Abrasive and Abrasion Minerals

Topic 2: Abrasive and Abrasion Minerals

Hassan Z. Harraz

[email protected]

2015- 2016

Prof. Dr. H.Z. Harraz Presentation Abrasive Minerals

mailto:[email protected]

http://en.wikipedia.org/wiki/File:Noe_schleifstein.jpg

http://en.wikipedia.org/wiki/File:Grinding_Wheels.jpg

Outline of Topic 2:

We will explore all of the above in Topic 2.

Abrasive

Factors Affecting Rate of Abrasion

Good Abrasive

Classification of Abrasives

Abrasive Minerals

Types of Abrasive minerals

Nature Abrasive Minerals

Synthetic Abrasive Minerals

Selected Nature and Synthetic Abrasive Minerals

21 November 2015 Prof. Dr. H.Z. Harraz Presentation Abrasive Minerals 2

Defined Abrasives are substances that are used to clean or dress the

surfaces of other minerals, or comminute materials by abrasion and

percussion.

An abrasive is a type of very hard material, (it can often be a

mineral).

Abrasives may be classified as either natural or synthetic.

Abrasives are shaped for various purposes.

Abrasives are used in a wide range of domestic, industrial and

technological applications.

Abrasives are used to finish or shape a work piece. Rubbing the

abrasive on the work piece leads to part of the work piece being

worn away. When finishing a material it is often thought of as a

means to polish the material to gain a smooth surface or even

reflective surface; however some finishes require roughening as in

beaded, matte or satin finishes.


Abrasive Materials Natural materials are divided into three groups:

1) High-grade natural abrasives, which include, in order of

hardness: Diamond, Corundum, Emery, and Garnet.;

2) Siliceous abrasives, consisting of various forms of silica; and

3) Miscellaneous abrasives, including buffing and polishing

powders.

High-grade natural

abrasives

Siliceous abrasives Miscellaneous abrasives

Diamond Sandstone Bauxite Silicon carbide (Trade names of Carborundum)

Corundum Quartzite Magnesite Fused alumina (Trade names of Alundum and

Aloxite)

Emery (mixture of

corundum and magnetite)

Novaculite Magnesium oxide Boron carbide

Garnet Flint Ground Feldspar Metallic oxides

Chert Chalk Lampblack

Silicified Limestone Lime Carbon black

Quartz China Clay

Sand Talc

Tripoli Tin oxide

Pumice Manganese oxide

Diatomite Chromium oxide

Iron oxide

Type of Abrasives Abrasives are structured for individual purposes.

Generally abrasives can be classified into synthetic or natural.

When discussing sharpening stones, natural stones have long been considered superior but advances in material

technology are seeing this distinction become less distinct.

Many synthetic abrasives are effectively identical to a natural mineral, differing only in that the synthetic mineral has

been manufactured rather than been mined.

Impurities in the natural mineral may make it less effective.

Natural abrasives:

Many minerals and rocks of diverse composition but with one thing in common “Hardness”

are used in the natural state, except for processing and bonding.

may be used: i) in natural form (example: Sand, Pumice); ii) after shaping (example millstone); and iii)

after being ground into grains or powders and made up into wheels or papers.

are often sold as dressed stones, usually in the form of a rectangular block.

Natural diamonds are used primarily in diamond-tipped drill bits and saw blades for cutting or shaping

rock, concrete, grinding wheels, glass, quartz, gems, and high-speed tool steels.

Other naturally occurring abrasive materials (including garnet, emery, silica sand, and quartz) are used

in finishing wood, leather, rubber, plastics, glass, and softer metals.

Synthetic abrasives

Many synthetic abrasives are productively equivalent to an organic mineral.

It differs only in the fact that synthetic minerals are manufactured instead of mined.

The largest application of synthetic diamonds has been in wheels for grinding carbides and ceramics.

Both natural and synthetic abrasives are commonly available in a wide variety of shapes, often coming as bonded or

coated abrasives, including blocks, belts, discs, wheels, sheets, rods and loose grains.

Manufactured abrasives are classified into three types namely: coated, bonded and super abrasives.


Naturally Abrasives Synthetic Abrasives

Coarse Abrasives Soft Scrubbing

Powders

Soft Abrasives

Diamond dust Diatomite Ground Feldspar Silicon carbide (Carborundum)

Emery (impure corundum) Pumice Chalk Tungsten Carbide

TripoliCorundum Kaolin Boron carbide

Garnet Calcite Borazon (Cubic Boron Nitride

”CBN”)Sand

Rouge (Fe2O3) Ceramic (FeO, MgO, Cr2O3, MnO,

TiO2, Al2O3)Sandstone

Staurolite Dry ice

Novaculite Glass powder

Steel abrasive

Zirconia alumina

Slags

Diamonds (synthetic diamonds)

21 November

2015

Prof. Dr. H.Z. Harraz Presentation Abrasive Minerals 6

Range of Abrasive Selling Prices


i) Bonded Abrasives A bonded abrasive is composed of an abrasive material contained within a matrix,

although very fine aluminium oxide abrasive may comprise sintered material.

This matrix is called a binder and is often a clay, a resin, a glass or a rubber.

This mixture of binder and abrasive is typically shaped into blocks, sticks, or wheels.

The most usual abrasive used is aluminium oxide (Al2O3), silicon carbide (SiC),

tungsten (IV) carbide (WC) and garnet.

Artificial sharpening stones are often a bonded abrasive and are readily available as

a two sided block, each side being a different grade of grit.

Bonded Abrasives are required to be dressed after they are used.

Assorted grinding wheels as

examples of bonded abrasives.

A grinding wheel with a reservoir to

hold water as a lubricant and

coolant

Honing


ii) Coated Abrasives Coated Abrasives are also minerals that are used in the same way as bonded

abrasives.

A coated abrasive is an abrasive fixed on to a form of backing material like paper,

metal, rubber, resin, cloth and polyester.

A bonding agent (often some sort of adhesive or resin) is applied to the backing to

provide a flat surface to which the grit is then subsequently adhered. A woven

backing may also use a filler agent (again, often a resin) to provide additional

resilience.

Sandpaper is a best example of coated abrasive. Sandpaper is a very common

coated abrasive.

Coated abrasives may be shaped for use in rotary and orbital sanders, for wrapping

around sanding blocks, as handpads, as closed loops for use on belt grinders, as

striking surfaces on matchboxes, on diamond plates and diamond steels. Diamond

tools, though for cutting, are often abrasive in nature.

A German sandpaper showing its backing and FEPA grit size.


iii) Super Abrasives Super Abrasives are one of a group of relatively expensive but effective materials

possessing superior hardness and abrasion resistance.

Super Abrasives include Borazon (Cubic Boron Nitride ”CBN”) and diamond.

Super Abrasives have been developed to meet the needs of modern industry.

CBN next hardest substance to diamond (i.e., its hardness is 14 Mohos, scale), CBN

is replacing the diamond and diamond dust for many abrasive purposes.

CBN is used for machining the hardest steels to precise forms and finishes.


Abrasives Manufacturing

General The abrasives industry is composed companies engaged in the following separate types of

manufacturing:

Abrasive grain manufacturing : produce materials for use by the other abrasives

manufacturers to make abrasive products.

Bonded abrasives product manufacturing : is very diversified and includes the

production of grinding stones and wheels, cutoff saws for masonry and metals, and other

products.

Coated abrasive product manufacturing : include those facilities that produce large rolls

of abrasive-coated fabric or paper, known as jumbo rolls, and those facilities that

manufacture belts and other products from jumbo rolls for end use.


Abrasive Grain Processing Abrasive grains for both bonded and coated abrasive

products are made by graded crushing and close

sizing of either natural or synthetic abrasives.

Raw abrasive materials first are crushed by primary

crushers and are then reduced by jaw crushers to

manageable size, approximately 19 mm.

Final crushing is usually accomplished with roll

crushers that break up the small pieces into a usable

range of sizes.

The crushed abrasive grains are then separated into

specific grade sizes by passing them over a series of

screens.

If necessary, the grains are washed in classifiers to

remove slimes, dried, and passed through magnetic

separators to remove iron-bearing material, before the

grains are again closely sized on screens. This careful

sizing is necessary to prevent contamination of grades

by coarser grains.

Sizes finer than 0.10 mm are separated by hydraulic

flotation and sedimentation or by air classification.

Figure -1. Process flow diagram for abrasive grain

processing


Abrasive Grain Manufacturing• The most commonly used abrasive materials are aluminum oxides (Al2O3) and silicon carbide (SiC).

These synthetic materials account for as much as 80 to 90 % of the total quantity of abrasive grains

produced domestically. Other materials used for abrasive grains are Borazon (cubic boron nitride: CBN),

synthetic diamonds, and several naturally occurring minerals such as garnet and emery. The use of

garnet as an abrasive grain is decreasing.

• The following paragraphs describe the production of aluminum oxide, silicon carbide, CBN, and synthetic

diamond.

a) Silicon carbide (SiC):

• is known under trade names Carborundum, Crystalon, and carbolon. Its hardness is 13 Mohos,

scale.

• is used mainly in cutting wheels and papers and cloths.

• is produced in large tonnages using the Acheson process by reacting of about 60 % high-purity silica

sand and 40 % finely ground low-sulfur coke in a resistance electric arc furnace for 36 hours at 2200-

2500oC .

SiO2 + 3C → SiC + 2CO(gas)

• A small amount of sawdust is added to the mix to increase its porosity so that the carbon monoxide (CO) gas formed during the process can escape freely.

• Common salt is added to the mix to promote the carbon-silicon reaction and to remove impurities in the sand and coke.

During the heating period, the furnace core reaches approximately 2200°C, at which point a large

portion of the load crystallizes.

At the end of the run, the furnace contains a core of loosely knit silicon carbide crystals surrounded by

unreacted or partially reacted raw materials.

The silicon carbide crystals are removed to begin processing into abrasive grains.

• The crystalline product is crushed, washed in acid and alkali, and then dried after iron has been removed magnetically.

• Granular material is used in refractories and bonded abrasives.

Abrasive Grain Manufacturingb) Fused aluminum oxide (Al2O3)

Fused alumina is trade names of Alundum and Aloxite.

Before processing, bauxite, the crude raw material, is calcined at about 950°C to remove both free and

combined water.

The bauxite is then mixed with ground coke (~3 %) and iron borings (~2 %) in a pot-type, electric-arc

furnaces for 24 hours at 2000oC.

An electric current is applied and the intense heat, on the order of 2000oC, melts the bauxite and

reduces the impurities that settle to the bottom of the furnace.

As the fusion process continues, more bauxite mixture is added until the furnace is full.

The furnace is then emptied and the outer impure layer is stripped off.

The core of aluminum oxide is then removed to be processed into abrasive grains.

c) Cubic Boron Nitride ”CBN”

is trade names of Borazon

is synthesized in crystal form from hexagonal boron nitride, which is composed of atoms of boron and

nitrogen.

The hexagonal boron nitride is combined with a catalyst such as metallic lithium at temperatures in the

range of 1650°C and pressures of up to 1,000,000 pounds per square inch [psi].

d) Synthetic Diamond.

is manufactured by subjecting graphite in the presence of a metal catalyst to pressures in the

range of 808,000 to 1,900,000 psi at temperatures in the range of 1400 to 2500°C.


Bonded Abrasive Products Manufacturing

The grains in bonded abrasive products are held together by one of six

types of bonds: vitrified or ceramic (which account for more than

50 % of all grinding wheels), resinoid (synthetic resin), rubber,

shellac, silicate of soda, or oxychloride of magnesium.

Figure 2 presents a process flow diagram for the manufacturing of

vitrified bonded abrasive products.

Measured amounts of prepared abrasive grains are moistened and

mixed with porosity media and bond material.

Porosity media are used for creating voids in the finished wheels and

consist of filler materials, such as paradichlorobenzene (moth ball

crystals) or walnut shells, that are vaporized during firing.

Feldspar and clays generally are used as bond materials in vitrified

wheels.

The mix is moistened with water or another temporary binder to make

the wheel stick together after it is pressed.

The mix is then packed and uniformly distributed into a steel grinding

wheel mold, and compressed in a hydraulic press under pressures

varying from 150 to 10,000 psi. If there is a pore-inducing media in the

mix such as paradichlorobenzene, it is removed in a steam autoclave.

Prior to firing, smaller wheels are dried in continuous dryers; larger

wheels are dried in humidity-controlled, intermittent dry houses.

Most vitrified wheels are fired in continuous tunnel kilns in which the

molded wheels ride through the kiln on a moving belt. However, large

wheels are often fired in bell or periodic kilns. In the firing process, the

wheels are brought slowly to temperatures approaching 1400°C for as

long as several days depending on the size of the grinding wheels and

the charge. This slow temperature ramp fuses the clay bond mixture so

that each grain is surrounded by a hard glass-like bond that has high

strength and rigidity. The wheels are then removed from the kiln and

slowly cooled.

Figure 2. Process flow diagram for the manufacturing

of vitrified bonded abrasive products.


Bonded Abrasive Products Manufacturing (Cont. )

• After cooling, the wheels are checked for distortion, shape, and size. The wheels are then machined to final size,

balanced, and overspeed tested to ensure operational safety. Occasionally wax and oil, rosin, or sulfur are applied

to improve the cutting effectiveness of the wheel.

• Resin-bonded wheels are produced similarly to vitrified wheels. A thermosetting synthetic resin, in liquid or powder

form, is mixed with the abrasive grain and a plasticizer (catalyst) to allow the mixture to be molded. The mixture is

then hydraulically pressed to size and cured at 150 to 200°C for a period of from 12 hours to 4 or 5 days

depending on the size of the wheel.

• During the curing period, the mold first softens and then hardens as the oven reaches curing temperature. After

cooling, the mold retains its cured hardness. The remainder of the production process is similar to that for vitrified

wheels.

• Rubber-bonded wheels are produced by selecting the abrasive grain, sieving it, and kneading the grain into a

natural or synthetic rubber. Sulfur is added as a vulcanizing agent and then the mix is rolled between steel

calendar rolls to form a sheet of the required thickness. The grinding wheels are cut out of the rolled sheet to a

specified diameter and hole size. Scraps are kneaded, rolled, and cut out again. Then the wheels are vulcanized in

molds under pressure in ovens at approximately 150 to 175°C. The finishing and inspection processes are similar

to those for other types of wheels.

• Shellac-bonded wheels represent a small percentage of the bonded abrasives market. The production of these

wheels begins by mixing abrasive grain with shellac in a steam-heated mixer, which thoroughly coats the grain

with the bond material (shellac). Wheels 3 mm thick or less are molded to exact size in heated steel molds.

Thicker wheels are hot-pressed in steel molds.

• After pressing, the wheels are set in quartz sand and baked for a few hours at approximately 150°C. The finishing

and inspection processes are similar to those for other types of wheels.

• In addition to grinding wheels, bonded abrasives are formed into blocks, bricks, and sticks for sharpening and

polishing stones such as oil stones, scythe stones, razor and cylinder hones. Curved abrasive blocks and abrasive

segments are manufactured for grinding or polishing curved surfaces.

• Abrasive segments can also be combined into large wheels such as pulpstones. Rubber pencil and ink erasers

contain abrasive grains; similar soft rubber wheels, sticks, and other forms are made for finishing soft metals.


Coated Abrasive Products Manufacturing Coated abrasives consist of sized abrasive grains held by a film of

adhesive to a flexible backing.

The backing may be film, cloth, paper, vulcanized fiber, or a

combination of these materials.

Various types of resins, glues, and varnishes are used as adhesives

or bonds.

The glue is typically animal hide glue. The resins and varnishes are

generally liquid phenolics or ureas, but depending on the end use of

the abrasive, they may be modified to yield shorter or longer drying

times, greater strength, more flexibility, or other required properties.

Figure 3 presents a process flow diagram for the manufacturing of

coated abrasive products.

The production of coated abrasive products begins with a length of

backing, which is passed through a printing press that imprints the

brand name, manufacturer, abrasive, grade number, and other

identifications on the back. Jumbo rolls typically are 1.3 m wide by

1,372 m in length. The shorter lengths are used for fiber-backed

products, and the longer lengths are used for film-backed abrasives.

Then the backing receives the first application of adhesive bond, the

"make" coat, in a carefully regulated film, varying in concentration

and quantity according to the particle size of the abrasive to be

bonded.

Next, the selected abrasive grains are applied either by a mechanical

or an electrostatic method.

Virtually all of the abrasive grain used for coated abrasive products is

either silicon carbide or aluminum oxide, augmented by small

quantities of natural garnet or emery for woodworking, and minute

amounts of diamond or CBN.

Figure 3. Process flow diagram for the manufacturing

of coated abrasive products.


Coated Abrasive Products Manufacturing (Cont.)• In mechanical application, the abrasive grains are poured in a controlled stream onto the

adhesive-impregnated backing, or the impregnated backing is passed through a tray of abrasive

thereby picking up the grains.

• In the electrostatic method, the adhesive-impregnated backing is passed adhesive-coated side

down over a tray of abrasive grains, while at the same time passing an electric current through the

abrasive. The electrostatic charge induced by the current causes the grains to imbed upright in the

wet bond on the backing. In effect the sharp cutting edges of the grain are bonded perpendicular

to the backing. It also causes the individual grains to be spaced more evenly due to individual

grain repulsion. The amount of abrasive grains deposited on the backing can be controlled

extremely accurately by adjusting the abrasive stream and manipulating the speed of the backing

sheet through the abrasive.

• After the abrasive is applied, the product is carried by a festoon conveyor system through a drying

chamber to the sizing unit, where a second layer of adhesive, called the size coat or sand size,

is applied.

• The size coat unites with the make coat to anchor the abrasive grains securely.

• The coated material is then carried by another longer festoon conveyor through the final drying

and curing chamber in which the temperature and humidity are closely controlled to ensure

uniform drying and curing. When the bond is properly dried and cured, the coated abrasive is

wound into jumbo rolls and stored for subsequent conversion into marketable forms of coated

abrasives.

• Finished coated abrasives are available as sheets, rolls, belts, discs, bands, cones, and many

other specialized forms.


Applications of Abrasives Abrasives have a wide application in all phases of industry, and their use rises and falls with

industrial trends.

Abrasives used in the soap industry (including scouring soap) include: pumice, feldspar, diatomite,

bentonite, talc, silica, chalk and clays.

Metal polishes use pumice, emery, diatomite, silica, Tripoli, chalk, clay, bauxite.

Aluminum Oxide is the most common mineral used in sandpapers, grinding wheels, cut-off tools

and other 3M abrasive products.

Many of the materials that serve as abrasives have greater use for other purposes. Natural

abrasives are being supplanted by artificial abrasives.

Common applications for abrasives include the following:

Buffing (Tripoli)

Honing

Drilling (Industrial Diamonds, Carbonados; Bort)

Grinding

Sanding

Polishing

Cutting

Sharpening


Abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing

which leads to part of the workpiece being worn away. While finishing a material often

means polishing it to gain a smooth, reflective surface it can also involve roughening as in satin, matte

or beaded finishes.

Abrasives are extremely common place and are used very extensively in a wide variety of industrial,

domestic, and technological applications. This gives rise to a large variation in the physical and chemical

composition of abrasives as well as the shape of the abrasive. Common uses for abrasives

include grinding, polishing, buffing, honing, cutting, drilling, sharpening, lapping, and sanding

ABRASION: is the process of wear of a material by another material through scratching, chiseling or other

mechanical means.

ABRASIVE:

is a material, often a mineral, that is used to shape or finish a work-piece through rubbing which

leads to part of the work-piece being worn away

is a hard substance used for grinding, finishing or polishing of a less hard surface, or the

material that causes wear is called abrasive.

SUBSTRATE: The material being abraded is called a substrate.

P.S ABRASIVE IS HARDER THAN THE SUBATRATE.

EROSION: Is caused by hard particles impacting a substrate surface, carried by a stream of either liquid or

air e.g. sandblasting.

BULK REDUCTION: Is the process of removing excess material by cutting or grinding by a rotary

instrument.

FINISHING: Process of removing surface defects/scratches.

POLISHING: Polishing is the process of providing luster or gloss on a material surface.

FINISHED & POLISHED RESTORATION: A prosthesis or a direct restoration whose outer surface has

been refined to a desired state of finish.


http://en.wikipedia.org/wiki/Honing_(metalworking)

http://en.wikipedia.org/wiki/Cutting

http://en.wikipedia.org/wiki/Drilling

http://en.wikipedia.org/wiki/Sharpening

http://en.wikipedia.org/wiki/Lapping

GRINDING

Is the process of

removing material by

abrasion with relatively

coarse particles.

CONTOURING

Is the process of

producing a desired

anatomical form by

cutting or grinding.

Factors Affecting Rate of Abrasion

21 November

2015


The following factors causes changes in the rate of abrasion of an abrasive:

HARDNESS: Hardness of an abrasive is directly proportional to the rate of its abrasion i.e. the harder the abrasive than the substrate the more abrasion will be produced.

PARTICLE SIZE: The particle size of a material is

Expressed in MICROMETRES.

By convention, particles are classified as

FINE 0 - 10µm

MEDIUM 10 - 100µm

COARSE 100 - 1000µm

Larger, coarse abrasive particles will abrade a surface more readily than smaller particles, but they tend to leave more coarser scratches in the substrate.

PARTICLE SHAPE: Sharp, irregular shaped particles will abrade a surface more rapidly than will rounded particles having dull cutting angles. However the former will produce deeper scratches than later.

SPEED & PRESSURE: Both speed & pressure are directly proportional to the rate of abrasion.

At higher speed greater friction is produced, which tends to produce higher temperatures.

Similarly, greater pressure causes higher temperatures & possibly patient discomfort.

LUBRICATION: Lubricants are used during abrasion for two purposes:

to reduce heat buildup

to wash away debris to prevent clogging

but too much lubrication can reduce the abrasion rate by preventing the abrasive from coming in contact

with the substrate.

Some factors which will affect how quickly a substance is abraded include:

Difference in hardness between the two substances: a much harder abrasive will

cut faster and deeper

Grain size: larger grains will cut faster as they also cut deeper

Adhesion between grains, between grains and backing, between grains and

matrix: determines how quickly grains are lost from the abrasive and how soon fresh

grains, if present, are exposed

Contact force: more force will cause faster abrasion

Loading: worn abrasive and cast off work material tends to fill spaces between

abrasive grains so reducing cutting efficiency while increasing friction

Use of lubricant/coolant/metalworking fluid: Can carry away swarf (preventing

loading), transport heat (which may affect the physical properties of the workpiece or

the abrasive), decrease friction (with the substrate or matrix), suspend worn work

material and abrasives allowing for a finer finish, conduct stress to the workpiece.


Good AbrasiveThey 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

21 November

2015


DIAMOND

is a transparent, colorless mineral composed of carbon. It is the hardest

known substance & is called a super abrasive because of its ability to abrade

any other known substance.

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

21 November

2015


Nature Abrasive Minerals Many minerals and rocks of diverse composition but with one thing in

common “Hardness”.

are used in the natural state, except for processing and bonding.

Are being supplanted by artificial abrasives.

Synthetic diamond

abrasives

are used far more commonly

than natural diamond due to its

consistent shape & size & low

cost.

Diamonds are mostly used on

ceramics & resin-based composite

materials.

C

Specific Gravity: 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)


http://www.google.com/imgres?imgurl=http://www.made-in-china.com/image/2f0j00VhTtIaQgBEwlM/Synthetic-Industrial-Diamond-Powder-Wheel-Grits-.jpg&imgrefurl=http://www.made-in-china.com/china-products/productviewiHExLJmYonwI/Synthetic-Industrial-Diamond-Powder-Wheel-Grits-.html&usg=__9c6dA349BBkbKlFh8nW2Qs7hUJ8=&h=352&w=470&sz=33&hl=en&start=1&tbnid=u4mUoQgHfzRZGM:&tbnh=97&tbnw=129&prev=/images?q=Industrial+Diamond+mineral+pictures&hl=en&sa=G

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

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


http://webmineral.com/specimens/picshow.php?id=1434

http://www.mineralminers.com/html/rbymins.stm

http://z.about.com/d/geology/1/0/k/T/1/minpiccorundum.jpg

EMERY

is a mixtute of fine-

grain grayish black

corundum, magnetite,

and some hematite

and spinel.

used for finishing and

polishing metals; Glass

grinding

CORUNDUMis a white mineral form of Al2O3.

It is used primarily for grinding metal

alloys.


http://www.mineralminers.com/html/rbymins.stm

Zircon

(or Zirconium

silicate)

is an off-white mineral.

It is frequently used as a

component of dental

prophylactic pastes.


GARNETconsists of a group of different minerals that have the same physical properties &

crystalline forms. Minerals included in this group are silicates of Al, Co, Fe, Mg & Mn. The type of

garnet used in dentistry is usually dark red. It is used in grinding metal alloys & acrylic resin materials.

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.

World Wide Garnet Mine Locations


Common Nesosilicates: Garnet(Mg,Fe,Mn,Ca)3(Fe3+,Cr,Al)2Si3O12

As mod-T metamorphic mineral formed from Al-rich source rocks

and ultramafic mantle rocks (eclogites)

Equigranular, euhderal to subhedral habit; poor cleavage

Optics: Colorless, isotropic, high relief (n~1.7-1.9)

Complex solid solution with the following end-member

compositions and their characteristic colors:

Pyrope Mg3Al2Si3O12 – deep red to black; S.G. 3.5 - 3.6;

Hardness 7.5

Almandine Fe3Al2Si3O12 – deep brownish red; S.G. 4.09 - 4.31,

Average = 4.19; Hardness 7-8

Spessartine Mn3Al2Si3O12 – brownish red to black

Grossular Ca3Al2Si3O12 – yellow-green to brown; S.G. 3.42 -

3.72, Average = 3.57 ; Hardness 6.5-7.5

Andradite Ca3Fe2Si3O12 – variable-yellow, green, brown, black;

S.G. 3.8 - 3.9; Hardness 6½ - 7½

Uvarovite Ca3Cr2Si3O12 – emerald green

Almandine

Grossular

Andradite


Garnet A3B2Si3O12

Usually B is Aluminum, A divalentAlmandine Fe3Al2Si3O8

B-site

Aluminum

octahedral

A-site Fe++,

Mg++, Ca++,

Mn++ in

distorted

octahedra


• Garnet Group (X3Y2 {SiO4}3)

X{A} –> divalent cations: Ca+2, Mn+2, Fe+2, Mg+2

Y{B} –> trivalent cations: Al+3, Fe+3, Cr+3

Generally high-grade (high temp and/or pressure)

metamorphic rock occurrence

Gem stone of high hardness: 7-7.5

Nesosilicates: Garnet Group


http://webmineral.com/specimens/Spessartine.shtml

http://www.johnbetts-fineminerals.com/jhbnyc/gifs/14394.htm

http://www.johnbetts-fineminerals.com/jhbnyc/gifs/14136.htm

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

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

Grossularite

Andradite Ca3Fe2(SiO4)3

S.G. 3.8 - 3.9;

Hardness 6½ - 7½

Color Green, yellow,

orange, reddish-

brown,

brown, black

Fluorescence not

reported

Pyrope

Mg3Al2[SiO4]3S.G. 3.5 - 3.6; Hardness 7.5

Color Blood red, orange red,

purple red, pink, or black red

Fluorescence not reported


http://www.mcrocks.com/images/RockLittlePineaBig.html

http://webmineral.com/specimens/picshow.php?id=1196

http://www.google.com/imgres?imgurl=http://www.cs.cmu.edu/~adg/images/minerals/grgarnets/grossularite2.jpg&imgrefurl=http://www.cs.cmu.edu/~adg/adg-pggimages.html&h=660&w=880&sz=184&tbnid=BzLwNrhiRvcIkM:&tbnh=110&tbnw=146&prev=/images?q=Grossularite+mineral+pictures&hl=en&usg=__6dTxQT0a6Ix4cEA3p5x3UNQ8a7s=&ei=Z3JXSuH1PI-4M6GX9Z0I&sa=X&oi=image_result&resnum=1&ct=image

http://www.google.com/imgres?imgurl=http://skywalker.cochise.edu/wellerr/mineral/garnet/6garnet-almandite172f.jpg&imgrefurl=http://skywalker.cochise.edu/wellerr/mineral/garnet/garnetL.htm&h=482&w=640&sz=52&tbnid=91BDDGbJGK3LOM:&tbnh=103&tbnw=137&prev=/images?q=Almandite+mineral+pictures&hl=en&usg=___4lNhk-AWC4RNBflX337JX1IrDU=&ei=hW9XSuvNEJDeMbDZmZ0I&sa=X&oi=image_result&resnum=4&ct=image

http://www.cs.cmu.edu/~adg/images/minerals/angarnets/andradite12.jpg

http://www.cs.cmu.edu/~adg/images/minerals/pygarnets/pyrope1.jpg

Staurolite Industrial application is as a “Sand Blasting Agent”

Also used as a gemstone

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2015


(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.


http://www.google.com/imgres?imgurl=http://www.crystalinks.com/staurolite.jpg&imgrefurl=http://www.crystalinks.com/gemstones.html&h=300&w=300&sz=41&tbnid=5rO3TaDP6CgYGM:&tbnh=116&tbnw=116&prev=/images?q=Staurolite+mineral+pictures&hl=en&usg=__jCzPsX83TTkzPjfvOdkmJ88H77Q=&ei=z3lXSvGgIoLCNq7o7J0I&sa=X&oi=image_result&resnum=4&ct=image

http://www.google.com/imgres?imgurl=http://z.about.com/d/geology/1/0/J/3/1/cruciform.jpg&imgrefurl=http://geology.about.com/od/minerals/ig/mineralhabits/cruciform.htm&h=436&w=500&sz=102&tbnid=6feJm1fUJXgTwM:&tbnh=113&tbnw=130&prev=/images?q=Staurolite+mineral+pictures&hl=en&usg=__jc3XLzUWpLikhsiFrGWZ-m3wvxw=&ei=z3lXSvGgIoLCNq7o7J0I&sa=X&oi=image_result&resnum=2&ct=image

http://www.yuprocks.com/slist/staurolite4.shtml

SilicaWhat is Silica?

“Crystalline Silica” and “Quartz” refer to the same thing

2nd most common mineral in the earth’s crust

Major component of sand, rock, granite and mineral ore

Toxic and less/nontoxic form

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

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2015


Types of Silica

TOXICSilica, Crystalline (as dust) Trade Names

Cristobalite

Tridymite

Tripoli

Quartz

Common-Sandblasters

NON/LESS TOXIC

Silica, Amorphous

Trade Names

Diatomaceous earth

Diatomaceous silica

Diatomite

Silica Gel

Silicon Dioxide (amorphous)


QUARTZ

is a hard, colorless,

transparent & most

abundant mineral. It is

used mainly to finish

metal alloys.

SAND

is a mixture of mineral particles,

predominantly composed of silica. The particles represent a mixture of colors, making it distinct in appearance. They are coated onto paper disks for grinding of metals. (Sandpaper and sandblasting)

SiO2

S.G. 2.6 - 2.65, Average = 2.62

Hardness 7

Color Brown, Colorless, Violet, Gray,

Yellow.



http://www.google.com/imgres?imgurl=http://www.dep.state.fl.us/geology/geologictopics/rocks/sand_gravel.jpg&imgrefurl=http://www.dep.state.fl.us/geology/geologictopics/rocks/sand_gravel.htm&h=360&w=504&sz=56&tbnid=zspH7snGAF9BvM:&tbnh=93&tbnw=130&prev=/images?q=Sand+mineral+pictures&hl=en&usg=__JYLlqEv-fnJ1Qmz5Ml1-HYx6wkk=&ei=eXxXSvaaBY6MMezVwZ0I&sa=X&oi=image_result&resnum=4&ct=image

http://www.google.com/imgres?imgurl=http://images.paraorkut.com/img/pics/images/h/heart_of_sand-1824.jpg&imgrefurl=http://www.graphicshunt.com/search/1/beach.htm&h=400&w=348&sz=41&tbnid=xTBXbjI16ctIoM:&tbnh=124&tbnw=108&prev=/images?q=Sand+pictures&hl=en&usg=__NK5rVjs7vLPBM1LGMvp8rhiyKbU=&ei=V3xXSpO8BoG6NbeD_Z0I&sa=X&oi=image_result&resnum=4&ct=image

TRIPOLI

is derived from a light-

weight, friable siliceous

sedimentary rock. Tripoli

can be white, gray, pink,

red or yellow.

It is used for soft abrasive,

buffing blocks and

powders

SiO2

S.G. 2.7

Hardness 7

Color

White, buff

Fluorescence

None

Magnetic- No


Soft Scrubbing PowdersDiatomite

Used in silver polishes

More common use is filtering media

Pumice

Main ingrediant in polishing powders and household cleanersIncluding tooth paste

Used in hard rubbers

Used for washing stones for blue jeans

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2015


KIESELGUHR

is composed of the

remains of minute aquatic

plants known as diatoms.

Its coarser form is called

diatomaceous earth & is

used as a filler in many

dental materials, such as

hydrocolloid impression

materials.

CUTTLE

commonly referred to as cuttlefish or cuttlebone, is a white calcareous powder made from the internal shell of a Mediterranean marine mollusk.

It is available as coated abrasive & used for polishing metal margins.


PUMICEis a light gray volcanic rock

derivative, used in polishing tooth enamel, gold foil, dental amalgam & acrylic resins.

• Pumice is about 60-70% silica

• It has no crystal structure – it is

a frothy glass

• S.G. < 1

21 November

2015


http://z.about.com/d/geology/1/0/L/W/pumiceoakland.jpg

http://www.google.com/imgres?imgurl=http://learn.uci.edu/media/OC08/11004/OC0811004_L6PumiceRock.jpg&imgrefurl=http://learn.uci.edu/oo/getOCWPage.php?course=OC0811004&lesson=006&topic=013&page=10&h=350&w=350&sz=35&tbnid=X5ZYtqlnzHRjMM:&tbnh=120&tbnw=120&prev=/images?q=pumice+rock+pictures&hl=en&usg=__K0b95mhbtkFbzzlouuoXcG7aZaM=&ei=YH9XSsShJpG6NcXGmJ0I&sa=X&oi=image_result&resnum=3&ct=image

Other Soft Abrasives

Ground Feldspar in window cleaners

Chalk for fine soft metal polishes

Kaolin

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2015


CHALK

Is a white abrasive composed of CaCO3. Chalk is used as a mild abrasive paste to polish tooth enamel, gold foil, amalgam & plastic materials.

Synthetic Abrasive

SILICON CARBIDE (SiC)

It was the first of the synthetic abrasives to be produced. It is

available in green & blue-black types, having equivalent physical properties.

Silicon carbide is extremely hard (Its hardness is 13 mohos,scale) & brittle

& results in highly efficient cutting of materials, including metal alloys,

ceramics & acrylic resins

It is available as an abrasive in coated discs, & bonded instruments.

.

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2015


ALUMINUM OXIDE (Al2O3)Fused aluminum oxide was the second synthetic abrasive to be developed.

Fused alumina is trade names of Alundum and Aloxite.

Is made of bauxite fused in an electric furnace with coke and iron for 24 hours at

1000oC.

Aluminum oxide (alumina) is much harder than corundum due to its purity.

Several grain sizes are available & has largely replaced emery for several abrasive uses.

Alumina is used in the form of vitrified wheels and powders & for finishing metal alloys, resin-based composites & ceramic materials.

21 November

2015


ROUGE

Fe2O3 is the fine, red abrasive

component of rouge.

Like tripoli, rouge is blended with various

soft binders into a cake form.

It is used to polish high noble metal alloys.

21 November

2015


TIN OXIDE

SnO is an extremely

fine abrasive used

extensively as a polishing

agent for polishing teeth

& metallic restorations.

It is mixed with water,

alcohol or glycerin to form

a mildly abrasive pastes.

ABRASIVE PASTES

The most commonly used abrasive pastes contain either alumina or diamond particles.

Alumina pastes should be used with a rotary instrument & increasing amounts of water.

Diamond abrasive pastes are used in dry conditions.

Abrasive pastes have several disadvantages like:

they are relatively thick & so don’t readily gain

access to embrasures.

they tend to splatter off of the instruments.

heat is generated when insufficient coolant is

used or when an intermittent polishing

technique is not used.

21 November

2015


What is Abrasive Blasting?

Operations where an abrasive is forcibly applied to a surface by pneumatic or hydraulic pressure or by centrifugal force. Does not apply to steam blasting or steam cleaning or hydraulic-

cleaning methods where work is done without the aid of abrasives

Frequently used for: cleaning sand from foundry castings

cleaning and removing paint from metal surfaces

finishing tombstones

etching and frosting glass

Surface Preparation With Garnet Abrasive


Thompson Valve

Thompson Valve II

MicroValve

Metering of Garnet Abrasive

Reduce Air Emissions with Garnet Blast

Blasting with slag


Date post:	11-Apr-2017
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Abrasive and Abrasion Minerals

Education