ORNL Research Research Articles

3D-printed defect-free tungsten components

ORNL researchers develop an electron-beam 3D-printer to deposit tungsten, layer by layer.

Tackling residual stress in large-scale additive manufacturing

ORNL researchers find that adding material in critical regions mitigates the accumulation of stress.

3D printing large metal steam turbine blades

ORNL researchers use wire arc additive manufacturing to produce large rotating components for the first time.

New inspection method for powder bed printing

ORNL researchers combine inspection of the printed part after it is built with information collected during the printing process.

High-Resolution Mapping of the PFSA Polymer Distribution in PEFC Electrode Layers

Perfluorosulfonic acid (PFSA) ionomer is a key component within the electrode layers of polymer electrolyte fuel cells (PEFCs) since this solid electrolyte provides an efficient proton transport path to the active catalyst sites. Both the average loading on a 100-nm scale as well as the actual film thickness distribution on a 1-nm scale of the PFSA ionomer in the porous layer structure are critical to electrode performance so quantitative measurements of both properties are highly desired.Scanning transmission electron microscopy (STEM) is one useful tool to map this PFSA distribution in the electrode layer [1]. However, it has long been recognized that fluorinated compounds are sensitive to electron beam radiation damage [2,3]. By maintaining an electron dose below 1x104 e-/nm2 at 100-nm lateral resolution and cooling the specimen below -100ºC, the total fluorine mass loss for Nafion® ionomer is held below 10% a/a whereby the electron beam damage threshold for a typical Pt/C electrode layer is improved by 2-3 orders-of-magnitude at this sample temperature. Atomic force microscopy (AFM) [4] is a complementary tool suitable to map the Nafion® coverage on a 1-nm length scale on the electrode surface. The adhesion of the AFM tip to Nafion® in air was measured to be very low as the fluorocarbon backbone was preferentially exposed at polymer-air interface. In this paper, we present ionomer mapping measurements of two common PEFC electrode constructions. Figure 1 shows Pt/C/Nafion® layers at 8 μm dry thickness that are coated from the same electrode ink onto either a decal substrate (CCD) or directly onto the gas diffusion media. The other electrode layer comprises a PtCoMn nanostructured thin film (NSTF) electrode [5] that is overcoated with Nafion® ionomer using a preferred adsorption scheme to a targeted 2.0 nm dry thickness. Figure 2 shows that a significantly different through-layer ionomer/carbon (I/C w/w) profile is measured by energy-dispersive X-ray spectroscopy (EDS) for the CCD and CCDM electrode layers that can be ascribed to partial permeation of the electrode ink solution into the porous gas diffusion media substrate. In addition, the AFM adhesion measurement in Figure 3 shows a linear increase in ionomer coverage on the NSTF electrode surface to the adsorption limit (at 2 nm dry thickness). ORNL Research sponsored by (1) the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and (2) the Shared Research Equipment (ShaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.

Environmental Tobacco Smoke: Incomplete Research or Author Bias?

Environmental Tobacco Smoke: Incomplete Research or Author Bias?

Clinical Bone Marrow Scanning with Radioisotopes

Abstract Thirty-two series of bone marrow scans were performed on 29 patients. The scans were made with three colloid preparations, the most satisfactory of which has been colloidal Au198. Distinct pictures exhibiting the distribution of hematopoietic marrow have been obtained with the ORNL Research Scanner. Local lesions within the marrow organ has been demonstrated and confirmed by histologic studies. Variations in the size and distribution of the marrow organ have been shown in a graphic fashion which have hitherto been impossible. The doses of Au198 required, although rather large, do not produce any detectable early radiation effects. The possibility of harmful effects years after administration limits the present method to selected patients. Bone marrow scanning using the procedure reported here can be of considerable assistance to the investigator, and with improvements anticipated in the technic, it may find its place as a practical clinical procedure.