Pure Metals and Alloys Study Notes

Classification of Substances

• Pure Substance: Consists of only one type of particle with a fixed composition. It can be an Element or a Compound. Examples include Distilled water, Oxygen gas, Gold (24K), Salt (sodium chloride), and Carbon dioxide.
• Mixture: Composed of two or more substances physically combined. These can be Homogeneous (uniform, like Air or salt water) or Heterogeneous (non-uniform, like Salad, Orange juice, or Milk). Steel is also categorized as a mixture.

Properties and Structure of Pure Metals

• Structure: Atoms are organized in regular, neat layers.
• Mechanical Properties: The layers slip past each other easily, making pure metals typically soft, malleable (hammered to shape), and ductile (drawn into wires).
• Electrical and Thermal States: They are good conductors of heat and electricity.
• Specific Examples & Melting Points:   * Iron: melts at about $1538\,^{\circ}\text{C}$   * Copper: melts at about $1085\,^{\circ}\text{C}$   * Gold: melts at about $1064\,^{\circ}\text{C}$
• Drawbacks: Often too soft, too reactive, or not durable enough for various applications.

Nature and Advantages of Alloys

• Definition: An alloy is a mixture of a metal with other metals or non-metals (such as carbon).
• Structure: The presence of different-sized atoms disrupts the regular layers, impeding the atoms from slipping past each other. This makes alloys harder and stronger than pure metals.
• Improved Properties: Alloys are used because they are typically harder, stronger, more durable, and more resistant to corrosion than pure metals.
• Common Alloys:   * Steel: Iron + Carbon.   * Brass: Copper + Zinc.   * Bronze: Copper + Tin.   * Solder: Lead + Tin (optimized for lower melting points; used for joining pipes or wires).   * Duralumin: Aluminium + Copper + Magnesium (strong yet light for aerospace).   * Stainless steel: Iron + Carbon + Chromium + Nickel (optimized for corrosion resistance).

Identification via Melting Points

• Pure Metals: Display a sharp, sudden melting point at one exact temperature. For example, Iron X melts at exactly $1535\,^{\circ}\text{C}$.
• Alloys: Melt gradually over a range of temperatures because they contain atoms of different sizes and bonding strengths. For instance, Iron Y melts between $1400\,^{\circ}\text{C}$ and $1450\,^{\circ}\text{C}$.
• Thermal Data:   * Pure Lead: $327\,^{\circ}\text{C}$   * Pure Tin: $232\,^{\circ}\text{C}$   * Optimal Solder: Mixture of $61\%\text{ tin}$ and $39\%\text{ lead}$ produces the lowest melting point.

Industrial Context

• The UAE is a global leader in industrial metal production, with one major company producing approximately $2.7\text{ million tonnes}$ annually.
• Metal serves as the country’s largest export following oil and gas, with over $50\text{ million tonnes}$ produced since $1979$.