Although you may not know it, the modern world has many reasons to be grateful for cenospheres.
Few people know of their existence, even fewer people know where they are from. Although a quick glance at Wikipedia, the source of all sources, will inform the uninformed that, “A cenosphere is a lightweight, inert, hollow sphere made largely of silica and alumina and filled with air or inert gas, typically produced as a byproduct of coal combustion at thermal power plants. The color of cenospheres varies from gray to almost white and their density is about 0.4–0.8 g/cm3 (0.014–0.029 lb/cu in), which gives them great buoyancy.”
However, that does little to describe the true beauty of these tiny, yet powerful, balls of fly ash. For their real strength lies in the diversity of their use. As the French industry journal, Industrie & Technologies, states, “Because of their low density, small size, spherical shape, mechanical strength, high melting temperature, chemical inertia, insulating properties and low porosity, microspheres [also known as cenospheres] find a wide range of applications in industry. In particular, [they are ideal] for reinforcing materials or imparting properties of resistance to corrosion, or thermal and sound insulation to coatings or paints. They can be described as multifunctional fillers and integrate well in resins and binders such as thermoplastics and thermosetting.”
Cenospheres in Paints and Coatings
There are a great many uses for cenospheres in the paint and industrial coating industry, due to the additional qualities they provide. For example, cenospheres are often used in coatings to control infrared radiation, giving those coatings an advantage over ones that merely attempt to limit thermal conductivity.
Meanwhile, coating experts at Petra Buildcare Products, explain how cenospheres, “… improve the quality of the paint by improving the volume and density of the product. After application on the wall, the ceramic beads tend to shrink thereby creating a tightly packed film on the wall.”
Cenospheres in Syntactic Foams
Cenospheres are often used to make ‘syntactic foams’. These are specialized solids which use cenospheres as a filler to provide any number of advantages, from lower cost, to added strength, sound proofing, buoyancy and thermal protection.
Experts at Engineered Syntactic Systems describe syntactic foam as follows;
“The ‘syntactic’ portion refers to the ordered structure provided by the hollow spheres. The ‘foam’ term relates to the cellular nature of the material. Thanks to its unique properties of high strength at low density, syntactic foam has become widely used in subsea buoyancy applications. Syntactic materials are resistant to the combined effect of hydrostatic pressure and long-term exposure which make them ideal for oceaneering projects such as cable and hardball floats and instrumentation support. They also provide strength and structural integrity at a significantly lower weight per volume than most traditional materials which make them an attractive choice in many defence and civil engineering applications.”
Cenospheres in Petroleum Drilling
For proof of the unknown importance of cenospheres, you need look no further that the vital role they play in the petroleum industry. For while everyone knows of the importance of oil in the modern world, it is a little known fact that cenospheres have, as the French industry journal, Industrie & Technologies, states, “…been used for several years in the field of oil drilling to reduce the density of a petroleum cement paste without increasing the water content.”
Cenospheres in Plastics and Polymers
Cenospheres also have a use in the manufacture of plastics and polymers, as their re-formable shape or strength helps to avoid shrinkage in thermoplastics and thermosetting plastics.
They are also being used in modern composites in the automobile industry. For example, the 2016 Chevrolet Corvette contains a “sheet molding compound in which glass microspheres replace calcium carbonate filler and shave 20 pounds [9kg] off the sports car’s Stingray Coupe model weight.” The Vice President of the manufacturer, Continental Structural Plastics Inc., Probir Guha, explains the reason for the inclusion of cenospheres in the composite, in saying that, “the typical SMC formula for this type of vehicle application comprises 20% by volume of glass fiber reinforcement, 35% resin and 45% filler, usually calcium carbonate,” adding that, “This new SMC [sheet moulding compound] is cost competitive with aluminium.”
Cenospheres in Concrete
For years, cenospheres have been a useful additive to concrete, providing additional strength, and or sound insulation, whilst also lowering density. Jeff Girard, President at The Concrete Countertop Institute, explains these advantages, saying, “In theory, cenospheres can replace some of the normal-weight sand used in concrete. Cenospheres have a density that is less than water (averaging 0.7 vs. Water’s 1.0); quartz sand particles typically have a density of about 2.65. This means that 1 pound of cenospheres takes up the same absolute volume as about 3.8 lbs. of sand.”
Industrie & Technologies, also outlines the use of cenospheres as a means of lowering noise pollution, stating that, “[Cenospheres are used] in building materials to lighten concrete, while maintaining a compressive strength of 30 MPa at a density of 1.6 T / m3, improving their tightness and reducing their sound transmission. For example, the St. Petersburg Scientific and Technical Center of Applied Nanotechnologies (STCAN) is involved in building bridges with such concretes in Russia, [for a quieter road surface]. Cenospheres are also used to improve the thermal and sound insulation qualities of plasters, mortars and plasters, used for walls, floors and ceilings. An addition of 40% volume cenospheres halves the noise transmission coefficient.”
Cenospheres in Pharmaceuticals
Cenospheres have been used in the pharmaceutical industry for many years, as the small balls can act as a near-perfect transport device when coated with drugs. Additionally, as the French industry journal, Industrie & Technologies, notes, “Cenospheres covered with silver oxide may, for example, be integrated into dressings in order to accelerate wound healing.”
Cenospheres in Advanced Industries
A great deal of research is being conducted to discover new uses for this versatile by-product. For example, new catalysts for the methane oxidation process are being developed using magnetic cenospheres.
Cenospheres are also being used in the development of metal matrix composites (MMC), a variety of materials that attempts to combine the high energy absorption, impact resistance, and low density of the spheres with the qualities of other substances. Others, such as Paul Biju-Duval of the Georgia Institute of Technology based in Atlanta, have worked hard in the development of cementless building materials. His work continues, adding to a cenosphere mix, items such as bamboo and metallic tubing as a means to finding alternative, cheaper, stronger, and more environmentally-friendly construction methods.
Meanwhile, the Institute of Chemistry and Chemical Technology of the Russian Academy of Sciences in Krasnoyarsk, is studying ways that cenospheres could be used in catalytic transformations. While BAE systems is attempting to use cenospheres in paint as a means to support invisibility in the infrared spectrum, thus enabling military craft to have ‘invisibility cloaks’.
With such a wide range of uses, and an even wider range of potential uses, it is no wonder why interest in cenospheres is growing. As long as product developers are looking for light weight fillers, improved drug delivery systems, improved coatings, cement substitutes, and composite additives, then there will be a need for cenospheres. Plus with increased research into new uses for these versatile spheres, then only time will tell where the future of cenospheres lies.