Listing description
Vermiculite is a hydrous phyllosilicate mineral. It undergoes
significant expansion when heated. Exfoliation occurs when the
mineral is heated sufficiently, and the effect is routinely produced in
commercial furnaces. Vermiculite is formed by weathering orhydrothermal alteration of biotite or phlogopite.
Detailed description
Occurrence
Vermiculite was
first described in 1824 for an occurrence in Millbury, Massachusetts, USA. Its name is from Latin vermiculare, to breed worms, for the manner in which
it exfoliates when heated.[4][2]
It typically occurs
as an alteration product at the contact between felsic and mafic or ultramafic rocks
such as pyroxenites and dunites. It also occurs in carbonatites and metamorphosed magnesium rich limestone. Associated mineral
phases include: corundum, apatite,serpentine and talc. It occurs interlayered with chlorite, biotite and
phlogopite.[1]
Structure
Vermiculite is a 2:1 clay, meaning it has 2 tetrahedral sheets for every one octahedral sheet. It is a
limited expansion clay with a medium shrink-swell capacity. Vermiculite has a high cation exchange
capacity at 100-150 meq/100
g. Vermiculite clays are weathered micas in which the potassium ions between the molecular sheets are replaced
by magnesium and iron ions.
Commercial uses
·
Moulded shapes: this
process involves mixing exfoliated vermiculite with inorganic bonding agents
such as sodium silicate and potassium to produce an 'earth damp' mixture.
This material is then hydraulically pressed into shape in a mold, and then heat
cured at temperatures up to 180 °C for up to 24 hours depending upon the
thickness of the moulded part. Such parts can withstand service temperatures of
up to 1150 °C and are often used in the aluminium smelting industry as
back-up insulation behind the carbon cathode in the potcells which contain the
molten mixture of cryolite and alumina. The moulded shapes and boards are used
in:
·
Open fireplaces
·
High-temperature or
refractory insulation
·
Acoustic panels
·
Calcium silicate boards:
exfoliated vermiculite is added to a calcium silicate slurry, this is then
dewatered by pressing or by using one of the Fourdriner/Magnani/Hatschek
processes to form a flat board which is then heat cured under pressure
(typically 10-15 bar) for periods up to 24 hours.
·
Brake linings: finer
grades of exfoliated vermiculite are being used in brake linings primarily for
the automotive market. The properties of vermiculite that make it an
appropriate choice for use in brake linings include its thermal resistance,
ease of addition to other raw materials to achieve a homogenous mix and its
shape and surface characteristics
·
Roof and floor screeds and insulating
concretes: exfoliated vermiculite (typically the finer grades) can be added at
site to Portland cement and other aggregates, rheological aids and water to
produce roof and floor concrete screeds or lightweight concrete which have the
benefit of being lightweight and insulating. In many cases vermiculite based
roof screeds are often used in conjunction with other insulation materials such
as polystyrene board to form a total roofing system. A bituminous binder can
also be used with exfoliated vermiculite can to produce a dry, lightweight roof
screed which has the advantages of low thermal conductivity, low moisture
content and ease of placement by pouring from the bag and then tamping.
·
Soilless growing media:
exfoliated vermiculite is combined with other materials such as peat or
composted pine bark compost to produce soilless growing media for the
professional horticulturalist and for the home gardener. These mixes promote
faster root growth and gives quick anchorage to young roots. The mixture helps
retain air, plant food and moisture, releasing them as the plant requires them.[5] These mixes were
pioneered by Boodley and Sheldrake. Exfoliated vermiculite is also used as a growing media for hydroponics
·
Seed germination: either
used alone or mixed with soil or peat, vermiculite is used to germinate seeds.
Very little watering is required. When vermiculite is used alone, seedlings
should be fed with a weak fertilizer solution when the first true leaves
appear. A tablespoon of soluble fertilizer per one imperial gallon (3.78 :
1) of water is the recommended mix
·
Storing bulbs and root
crops: pour vermiculite around bulbs placed in container. If clumps are dug,
allow to dry for a few hours in the sun and then place in cartons or bushel
baskets and cover with vermiculite. The absorptive power of vermiculite acts as
a regulator that prevents mildew and moisture fluctuation during the storage
period. It will not absorb moisture from the inside of stored tubers, but it
does take up free water from the outside, preventing storage rot.
·
As a soil conditioner:
Where the native soil is heavy or sticky, gentle mixing of vermiculite up to
one-half the volume of the soil is recommended. This creates air channels and
allows the soil mix to breathe. Mixing vermiculite in flower and vegetable
gardens or in potted plants will provide the necessary air to maintain vigorous
plant growth. Where soils are sandy, mixing of vermiculite into the soil will
allow the soil to hold water and air needed for growth.
·
As loose-fill insulation: Exfoliated vermiculite treated with a water repellent is used
to fill the pores and cavities of masonry construction and hollow blockwork to
enhance fire ratings (e.g. Underwriters Laboratories Wall and Partition
designs), insulation and acoustic performance. Coarse grades of exfoliated
vermiculite can be used to insulate lofts and attics. Exfoliated vermiculite
has the benefit of being easy to use with application consisting of pouring the
vermiculite between the joists and then leveling
·
Refractory/Insulation
gunning and castable mixes: exfoliated vermiculite can be combined with high
alumina (also known as calcium aluminate) cements and other aggregates such as
expanded shale, clay and slate to produce refractory/insulation concretes and
mortars. In the early days of their uses these products were batched at or very
close to the place of installation, this continues to be the case in some
limited circumstances, however more and more use is being made of pre-batched
proprietary mixes. Mixes containing vermiculite are used in areas where
strength and corrosion/abrasion resistance are of secondary importance, the
most important factor being the insulation performance of the in place
refractory lining. These mixes find their uses in such areas in industries
including iron/steel, cement and hydrocarbon processing
·
As a constituent of a
coating: vermiculite dispersions are typically either chemically or physically
very finely delaminated vermiculite in a fluid medium. These dispersions can be
used to make vermiculite 'paper' sheet by simply pouring them on to a piece of
smooth low surface energy plastic and allowing to dry, the resulting sheet can
then be peeled off the plastic.Typical end uses for vermiculite dispersions
include in high temperature coatings or binders for construction materials,
gaskets, specialty papers/textiles, oxidation resistant coating on carbon based
composites, and as barrier coatings for films.
·
As a packing material,
valued for its high absorbency
·
Waste treatment: the
cation exchange capacity (up to 1000 milliequivalents per kg) of vermiculite
allows it to be used in fluid purification processes for waste water, chemical
processing and the pollution control of air in mines and gases in industrial
processes. In addition to its ion exchange properties exfoliated vermiculite
will retain liquids within the inter-laminar voids of the individual particles
as well as between the particles themselves.
·
As a lightweight
aggregate for plaster, proprietary concrete compounds, firestop mortar
and cementitious spray fireproofing: Exfoliated vermiculite
is used in both hand and spray applied general building plasters to improve
coverage, ease of handling, adhesion to a wide variety of substrates, fire
resistance, and resistance to chipping/cracking/shrinkage.
·
As a carrier for dry
handling and slow release of agricultural chemicals
·
As a hot topping: both exfoliated
and crude vermiculite have been used for hot
topping in the steel
industry. When poured onto molten metal crude vermiculite exfoliates
immediately and forms an insulating layer allowing the material to be
transported to the next production process without losing too much heat.
·
Used to permit slow cooling of hot pieces in glassblowing, lampwork, steelwork, and glass beadmaking
·
Used in in-ground
swimming pools to provide a smooth pool base: Finer grades of exfoliated
vermiculite plus Portland cement may be combined either on site or a factory
premix to provide a base for swimming pool vinyl liners. These mixes are either
pumped into place using a rotor stator pump or hand poured.
·
Used to absorb hazardous
liquids for solid disposal
·
Used in gas fireplaces
to simulate embers
Commercial manufacture of exfoliated vermiculite
In 2014, South
Africa, Brazil, the US and China were the top producers of mined, concentrated
and unexfoliated vermiculite, with about 90% world share. South Africa's
production is decreasing, while Brazil's is significantly increasing.
PRICE
$11.95/KG
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
No comments:
Post a Comment