First up, my sympathies to
@lerenau for this unfortunate event. If it provides any comfort, I did something similar with the plastic case of a beautiful vintage razor last year.
A wee bit of research on this topic reveals that the three active ingredients in Steradent are:
- sodium carbonate
- sodium bicarbonate
- peroxide salts (varies slightly from product to product).
- citric acid
The sodium carbonate and bicarbonate create an alkaline solution (high pH), but this is offset by the citric acid, with the final solution typically being slightly acidic. The peroxide salt creates a strongly oxidizing action, as noted by Alfie.
The sodium carbonate and bicarbonate compounds dissolve and release CO2, hence providing the "fizz" and the agitation. The peroxide salt also dissolves, releasing oxygen into the solution, but tellingly creating an aggressive oxidizing action (more aggressive than hydrogen peroxide).
The citric acid provides cleaning action (it is the primary ingredient in the Nespresso Machine cleaning solution pouches), and also buffers the alkaline action of the carbonates.
When casually reading the info on Steradent, it would be easy to think that it's use is safe for metals, as they note that it is safe for the metal components of dentures. Here is the rub, however. The metallic components of dentures are specialist alloys that are highly corrosion resistant (they need to be, as no one wants dissolved metal disappearing down the gastro-intestinal tract; imagine the health consequences, and lawsuits!)
So, whilst the product is safe for denture metal, it most certainly has the potential to attack certain metals used in Razors. Aluminium and Pot Metal for sure, and also potentially Nickel and Chrome, depending on the integrity of the plating, the ambient temperature, and the period of immersion.
Alfie, my friend, in my opinion you are spot-on.
A quick search on the net reveals several hits such as "10 great cleaning tips using denture tablets" etc. A scan of these reveals that the cleaning targets are non-metallic, such as glassware, china, coffee machines, enamel cookware, toilet bowls, etc. The one exception is the application to clean jewelry (this would be due to the fact that gold is extremely inert and would be safe from attack), but there is a warning not to use with silver jewelry, which is telling.
As a side note, I ran a small pilot plant as a young professional, and used peroxide salts as an oxidising agent in an acidic environment. The end product of the process was pure cobalt oxide. I had done all of the trial runs in a Plastic-lined vessel, but the process required heating to approx 60C, which the plastic couldn't handle, so I used a stainless steel vessel for the production run. To my horror, once the vessel was drained, I could see that the internal metal surface of the stainless steel had been attacked significantly. This resulted in significant Nickel and Chrome contaminating the product. Whilst this environment was more aggressive than the Steradent example, I'm sure you can draw the parallels to the attack/discoloration of the Razor parts.