NETL Researcher Sheds Light on Chemistry of Hydrogen Sulfide Dissociation on Surfaces

	NETL scientist Dominic Alfonso examines the structure of hydrogen sulfide on a metal surface calculated by density functional theory.

NETL researcher Dominic Alfonso has probed the chemistry of hydrogen sulfide (H₂S) dissociation process on the surfaces of a number of important noble metals and transition metals using density functional theory (DFT) calculations.

The study was done to improve the understanding of the behavior of H₂S (a typical contaminant in fossil fuels) on metals. It gave new insights to questions that had eluded experimentalists. The new information may be helpful in the design of materials with improved sulfur tolerance.

DFT is an efficient method for calculating the average number of electrons at any point in space. Using this information, Alfonso was able to calculate many important properties of metals. To study the behavior of H₂S on the metals, Alfonso combined DFT with concepts from transition state theory. DFT is a computer-based approach and Alfonso used NETL’s parallel computer platforms in his work.

Questions addressed include what are the energy barriers and where are the corresponding sulfur and hydrogen atoms of the H₂S molecule adsorbed as it dissociates on these metals.

The new insights will also help scientists understand past experiments.

The results have been published in a recent edition of Surface Science.

Researchers Observe Flows Through Porous Media

	Dustin Crandall, a postdoc at NETL; Duane Smith, an NETL researcher, and Goodarz Ahmadi, dean of Engineering at Clarkson University, study a stereo- lithography flow cell used by researchers for direct observation of flow mechanisms that are important to geological sequestration or oil production.

NETL researchers have utilized optical imaging of flows through transparent, artificial media for direct observation of flow mechanisms that are important to geological sequestration or oil production.

The flow of two fluids (for example, gas and water or gas and oil) through porous rocks is the fundamental mechanism by which the greenhouse gas carbon dioxide is sequestered geologically, or oil is produced from deep underground. 

Researchers at NETL have been studying these flow phenomena by carefully combining experimental and modeling methodologies. The findings potentially have broad applications that can be incorporated into models; for instance, even snow avalanches follow the patterns identified in the NETL experiments.

In the NETL experiments, researchers caused gas to displace water by irregular bursts of motion, suddenly invading small portions of the medium that has a strong affinity for water.

These periods of activity, followed by dormancy, are similar to systems where a slight disturbance may induce an avalanche of activity.

While the apparent relationship between self-organized criticality and invading mass-bursts has been investigated with numerical simulations, very few experimental studies have examined this phenomenon.

A presentation that describes this work, “Experimental Examination of Localized-Bursts of Fluid Advancement during Immiscible Drainage in Porous Media,” was prepared by Dustin Crandall, Martin Ferer, and Duane H. Smith, and presented at the 2008 American Geophysical Union Fall Meeting in San Francisco.

NETL Wet Spray Bond Coat System Demonstrates Enhanced Performance

Tests of a potentially lower cost, modified wet spray bond coat system being developed by NETL researcher Mary Anne Alvin show comparable life cycle and enhanced performance compared to commercially available coating systems.

Alvin has been developing the system with commercial supplier Coatings for Industry (CFI) for application along the surface of nickel-based superalloy and single crystal structural materials.

In high temperature applications – such as future hydrogen-fired and oxy-fuel land-based gas turbines – the requirement of the bond coat is to provide oxidation resistance to the underlying substrate metal, as well as to serve as an interface layer between the base metal substrate and the additionally applied thermal insulating yttria stabilized zirconia (YSZ) top coat, and overcoat layers. 

Alvin’s research using the wet spray bond coat thermal barrier system has demonstrated comparable cycle-life-to-failure at 1100ºC during laboratory bench-scale testing at the University of Pittsburgh, to coatings manufactured with a commercially applied bond coat architecture. 

Testing has also shown enhanced performance of the wet spray bond coat system with an applied electron beam physical vapor deposited YSZ in comparison to a commercially applied architecture.