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Cenospheres, Alumosilicate microspheres

Cenospheres (aluminosilicate microspheres) are hollow aluminosilicate glass ceramic beads ranging in size from 400-500 microns 20-50mkm (most often – from 100 to 250 microns), which are formed during high-temperature combustion of pulverized coal. Qualitative characteristics of aluminosilicate microspheres are directly dependent on the characteristics of the ash waste produced by a power station.

The chemical composition of the main component of the cenospheres is silicon oxide SiO2 (45-60%), aluminium oxide Al2O3 (15-40%), iron oxide Fe2O3 (1.0-10%), calcium oxide CaO (1.5- 4.5%), potassium oxide K2O (2.0-4.5%) and other certain oxides that make up the balance of the content are typically less than 1.0%.

Due to the unique set of physical and chemical characteristics of the cenospheres, they are used in the manufacturing of various composite materials. They are used in solving technical issues that require: reduction in the weight material with a low thermal conductivity, high strength, volume efficiency, increased resistance to erosion and aggressive environments.

Applications of the cenospheres are described below.

Cellular concrete prepared using microspheres can be used for the production of thermal insulation panels with much greater strength in comparison with other slab-type insulating materials (boards of mineral fiber, slabs of foam or polyurethane)! The use of microspheres in the production of thermal insulation and structural and construction of cellular concrete products allows increasing their strength while maintaining the density and thus to produce solid products with lower density, which ultimately leads to improved thermal characteristics of the product.


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Depending on the type of cellular concrete, and, accordingly, to the thickness of the wall between the air pores, microsphere particles are either contained in a dense matrix of a concrete pore wall, or partially located in themselves air pores, greatly increasing thereby the internal surface area of air pores, which in its turn more effectively detains heat flow.

Excellent heat and sound insulation properties of cellular concrete are similar to the parameters of the existing slab insulation materials. Moreover, unlike most conventional insulation materials it provides:

– The possibility of constructing ‘breathing’ single-layer walls (with good water vapor permeability);

– Reducing the cost of construction by reducing the wall thickness to the required structural-carrying thickness and by reducing the load on the foundation;

– Reducing the cost of construction due to the absence of complex manufacturing operations for arrangement of additional insulation, as well as reducing the time of construction;

– Universality:  the possibility of using cellular concrete both for internal and external works, and for heat and sound insulation of floors and ceilings;

– Workability – higher strength as compared with the existing insulating materials (such as fiber or expanded plastics).

  • Heat-insulating refractory concretes

Microspheres, due to their fire resistance and high heat-insulating properties, are used in the production of thermal insulation materials. The high temperature of microsphere shell softening allows, with the appropriate selection of the binder, creating refractory coating and insulating materials for industrial equipment. Together with silicone resin, and an aqueous solution that acts as a hardener, the microspheres can be used for thermal insulation of the exterior surfaces of steel vessels such as tanks for transportation of viscous petroleum products

  • Manufacture of compositions for protection of surface against adhesion of welding spatters

The protection coating consists of a compound whose main components are hollow aluminum silicate microspheres. The composition includes the following components: hollow aluminosilicate microspheres, starch, and water. The protective coating on the basis of the microspheres possesses improved processing characteristics, which allow using it for protection of various surfaces located (vertical, horizontal and ceiling, and a fairly simple way to remove it from the product after the welding process. The composition may be used in machine building and boiler construction, the manufacture of complex steel structure forms a welding method

  • Manufacture of insulation for heating lines,
  • Manufacture of syntactic foam plastics

In the process of molding it is often necessary to fill small depressions and inaccessible spaces. Solid fiberglass is heavy enough (the bulk density is 1.5 g / cm3) and expensive. Conventional resin-based putties are cheaper, but heavier (bulk density of 2.0 g / cm3). In addition, and fiberglass and putties, taken in large enough amounts, have a pronounced exothermic properties, i.e. curing soon after they become hot. The resulting thermal stress can cause extensive cracking and damage to the surrounding areas of a fiberglass structure.

Syntactic foam plastic is essentially resin-based putty with lightweight filler. Typically, the filler consists of phenol-formaldehyde resin microspheres, glass ‘eccospheres’, etc. Polystyrene beads with epoxy resin are also used. One can also use lightweight materials such as vermiculite, pumice, diatomaceous earth, sawdust, but porous materials absorb resin and become heavy and expensive.

To provide ease and economy, they must be granulated. By using large granules, one can obtain heavy putty. Fine granules are used to make resin lighter. The decisive role is played by the accuracy of conforming to the required proportions in the mixing process.

With an excess of resin, the putty becomes liquid and heavy; with deficiency of resin, it becomes dry and non-sticky.

In comparison to other foams, syntactic foams are relatively heavy (bulk density of 0.3-0.4 g / cm3 with microspheres made from phenol-formaldehyde resin), but they are very easy to handle, can be prepared quickly, and easily take the desired shape, since they are applied to directly to the desired location. For filling large volumes, light and cheap polyurethane (expanded in the ready product) is best used.

Syntactic foams are often used for sealing tapered edges of sandwich molded products, especially those of curved shape. The compressive strength of this material is typically high, and it can be used for manufacturing inserts, which are inserted in a three-layer structure after its fabrication.

  • Manufacture of highly porous grinding wheels featuring closed design and high performance

Highly porous grinding wheels of closed design and high performance have been developed and are being successfully introduced into industry as a fundamentally new type of abrasive tool. They feature a wide range of process properties at operating speeds up to 120 m / s.

  • Manufacture of thermoplastic road marking compositions

It is used for the marking of roads and airfields with asphalt or asphalt-concrete pavement. Using thermoplastic road marking composition can improve cold resistance, salt resistance, and crack resistance due to the fact that the formula contains polyester resin, which is based on dimethyl or on polyethylene terephthalate, ethylene glycol and phthalic anhydride, or polyester resin, which is based on adipic resin, ethylene glycol, titanium dioxide, transformer oil, quartz sand, and aluminosilicate hollow microspheres with particle size of 80-100 microns.

Below are the main applications of cenospheres:

                        Oilfield                                                               Construction                                                       Ceramics

Cenospheres in oilfield           Cenospheres in construction - block            Cenospheres in construction - ceramics

               Chemical industry                                                          Plastics                                                              Paints     

Cenospheres - chemical industry        Cenospheres in plastics         Application of Foam Glass in Pains and Wallpapers




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