Question

Why don't glass test tubes corrode, when corrosive acids are poured in it.

Answer 1

Answer:

Now, laboratory-grade glassware is mostly Borosilicate glass (silicon dioxie and boron trioxide). Both of these chemicals are very, very chemically inert. They tend to be quite "content" with their bond configurations, so they generally to not react (to any appreciable level) with acids.

Answer 2

Answer:

Chemical attack can happen to the glass lining, repair materials or steel.

Glass

Minimum available glass thickness:

While glass lining is well known for its exceptional corrosion resistance, you still need to take into account that it does corrode. The rate will normally be determined by the chemistry and temperatures involved in the process. Still, there is a diminishing of the glass thickness over time that needs to be taken into account and checked periodically. When glass thickness becomes excessively worn you may notice a number of symptoms like loss of fire polish, smoothness and even chipping and pinholes. Also, as we discussed in our post about how glass-lined vessels are made, the initial ground coat (roughly 0.015-0.025") is not as corrosion-resistant as the rest of the lining, so when the thickness gets below 0.030", there is usually not a lot of corrossion-resistant glass left. The only way to repair the depletion in the lining is to add a new one via reglassing.

Corrosion by water:

The alkaline ions that are found in distilled, hot water can actually leach onto the glass surface when they are in the vapor phase and lead to a roughening of the glass surface and possibly chipping. You may also find vertical ridges if the damage is caused by condensate running down the wall. The preventative solution is to clean the vessel with water that includes a small amount of acid. Once the damage has occurred, reglassing is necessary.

Corrosion by acids:

While glass provides excellent resistance to most acids, there are three types which cause significant damage – hydrofluoric acid, phosphoric acid, and phosphorus acids. When glass is attacked by these acids, especially when they are concentrated solutions, corrosion can occur quickly. Temperature also plays a key role in speeding up the contamination process.

The following isocorrosion curves have been established to illustrate acid concentrations in relation to temperatures at which the weight losses correspond to 0.1 and 0.2 mm/year. The red area indicates where the use of glass is not advisable; yellow identifies that care must be taken of the advance of corrosion, and the green area advises that glass can be used without problems