The application of silicon carbide particularly the sintered type is becoming more and more widespread,
not only for critical applications but also because even in more normal cases, its good performance - price ratio has helped make it the preferred material.

Advantages:

1) good wear - resistance properties even under particularly harsh conditions
2) high thermal conductivity as compared with other ceramic materials
3) good resistance to thermal shock
4) high tensile modulus
5) good chemical inertia
6) lower density than tungsten carbide
7) less expensive than tungsten carbide
8) easily obtainable raw material

Disadvantages:
1) lower impact strength than tungsten carbide
2) low stress resistance
3) requires special attention in selecting couplings. In fact, the wrong choice can lead to great generation of heat and thus to possible vaporization of the fluid interface film, thus inevitably damaging the seal.

Counterfaces

Silicon carbide with carbon is a combination that can ensure long seal life under a wide variety of conditions, since it offers excellent resistance to thermal shock, transients and to boundary conditions.
Instead, the silicon carbide - silicon carbide combination is generally used when high wear - resistance characteristics are required.

Carbon - Graphite

The term "carbon - graphite" or more simply, "carbon", is used for a wide range of carbonaceous materials
that are generally used for one of the two retainers.

Advantages:
1) good lubricating capacity even under conditions of boundary friction or dry friction
2) tendency to mitigate and fill in small imperfections in the sliding track
3) good chemical strength
4) good resistance to temperature, going from ultralow temperatures to 250 °C. This upper limit can be raised to 350 °C through the use of several metallic carbons and up to 450 °C with electrographite - type carbons
5) adequate compression resistance
6) low production cost

Disadvantages:
1) low tolerance in the presence of abrasives
2) strong oxidizing agents (nitrates, chlorates, etc.) can chemically attack the carbon and/or impregnator
3) decreased rigidity and greater tendency to warp at high temperatures, as compared to metals and ceramics
4) several industrial applications cannot tolerate the presence of carbon powder
5) low tensile strength
6) the finished product must be handled with care
7) low thermal conductivity (for several types)

Counterfaces
Carbon's ready tendency to be coupled with a wide variety of counterfaces justifies its widespread use as a seal component.

Advantages:
1) it is one of the most economical hard materials and offers excellent resistance to wear
2) it has excellent chemical resistance properties that depend on the degree of purity
3) in water or aqueous solutions, it has excellent properties when carbon is used as a counterface.
4) it also offer good resistance in the presence of abrasive solutions

Disadvantages:
1) low thermal conductivity: it dissipates very little heat under critical conditions
2) adequate resistance to thermal shock only with particular types of carbon.
3) it is a fragile material that is subject to mechanical damage under certain conditions

Counterfaces
Ceramic is general coupled with various types of carbon or with PTFE. The latter coupling is used for highly corrosive conditions.

While PTFE's good self - lubricating properties have often been a basic factor in making it preferable over other materials, its tendency to warp permanently under certain conditions has greatly limited its use.

Advantage:
1) good selflubricating properties
2) almost complete chemical inertia, although this inertia is decreased in the presence of fiber reinforcement

Disadvantages:
1) it warps easily and, even when reinforced with fiberglass, its mechanical characteristics are not as good as those offered by carbon
2) despite PTFE's noteworthy self - lubricating characteristics, its operation is less than perfect under boundary lubrication conditions and in fact, the high temperatures that are generated can cause considerable warping and lead rapidly to fault conditions.

3) limited use in the presence of abrasives
4) low thermal conductivity
5) relatively expensive

Counterfaces
PTFE is usually used against alumina. This coupling is highly resistant to a wide range of liquids, including liquids that attack carbon.
Nevertheless, this application has remained limited due to the low thermal conductivity of both materials.

This material is composed of very hard carbon particles alloyed with a ductile metal. It is used in particularly harsh conditions (in terms of PV). Despite the fact that it is the most costly of all the materials we have examined so far, it is often used because it offers various advantages in terms of seal performance and life.

Advantages:
1) highly wear - resistant even under particularly harsh working conditions
2) excellent thermal conductivity
3) high tensile modulus and thus less tendency to warp under pressure as compared with other metals
4) better resistance to mechanical shock than other hard non - metallic materials

Disadvantages:
1) limited chemical resistance, particularly in acid environments
2) high density, which can compromise the performance of this material at high rotational speeds
3) limited resistance capacity in dry operating conditions or with boundary lubrication in carbide - carbide coupling
4) high cost of raw material

Counterfaces
Since it is used in the presence of abrasive liquids, it is generally coupled either with itself or with alumina.
Given the fact that in these cases it has a very low dry - operation tolerance, it is increasingly being replaced with silicon carbide.