Getter metals

Chemical Properties. In the uses of chemical properties the high affinity of the rare earth metals for os gen is primarily involved. This leads to their application as flints, vdierein their highly exothermic reaction with os gen in air is used. On the same properties rests their application as getter metals, vherein residual os gen, as for exanple in amplifier tubes, is bound up. 

A method of repurifying helium by adsorbing impurities into "getter metals" at high temperatures is being used by at least one industry [7]. This method has been extended to determining trace impurities in Grade-A helium [8]. 

The authors (Radhakrishnan et al. 2012) present also the SIMS depth profiling revealing large metal concentrations (10 - 10 at/cm ) in the depth associated with PSi, while the metal concentrations were below detection limits in the surrounding area (10 - 10 at/cm ), suggesting a gettering coefficient (defined as the ratio between the concentration of gettered metal, and the... 

Extended defects range from well characterized dislocations to grain boundaries, interfaces, stacking faults, etch pits, D-defects, misfit dislocations (common in epitaxial growth), blisters induced by H or He implantation etc. Microscopic studies of such defects are very difficult, and crystal growers use years of experience and trial-and-error teclmiques to avoid or control them. Some extended defects can change in unpredictable ways upon heat treatments. Others become gettering centres for transition metals, a phenomenon which can be desirable or not, but is always difficult to control. Extended defects are sometimes cleverly used. For example, the smart-cut process relies on the controlled implantation of H followed by heat treatments to create blisters. This allows a thin layer of clean material to be lifted from a bulk wafer [261. 

Gettering is a black art. It consists in forcing selected impurities (typically, transition metals) to diffuse toward unimportant regions of tlie device. This is often done by creating precipitation sites and perfoniiing heat treatments. The precipitation sites range from small oxygen complexes to layers such as an A1 silicide. The foniiation of such a... 

Because of it has great affinity for oxygen, the metal is used as a "getter" in electron tubes. It is also used in photoelectric cells, as well as a catalyst in the hydrogenation of certain organic compounds. 

Titanium hydride is used as a source for Ti powder, alloys, and coatings as a getter in vacuum systems and electronic tubes as a sealer of metals and as a hydrogen source. 

Barium is prepared commercially by the thermal reduction of barium oxide with aluminum. Barium metal is highly reactive, a property which accounts for its principal uses as a getter for removing residual gases from vacuum systems and as a deoxidiser for steel and other metals. 

Cesium was first produced ia the metallic state by electrolysis of a molten mixture of cesium and barium cyanides (2). Subsequentiy the more common thermochemical—reduction techniques were developed (3,4). There were essentially no iadustrial uses for cesium until 1926, when it was used for a few years as a getter and as an effective agent ia reduciag the electron work function on coated tungsten filaments ia radio tubes. Development of photoelectric cells a few years later resulted ia a small but steady consumption of cesium and other appHcations for cesium ia photosensing elements followed. 

Metallic Sr and Ba are best prepared by high-temperature reduction of their oxides with Al in an evacuated retort or by small-scale electrolysis of fused chloride baths. They have limited use as getters, and a Ni-Ba alloy is used for sparkplug wire because of its high emissivity. Annual production of Ba metal is about 20-30 tonnes worldwide and the 1991 price about 80-140/kg depending on quality. 

Rare earth metals, as well as alkali earth metals, can be used as oxygen getters in the purification of tantalum powder. Osaku and Komukai [608] developed a method for the production of tantalum and niobium metal powder by a two-step reduction of their oxides. The second step was aimed at reducing the oxygen content and was performed by thermal treatment with the addition of rare metals. The powder obtained by the described method is uniform, had a low oxygen level and was suitable for application in the manufacturing of tantalum capacitors. 

Many of the techniques available to purify alkali metals were initially developed to use with liquid sodium as a consequence of its large-scale application in liquid-metal-cooled fast-breeder reactors. These techniques can be summarized as filtration or cold trapping distillation or chemical (gettering). 

Neither Ca, Sr nor Ba metal has any structural integrity. The principal application of metallic Ca is as a reducing agent in the preparation of metals, such as Th and Zr. Like Mg, it can be used in the deoxidation and desulfurization of steels. Small quantities are used for alloying with Al and for the removal of Bi from Pb. Neither Sr nor Ba have any significant commercial uses. Barium is used to a limited extent as a getter to remove reactive gases from vacuum tubes. 

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