M. Handke

Vibrational spectroscopy of the amorphous silicates

Abstract It has been demonstrated that the Si 2 O unit instead of the SiO 4 unit approach would much better explain the IR spectra of crystalline and vitreous silica and framework alumino-silicates. In this approach all modes are lattice vibrations other than Si 2 O unit vibrations. Within the lattice vibrations it is suggested to distinguish: high-wavenumber pseudo-lattice vibrations in the 700-400 cm −1 range and low-wavenumber lattice vibrations below 300 cm −1 . The first range is responsible for some kind of order larger than a single unit, while the second one covers the long range order in the structure. Similarities between the spectra of crystalline and vitreous forms of respective silicates indicate a structural relationship between the medium range structural order of glass and the relevant crystal structure. The detailed discussion and conclusions are based on the far-infrared, mid-infrared and Raman spectra measured for vitreous and crystalline potassium silicates and potassium alumino-silicates. The spectra of silica polymorphs measured at different temperatures are also presented and discussed.

Vibrational spectra of phosphate–silicate biomaterials

Abstract For substitutive and reconstruction surgery different classes of materials (e.g. metals, polymers, ceramics composites) as implant materials are employed. Among them the ceramics as potentially biologically active materials seem to be most promising for further applications. In presented work the oxide ceramic materials in the Na 2 O–CaO–Al 2 O 3 –P 2 O 5 –SiO 2 system were obtained. The materials in the glass, glass–ceramics and crystalline form were studied. With IR and Raman spectroscopy the phase composition of these materials was found. With vibrational spectroscopy methods the glassy or crystalline state can be recognized. The short-range structural order of the glass phase was determined also. The most interesting results concern the glass–ceramics materials whose chemical and phase composition indicates its potential biological activity and good enough mechanical properties.

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.

MAS NMR and FTIR spectra of framework aluminosilicates

Abstract In the work, the results of 27 Al MAS NMR studies carried out for structures of different framework aluminosilicates are presented. The spectra of natural clinoptilolite and its sodium and hydrogen forms were measured. The zeolite spectra were obtained before and after incorporation of heavy metal cations (Pb 2+ , Cd 2+ , Ni 2+ and Cr 3+ ) into the zeolite structure. After decomposition of the spectra into component peaks differences caused by ion exchange were observed. Additionally, NMR spectra of kalsilite (framework aluminosilicate, not belonging to zeolite group) and other zeolites (chabazite, heulandite and analcime) were measured. 27 Al MAS NMR spectra of all the samples studied were compared with the FTIR spectra measured in the middle infrared region. Based on the results obtained it has been proved that the interpretation of spectra obtained using these two different techniques can give some information concerning changes occurring in various framework aluminosilicate structures.

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).

Siloxane and silsesquioxane molecules—Precursors for silicate materials

Preparation of ceramics by sol-gel method has been known for many years, but recently it has been developed as a method for the synthesis of nanostructural ceramic materials. Hydrolytic polycondensation of simple molecules [e.g. most widely used tetraethoxysilane (TEOS)] leads to xerogel materials that can contain macromolecules of distinct random, ladder and cage or partial cage structure. In order to obtain well-defined silsesquioxanes it is preferred to start the process with more complex molecules, bringing in a specific framework that can govern the structure of the product. In the presented work alkoxy derivatives of cyclosiloxanes and polysiloxanes as well as a hydride derivative of octahedral silsequioxane (T(8)(H)) were applied as precursors in the process of hydrolytic polycondensation. Depending on the reaction conditions, silsesquioxane macromolecules or silica material of ordered structure were obtained. We have prepared mesoporous organiosilica materials without using any template or surfactant whatsoever. The meso-pores are created due to the unique structure of initial oligosiloxane or silsequioxane molecules and the specific interactions in the used catalyst/solvent system. In the case of octasilsesquioxane precursor, the condensation process gives directly mesoporous silica material. Dried polysilsesquioxanes were heated at the temperature of 600°C in argon or air atmosphere (pyrolysis or ceramization). In the atmosphere of argon SiC(x)O(y) glass materials were obtained.

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.

Alkoxymethylcyclosiloxanes - new efficient precursors of crystalline (CH3SiO3/2)8 silsesquioxane and polymethyl silsesquioxanes

Abstract A new, highly efficient and very simple method for the synthesis of pure octahedral methylsilsesquioxanes (CH3SiO3/2)8, from cyclic 2,4,6,8-tetraalkoxy- 2,4,6,8-tetramethylsiloxane, was developed. We have found that T8Me can be synthesized from a mixture of alkoxymethylcyclosiloxane isomers in the hydrolytic condensation process, utilizing an ionic catalyst - tetrabutylammonium fluoride (TBAF). The reaction was carried out under very mild conditions, at room temperature, in a variety of solvents of different polarity. A substantial solvent effect was observed. THF helped in the formation of pure T8Me, whereas in other solvents mixtures of T8Me and poly(methylsilsesquioxanes) (PMQS) of substantial degree of regularity, were obtained.

Transmission, emission, and specular-reflection FTIR spectra of the thin forsterite (MG2SiO4) film

The forsterite ceramics is a promising material for electric and engineering applications because of its low dielectric loss and low thermal expansion coefficient. The aim of this work is to characterize the thin films of forsterite deposited on steel sheet and silicon wafer by means of FT-IR spectroscopy. In the case of thin films on a flat solid surface the most useful IR measurement technique is specular reflection. However, as it was reported in many papers, these spectra may differ drastically from the transmission spectra. Therefore, the second aim of this work is the comparison between forsterite filmss spectra recorded with different sampling techniques including specular reflection, transmission and emission.