About Yellow Gold
Pure gold is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. It is one of the least reactive chemical elements and is solid under standard conditions. Gold is thought to have been produced in supernova nucleosynthesis, from the collision of neutron stars. Yellow gold is usually pure gold, but in jewelry gold alloys widely are used to increase strength of pure metal.
|Phase at STP||solid|
|Ultimate Tensile Strength||300 MPa|
|Young’s Modulus of Elasticity||75 GPa|
|Brinell Hardness||80 BHN|
|Melting Point||912 °C|
|Thermal Conductivity||320 W/mK|
|Heat Capacity||200 J/g K|
Composition of Yellow Gold
Examples of the common alloys for 18K yellow gold include: 18K yellow gold: 75% gold, 12.5% copper, 12.5% silver and 18K yellow (darker) gold: 75% gold, 15% copper, 10% silver.
Applications of Yellow Gold
Gold is used extensively in jewellery, either in its pure form or as an alloy. About 75% of all gold produced is used in the jewelry industry. Pure gold is too soft to stand up to the stresses applied to many jewelry items. Craftsmen learned that alloying gold with other metals such as copper, silver, and platinum would increase its durability and it also changes its color. The term ‘carat’ indicates the amount of gold present in an alloy. 24-carat is pure gold, but it is very soft. 18- and 9-carat gold alloys are commonly used because they are more durable.
Mechanical Properties of Yellow Gold
Strength of Yellow Gold
In mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. Strength of materials basically considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. In designing structures and machines, it is important to consider these factors, in order that the material selected will have adequate strength to resist applied loads or forces and retain its original shape.
Strength of a material is its ability to withstand this applied load without failure or plastic deformation. For tensile stress, the capacity of a material or structure to withstand loads tending to elongate is known as ultimate tensile strength (UTS). Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. In case of tensional stress of a uniform bar (stress-strain curve), the Hooke’s law describes behaviour of a bar in the elastic region. The Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests.
See also: Strength of Materials
Ultimate Tensile Strength of Yellow Gold
Ultimate tensile strength of Yellow Gold is 300 MPa.
Yield Strength of Yellow Gold
Yield strength of Yellow Gold is N/A.
Modulus of Elasticity of Yellow Gold
The Young’s modulus of elasticity of Yellow Gold is 75 GPa.
Hardness of Yellow Gold
In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. Brinell hardness test is one of indentation hardness tests, that has been developed for hardness testing. In Brinell tests, a hard, spherical indenter is forced under a specific load into the surface of the metal to be tested.
The Brinell hardness number (HB) is the load divided by the surface area of the indentation. The diameter of the impression is measured with a microscope with a superimposed scale. The Brinell hardness number is computed from the equation:
Brinell hardness of Yellow Gold is approximately 80 BHN(converted).
See also: Hardness of Materials
Thermal Properties of Yellow Gold
Yellow Gold – Melting Point
Melting point of Yellow Gold is 912 °C.
Note that, these points are associated with the standard atmospheric pressure. In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium. For various chemical compounds and alloys, it is difficult to define the melting point, since they are usually a mixture of various chemical elements.
Yellow Gold – Thermal Conductivity
Thermal conductivity of Yellow Gold is 320 W/(m·K).
The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.
The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:
Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.
Yellow Gold – Specific Heat
Specific heat of Yellow Gold is 200 J/g K.
Specific heat, or specific heat capacity, is a property related to internal energy that is very important in thermodynamics. The intensive properties cv and cp are defined for pure, simple compressible substances as partial derivatives of the internal energy u(T, v) and enthalpy h(T, p), respectively:
where the subscripts v and p denote the variables held fixed during differentiation. The properties cv and cp are referred to as specific heats (or heat capacities) because under certain special conditions they relate the temperature change of a system to the amount of energy added by heat transfer. Their SI units are J/kg K or J/mol K.
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