What is perlite?
Perlite is a natural acidic medium volcanic rock that is formed in wet or watery environment because of magma freezing at Earth's surface. Perlite has a glassy texture and due to including water, spherical shapes have been created in it. The water measure in perlite is almost 2_6%. Various names have been chosen for this mineral such as pirlesten or pirlit, during the years. But since 1992 perlite has been chosen as official name of this mineral. Perlite is inspired from French word perl, meaning pearl. In Dana's Fundamentals of Mineralogy book, perlite has not considered as a mineral, but it has been considered as a known type of volcanic rock, riolit.
Until 1928, it was just known that there were some volcanic glasses that they would increase in mass by increasing temperature suddenly.
In 1929, for the first time in Japan, surveys have been accomplished about this mineral and it did not take long that several American experts have been started working to achieve different applications of this mineral, in mid_1930s.
In 1938, some tests were started by Lee Bayer in North Arizona, which caused to the publication of first license about process of perlite expansion and converting it to an insulating or reflective material.
General Characteristics of Perlite
Perlite is a glassy volcanic rock, that has pearl network with concentric circles or onion shaped shell and in original shape has hyaline texture with 2_6% water.
Perlite is used in various industries because of its low density, low conductivity, neutrality, incombustibility, low hardness, good radiance, absorbability and resistance to other aggregates such as vermiculite.
Process of Perlite Expansion
A unique feature of perlite compared to other volcanic glasses, is expansion by heating suddenly up to appropriate temperature and increasing in mass by 4_20 times its original mass. The resulting composition of this process has lower specific gravity than the raw composition. Actually, releasing existing water in the perlite, that occurs as a result of quick changes of temperature from 700 to 1100 C°, causes to quick expansion of rock, increasing its mass and producing hollow material with low density.
In fact, this expansion is accompanied with creating numerous tiny bubbles in softened glassy particles with pastiness formation such as popcorn that gives physical individual features to bloated perlite.
Expansion process, is one-way and irreversible and its restitution rate depends on sort and chemical composition of primary raw perlite and rate of expandability has direct ratio with amount of water in it. Due to expansion, its density decrease from 1200 kg/m3 to30_150 kg/m3 and its color turns white to light gray.
Briefly, for perlite expansion, at first the perlite is crushed and then granulated. Granulated perlite, according to the required size (with or without preheating) is directing to vertical furnace. The temperature inside of furnace is setting between 700_1100 C°, based on the chemical composition and amount of water in perlite. Perlite is expanding inside the furnace and with help of air flow it is directed to the top, and the waste materials fall to bottom of the furnace. Countries like: U.S.A, Greece, Japan, Argentina, Turkey, Hungary, Iran and some of other countries are counted as the largest manufactures of this industrial product.
Due to unique properties and benefits of this material, uncontrolled increase of its applications and the need of the legal reference for coordinate between perlite miners and other industries that are related to this material, the Perlite Association established in 1994.
According to reported statistics by the Perlite Global Institute, expanded perlite consumption, is including three main categories such as construction, agriculture and industry and with more than 300 main applications, has possessed the most diverse consumption among the all types of minerals.
Generally, perlite consumption in industries is as follows:
1_Building industry 45%
2_Food industry(filtration, water purification, juicing, edible oils, sugar, fructose,...)39.5%
3_Agriculture (cultivation, horticulture, greenhouse, producing types of dungs) 14%
4_livestock and poultry farming 1%
5_Other industries such as military, … 5%
