TMOS) and tetraethyl-orthosilicate (TEOS). In addition, pure silica aerogel has low absorption of infrared radiation at 3 – 8 μm and led to increase in thermal conductivity at high temperature. Carbon is commonly used as an opacifier in silica aerogel to absorb the radiation and therefore suppress thermal conductivity of aerogel. However, separated source of carbon is required for the opacification of aerogel. Biomass such as bamboo leaves and cogon grass contain both silica and carbon. They can provide both sources to synthesize carbon-opacified silica aerogel (COSA). The use of biomass in the synthesis of COSA not only can reduce the cost of expensive raw materials, but also to minimize agriculture waste. Hence, this work is aimed to synthesize COSA by using biomass as a single source of raw material. Effects of gelation pH, carbon loading, silica concentration and temperatures on the thermal conductivity of COSA were investigated and optimized by using statistical model. Its thermal insulative performance was compared with the silica aerogel synthesized via conventional method including TEOS and carbon black. The study revealed that thermal conductivity of silica aerogel opacified with activated carbon is comparable to those opacified with carbon black. The result showed that optimal carbon loading which minimized the thermal conductivity present at different temperatures. Such optimal loading increased as temperature applied to the opacified aerogel increased. Tie lines that optimized thermal conductivity at different temperatures were obtained for various combinations of carbon loading and silica concentration. Thermo-gravimetry (TGA) results of the aerogels also indicate that opacified aerogel is thermally stable up to 495 °C and therefore suitable be used at high temperature

Thermal insulative performance of bamboo leaf aerogel opacified usingactivated carbon compared with carbon black

Silica aerogel with extremely low thermal conductivity has great potential to be used as thermal insulating material. Opacification using carbon black is normally applied to reduce radiative heat loss in silica aerogel. This work attempted to replace carbon black with activated carbon as opacifer. Both the silica aerogel and activated carbon were synthesized via bamboo leaf. Effects of carbon loading and temperatures on the thermal conductivity of opacified aerogel were studied.The results show that an optimal carbon loading that minimizedthe thermal conductivity present at different temperatures. Such optimal loading increased as temperature applied to the opacified aerogel increased. Properties of aerogels opacified with activated carbon were also compared with aerogels opacified with carbon black

Effect of magnetic field on nano-magnetite composite exhibits in ion-adsorption

Nano-magnetites are widely researched for its potential as an excellent adsorbent in many applications. However, the efficiency of the nano-magnetites are hindered by their tendency to agglomerate. In this work, we dispersed and embedded the nano-magnetites in a porous silica gel matrix to form a nanocomposite to reduce the extent of agglomeration and to enhance the adsorption performance. Our experimental results showed that the removal efficiency of Cu ion has improved by 46% (22.4 ± 2.2%) on the nano-magnetite-silica-gel (NMSG) nanocomposite as compared to pure nano-magnetites (15.3 ± 0.6%). The adsorption capacity is further enhanced by 39% (from 11.2 ± 1.1 to 15.6 ± 1.6 mg/g) by subjecting the NMSG to a magnetic field prior to adsorption. We infer that the magnetic field aligned the magnetic domains within the nano-magnetites, resulting in an increased Lorentz force during adsorption. Similar alignment of magnetic domains is near to impossible in pure nano-magnetites due to severe agglomeration. We further found that the adsorption capacity of the NMSG can be manipulated with an external magnetic field by varying the strength and the configurations of the field. Equipped with proper process design, our finding has great potentials in processes that involve ion-adsorptions, for example, NMSG can: (i) replace/reduce chemical dosing in controlling adsorption kinetics, (ii) replace/reduce complex chemicals required in ion-chromatography columns, and (iii) reduce wastage of nano-adsorbents by immobilizing it in a porous matrix. 2