Cenosphere

Cenosphere are one of the most valued fractions of coal fly ash. They have a hollow spherical structure and can be applied in many industrial applications, due to their superior properties; such as low bulk density, high thermal resistance, high workability and high strength. This review, focuses on the formation of Cenosphere, their characterization, including the chemical composition, their recovery from fly ash and the influence on mechanical properties when mixed with different materials.

The process of burning coal in thermal power plants produces fly ash containing ceramic particles made largely of alumina and silica. These particles form a part of the fly ash produced in the burning process. They are produced at the high temperature of 1450 to 1700 degrees Celsius through complicated chemical and physical transformation. Cenosphere are the lighter particles that are contained within the fly ash. These are hollow, hard-shelled, ultra-low-density spheres, which form unique free flowing powders. Their chemical composition and structure varies considerably depending on the composition of coal that generated them.

The ceramic particles in fly ash have three types of structures. The first type of particle is a solid and is called a Precipitator. The second type of particle is hollow and is called Cenosphere. The third type of particles are called Plerospheres, which are hollow particles of large diameter filled with smaller size Precipitator and Cenosphere.

Cenosphere grades can be classified into categories based on the following:

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 colour of Cenosphere 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 provides them with buoyancy. Physically, Cenosphere is hard, rigid, light, waterproof, innoxious, and insulative. By utilizing these characteristics of Cenosphere it is possible to produce materials with excellent heat insulating properties. Cenosphere combine all the advantages of spherical shape with the additional benefits of low density at an economic cost. With low densities Cenosphere reduces the weight of formulated products.

Cenosphere behaves like tiny ball bearings to improve workability, flow under pressure, reduce shrinkage, enhance isotropic properties and reduce resin, binder or water demand due to their low oil absorption level and high packing factor.

The advantage of significantly improved flow and workability which are desirable in a range of applications, such as Oilwell Cementing, Refractories & Foundries, Cement based Products, Joint-Compounds, Bitumen Sound-Dampening, Adhesives, and many more.

Products such as Fillers is another area where Cenosphere is making a major impact. Cenosphere are used as Fillers in cement to produce low-density concrete. Another popular Filler product is Syntactic Foam which is Cenosphere filled in metals and polymers to make lightweight composite materials with higher strength than other types of foam materials. Syntactic foams using Aluminum are being applied in the automotive sector.

Silver-coated Cenosphere is being used to create conductive coatings, tiles and fabrics. Conductive paints are used for antistatic coatings and electromagnetic shielding.

Radar-absorbing coatings are being created using Cenosphere. These coatings are applied to the surface of the desired vessel that effectively scatters or absorbs the energy of the radar signal thereby creating a stealth vessel.

The process of burning coal at very high temperature in thermal power plants produces fly ash containing ceramic particles made largely of alumina and silica. They are produced at temperatures of 1,500 to 1,750 °C (2,730 to 3,180 °F) through complicated chemical and physical transformation. Their chemical composition and structure varies considerably depending on the composition of coal used.

The final product formed which is referred to as Cenosphere, is an inert, pH neutral, durable material that is ideally suited for various applications where the few or more of the following properties are required:

Due to its inert nature, Cenosphere is suitable for any application and binding system. Resistance to acids and alkalis is an added advantage which prevents the interference with products into which it is blended.

Cenosphere is a by-product of coal combustion. It does not have a manufacturing process resulting in being classified as a “Green” product with a low carbon footprint. Extensive testing in various scenarios has demonstrated that Cenosphere is non-toxic, non-hazardous and harmless to the environment.