Microwave-sintered tools are known to have much better material properties than conventional temperature/pressure-sintered tools. NETL is interested in microwave processing for producing improved drillbits and other drilling components. The origin of the differences between microwave and conventional processing is not known to a satisfactory degree.

National Energy Technology Laboratory
Pittsburgh, PA

Pennsylvania State University
State College, PA

Recent developments in the use of microwave processing of materials to produce long-lived drillbits have underscored the need to better understand the interaction of high-frequency electromagnetic radiation with condensed matter. Computational modeling will help explain these events that are not readily determined experimentally and assist in directing future improvements.

Results 
NETL has carried out extensive calculations of the tungsten surface, especially relative to adsorption, diffusion, and reaction to dopants on the w(iii) surface. Errors have been identified in the previous calculations performed and published by other groups. First-principles density functionality theory has been used to compute the structural and energetic properties of the tungsten cobalt (WC/Co) interfacial systems. Work continues on modeling the atomic-level details of microwave sintering of WC/Co parts.

Benefits 
Industry would benefit by having metal components that are cheaper, more durable, and easily manufactured. In addition to more-durable metals and drillbits in the oil and gas industry, there is significant application potential in mining and materials.

Summary 
Experimental and empirical investigations are being performed at Pennsylvania State University. Complementary modeling is being done at NETL to provide a complete description of microwave processing.

Project highlights including the following: • Modeling the diffusion of vacancy defects within bulk Co. • Identifying diffusion energies and path-ways for single and multiple vacancy defects. • Computing the energetic and structural properties of W impurities within bulk Co. • Computing the diffusion mechanism for W diffusion in defective Co.

(July 2006) 
NETL researchers have studied microwave interactions with metal oxides using semi-empirical model potentials as a preliminary step to studying metals, alloys, and ceramics in a microwave field. Also, ab initio density functional theory calculations have been carried out on the Co/W/C system, in parallel with the microwave interactions work using semi-empirical potentials and classical simulation techniques.

Efforts over the past several months have been devoted to understanding vacancy mediated diffusion mechanisms in bulk Co. NETL has studied the fcc phase of bulk Co as that is the phase that is germane to both conventional and microwave sintered materials. The fcc structure of Co is stable above a temperature of 695K and only at temperatures greater than this is diffusion of interest. Several different diffusion pathways for vacancy mediated diffusion in Co have been identified.

Funding 
This project was selected through the NETL In-House Research Program.

$1,066,000

NETL – Sue Mehlhoff (sue.mehlhoff@netl.doe.gov or 918-699-2044)
NETL – Dan Sorescu (dan.sorescu@netl.doe.gov or 412-386-4827)