Brass Lecture Notes

Introduction to Brass

• Brass is an alloy of copper and zinc, composition varied for different properties.
• Typically, brass is 60-70% copper and 30-40% zinc.
• Used since prehistoric times; a substitutional alloy.

Comparison with Bronze

• Bronze: Copper alloy with tin instead of zinc.
• Both may contain other elements like arsenic, lead, phosphorus.
• Museums often refer to these as "copper alloys."

Properties and Uses

• Brass has a bright, gold-like appearance.
• Used for decorative purposes: drawer pulls, doorknobs.
• Low melting point, high workability, durability.
• Good electrical and thermal conductivity.
• High copper content: softer, more golden; high zinc: harder, more silvery.
• Used in applications requiring corrosion resistance and low friction: locks, hinges, gears, bearings, ammunition, zippers, plumbing.
• Also used in musical instruments, costume jewelry, and some electrical applications.

Mechanical and Physical Properties

• Malleable, more so than bronze or zinc.
• Melting point: 900 to 940°C.
• Density: 8.4 to 8.73 g/cm³.

Recycling and Environmental Impact

• 90% of brass alloys are recycled.
• Non-ferromagnetic, separated from ferrous scrap using magnets.

Enhancements and Variants

• Aluminium: increases strength, corrosion resistance.
• Tin: makes brass suitable for seawater applications.
• Iron, aluminium, silicon, manganese: improve wear and tear resistance.

Corrosion and Chemical Reactions

• Corrodes with moisture, chlorides, acetates, ammonia.
• Galvanic corrosion: possible when in contact with more noble metals in corrosive environments.

Machinability

• Lead is often added to enhance machinability.
• Lead tends to settle in globules, affecting surface and leaching.

Legal and Environmental Considerations

• California reduced permissible lead content in brass.

Dezincification-Resistant Brass (DZR)

• Used in harsh environments, like high water temperatures.
• Example: C352 brass with specific zinc, copper, lead, arsenic composition.

Use in Musical Instruments

• Brass is common in musical instruments due to malleability, acoustic properties.
• Includes trombone, tuba, trumpet, etc.
• Percussion instruments like cymbals and bells.

Antimicrobial Applications

• Brass has bactericidal properties, useful in marine environments.

Historical Context

• Early use in West Asia, Eastern Mediterranean, India.
• Roman period: widespread deliberate production.
• Middle Ages: brass production centers in Europe and the Middle East.

Renaissance and Post-Medieval Europe

• Use of cementation and later speltering to produce brass.
• Development of large-scale distillation of zinc.

Summary

Brass is a versatile alloy with historical significance and modern applications, ranging from decorative uses to industrial applications, musical instruments, and antimicrobial surfaces.