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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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