The conductivity coefficient is equivalent to resistivity.
Conductors can be classified according to their conductivity coefficients as follows: Silver, Copper, Gold, Aluminum, Tungsten, Nickel, Iron.
I. Conductive Metal Materials
Commonly used conductive metal materials can be divided into four categories: Metallic elements, Alloys (like copper alloys, aluminum alloys, etc.), Composite metals, and Special-purpose conductive materials where conductivity is not the primary function:
1. Metallic elements (arranged by conductivity) include: Silver (Ag), Copper (Cu), Gold (Au), Aluminum (Al), Sodium (Na), Molybdenum (Mo), Tungsten (W), Zinc (Zn), Nickel (Ni), Iron (Fe), Platinum (Pt), Tin (Sn), Lead (Pb), and others.
Copper alloys include: Silver Copper, Cadmium Copper, Chromium Copper, Beryllium Copper, Zirconium Copper, etc.;
Aluminum alloys include: Aluminum Magnesium Silicon, Aluminum Magnesium, Aluminum Magnesium Iron, Aluminum Zirconium, etc.
3. Composite metals, which can be obtained by three processing methods: Plastic working composite, Heat diffusion composite, and Coating composite.
High mechanical strength composite metals include: Aluminum-clad Steel, Steel Aluminum Trolley Wire, Copper-clad Steel, etc.;
High conductivity composite metals include: Copper-clad Aluminum, Silver-clad Aluminum, etc.;
High elasticity composite metals include: Copper-clad Beryllium, Spring Copper-clad Copper, etc.;
High temperature-resistant composite metals include: Aluminum-clad Iron, Aluminum Brass-clad Copper, Nickel-clad Copper, Nickel-clad Silver, etc.;
Corrosion-resistant composite metals include: Stainless Steel-clad Copper, Silver-clad Copper, Tin-plated Copper, Silver-plated Copper-clad Steel, etc.
4. Special-purpose conductive materials refer to conductive materials that do not primarily focus on conductivity but exhibit good performance in electric heat, electromagnetism, photoelectricity, and electrochemical effects.
They are widely used in the technical fields of electrical instruments, thermal instruments, appliances, electronics, and automation devices. Examples include high-resistance alloys, electrical contact materials, electric heating materials, temperature control thermoelectric materials.
Important ones include alloys of elements like Silver, Cadmium, Tungsten, Platinum, Palladium, etc., and materials like Iron Chromium Aluminum alloy, Silicon Carbide, Graphite, etc.
Within a general temperature range, resistivity exhibits a linear relation with temperature change, which can be expressed as follows:
In the equation, ρ represents the resistivity at temperature t, ρ0 is the resistivity at temperature t0, which typically is 0°C or 20°C, and α is the temperature coefficient of resistivity. For pure metals, α ranges from 10-3 to 10-4°C-1, while for alloy conductors, α is between 10-4 and 10-5°C-1.
The impact of alloys and impurities manifests as distortions in the metal lattice caused by these elements, increasing the probability of electron scattering, hence elevating resistivity.
Therefore, high-resistance conductive materials are composed of alloys.
The influence of cold deformation is often represented by the stress coefficient of resistivity. During elastic compression or tension, the resistivity of metal generally changes according to the following rule.
In the formula, σ represents stress and K is the stress coefficient. When compressed, K is negative, and resistivity (ρ) decreases. When stretched, K is positive, and resistivity (ρ) increases.
Hence, the resistivity increases after the conductor is stretched. The impact of heat treatment is that after the conductive metal undergoes cold drawing deformation, its strength and hardness increase, while its conductivity and plasticity decrease.
After annealing, grain recovery and recrystallization occur, grain defects decrease, lattice distortion decreases, internal stress is eliminated, and resistivity decreases.
Metals with high electrical conductivity also have high thermal conductivity. The thermal conductivity of pure metals is higher than that of alloys.