What Is Kaolin?
• Chemistry: Al2Si2O5(OH)4, Aluminum Silicate Hydroxide
• Class: Silicates
• Subclass: phyllosilicates.
• Groups: The Clays and the Kaolin Group.
• Uses: In the production of ceramics, as a filler for paint, rubber and
plastics and the largest use is in the paper industry to produce a glossy paper
such as is used in most magazines.
• Specimens
Kaolin, which is named for its type locality, Kao-Ling, is a common
phyllosilicate mineral. It lends it name to the Kaolin Group, members of which
also belong to the larger general group known as the Clays. Kaolin's structure
is composed of silicate sheets (Si2O5) bonded to aluminum oxide/hydroxide layers
(Al2(OH)4) called gibbsite layers.
ibbsite is an aluminum oxide mineral that has the same structure as these
aluminum layers in Kaolin. The silicate and gibbsite layers are tightly bonded
together with only weak bonding existing between these silicate/gibbsite paired
layers (called s-g layers). The weak bonds between these s-g layers cause the
cleavage and softness of this mineral. The structure is very similar to the
Serpentine Group and at times the two groups are combined into a
Kaolin-serpentine Group.
Kaolin shares the same chemistry as the minerals halloysite, dickite and nacrite.
The four minerals are polymorphs; meaning they have the same chemistry, but
different structures. All four minerals form from the alteration (mostly
weathering) of aluminum rich silicate minerals such as feldspars. Kaolin is by
far the most common and most clay deposits contain at least some Kaolin. In
fact, clay deposits will frequently be nearly 100% Kaolin pure!
Kaolin is important to the production of ceramics and porcelain. It is also used
as filler for paint, rubber and plastics since it is relatively inert and is
long lasting. But the greatest demand for Kaolin is in the paper industry to
produce a glossy paper such as is used in most magazines.
Kaolin Powder
| Kaolin - KSP1 |
Physical |
| 100 |
<32 |
Particle Size
Distribution [¥ì m] |
| 100 |
<20 |
| 50 |
<2 |
| 10.5 |
At 105 ¢ªC |
Modulus of
Rapture (kg/cm2) |
| 18.8 |
At 900 ¢ªC |
| 2.9 |
At 105 ¢ªC |
Shrinkage (%) |
| 6.7 |
At 1250 ¢ªC |
| 11.9 |
At 1400 ¢ªC |
| 16.5 |
At 1250 ¢ªC |
Water Absorption
(%) |
| 10.9 |
At 1400 ¢ªC |
| 93 |
Green |
Brightness (%) |
| 97 |
At 1250 ¢ªC |
| 98 |
At 1400 ¢ªC |
| 2.31 |
Density Power
(g/Cm3) |
| 46 |
Plasticity (
Peff) H= 16 |
| 12500 |
Viscosity [CP]
Sp: 3 R.P.M:5
Solid = 40% Water = 60% |
| 7.3 |
Ph |
| 48.10 |
SiO2 |
Chemical
Analysis (%) |
| 36.85 |
Al2O3 |
| 0.05 |
Fe2O3 |
| 0.52 |
TiO2 |
| 0.28 |
CaO |
| - |
MgO |
| 0.15 |
Na2O |
| 0.36 |
K2O |
| 13.69 |
L.O.I |
| >91 |
Kaolin |
Mineralogical Composition (%) |
| <2 |
Montmorilonit |
| <3 |
Lllite |
| - |
Calcite |
| <5 |
Quartz |
| - |
Feldspare |
Kaolin (Lump)
| SiO2 |
68.050 |
|
| Al2O3 |
22.298 |
| TiO2 |
0.290 |
| Fe2O3 |
0.160 |
| CaO |
0.140 |
| MgO |
0.275 |
| K2O |
0.173 |
| Na2O |
0.206 |
| LOI |
8.150 |
Kaolin Physical Properties and Chemical Analyse
| Hardness |
1.5 - 2 (can leave marks on
paper) |
| Specific gravity |
2.6 (average) |
| Cleavage |
Perfect in one direction, basal |
| Color |
Usually white, colorless,
greenish or yellow |
| Fracture |
Earthy |
| Luster |
Earthy |
| Streak |
White |
| Transparency |
Crystals are translucent |
| Crystal System |
Triclinic; 1 |
| Crystal Habits |
Foliated and earthy
masses. Crystals of any size are quite
rare, usually microscopic. |
| Other Characteristics |
Clay like properties when
water is added. |
| Best Field Indicators |
Habit, softness, color, luster and clay like properties |
Kaolin Usage
* Kaolin (a clay mineral) and mica
can be substituted for talc in the
production of rubber, paint, and
plastics.
* Kaolin can be used in place of talc in
paper production.
* Kaolin (a clay mineral) and mica can
be substituted for talc in the
production of rubber, paint, and
plastics.
|
