Nanofabrication Techniques—Sol-Gel Chemical Processing

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A Sol-Gel is a series of colloidal—solid nanoparticles with a diameter between 1-100 nanometers—solids structured into a rigid, interconnected rigid network—in essence a gel—of polymeric chains with pore sizes in the sub-micrometer to nanometer range[1].  Simply put, Sol-Gels are very porous, highly ordered structures analogous to sponges.  Sol-Gels can be manufactured through a number of processes, three of which make the basis of the Sol-Gel Process[2].  However, these three processes follow the same seven general steps.

The initial step is the mixing of colloidal powders created by chemical vapor deposition.  The second step is the casting of the resultant low-viscosity liquid in a non-stick cast.  The third step is gelation; the process where the colloidal powders link together to greatly increase the viscosity of the solution and creating a near solid that fits the shape of the mold.  The fourth and fifth steps are the aging and drying of the newly created structure, further stiffening the material.  The sixth step is the dehydration or chemical stabilization of the Sol-Gel to create the ultrastable, porous material.  The final step is densification, tempering the gel with high heat to solidify the gel.

Sol-Gels can be used for a number of applications and can exhibit a number of properties.  Gels made with this process can exhibit light-weight, high-strength properties that make them useful for things such as energy production and storage, biosensing and zeolite synthesis.  Additionally, the Sol-Gel process is used in the cost effective manufacture of high quality mirrors and optics as well as in the manufacture of nanoscale powders.


References

  1. Biswas A, Bayer IS, Biris AS, Wang T, Dervishi E, Faupel F. Advances in top–down and bottom–up surface nanofabrication: Techniques, applications & future prospects. Advances in Colloid and Interface Science. 2012 ;170(1-2):2 - 27.
  2. Hench LL, West JK. The Sol-Gel Process. Chemical Review: The American Chemical Society. 1990 ;90(1):39.

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The Sol-Gel process allows for the control of the chemical variability of homogeneous structures at the nanoscale to produce materials to achieve a wide variety of unique physical properties. This technology allows for the creation of well-ordered nanostructured materials such as ceramics or organic-inorganic hybrid materials.

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This technology is an enabling technology in designing and fabricating different nano materials and aerogels. The applications of these materials range from heat resistant structures for industrial insulation, to gels used in the cleanup of radioactive materials, to ceramic structures designed to protect people in dangerous environments. The potential benefits of this technology are ambiguous, but include safety and security, energy and resource conservation, energy storage and environmental protection and remediation.

Risk Summary: 

The risks associated with this process are related to well understood chemical processes. The risks are ambiguous and hard to define because they are dependent on the material fabricated and the colloids used in the process. These risks can range from ecological, explosive and health risks to risks to the human condition.

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