Physicochemical Properties and Process Performance of Materials

1. Physicochemical Properties of Materials

1.1 Physical Properties

• Thermal Properties: Characteristics related to temperature changes
  • Melting point/Solidification point: The temperature at which a material transitions from solid to liquid (or vice versa). For example, the melting point of steel is approximately 1538°C, which defines the temperature range for its hot working.
  • Thermal conductivity: The material’s ability to transfer heat. Copper has high thermal conductivity (~401 W/(m·K)) and is suitable for heat-dissipating components; thermal insulation cotton has low thermal conductivity and is used for heat insulation.
  • Coefficient of thermal expansion: The rate of dimensional change of a material with temperature. For instance, the thermal expansion coefficients of glass and metal must match to avoid cracking during packaging.
• Electrical Properties: The material’s response to electric current
  • Resistivity: Measures the material’s conductivity (low resistivity for conductors like copper; high resistivity for insulators like rubber; intermediate resistivity for semiconductors like silicon).
  • Dielectric constant: Characterizes the material’s ability to store electrical energy, used for selecting capacitors and insulating materials (e.g., ceramics have a high dielectric constant and are suitable for high-frequency capacitors).
• Optical Properties: The interaction between the material and light
  • Light transmittance: The proportion of light transmitted through the material (e.g., glass has a transmittance >80% for windows; plastic films have adjustable transmittance for agricultural greenhouses).
  • Reflectivity/Absorptivity: Mirrors have high reflectivity, while coatings on solar panels have high absorptivity to improve photoelectric conversion efficiency.
• Magnetic Properties: The material’s response to magnetic fields
  • Magnetic types: Classified as ferromagnetic (e.g., iron, nickel, attractable by magnets), paramagnetic (e.g., aluminum, weakly attractable), and diamagnetic (e.g., copper, weakly repellent), used in motors and magnetic storage devices.

1.2 Chemical Properties

• Corrosion resistance: The material’s ability to resist erosion by chemical media such as acids, alkalis, and salt solutions (e.g., stainless steel resists atmospheric corrosion; titanium alloys resist seawater corrosion and are used in ship components).
• Oxidation resistance: The material’s ability to resist reaction with oxygen at high or room temperatures (e.g., superalloys resist oxidation in engines to prevent surface spalling).
• Chemical stability: The material’s characteristic of not reacting with contacting substances (e.g., polytetrafluoroethylene, known as "resistant to all chemicals," is used as a lining for chemical pipelines).

2. Process Performance of Materials

3. Core Relationship: Physicochemical Properties vs. Process Performance

• Physicochemical properties define the upper limit of process performance: For example, high-melting-point materials (e.g., tungsten, melting point 3422°C) are difficult to cast (requiring extremely high temperatures) and can only be processed via powder metallurgy; brittle materials (e.g., ceramics) have poor deformation processing performance and can only be formed via sintering.
• Process performance affects the realization of physicochemical properties: For example, heat treatment can change a material’s internal structure, thereby adjusting its mechanical properties (e.g., 45 steel exhibits increased hardness and strength, with slightly reduced plasticity, after quenching and tempering); the cooling rate during casting affects the grain size of castings, which in turn changes their tensile strength and corrosion resistance.