Gettering, oxygen

NaK (contamination control) An alloy of sodium (20-50%) and potassium that is liquid at room temperature and is used to getter oxygen and moisture in an inert gas dry box. 

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. 

Hafnium is used in gas-filled and incandescent lamps, and is an efficient getter for scavenging oxygen and nitrogen. 

Orlov et al. [607] investigated the process of tantalum powder deoxidation using both calcium and magnesium chips as oxygen getters. It is recommended to perform the process with calcium chips at temperature of 900-1300°C for... 

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. 

A more comprehensive purification procedure uses a sequence of steps as follows filtration at 200°C through a stainless steel powder compact filter of 10-jum pore size reduces the oxygen content and removes any solid impurities. Gettering with Zr foil for 46 h at 760°C reduces the oxygen concentration to 200 ppm. The weight ratio of K to Zr is 13 1 with a surface area to volume ratio of Zr to K 4 1. A second gettering with zirconium foil for 72 h at 800°C reduces the oxygen content 50 ppm. 

In the lean-burn stage all exhaust components are oxidized by the platinum particles in the catalyst. In particular, NO is oxidized to NO2. The latter reacts with BaO getter to form Ba(N03)2- In the rich mode, which only lasts for seconds, the exhaust stream is deficient in oxygen, and reducing components such as CO, H2 and hydro-... 

Rubidium metal and its salts bave very few commercial apphcations. They are used in research involving magnetohydrodynamics and thermoionic experiments. Rubidium is used in pbotocells. The metal also is a getter of oxygen in vacuum tubes. The beta-emitter rubidium -87 is used to determine age of some rocks and minerals. Radioisotopes of rubidium have been used as radioactive tracers to trace the flow of blood in the body. The iodide salt treats goiters. Rubidium salts are in pharmaceuticals as soporifics, sedatives, and for treating epilepsy. 

---