W. Mozgawa

Spectroscopic studies of different aluminosilicate structures

Abstract The applicability of the MIR spectroscopy for aluminosilicate structures description of some natural zeolites has been shown in this work. The suitability of the spectra for a “convenient” recognition and identification of the kind of SiO 4 and AlO 4 tetrahedra rings predominating in a given zeolite structure has been described. The interpretation process was supported by the decomposition of the spectra into component bands. The estimation of Si:Al ratio in zeolites and the degree of ordering in the sequence of both building space framework tetrahedra can be done on the basis of parameters (band position and intensity) of the main bands due to Si(Al)–O bond vibrations. The results based on the spectra of zeolites were then compared with the data obtained in the previous works on potassium aluminosilicates (also having framework structures thought not classified as zeolites) and ring silicates (containing isolated silicooxygen rings). Such comparison allows to draw more general conclusions relating to the interpretation of MIR spectra of different silicate structures.

Specific features of the IR spectra of silicate glasses

Abstract The glassy state of matter, in contrast to crystalline solids, is characterized by a lack of long-range order. In the structure of glasses, the bond lengths and bond angles are not fixed. As a consequence the vibrational spectra of glassy sustances exhibit various band shapes. The bands in these spectra are characterized by complex shapes and significant widths resulting in difficulties in the determination of the main spectral parameters, such as the number of bands, their positions and intensities. These difficulties limit the application of vibrational spectroscopy in the study of the structure of glasses. The main goal of the present work is to show that an appropriate procedure of decomposition of the complex bands in the spectra makes it possible to obtain important information on the structure of solid glassy substances. The procedure proposed is based on (a) minimization of the number of bands, and (b) comparison with the spectra of crystalline analogues. The number of components in a complex band and its parameters are found by analysis of the second derivative of the spectrum, using Fourier self-deconvolution as proposed by Griffiths and Pariente (Trends Anal. Chem., 5 (1986) 209). According to the procedure proposed, the spectra of the crystalline and glassy analogues of the following substances were decomposed: SiO2 (silica), K[AlSi2O6] (leucite) and Li(AlSi2O6) (spodumene). This decomposition of the complex bands in the spectra of glassy substances meant that their structures could be more readily deduced. It was shown that as well as the bands corresponding to the crystalline analogues in the spectra of glasses, there are bands responsible for characteristic features of the structure of glasses.

The AIPO4 polymorphs structure in the light of Raman and IR spectroscopy studies

Abstract Raman spectra of low-temperature polymorphic forms of AlPO 4 (berlinite, phosphocristobalite and phosphotridymite) are presented. The interpretation of the spectra has been carried out using the model of [PO 4 ] 3− tetrahedron isolated by Al 3+ cations. The theoretical number of Raman active modes has been determined using the factor group analysis. Raman and IR spectra have been compared regarding adequate selection rules. The crystalline field splitting and Davydov effects have been discussed. It has been shown that AlPO 4 polymorphs, usually classified as a framework structure, because of the similarity to SiO 2 , should be rather treated as an orthophosphate structure. Thus the model of the oxygen bridge, commonly used for interpretation of framework structures, should not be used in the case of AlPO 4 .

Vibrational spectra of complex ring silicate anions — method of recognition

Abstract In this work is presented an attempt to apply vibrational spectroscopy to study the structure of ring silicates, in particular to recognize the number of members in tetrahedra. A number of synthetic ring silicates prepared by various methods was subjected to the studies. They contained cations of various metals (Na, Ca, Sr, Pb), and the polyanions occurring in their structures differed in both the number of ring members ( n = 3, 4 and 6) and the extent of deformation. The bands characteristic of the ring systems are located mainly in the middle IR spectra in the range 780-500 cm −1 . The bands due to SiO vibrations were assigned as originating from both subunits containing bridging oxygen atoms (SiOSi) and those containing terminal oxygen atoms (SiO − , broken bridges). The influence of crystalline field on the spectra has been analyzed.

Calculations of silicooxygen ring vibration frequencies

Abstract In the work model calculations of the vibrations of ideally isolated silicooxygen rings (using PM3 method) have been carried out. three-, four-, and six-membered rings have been considered. It has been found that that the three-membered silicooxygen rings are flat and practically undeformed showing D3h symmetry. The rings of higher number of ring members (i.e. n>3) are deformed to some extent. The deformation reveals itself most significantly in the Si–O–Si bond angles distribution. In the case of all the rings the bridging Si–O–Si bonds are ca. 0.02–0.04 A shorter than the non-bridging Si–O− bonds. Hypothetical IR spectra for all the rings considered have been also calculated. Analysis of these hypothetical spectra leads to the conclusion that the whole spectrum can be divided into four wavenumbers regions, 1200–1100 cm−1 stretching Si–O(Si) vibrations; 1000–800 cm−1 stretching Si–O− vibrations; 800–600 cm−1; the region in which a band characteristic of silicooxygen rings appears, and below 600 cm−1 bending −O–Si–O− and (Si)O–Si–O(Si). It has been also found that as the number of ring members increases the ‘ring band’ shifts to lower wavenumbers: 725 cm−1 for three-membered rings, 650 cm−1 for four-membered rings and 610 cm−1 for six-membered rings. Calculated spectra have been compared with the experimental spectra of cyclosilicates. They showed good agreement in the 1200–600 cm−1 region. In the experimental spectra as well as in the calculated ones, with increasing the number of ring members the ‘ring band’ shifts towards lower wavenumbers.

The non-ring cations influence on silicooxygen ring vibrations

Abstract In this work IR spectra of synthetic and natural ring silicates (cyclosilicates) containing in their structure isolated silicooxygen rings of various numbers of members ( n =3,4,6) have been presented. By means of factor group analysis it has been shown that only one intensive band characteristic of ring structures (“ring band”) should be observed in the IR spectra of cyclosilicates. The ring band position is related to the number of ring members [M. Handke, M. Sitarz, W. Mozgawa, J. Mol. Struct. 450 (1998) 229] and strongly depends on the kind of non-ring cations connecting the rings. The existence of the cations such as Ti 4+ , Zr 4+ , Cu 2+ etc. in the cyclosilicates structure causes the conjugation of the vibrations, making the interpretation of the spectra more difficult. In this work we have shown that the presence of such non-ring cations causes the shifting of the “ring band” to the higher wavenumbers. In the case when Al 3+ are non-ring cations it is almost impossible to identify the “ring band” (6-membered cyclosilicates).

Spectroscopic studies of polymorphs of AlPO4 and SiO2

Abstract IR spectra of basic polymorphic forms of AlPO4, measured at different temperatures, are presented. Diffuse reflectance spectroscopy has been used for high temperature measurements. According to the crystal structures of different AlPO4 forms by means of factor group analysis, a number of modes and their activities have been determined. An attempt to assign bands to specific normal vibrational modes has been undertaken, comparing spectra of subsequent forms of AlPO4 with each other. The obtained results have been discussed with regard to data referring to various isomorphous polymorphic forms of SiO2, comparing, respectively, cristobalite with phosphocristobalite, berlinite with quartz, and phosphotridymite with tridymite (M. Handke and W. Mozgawa, Vib. Spectrosc. 5 (1993) 75; M. Handke, W. Mozgawa and M. Rokita, Michrochim. Acta [Suppl] 14 (1997) 511). Differences and similarities have been shown for the spectroscopic data and thus for structures of AlPO4 and SiO2.

Use of clinoptilolite for the immobilization of heavy metal ions and preparation of autoclaved building composites

The work presents the results of application of natural clinoptilolite for immobilization of heavy metal cations (Ag(+), Pb(2+), Cd(2+) and Cr(3+)) from aqueous solutions and uses zeolite to prepare autoclaved building composites. Sorption has been conducted on sodium form of natural clinoptilolite originated from Poland. Clinoptilolite (sodium form containing heavy metal cations) has been applied to obtain new building materials which have good physical properties. Samples produced by autoclaving process showed relatively low bulk density (about 1.35 g/cm(3)). The compressive strength depended on the amount of CaO in the initial mixture. Its maximum value was about 40 MPa. The influence of heavy metal cations on the compressive strength values was insignificant (except for the Cr(3+) ions). However, all the cations modified the microstructure and the ordered state of C-S-H phase. Efficiency of Ag(+), Cd(2+) and Pb(2+) ions immobilization on the mineral matrix was shown. In the work, results of IR spectroscopy, atomic absorption spectroscopy (AAS) studies, X-ray diffraction analysis, SEM observations and technological investigations are presented.

Investigation of the coal fly ashes using IR spectroscopy.

The results of FT-IR spectroscopic studies of coal fly ashes, originated from various polish power plants are reported. The results of MIR investigations were compared to the X-ray diffraction (XRD) measurements and chemical analyses. They are mainly composed of silica, alumina and lime. The infrared spectrum in the middle range can be used to describe both the structure of phases present in the fly ash and to identify the characteristic elements of the individual components of ash. The results indicate that the amount of aluminosilicate and its Si/Al ratio induce a shift in the T-O stretching band appearing at 950-1100 cm(-1). Moreover, FWHM of these bands indicates the participation of the crystalline phase relative to amorphous. The presence of carbonate phases generates substantial changes in the 1450-1400 cm(-1) area of the spectra. The presence of such phases as anhydrite, mullite or illite has also been established on the basis of IR spectra.

FTIR studies of the cyclosilicate-like structures

Abstract Ring silicates (cyclosilicates) form a subgroup of oligosilicates. Cyclosilicates include isolated silicooxygen rings of different numbers of members in their structure. Isolated rings occur also in other structures described as cyclosilicate-like ones. In the present paper infrared and Raman study of cyclogermanates, cyclosilicates and cycloaluminosilicates have been carried out. Studies of SrO–SiO 2 , SrO–GeO 2 , BaO–GeO 2 , MgO–Al 2 O 3 –SiO 2 systems allowed to show the influence of different, tetrahedral ring cations (Si +4 , Al +3 , Ge +4 ) on the ‘ring band’ positions. Presence of aluminium cations, lighter than silicon cations, causes the shift of ring band to higher wavenumbers. In the case of cyclogermanates, as there is the big mass difference between germanium and silicon, the ring band is observed in significantly lower wavenumber range. The examinations of cyclogermanates with different non-ring cations such as Sr +2 and Ba +2 can show the influence of these cations on the position of the bands.