Transcript Abrasives - Supplemental Teaching Resources

Abrasives
©2009 Dr B C Paul
Acknowledgement is given to the following sources SME Industrial Minerals,
mcrocks.com, geology.com, webmineral.com, mindat.org, USGS, cs.cmu.edu,
yuprocks.com, gc.maricopa.edu
Good Abrasives
• They are cheap
• They last a long time
• They cut or wear surfaces that you want
cut or worn quickly
• They don’t cut things you don’t want them
to
• Hardness is an obvious important factor
• Size and shape also are important
Diamonds
• Hardness of the diamond is unmatched
and for many applications they are
irreplaceable for cutting
– Industrial diamonds lack the color and
perfection of jewlery
• Major uses
– Diamond bits for rock and concrete
– Diamond dies for wire drawing
– Diamond tipped tools and wheels
(from Rockhoundblog.com)
Diamond Locations
• Diamonds are typically found in Kimberlite
and Lamproite
intrusions
• The intrusions can be as recent as the
Cenozoic
– Diamonds themselves are usually older
• Most are 3,200,000,000 to 990,000,000 years old
• A few have been found back to 4,200,000,000
• All seem to be associated with Archean
basement (maybe a few younger)
Roots of Continents Deeper than
Crust
At these depths stable form of carbon switches from graphite to
Diamond
Melts Coming Up from Depth Drag
Diamonds to the Surface
Kimberlite does not make diamonds
It drags them
Where is Archean Crust Known to
be Found
Red and Dark Green Mark the Spot
The Missing Crust Problem
• Stabilization of the Mantle Composition
relative to earth’s crust appears to happen
around 2,700,000,000 years ago
– We should have 70 to 80% of the continental
crust by then
Closer View of North American Old
Crust Areas
Industrial Diamonds
C
S.G. 3.5 - 3.53
Hardness 10
Color Colourless,
yellowish to yellow
, brown, black, blue
, green or red, pink
, champagne-tan,
cognac-brown
, lilac (very rare)
How Diamonds are Processed
• Crushing and Grinding
– (if the deposit is weathered or a placer this may not
be needed)
• Gravity Concentration
– Diamonds are heavier than surrounding minerals
– some unique designs produce a concentrate of
heavy minerals
Rotary washing pan
Make mud and the
Heavies settle
Heavy Media
This diagram shows how cones (left) and cyclones (right) use heavy-media
separation. Diamond-bearing concentrate is mixed with a fluid near the density of
diamond. Separation occurs in cones and cyclones by swirling the mixture at low
and high velocities respectively. In the cone, rotational mixing permits lighter
minerals to float to the top and run out as overflow, while diamonds and dense
minerals sink to the bottom and are sucked out with a compressed air siphon. In
the cyclone, fast rotation of the suspension drives heavy minerals to the conical
wall, where they sink to the bottom and are extracted, while float waste minerals
are sucked from the center of the vortex. Cyclones are about 99.999% efficient at
concentrating diamonds and similarly dense minerals from the original
ore. Adapted from Bruton (1978)
Other Minerals Besides Diamonds
are Heavy
• The grease method
– Freshly exposed
diamonds grab onto
axle grease
– Use greased shaking
tables to pull out
diamond
An Alternative to Hand Sorting of
Concentrates
Using Fluorescence
Reserves and Production
Industrial Diamond Reserves
90
Millions of Carrats
80
70
Other
60
South Africa
Russia
50
Congo
40
China
30
Botswana
20
Australia
10
0
Production
Reserves/7
Catch – 88% of industrial diamonds are now synthetic
What are Diamonds Worth
Ability to make synthetic diamonds has brought down the price but they are
Still over $1,000,000 per ton (of course they are sold by carrots)
Corundum/ Emery
• Lots of gems are corundum
• Much of abrasive market has been taken
by synthetic minerals
– Get more uniform material without random
natural weaknesses
– Still used for super heavy duty concrete and
durable anti-skid material
Corundum
Al2O3
S.G. 3.98 - 4.1
Hardness 9
Color Colourless, blue, red, pink, yellow, grey,
golden-brown
Gem forms include Rubies and Sapphires, Emery
Where Corundum is Found
Garnet
• Use as a grinding and polishing agent
– Garnet papers still common abrasive
– Also used as a “sand blasting agent”
• It does not cause silicosis
– Filtering material
– A lot of natural sharpening rocks in fact get
their properties from well distributed small
garnet crystals
Almandite
Fe3Al2(SiO4)3
S.G. 4.09 - 4.31, Average = 4.19
Hardness 7-8
Color Brown, Brownish red, Red, Black,
Black red.
Fluorescence None
Grossularite
Ca3Al2(SiO4)3
S.G. 3.42 - 3.72, Average = 3.57
Hardness 6.5-7.5
Color Brown, Colorless, Green,
Gray, Yellow.
Fluorescence None
Pyrope
Mg3Al2[SiO4]3
S.G. 3.5 - 3.6
Hardness 7.5
Color Blood red, orange red,
purple red, pink, or black red
Fluorescence not reported
Andradite
Ca3Fe2(SiO4)3
S.G. 3.8 - 3.9
Hardness 6½ - 7½
Color Green, yellow, orange, reddish-brown,
brown, black
Fluorescence not reported
Staurolite
• Industrial application is as a “Sand
Blasting Agent”
• Also used as a gemstone
Staurolite
(Fe,Mg)2Al9(Si,Al)4O20(O,OH)4
S.G. 3.65 - 3.77, Average = 3.71
Hardness 7-7.5
Color Brownish yellow,
Brownish black, Yellow brown,
Dark brown, Reddish brown.
Fluorescence not reported
Silica
• Sand is still dominant material for “Sand
Blasting”
• Carefully graded and sized sand is used for
“flint” sandpapers
– Dominant market is home use
• Fine pure sands are an important raw material
for glass, ceramics, and synthetic abrasives
• Naturally fine almost amorphous material that
breaks up easily is called Tripoli
Sand
SiO2
S.G. 2.6 - 2.65, Average = 2.62
Hardness 7
Color Brown, Colorless, Violet, Gray,
Yellow.
Fluorescence not reported
Tripoli
SiO2
S.G. 2.7
Hardness 7
Color
White, buff
Fluorescence
None
Magnetic- No
Soft Scrubbing Powders
• Diatomite
– Used in silver polishes
– More common use is filtering media
• Pumice
– Main ingrediant in polishing powders and
household cleaners
• Including tooth paste
– Used in hard rubbers
– Used for washing stones for blue jeans
Pumice
Pumice is about 60-70% silica
It has no crystal structure – it is a frothy glass
S.G. < 1
Other Soft Abrasives
• Ground Feldspar in window cleaners
• Chalk for fine soft metal polishes
• Kaolin
Synthetic Abrasives
• Silicon Carbide and related (Tungsten
Carbide)