A Combined Thermodynamic/Kinetic Modeling Approach to Predict SiC Recession Due to SiO2 Scale Volatility Under Combustion Environments

Significance Statement

Adjusting materials chemistry and processing conditions have been a common practice of materials scientists/engineers in the design of new materials and the improvement of the existing materials. Traditional approaches relying on trial-and-error are no longer viable due to limited resources. Integrated Computational Materials Engineering (ICME), which integrates materials information obtained from computational tools with engineering product performance analysis, has recently been highlighted as a methodology that can unlock great potential for significant benefits in cost-effective materials and process design.

 

Phase diagrams are road maps of materials scientists/engineers in understanding the effect of chemistry on the microstructure of an alloy. Although determination of phase diagrams purely by experiments is feasible and necessary for binaries and simple ternaries, it is not realistic for multi-component systems. Yet, most if not all of the commercial alloys are multicomponent in nature. The CALPHAD approach, which was emerged in the late 1950s primarily aimed at calculating phase equilibria and thermodynamic properties of complex multi-component, multi-phase systems, has in recent years been applied to a broader field of materials science and engineering beyond phase diagrams, such as solidification, coating, joining, and phase transformation. Simulation tools developed by the CALPHAD method have become available and are currently being used by ICME practitioners on a daily basis.

 

CompuTherm, LLC has been developing CALPHAD type of simulation tools since 1996. These modeling tools include PandatTM software and thermodynamic/mobility databases for variety of metal alloys and oxides. PandatTM software is designed as a workspace which allows the calculation engine, PanEngine, be connected with variety of simulation modules. Currently PandatTM software includes four modules: (1) PanPhaseDiagram for multi-component phase diagram calculation, (2) PanOptimizer for model parameter optimization, (3) PanPrecipitation for precipitation simulation, and (4) PanDiffusion for diffusion simulation. The current design allows easy extension of PandatTM software to include other modules for performing variety of simulations as shown in Figure 1.

 

Our paper, which is entitled “A Combined Thermodynamic/Kinetic Modeling Approach to Predict SiC Recession due to SiO2 Scale Volatility under Combustion Environments”, shows one example of using the CALPHAD type of modeling tool in aiding the design of enviromental barrier coatings (EBCs). In this work, thermodynamic calculation was integrated with a gaseous-diffusion model to calculate the fluxes of volatile species produced by the reaction of SiO2 scale with the combustion air and the resulted weight loss of SiC under variety of combustion environments. EBCs that may help prevent the SiC loss can be identified from such calculations.

Our paper, which is entitled “A Combined Thermodynamic/Kinetic Modeling Approach to Predict SiC Recession due to SiO2 Scale Volatility under Combustion Environments”, shows one example of using the CALPHAD type of modeling tool in aiding the design of enviromental barrier coatings (EBCs). In this work, thermodynamic calculation was integrated with a gaseous-diffusion model to calculate the fluxes of volatile species produced by the reaction of SiO2 scale with the combustion air and the resulted weight loss of SiC under variety of combustion environments. EBCs that may help prevent the SiC loss can be identified from such calculations.

 

Figure : Applications through the integration with PanEngine API.

 

Zhang et al

 

 

 

 

 

 

Journal Reference

Journal of Phase Equilibria and Diffusion, September 2014.

F. Zhang, C. Zhang, S.-L. Chen, W.-S. Cao, J. Zhu.

CompuTherm LLC, Madison, WI, 53719, USA.

 

Abstract

A computational approach, which targets on the prediction of SiC recession caused by SiO2 scale volatility under combustion environments, was developed in this study. In this approach, thermodynamic calculation was integrated with a gaseous-diffusion model to calculate the fluxes of volatile species, such as SiO(g), Si(OH)4(g), SiO(OH)2(g), and SiO(OH)(g), produced by the reaction of SiO2 scale with the combustion air. The resulted weight loss of SiC was then calculated under a variety of combustion environments. The benefit of using environmental barrier coating (EBC) in the protection of SiC from recession was demonstrated by the calculation. It is shown that the weight loss of SiC-based ceramics could be significantly reduced when EBCs, such as mullite (Al6Si2O13or written as 3Al2O3·2SiO2) or SrAS2 (SrO·Al2O3·2SiO2), are used. The effects of combustion conditions, such as temperature and total pressure, on the volatility of SiO2 scale were also discussed.

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