Robí nikel hrdza? Pochopenie korózneho správania niklu

Na vyriešenie otázky „Hneď nikel hrdza?”Komplexne, Najprv objasňujeme kritické rozlíšenie: rust is the common term for iron oxide (Fe₂O₃ or Fe₃O₄), a red-brown corrosion product exclusive to iron and iron-containing alloys.

Nikel, a transition metal with no iron in its pure form, cannot form rust.

Avšak, nickel can corrode—developing thin, protective oxide layers or, v drsnom prostredí, more damaging compounds like nickel hydroxides or sulfides.

1. Hrdza vs. Korózia: Prečo nikel nemôže hrdzaviť

To resolve the core question, we must first define key terms:

• Hrdzavenie: A hydrated iron oxide (Napr., FeO(Oh)·nH₂O) formed when iron reacts with oxygen and moisture.
  It is porous, flaky, and offers no protection against further corrosion—this is why uncoated steel rusts rapidly in wet environments.
• Korózia: The electrochemical degradation of any metal due to reactions with its surroundings.
  For non-ferrous metals like nickel, corrosion produces oxides, hydroxides, or salts that may be protective (passive) or destructive.

Pure nickel (Je ≥ 99.0%) contains no iron, so it cannot form iron oxide (hrdzavenie). Namiesto toho,
nickel’s corrosion products are primarily nickel oxide (Nio), nickel hydroxide (V(Oh)₂), alebo nickel carbonate (NiCO₃)—compounds that behave very differently from rust.

2. Odolnosť proti korózii niklu: Vrstva pasívneho oxidu

Nickel’s reputation for corrosion resistance stems from its ability to form a tenký, adherent passive oxide layer on its surface—an electrochemical barrier that blocks further reaction with the environment.

Here’s how this process works:

Tvorba pasívnej vrstvy

Keď je vystavený kyslíku (vysielať, vodná voda, or oxidizing environments), nickel undergoes a rapid reaction: 2Ni+O2→2NiO
This NiO layer is just 2–5 nanometers (nm) hrubý (1 nm = 10⁻⁹ meters)—invisible to the naked eye—but densely packed and chemically stable.

Unlike porous rust, the NiO layer adheres tightly to the nickel surface, preventing oxygen and moisture from reaching the underlying metal.

In aqueous environments (Napr., vodná voda, morská voda), the layer evolves to include nickel hydroxide (V(Oh)₂) a, in carbonated environments, nickel carbonate (NiCO₃)—both of which reinforce the passive barrier.

Stabilita pasívnej vrstvy

The NiO layer remains stable across a wide range of conditions:

• pH Range: Effective in neutral (Ph 6–8) and slightly alkaline (pH 8–12) prostredie.
  In mild acids (Napr., 5% acetic acid), the layer dissolves slowly, but in strong acids (Napr., 37% kyselina chlorovodíková), it breaks down completely.
• Teplota: Stable up to ~600°C in air. Above this, NiO thickens and becomes porous, reducing its protective ability (Napr., at 800°C, nickel corrodes at ~0.1 mm/year in air, vs. <0.001 mm/year at room temperature).
• Oxygen Availability: Requires minimal oxygen to maintain—even in stagnant water, the layer persists, making nickel suitable for submerged applications (Napr., morské komponenty).

Miera korózie čistého niklu

3. Faktory, ktoré znižujú odpor korózie niklu

Although nickel is highly corrosion-resistant due to its passive oxide layer, several environmental and material-related factors can compromise this protection.

Understanding these factors is crucial for predicting nickel’s performance and preventing localized or accelerated corrosion.

Chlorid a halogenidové ióny: Jamka a štrbina korózie

Chloridové ióny (Cl⁻)—found in seawater, cestná soľ, and industrial brines—are nickel’s greatest enemy.

They penetrate the passive NiO layer at weak points (Napr., škrabance, grain boundaries) and initiate korózia jamiek: tiny, localized holes that grow over time.

• Mechanizmus: Chlorides react with nickel to form soluble nickel chloride (NiCl₂), which dissolves the oxide layer locally.
  The exposed nickel then corrodes rapidly, creating pits as small as 10 μm in diameter.
• Risk Factors: High chloride concentrations (>1,000 ppm), vysoká teplota (>50° C), and stagnant conditions (Napr., crevices between bolted nickel parts).
• Údaje: Na morskej vode (35,000 ppm cl⁻) pri 60 ° C, pure nickel’s corrosion rate jumps to 0.05–0.1 mm/year (5–10× higher than at room temperature) due to pitting.

Nečistoty: Oslabenie pasívnej vrstvy

Commercial nickel (Napr., ASTM B162 Grade 200, 99.0-99,5% pri) contains trace impurities like iron (FE), síra (Siež), a uhlíkom (C)—all of which reduce corrosion resistance:

• Žehlička (FE): Rovnomerný 0.5% Fe creates microgalvanic cells (iron acts as an anode, nickel as a cathode), accelerating corrosion in wet environments.
  Napríklad, nickel with 1% Fe has a seawater corrosion rate of 0.02 mm/rok (double that of 99.99% čistý nikel).
• Síra (Siež): Forms nickel sulfide (NiS) in sulfidic environments (Napr., oil and gas wells with H₂S), which is brittle and prone to cracking.
• Uhlík (C): Na >0.1% C, forms nickel carbide (Ni₃C), which disrupts the passive layer and increases pitting risk.

Nikel (99.99% V) avoids these issues, making it ideal for critical applications like semiconductor manufacturing.

Silné kyseliny a redukčné prostredie

The passive NiO layer dissolves in strong reducing acids (Napr., kyselina chlorovodíková, Hcl) or non-oxidizing acids (Napr., kyselina sírová, H₂so₄ > 20% koncentrácia). Napríklad:

• V 37% Hcl (room temperature), pure nickel corrodes at 1–2 mm/year (rapid degradation, no passive layer).
• In oxidizing acids (Napr., kyselina dusík, Hno₃), the layer is reinforced (nitric acid acts as an oxidizer), so nickel resists corrosion (miera <0.01 mm/rok v 65% Hno₃).

4. Zliatiny niklu: Zvýšenie odolnosti proti korózii

5. Bežné mylné predstavy: „Hrdza“ na niklových alebo niklových predmetoch

People often mistake nickel corrosion for rust—here’s what’s really happening:

Mylná predstava 1: "Moja nikelová oceľ sa zhrdzavila."

Skutočnosť: The rust comes from the steel base metal, not the nickel plating.

Výtvarné pokovovanie (5–50 μm thick) protects steel by acting as a barrier, but if the plating is scratched or worn, steel is exposed to oxygen and moisture, forming rust.

Aby tomu zabránil, nickel-plated steel is often coated with a clear lacquer or used in low-moisture environments.

Mylná predstava 2: "Nikel zhnedne - nie je to hrdza."?“

Skutočnosť: Brown discoloration on nickel is tarnish, nie hrdzavec. It forms when nickel reacts with sulfur compounds in air (Napr., from pollution or natural gas) to create nickel sulfide (NiS) or nickel carbonate (NiCO₃).

Tarnish is thin and can be removed with a mild abrasive (Napr., baking soda), unlike rust, which is destructive.

"Nikel v mojej sprche zhrdzavil."

Skutočnosť: Shower water contains chlorides (from tap water treatment) a vlhkosť, which cause korózia jamiek on nickel (nie hrdzavec).

The small holes or white spots you see are nickel hydroxide (V(Oh)₂), Nie oxid železa. Using nickel-chromium alloys (Napr., Odvoz) in showers prevents this.

6. Testovanie odporu korózie niklu: Priemyselné štandardy

To ensure nickel and its alloys meet corrosion requirements, manufacturers rely on standardized tests:

Test soľného rozprašovania (ASTM B117)

Evaluates resistance to chloride-rich environments. Samples are exposed to a 5% NaCl mist at 35°C for 100–1,000 hours. Pass criteria for pure nickel: no pitting or corrosion after 500 hodiny.

Elektrochemická impedančná spektroskopia (Eis)

Measures the integrity of the passive layer by applying a small AC voltage to the nickel surface.

A high impedance (resistance to current flow) indicates a stable layer—pure nickel typically has an impedance of >10⁶ ohms·cm² in neutral water.

Testovanie na chudnutie (ASTM G1)

Measures corrosion rate by weighing a nickel sample before and after exposure to a corrosive environment. For pure nickel in seawater, weight loss should be <0.01 g/m²/day.

7. Priemyselné aplikácie zliatiny niklu

Nickel’s inability to rust and its strong corrosion resistance make it irreplaceable in key sectors:

Morské inžinierstvo

Monel 400 and Inconel 625 are used for ship propellers, komponenty platformy na mori, and seawater pumps—where their resistance to chloride pitting and seawater corrosion ensures 20–30 years of service (vs. 5–10 years for steel).

Chemické spracovanie

Nickel alloys handle aggressive chemicals like sulfuric acid (Monel 400) a kyselina chlorovodíková (Hastelloy C-276, a nickel-molybdenum alloy).

Napríklad, Hastelloy C-276 has a corrosion rate of <0.01 mm/rok v 20% HCl at 60°C—far better than pure nickel.

Elektronika

Ultra-pure nickel (99.99%) is used in semiconductor wafers and battery terminals, where tarnish-free surfaces and resistance to mild acids (Napr., cleaning solutions) sú kritické.

Architektúra

Nickel-chromium alloys (Napr., Odvoz 600) are used for building facades and monuments—they retain their silver appearance for decades (žiadna hrdza, minimal tarnish) and withstand urban pollution.

8. Záver: Nikel nie je hrdzavý, ale môže korodovať

Nikel never rusts, because rust is iron oxide and nickel has no iron. Its natural oxidová vrstva protects it from most corrosion, keeping it far more durable than steel in normal conditions.

But nickel can corrode under certain situations: chloride-rich water, impurities in the metal, or strong acids can damage its protective layer.

By alloying nickel with metals like chróm, molybdén, alebo meď, engineers create alloys such as Odvoz a Monel, which resist harsh chemicals, vysoká teplota, a morská voda.

Časté otázky

Môžu byť niklové predmety niekedy odolné voči hrdzaveniu?

No—nickel plating is a barrier, but if it’s damaged, the underlying metal (often steel) will rust.

For “rust-proof” nickel-plated items, use a duplex coating (nikel + chróm) or select a nickel alloy base material (Napr., Monel) instead of steel.

Is nickel more corrosion-resistant than stainless steel?

It depends on the stainless steel grade. Pure nickel is more resistant to seawater than 304 nehrdzavejúca oceľ (prone to pitting),

ale 316 nehrdzavejúca oceľ (s molybdenom) matches or exceeds pure nickel’s chloride resistance at a lower cost.

Does nickel corrode in saltwater pools?

Yes—saltwater pools have 3,000–5,000 ppm Cl⁻, which can cause pitting in pure nickel.

Use Inconel 625 alebo 316 stainless steel for pool components (Napr., rebrík, príslušenstvo) to avoid corrosion.

How can I clean tarnished nickel without damaging it?

Use a mild solution of warm water and dish soap, or a paste of baking soda and water (abrasive enough to remove tarnish, gentle enough not to scratch the passive layer).

Avoid harsh chemicals like bleach, which dissolve NiO.

Is nickel used in rust-preventive coatings for steel?

Yes—electroless nickel plating (a uniform, thick coating) is applied to steel parts (Napr., automotive bolts, hydraulické valce) to prevent rust.

The nickel layer acts as a barrier, and its passive oxide layer resists moisture.