Pyroelectricity minerals

The Curie brothers were drawn to the subject of piezoelectricity because of their familiarity with a phenomenon known for many centuries, that of pyroelectricity. Pyroelectricity refers to the tendency of certain materials to generate an electric current when they are heated. The phenomenon was first described in 314 b.c.e. by the Greek philosopher Theophrastus (ca. 370-ca. 285 b.c.e.), who observed the effect with the mineral tourmaline. Little research was done on pyroelectricity until the early 1800s, when the effect was rediscovered and studied in detail by the Scottish physicist Sir David Brewster (1781-1868). Then in 1878, William Thomson, Lord Kelvin (1824-1907), offered an explanation of the atomic changes that take place when pyroelectric effects occur. These developments in the understanding of pyroelectricity led the Curie brothers to study the possibility of producing electricity from crystals by physical means other than heating. 

Pyroelectric Separator—The pyroelectric effect is used mainly for the separation of quartz from feldspar. The mixture is heated in the hopper feeder by means of steam. On passing to a cold rotating cylinder below, the material causes pyroelectric polarization to appear on the quartz. This mineral adheres to the cylinder, while the feldspar is not affected. 

Pyroelectric materials exhibit a spontaneous polarization that is a strong function of temperature because the dipole moments vary as the crystal expands or contracts. This was observed in the mineral tourmaline in the seventeenth century. Pyroelectricity occurs in organic crystals such as triglycine sulfate (TGS), ceramics such as... 

Colorless amorphous (i.e., fused silica) or crystalline (i.e., quartz) material having a low thermal expansion coefficient and excellent optical transmittance in far UV. Silica is insoluble in strong mineral acids and alkalis except HE, concentrated HjPO, NH HE, concentrated alkali metal hydroxides. Owing to its good corrosion resistance to liquid metals such as Si, Ge, Sn, Pb, Ga, In, Tl, Rb, Bi, and Cd, it is used as crucible container for melting these metals, while silica is readily attacked in an inert atmosphere by molten metals such as Li, Na, K Mg, and Al. Quartz crystals are piezoelectric and pyroelectric. Maximum service temperature 1090°C... 

If lyngourion and the mineral tourmaline are identical then the words written by the Greek philosopher Theophrastus some 23 centuries ago cotrld be the earliest description of the pyroelectric effect of tourmaline. Two thorrsand years after Theophrastus strange properties of tourmaline became known in Europe thanks to the book of Joharm Georg Schmidt in 1707 and entitled Curious Speculations during Sleepless Nights (Lang 1974). 

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