Oxygen filters

Wafers were prepared, sulfided and evacuated (2 h at 673 K) as described above. The temperature was then set at 423 K and 80 kPa of purified deuterium (Air Liquide, N28) was admitted into the cell. The purification procedure consisted of passing the gas through a moisture filter (Chrompack Gas Clean 7971), an oxygen filter (Chrompack Gas Clean 7970) and a liquid nitrogen trap. 

After normal operation for an extended period, the cooling system should be capable of holding 3 MS2 cm until the filter beds become contaminated and must be replaced. The need to replace the filter bed resins is indicated when the purification loop output water falls below 5 Mfi cm. Although the resistivity measurement is not a test for free oxygen in the coolant, the oxygen filter bed should always be replaced... 

If preferred, the reaction mixture may be cooled, and the crude furil filtered through a sintered gla.ss funnel. The filtrate (containing the copper sulphate-pyridine mixture) is re-oxidised by passing oxygen tlirough it for about 15 hours. An excellent alternative method of preparation is provided by suitable adaptation of Section IV,126, Method 2. 

Add 40 ml. of ethyl alcohol to 21 -5 g. of 70 per cent, ethylenediamine solution (0 -25 mol) dissolve 36 -5 g. of adipic acid (0 -25 mol) in 50 ml. of a 6 1 mixture of ethyl alcohol and water. Mix the two solutions, stir and cool. Filter off the resulting salt and recrystalliae it from 60 ml. of a 6 1 ethyl alcohol - water mixture, and dry the salt in the air. Heat the salt in an atmosphere of oxygen-free nitrogen or of carbon dioxide in an oil bath until it melts (ca. 160°) the product will sohdify after a short time. Reduce the pressure to 15 mm. of mercury or less and raise the temperature of the oil bath until the product remelts (about 290°) and continue the heating for 4r-5 hours. Upon coohng, a nylon type polymer is obtained. 

The purity of oxygen from chlorate candles before and after gas filtration is indicated in Table 2. A particulate filter is always used. Filter chemicals are HopcaUte, which oxidizes CO to CO2 molecular sieves (qv), which remove chlorine compounds and basic materials, eg, soda lime, which removes CO2 and chlorine compounds. Other than H2O and N2, impurity levels of <1 ppm can be attained. Moisture can be reduced by using a desiccant (see Desiccants). Gas purity is a function of candle packaging as well as composition. A hotter burning unit, eg, one in which steel wool is the binder, generates more impurities. 

Transparent yeUow pigment is composed of needle particles of EeO(OH) having a thickness of 2—5 nm, a width of 10—20 nm, and a length of 50—100 nm. They are prepared by the precipitation process from a very diluted solution of ferrous salt, eg, 6 wt % ferrous sulfate, foUowed by the oxidation of the precipitate with atmospheric oxygen at a temperature of less than 25°C. The precipitate is left to mature for about one day, then filtered, dried, and milled. 

The treatment units used for color removal are the same as those used for turbidity removal. However, the pH must be increased prior to filtration so that the metal hydroxides are removed by the filters. At low pH values, metal ions or their soluble complexes readily pass through the filters and form insoluble species in storage tanks and in the distribution system. For iron salts, it is important that the pH be greater than 6 as the oxidation of iron(II) to iron(III) occurs rapidly above this pH in the presence of dissolved oxygen or other strong oxidants (18). 

---