51313-02159-Ceramic Sacrificial Coatings for Improved Alkali-Induced Corr. Protection in Biofuel-Fired Boilers

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Product Number: 51313-02159-SG

ISBN: 02159 2013 CP

Author: ROBERT POMPE

Publication Date: 2013

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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 the austenitic high temperature steel 253MA as a substrate. The results indicated 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 layer. In addition the oxide layer formed on the coated specimens appeared more crack-free. A significant enrichment of Ni at the steel-oxide interface also occurred that can favor long-term high temperature corrosion resistance.