Chrome and chrome plating are often used interchangeably, but they refer to two very different things. Chrome is a chemical element, while chrome plating is a surface finishing process. Understanding the distinctions between the two is important for selecting the right materials and treatments across various industries and applications.
What is Chrome?
Chrome refers to the metallic chemical element chromium, which is represented by the symbol Cr and has an atomic number of 24. Chromium is a steel-gray, lustrous, hard metal that takes a high polish. It is odorless, tasteless, and malleable.
Some key facts about chromium:
- It has a melting point of 1907°C and a boiling point of 2671°C.
- Chromium is the 21st most abundant element found in the Earth’s crust.
- The primary countries where chromium is mined include South Africa, Zimbabwe, Finland, India, Kazakhstan, and Turkey.
- Chromium is resistant to tarnishing and has good hardness. It is used to provide corrosion resistance, improve hardness, and add decorative finish.
- The major applications of chromium are in stainless steels, alloy steels, nonferrous alloys, pigments, leather processing, refractory products, and metal finishing and plating.
- Chromium compounds are used for chrome plating. Hexavalent chromium compounds are toxic and carcinogenic.
- The health effects of chromium exposure depend on the valence state. Hexavalent chromium (Cr6+) is hazardous and can cause lung cancer. Trivalent chromium (Cr3+) is an essential nutrient for humans.
What is Chrome Plating?
Chrome plating, also known as chromium plating or chromium electroplating, is a surface finishing treatment that involves electrolytically depositing a thin layer or coating of chromium onto a metal object.
The chrome plating process has several steps:
- Surface preparation – The object to be chrome plated must be thoroughly cleaned and polished to ensure proper plating adhesion. This may involve alkaline cleaning, degreasing, pickling, abrasive blasting, or polishing.
- Activation – The surface is activated, often using an acidic etching or electrocleaning process, to remove any oxides and improve plating uniformity.
- Plating – The object is submerged in a chromium electroplating solution along with an anode. As current is applied, chromium metal builds up on the object’s surface via reduction reactions. Hexavalent chromium compounds are commonly used.
- Rinsing – The plated object is rinsed thoroughly to remove chrome solution dragout.
The thickness of the chrome layer can range from 0.2 to several microns. Decorative chrome plating is usually 0.2 to 2 microns. Hard chrome plating for engineering applications can be 10 to 250 microns thick. The chrome plating bath temperature is maintained around 40–65°C.
Chrome plating offers many benefits:
- Excellent corrosion resistance
- Decorative shiny metallic finish
- Good wear resistance and hardness
- Improved surface smoothness
- Allows easier cleaning
- Can be applied to wide range of materials
However, there are also some downsides:
- Toxic hexavalent chromium compounds are used
- Plating process generates hazardous wastes
- Brittle coating prone to cracking if too thick
- High energy consumption during plating
- Requires high operator skill
Key Differences Between Chrome and Chrome Plating
Now that we’ve defined chrome and chrome plating separately, let’s summarize the main differences between the two:
| Chrome | Chrome Plating |
| Refers to the metallic chemical element chromium (Cr) | A surface finishing process that deposits a thin layer of chromium onto objects |
| Naturally occurring element, not a process | Involves an electroplating process with multiple steps |
| Used to make alloys like stainless steel | Applied as a coating onto alloys, metals, plastics |
| Toxicity depends on chromium compound used | Uses hexavalent chromium compounds which are quite toxic |
| Main applications are in metallurgy, alloying | Main uses are decorative finishing and corrosion protection |
| No specific regulations | Highly regulated due to use of toxic chemicals |
- Chrome is a material while chrome plating is a surface treatment
- Chrome plating allows applying a chrome coating onto objects made of other materials
- The chrome plating process uses hazardous chromium compounds
Applications of Chrome
As highlighted earlier, chromium has a wide range of applications across various industries:
Stainless Steel Manufacturing
The addition of 10-30% chromium to iron results in stainless steel, which has excellent corrosion resistance. Stainless steels contain at least 10.5% chromium content by mass. Chromium reacts with oxygen to form a passive oxide layer that protects the iron from rusting. Some examples of stainless steels containing chromium include:
- 304 stainless steel (18% chromium, 8% nickel)
- 316 stainless steel (16-18% chromium, 10-14% nickel, 2-3% molybdenum)
- 410 stainless steel (11.5-13.5% chromium)
Alloy Steels
Chromium is alloyed with iron along with other elements like nickel and molybdenum to produce alloy steels optimized for properties like hardness, toughness, and resistance to high temperatures and corrosion. About 80% of the chromium produced is used in alloy steel manufacturing. Some chromium alloy steels include:
- Chrome-molybdenum steel (Cr-Mo steel)
- Chrome-vanadium steel (Cr-V steel)
- High-speed steel (contains 18% chromium)
Nonferrous Alloys
Chromium is also used to make nonferrous alloys of metals like aluminum, cobalt, copper, nickel, titanium, and zinc. Adding chromium improves high temperature strength, corrosion resistance, and wear resistance. Some examples include nickel-chromium superalloys used in jet engine components.
Pigments and Dyes
Chromium oxide green and chromium orange are two pigments made from chromium compounds widely used in paints, inks, glasses, ceramics, and plastics for their vibrant colors. Chromium compounds like chromium fluoride are used to make chromium-doped emerald gems.
Refractory Materials
Refractory bricks containing chromium oxide have high melting points and are resistant to thermal shock and chemical attacks. They are used to line high temperature furnaces and kilns. Chromium is also used in making refractory cements and mortars.
Leather Tanning
Chromium(III) salts such as chromium sulfate are used to produce chromium tanned leather, which is supple, strong, and stable. Chromium tanning produces a distinctive blue color. About 80% of commercially produced leather uses chromium for tanning.
Wood Preservation
Chromated copper arsenate (CCA) and ammoniacal copper zinc arsenate (ACZA) are wood preservatives containing chromium that provide protection against termites, fungi, molds, and other pests. Treated wood is used extensively in decks, utility poles, railroad ties, etc.
Other Uses
Other niche applications of chromium compounds include uses in magnetic tape production, drilling muds, catalysts, textile mordants, anodizing aluminum, and as coloring agents in glass, glazes, and enamels.
Chrome Plating Applications
Chrome plating not only enhances aesthetic appeal but also improves surface properties. Some major applications include:
Automotive Parts
Chrome plating is extensively used in the automotive industry for plating parts like bumpers, grilles, wheels, mirrors, door handles, emblems, and trim parts. This provides a shiny decorative finish along with improved wear and corrosion resistance. Hard chrome plating is also used on high wear engine components like piston rings and rollers.
Bathroom Fixtures and Fittings
Chrome plating is ideal for bathroom fixtures like faucets, shower heads, towel racks, and other hardware as it prevents corrosion in humid conditions and allows easy cleaning. The bright finish lends a modern and sleek look.
Household Appliances
Home appliances like refrigerators, ovens, microwaves, mixers, and other kitchenware often use chrome plating on handles, doors, trim parts, and fronts for aesthetic appeal and surface protection. It also hides fingerprints well.
Furniture Hardware
Hinges, drawer pulls, legs, and other metallic furniture hardware are frequently chrome plated to coordinate with chrome-finished kitchen or bathroom fixtures and prevent tarnishing. This helps them withstand repeated handling.
Electronics
Electronic equipment like cell phones and laptops use chrome plating on outer metallic casings, bezels, and other parts to provide scratch resistance along with a shiny and pleasing finish.
Bicycles and Motorcycles
Many moving parts on bicycles and motorcycles, like handlebars, shocks, rims, spokes, forks, brake parts, and frames are chrome plated for both decorative and functional benefits.
Medical Equipment
Surgical tools, dental instruments, and medical equipment containing metals can be chrome plated to prevent corrosion and facilitate sanitization in hospital environments. Stainless steels are also often used.
Other Uses
Other common chrome plated products include jewelry, eyeglass frames, light fixtures, firearms, industrial valves and fittings, shopping carts, and metallic decorative pieces like sculptures and trophies.
Overall, the shiny metallic finish and excellent surface properties of chrome plating make it a ubiquitous surface treatment across many consumer and industrial products.
Conclusion
Chrome and chrome plating are two very distinct things that are often confused. Chrome refers to the metallic element chromium, which is used to make stainless steels, alloys, pigments, and other products where it provides hardness, durability, and corrosion resistance.
Chrome plating is a surface finishing process where a thin layer of chromium is electroplated onto objects to provide decorative and functional benefits ranging from improved wear resistance to enhanced aesthetic appeal. However, chrome plating does utilize toxic hexavalent chromium compounds and generates hazardous wastes.
