Palladium cermets

J Cf is encapsulated and shipped in eight standard Special Form capsules and packages to meet the needs of the different medical, industrial, and research applications used. The isotope is available as californium oxide, californium-palladium cermet wire or pellets, and, in the case of medical therapy sources, californium-palladium cermet sheathed in platinum-iridium alloy. Capsules are available in a variety of metals and alloys (Table 1, Figures 1 through 8). 

Brachytherapy Sources. The first 252cf sources for radiotherapy research were prepared at SRL about fourteen years ago (4 5). Initially, these sources resembled the classical radium needles familiar in clinical radiotherapy. Eventually, afterloading cells and applicator tubes were supplied to medical evaluators, and all medical sources were improved by the use of californium-palladium cermet wire sheathed in Pt - 10% Ir alloy (6, 7). The most recent designs for medical sources produced in quantity for therapy research are line sources and point sources containing a range of Cf from iess than 1 yg to 200 yg (Figures 9 and 10). 

Normal production requires Containment Boxes 1 and 2 to contain approximately 400 yg of 252cf as californium-palladium cermet. While operating in this mode, general area dose rates are about 1 mrem/h where personnel usually operate in front of the boxes. Dose rates behind the cells in normally unoccupied areas range from 4 to 6 mrem/h (3). 

Medical sources are fabricated with remotely operated, specially designed machines (8). The fabrication process involves production of Pt - 10% Ir-clad wire with a californium oxide-palladium cermet core. The wire is swaged and drawn to size, cut to length, and welded in a Pt - 10% Ir capsule. Nominally, medical sources contain from 0.3 yg 252cf in an individual seed (Figure 8) to 30 yg 252cf in an applicator tube (Figure 7). 

The term composite membrane, as defined in membrane technology, refers to membranes with two or more distinct layers. A layer within a composite membrane could itself be a composite material possessing two or more distinct components, as in membranes employing a layer of palladium cermet (ceramic-metal) supported by a layer of porous ceramic. The layers need not be composite, as in membranes using films of palladium on both sides of foils of niobium, tantalum, vanadium or zirconium. 

Palladium cermets have a number of advantages over thin films of Pd supported by porous ceramics. For systems which wet, sintering cermets at very high temperatures (well above membrane operating temperatures) produces dense, pinhole-free composites (see Fig. 8.5). Because Pd is closely confined within a matrix of ceramic and because small, individual, micron-size Pd crystallites already possess a small surface-to-volume ratio of low surface energy, the Pd has relatively low driving... 

These sources were prepared by a modified chemical plating technique similar to that used to prepare palladium-californium oxide cermet for industrial applications (6). Design of the... 

Mosley, W. C. Smith, P. K. McBeath, P. E. "Neutron Sources of Palladium-Californium-252 Oxide Cermet Wire," USERDA Report CONF-720902, Proceedings of the American Nuclear Society Topical Meeting, September 11-13, 1972, (1975),... 

For ill-designed composite membranes, for example, formed by depositing palladium onto substrates which it does not wet, surface tension will force the thin film to contract and ball up if the palladium atoms acquire sufficient surface mobility. Pinholes may form as a prelude to complete de-wetting, or pinholes may remain from the initial fabrication if the palladium did not fully wet its substrate. Kinetics of de-wetting is accelerated at elevated temperature and in the presence of adsorbates such as CO, which increase surface mobility of Pd. If molten metals do not wet ceramics, they will be expelled from ceramic pores. During sintering of cermets, Pd and other metals will not adhere to the ceramic phase, if the metal and ceramic do not wet. 

Fig. 8.5 Scanning Eiectron Microscope image of a perovskite-paliadium cermet (ceramic-mettii) made by sintering together LaFeo.wCro.ioOs-x and Pd powder to form dense continuous matrices of both metal and ceramic. The palladium and ceramic were lattice matched to minimize stiain and interfacial dislocations. (S. Rolfe, Eltron Research) (Copyright Elsevier, 2005. Adapted with permission from [11], Ctubon Dioxide Capture and Storage in Deep Geological Formations.)...

Okada S, Mineshige A, Kikuchi T, Kobune M, Yazawa T (2007) Cermet-type hydrogen separation membrane obtained from fine particles of high temperature proton-conductive oxide and palladium. Thin Solid Films 515 7342-7346... 

The resistance of a cermet film is determined by the metal-to-glass ratio. For example, the resistance of lead-borosilicate glass and either Ag or Au changes by five orders of magnitude with a few percent change in metal content (see Fig. 2.56), whereas either Pd or Pd -I-Ag glass mixtures are much less sensitive therefore, they are more easily reproduced on a production basis. The addition of silver to palladium improves the temperature coefficient of resistance and decreases the electrical noise and resistivity of the films (see Table 2.23). 

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