In the primary perlite, the water is contained in two basic forms – free (on the surface of the rock) and bonded form. Availability of the constitutional water provides the perlite’s capability to expand while being heated. The water decreases the rock melting point value and acts as a means for the rock expansion in the molten state. Expansion of the perlite is performed in furnaces using the method of thermal blast at the temperature of 900-1100°С. At that, the perlite is transferred into a pyroclastic flow state. Separation of gases, primarily Н2О, is undergoing in the form of a blast, and the glass becomes foamed forming up a high-viscosity expanded perlite. Alongside with the water some other gases – Н2, N2, СО2, СО – are participating in the process of expansion, however, they play a secondary role therein. While evaporating, bonded water forma multiple tiniest air bubbles in the softened mass. The rock is decomposed into the spherically shaped kernels with increasing the volume by 4-20 times and the porosity value – up to 70-90%. Expansion of the perlite can be performed in one or two stages of thermal processing that is determined by the percentage of water content in the primary raw material. If the water content is not exceeding the value of 3.5% then expansion of the perlite is performed during a single kiln roasting at the temperatures of 900-1100° С. If the water content is higher, then its excessive volume is preliminary removed at 300…450° С.
«These characteristics, along with the fact that the energy consumed in the process is low will make perlite an ECO-CLEAN product.»
CHEMICAL ANALYSIS OF EXPANDED PERLITE
|Perlite has been classfied as a natural product|
|Typical chemical composition:||Alumina - alkali silicate (amorphous silicate).|
|Typical chemical composition(on dry sample):||% weight|