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At about 6:55 into the video Why Moon Mining Will DEFINITELY Be A Thing it is stated that lunar silica (SiO2) could be turned into silane (SiH4), which is the silicon analogue of methane. It also states that silane could be used as a rocket fuel, which when combined with oxygen would produce water and silica.

Two questions come to mind:

  1. Has silane ever seriously been considered as a potential rocket fuel and,
  2. With silica being a product of combustion with oxygen there is a possibility that silica could be deposited on the inside of the exhaust nozzle. Would this be a serious problem?
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    $\begingroup$ actually silica deposits could be a huge plus. some engines add silicon oils into the fuel mixture to coat the nozzle and chamber walls and protect it from heat. It doesn't get out of hand either, with it being added on as fast as it is stripped away. $\endgroup$
    – R. Hall
    Commented Aug 5, 2021 at 4:19
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    $\begingroup$ Semiconductor manufacturing uses (or at least used) silane in several processes, so does optical fiber manufacturing. We are taught in safety class that when it burns in oxygen it just precipitates silica smoke or sand; I don't think the prospects are good for several reasons. $\endgroup$
    – uhoh
    Commented Aug 5, 2021 at 8:48
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    $\begingroup$ Oh, no wonder this sounded familiar Can Pyroxene and other silicon compound be used as a theoretical spacecraft fuel? $\endgroup$
    – uhoh
    Commented Aug 5, 2021 at 8:50
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    $\begingroup$ @uhoh - you make it sound so safe! Venting silane certainly makes a very nice flame, although I can't say much about whatever is left since it was being sucked up the gas cabinet exhaust quickly. Disilane was much more exciting, since its LEV is substantially lower, making a much longer burn time when purging the regulator while changing bottles. $\endgroup$
    – Jon Custer
    Commented Aug 5, 2021 at 14:55
  • $\begingroup$ It sounds like you had much more fun than I did; I was simply told to run away! $\endgroup$
    – uhoh
    Commented Aug 5, 2021 at 14:57

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  1. Has silane ever seriously been considered as a potential rocket fuel and,

Yes silanes has been considered as fuels, at least during the early scramble to develop storable hypergolic propellants for missiles in the 40s and 50s.

In his book "Ignition!", rocket propellant pioneer John D. Clark mentions that the University of Texas tried silanes as an additive to make gasoline hypergolic with red fuming nitric acid (RFNA), the leading storable oxidizer of the time.

Gasoline was a tempting candidate for rocket fuel due to its availability, but unfortunately it was not hypergolic with RFNA, making it unsuitable. Considerable research effort was put into finding additives that could make it hypergolic.

Silanes worked for that. 30% tetra-allyl silane makes gasoline hypergolic.

But as many other attempts this did not manage to replace aniline-based fuels, and later low freezing derivatives of hydrazine made all of this obsolete.

It was also considered as a monopropellant too for some reason:

Stan [Tannenbaum] worked with N₂O₄ and with perchloryl fluoride. He found that he could mix bicyclooctane or decalin in N₂O without immediate disaster, but that the mixture was too touchy to live with. He tried tetramethyl silane too, in the hope (unrealized) that it would be safer

So at least there's a testimonial for it being less safe than straight up mixing hydrocarbons into perchloryl fluoride...

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