Evaluation of ceramic sacrificial coatings for improved alkaliinduced corrosion protection in biofuel-fired boilers

• In the combustion of bio-based fuels the critically exposed burner parts in small boilers are typically uncooled and are usually made of FeCrNi alloys. These materials can suffer attack from the ashes because of the formation of alkali chromate. The reaction depletes the protective oxide in chromia, leading to accelerated corrosion. Selected "acidic" ceramic coatings based on Ti, Si, B and P have been evaluated for use as sacrificial layers to prevent the initial reaction of alkali and chromium. An accelerated oxidation test method including mild thermal shock has been utilized that previously proved useful to provide application-relevant results. A comparison of coated and uncoated specimens was performed with an austenitic high temperature steel as a substrate. The results indicate that the alkali released from the ash reacts with the respective "acidic" elements in the deposited coatings. This reaction has promoted initial formation of a thin and continuous chromium-rich protective oxide sub-layer. In addition, the oxide scale formed on the coated specimens appeared more coherent and crack-free. A significant enrichment of Ni at the steel-oxide interface also occurred that can promote high temperature corrosion resistance.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Naturresursteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Environmental Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Keramteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Ceramics (hsv//eng)

Nyckelord

Corrosion resistant alloys

Sacrificial coatings

Accelerated corrosion

Thermal shock

Scale (deposits)

Bio-fuel

Testing

High temperature corrosion-resistant alloys

Ceramic coatings

Biofuels

Accelerated oxidations

High temperature corrosion resistance

Pellet ash

Boilers

Alkali corrosion

Chromium

Deposited coatings

Corrosion resistance

Coatings

Steel-oxide interfaces

Screening

Protective oxides

Residential boilers

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