- Chemical Properties Definition: Chemical properties involve how materials react chemically when they contact other substances, affecting their integrity and function.
- Physical Properties of Materials: Understanding the physical properties helps in assessing material behavior under mechanical stresses and environmental conditions.
- Atomic Bonding Impact: Atomic bonding determines key material characteristics such as melting point and electrical conductivity.
- Corrosion Resistance: A material’s ability to withstand environmental degradation without losing strength, primarily through its composition and treatment.
- Acidity and Alkalinity: The pH value of a material indicates its acidity or alkalinity, which affects how it interacts with other materials.
Chemical properties describe how a material reacts with its environment and whether that reaction changes composition or performance. Engineers use these properties to choose compatible materials, estimate service life and select corrosion controls. This page covers four related topics:
- Chemical composition
- Atomic bonding
- Corrosion resistance
- Acidity or basicity of solutions and extracts
Chemical Composition
The chemical composition of an engineering material states which elements or compounds are present and, for an alloy, their permitted or measured amounts. Composition affects strength, hardness, ductility, corrosion, weldability and electrical behaviour, but processing, microstructure, heat treatment and service conditions also matter.
The table gives nominal educational examples. Alloy-family names cover many grades, so design and purchasing must use the governing material standard and a supplier’s material certificate rather than these rounded values.
| Sl. No. | Material | Nominal or grade-based composition |
| 1. | Carbon steel, generic | Fe with C; Mn and other additions depend on grade |
| 2. | Cartridge brass C26000 | Cu = 68.5-71.5%; Zn = remainder |
| 3. | Tin bronze, nominal example | Cu ≈ 90%; Sn ≈ 10% |
| 4. | Invar 36 | Fe ≈ 64%; Ni ≈ 36% |
| 5. | Gunmetal, nominal example | Cu ≈ 88%; Sn ≈ 10%; Zn ≈ 2% |
| 6. | Nickel silver, nominal example | Cu ≈ 50%; Zn ≈ 30%; Ni ≈ 20% |
| 7. | Nichrome, nominal example | Ni ≈ 60%; Cr ≈ 15%; Fe ≈ 25% |
| 8. | Phosphor bronze, grade-dependent | Cu = balance; Sn ≈ 3.5-10%; P generally below 0.35% |
| 9. | Manganin, nominal example | Cu ≈ 84%; Mn ≈ 12%; Ni ≈ 4% |
| 10. | Constantan, nominal example | Cu ≈ 55%; Ni ≈ 45% |
Atomic Bonding
Atomic bonding describes the forces that hold atoms or ions together. Bonding, crystal structure, defects and microstructure together influence melting behaviour, stiffness, fracture response and electrical conductivity. Three simplified primary-bond models are:
- Ionic bond – electrostatic attraction between oppositely charged ions, often formed after valence-electron transfer.
- Covalent bonds – atoms share electron density, often described as shared electron pairs.
- Metallic bonds – delocalised valence electrons bind a lattice of positive metal-ion cores.
Corrosion Resistance
Corrosion is deterioration caused by a chemical or electrochemical reaction between a material and its environment; metals are the usual subject. The reaction products may include oxides, salts or other compounds. Corrosion can reduce section thickness, change a surface, contaminate a process or start a crack; the rate and form depend on the material, electrolyte, temperature, flow, stress, geometry and contact with other metals.
Corrosion resistance of a material is its ability to withstand corrosion in a specified environment and covers more than atmospheric oxidation. Alloying can improve resistance in a particular service, but no alloy is resistant to every environment. Selection can be combined with coatings, inhibitors, cathodic protection, drainage, isolation of dissimilar metals and inspection.
Acidity or Alkalinity
pH describes hydrogen-ion activity in an aqueous solution. A dry bulk solid does not have an intrinsic pH, although engineers may measure the pH of a water extract, pore solution or wetted surface under a stated method. At 25 °C, pH 7 is neutral for pure water, lower values are acidic and higher values are basic. Neutral pH changes with temperature, and concentrated solutions can fall below 0 or above 14. Alkalinity is the solution’s acid-neutralising capacity and is not the same quantity as pH. A useful result therefore states sample preparation, liquid-to-solid ratio, temperature, calibration and test method.
