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Pavleta Knutsson

Research

Materials at high temperature

Four connected themes: how alkali and ash attack alloys; how bed materials and oxygen carriers behave in biomass conversion; what happens where a metal meets its oxide; and, most recently, how residues become porous carbons for CO2 capture.

01

High-temperature corrosion and ash

30 papers

When biomass or waste is burned or gasified, the ash releases alkali compounds such as Na2SO4, KCl and KOH. On boiler tubes and other hot surfaces they attack the protective oxide that makes steel and nickel alloys last. Understanding that attack, and designing around it, decides whether a plant runs for months or for decades.

Why it matters: renewable energy depends on materials that survive the fuels we want to use.

Hot corrosion by gaseous and condensed alkali, ash chemistry, and how alkali is taken up and released in fluidized beds.

Alkali attack on an oxide-covered alloyCross-section: Na2SO4 and KCl vapour and particles drift down onto an alloy covered by a columnar oxide scale. A salt deposit sits on the scale and a jagged crack leads through the scale into the alloy, which shows grain boundaries. Na2SO4 and KCl in the hot gas salt deposit oxide scale alloy attack through the scale
Schematic: alkali attack on an oxide-covered alloy. Cross-section: Na2SO4 and KCl vapour and particles drift down onto an alloy covered by a columnar oxide scale.

Key findings

High-temperature corrosion and ash · Bed materials and oxygen carriers

Ilmenite draws potassium into its core

Up to 40 wt% of the sand in Chalmers' 12 MW boiler was replaced by the natural ore ilmenite. Iron moved to the particle surfaces, titanium concentrated in the core, the ash formed a calcium-rich double layer, and potassium diffused into the core to form KTi8O16. Locking potassium inside the particle could reduce both bed agglomeration and corrosion.

Energy & Fuels (2014) · 103 citations

High-temperature corrosion and ash · Bed materials and oxygen carriers

How biomass ash migrates into, and grows on, an oxygen carrier

Ilmenite samples taken from the 12 MW boiler after 5 to more than 300 hours of oxygen-carrier-aided combustion show potassium migrating into the particle core over time, and a calcium layer forming at longer times while calcium also moves inward. Combined with thermodynamic calculations, the paper proposes a mechanism for the ash–bed material interaction.

Energy & Fuels (2018) · 75 citations

Related papers

Article

2025

62 citations

Tailoring highly surface and microporous activated carbons (ACs) from biomass via KOH, K₂C₂O₄ and KOH/K2C2O4 activation for efficient CO₂ capture and CO2/N2 selectivity: characterization, experimental and molecular simulation insights

B. Dziejarski, J. Serafin, D. F. Hernández-Barreto, E. Naumovska, J. Sreńscek-Nazzal, N. Klomkliang, E. Tam, R. Krzyżyńska, K. Andersson, P. Knutsson

Chemical Engineering Journal 524, 169677 (2025)

High-temperature corrosion and ash · Porous carbons and CO2 capture

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02

Bed materials and oxygen carriers

47 papers

In a fluidized-bed boiler or gasifier, a hot, sand-like bed carries fuel and heat. The bed particles are not passive: minerals such as olivine, ilmenite and feldspar react with the ash, take up potassium and sulfur, and can carry oxygen from the air to the fuel. Choosing and understanding the right bed material improves conversion and protects the plant.

Why it matters: the bed is the working heart of gasification and combustion, and it changes as it runs.

Studied in the Chalmers 12 MW boiler, the research gasifier, the 100 kW chemical-looping unit and laboratory reactors.

A bed particle gaining an ash-derived layerLeft: a round bed particle (for example olivine) with a core and an outer ash-derived layer, surrounded by small ash particles drifting toward it. Right: an oxygen-carrier cycle, in which the particle takes up oxygen from air and releases it to the fuel. K, Na, Ca … from the fuel ash core ash-derived layer (grows as the bed ages) O2 from air O2 to fuel Oxygen carrier particle
Schematic: a bed particle gaining an ash-derived layer. Left: a round bed particle (for example olivine) with a core and an outer ash-derived layer, surrounded by small ash particles drifting toward it.

Key findings

Bed materials and oxygen carriers

A route for turning existing boilers into biomass gasifiers

Ten years of operating the 2–4 MW Chalmers research gasifier and the 20 MW GoBiGas biomethane plant, distilled into a route to commercial use. Two findings carry it: constituents of the biomass ash itself act as a catalyst for the process, and with coated heat exchangers ordinary fluidized-bed boilers can be retrofitted into gasifiers. The paper estimates that Sweden's existing fluidized-bed boilers alone correspond to a jet-fuel capacity of about 10% of current global consumption.

Energy Science & Engineering (2018) · 179 citations

High-temperature corrosion and ash · Bed materials and oxygen carriers

Ilmenite draws potassium into its core

Up to 40 wt% of the sand in Chalmers' 12 MW boiler was replaced by the natural ore ilmenite. Iron moved to the particle surfaces, titanium concentrated in the core, the ash formed a calcium-rich double layer, and potassium diffused into the core to form KTi8O16. Locking potassium inside the particle could reduce both bed agglomeration and corrosion.

Energy & Fuels (2014) · 103 citations

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03

Metal–oxide interfaces and coatings

5 papers

A protective oxide scale is only as good as its grip on the metal underneath. As Al2O3 grows on NiAl and Pt-modified aluminide coatings, atoms move, vacancies gather, and voids can open at the interface and weaken adhesion. This work looks at how those voids form, and how they sometimes heal.

Why it matters: coated components fail where the oxide lets go.

Alloys and coatings studied include NiAl and Pt-modified aluminides; the subject of the 2011 doctoral thesis.

Voids forming and healing at the metal–oxide interfaceTwo cross-sections of an Al2O3 scale on NiAl. In the first, vacancies collect into a row of voids along the interface as aluminium moves outward through the scale. In the second, the interface is mostly closed and only a single small void remains. Al out Al2O3 NiAl Void formation Al out Al2O3 NiAl Healing
Schematic: voids forming and healing at the metal–oxide interface. Two cross-sections of an Al2O3 scale on NiAl.

Key findings

Metal–oxide interfaces and coatings

What platinum does at the NiAl–oxide interface

A study of how platinum influences the interface between NiAl and its oxide during high-temperature oxidation of bulk material, part of the work on Pt-modified aluminide coatings.

Corrosion Science (2008) · 101 citations

Metal–oxide interfaces and coatings

Voids at the metal–oxide interface can form and heal

A study of how voids form at, and heal from, the interface between NiAl alloys and their oxide scale.

Oxidation of Metals (2009) · 38 citations

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04

Porous carbons and CO2 capture

5 papers

The newest direction turns residues into useful materials. Pine wood, carbon black recovered from scrap tyres and graphite from spent lithium-ion batteries are activated with potassium compounds into carbons full of sub-nanometre pores, which can capture CO2 selectively.

Why it matters: waste becomes a sorbent for carbon capture.

Next: perovskite-based redox materials for energy conversion and base chemicals (Swedish Research Council, 2026–2030).

Activated carbon capturing CO2 in sub-nanometre poresLeft: biomass or residue is heated with a potassium compound (KOH) to about 800 °C. Right: the resulting carbon particle, cut open to show branching pores; small CO2 molecules sit in the narrowest pores while N2 passes by. biomass or residue + KOH, 800 °C activation porous carbon: CO2 held in the narrowest pores
Schematic: activated carbon capturing CO2 in sub-nanometre pores. Left: biomass or residue is heated with a potassium compound (KOH) to about 800 °C.

Key findings

High-temperature corrosion and ash · Porous carbons and CO2 capture

Carbons from pine wood that capture CO2

Pine wood activated at 800 °C with KOH, K2C2O4 or mixtures of the two. Co-activation gave a surface area of 2029 m2/g; the KOH carbon reached the highest CO2 uptake (9.65 mmol/g at 0 °C), while the K2C2O4 carbon gave the best CO2/N2 selectivity. Molecular simulations link the performance to sub-nanometre pores and carbonyl-rich surfaces.

Chemical Engineering Journal (2025) · 62 citations

Related papers

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