How long SiH4 will remain stable in the air in ppm-ppb concentrations and how the humidity affects its stability?
SiH4 is highly reactive and flammable due to easy oxidation. It will be oxidized by air oxygen, and although this reaction rate depends on the concentration of both components, I think that in the presence of high O2 concentration even much diluted silane will be oxidized very quickly. Its individual molecule at each time point is surrounded by several O2 molecules, and collisions should happen quite quickly resulting in chemical reaction. Unfortunately I cannot give a quantitative estimation. As to water, SiH4 is hydrolyzed quickly as well, so the moisture should additionally decrease its life time in the air.
Dear Igor, Thank you for the answer. I would like to find precise data on silane stability. The best will be to find graphs for stability/concentration.
There are many commercially available silane detectors, because silane is often used in the industry. I contacted producers of detectors with my question, but I have no response so far. I searched also in scholar articles, but wasn't lucky to find what I need.
Jonathan,
Thank you for the link. I checked the database, but I did not find information about the reaction of very diluted silane with oxygen and water vapor
I realize this is anecdotal but this is my experience: I've created silane in air mixtures on the order of 2-3 ppm, at pressure up to 2000 psig in steel cylinders, and have tracked them for extended periods of time (I believe my first candidate was produced early 2019). So far, they have remained stable within analytical error of my FTIR analyses.
I think people often neglect to consider is the very nature of oxidation in the context of carbon compounds when they think of "combustion." In its own right, combustion of hydrocarbons is a spin-forbidden reaction. The ground state of O2 (famously paramagnetic that student mistake when they attempt to use Lewis structure theory) does not inherently want to react with diamagnetic hydrocarbons. As such, an ignition or even sufficient pressure (collisions with inert molecules like N2 via the Lindemann-Hinshelwood consideration) could create a sufficient quantity of diamagnetic oxygen to facilitate wholesale chemical interactions.
Silicon is one below carbon on the periodic table. As a starting point for consideration, I will look to methane as a template to consider silane.
Please don't construe my answer as an "expert" answer on this; I am only sharing my experience. I consider my work with my silane in air samples to be "on going."
James McHale Thank you, your experience is very interesting! Do you know if your air was completely dry or if there were any humidity?
On a side note: I'm surprised I'm unable to find any systematic study on this question. Silane is highly used industrial gas, but there is no data (or I can not find it) about silane's stability in the air in ppm concentrations.
I will be glad James McHale if you will be able to provide with updates of your ongoing experiments;)
Viacheslav Zgonnik , I can definitively say that the air in my silane mixture samples are dried to ~ 20-50 ppb H2O. It's not "natural air," so it's lacking all the other components other than O2, N2. By "other components," I'm referring to all the other atmospherics: CO, CO2, CH4, N2O, Ar, rare gases, etc...
James McHale Please consider writing a paper on this. There may be others interested in the silane-oxygen reaction topic. At higher silane concentrations, an outcome of a silane -oxygen reaction may be described as pyrophoric. The term "pyrophoric" is not scientifically well defined though. Knowing under what concentration, temperature and pressure combinations a silane oxygen mixture becomes self-reactive may advance scientific knowledge. Just stay within silane safety margins in your experimental set up.
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