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CORROSION RESISTANCE
Fibre processing requires spin finishes and lubricants.
Their composition is in most cases unknown and they can produce corrosive
effects on different thread guide materials.
Metals are susceptible to chemical attack, while ceramic materials have
excellent corrosion resistance.
For example, alumina is resistant to:
- neutral solutions;
- inorganic acids (except hydrofluoric acid);
- organic compounds (hydrocarbons, fatty acids, alcohols, etc).
The following table shows the corrosion behaviour of Bettini ceramic materials
compared with various conventional materials.
| |
Bettini
ceramic products |
Reference
materials |
| |
ALUMINIUM OXIDE |
TITANIUM OXIDE |
HARD METAL |
TEMPERED STEEL |
| INORGANIC ACIDS |
Very resistant |
Resistant |
Not resistant |
Not resistant |
|
INORGANIC BRINES |
Very resistant |
Very resistant |
Partially
resistant |
Partially
resistant |
|
INORGANIC NEUTRAL SALT SOLUTIONS |
Very resistant |
Very resistant |
Resistant |
Resistant |
|
ORGANIC SOLVENTS |
Very resistant |
Very resistant |
Very resistant |
Resistant |
|
ORGANIC ACIDS |
Very resistant |
Very resistant |
Resistant |
Partially
non resistant |
In general, ceramics are recognised to be chemically stable;
however, they are not at all times and are corrupted on certain conditions,
corrosion depends on the agent, its concentration, its temperature, exposure
time, etc. It is therefore necessary to know the operating conditions
to choose the most suitable material.
In general, chemical properties of ceramics are shown in the table.
| Chemicals |
Concentration |
Temperature (°C) |
Time |
Alumina |
Zirconia |
Silicon carbide |
Silicon nitride |
| HCl |
35% |
Boiling |
30 min. |
A |
B |
A |
A |
| HNO3 |
70% |
Boiling |
30 min. |
A |
B |
A |
A |
| H2SO4 |
98% |
Boiling |
30
min. |
A |
C |
A |
A |
| H3PO4 |
90% |
Boiling |
30
min. |
B |
B |
B |
A |
| HF |
60% |
20 |
24 hr |
C |
D |
A |
C |
| KOH solution |
10% |
80 |
7 days |
A |
A |
C |
A |
| KOH boiling |
|
500 |
24 hr |
C |
C |
D |
D |
| NaOH boiling |
|
500 |
24 hr |
B |
C |
D |
D |
| Na2CO3
boiling |
|
900 |
24 hr |
B |
C |
D |
D |
| Na2SO4
boiling |
|
100 |
24 hr |
A |
B |
D |
D |
| KF boiling |
|
90 |
24 hr |
D |
C |
D |
D |
A= No corrosion observed
B= Slightly corroded
C= Middle degree of corrosion
D= Heavily corroded
ATTENTION: All the data in the tables are indicative only.
For further information please contact our technical staff.
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