Scratch the coating of galvanized steel down to bare metal, and rust still will not appear at that spot. This is no accident but the effect of cathodic protection: zinc corrodes instead of the steel and shields it electrochemically even at the point of damage. This single property has made zinc the fourth most widely used metal in the world and the foundation of industrial corrosion protection.
Zinc - Basic Properties
Zinc (symbol Zn, from the Latin zincum) is a metal with atomic number 30, belonging to group 12 of the periodic table - the zinc group. In its pure state it is bluish-white in color with a characteristic metallic luster. In air it becomes covered with a thin, tight layer of oxides and carbonates that slows further oxidation - a phenomenon known as passivation, which proceeds similarly to that of aluminum.
Zinc is relatively brittle at room temperature, but in the range of 100-150°C it becomes ductile and can be rolled. It is a low-melting-point metal, which directly affects the technology of hot-dip galvanizing.
| Property | Value |
|---|---|
| Chemical symbol | Zn |
| Atomic number | 30 |
| Atomic mass | Approx. 65.38 u |
| Group / period | 12 (zinc group) / 4 |
| Color | Bluish-white |
| Melting point | 419.5°C |
| Boiling point | 907°C |
| Density | 7.14 g/cm³ |
| Crystal structure | Hexagonal |
| Main oxidation state | +2 |
Where Does Zinc Come From? Zinc Ores and Extraction
In nature, zinc does not occur in its free form - it is always bound in minerals. The most important zinc ores are:
- sphalerite (zinc blende, ZnS) - zinc sulfide, the primary and most common source of this metal;
- smithsonite (ZnCO₃, formerly known as calamine) - zinc carbonate;
- hemimorphite and wurtzite - accompanying minerals of lesser industrial importance.
In Poland, the largest zinc ore deposits are located in the Upper Silesian Coal Basin, including the area around Olkusz.
Extracting the metal comes down to two metallurgical methods:
- Pyrometallurgical method (thermal) - the ore concentrate is first roasted, converting the sulfide into zinc oxide (ZnO), and then reduced with coke at high temperature, with the zinc vapors collected in a condenser.
- Hydrometallurgical method - yields zinc of higher purity and is the dominant method today. Zinc oxide is leached with sulfuric acid, and pure metal is recovered from the purified solution by electrolysis.
Applications of Zinc
The applications of zinc are extremely wide - from steel structures, through alloys and batteries, to medicine and agriculture. Its importance is best illustrated by its consumption structure: about half of the world's production goes to galvanizing steel, and the rest is divided among alloys, chemical compounds, and other sectors.
Corrosion Protection of Steel
This is by far the most important application of zinc and the reason it is so highly valued in industry. By coating steel with a layer of zinc, we obtain galvanized steel - a material that is resistant to rusting, used in construction, power generation, the automotive industry, and road infrastructure. The most durable protection is provided by hot-dip galvanizing, that is, immersing finished components in a bath of molten zinc. The mechanism of this protection is discussed later in the article.
Zinc Alloys
Zinc is a component of many useful alloys:
- brass - an alloy of copper and zinc (zinc content usually 5-45%), valued for its strength, corrosion resistance, and ease of machining, used for fittings, hardware, and decorative elements;
- ZAMAK-type casting alloys (zinc with additions of aluminum, copper, and magnesium) - used in die casting of small, precise parts, including in the automotive industry and power tools.
Other Applications
Zinc is also the anode in common zinc-carbon and zinc-air batteries. Zinc oxide (ZnO), known as zinc white, is used as a white pigment for paints, as a filler and stabilizer for rubber and plastics, and as an ingredient in cosmetics and sunscreens. Zinc is also an essential trace element - it is a component of about 200 enzymes and is involved in wound healing, immune system function, and insulin secretion.
Zinc vs. Tin - What Is the Difference?
Zinc and tin are sometimes confused because of their similar names and appearance, but they are two completely different elements with different properties and applications. Zinc belongs to the zinc group (group 12), tin to the carbon group (group 14). They also differ in melting point and intended use.
| Characteristic | Zinc (Zn) | Tin (Sn) |
|---|---|---|
| Atomic number | 30 | 50 |
| Periodic table group | 12 (zinc group) | 14 (carbon group) |
| Melting point | 419.5°C | 231.9°C |
| Density | 7.14 g/cm³ | Approx. 7.29 g/cm³ |
| Typical application | Galvanizing of steel, brass | Solders, coatings on sheet metal (tinplate), bronze |
How can you tell them apart in practice? Tin is much softer and melts at a distinctly lower temperature - hence its role in soldering. Zinc is harder, brittle when cold, and it is the one responsible for corrosion protection of metals.
How Does Zinc Protect Steel from Corrosion?
Corrosion of steel is an electrochemical process in which iron, under the influence of moisture and oxygen, turns into rust. Zinc counteracts this in two complementary ways:
- Barrier protection - a tight, well-adhering zinc coating cuts the steel off from moisture and oxygen. The durability of this barrier is proportional to the coating thickness: greater thickness means longer protection.
- Cathodic (sacrificial) protection - zinc is more electrochemically active than iron, so if the coating is scratched or damaged, it is the zinc that corrodes first, "sacrificing itself" in place of the steel. The exposed section of steel remains protected as long as zinc is nearby - without the need to repair the coating.
Zinc in Hot-Dip Galvanizing - How It Works in Practice
In hot-dip galvanizing, prepared steel components are immersed in a bath of molten zinc at a temperature of about 450°C. At the boundary between the steel and the zinc, a metallurgical reaction takes place, resulting not in an ordinary coating "applied" to the surface but in a lasting metallurgical bond with the substrate. The zinc also reaches the inside of closed sections and hard-to-reach recesses, so the protection covers the entire component.
The result is a coating that is resistant to mechanical damage and performs well in harsh weather conditions - less precise, but far more durable than in the electroplating method (we compare the two technologies in a separate article: Hot-Dip Galvanizing vs. Zinc Electroplating).
At Strumet we carry out hot-dip galvanizing of steel structures and products in compliance with coating thickness standards. If you are planning to protect components against corrosion, contact the sales department of our hot-dip galvanizing plant - we will help you choose a solution suited to the service conditions.
FAQ - Most Common Questions About Zinc
What is the difference between zinc and tin?
They are two different elements: zinc (Zn, atomic number 30) belongs to the zinc group, and tin (Sn, atomic number 50) to the carbon group. Zinc is used mainly to protect steel against corrosion and as a component of brass; tin is used for soldering and for coatings on sheet metal.
What ores is zinc extracted from?
Primarily from sphalerite (zinc blende, ZnS) and smithsonite (ZnCO₃). The metal is recovered from them by a pyrometallurgical or hydrometallurgical method.
Why does zinc protect steel from corrosion?
It acts at the same time as a tight barrier separating the steel from moisture and as a sacrificial anode - if the coating is damaged, it corrodes instead of the steel, protecting it electrochemically.
What are the main industrial applications of zinc?
Galvanizing of steel (the most important application), production of alloys such as brass and ZAMAK, batteries, pigments (zinc white), and chemical compounds used in rubber and plastics.
Does zinc rust?
No - rust applies to iron and steel. Zinc oxidizes at the surface, forming a tight patina that protects it from further corrosion, which is why it protects steel so well.
What is the melting point of zinc?
Zinc melts at 419.5°C and boils at 907°C. The low melting point makes dip galvanizing possible in a bath at about 450°C.
