thermochromic

Zinc Oxide: Thermochromic Color Change

Zinc oxide is an inorganic compound with the formula ZnO. It’s a white powder that is insoluble in water, and it is widely used as an additive in numerous materials and products including rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments,foods, batteries, ferrites, fire retardants, and first-aid tapes. It occurs naturally as the mineral zincite, but most zinc oxide is produced synthetically.

ZnO is a wide-bandgap semiconductor of the II-VI semiconductor group. The native doping of the semiconductor due to oxygen vacancies or zinc interstitials is n-type. This semiconductor has several favorable properties, including good transparency, high electron mobility, wide bandgap, and strong room-temperature luminescence. Those properties are used in emerging applications for transparent electrodes in liquid crystal displays, in energy-saving or heat-protecting windows, and in electronics as thin-film transistors and light-emitting diodes.

Crystalline zinc oxide is Thermochromic, changing from white to yellow when heated and in air reverting to white on cooling. This color change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 °C, x = 0.00007.

Giffed from: this video
More Science and Gifs on: rudescience 

4

AND IT WORKS!

A brand new thermofluorescent compound what emits a much brighter color when cooled down to circa -100 °C. On the first pics there is a filter paper with compound A in an α and in a ß crystal form. The α form emits a yellow and the ß emith a green color. Same compound, with a similar crystal form. When it’s cooled down with a small amount of liquid nitrogen (seen on the gifs) the intensity of the emitted light increases +100 fold compared to the room temperature emission with a quite similar wavelenght. On the last picture the cooled filter papers are seen when cooled down to -100 °C.

SCIENCE!

Thermochromic pads on tube station escalators. For a shirt time, whatever mark is left on the pad will stay on it (depending how hot a persons hand is). Messages, pictures, marks and prints can be left, but will never stay there permanently. Promotes interacting with the environment/other people on the tube.