Microsilica containing refractory castables - Elkem

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The unshaped refractories, commonly known as Monolithic refractories are manufactured by suitably blending graded refractory aggregates, binders, fillers & (/or) special additives used for modification of ultimate properties. The refractory aggregates chosen for the formulation of refractory castables have a major contribution in determining their ultimate product quality. Along with this and many other input parameters, especially the high temperature properties of all type of Castables (Aluminous / Basic) depend a lot on the additive’s level and type used. All ingredients, binders, and additives of different chemical compositions and grading are chosen, blended to provide the proper characteristics for various applications of monolithics. 

Effect of Water Addition vs. Ultrafine Additives (Silica Fume) in Castable Refractories

For castable refractories the mobility of various particles is essential for proper placement of the castable. One method to achieve mobility is by adding more water, but this increases porosity & thus affects the performance both at normal & elevated temp. Therefore, addition of water should be minimized. The desired fluidity can be achieved by maintaining the coarser particles separated from one another by suspension of fines and ultrafine additives combined with the state of flocculation within the suspension. The role of the grains of these ‘Microfines or Ultrafine Additives’ can be compared with those of the balls in a ball-bearing.

What are the commonly used Ultrafine Additives in Refractory Castables?

Read: Benefits of using Steel Fibers and Organic Fibers in  Refractory Castables and other Monolithic refractories

For more information, please visit Microsilica Used in Refractory.

The commonly used microfines or ultrafine additives are Silica Fume also known as Microsilica or Fumed Silica, microfine Alumina (Al2O3), ultrafine green Chrome Oxide (Cr2O3) etc. Silica fume is a by-product of producing silicon metal or ferrosilicon alloys. Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide (SiO2). Because of its super fine particles, large surface area, and the high SiO2 content, silica fume is a very reactive.

The addition of Microsilica or Silica Fume has other advantages also, since these micro fine silica particles easily react with alumina present in the material to form Mullite which, in turn, helps in enhancing refractory properties of the product.

The addition of certain percentage of superfine green Chrome Oxide (Cr2O3) in Alumina castables increases the slag corrosion resistance & HMOR of the product significantly because of the formation of Alumina-Chrome (Corundum) solid-solution.

There are several manufacturers of fumed silica. Some well-known global brands of fumed silica are of Elkem Materials, AEROSIL of Evonik Industries, Norchem Concrete Products. 

Read: Advantages of using Gel Bond and Colloidal Silica in Monolithic Refractories

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