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Perlite is not a trade name but a generic
term for naturally occurring silicous rock. The distinguishing
feature which sets perlite apart from other volcanic
glasses is that when heated to a suitable point in its
softening range, it expands from four to twenty times
its original volume.
This expansion is due to the presence
of two to six percent combined water in the crude perlite
rock. When quickly heated to above 1600°F (871°C), the
crude rock pops in a manner similar to popcorn as the
combined water vaporizes and creates countless tiny
bubbles which account for the amazing light weight and
other exceptional physical properties of expanded perlite.
This expansion process also creates one
of perlite's most distinguishing characteristics: its
white color. While the crude rock may range from transparent
light gray to glossy black, the color of expanded perlite
ranges from snowy white to grayish white.
Expanded perlite can be manufactured
to weigh as little as 2 pounds per cubic foot (32kg/m3)
making it adaptable for numerous applications.
Since perlite is a form of natural glass,
it is classified as chemically inert and has a pH of
approximately 7.
Typical Elemental Analysis
| Silicon |
33.8 |
| Aluminum |
7.2 |
| Potassium |
3.5 |
| Sodium |
3.4 |
| Iron |
0.6 |
| Calcium |
0.6 |
| Magnesium |
0.2 |
| Trace |
0.2 |
| Oxygen (by difference) |
47.5 |
| Net Total |
97.0 |
| Bound Water |
3.0 |
| Total |
100.0 |
| *
All analyses are shown in elemental form
even though the actual forms present are
mixed glassy silicates. Free silica may
be present in small amounts, characteristic
of the particular ore body. More specific
information may be obtained from the ore
supplier involved. |
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Typical Physical Properties
| Color |
White |
| Refractive
Index |
1.5 |
| Free Moisture,
Maximum |
0.5% |
| pH (of water
slurry) |
6.5
- 8.0 |
| Specific Gravity |
2.2
- 2.4 |
| Bulk Density
(loose weight) |
As
desired but usually in the 2-25 lb/ft3
range (32-400 kg/m3) |
| Mesh Size Available |
As
desired, 4-8 mesh and finer |
| Softening Point |
1600-2000°F
(871-1093°C) |
| Fusion Point |
2300-2450°F
(1260-1343°C) |
| Specific Heat |
0.2
Btu/lb·°F (837 J/kg*K) |
| Thermal Conductivity at
75°F (24°C) |
.27-.41 Btu·in/h·ft2·°F(.04-.06
W/m·K) |
Solubility
.......
- Soluble in hot concentrated alkali
and HF
- Moderately soluble (<10%) in 1N
NaOH
- Slightly soluble (<3%) in mineral
acids (1N)
- Very slightly soluble (<1%) in
water or weak acids |
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Uses for
Perlite...
There are many uses for perlite. These
uses can be broken down into three general categories:
construction applications, horticultural applications,
and industrial applications.
Construction ApplicationsBecause
of perlite's outstanding insulating characteristics
and light weight, it is widely used as a loose-fill
insulation in masonry construction. In this application,
free-flowing perlite loose-fill masonry insulation is
poured into the cavities of concrete block where it
completely fills all cores, crevices, mortar areas and
ear holes. In addition to providing thermal insulation,
perlite enhances fire ratings, reduces noise transmission
and it is rot, vermin and termite resistant. Perlite
is also ideal for insulating low temperature and cryogenic
vessels. When perlite is used as an aggregate in concrete,
a lightweight, fire resistant, insulating concrete is
produced that is ideal for roof decks and other applications.
Perlite can also be used as an aggregate in Portland
cement and gypsum plasters for exterior applications
and for the fire protection of beams and columns. Other
construction applications include under-floor insulation,
chimney linings, paint texturing, gypsum boards, ceiling
tiles, and roof insulation boards.
Horticultural ApplicationsIn horticultural
applications, perlite is used throughout the world as
a component of soilless growing mixes where it provides
aeration and optimum moisture retention for superior
plant growth. For rooting cuttings, 100% perlite is
used. Studies have shown that outstanding yields are
achieved with perlite hydroponic systems. Other benefits
of horticultural perlite are its neutral pH and the
fact that it is sterile and weed-free. In addition,
its light weight makes it ideal for use in container
growing. Other horticultural applications for perlite
are as a carrier for fertilizer, herbicides and pesticides
and for pelletizing seed. Horticultural perlite is as
useful to the home gardener as it is to the commercial
grower. It is used with equal success in greenhouse
growing, landscaping applications and in the home in
house plants.
Industrial ApplicationsIndustrial
applications for perlite are the most diverse, ranging
from high performance fillers for plastics to cements
for petroleum, water and geothermal wells. Other applications
include its use as a filter media for pharmaceuticals,
food products, chemicals and water for municipal systems
and swimming pools.
Additional applications include its use
as an abrasive in soaps, cleaners, and polishes; and
a variety of foundry applications utilizing perlite's
insulating properties and high heat resistance. This
same heat resistant property is taken advantage of when
perlite is used in the manufacture of refractory bricks,
mortars, and pipe insulation.
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