Technical Information

What are Cenospheres?

Cenospheres are hollow ceramic microspheres that are a by-product of coal burning power plants. When pulverized coal is burned at power plants fly ash is produced. Cenospheres are the lighter particles that are contained within the fly ash.
Most cenospheres are "harvested" or scooped up from ash ponds. Ash ponds are the final resting place for fly ash when wet disposal is carried out. Some cenospheres are also collected at the power plants themselves. The wet microspheres are than dried, processed to specifications, and packaged to meet customer requirements.
Not all cenospheres are alike. In fact, they can be quite different. The properties of cenospheres depend on the consistency of the coal used and the operating parameters of the power plant. As long as these two factors remain constant, thecenospheres will be quite consistent.
Cenospheres have a particle size range of 10-600 micron. The most typical products we produce range 10-500, 10-300, 10-150, and 300-600 micron respectively.

Production Process

The process of burning coal in thermal power plants produces fly ash containing ceramic particles made largely of aluminaand silica. These particles form a part of the fly ash produced in the burning process. They are produced at the high temperature of 1,500 to 1,750 degrees Celsius through complicated chemical and physical transformation. 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 particles are solid and are calledprecipitator. The second type of particles are hollow and are called cenospheres. The third type of particles are calledplerospheres, which are hollow particles of large diameter filled with smaller size precipitator and cenospheres. Due to the hollow structure cenospheres have low density.

Shipment and Storage

Hollow glass Spheres are easy to transport and store. The high-performance hollow glass microspheres can be packaged with plastic boxes or texture bags and can be transported in bulk by various ways. Packaging weight depends on the density level of the hollow glass microspheres and the actual needs of customers. In order to extend the storage time to its maximum, it should avoid humid environment, and be stored in a cool dry place. After opened, the bag should be firmly resealed. If the package is damaged during the process of shipment and storage, the damaged bag should be replaced by a new one in time.

Product Selection

Product Selection: Why should we choose Hollow Glass Microspheres?

l Improve flow properties Hollow glass microspheres are a tiny sphere with high ball-type rate. It's ball-bearing effect can improve its mobility and reduce the viscosity and internal stress of resin mixture. Therefore, during processing, less heat is produced in composite materials so as to prevent inadequate lubrication and partial thermal decomposition. It is more likely to extrude when molding, which can not only reduce defects in products, but also improve the production efficiency by 15% -20%.

l A superior substitute of resin Hollow glass microspheres occupy less surface area, low oil-absorption rate, and evenly disperse in mixture. Its easy compression and integration permit high filler loadings. It significantly reduces the consumption of resins, increases the amount of filler, and effectively reduces VOC indicators, and costs as well.

l Low shrinkage and warpage Hollow glass microspheres have the feature of isotropism and high-filling, hence the dimensional stability of the product will be very high and it will reduce the shrinkage and warpage. With an appropriate filling ratio, the toughness of the products, impact-resistance and surface hardness can be significantly improved.

l More economical The density of high-performance hollow glass microspheres is only a fraction of that of the resin. A small amount of hollow glass microspheres will be able to replace heavier materials. When considering the cost per unit volume, rather than cost per unit weight, high-performance hollow glass microspheres can significantly reduce costs.

l Adjusting product density The density of hollow glass microspheres is usually 0.20 ~ 0.60g/cm3, and the density of mineral filler is generally around 2.7 ~ 4.4 g/cm3 (The data adopted is the true particle density). In order to obtain the equal size, 14 kilograms or more of talc must be used to obtain the same effect of 1 kg of hollow glass microsphere. Hence the desired ideal density can be obtained by adding appropriate proportions of hollow glass microspheres.


Several alternatives have been used to adjust cement slurry density. These methods may be used individually or in various combinations. The optimum means to adjust slurry density depends in part on the formation conditions of the well and logistics such as onsite availability of specialists, materials and equipment and the service company's experience, hardware and preferred practices.

(lift fig. 1 graph from Diversified Cementing Products website cenospheres page)

Cement Density Adjustment Alternatives

It is more common to reduce rather than increase slurry density in order to achieve zonal isolation and protect the geologic structure. Several methods and materials are available for use individually or in combination for this purpose.

Water extension The simplest means for density reduction is the addition of water, along with extenders such as bentonite, sodium or potassium silicates, or diatomaceous earth. This process is economical, but it degrades ultimate cement performance in proportion to the amount of excess added water. Slurry weight can be reduced to approximately 11.5 lbs/gal using water alone; further density reduction with water results in unacceptable permeability, low compressive strength and extended cure time.

Extension with hollow beads Low specific-gravity hollow ceramic beads (Hollow Glass Microspheres) added to the slurry effectively displace water and cement components with tiny encapsulated air bubbles. They range in diameter from approximately 25 to 300+ microns. This method yields a homogeneous mix, and finished cement containing cenosphereswill have an increased strength-to-density ratio and lower permeability compared to water-extended slurry. Cenospheres are relatively inexpensive, but quality can vary from batch-to-batch, and availability may be an issue. This density reduction option has several limitations: the variability and unpredictability of cenosphere physical properties, and the inability of this additive to tolerate the pressure levels that can be encountered in wellbore cementing. As a commodity rather than an engineered product, cenospheres do not have well-defined values or quality parameters. The material is commonly segregated by flotation rather than graded by size or other parameters, and those cenospheres that float are shipped for use in the field. Nominal cenosphere density is 0.7 g/cc, but under minimal pressure of 500 psi or more this value can increase to 0.85 g/cc, greatly reducing the functional value of the material as a slurry additive. Cenospheres may also segregate partially by size during transport and handling, resulting in density variations in the slurry. In some oil producing areas there are environmental concerns associated with use of cenospheres in wellbore cementing.

Hollow glass microspheres can be used as a continuous medium in low-density cement slurries. with addition of hollow glass microspheres, The slurry is incompressible and all wells are uniform in density. Used in drilling fluid, Sludge cakes formed have good lubrication, reducing the risk of sticking. Hollow glass microspheres have an irreplaceable advantage for it cannot affect the system signal. Hollow glass microspheres have a good rolling performance, and can increase the drilling rate, and significantly improve the drilling efficiency. Cementing with hollow glass microspheres has feature of high temperature resistance, high pressure resistance, stability, durability, and can be recycled. With the increase of pressure layer, low-density slurry cementing with hollow glass microspheres were adopted to consolidate the wells to prevent or reduce leakage, increase the cement top. It will improve single well production, and can be used effectively to obtain underground oil and gas and high temperature geothermal resources.

Unique performance High-performance hollow glass microspheres is a kind of ultra-lightweight inorganic non-metallic powder with hollow microsphere, and it is a versatile and high-performance new lightweight material developed in recent years. It will be the new composite mainstream materials at 21 century. Its true density is 0.15-0.60g/cm3 with 2-130μm in diameter. It owns features with light weight, large bulky, low thermal conductivity, high compressive strength, smoothly mobility. It can be used in paint, rubber, plastics, FRP, artificial stone, putty and other products as filler and weight-reducing agent. It can also be the excellent sensitizer for emulsion explosives; Because of its high compressive properties, it can be used to produce high-strength low-density cement slurry and low density drilling fluid in oil and gas extraction industry.


Other applications for hollow glass microspheres include:

Thermal insulation coating, putty, plastic casting polyester, FRP, SMC, radome, synthetic foam board, adhesives, printed circuit board substrate, RTM, bowling, fan blades, emulsion explosives, golf, sealant, pipeline insulation materials, artificial marble, low density oil drilling, light cement, and other deep-sea buoy etc.


Product Series



Model  Color   Diameter (μm) True  Pressure Equivalent to
density(g/cm3) (MPa) 3M product      
HS20 white 2-120 0.20 3-4 K20
HS25 white 2-110 0.25 5-7 K25
HS32 white 2-90  0.32 12-15 S32
HS40 white 2-85 0.40 28-33 S38
HS46 white 2-80 0.46 38-42 K46
HS60 white 8-65  0.60 >60 S60



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