The Raman Spectra Of Silicate Minerals And The Study Of Effect By Six-coordinate Aluminum On Silicates' High Frequency In Raman Spectra

The minerals of silicate and silicate containing six-coordinate aluminum have been studied by Raman spectra test. The test results show that the shift which is symmetrical stretching vibration of Si-O_nb in Raman spectra high frequency, is more in silicate minerals with six-coordinate aluminum than in silicate that don't have six coordinate. The Raman shift of symmetrical stretching vibration of Si-O_nb with no six-coordinate aluminum is liner with the Stress Index of Tetrahedron (SIT). On account of ionic and covalent existing in aluminum at the same time, the degree of symmetry in silicate with six-coordinate aluminum degrades, energy level cleavages, the typical peak of symmetrical stretch vibration of Si-O_nb in Raman spectra divides.The silicate tetrahedron clusters with six-coordinate aluminum have been designed, and their Raman spectra are calculated by the qutantum chemistry software named Guassian03W. The result indicates that the typical peak of symmetrical stretching vibration of Si-O_nb in Raman spectra is more of the clusters with six-coordinate aluminum than which clusters have not. This calculate result is in consistent with the result of experiment. Aluminum is more covalent than sodium of alkali metal and magnesium of alkaline-earth metal, six-coordinate aluminum connects with oxygen of silicate tetrahedron, they have more chance to form covalent bond. Its typical peak of Si-O_nb symmetrical stretching vibration increases graduately. The covalaent bond impels the symmetrical degree of silicate tetrahedron degrading. The tetrahedron behaves as"achiral molecule". The peak of symmetrical stretching vibration of Si-O_nb diveds.An In-situ Raman spectroscopic test and study for the hemimorphite has been carried out by high temperature Raman spectra technique. Taking into account the relationship between SIT and Raman shift of the symmetrical stretching vibration of Si-O_nb in minerals, the test result shows that the characteristic Raman peak of 3470cm^-1 representing O-H stretching vibration in the molecular H₂O has disappeared as the hemimorphite being heated 800K, but the characteristic peak 926cm^-1 marked Q₁ of the main framework [Si₂O₇] has been retained, which means the structure of the hemimorphite has not been changed as the H₂O lost. The characteristic peak of 3580cm^-1 related to stretching vibration of the O-H in the structure water (OH) has been disappeared as the sample being heated 1050 K .The relative intensity of the characteristic peak 926cm^-1 related to symmetric stretching vibration of non-bridging oxygen of structure unit Q₁ gradually decreases, and comparing with the growing Raman band of Q₀ characteristic peak at 825.4 cm^-1 which indicates the phase transformation of the hemimorphite has started out at 1050 K . The structure water (OH) has been dehydrated completely as the temperature is over 1100 K, the characteristic peak (3580cm^-1) of the structure water (OH) disappeared completely, the characteristic peak related to Si-O_nb stretching vibration becomes 855cm^-1, which shows that primary Q₁ of the hemimorphite has been returned to Q₀ (i.e. [SiO₄] ), which means the hemimorphite has been completely transformed to willemite .