Journal of Chemical, Biological and Physical

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Apr 16, 2015 - chemical, oil and gas lines, power generation, military, etc. .... S.S.Latthe, S.L.Dhere, S.S.Pawar, H.Imai, V.Ganesan, S.C.Gupta, P.B.Wagh ;.

JCBPS; Section C; Feb 2015 – Apr. 2015, Vol. 5, No. 2; 1944-1949.

E- ISSN: 2249 –1929

Journal of Chemical, Biological and Physical Sciences An International Peer Review E-3 Journal of Sciences Available online atwww.jcbsc.org Section C: Physical Sciences Research Article

CODEN (USA): JCBPAT

Comparative Studies of Commercially Available Thermal Insulation Materials and Sol – Gel Processed Thermal Insulation Materials 1

P. B. Wagh*, 1S. V. Ingale, 1Ratanesh Kumar, 1R. P. Patel, 1Satish C. Gupta, 2 A. A. Pisal, 2A. V. Rao 1

Applied Physics Division, Bhabha Atomic Research Centre, Mumbai, India - 400 085 2 Department of Physics, Shivaji University, Kolhapur, India - 416 004. Received: 27 March 2015; Revised: 16 April 2015; Accepted: 22 April 2015

Abstract: Thermal insulation materials have different applications in insulation and safety products. Their application could be limited due to water adsorption which may deteriorate performance. We have demonstrated a method in which the commercially available thermal insulation materials fabric was modified with silica gel which leads to improve thermal insulation properties along with imparting hydrophobicity to the materials. The unmodified insulation materials fabric was put in the silica sol prepared at optimized molar ratio of the precursor chemicals viz. Tetramethoxysilane: Methanol: H2O: :1:12:4, respectively. The materials fabric was then dried so as to get coated with silica gel. The modified insulation materials fabric was characterized by IR studies to confirm the coating of fabric by silica gel. The SEM characterization showed that the insulation materials get uniformly coated with silica gel adhered to fabric. The modified materials were found hydrophobic as revealed from contact angle method (contact angle 147o). Thermal conductivity measurements showed that thermal insulation property of modified materials has been improved as compared to unmodified materials (thermal conductivity decreased from 0.375 W/mK to 0.234 W/mK). Keywords: Thermal insulation materials; hydrophobic; thermal conductivity; silica gel. INTRODUCTION High temperature thermal insulation materials find potential applications particularly in insulation and safety products like reusable insulation blankets, composite insulations, refrigeration, sound attenuators, 1944

J. Chem. Bio. Phy. Sci. Sec. C, February 2015 – April 2015; Vol.5, No.2; 1944-1949.

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exhaust pipes, turbines, hose wraps, etc. Therefore, they are in useful in industries like petrochemical, chemical, oil and gas lines, power generation, military, etc. One of its crucial applications is liquid or gas fuel transportation for which thermal insulation is an extremely important aspect1. The thermal insulation materials with the lowest possible thermal conductivity are in demand for this purpose. The widely used materials for such insulation coating purpose are thermal wrapper consisting of glass wool or foam. However, the water adsorption is critical parameter in the thermal insulation materials as it may deteriorate performance. To get the advantage of thermal insulation wrappers in such applications, it is important to prevent the water adsorption that may be achieved by use of hydrophobic materials. Silica aerogel is one of the best known thermal insulators but have limitations in use due to its very fragile nature2. However, it has advantage that with suitable chemical modifications, the silica aerogels can be made hydrophobic3. Therefore suitable amalgamate of the hydrophobic and thermal insulation properties of silica aerogel with available thermal wrappers can improve the performance of these wrappers and their suitability in various applications. In the present article we have demonstrated a method to develop the water resistant thermal wrappers by impregnating hydrophobic silica aerogel materials to it. This has improved thermal insulation property as well as hydrophobic property of the thermal wrappers along with retaining the flexibility of these wrapper material and these results are presented in the research paper. The composite materials have been characterized by Fourier transform infrared spectroscopy for composition analysis, scanning electron microscopy to study the microstructure, thermal conductivity measurements and hydrophobic property studies and have been found superior to commercially available insulation material. EXPERIMENTAL The thermal insulation materials were purchased from local market which was modified with silica gel. To prepare silica sol, Tetramethoxysilane (TMOS), Methyl alcohol (MeOH) and NH4OH (0.05M) was mixed together at an already optimized molar ratio 1:12:4, respectively4 and stirred for 10 minutes. Methyltrimethoxysilane (MTMS) was added to this solution as a hydrophobic reagent and the solution was stirred for another 5 minutes. The unmodified insulation materials fabric was dipped in the sol and retained for 10 minutes. The materials fabric was then withdrawn from the sol and dried in vacuum oven. This resulted in silica gel layer coating on the insulation materials fabrics and embedded in pores of materials fabric. TMOS and MTMS were of purum grade and purchased from Fluka Chemicals, Switzerland. MeOH and NH4OH were of analytical grade. Fourier Transform Infra Red (FTIR) spectra of silica aerogel, commercially available unmodified thermal insulation material fabric and the modified fabric by impregnating silica gel using sol - gel processing method are recorded with ALPHA T FTIR spectrometer (Bruker, Germany) using attenuated total refection (ATR) technique. The spectra were recorded at the wave numbers ranging from 500 cm-1 to 4000 cm-1 at a resolution of 4 cm-1. The microstructure of the unmodified and silica gel modified insulation materials has been studied by using Scanning Electron Microscope (JEOL, JEM-6360, Japan). The hydrophobic property of the silica gel modified materials was evaluated using contact angle water drop method. The angle between the wetting surface and tangent made to water droplet is measure of hydrophobicity. For contact angle measurement, a water droplet of about 10 µL was placed on the surface of silica gel modified materials using micro-syringe. The contact angle is evaluated using photographic method. The thermal conductivity and heat capacity data of the unmodified and modified thermal insulation materials have been measured using CT METRE, Teleph, France using the ring probe method. 1945

J. Chem. Bio. Phy. Sci. Sec. C, February 2015 – April 2015; Vol.5, No.2; 1944-1949

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RESULTS AND DISCUSSION The FTIR spectra of silica, commercially available thermal insulation materials and the modified materials impregnated with silica gel are shown in Fig. 1 a, b and c, respectively.

Figure 1: FTIR Spectra of a) Silica b) Commercially available thermal insulation materials and c) Silica gel impregnated modified materials The marked portion shows the signature peaks of silica (Fig. 1 a) replicated in silica impregnated material (Fig. 1 c). The spectrum of silica impregnated insulation material shows the absorbance band at 1100 cm-1 attributed to Si-O bonding in silica5. It indicates that silica has been infused in fabric. The absorbance peak at about 1260 cm-1 is assigned to Si-C peak6. This has been attributed to modified silica network by methyl group (Si-CH3) in the hydrophobic reagent methyltrimethoxysilane. It reveals that the silica gel impregnated material has hydrophobic properties. Fig. 2 shows the SEM pictures of unmodified insulation fabric materials and materials modified with silica gel. In SEM picture of commercially available thermal insulation materials (Fig. 1 a), the entangled fabric of about 10 µm in diameter are observed. In SEM picture of silica gel modified materials (Fig. 2 b), the coating of silica gel layers on insulation material fabric is clearly observed. It reveals that insulation material fabrics are uniformly coated with silica gel. It offers the better thermal insulation and hydrophobic properties as compared to unmodified materials. 1946

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Figure 2: SEM pictures of a) Unmodified insulation materials b) Materials modified with silica gel The hydrophobic property of the silica gel modified materials was studied by using water drop contact angle method7. Fig. 3 shows image of water droplet on the surface of silica gel modified materials. Contact angle is a measure of the hydrophobic nature of the surface. If the water drops spreads out on the surface and the contact angle is less than 90o, the surface is referred as hydrophilic8 and prone to water adsorption which may deteriorate the properties. The wetting surface that makes contact angle greater than 90o is referred as hydrophobic. Highly hydrophobic surfaces that have water contact angles higher than 150o are termed as super hydrophobic9. The contact angle made by silica gel modified material surface with water drop has been found to be 147o. It shows that the material modified with silica gel has highly hydrophobic surface and suitable for use in moist environment.

θ = 147°

Figure 3: Image of water droplet placed on surface of silica gel modified materials The comparative data of the thermal conductivity and heat capacity values of the commercially available unmodified thermal insulation materials and silica gel modified insulation materials are given in Table 1.

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Table 1: Data on thermal conductivity and heat capacity for unmodified and silica gel modified insulation materials Sample Commercially available unmodified thermal insulation materials Modified materials impregnated with silica gel

Thermal conductivity K (W/mK) 0.375

Heat capacity Cp (KJ/M3K) 806

0.234

587

From the thermal conductivity and heat capacity data, it is observed that thermal properties of the silica gel modified materials are improved as compared to unmodified materials. The decrease in thermal conductivity value from 0.375 W/mK to 0.234 W/mK for modified materials attributes to silica aerogel coating on materials fabric. The silica aerogel has nano-structured pores which confines the free path for air and reduce the thermal conductivity significantly10. The decrease in heat capacity values for the modified materials is expected due to lower thermal conductivity value which may lead to slower heat dissipation from the materials. CONCLUSIONS A method has been demonstrated successfully to develop the modified thermal insulation materials by sol gel processing to improve the thermal properties and hydrophobic property of the insulation materials. The commercially available thermal insulation material has been modified by impregnation of silica gel. The unmodified materials fabric has been dipped in silica sol and then dried to extract the gel solvent that resulted in material fabric coated with silica gel. The silica gel modified materials showed improved thermal insulation property as compared to unmodified materials (thermal conductivity decrease from 0.375 W/mK to 0.234 W/mK). The modified materials have added advantage that it has hydrophobic surface as proven by contact angle method. The silica gel modified materials have expanded the scope of application for the thermal insulation materials in areas where improved thermal properties are required and moist environments are concerned. REFERENCES 1. Dorde Dobrota, Branko Lalic, Ivan Komar, Problem of Boil - off in LNG Supply Chain, Transactions on Maritime Science, 2013; 02, 91-100. 2. Hajar Maleki, Luisa Durães, António Portugal, Synthesis of lightweight polymer-reinforced silica aerogels with improved mechanical and thermal insulation properties for space applications, Microporous and Mesoporous Materials, 2014, 197, 116–129. 3. P. B. Wagh, S.V. Ingale, Comparison of Some Physico-Chemical Properties of Hydrophilic and Hydrophobic Silica Aerogels, Ceramics International, 2002, 28, 43–50. 4. P. B. Wagh, S. V. Ingale and Satish C. Gupta, New Technology for Rapid Processing and Moulding of Silica Aerogel Materials in Prescribed Shapes and Sizes and their Characterization, J. Sol-Gel Sci Technol, 2011, 58 481-489. 5. H. Amir; M.Tavakoli, Matthew, Armentrout, Masaki Narisawa, Sabyasachi Sen and Alexandra Navrotsky; White Si–O–C Ceramic: Structure and Thermodynamic Stability, Journal of the American Ceramic Society; 2015, 98 (1), 242–246. 1948

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6. S.V.Ingale, P.B.Wagh, A.K.Tripathi, V.S.Kamble; Ratanesh Kumar and Satish C. Gupta, Physicochemical Properties of Silica Aerogels prepared from TMOS/MTMS mixtures, Journal of Porous Materials; 2011, 18, 567-572. 7. A.Venkateswara Rao, S.S.Latthe, S.L.Dhere, S.S.Pawar, H.Imai, V.Ganesan, S.C.Gupta, P.B.Wagh ; Control on Wetting Properties of Spin-deposited Silica Films by Surface Silylation Method, Appl Surf Sci; 2010, 256(7), 2115-2121. 8. P. B. Wagh, S. V. Ingale, Satish C. Gupta; Comparison of hydrophobicity studies of silica aerogels using contact angle measurements with water drop method and adsorbed water content measurements made by Karl Fischer’s titration method , J Sol-Gel Sci Technol; 2010, 55,73–78 9. J.Dong, Z.H.Yao, T.Z.Yang, L.L.Jiang & C.M.Shen; Control of Superhydrophilic and Superhydrophobic Graphene Interface. Sci. Rep; 2013, 3, 1733. 10. Prakash C. Thapliyal and Kirti Singh; Aerogels as Promising Thermal Insulating Materials: An Overview Journal of Materials; 2014, 2014, Article ID 127049, 10 pages, doi:10.1155/2014/127049

Author for Correspondence: P. B. Wagh Applied Physics Division, Bhabha Atomic Research Centre, Mumbai, India - 400 085

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J. Chem. Bio. Phy. Sci. Sec. C, February 2015 – April 2015; Vol.5, No.2; 1944-1949