Syntactic foam

Syntactic foams are composite materials synthesized by filling a metal, polymer,[1] or ceramic matrix with hollow spheres called microballoons[2] or cenospheres or non-hollow spheres (e.g. perlite).[3] In this context, "syntactic" means "put together."[4] The presence of hollow particles results in lower density, higher specific strength (strength divided by density), lower coefficient of thermal expansion, and, in some cases, radar or sonar transparency. A manufacturing method for low density syntactic foams is based on the principle of buoyancy.[5][6]

Syntactic foam, shown by scanning electron microscopy, consisting of glass microspheres within a matrix of epoxy resin.

The term was originally coined by the Bakelite Company, in 1955, for their lightweight composites made of hollow phenolic microspheres bonded to a matrix of phenolic, epoxy, or polyester.[7]

Tailorability is one of the biggest advantages of these materials.[8] The matrix material can be selected from almost any metal, polymer, or ceramic. Microballoons are available in a variety of sizes and materials, including glass microspheres, cenospheres, carbon, and polymers. The most widely used and studied foams are glass microspheres (in epoxy or polymers), and cenospheres or ceramics[9] (in aluminium). One can change the volume fraction of microballoons or use microballoons of different effective density, the latter depending on the average ratio between the inner and outer radii of the microballoons.

The compressive properties of syntactic foams, in most cases, strongly depend on the properties of microballoons. In general, the compressive strength of the material is proportional to its density.

The matrix material has more influence on the tensile properties. Tensile strength may be highly improved by a chemical surface treatment of the particles, such as silanization, which allows the formation of strong bonds between glass particles and epoxy matrix. Addition of fibrous materials can also increase the tensile strength.

Applications
Syntactic foam sphere used as a subsurface float in oceanographic mooring.

These materials were developed in early 1960s as improved buoyancy materials for marine applications.[10] Other characteristics led these materials to aerospace and ground transportation vehicle applications.[11] Current applications for syntactic foam include buoyancy modules for marine riser tensioners, remotely operated underwater vehicles (ROVs), autonomous underwater vehicles (AUVs), deep-sea exploration, boat hulls, and helicopter and airplane components. Structural applications of syntactic foams include use as the intermediate layer (that is, the core) of sandwich panels.

Other applications include;

  • Deep-sea buoyancy foams. A method of creating submarine hulls by 3D printing was developed in 2018.[12]
  • Thermoforming plug assist
  • Radar transparent materials
  • Acoustically attenuating materials
  • Cores for sandwich composites[13][14]
  • Blast mitigating materials
  • Sporting goods such as bowling balls, tennis rackets, and soccer balls.[15]
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See also

References
  1. Shutov, F.A. (1986). "Syntactic polymer foams". Advances in Polymer Science. 73-74: 63–123. doi:10.1007/3-540-15786-7_7.
  2. H. S. Kim and Pakorn Plubrai, “Manufacturing and failure mechanisms of syntactic foam under compression”, Composites Part A : Applied Science and Manufacturing, Vol 35, pp.1009-1015, 2004.
  3. Dipendra Shastri and H. S. Kim, “A new consolidation process for expanded perlite particles”, Construction and Building Materials, Vol 60, June, 2014, pp.1-7.
  4. "What is Syntactic Foam?". Cornerstone Research Group. Archived from the original on 20 July 2012. Retrieved 7 August 2009.
  5. Md Mainul Islam and H. S. Kim, “Manufacture of syntactic foams: pre-mold processing”, Materials and Manufacturing processes, Vol 22, pp.28-36, 2007.
  6. Md Mainul Islam and H. S. Kim, “Manufacture of syntactic foams using starch as binder: post-mold processing”, Materials and Manufacturing processes, Vol 23, pp.884-892, 2008.
  7. From the Oxford English Dictionary citation of Sci. News Let. 2 Apr. 213/3
  8. Bardella, L.; Genna F. (2001). "On the elastic behavior of syntactic foams". International Journal of Solids and Structures. 38 (2): 7235–7260. doi:10.1016/S0020-7683(00)00228-6.
  9. Shubmugasamy, V. (2014). "Compressive Characterization of Single Porous SiC Hollow Particles". JOM. 66 (6): 892–897. doi:10.1007/s11837-014-0954-7.
  10. Kudo, Kimiaki (January 2008). "Overseas Trends in the Development of Human Occupied Deep Submersibles and a Proposal for Japan's Way to Take" (PDF). Science and Technology Trends Quarterly Review. 26: 104–123. Archived from the original (PDF) on 21 July 2011. Retrieved 10 August 2009.
  11. Karst, G (2002). "Novel Processing of High-Performance Structural Syntactic Foams". Society for the Advancement of Material and Process Engineering. Archived from the original on 23 July 2011. Retrieved 7 August 2009.
  12. "3-D Printing Breakthrough for Lightweight Syntactic Foams Could Help Submarines Dive Deeper | NYU Tandon School of Engineering". engineering.nyu.edu. Retrieved 22 September 2018.
  13. Md Mainul Islam and H. S. Kim, “Sandwich composites made of syntactic foam core and paper skin: manufacturing and mechanical behavior”, Journal of Sandwich Structures and Materials, 2012, Vol 14(1), pp.111-127.
  14. Md Arifuzzaman and H. S. Kim, Novel flexural behaviour of sandwich structures made of perlite foam/sodium silicate core and paper skin, Construction and Building Materials, Construction and Building Materials, Vol 148 2017, pp 321–333.
  15. Thim, Johann (3 February 2005). "Performing Plastics - How plastics set out to conquer the world of sports". European Chemical Industry Council. Retrieved 10 August 2009.
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