Design an airbag that contains 500. g of solid material and meets the design lim

Question

Design an airbag that contains 500. g of solid material and meets the design limitations below. Design limitations:

1.) NaN3 is acutely toxic. (http://en.wikipedia.org/wiki/Sodium_azide) It is essential that all of the NaN3 is consumed.

2.) NaN3 is relatively expensive. It would be most cost effective to use as little as possible.

3.) Sodium metal is highly reactive and will ignite in the presence of water (http://www.youtube.com/watch?v=ODf_sPexS2Q). It is essential that the Na (s) is completely consumed.

4.) K2O, and Na2O are caustic and will eat your skin. They need to be completely consumed.

5.) KNO3 and SiO2 are relatively non-toxic and cheap.

6.) A driver’s airbag needs to fully inflate to 70. L with a pressure between 20 psi and 21 psi. Note: Within these limitations, the reactions will release enough heat to raise the temperature of the gas to between 50 °C and 60 °C.

Explanation / Answer

Inside the airbag is a gas generator containing a mixture of NaN3, KNO3, and SiO2 . So, if there is 500 gm
of the total solid material, the percentage of NaN3 in the mixture can be used in lesser quantites when compared
with others since it is expensive. At working conditions the maximum concentration of NaN3 allowed is 0.2 mg/m3 air.
The Na in formed will be consumed by KNO3 to form K2O , Na2O and N2 . The nitrogen gas formed will fill the
air bag, and rest of the products that is K2O, Na2O will react with SiO2 to form glass. They are made to completely
react with SiO2 to form glass , hence they will be consumed completely. The remaining products are non-toxic .
Volume = 70 litres at average pressure Pguage = 20.5 psi (guage pressures are in between 20 psi and 21 psi)
Now calculate the absolute pressure,
Pabs = Pgauge + Patm = 20.5 psi + 14.7 psi = 35.2 psi
With such moderate pressure, enough heat is released to raise the the temperature of the gas

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