SMART DOG MININGTM
It
takes a smart dog to find hidden treasures
Graphite: the other key battery mineral
Graphite: where being a big lump or a
just flake can be good!
Graphite is a form
(allotrope) of carbon. named by Abraham G Werner in 1789 from the
Ancient Greek (graphō), "to draw/write". It is one of the three
allotropes of element carbon that exist in nature, the other two
being coal and diamond. Unlike diamond, graphite is an
electrical conductor, making it a semimetal. Graphite is the most
stable form of carbon under standard conditions. Graphite may be
considered the highest grade of coal, just above anthracite and
alternatively called meta-anthracite, although it is not normally
used as fuel because it is difficult to get it to ignite.
It has black to steel grey color, usually
leaves a black streak on the hand when touched because of its
extreme softness and greasiness. It is opaque even in the finest
particles. Graphite is a good conductor of heat and electricity. It
has high refractoriness. It can stand a temperature upto 3000ºC in
an inert atmosphere though in the presence of oxygen it burns
between 620ºC to 720º C. It is unaffected by most of the acids and
reagents but yields graphitic acid on treatment with a mixture of
potassium nitrate and nitric acid.
There are two major types natural and synthetic
(artificial).
Naturel graphite is
of metamorphic origin and usually found as veins, lenses, pockets
and as thin laminae disseminated in the gneisses, schists and
phyllites. Depending upon the mode of occurrence and origin, it is
graded into three forms:
Flake - found in metamorphosed rocks as vein
deposits.(approximately 90% carbon)
Crystalline (lumpy) - found as fissure filled
veins.(approximately (95+% carbon)
Cryptocrystalline (amorphous) - form in
metamorphosed coal beds.(approximately 85% carbon)
Synthetic graphite is also called artificial
graphite, is a man-made form of graphite (approximately 98+%
carbon). It is obtained by processing a feed stock (often petroleum
coke). After crushing, grinding, screening and sieving of the dry
raw materials, these are mixed with the tar pitch and molded in
blocks. Blocks are then baked or carbonized at 800-1330°C and
graphitized at 2600-3000°C in furnaces. During this
processing graphite powders are generated. This byproduct of
the production of graphite is called secondary synthetic graphite.
Uses of Graphite
Graphite is used in a wide variety of
applications: refractories, carbon brushes, lubricants, steelmaking,
metal casting, brake linings, fuel cells, batteries, and pebble
nuclear reactors. The largest market for graphite is in traditional
industries like carbon raiser for steel and refractories.
Below are reported the main applications of
graphite.
Steel, foundries, & refractories – 41%
Automotive parts – 14%
Lubricants – 14%
Carbon brushes – 11%
Batteries – 10%
Others – 10%
Steel industry: In steel-making graphite is
used to increase the carbon content of steel. Graphite is also
required in liners for ladles, crucible and in thermal blanket for
the continuous steel casting process.
Lubricants: Graphite can be used as a solid
lubricant or dispersed in water or in oil and grease. Water based
dispersion are exploited in the production of seamless tube or in
the hot metal forming industry (forging, extrusion, etc.).
Friction Materials: Graphite powders are used
in brake pads in automotive, heavy-duty vehicles (trucks, trains,
airplanes) and in industrial machines. Graphite has to provide the
required level of friction coefficient at different operant
conditions. it also contributees to temperature vibration, noise and
wear control.
Carbon Brushes: Graphite is a main component
of carbon brushes used in the majority of electrical motors.
Graphite fixes the electrical conductivity of the brush and also
contributes to reduce wear while lubricating and increasing the
mechanical strength.
Batteries: Due to their electrical
conductivity graphite powders are used in zinc-carbon batteries,
alkaline batteries, lithium-ion batteries, fuel cells and super
capacitors. In alkaline batteries graphite is used as a
conductive additive in the cathode, together with electrolytic
manganese dioxide (EMD). In lithium-ion rechargeable batteries,
graphite is used as active material in the negative electrode of
lithium and as a conductive additive in the positive electrode.
Most bipolar plates of fuel cell bipolar are manufactured by
compression moulding using graphite and polymer compound (graphite
content: 75-85%). Graphite is also used as a coating for metallic
bipolar plates to avoid corrosion.
Thermal conductive and electrical conductive
polymers: Graphite finds wide applications as a polymer additive
thanks to its properties: low friction, lubricating
(self-lubricating polymers), chemical inertness, high thermal
conductivity, thermal stability and electrical conductivity. In
alternative to metal flakes or powders, graphite can increase the
thermal conductivity of polymers when the heat generated from a
device needs to be evacuated resulting in temperature reduction.
Some end-use applications are: heat sink, geothermal pipes, LED
light sockets, heat exchanger, temperature sensors, etc.
Various applications: Graphite in also used in
various other applications: pebble bed nuclear reactors, seals,
foils, coatings, paints, pencils, ceramics, catalyst support,
synthetic diamond and hard metals.
How does Graphite form: from pressure & temperature
Review: What is Graphite?
Graphite is a soft, crystalline form of carbon,
and while it shares the same chemistry as diamond the two have very
different physical properties. Diamond forms in the mantle
under extreme heat and pressure. Most graphite found near Earth's
surface was formed within the crust at lower temperatures and
pressures. Graphite and diamond share the same composition but have
very different structures.
The carbon atoms in graphite are linked in a
hexagonal network that forms sheets that are one atom thick. These
sheets are poorly connected and easily cleave or slide over one
another if subjected to a small amount of force. This gives graphite
it’s very low hardness, its perfect cleavage and its slippery feel.
In contrast, the carbon atoms in diamond are
linked into a frameworks structure. Every carbon atom is linked into
a three dimensional network with four other carbon atoms with strong
covalent bonds. This arrangement holds the atoms firmly in place and
make diamond an exceptionally hard material.
Graphite exhibits both metallic and
non-metallic properties. The metallic properties include thermal and
electrical conductivity, while the non-metallic properties include inertness,
high thermal resistance, and lubricity. Some of the major end uses
of graphite are in high-temperature lubricants, brushes for
electrical motors, friction materials, battery and fuel cells, and
pencil "lead".
How does Graphite occur: Geologic
Occurrence
Graphite is a mineral that forms when carbon is subjected to heat
and pressure in Earth’s crust and in the upper mantle. Pressures in
the range of 75,000 pounds per square inch and temperatures in the
range of 750 degrees Celsius are needed to produce graphite. These
correspond to the granulite metamorphic facies.
Graphite from Regional Metamorphism (Flake Graphite)
Most of the graphite seen at Earth’s surface today was formed at
convergent plate boundaries where organic-rich shales and limestones
were subjected to the heat and pressures of regional metamorphism.
This produces marble, schist and gneiss that contains tiny crystals
and flakes of graphite.
When graphite is in high enough concentrations these rocks can be
mined, crushed to a particle size that liberates the graphite flakes
and processed by specific gravity separation or froth flotation to
remove the low density graphite. The product produced is known as
“flake graphite”.
Graphite from Coal Seam Metamorphism ("Amorphous" Graphite)
Some graphite forms from the metamorphism of coal seams. The organic
material in coal is composed mainly of carbon, oxygen, hydrogen,
nitrogen and sulfur. The heat of metamorphism destroys the organic
molecules of coal, volatilizing the oxygen, hydrogen, nitrogen and
sulfur. What remains is a nearly pure carbon material that
crystallizes into mineral graphite.
This graphite occurs in “seams” that correspond to the original
layer of coal. When mined the material is known as “amorphous
graphite”. The word “amorphous” is actually incorrect in this usage
as it does have a crystalline structure. From the mine this material
has an appearance similar to lumps of coal without the bright and
dull banding.
Amorphous graphite is the most abundant
graphite form and the least valuable. Deposits of amorphous graphite
are often found with coal deposits; however, separation of amorphous
graphite from coal is a far from trivial process and results in a
lower quality product.
Graphite from Hydrothermal Metamorphism (Lump Graphite)
A small amount of graphite forms by the reaction of carbon compounds
in the rock during hydrothermal metamorphism. This carbon can be
mobilized and deposited in veins in association with hydrothermal
minerals. Because it is precipitated it has a high degree of
crystallinity and that makes it a prefered material for many
electrical uses.
Graphite in Igneous Rocks and Meteorites
Small amounts of graphite is known to occur as a primary mineral in
igneous rocks. It is known as tiny particles in basalt flows and
syenite. It is also known to form in pegmatite. Some iron meteorites
contain small amounts of graphite. These forms of graphite are
occurrences without economic importance.
Synthetic Graphite
“Synthetic graphite” is made by heating high
carbon materials like petroleum coke and coal tar pitch to
temperatures in the range of 2500 to 3000 degrees Celsius. At these
high temperatures, all volatile materials and many metals in the
feedstock are destroyed or driven off. The graphite that remains
links into a sheet-like crystalline structure. Synthetic graphite
can have a purity of over 99% carbon, and is used in manufactured
products where an extremely pure material is required.
Graphene & Beyond
One single layer of graphite is called
“graphene sheet”. Expandable graphite and graphene are normally
produced from flake graphite. Expandable graphite is formed by
expanding the carbon layers of flake graphite and introducing atoms
or small molecules to this space. Expandable graphite is primarily
used as a flame retardant; in comparison to other flame retardants
it is free from halogens and heavy metals, is low cost and suitable
for a wide range of applications. Graphene that could be obtained
starting from graphite is a relatively new discovery and as of today
it is produced in limited quantities, but it is considered a very
promising material to be exploited in various applications like
battery, thermal management, polymer composites, sensors, flat-panel
displays, etc.
o
40+ years’ experience in the mining industry with strong mineral
processing experience in precious metals, copper, industrial
minerals, coal, and phosphate
o
Operational experience in precious metals, coal, and phosphate plus
in petrochemicals.
o
Extensive experience performing studies and determining feasibility
in the US and international (United States, Canada, Mexico, Ecuador,
Columbia, Venezuela, Chile, China, India, Indonesia, and Greece).
o
E-mail:
info@smartdogmining.com
