Maciej Sitarz

Infrared spectroscopy of different phosphates structures

Infrared (IR) spectroscopic studies of mineral and synthetic phosphates have been presented. The interpretation of the spectra has been preceded by the isolated [PO(4)](3-) tetrahedron spectra analyse. The K(3)PO(4) saturated aqueous solution was measured in the special cell for liquids. The obtained IR results have been compared with the theoretical number of IR-active modes. The number and positions of the bands due to P-O vibrations have been established. The phase composition of the phosphates has been determined using XRD and IR spectroscopy methods. The influence of non-tetrahedral cations on the shape of the spectra and the positions of bands has been analysed and the crystalline field splitting effect has been discussed.

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.

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.

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).

SiOC glasses produced from silsesquioxanes by the aerosol-assisted vapor synthesis method

In this paper, we describe a new method based on aerosol-assisted vapor synthesis for making glass materials by pyrolysis of readily available silsesquioxanes CH3Si(OCH3)3 and CH3Si(OC2H5)3. Combined powder X-ray diffraction (XRD) and spectroscopic studies in the far infrared region (FIR) showed that under applied conditions the method yielded amorphous materials. Subsequent structural studies with the application of the (29)Si and (13)C MAS NMR, Raman, and middle infrared (MIR) techniques led to the conclusion that the pyrolysis of the silsesquioxane precursors resulted in glass materials with a structure of amorphous silica v-SiO2. In the case of certain glasses prepared from CH3Si(OCH3)3, they were also shown to possess in the structure some Si-C bonds (black glasses), whereas those originated from CH3Si(OC2H5)3 were composites that in addition to the silica glass phase contained domains of free/unbound carbon.

Structural studies of the NaCaPO4-SiO2 sol-gel derived materials

Structural studies of the NaCaPO4– SiO2 materials have been carried out. Amorphous materials from this system, after controlled crystallization process, can be used as potential nanomaterials. Structural studies of nanomaterials are of fundamental importance in view their future applications. Materials of different [PO4] 32 /[SiO4] 42 tetrahedra proportion have been prepared. Na þ and Ca 2þ cations have compensated the negative charge of the lattice. Amorphous and crystalline materials have been obtained by sol – gel as well as conventional melting methods. The XRD phase identification has enabled amorphous and crystalline materials identification and suggests the separation of phosphorus and silicate crystalline phases. The obtained materials were examined using the electron scanning microscope and EDX spectrometer. Analysis of electron scanning microscope maps shows considerable inhomogeneity of crystalline samples. Fluctuations in ions distribution, in case of amorphous materials, have been noted too. DTA investigations have enabled to find the probable characteristic temperatures of glass crystallization. Detailed infrared spectroscopy measurements have been carried out. The spectra of obtained materials have been compared with the spectra of cristobalite. Spectroscopic studies confirm the inhomogeneity of materials. q 2003 Elsevier Science B.V. All rights reserved.

FT-IR and FT-Raman studies of cross-linking processes with Ca2+ ions, glutaraldehyde and microwave radiation for polymer composition of poly(acrylic acid)/sodium salt of carboxymethyl starch – In moulding sands, Part II

FT-IR and FT-Raman spectroscopic methods allowed to identify the cross-linking process of the aqueous composition of poly(acrylic acid)/sodium salt of carboxymethyl starch (PAA/CMS-Na) applied as a binder for moulding sands. The cross-linking was performed by chemical methods by introducing cross-linking substances with Ca(2+) ions or glutaraldehyde and by physical way, applying the microwave radiation. It was found that Ca(2+) ions cause formation of cross-linking ionic bonds within carboxyl and carboxylate groups. Glutaraldehyde generates formation of cross-linking bonds with hemiacetal and acetal structures. Whereas in the microwave radiation field, due to dehydration, lattices are formed by anhydride bonds.

The effect of SiO2/Al2O3 ratio on the structure and microstructure of the glazes from SiO2–Al2O3–CaO–MgO–Na2O–K2O system

Ceramic glazes are commonly used to covering of the facing surface of ceramics ware. A well-chosen oxide composition and firing conditions of glazes causes significant improvement of technical parameters of ceramic products. Modern glazes are classified as glass-ceramic composites with different crystalline phases arising during firing. The presence of crystals in the glass matrix is influenced by many factors, especially by oxides molar composition. A crucial role is played by the molar ratio of SiO₂/Al₂O₃. In this work the six composition of glazes from SiO₂-Al₂O₃-CaO-MgO-Na₂O-K₂O system were examined. The only variable is the ratio of the silicon oxideto alumina at a constant content of other components: MgO, CaO, K₂O, Na₂O, ZnO. In order to determine the real phase composition of the obtained glazes research on fluorescence spectrometer (XRF) were done. For structural studies X-ray diffraction (XRD) and spectroscopic in the middle infrared (MIR) were performed. In order to determine the state of the surface (microstructure) research on the scanning electron microscope (SEM) with EDX. The research allowed to determine the influence of SiO₂/Al₂O₃ ratio on the structure and phase composition of glazes and the nature, and type of formed crystalline phases.