By Prakash Chander Thapliyal & Kirti Singh
Thapliyal is a Principal Scientist while Kirti is Project Fellow at Organic Building Materials Group,
CSIR-Central Building Research Institute, Roorkee
Thermal insulation is the key to energy-efficient buildings. Building Insulation reduces the amount of energy required to maintain a comfortable environment by reducing energy consumption. Aerogels are ultra-low density highly porous solids. All over the world, researchers are examining the potential for nano-based aerogels material to be used as insulating coatings on buildings. The main aim is to produce affordable coatings that could improve thermal efficiency in both new and retrofitted buildings.
Thermal insulation is one of the key aspects of achieving energy-efficient buildings. There are many materials that are being used for insulation such as wool, glass fibers, polystyrene foams, sandwich panels, etc. Aerogel is an ultra-low density solid and is a gel in which liquid is replaced by air and is also known as the lightest solid in the world. But the point of importance is that despite its lightness aerogel can support over 2000 times its own weight. Aerogels can bind various gases for use as detectors and can be colored or ground into very small particles and applied like ink using a printer. Being transparent and having a low refractive index, makes them useful as lightweight optical materials. Aerogels together with vacuum insulation panels are one of the new promising high-performance thermal insulation materials for possible building applications as thermal and acoustic insulation materials are currently the main market for aerogels, whereas other applications such as absorbents, shock absorbers, nuclear waste storage, batteries, and catalysts are also possible. If we can develop nano-based aerogels and incorporate them in the coatings; these can be applied as thin films to concrete, steel, glass, and fabrics. These insulating coatings can also be painted or sprayed easily. As nano-based aerogels can trape air at the molecular level, insulating nanocoating even a few nanometers thick can have a dramatic effect. This is a tremendous advantage as nanocoatings offer over the more conventional bulk insulator like fiberglass, cellulose, and polystyrene boards, requiring the removal of building envelope components for installation.
Preparation of nano-based aerogels
Sol is defined as a solution of different reactants undergoing condensation and hydrolysis. The molecular weight of the oxide species produced in a sol continuously increases because of the formation of a three-dimensional network. At the gel point, the mixture forms a rigid alcogel consisting of a solid and a liquid part. The solid part is the three-dimensional network of oxide particles and the liquid part is the original solvent of the sol occupying the free space surrounding the solid part. Aerogel is obtained when the liquid part of an alcogel is removed without damaging the solid part at ambient conditions of pressure but most often by supercritical extraction. Under strict control, the aerogel (nano-based aerogels) retains the original shape and at least 50 percent (typically >85 percent) of the original alcogel’s volume.
In a typical method, aerogel can be prepared from water glass using an amber lite column. The collected silica sol had a pH value in the range of 2.7 and ammonia solution is added to start the gelation process. It was allowed for aging at normal temperature and pressure conditions for 24 hours. The aged wet gel was then immersed in IPA/n-hexane solution and allowed to dry at ambient conditions.
Current scenario of aerogels
In the building industry, nanotechnology has already brought to market self-cleaning windows, smog-eating concrete, and many other advances. But these advances and currently available products are minor compared to those incubating in the other labs today.
Thermal conduction in aerogel materials through the solid portion is hindered by the short connections between the particles making up the conduction path, and the solids that are present consist of very small particles. As a result thermal transfer through the solid portion occurs through a very complicated maze and is poor. Use of nanotechnology will enable sustainable thermal insulation materials with excellent thermal insulation behavior.
Some researchers are examining the potential for nano-based aerogel materials to be used as insulating thin-film coatings on buildings. The innovative material is said to be suitable for application in liquid form on the exterior of buildings. If the material can be affordably manufactured on an industrial scale, it could offer significant enhancements to current insulating materials. A wall which comprises of plastered block wall, insulated with panels and painted could demonstrate the full benefits of high performance insulation based on nanostructured encapsulation of air (HIPIN) technology.
With new materials and technologies come new concerns. Building Insulation reduces the amount of energy required to maintain a comfortable environment by reducing energy consumption. Uncertainty surrounding the interaction of nano scale particles with the environment and the human body has led to caution and concern about toxicology, worker health and safety and regulation. More studies and proper applications will lead to better use of all nanomaterials including aerogels in building insulation.
Work at CBRI
Energy-efficient materials are a thrust area of research for CSIR. CBRI scientists have done work in the area of thermal insulation, green materials etc. and published papers. At present focus is now on nanotechnology and a group under the guidance of Prof S K Bhattacharyya, Director CBRI, is working on different aspects of nanomaterials such as cementitious materials, protective coatings and phase change materials. In the area of nano-based aerogels, preparation at ambient conditions is still a challenge and hence this research group is focusing in that direction. Moreover application of aerogels in building applications is still not well explored particularly in coatings which will improve the thermal efficiency in both new and retrofitted buildings.
Conclusion
Aerogels are known since long time and are now commercially available but there are still areas where we need to improve such as their preparation at ambient conditions and use in buildings. The technology has the potential to improve the insulation properties of a wide range of building materials including plasterboard, panels and even paint and coatings.
Acknowledgment
The authors are grateful to the Director, CSIR-CBRI, for his continuous guidance and encouragement.
Further Reading
- W M Risen, S Ji, X Hu and R Zhang, ‘Aerogel Material and Detectors, Liquid and Gas Absorbing Objects, and Optical Devices Comprising Same’, US Patent No 6,303,046 B1, 2001.
- G H Hart, ‘Thermal Insulating Coatings’, last accessed on 8th September 2014 http://www.insulation.org/articles/article.cfm.
- T Gao, Chapter-‘Nano insulation materials for energy-efficient buildings: A case study on hollow silica nanospheres’, Book- Fuelling the future; advances in science and technologies for energy generation, transmission, and storage, Publisher- Brown Walker Press, USA, Editors – AA Mendez –Vilas, 535-53.
- A Brister, ‘Nanotechnology drives insulation research’, last accessed on 27 August 2014. http://www.technology4change.com/article.jsp?id=215#.U22mdK1ZRs.
- R D Schlanbusch, ‘A New Nano Insulation material for applications in Zero Emission Buildings’, M Sc Thesis, Norwegian University of Science and Technology (NTNU) Norway, January 2013.
- G Elvin, ‘Nanotechnology for green building’, 2007, last accessed on 8th September 2014. http://esonn.fr/esonn2010/xlectures/mangematin/Nano_Green_Building55ex.pdf
- P C Thapliyal and Kirti Singh, ‘Aerogels as Promising Thermal Insulating Materials: An Overview’, Journal of Materials, Volume 2014, Article ID 127049, 10 pages, http://dx.doi.org/10.1155/2014/127049.
- Insulating Coatings Feature Aerogel, PaintSquare, Paint, and Coating Industry News, April 2012, last accessed on 8th September 2014. http://www.paintsquare.com/news/?fuseaction=view&id=7618.
