The metal gold is extremely malleable. Gold is also ductile and one ounce can be drawn into 80 km of thin gold wire (5 microns diameter) to make electrical contacts and bonding wire. Gold has a Young's modulus of 79 GPa which is very similar to silver, but significantly lower than iron or steel.
The purity or fineness of gold in the jewelry is indicated by its karat number.
Gold (Au) is renowned for its extreme malleability and ductility. One ounce of gold can be drawn into 80 km of thin gold wire, which is commonly used for electrical contacts and bonding wire. Gold’s Young's modulus is 79 GPa, similar to silver but significantly lower than iron or steel.
Gold has an atomic number of 79, meaning each gold atom has 79 protons in its nucleus. The atomic mass is 196.967, and the atomic radius is 0.1442 nm. Gold's unique yellow color is due to the arrangement of its outer electrons and their transitions between energy bands, which produce the characteristic gold color when they absorb light at specific wavelengths.
Gold has only one stable non-radioactive isotope in nature, despite the existence of various isotopes due to varying numbers of neutrons.
The purity of gold in jewelry is measured by its karat number:
Gold alloys can vary in color based on the metals added:
Adding copper to gold makes it redder, while adding silver, zinc, or other metals makes gold paler. Lower karat golds can exhibit a wider range of colors due to more alloying metals.
White golds were developed in the 1920s as a platinum substitute. The color of white gold can be achieved by adding nickel, palladium, or platinum, which are strong bleaching agents. Other metals like silver and zinc also contribute to the whitening effect but to a lesser extent.
Palladium increases the melting point, modulus of elasticity, strength, and hardness of gold. Palladium white gold is primarily used in jewelry, dentistry, and spark plug electrodes.
In response to European demand for nickel-free alternatives, new white gold alloys with manganese, chromium, or iron as whiteners are being developed. These alloys may require rhodium plating due to less desirable white color and potential issues with cracking and tarnishing.
Alloying gold generally increases its strength and hardness while reducing malleability and ductility. The effects of alloying metals are as follows:
Reducing karatage from 24K to 18K increases strength and hardness. Further reduction from 18K to 9K has less impact. Lower karat alloys have a lower melting range and density, and copper-containing golds (8K to 18K) can be further hardened by precipitating hard second phases in the solid state.
Mechanical properties for typical karat golds vary with composition and are detailed in Table 3.
Table 1: Chemical Composition of Colored Gold Alloys
Color | Karat | Gold (%) | Copper (%) | Silver (%) | Other Metals (%) |
---|---|---|---|---|---|
Yellow | 18K | 75 | 12.5 | 12.5 | - |
Red | 18K | 75 | 25 | - | - |
White | 18K | 75 | - | - | 25 (Nickel, Palladium, etc.) |
Table 2: Composition of Palladium Containing White Gold
Gold (%) | Palladium (%) | Silver (%) | Other Metals (%) |
---|---|---|---|
75 | 15 | 10 | - |
Table 3: Mechanical Properties of Typical Gold Alloys
Karat | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
---|---|---|---|
24K | 120 | 35 | 40 |
18K | 300 | 180 | 25 |
14K | 450 | 250 | 15 |
10K | 500 | 300 | 10 |
Total Materia, metalik ve metalik olmayan malzeme özellikleri ve diğer malzeme kayıtları hakkında en kapsamlı bilgileri sağlayan lider malzeme bilgi platformudur.
Tüm bu bilgiler, 540.000'den fazla malzemeye benzersiz erişimin yanı sıra seçilmiş ve güncellenmiş referans verileri sağlayan nihai malzeme bilgi ve seçim aracı Total Materia Horizon'da mevcuttur.
Toplam Materia Horizon şunları içerir: