Bismuth is a silvery white, brittle, low toxic metal in the periodic table. It has a low thermal conductivity and melting point. Since it quickly oxidizes in air, the metal is naturally available in bismuth sulfides and bismuth oxides with exemplary optical and electronic activities.
Due to its redox reactions, different compounds like bismuth sulfides and oxides can be easily tested in supercapacitor technologies. This post will focus on the various applications of bismuth sulfides.
Properties & Occurrence of Bismuth Sulfide
Before we take a look at the use of bismuth sulfide, let’s first take a look at its theoretical properties.
- Compound Formula: Bi2S3
- Appearance: solid
- Density: 6.78 g/ cm3
- Molecular Weight: 514.16
- Melting Point: 775 °C (1427 °F)
It is commonly found in Bismuthinite mineral, which has a tin white or a lead-grey appearance. However, it can also be produced synthetically from bismuth (III) salt and hydrogen sulfide reactions. Bismuth (III) sulfide is used as a raw material to create other bismuth compounds for different applications.
Application of Bismuth Sulfide in Brake Pads
Bismuth trisulfide is used as a solid lubricant at temperatures of 80 – 260 °C. It enhances brake pad material’s fade resistance capabilities at increased temperatures above 260 °C, thus playing a critical role in the safe movement of vehicles.
As the brake pad slides against another surface, kinetic energy becomes frictional heat. This heat causes the automobile to slow down since its momentum is dissipated in the form of heat in the rotors and the pads.
It then causes binder degradation, which makes the stability of the friction coefficient questionable. Therefore, the bismuth trisulfide comes in as a solid lubricant that reduces abrasion. They delay the binder’s thermal degradation since they increase oxidation resistance. These solid lubricants provide a secondary film-creating ability that reduces wear due to their adhesion properties.
Another trisulfide commonly used in the braking industry is antimony trisulfide. It is a finely processed stibnite used in brake pads and as a flame retardant. Like bismuth trisulfide, its antiwear properties make it a suitable material in grease applications.
In the grease and lubricants industry, it can be used as an alternative to graphite, tungsten selenide, molybdenum disulfide, and boron nitride. Its lamellar crystal structure, oxidation state change, and oxide formation make it a suitable lubricant.
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