红磷锰矿的常压回流合成、表征及Rietveld结构精修

Prismatic hureaulite was synthesized by refluxing of 100 mL 0.3 mol/L Mn(H2PO4)2 solution at atmospheric pressure under different temperatures (40, 50, 60, 80 and 100 ℃). Powder X-ray diffraction, Rietveld refinement, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the crystal structure and micro-morphologies of hureaulite. Products obtained from different reactants had various morphologies. Needle-like hureaulite was fabricated at 100 ℃ when 30 mmol H3PO4 was added into 100 mL 0.3 mol/L Mn(H2PO4)2 solution. Hureaulite was prepared by further adding NaClO solution into the reaction system. Hureaulite was not formed when Mn(H2PO4)2 was substituted by MnCl2 and H3PO4, but it came into being by further adding an amount of NaClO solution in the reaction solution. The transformation process of hureaulite at mild conditions was investigated. Mixture of hureaulite and MnHPO4o3H2O was produced by reflux of 100 mL 0.3 mol/L Mn(H2PO4)2 at 40 ℃ for 12 h, and the former was about 59.24% in mass. MnHPO4o3H2O was then transformed into hureaulite by further prolonging the reflux time. After refluxing for 24 h and 48 h, the content of hureaulite increased to 86.11% and 100% respectively. Synthesized hureaulite crystallized in the space group C12/c1, belonging to the monoclinic system. The unit-cell parameters obtained from Rietveld refinement are: a=17.64183(56)A, b=9.14788(28)A, c=9.51034(32)A, β=96.5665(17)deg ，M=718.57 g/mol，V=1524.761(85) A3，ρ=3.01058(17) g/cm3，Z=4. Most of the crystal parameters were closely similar when products were fabricated at different temperatures, however, the unit cell was compressed in the c axis direction and β decreased with the increase of temperature. The calculated densities of hureaulite increased with the increase of reaction temperature. That was to say, the density of hureaulite in supergene soil is lower than that of those formed by hydrothermal reaction, which help us distinguish the formation mechanism of hureaulite. Hureaulite was successfully prepared in mild conditions, which was similar to the natural temperature in soils, and the genetic mineralogy of hureaulite should be re-recognized. The new preparation method also facilitated the exploitation and application of hureaulite in the field of chemistry and materials science.