Overview of surface studies on high energy materials at Mound

Since 1975 Mound has been examining the surface structure of high energy materials and the interaction of these materials with various metal containers. The high energy materials that have been studied include: the pyrotechnic TiH/sub x//KClO/sub 4/, the Al/Cu/sub 2/O machinable thermite, the PETN, HMX and RDX explosives, and two plastic bonded explosives (PBX). Aluminum and alloys of Fe, Ni and Cr have been used as the containment materials. Two aims in this research are: (1) the elucidation of the mechanism of pyrotechnic ignition and (2) the compatibility of high energy materials with their surroundings. New information has been generated by coupling Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) with thermal data. In particular, AES and XPS studies on the pyrotechnic materials and on thermites have shown the mechanism of ignition to be nearly independent of the type of oxidizer present but directly related to surface chemistry of the fuels. In studies on the two PBX's, PBX-9407 and LX-16, it was concluded that the Exon coating on 9407 was complete and greater than or equal to 100A; whereas in LX-16, the coating was < 100A or even incomplete. AES and scanning Auger have been used to characterize the surface composition and oxide thickness for an iron-nickel alloy and showed the thicker oxides to have the least propensity for atmospheric hydrocarbon adsorption. Data are presented and illustrations made which highlight this new approach to studying ignition and compatibility of high energy materials. Finally, the salient features of the X-SAM-800 purchased by Mound are discussed in light of future studies on high energy materials

Dissolution of surface oxide layers on titanium and titanium subhydride between 25/sup 0/ and 700/sup 0/C

The surface-sensitive, spectroscopic techniques of Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) have been applied to the study of oxide dissolution on titanium and titanium subhydride. In an earlier study it was shown, using AES, that the rate of oxygen dissolution into titanium increased sharply at about 350/sup 0/C. These data correlated well with physical property measurements that indicated that at these temperatures an exothermic reaction, corresponding to the reaction of free titanium with atmospheric oxygen, was occurring. In the present study the work has been expanded to include studies of TiH/sub x/ (x = 1.15, 1.62). It has been found that dissolution of the native oxide on titanium subhydride occurs at a substantially higher temperature (about 500/sup 0/C) than for titanium. It appears that the outward diffusion of hydrogen is inhibiting the inward diffusion of oxygen on the subhydride samples at temperatures below 500/sup 0/C. Further studies of the dissolution of oxides on titanium at fixed temperatures in the range of 300 to 350/sup 0/C have shown that there is a semi-logarithmic relationship between the surface oxygen level and the time at temperature. This is in agreement with earlier gravimetric studies on titanium oxidation in this temperature range

The Dissolution of Native Oxide Films on Titanium for Pyrotechnic Applications

The dissolution of native oxides on Ti were studied over the temperature range 25 degrees - 730 degrees C to determine their role in the pyrotechnic reaction of Ti with KCl0{sub}4. From AES data it was found that the solubility of the oxide in Ti increased sharply at 350 degrees C. High resolution AES scans of the Ti LMM transitions as well as XPS scans of the Ti 2 p level showed that free Ti is present at the surface above 350 degrees C. The O 1s XPS data shows that the surface contains hydroxyl as well as oxide groups. The hydroxide to oxide ratio begins to decrease below 250 degrees C, and at 450 degrees C the remaining oxygen is bound predominatly as oxide. Additionally, the XPS data shows that the dissoluton process proceeds through the formation of titanium suboxides. These AES and XPS results complement physical property measurements which have also been made on the Ti/KCl0{sub}4 mixture. These physical property measurements show that 1) below 300 degrees C no reaction occurs and 2) just above 300 degrees C an exothermic reaction occurs corresponding to the reaction of free Ti with atmospheric oxygen

Hemodynamic and recirculation performance of dual lumen cannulas for venovenous extracorporeal membrane oxygenation

Abstract Venovenous extracorporeal membrane oxygenation (ECMO) can be performed with two single lumen cannulas (SLCs) or one dual-lumen cannula (DLC) where low recirculation fraction ( $${R}_{f}$$ R f ) is a key performance criterion. DLCs are widely believed to have lower $${R}_{f}$$ R f , though these have not been directly compared. Similarly, correct positioning is considered critical although its impact is unclear. We aimed to compare two common bi-caval DLC designs and quantify $${\mathrm{R}}_{\mathrm{f}}$$ R f in several positions. Two different commercially available DLCs were sectioned, measured, reconstructed, scaled to 27Fr and simulated in our previously published patient-averaged computational model of the right atrium (RA) and venae cavae at 2–6 L/min. One DLC was then used to simulate ± 30° and ± 60° rotation and ± 4 cm insertion depth. Both designs had low $${R}_{f}$$ R f ( 413 Pa) and RA (> 52 Pa) even at low flow rates. Caval pressures were abnormally high (16.2–23.9 mmHg) at low flow rates. Rotation did not significantly impact $${R}_{f}$$ R f . Short insertion depth increased $${R}_{f}$$ R f (> 31%) for all flow rates whilst long insertion only increased $${R}_{f}$$ R f at 6 L/min (24%). Our results show that DLCs have lower $${R}_{f}$$ R f compared to SLCs at moderate-high flow rates (> 4 L/min), but high shear stresses. Obstruction from DLCs increases caval pressures at low flow rates, a potential reason for increased intracranial hemorrhages. Cannula rotation does not impact $${R}_{f}$$ R f though correct insertion depth is critical

Surface studies of plastic-bonded PETN and RDX by X-Ray Photoelectron Spectroscopy (XPS) and Ion-Scattering Spectroscopy (ISS)

Surface structures of plastic bonded PETN and RDX were studied by high resolution X-Ray Photoelectron Spectroscopy (XPS) and Ion Scattering Spectroscopy (ISS). The coating material is a copolymer of vinyl chloride and chlorotrifluoroethylene. Specimens with 6 wt % of the coating on RDX and 4 wt % on PETN were used in these studies. High resolution elemented XPS spectra of F 1s, N 1s, C 1s, and Cl 2p indicate that the surface of coated RDX (PBX-9407) is covered and the coating film is thicker than 100A; the results with coated PETN (LX-16) show the surface layer to be thinner than 100A. /sup 3/He/sup +/ ISS data on LX-16 suggest that the coating on PETN is not uniform and is, in fact, absent in some regions

Electrochemical Evaluation of the Compatibility of Fresh and Aged NovecTM 71IPA with Beryllium, Stainless Uranium, 304L Stainless Steel, and 2024-T3 Aluminum Alloy

This study was a material compatibility assessment of four metals (beryllium, stainless uranium, 304L stainless steel, and 2024-T3 aluminum) with an environmentally benign, non-aqueous, near-azeotropic mixture of hydrofluoroether (Novec™ 7100) with 4.5 wt% isopropanol designated Novec™ 71IPA. The intent is to use the Novec™ 71IPA to clean materials in sensitive, long-term assemblies. There is concern when an aged solvent is used to clean a metal surface, it may cause corrosion due to fluoride formation as the solvent ages. Two solvent conditions, one having no detectable fluoride (fresh) and the other with ≥17 ppm fluoride (aged) were evaluated. Electrochemical evaluations using impedance spectroscopy were performed to monitor the metal surfaces for signs of reaction. Microscopic and spectroscopic techniques, including X-ray photoelectron spectroscopy, were used to characterize the metal surfaces before and after electrochemical tests. Increased impedance was observed when beryllium substrates were exposed to fresh or aged Novec™ 71IPA and was attributed to formation of organic and/or inorganic films on native beryllium oxide. Other metals exhibited insignificant changes in impedance but did show some passive film formation. Results confirmed Novec™ 71IPA, containing up to 17 ppm fluoride, had no corrosive effect on the four tested metals and may be used to safely clean them