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Oxygen Sources for Space Flights

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Oxygen Sources for Space Flights Oxygen Sources for Space Flights ROBERT M. BOVARD, M.S. XYGEN IS combined in many extensively in high altitude flights and solid chemical forms, but only are currently attracting attention for O a few of these have the capa,c- a number 04 other applications. ity to readily release pure oxygen. One such group is composed of t,he alkali Demand Chemicds.--Potassium su- and alkaline earth peroxides, sup.er- peroxide (KO2) and sodium peroxide oxides and o,zonides. A second group (Na202) have been the most frequent- is composed of the chlorates and per- ly used demand chemicals. Sodium chlorates of the same metals. The for- superoxide has also been prepared in mer group releases oxygen upon reac- pilot plant quantities and tested for tion with water or cartoon dioxide and personal breathing apparatus applica- can be classified as demand chemicals. tions with results similar to KO2. That is, the supply of oxygen released Other heavier metal superoxides such can be made self-regulating by reac- as CaO4 have ,been prepared only in tion of water and carb.on dioxide in low purities; this compound wonld the expired breath. offer a slight advantage in amount of In the second class of compounds, oxygen released per unit weight. As oxygen is released either by direct the atomic weight of the metal in the heating or .by mixing with the oxygen- superoxide increases, the difficulty of containing chemicals, a substance vchieh formation usually increases. Efforts will ,be oxidized by part of the evo.lved are being made at several locations to oxygen and thus generate sufficient synthesize the heavier superoxides. heat to sustain the reaction. This type For purposes of this discussion, potas- of reaction is generally known as a sium superoxide will be taken as typi- controlled type since the rate of oxy- ca! and available. gen evolution depends on the compo.si- l'otassium su.peroxide is a canary tion, size, and shape, of the preformed yellow solid at room temperature, but chemical mixture. changes to. white v~hen cooled to liquid The combination o.f oxygen supply nitrogen temperature. It is mamffac- and carbon dioxide absorbent is unique tured by atomizing molten potassium to .the demand chemicals; the long into dry air, forming a yellow fluffy shelf life and high oxygen density o,f material which is later compacted and the controlled oxygen .sttp.plied is also crushed to. the desired particle size. deserving of consideration. Both During manufacture there is some ,con- classes .of compounds have been used tamination with KzCO:~ and KOH by reaction with CO2 and water vapor in From the MSA Research Corporation, Callery, Pennsylvania. the air: the product a.s packed in corn- MAY, 1960 407 OXYGEN SOURCES FOR SPACE FLIGHTS--BOVARD mercial canisters contains less than 2 Significant differences have been per cent total of the two contaminates. noted in using KO2 in a personal can- "['he oxygen producing characteristics ister (Chemox) where a single tem- are not significantly affected by these perature 'front traverses the KO2 bed, while a series of fronts was noted in a TABLE I. dosed cycle forced circulating system. Potassium Superoxide (KO~) Reactions Primary differences in canister inputs was the higher, pulsing CO 2 concen- J 1. 2KOa+H20 ] 2KOH+3/2 02+9.4 Kcal . 2KO~+CO~ [ K~C03+3/2 0s+43.1 Kcal tration and high temperature in one 54~ 2KOH+COt i K~COs+H~O+33.7 Kcal KOH+CO2 I KHCOa+33.1 Kcal case as opposed to a low continuous ~i KOH+3/4 H~O [ KOH 3/4 tI20+16.57 Kcal KOH+H~O J KOH * H20+20,0 Keal CO2 concentration in the other. T'he KOI-I+2Hz0 i KOH * 2H~O+33.8 Kcal 91 K~GOa+I/2 H~O ] K~COs* 1/2 H~O+7.6 Kcal personal KO2 ,canister also retained a 1K~CO,+3/2 H~O I K2CO3,3/2I-I~O+22.77 Keal 10. K2COs+H20+COt J 2KHCO3+33.8 Kcal smaller amount of water than in the J circulating system. Utilization of avail- Sodium Chlorate (NaClOs) Reactions able oxygen was greater in the circu- lating system, up to, 99.8 per cent 11. 2NaC10~ 2NaCl+3Ot+25.02 Keel 12. 2Fo+O~ [ 2Fe O-1-127.4 Kcal being used in a 12 per man-hour test 13. 2NaCIO3 j Na20+ChTh/202--72.06Kcal 14. BaOs+Ch I BaCh+02%53 Kcal [ in a 210 cu. ft. compartment with con- trol,led humidity. impurities and the guaranteed avail- Recent experiments at Mine Safety able oxygen is 32 + per cent by weight, Appliances Research Corporation have giving an oxygen evolution of 224 co. shown that COs does not react readily per grn. of KO2. Density of the with completely dry KO2; however, a granules controls the reaction rates trace of moisture initially present in and abrasion resistance. Bulk density the canister or on the KO2 can suffice of 2-4 mesh material is 41 lb./cu, ft. to sustain reaction for a much longer Reactions of KO2 with water and time than would be suspected if the cxvbon dioxide, which are readily un- moisture were to produce KOH, which derstood, are shown in Table I. What in turn would react with 'CO2. This actually occurs in a KO2 bed is some- also attests to the complexity of equili- wahat more complicated, with two points bria within a KO~ .'bed. Examination being immediately evident: 1. Water by x-ray has shown that some bicarb- is absorbed without oxygen evolution. onates are formed. If conditions could 2. Measured heat releases are not as be controlled so that bicarbonates were high as may be suggested by some of preferentially formed the CO2 absorp- the reactions. The first of these is ex- tion would be considerably enhanced plained on the basis of hydrate forma- with no penalty on oxygen evolution tion as .per equations 5, 6, 7, 8 and 9, Approximately equal volumes of KO2 a happy circumstance which aids in and LiOH would remove the same preventing over-production o.f oxygen. quantity of C02, while the KO2 would Since the balance between carbonate, also st~pply excess oxygen to meet the bicarbonate and hydrate formation is met,zbolic requirements. unknown the heat balance cannot be Odoriferous compounds are removed calculated. by a KO2 bed, as can be attested by 408 AEa0SPACE MEDICINE OXYGEN SOURCES FOR SPACE FLIGHTS--BOVARD anyone w'ho has used a Chemox breath- furnish oxygen for the metabolic re- ing apparatus or participated in manned quirements of a man for approxi- chamber tests. mately fifteen minutes. Ignition can be performed at a spot enriched with Controlled Oxygen Supply. -- The iron, using a modified percussion cap, sodium chlorate oxygen candle will be phosphorous match or electric squib. considered representative of the con- There is no disintegration during burn- trolled supply chemicals. 5,~ It is corn- ing. Shelf life appears to be unlimited posed of sodium chlorate, an inorganic since candles 'have been stored indoors binder, a source of heat, usually iron for fifteen years without any protec- powder; and barium peroxide, which tive covering and without undergoing combines with any free chlorine that any noticeable change. may be formed. The principal .equa- APPLICATIONS tions are .shown in Table I. The barium peroxide acts as a heat source as well Demand Chemicals.--Potassium su- as the iron; therefore, the two must peroxide has been used in self-con- be balanced to produce the desired mined breathing apparatus for over burning rate. Hydrogen reduced iron fi'fteen years. This apparatus was de- is generally used 'because a very active veloped during Wo.r,ld War !II by form is required. These materials may Mine Safety Appliances Company .for eitJher be mixed with water, pressed personnel protection on naval vessels. into a mold and dried, or the sodium It is now being used by several of the chlorate can be melted, the other ma- services, industrial companies, fire teriNs thoroughly dispersed and the companies, and in mining operations. resultant st~spension cast into a mold. Many thousands o.f canisters employed The cast candle has a density of 2.4 in this breathing apparatu,s have been and contains approximately 40 per cent manufactured and success'fully used. oxygen by weight. The pressed candle The canisters have even been used on is less expensive, but until recently it several mountain climbing expeditions. did not have the same oxygen produc- In a series of recently conducted tests ing capacity as the cast candles. How- at Mine Safety App.liances Research ever, improvements in manufacture Corporation, 1,2 it was found that a have raised the oxygen content to C.hemox canister could be used to con- wit~hin several per cent o.f that of the trol a closed chamber atmosphere. The cast candle. The rate of oxygen evolu- metabolic requirements of two men tion is directly proportional to the were satisfactorily fulfilled for six burning area, and the duration of evo- hours by one canister containing ap- lution is proportional .to the length of proximately 850 grams KO2. The can- the .candle. The candles may ,be .fo.rmed ister supplied the oxygen, removed the in various shapes to give any desired carbon dioxide and a portion of the oxygen evolution ,pattern. As an illus- water vapor. It is possible to produce tration of the oxygen storage capacity oxygen with KOz by reacting it with of chlorate candles, it can be noted that water. An apparatus called an Oxygen a candle the size of a cigar would Generator was used during World MAY, 1960 409 OXYGEN SOURCES FOR SPACE FLIGHTS--BOVARD War II to supply welding oxygen by decreasing flow.
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