Let's assume that a country with technology at about the same level as Germany in the early 1930s wants to weaponize ClF3.
Would they be able to use them it as the payload of artillery shells? What kind of modifications would they have to refit their existing artillery pieces with?
Interestingly, this is one of those worldbuilding questions that is actually a history question in disguise. Nazi Germany did in fact try to weaponize the stuff, but deploying it proved a challenge.
... by the end of the war only about 30 tons of it was ever produced. The reason? The stuff was simply so unstable and so dangerous there was no practical way to use it. One plan to put it into flamethrowers had the simple problem of it eating through all the components of the flame thrower that weren’t steel and then setting fire to everything just for good measure.
This is nasty stuff, by the way. One answer here mentioned that you have to store it in glass or plastic. Any would be 1930s despots beware: do not listen to them! ClF3 burns through plastics and glass. It will burn sand or gravel if given a chance. In fact, it can set fire to asbestos. Nasty stuff!
This is actually WW-I era (1914-18) technology and there exists a¹ large² body³ of⁴ documentation⁵ on the subject how to perform these and to counteract them.
Nazi Germany (1930s) already had nerve gas but decided not to use it as they assumed (wrongly) that the allies had it as well.
Specifically for ClF3 you'd have to make your shells out of old-fashioned copper or coat the interior of your shells with aluminium as it corrodes most metals, just like they did in WW-I and use standard guns and cases and only lightly modified propellant.
A country with WWII technology could weaponize ClF$_3$ pretty easily, taking advantage of the fact that it will quickly cease being ClF$_3$.
Under elevated temperatures, this compound dissociates to its constituent components chlorine and fluorine. Both of these are heavier than air, and highly toxic. So, a shell filled with this substance will release both poisonous gasses upon exploding/impacting.
Another benefit is that Chlorine Triflouride is liquid under cool conditions (below 11 C). In its liquid state, its density is high, roughly 1850 kg/m$^3$, where as chlorine and fluorine gases have a density of 3.2 and 1.7 kg/m$^3$, respectively. Thus, a shell filled with liquid Chlorine Triflouride, and strong enough to handle the gas's vaporization under normal room temperatures, will yield a very large gas cloud relative to the size of the shell.
Why? It will be hazzard for your own army. Chlorine trifluoride is insanely hard to work with and will not give any substantial advantage over explosives.
Chlorine trifluoride will react with close to everything there is and big part that can hold have problems with shocks(quartz) and temperature(wax)...
So from more simple not-so-risky shell production you would make hazard production on level of more tricky chemical weapons. Treated with fluorine gas: steel, iron, nickel, copper or alloys like monel or inconel, teflon can be used for vessels.
Teflon ignites at 180-200°C, fluorine gas from decomposition leaks through it, so shells metal still would need to be treated.
Most likely, only way to go would be to use steel shells treated with fluorine gas. Other options are hard to work, have worse physical properties and cost way more.But steel needs to be pure from many alloying metals and dry, one mistake and you have a disaster. This shells would need extra care not to be dropped or hit, if coating or walls of one shell are damaged, your solders better train to run fast.
is that it just isn't worth the effort. Many Nazi secret weapons seem to have been invented by a 12 year old boy: grandiose (indeed, often pointlessly gigantic); super-scary; sci-fi cool; but zero common sense.
Chlorine trifluoride is the same. Yes, it can set fire to glass and sand, which is crazy scary, but there actually isn't an enormous amount of strategic military value in setting fire to sand. Especially when sand costs pennies per ton, but chlorine trifluoride cost about 100,000 Reichsmarks per ton. (Sure, that was with 1930s technology -- but it still ain't cheap even today.)
And yes, it sets fire to people too, but so does napalm, and guess which one is cheaper?
Long story short: you can make chlorine trifluoride artillery shells by lining the shells with anything that is resistant to its attack (basically anything with a fairly tough fluoride salt: iron will work.) But to make this a practical weapon, you need some way to make it that lowers the price by a factor of at least 10,000 times. Until you do that, your secret N-stoff factory is just a cushy job for cackling mad Nazi scientists.
