NATIONAL INSTITUTE OF TECHNOLOGY, HAMIRPUR

TRIBOCHEMICAL POLISHING

CONTENTS

1. Corrosive wear and oxidation wear

2. Tribochemistry

3. Tribochemical polishing

4. Conditions

CORROSIVE WEAR AND OXIDATION WEAR

Corrosive and oxidative wear occur in a wide variety of situations both

lubricated and unlubricated.

The fundamental cause of these forms of wear is a chemical reaction between

the worn material and a corroding medium which can be either a chemical

reagent, reactive lubricant or even air.

Corrosive wear is also known as chemical wear.

These wear occurs when sliding takes place in the corrosive environment,

air is the most dominant corrosive medium is oxygen.

These wear requires both chemical reaction (corrosion) and rubbing , so in

the absence of sliding there will be no corrosive wear.

These wear are important in number of industries such as mining ,

mineral processing , chemical processing and handling.

Chemical corrosive occurs because of chemical and electrochemical

intersection of interface with the environment.

Chemical corrosion occurs in a highly corrosive environment and in high

temperature and high humidity environment.

Electrochemical corrosion is a chemical reaction accompanied by the passage

of an electric current for the occurrence of potential difference between two

regions.

Fig no.1 Models of interaction between a corrosive agent and a worn surface

The first process is dominated by the formation of durable lubricating films. If

such films are prevail then worn contacts are well lubricated and corrosive wear

does not occur.

The second process is related to the formation of a sacrificial or short lifetime

corrosion product film under sliding contacts.

The third process relates to wear in highly corrosive media.

In the forth step rapid corrosion occurs on the exposed surface.

Fig no.2

TRIBOCHEMISTRY

Chemistry dealing with the modification of chemical reaction by friction or

mechanical energy is called turbo chemistry.

It is also defined as the chemical reactions between the surface and the

lubricant molecules inside a sliding contact under boundary lubrication

conditions.

These reactions controls the lubrication processes.

They determine the reliability and durability of moving parts in machines.

The wear controlled by this reaction as called as Tribochemical wear.

The mechanism by which friction increases the rate of chemical reaction are:-

Heat produced at contacting asperities.

Removal of product scale resulting in fresh surfaces.

Accelerated diffusion.

Mechanochemical excitation of surface bonds.

TRIBOCHEMICAL POLISHING

The corrosive wear is not always an entirely destructive process.

Corrosive wear can be utilized to produce very smooth surfaces where the

component is polished in a moderately active chemical reagent or water. This

technique is known as tribochemical or chemo-mechanical polishing.

Tribochemical polishing has been used to generate very smooth surfaces on

silicon nitride, silicon and silicon carbide.

Tribochemical polishing (TCP) is a new technique for polishing

materials that is based on the friction‐stimulated dissolution of material in a

liquid.

Fig no. 3 Mechanism of tribochemical polishing

STEPS OF MECHANISM

Chemical reaction between worn surface and corroding medium.

Preferential removal of successive layers of oxide at asperity peaks.

Worn surface becomes very smooth after initial wear.

Tribochemical polishing is effective only when the following

conditions are satisfied:

Friction at the asperities is sufficient to generate tribocorrosion

products.

Mechanical stresses are low to avoid any surface deformation or

fracture.

Corrosive medium is not too aggressive to cause corrosion outside the

frictional contact.

ADVANTAGES

High hardness.

High thermal conductivity.

Service life increases.

Reliability increases.

Fig. 4 Tribochemical polishing of sic

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