Melting Point of Zinc

1. Introduction: Overview of the Melting Point of Zinc

Melting point of zinc sits at 692.68K (419.53°C, 787.15°F), a key fixed point on the ITS‑90 temperature scale that industry and science rely on for calibrations and process control.

A pure substance melts at the temperature where its solid and liquid phases coexist in equilibrium.

Its relatively low melting temperature—alloy engineers exploit it for die casting and galvanizing—yet its thermal robustness makes zinc indispensable across sectors.

1.1 Basic Definition of Melting Point

The melting point marks the temperature at which a material’s solid and liquid phases exist together in equilibrium at a given pressure.

In practice, one heats the solid until it reaches this temperature; further heat intake converts solid into liquid without changing temperature until the last crystal dissolves.

• Scientific definition: Temperature at which Gibbs free energy change (ΔG) for solid→liquid equals zero, while enthalpy (ΔH) and entropy (ΔS) increase.
• Standard conditions: Unless otherwise noted, melting points report at 1atm (101.325kPa).

Zinc melts at 692.68K (419.53°C, 787.15°F) under 1atm, placing it among the lower‑melting transition metals.

1.2 Background Information on Zinc

• Basic facts:
  • Atomic number: 30
  • Electron configuration: [Ar]3d¹⁰4s²
  • Category: d‑block, group12 element
• Physical properties:
  • Density (20°C): 7.14g/cm³ (solid), 6.57g/cm³ (liquid at m.p.)
  • Heat of fusion: 7.32kJ/mol
  • Boiling point: 1180K (907°C, 1665°F)

Zinc’s metallic bonding arises from delocalized 4s electrons interacting in a hexagonal close‑packed lattice, yielding moderate bond strength and its characteristic melting point.

1.3 Importance of Zinc in Industry and Daily Life

1. Galvanization
   Zinc coating on steel protects against corrosion. Zinc’s melting point (~420°C) allows spray or dip processes in economical electric or gas furnaces.
2. Die casting
   Low melting temperature enables fine‑detail castings for automotive, hardware, and consumer goods.
3. Batteries
   Zinc’s electrochemical properties power alkaline and zinc‑air cells; Melting point influences recycling and electrode fabrication.
4. Alloys
   Brass (Cu–Zn) and specialized low‑melting safety alloys (e.g., Wood’s metal) leverage zinc’s melting behavior.

2. Melting Point of Zinc: Physical and Chemical Basis

2.1 Atomic Structure and Bonding Types of Zinc

Zinc atoms carry a filled d‐shell (3d¹⁰) and two 4s electrons. Delocalization of these 4s electrons produces metallic bonding, whose strength sets the energy required for melting.

• Electron shells: 2,8,18,2
• Bonding: Predominantly metallic; no directional covalent component.

2.2 Crystal Structure of Zinc

Zinc crystallizes in a hexagonal close‑packed (hcp) lattice, with two atoms per unit cell at positions (1/3,2/3,1/4) and (2/3,1/3,3/4). This arrangement yields a packing efficiency of ~74% and contributes to moderate melting enthalpy.

2.3 Thermodynamic Properties of Zinc

These values reflect the energy and disorder change as zinc transitions from its solid hcp form to liquid.

3. Thermodynamic Basis of Melting Point

3.1 Thermodynamic Principle of Phase Change

At the melting point, the Gibbs free energies of solid (Gₛ) and liquid (Gₗ) phases coincide (ΔG=0), satisfying:

$$ΔG = ΔH – TΔS = 0$$ $$ΔS = \frac{ΔH}{Tₘ} = \frac{7.32×10³\ \mathrm{J/mol}}{692.68\ \mathrm{K}} \approx 10.57\ \mathrm{J/(mol·K)}.$$

where ΔH is enthalpy of fusion and ΔS is entropy of fusion.

3.2 Enthalpy of Fusion and Melting Point

Zinc’s enthalpy of fusion (7.32kJ/mol) defines the latent heat required to break its metallic bonds per mole of atoms at the m.p.. The ratio ΔH/Tₘ yields entropy change:

$$\mathrm{\Delta }S=\frac{\mathrm{\Delta }H}{T_m}=\frac{7.32\times {10}^3\mathrm{J}\mathrm{/}\mathrm{m}\mathrm{o}\mathrm{l}}{692.68\mathrm{K}}\approx 10.57\mathrm{J}\mathrm{/}(\mathrm{m}\mathrm{o}\mathrm{l}\cdot \mathrm{K})\mathrm{.}$$

3.3 Effect of Pressure on Melting Point

Melting point shifts with pressure according to the Clausius–Clapeyron relation:

 

$$\frac{dT}{dP}=\frac{\mathrm{\Delta }V}{\mathrm{\Delta }S},$$

 

where ΔV is volume change on melting. Because zinc’s liquid is slightly less dense than its solid, raising pressure generally increases Tₘ, though the sensitivity remains small compared to boiling transitions.

4. Factors Affecting the Melting Point of Zinc

4.1 Effect of Purity

Impurities broaden the melting range and depress Tₘ. Even ppm‑level contaminants in zinc shift its liquidus downward and extend its pasty range, a key concern for calibration cells.

• High-Purity Zinc: Ultra-pure zinc (≥99.99%) exhibits a sharp melting point at 419.58°C.
• Impurities:
  • Lead (Pb): Lowers melting point to ~400°C by disrupting the crystal lattice .
  • Iron (Fe): Raises melting point due to intermetallic compound formation.

4.2 Pressure and Environmental Conditions

High‑pressure environments (e.g., >1GPa) can alter zinc’s Tₘ by tens of degrees, but industrial processes at near‑ambient pressure see negligible shift.

• Altitude: Reduced atmospheric pressure at high altitudes lowers the melting point marginally (e.g., 419.5°C at sea level vs. ~419°C at 5,000 meters).
• Oxidation: Zinc oxide (ZnO) forms at high temperatures, increasing the effective melting point due to its higher melting temperature (1,975°C).

4.3 Alloying Effect

Adding elements (Cu, Al, Mg) forms alloys with eutectic or peritectic behavior. Brass (≈60%Cu,40%Zn) melts between 900–940°C, far above pure zinc, while safety alloys (e.g., Bi–In–Zn–Sn) exploit zinc’s low m.p. to create fusible links around 100–250°C.

• Zinc-Aluminum Alloys:
  • Al content of 4–11% lowers melting point to 380–460°C, ideal for die casting.
• Zamak Alloys:
  • Zamak 12 (Zn-Al-Cu) melts at 377–432°C, balancing strength and castability.
• Brass (Zn-Cu):
  • Melting point decreases from 1,085°C (pure Cu) to 900–940°C with 30% Zn.

5. Practical Applications of Zinc Melting Point

5.1 Industrial Metallurgy and Casting

Zinc melts at just 419.5 °C, significantly below competing melting point of aluminum (648.8 °C), which translates into lower furnace temperatures and energy savings in die‑casting operations.

Hot‑chamber die‑casting immerses the injection system directly in the molten zinc, capitalizing on zinc’s fluidity at low temperatures to achieve thin‑wall, net‑shape parts down to 0.13 mm thickness.

Zinc yields nearly 100 % recyclability; scrap and sprues retain their metallurgical quality and remelt without degradation, reducing waste and carbon footprint compared to other casting materials.

• Die Casting: Zinc’s low melting point reduces energy consumption and tool wear, enabling mass production of components for automotive and electronics.
• Galvanization: Molten zinc (450–460°C) coats steel, forming a corrosion-resistant layer via hot-dip processes.

5.2 Batteries and Energy Fields

Thermal recovery processes heat battery residues to over 1200 °C, volatilizing organics and enabling 99 % zinc recovery with 97 % purity—parameters directly guided by zinc’s melting and vaporization behavior.

In rechargeable zinc‑air and alkaline cells, molten zinc processing informs electrode recycling and remanufacturing workflows, ensuring material integrity and cost‑effective energy storage solutions.

• Zinc-Air Batteries: Zinc’s low melting point aids in anode production, while its high theoretical energy density (1,086 Wh/kg) makes it promising for electric vehicles.
• Thermal Energy Storage: Molten zinc stores heat efficiently for solar and industrial applications.

5.3 Construction and Anti-Corrosion

Hot‑dip galvanizing immerses steel in a kettle of ≥98 % pure molten zinc at ~449 °C to deposit a metallurgically bonded Zn–Fe alloy layer that resists rust and abrasion for decades.

High‑temperature galvanizing (“delta galvanizing”) at 560–630 °C creates a harder, thinner coating with specialized applications in automotive sheet and hardware.
When weld repairs breach the zinc layer, zinc‑rich paints or flame‑spray zinc restore corrosion resistance without overheating the steel substrate.

• Roofing and Gutters: Zinc’s corrosion resistance and malleability at high temperatures allow seamless installation.
• Architectural Coatings: Zinc-rich paints protect steel structures by sacrificially corroding.

5.4 Welding and Electronics

During arc welding of galvanized steel, zinc vaporizes at ~871 °C, far below steel’s melting point, posing fume hazards and risking porosity; proper ventilation and joint design mitigate these challenges.

Zinc chloride flux (melting ≈280 °C) serves in soldering electronics and industrial piping, removing oxides and promoting strong metal bonds without reaching zinc’s bulk melting temperature .

Low‑m.p. zinc‑based alloys (e.g., eutectic Bi–In–Zn–Sn) melt between 100–250 °C, enabling fusible plugs and thermal safety devices in fire‑protection systems.

• Soldering: Zinc-based solders (e.g., Zn-Al) melt at 380–460°C, suitable for joining metals without damaging sensitive components.
• Printed Electronics: Zinc nanoparticles enable low-temperature sintering in flexible circuits.

5.5 Alloy Development

Zamak alloys (Zn–Al eutectic at 381 °C) combine low m.p. with high fluidity, ideal for high‑pressure die‑casting of intricate components in automotive and hardware industries.

Specialized zinc alloys, such as creep‑resistant formulations, extend service temperatures above 80–90 °C by tailoring Al and Cu content, directly modulated by melting range considerations.

Biomedical research explores biodegradable Zn alloys for stents and implants; controlling melting point and solidification paths ensures biocompatibility and processability.

• Zamak Alloys: Used in jewelry and hardware due to their low melting range (379–390°C) and high strength.
• Superalloys: Zinc improves creep resistance in aerospace materials when alloyed with nickel and titanium.

6. Measurement Technology for Zinc’s Melting Point

6.1 Laboratory Methods

6.2 Industrial Practice

• Non‑contact Pyrometry
  Infrared and optical pyrometers measure melt pools in galvanizing lines.
• Fixed‑Point Cells
  NIST SRM1748 zinc cells (≥99.9999%) provide a reference freezing plateau at 419.527°C (692.677K) with uncertainty ≤1.12mK, vital for ITS‑90 dissemination.

7. Comparison with Other Metals

Zinc sits between In and Cu; its moderate Tₘ fits many alloy and calibration roles.

Temperature Unit Converter：

8. FAQs

Q1: Does zinc melt easily in a house fire?
A: House fires reach ~600°C—sufficient to melt zinc (419.5°C), but structural steel rarely exceeds 500°C.

Q2: Can impurities raise zinc’s melting point?
A: No. Impurities typically form eutectic mixtures, lowering the melting point.

Q3: Why is zinc’s melting point lower than aluminum’s?
A: Zinc’s weaker metallic bonds and filled d-orbitals reduce bond strength.

Q: Can zinc be melted in a home oven?
A: Not recommended due to safety concerns and potential for inconsistent heating.

Q: Why is zinc’s melting point important in alloy development?
A: It allows for the creation of materials with tailored properties for specific applications.

9. Conclusion

Zinc’s melting point reflects its metallic bonding, hcp crystal geometry, and thermodynamic parameters (ΔHₘ, ΔSₘ).

At 419.53°C, it offers a balance of low‑energy processing and thermal stability, underpinning galvanizing, casting, calibration, and advanced alloy design.

Its role as an ITS‑90 fixed point ensures temperature accuracy worldwide.

Understanding the factors—purity, pressure, alloying—that shift zinc’s melting behavior empowers engineers and scientists to harness its unique properties in applications from corrosion protection to precision thermometry.