A couple of interesting old papers on ammonium perchlorate and ammonium iodate that might be of interest to those looking to improve strobe rockets

[PyroGnome]

Since everyone loves strobe rockets (maybe unless they've been on the firing line trying to fire shells with no delay fuse on the leader while some 6lbers start going wrong and detonating a couple hundred feet away) I found some old papers that might be of interest.  This post contains heavy speculation based on what I'm searching around for but I thought the papers were interesting enough to post.  Despite their age, less was known in general rocketry about AP so more variables were studied whereas most newer papers focus on very specific issues and optimizations of solid rocket boosters where AP sees the most use these days.  The cost has also gone up.  AP is more expensive than any other compound / metal used in strobe rockets but is usually the bulk of the composition which isn't optimal for those and maybe even worse for stars which should ideally be cheap to make in bulk if for no other reason than scalability of shell size.  The only commonly used chemical that costs more right now is antimony trisulfide and it can usually be replaced by something else in glitters with little change in effect; and the percentages are very low anyway; and generally isn't needed at all otherwise (some organic fuel white stars maybe if you're trying to keep even brightness in a multi-colored break) although I use tiny amounts for a couple of other things.  A substitute for AP that doesn't have godawful reactions with practically every element and compound known to man would be even more desirable.   Hydroxylamine sulfate which is also covered in the second paper (which is mainly on ammonium iodate) probably doesn't fit that bill as it suffers the same issues with metals as ammonium perchlorate and free hydroxylamine is explosive but it might have some use somewhere. 

AFAICT this is the first English paper describing what was probably the strobe effect (although they're mainly focusing on not producing it for obvious reasons) of ammonium perchlorate in certain situations, including some that probably haven't  been abused for pyrotechnics yet:

https://apps.dtic.mil/sti/pdfs/AD0688944.pdf

Quote

When the propellant is severely underoxidized, has small AP particles, and/or has a fuel that melts easily, ab-normal burning in the form of plateaus, mesas, or extinctions, at intermediate pressure (20-200 atm) is the result. No burning rate evaluation has been proposed that applies to this category of propellants.

Existing strobe formulas contain relatively huge amounts of oxidizer (or things that will act as oxidizers when burned with metal fuels) for the fuel amount and it's almost more surprising that they don't generate enough thrust to be used alone, as the next paper seems to indicate that many of them contain enough nearly enough catalysts that the AP should be burnable (emitting basically nothing but gases) without additional fuel at 1 ATM and room temperature conditions as the following paper touches on.  This is in fairly large contrast to the nitrate-based strobe star formulas, and if one examines the AP strobe star formulas many seem to have nearly copied the ratios without accounting for the very high MW of strontium and barium...  the rocket formulas aren't too far off.  The nitrate formulas tended heavily towards being under-oxidized and although they could also allow for magnesium's ability to use nearly any atmospheric gas of importance as an oxidizer once it reaches a high enough temperature and rockets can't really even if a vacuum is created after a strobe flash phase, this doesn't account for AP strobe star ratios.  To me it "feels" more like materials were swapped 1:1 and it luckily worked by some mechanism (probably the low temperatures required for the oxidizer itself to decompose and oxidizing gases escaping without reaction or with self-reactions due to the higher volume of gas generated) so nobody messed with it.  Given how flakey strobe formulas are I don't blame them. 

The small particle thing is kind of standard for most pyro formulations anyway, they define it as less than 250 micron particle size.   I've seen people milling their 200 micron to dust for these.  I consider this dangerous (< 90 micron AP being explosive) and based on this it probably isn't necessary.  The fineness of the oxidizer is more important for something like potassium perchlorate that doesn't decompose at low temperatures.  There's a ton of information in that paper and I'm nowhere near going through it, but it would be interesting to find a strobing propellant mix that generated enough thrust to be used without whistle booster (as composition boundaries can be a major failure source in rockets) that potentially didn't require a metal powder since they're mostly dangerous to use with AP and are likely the largest cause of the rockets having poor shelf life along with the seemingly generalizable issue of catalysts decreasing thermal stability in storage. 

Even more ideally (and probably solving most issues with metal powders by fully coating them) would be finding a resin that could be used to cast engines rather than press them while maintaining strobe.  Casting the fuel rather than pressing eliminates at least one of the most dangerous manufacturing steps since a press is no longer required, and low-medium  viscosity resins may allow for fuel mixing to be performed in one of the resin parts before mixing / casting / vacuum degassing.  The very large scale model rocketry people (and NASA) have been doing it this way for years but it seems to have been mostly ignored in pyro.  This makes sense for whistle and most traditional fuels where the oxidizer percentage is necessarily high enough that a resin mix would be a huge pain, but ammonium perchlorate is practically all oxidizer by molecular weight.   

This paper focuses on some characteristics of ammonium iodate as a fuel;  apparently iodates have none of the issues of chlorates regarding stability so might end up being safer but they aren't cost-effective.  Most full scale rocketry passed over them due to the lower gas generation thanks to the high weight of iodine lowering the oxygen ratio.  If ammonium iodate could be sourced cheaply the bright purple iodine trail might make it worth developing a fuel around for daytime rockets even if it wasn't a strobing composition.  It has similar ignition characteristics as AP.  They only tested burn rates with 2 component mixes of the compound + catalyst.  There's also some useful information about potassium dichromate and a few other catalysts' effects on minimum combustion temperature of AP, and on hydroxylamine sulfate which probably has some use for something and is more readily available.  Someone on eBay is selling it at prices that end up being higher than AP by a bit, but it's not so expensive that testing would be prohibitive if someone wants to dig up more information on it and attempt to find some use or just finds a better deal on it. 

https://web.archive.org/web/20161028010226/http://www.dtic.mil/dtic/tr/fulltext/u2/295766.pdf