How does an exploding dragon's scale work?

Question

I'm designing a unique dragon called Vehement Dragon, I need it to be extremely hostile to all life. It evolved a trait that put it high up on the food chain, this is the only dragon whose scales can pop out and explodes burning everything in the vicinity. It has a special type of glands that can secrete a mucus coating on the scale like a fire retardant, once the mucus dried it will trigger the explosion of the scales. So as long as the scale is still stick to the dragon skin, it never explodes and my question is how can such a mechanism be feasible?

Answer 1

There are chemicals which are stable when wet but highly unstable when dry.

Nitrogen Triiodide

As explained here

The wet paste of Nitrogen Triiodide is very stable. However, when it is dry, it becomes highly unstable. In fact, one can detonate the dry explosive with a light touch, a loud noise, a gentle breeze, or a feather.

Picric Acid

As told here

Picric acid is typically sold moisten with at least 30% water for safety purposes. As the water evaporates over time, the substance becomes dry picric acid crystals. Dry picric acid is highly sensitive to heat, shock and friction. Picrate salts of heavy metals such as copper, zinc, iron and lead are even more sensitive than picric acid itself. It will also react with alkaline materials including plaster and concrete to form explosive materials. The rapid decomposition generates nitrogen, carbon dioxide, water, and other toxic substances.

The Dragon

Somehow, the dragon scales have any of the chemicals above. The glands secrete just water to keep the chemicals wet. When scales are popped out, they dry after some time and explode with with a light touch, a loud noise, a gentle breeze, or a feather.

Answer 2

Chlorine Trifluoride burns sand, water, and people

This question is looking for a Vehement dragon which can burn everything in the vicinity.

Will it burn everything in the vacinity? It so happens that I asked for a creature that burns everything on earth not too long ago. This is one fairly simple chemical which will literally cause glass, sand, meat, and even water to go up in violent flames on contact. Douse anything near this dragon with ClF$_3$ and it will be burning violently.

Let’s say your dragon is in a peaceful wooded lakeside beach, enjoying a freshly caught deer. It becomes aggravated by some time traveling researchers in flame-proof asbestos suits, plexiglass goggles and safety gloves hiding inside a solid concrete bunker who had a camp out on this beach and we’re now pointing a fire hose at him. A vehement dragon will make it a Bad Day for them. When these scales throw off him, the concrete will catch fire. Cotton lab coats will explode. Their asbestos fire-proof coats will catch fire. The plexiglass shields will explode. Safety masks will explode and catch fire. Their safety gloves will catch fire. Eyeglasses will explode. Rubber boots will explode. Researcher’s skin will explode and catch fire. The researchers will catch fire. The ashes in the fire pit will catch fire. The beach will catch fire. The forest will explode and catch fire. The fire hose will catch fire. The lake will catch fire.

Unfortunately, the dragon will need to catch another deer.

But will it explode? A drop of ClF$_3$ is held inside the dragon’s scales inside a mineralized aluminum “flask” which has been carefully fluoridated. Any slight dent or fracture in the small metal flask, will bring the ClF$_3$ in contact with the metal, and cause it to explode, spreading the chemical around a small blast radius.

Toxic death bonus round: Burning ClF$_3$ lets off toxic chlorine gas and caustic hydrofluoric acid, destroying their time machine as well as poisoning anyone (or anything) that may be left alive.

Why doesn’t the dragon go boom? Because the cells accreting the scales are depositing a fluoridated membrane over the scale carapace. Launch the scale, the membrane stays with the dragon. A slight scratch to the surface of the scale removed the protective layer.