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.
Photo credit: dopcreator
Photo credit: syntactic foam suppliers, ESS
The importance of cenospheres can be summed up in a not-so-recent quote by an anonymous chemical trader from India, who wrote on the Go4worldbusiness trading platform, “We require Cenospheres immediately.”
It is unknown whether the request was successful or not, for the post had no positive feedback listed. Instead, the request was met with a further 8 postings of chemical traders also hoping to buy. Clearly there is a demand for cenospheres, but what is less clear is exactly what they are.
With this in mind, here is a brief outline of the what, the where, the when, and perhaps most importantly, the how much of cenospheres.
What are Cenospheres?
Named from the Greek words kenos (hollow) and sphaera (sphere), cenospheres are balls of aluminium silicate, a material similar to glass, that are filled with a mix of oxygen, nitrogen and carbon dioxide. They measure between 10 and 600 micrometers, and so appear dust like to the human eye.
They can be extracted from underground deposits laid down 65 million years ago (when the meteor that killed the dinosaurs impacted Earth), or more commonly, they are taken from the fly ash that is created as a by-product from coal-fired power stations. As a result, many power plants adjust their combustion parameters so as to obtain desired quantities and qualities of recoverable cenospheres.
Although they are a product of a fossil fuel resource, they are often seen as a more ecologically friendly chemical feedstock, as they find a use for a waste product. Even though cenospheres constitute only 1%-3% of fly ash, this waste would normally be buried, or taken away on the wind where it pollutes the air.
Tackling even a small part of the waste from power stations is environmentally helpful, as the amount of waste created by power generation is huge. According to National Geographic, “Fly ash and the other residuals of burned coal add up to one of the largest waste streams in the United States: More than 136 million tons per year. In Europe, coal waste totals 100 million tons per year by some estimates. Similar figures aren’t available for China, but since it is now burning more coal than the United States, the waste generation is significant. Scientists at the China Building Materials Academy and the Institute of Technical Information for Building Materials Industry calculate that their country has accumulated 2.5 billion tons of coal ash.”
How Much are Cenospheres Worth?
This is a very difficult question to answer, as due to cenospheres relative low weight and high volume they are often used as fillers for more expensive plastics, construction materials and composites. So the value of cenospheres is largely set by the value of the raw material they are replacing.
However, Karen Wood in the industry journal Composites World notes that, “The cost of microspheres varies considerably depending on a variety of factors, including material, density, strength and volume. Expancel microspheres, for example, range in price from $5/lb to $30/lb [$12/kg to $70/kg], depending on grade and volume. The manufacturing process employed in the production of the microsphere also affects cost.” While plastics consultant Paul A. Tres, former president of ETS Inc. points out that, “In general, high-strength, glass microspheres cost two to three times more than chopped glass fiber.”
However, the French industry journal, Industrie & Technologies, states that, “[While the price of cenospheres is] difficult to assess, the market is certainly growing. One good indicator, [is that] the price of a ton has doubled in the past two years.”
Where are Cenospheres From?
In general, where ever there is fly ash, there are cenospheres, which means that the world’s largest producers are based in China, Russia, the U.S. and India. Although, there is plenty of fly ash to go around, with the journal, Industrie & Technologies estimating that, “[The] More than 50,000 [coal-fired power] plants worldwide produce more than 1 billion tons of fly ash every year.”
The journal continues to explain how, “The main method of recovering cenospheres is a wet method, as due to their low density and hollow nature, cenospheres float. They are then collected on the surface of settling ponds, either by suction or mechanically, and then dried. Triboelectric [separation by use of electrical charge] or centrifugal systems are also in use, depending on the quantities to be treated, [which] then allows them to be separated from heavier particles containing carbon and iron.”
A cenosphere settling pool in the Netherlands, courtesy of cenosphere supplier PMS.
What are the Technical Specifications of Cenospheres?
As a rough guide, the ceramic particles in fly ash have three types of structure. The first type are hollow and are called cenospheres. The second are solid and called precipitator, while the third type of particles are called plerospheres [from the Greek pleres meaning filled], and are hollow particles with a larger diameter that contain smaller precipitators and cenospheres.
They vary in colour, from white to dark grey, depending on the raw material used, their size, the burning process used, their wall thickness, and the materials that they are made from. So, to quote Industrie & Technologies, “The smaller cenospheres have a higher content of silica (SiO2) and aluminum oxide (Al2O3) with a perfectly empty internal structure, while the larger ones have a lower SiO2 and Al2O3 content, but a more resilient inner structure.” Their chemical make-up also gives them their alternative name of alumosilicate microspheres.
The journal continues by outlining that, “The thickness of the wall also varies greatly according to their size, [which is] between 2.5% and 10.5% of the diameter of the cenosphere. Also, their magnetic properties may vary according to their composition. The structure of the cenospheres defines their density (apparent 0.3-0.5g/cm3, actual 0.6-0.7g/cm3), their thermal conductivity (0.1-0.2 W/mK), their mechanical strength (210-350kg /cm2), their thermal stability (sintering between 1000-1450°C), and their resistance to acids. They are also chemically inert.”
Who Trades Cenospheres?
What is key, is that the specifications of cenospheres differ greatly from place to place and plant to plant, and this can make for a number of niche markets which smart chemical traders are able to exploit.
Buyers must therefore spend time either nurturing relationships between existing suppliers, or by doing the leg work in finding a new cenosphere supplier whose product meets the necessary standards.
Recommended contacts include the Expancel wing of AkzoNobel, which is one of the world’s largest suppliers of cenospheres, and Alibaba of course, who seems to sell everything. Cenosphere buyers who prefer a more trustworthy source are also advised to contact AG Chemi group (who pay for this blog), as all traders working through them are certified as genuine.
Overall, the cenosphere market can be described as expanding, with the number of applications available to these small balls of alumosilicate microspheres growing. New markets have been established among battery manufacturers, plastics producers, in paints and industrial coatings, as well as in the construction industry. While developers of modern composites are finding new uses all the time, including in the automobile industry as a lightweight alternative to aluminium.
You can read more about the growing number of applications for cenospheres in part two of this blog here.
Photo credit: IndiaMart
Microspheres have been known for years, but as demand for improved materials and increased functionality from everyday products grows, so too has demand for these strong yet intricate little balls. Microspheres are big.
But what exactly are these tiny materials that are making such a large impression in so many markets?
Well, to quote Webster’s dictionary, they are, “spherical shells that are usually made of a plastic polymer or glass. They have a very small diameter usually in the micron or nanometer range. Sometimes they are filled with a substance (such as a drug) for release as the shell is degraded.”
All of which, is true. Who would want to argue with Webster’s dictionary? But there is in fact much more to microspheres than this simple definition. In the world of modern engineering, microspheres can be made from a variety of materials, for a vast range of uses, function in numerous industries, and are beginning to become an indispensible world commodity.
With this in mind, here are some facts about these powerful spheres.
One of the best selling forms of microsphere are those made from glass. They are made from a multi-step process, in a manner described by Karen Wood in the industry journal Composites World, as follows; “In general, a multistep process is used to produce high-temperature glass microspheres. Glass is initially produced at high temperatures from soda-lime-borosilicate, after which it is milled to a fine particle size. Trace amounts of a sulfur-containing compound, such as sodium sulfate, are then mixed with the glass powder. The particles are run through a high-temperature heat transfer process, during which the viscosity of the glass drops and surface tension causes the particles to form perfect spheres. Continued heating activates the blowing agent, which releases minute amounts of sulfur gas that form bubbles within the molten glass droplets. The result is a rigid, hollow sphere manufactured with an eye to increasing crush resistance (that is, the ability to withstand external pressure and avoid fracture of the bubbles) without sacrificing low density.”
Along with glass, the other most common form of microsphere are those made from plastic. This is largely because polymer microspheres are able to collapse (due to heat and/or pressure) and then bounce back into shape when conditions return to normal.
As Chris Rosenbusch, marketing manager for microsphere manufacturer Expancel Inc., explains, “Excessive pressure will cause the plastic sphere to flatten but not burst. [So]When the pressure is released, the microspheres tend to recover. In a spray-up application, for instance, the microspheres will deform when the resin is pressurized prior to spraying. However, once the material hits the mold and returns to ambient pressure, the microspheres will rebound to their spherical shape.”
The same is true for microspheres used in heat manufactured composites, as Rosenbusch makes clear, saying, “The heat of exotherm during cure can be problematic in composite manufacture. [But] By incorporating plastic microspheres, as the part heats up, the resin is able to expand inward, causing the microspheres to compress. Once the heat dissipates, the spheres rebound.” This gives plastic moulding manufacturers greater control over thermal expansion.
Hollow plastic microspheres have incredibly low densities, with some having specific gravities as low as 0.025. This gives them a very large displacement to weight ratio, making them a popular resource in the manufacture of, amongst other things, spray-up fiber-reinforced thermosetting composites and extrusion applications.
One of the world’s leading manufacturers of microspheres, Expancel (which is part of the Akzo-Nobel group) explains more about the production and many applications of gas filled polymer microsphere in this YouTube video.
Cenospheres are made from the pulverized fuel ash produced as a waste product from coal-fired power stations. These alumina-silicate balls range in size from 5 to 500 µm and are usually hollow, giving them a very low-density. This makes them very useful for any number of filler purposes for construction products, as well as in the manufacture of composites with “spray-up, hand lay-up, resin transfer molding and syntactic foam applications.”
You can learn more about the manufacture of cenospheres in this YouTube video.
Ceramic microspheres are usually found being used in the paint and coatings industries. Current manufacturers include 3M, which boasts of their use as, “ideal options for increasing hardness, providing gloss control, reducing VOC, increasing filler loadings, and improving hardness and burnish, scrub and abrasion resistance.“
A less common form or microsphere, they are made from the carbonization of phenolic microspheres. Similarly pitch can be treated and carbonized for use in a variety of composites and foams. As the industry journal Composite World explains, “Due to their smooth surface, good mobility and thin walls, which permit deformation in response to sound pressure, carbon microspheres have been effectively used in the production of carbon microphones. Also, specially processed pitch carbon microsphere composites are suitable for use as honeycomb fillers for high-temperature or ionizing radiation fields.”
Aluminum and copper/silver microspheres are currently the most popular, although many companies are researching different metallic constructions to suit specific needs. These include, “polymer-metal spheres that combine a polymer core with a metal shell as well as a product in which multi-walled carbon nanotubes are bonded to the surfaces of polystyrene microspheres.”
Microspheres for All Purposes
One of the key advantages of microspheres as an engineering or production material is their diversity. As already explained, they can be manufactured from numerous materials. They can be either solid or hollow, have porous or non-porous walls, have low density and mass, or be made with thick walls for maximum strength. They can be crushed and heated and still return to shape, as well as be filled with gas or other chemical, or coated with any number of products.
With such a wide variety of specifications, it is no wonder that microsphere manufacturers are eager to boast of their products adaptability. Indeed, it is no wonder that the market for this wonder-product is growing.
Photo credit: Monika Mekala