| 摘要 |
Novel monocrystalline boracites having the general formula M3B7O13Hal, wherein M is an ion of a bivalent metal, e.g. Cr, Ni, Co, Fe, Cu, Cd, Zn, Mg, Mn, Pt, Ca, Ti, V, Sr, Zr, Nb, Mo, Ru, Rh, Pd, Sn, Ba, Hf, Ta, W, Re, Os, Ir, Hg and Pb; and Hal is a halogen ion, e.g. I, Cl or Br, are produced by providing a reaction vessel containing a halide of a bivalent metal, the oxide of this bivalent metal and boron oxide as reactants, heating these reactants to above 300 DEG C., usually to 900 DEG C., in the presence of a substance which is water, oxygen, a halogen or hydrohalogenic acid (or compounds releasing these), whereby the reactants are brought into physical contact with each other as a result of at least one chemical transport reaction and are caused to react to produce the boracite. The reaction may be carried out in a hermetically closed vessel with the 3 reactants in separate, spaced containers, boron oxide being placed in an intermediate position. Gaseous phase metal halide and water vapour or oxygen may be introduced into the vessel containing liquid phase boron oxide e.g. by means of a stream of inert gas, e.g. nitrogen or helium, the metal oxide being produced in the vessel by a part of the metal halide undergoing a chemical transport reaction with the water vapour or oxygen. The metal halide may be obtained by reaction in the vessel of a bivalent metal and halogen or a halide of a metal having a valency greater than 2 and the metal. The metal halide and water vapour may be obtained by reaction in the vessel of a bivalent metal oxide and of a hydrohalogenic acid; similarly, the metal oxide is obtained by the reaction of a metal oxide of valency greater than 2 and the metal. |
