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This book explores the improvement in thermal insulation properties of protein-based silica aerogel composites fabricated by a novel, inexpensive and feasible method. The resulting material exhibits polymeric foam behavior including high compressibility, super-hydrophobic qualities and excellent strain recovery in addition to low thermal conductivity. The fabrication methodologies are explained in great detail and represented in flowcharts for easy reference and understanding. This monograph gives readers a new perspective on composite fabrication using methods other than the traditional ones and explores the endless ways of altering the composition to modify the properties of the silica aerogel composites. Applications for this novel composite are diverse and range from those in the pharmaceutical and aerospace industries to the oil and gas industries.



Chapter 1. Introduction

Aerogels were first discovered by an American scientist Samuel Stephens KistlerSamuel Stephens Kistler” \i in the 1930s (Hunt et al. in Insulation Materials: Testing and Applications, ASTM, USA, 1991) but the interest in these materials was renewed during 1970s and 1980s as a catalystCatalyst” \i to enhance greener environment. These materials present enormous opportunities in the fields of engineering. Aerogels are a group of very light solid materials, highly porous and known to possess significantly higher thermal insulationThermal insulation” \i properties (Rao et al. in Journal of Sol-Gel Science and Technology 27:103–109, 2003). They appear as “foam like”Foam like” \i translucent substance referred to as “Frozen SmokeFrozen Smoke” \i”.

Mahesh Sachithanadam, Sunil Chandrakant Joshi

Chapter 2. Aerogels Today

The term “aerogel” is not a name associated with a specific mineralMineral” \i or material with a specific formula, but rather a term that encompasses certain materials with unique geometryGeometry” \i and structureStructurestructures” \i. Aerogels are a special class of nanoporousNano-porous” \i solids with complex interconnectivity and branched structureStructurestructures” \i of a few nanometers. It comes in a variety of forms, colors, and shapes from monolithicMonolithic” \i to powdersPowderspowdery” \i. Aerogels have very little solid component and almost made up of 99.8 % of air, which gives the product an almost ghostly appearance.

Mahesh Sachithanadam, Sunil Chandrakant Joshi

Chapter 3. Fabrication Methods

The high porosity and nanoscaled pores with many dead ends in silica aerogels structure have contributed to their ultralow density, low thermal conductivityThermal conductivity” \i, high opticalOpticaloptics” \itransmittanceTransmittance” \i, acoustic attenuationAcoustic attenuation” \iand hydrophobicHydrophobic” \i properties. However, silica aerogels are brittle with very low strengthStrength” \i, and modulusModulus” \i, which compromise their commercial use. These limitations have warranted the need to broaden and optimize the usefulness for a variety of applications. To overcome this drawback, silica aerogels have since been added with another material, such as polymers and metals, prior to gelationGelation” \i stage of manufacturingManufacturing” \i before the drying the process.

Mahesh Sachithanadam, Sunil Chandrakant Joshi

Chapter 4. Microstructural Analysis

Gelatin is the main binder in the fabrication of composites and it is therefore essential to evaluate its properties.

Mahesh Sachithanadam, Sunil Chandrakant Joshi

Chapter 5. A New Phenomenon—Brittle to Ductile Transition

Most published literature analyzed the elastic modulus of silica aerogels by drawing inspiration from the cellular solids models. For example, Ashby and Gibson (Cellular solids—structure and properties. Cambridge University Press, Cambridge, 1997) describe the open cellular foam model compressive modulus to follow power law dependence on the relative density as shown in Eq. 5.1 where C and μ are geometric constants that depend on the topological features and microstructure undergoing cell wall bending as the dominant deformation.

Mahesh Sachithanadam, Sunil Chandrakant Joshi

Chapter 6. Superhydrophobic and Ultralow Thermal Insulation

Silica aerogels are very light, highly porous nanomaterial with large internal surface area possessing excellent thermal insulation that may get affected when the binders and additives used in aggregation. The most significant of all the properties is the extremely low thermal conductivity, reportedly to be in the range 0.017–0.024 W/m-K as highlighted by Schmidt and Schwertfeger (J Non-Cryst Solids 225:364–368, 1998).

Mahesh Sachithanadam, Sunil Chandrakant Joshi

Chapter 7. Acoustic Performance of Silica Aerogel Composites

Acoustics is the interdisciplinary science that deals with the study of mechanical waves and vibrations in the three states of matter with the aid of a medium to propagate. Sound is often described as audible waves and vibrations in the spectrum of 20–20 kHz.

Mahesh Sachithanadam, Sunil Chandrakant Joshi


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