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Chemical oxygen generator

From Wikipedia, the free encyclopedia

A chemical oxygen generator is a device that releases oxygen via a chemical reaction. The oxygen source is usually an inorganic superoxide,[1] chlorate, or perchlorate; ozonides are a promising group of oxygen sources. The generators are usually ignited by a firing pin, and the chemical reaction is usually exothermic, making the generator a potential fire hazard. Potassium superoxide was used as an oxygen source on early manned missions of the Soviet space program, for firefighters, and for mine rescue.

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Transcription

Hello I am Jared welcome to Fun Science Demos. Through science we have discovered that when certain substances are combined a chemical change happens and with that chemical change a new substance can be formed. Today we have two things we are going to mix together are yeast and peroxide and when we mix yeast and peroxide we are going to create a chemical change and we want to take a closer look at that new substance that is formed in that chemical change. Now this chemical change is going to happen so quickly we have to keep the yeast and the peroxide separated so that we have enough time to capture that new substance that is formed to do that I am going to pour some yeast into this balloon I put the balloon on the end of the funnel we are going to dump some yeast and fill the balloon up from the jar into the funnel. Going to just feel the balloon to make sure it is filled with yeast and yep pull the balloon off now I need to get some peroxide into the bottle. Put the safety glasses on and get the peroxide into the bottle. I will fill the bottle up about half way. We have zoomed in so you can see the yeast mix with the peroxide here we go. I am dumping the yeast into the peroxide now I am going to shake it up and you can see the balloon is already starting to fill up it is capturing this new substance that is being formed when the yeast mixes with the peroxide. Let us shake it up really mix it together and watch our balloon capture that new substance. So now I have a balloon that is filled with this new substance that was formed and we want to take a closer look at what that new substance really is. To take a closer look at this new substance that was formed we have a different setup. We have three glass jars in this jar I filled it with yeast I put a little foil cap on the top punch some holes in the foil and set a candle on and now I have this nice glass globe that is going to keep that flame from being blown out by me this jar I have filled with peroxide same thing little foil cap with holes punched in a little candle and a glass globe to take a closer look at what is being formed in this jar we are going to mix the yeast and peroxide we are going to light the candle and set it on top and put another glass globe and we are going to see what happens to these flames we are going to compare them and see what is different or is there going to be anything that's different it will help us decide what is this new substance that is being formed by watching what happens to these candle flames so now I am going to add some peroxide to this yeast that is in the jar put the candle on and then we are going to turn the lights off so you can really get a good look at the candle flames. Here we go! So we want to watch this middle candle flame to see if it changes if there is anything different about this middle candle flame compared to these two side candle flames. Remember just yeast in this one side jar. Just peroxide in this side jar and what you should begin to see happening is that this middle flame is all of a sudden getting brighter. A lot brighter than these two side flames! Well that is because flames need something to burn flames need oxygen to burn and with more oxygen flames burn brighter and this little flame It does not look like it is getting bigger but it sure is getting brighter That is because the chemical change that is happening when I mix yeast and peroxide is forming oxygen so if you are watching that middle flame carefully. They got a lot brighter than the two side flames. That is because of the new substance being formed is oxygen. We are going to do another little demonstration. to see if we can look at the oxygen that was formed in this balloon. To do that I have a little candle burning and I am going to blow this balloon up with my own air in my lungs It is about the same size as the balloon we filled up with oxygen except I did not fill this up with oxygen. Watch what happens when I let the air out inside this balloon toward the candle. What do you think is going to happen! The lights go out Now we are going to try that again but I am going to use the oxygen inside the balloon that captured our chemical change I have my balloon so what do you think is going to happen when I hit this candle with the oxygen that is in this balloon. Well let us see I am going to put a cup over the candle to make sure that it captures all the oxygen. Here we go three two one. That was absolutely amazing the candle did not get blown out by the air in this balloon because the air in this balloon was oxygen and this candle needs oxygen to burn so if I gave it more oxygen the candle burned brighter. Now remember that chemical changes are happening around us all the time we just might not think about it or see it or notice it chemical changes are even happening inside of our body. Remember here we created oxygen Well candles need oxygen to burn what do we need in order to live we need oxygen. When we breathe in we breathe in oxygen from the air but through science we have discovered when we breathe out we are not breathing out oxygen. We are breathing out carbon dioxide. Well where did that carbon dioxide come from It came from a chemical change that is happening inside of our bodies. Science is so cool! If you want to learn more about chemical changes or physical changes check out our links in the video description. Thanks for watching!

Contents

In commercial airliners

Diagram of a chemical oxygen generator system
Diagram of a chemical oxygen generator system
Chemical Oxygen Generator, Cut-away View
Chemical Oxygen Generator, Cut-away View

Commercial aircraft provide emergency oxygen to passengers to protect them from drops in cabin pressure. Chemical oxygen generators are not used for the cockpit crew, who are typically supplied using compressed oxygen canisters also known as oxygen bottles. In narrow body airliners, for each row of seats there are overhead oxygen masks and oxygen generators. In some wide-body airliners, such as the DC-10 and IL-96, the canisters and oxygen masks are mounted in the top portion of the seat backs, since the ceiling is too high above the passengers. If a decompression occurs, the panels are opened either by an automatic pressure switch or by a manual switch, and the masks are released. When the passengers pull down on the mask they remove the retaining pins and trigger the production of oxygen.

The oxidizer core is sodium chlorate (NaClO3), which is mixed with less than 5 percent barium peroxide (BaO2) and less than 1 percent potassium perchlorate (KClO4). The explosives in the percussion cap are a lead styphnate and tetrazene explosive mixture. The chemical reaction is exothermic and the exterior temperature of the canister will reach 260 °C (500 °F). It will produce oxygen for 12 to 22 minutes.[2][3] The two-mask generator is approximately 63 mm (2.5 in) in diameter and 223 mm (8.8 in) long. The three-mask generator is approximately 70 mm (2.8 in) in diameter and 250 mm (9.8 in) long.

Accidental activation of improperly shipped expired generators caused the ValuJet Flight 592 crash, killing all on board. An ATA DC-10, Flight 131, was also destroyed while parked at O'Hare Airport, on August 10, 1986. The cause was the accidental activation of an oxygen canister, contained in the back of a broken DC-10 seat, being shipped in the cargo compartment to a repair station. There were no fatalities or injuries because the plane contained no passengers when the fire broke out.[4]

Oxygen candle

A chlorate candle, or an oxygen candle, is a cylindrical chemical oxygen generator that contains a mix of sodium chlorate and iron powder, which when ignited smolders at about 600 °C (1,112 °F), producing sodium chloride, iron oxide, and at a fixed rate about 6.5 man-hours of oxygen per kilogram of the mixture. The mixture has an indefinite shelf life if stored properly: candles have been stored for 20 years without decreased oxygen output. Thermal decomposition releases the oxygen. The burning iron supplies the heat. The candle must be wrapped in thermal insulation to maintain the reaction temperature and to protect surrounding equipment. The key reaction is:[5]

2 NaClO3 → 2 NaCl + 3 O2

Potassium and lithium chlorate, and sodium, potassium and lithium perchlorates can also be used in oxygen candles.

An explosion caused by one of these candles killed two Royal Navy sailors on HMS Tireless (S88), a nuclear-powered submarine, under the Arctic on 21 March 2007.[6] The candle had become contaminated with hydraulic oil, which caused the mixture to explode rather than burn.[7]

In the Vika oxygen generator used on some spacecraft, lithium perchlorate is the source of oxygen. At 400 °C, it releases 60% of its weight as oxygen:[8]

LiClO4 → LiCl + 2 O2

Pressure swing adsorption (PSA) oxygen generators

Advances in technology have provided industrial oxygen generator systems for use where air is available and a higher concentration of oxygen is desired. Pressure swing adsorption (PSA) incorporates a material called molecular sieve for gas separation. In the case of oxygen generation a zeolite-based sieve forces preferential adsorption for nitrogen. Clean, dry air is passed through the sieve beds on the oxygen generator, producing an oxygen-enriched gas. Nitrogen separation membrane equipment is also used.

Uses

Chemical oxygen generators are used in aircraft, breathing apparatus for firefighters and mine rescue crews, submarines, and everywhere a compact emergency oxygen generator with long shelf life is needed. They usually contain a device for absorption of carbon dioxide, sometimes a filter filled with lithium hydroxide; a kilogram of LiOH absorbs about half a kilogram of CO2.

See also

References

  1. ^ Hayyan M., Hashim M.A., AlNashef I.M., Superoxide Ion: Generation and Chemical Implications, Chem. Rev., 2016, 116 (5), pp 3029–3085. DOI: 10.1021/acs.chemrev.5b00407
  2. ^ Yunchang Zhang; Girish Kshirsagar; James C. Cannon (1993). "Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen". Ind. Eng. Chem. Res. 32 (5): 966–969. doi:10.1021/ie00017a028.
  3. ^ William H. Schechter; R. R. Miller; Robert M. Bovard; C. B. Jackson; John R. Pappenheimer (1950). "Chlorate Candles as a Source of Oxygen". Industrial & Engineering Chemistry. 42 (11): 2348–2353, . doi:10.1021/ie50491a045.CS1 maint: extra punctuation (link)
  4. ^ Airliners.net, Photograph, Dave Campbell
  5. ^ Greenwood, Norman  N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  6. ^ Johnson, C. W. "Degraded Modes and the 'Culture of Coping' in Military Operations: An Analysis of a Fatal Incident on-board HMS Tireless on 20/21 March 2007" (PDF).
  7. ^ Page, Lewis (22 March 2007). "'Oxygen candle' caused explosion". The Register. Retrieved 2013-09-04.
  8. ^ M. M. Markowitz, D. A. Boryta, and Harvey Stewart Jr. (1964). "Lithium Perchlorate Oxygen Candle. Pyrochemical Source of Pure Oxygen". Ind. Eng. Chem. Prod. Res. Dev. 3: 321–330. doi:10.1021/i360012a016.CS1 maint: uses authors parameter (link)
  9. ^ Barry, Patrick (2000). "Breathing Easy on the Space Station". National Aeronautics and Space Administration. Retrieved 9 September 2012.
This page was last edited on 27 October 2019, at 22:19
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