Refractory (planetary science)
The refractory group includes elements and compounds like metals and silicates (commonly termed rocks) which make up the bulk of the mass of the terrestrial planets and asteroids in the inner belt. A fraction of the mass of other asteroids, giant planets, their moons and trans-Neptunian objects is also made of refractory materials.
The refractory elements can be divided into several categories:
- the super-refractory having condensation temperatures higher than 1700 K (Re, Os, W, Zr and Hf);
- refractory with condensation temperatures lying between 1500–1700 K (Al, Sc, Ca, Ti, Th, Lu, Tb, Dy, Ho, Er, Tm, Ir, Ru, Mo, U, Sm, Nd and La);
- moderately refractory with condensation temperatures from 1300 to 1500 K (Nb, Be, V, Ce, Yb, Pt, Fe, Co, Ni, Pd, Mg, Eu, Si, Cr);
- moderately volatile with temperatures in the range of 1100–1300 K (Au, P, Li, Sr, Mn, Cu and Ba);
- volatile—700–1100 K (Rb, Cs, K, Ag, Na, B, Ga, Sn, Se and S) and
- very volatile—less than 700 K (Pb, In, Bi and Tl). This temperature is close to the condensation temperature of troilite (FeS).
The condensation temperatures are the temperatures at which 50% of the element will be in the form of a solid (rock) under a pressure of 10−4 bar. However, slightly different groups and temperature ranges are used sometimes. Refractory material are also often divided into refractory Lithophile elements and refractory Siderophile elements.
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