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| Raw perlite - A result of volcanic action |
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Perlite belongs to the group of volcanic rhyolites,
or quartz porphyry glasses. It is a natural glass, formed from lava very rapidly cooled
in contact with water or steam whilst under high pressure.
Knauf Perlite has a stake in
a mine in the best-known extraction area in Europe - on Milos in the Cyclades in Greece.
The perlite there is strip-mined and brought by sea to Dortmund via Rotterdam.
Perlite is an
aluminium silicate with a content of more than 70% SiO2 silicon dioxide.
A particular characteristic of Greek raw perlite is a water content of 2 - 5%, in the form of
water crystallisation, which gives it an enormous expandability. Delivered in large quantities,
the raw mineral is broken up and graded at a processing plant in Dortmund. Through thermal
pretreatment, a homogeneous and balanced molecular water distribution is obtained in the raw
perlite granules.
Subsequently, the reduced, sieved and pre-dried raw perlite can be easily
expanded in the perlite kiln at a temperature of around 1000 degrees Celsius. The water content
produces even expansion of the raw perlite and guarantees a low proportion of dust in the final
product. The result: a very light and porous granular material which can be used in the most
diverse applications. |
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| Physical properties |
Colour |
Greyish brown |
Moisture content |
< 1 % |
pH value |
6 - 8,5 |
Thermal stability |
Up to 800 °C |
Melting point |
About 1400 °C |
Flammability |
Non-flammable |
Organic components |
Less than 0,1% by weight |
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| Advantages |
- Size reduction in Germany, near our customers
- Thermal pre-treatment in a pre-drier
- High kiln power
- No separation, via direct loading into silo transporters
- Flexible delivery and customer-oriented solutions
- Quality assurance system – certified to ISO 9001:2000
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| Summary of raw perlite product |
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Fine raw perlite |
Medium raw perlite |
Coarse raw perlite |
Granule size (mm) |
0 - 0,5 |
0,5 - 1,0
Proportion of non-expandable parts (%)* approx. 10 approx. 10 approx. 10 |
0,8 - 2,5
Attainable bulk density (kg/m3)* 48 - 72 64 - 96 72 - 108 |
Bulk density (kg/m3) 0 - 15 % < 125 µm 45 - 65 % 0.5 - 0.8 mm 0 - 10 % 0.8 - 1.0 mm |
approx. 1000-0 -10 % < 0.5 mm 0 - 20 % < 0.8 mm |
approx. 1000*in expanded condition |
approx. 1000 |
Proportion of non-expandable parts (%)* |
approx. 10 |
approx. 10 |
approx. 10 |
Attainable bulk density (kg/m3)* |
48 - 72 |
64 - 96 |
72 - 108 |
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| Grading |
5 - 20 % |
> 500 μm |
0 - 3 % |
> 1,25 mm |
0 - 5 % |
> 2,5 mm |
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45 - 60 % |
250 - 500 μm |
5 - 20 % |
1,0 - 1,25 mm |
5 - 30 % |
2,0 - 2,5 mm |
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15 - 30 % |
125 - 250 μm |
20 - 40 % |
0,8 - 1,0 mm |
50 - 75 % |
1,0 - 2,0 mm |
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0 - 15 % |
< 125 μm |
45 - 65 % |
0,5 - 0,8 mm |
0 - 10 % |
0,8 - 1,0 mm |
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0 -10 % |
< 0,5 mm |
0 - 20 % |
< 0,8 mm |
*in expanded condition |
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Raw Perlite in the iron foundry
The use of raw perlite as slag cement in iron foundries is based on physical-chemical processes.
The relatively high alkali content (Na2O + K2O) of raw perlite lowers the melting point of the
slag cement (SiO2) to around 1,100 -1,150 degrees Celsius. The melting of raw perlite granules
results in binding to the slag of the liquid iron on the surface of the melt. Slag so formed may
easily be removed.
Knauf Perlite – Germany's market leader in this area – produces slag cement with
a defined granule size characterised by low fines. |
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Industry