News Column

Patent Issued for Superinsulation with Nanopores

August 5, 2014



By a News Reporter-Staff News Editor at Journal of Technology -- Industrial Science & Technology Network, Inc. (York, PA) has been issued patent number 8785509, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventor is Yang, Arthur J. (York, PA).

This patent was filed on May 1, 2009 and was published online on July 22, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The first generation of thermal insulation included materials with naturally low densities such as cotton, wool, cork and asbestos. Since entrapped air (with thermal conductivity as low as 23 mW/M.degree. K) was the primary insulator, a lower density (more air) corresponded to a higher insulation value (i.e. lower thermal conductivity). The second-generation insulations were industrially processed, porous substrates containing even more air (lower density and more insulating). These insulations included fiberglass, rubber and plastic foams, and other man-made porous substrates. The scheme used by the second generation, lowering the thermal conductivity (K value) by reducing density, finally reached its bound (.about.30 mW/M.degree. K).sup.1 when such practices began compromising insulation strength and performances, attributed to too much air as well as excessive radiation heat loss. The third generation has evolved with the emergence of nanotechnology. Modeling results demonstrated that if the pore size of insulation could be reduced to below mean free path.sup.2 of air, i.e.

"Between 1992 and 1995, we demonstrated this feasibility while working at Armstrong World Industries on a $4.5 million project awarded by the Advanced Technology Program.sup.3. By reducing the pore size to nanometer scales, we successfully made several nanopore composites with super insulation properties. The following table listed data of previous samples in comparison with a second generation insulation, fiberglass:

"TABLE-US-00001 Insulation Material Thermal K (mW/M .degree.K) R/inch* Fiber Glass 45 3.2 Granular Silica Aerogel 23 6.3 Aerogel with Layered Silicates Panels 16 9 Inverse-Emulsion Composite Panels 20 7.2 Aerogel-Polymer Microcomposites 17 8.7 Inorganic-Organic Composite 13 10.5 Aerogel *R-per-inch is a commonly used measure of insulation value. It is equivalent to the reciprocal of the thermal conductivity in unit of Btu in/hr ft.sup.2 .degree. F. The energy code is given by R-value, i.e. R-per-inch times thickness.

".sup.3 'Thermal Insulation Materials-Morphology Control and Process for the Next Generation of Performance,' ATP award to Armstrong World Industries, Inc. (1992).

"These new materials failed to reach markets because of their high processing costs. This class of material is a super insulation due to a combination of high porosity and nanometer-size pores. These special structural attributes are also causing its processing difficulties. The high porosity material is mechanically weak. When drying under ambient conditions, capillary stress from the liquid meniscus in the pore shrinks the material and results in significant structural damages. For pores of nanometer size, this stress can be in the range of a hundred bars (.about.1500 pounds per square inch); the smaller the pore, the higher the stress. The shrinkage due to high stress reduced the porosity and the number of nanometer pores in the material structure; resulting in substantial loss of its super insulation value after ambient processing.

"One solution to this problem was to dry the wet gel under supercritical conditions of a fluid (most conveniently, by, using supercritical CO.sub.2 fluid). This had allowed the liquid system to bypass the coexisting (infinitely compressible) region and avoid generating any meniscus within the pores. This processing requirement, drying the material under a supercritical condition, instead of ambient condition, was the reason for the high capital and processing costs associated with the production of nanopore insulation. The following table provides direct comparisons of making insulation by solution process to that by gas foaming process, which is the most widely process used for making the second generation of insulation.

"TABLE-US-00002 Process Gelation and Drying Direct Gas Foaming Characteristics (Aerogel, Hydrogel) (Gas Blown Polymer Foams) a. Porosity is Created by: Liquid solvent Gas Bubbles b. Fluid Weight % Needed 2000% 5~10% for Creating 95% Porosity c. Processing Speed Fluid diffusion, depending on Gas blown, instantaneous sample thickness (.delta.), .varies..delta..sup.2, slow d. Pore Size Control 10 nm, needs special 100-500.mu., very difficult to processing care to preserve control the nanopores e. Thermal Conductivity 20 mW/M.degree.K 30-35 mW/M.degree.K

"If we can replace the solution drying process and make nanopore insulation by foaming, the cost reductions will be well beyond those needed to make the technology commercially viable. Recently, we had successfully developed the technology of producing low-density (density .about.0.03 g/cc) Styrofoam insulation by foaming with 100% CO.sub.2. By integrating the two technologies together, we could design a system that utilizes supercritical CO.sub.2 to first create and preserve nanometer gas embryos (by a nucleation process), and, then to expand gas bubbles (by a foaming process) for making low-density insulation. Such a system could produce high-porosity foams with extremely small pore sizes. The challenge, of course, remained as how to effectively control the bubbles' size during the rapid foaming process.

"A foaming process consisted of rapid generation of numerous gas bubble nuclei, followed by their fast growth during the foam's expansion. We could envision two approaches to control the pore size during such a rapid bubbling process. First, we plan to induce the homogeneous nucleation process (already demonstrated by pressure vessel experiments) in a foam extrusion process to generate extremely small gas embryos, followed by controlling the bubbles' growth. Or, we can use a reactive system, such as the polymerization of styrene or urethane, which secrete out volatile solvent, or co-solvent, during its polymerization and depressurization, to create a spinodal decomposition, followed by controlled expansion of the entrapped volatile fluid phase. Both processes required a low initial interfacial tension, as well as a controlling mechanism to slow down the bubble growths. Either process, if successful in generating fine pores and high porosity, would lead to a breakthrough in producing nanopore insulation because of the tremendous cost savings attributed to the rapid depressurization of supercritical CO.sub.2 (or similar volatile fluids). Obviously, such a breakthrough process would be difficult, because it would require orders of magnitude improvement in pore size controls (from .about.100 microns to 0.1 micron) comparing to prior foaming arts."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "This invention relates to the field of thermal insulation. In particular, the invention describes superinsulation articles having a desired porosity, reduced pore size and cost-effective methods for manufacturing such articles. In one aspect of the present invention, the article may comprise a material system with at least about 20% porosity. In a further aspect of the invention, an article may comprise greater than about 25% of nanopores having a pore size no greater than about 1500 nanometers in its shortest axis.

"The articles of the present invention may be used for a variety of sound and/or thermal insulation applications including building insulation, refrigeration insulation, industrial insulation, and HVAC insulation products. The articles may also be used for specialty insulation products including space vehicles, space stations, aviation, and superconducting devices and equipment. Finally, the articles of the present invention may be used as a foam product for structural support, cushioning, protection, packaging, sports, entertainment, sound insulating, medical devices, and decoration."

For the URL and additional information on this patent, see: Yang, Arthur J.. Superinsulation with Nanopores. U.S. Patent Number 8785509, filed May 1, 2009, and published online on July 22, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8785509.PN.&OS=PN/8785509RS=PN/8785509

Keywords for this news article include: Industrial Science & Technology Network Inc..

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Source: Journal of Technology


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