Chemical Surface Coating: Synthesis and Characterization of a Silicon Oxynitride Coated Silica Sel

Mesoporous silica gel has been coated with a thin silicon oxynitridefilm via chemical surface coating. In the first part of the synthesis, achemically bound preceramic polysilazane coating is formed layer by layer onthe pore walls at low temperature, using SiCl₄ andNH₃ as reagents. In the second part of the synthesis, thepolysilazane coated silica gel is pyrolysed, yielding a chemically bound,thin oxynitride coating.During the synthesis, the evolution of the chemical and morphologicalcomposition has been investigated with several elemental and spectroscopicanalysis techniques as well as with nitrogen porosimetry.     

Centred TVD schemes for hyperbolic conservation laws

New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented.     

Waste water analysis by purge and trap capillary GC-FTIR spectrometry

Gas chromatography with Fourier transform infra-red spectroscopic detection (GC-FTIR) is used for the analysis of waste water samples. Compared to GC-MS, this technique offers a more complete identification of organic compounds. Lower concentrations of organic volatiles however require preconcentration techniques such as a Purge and Trap (P&T) preconcentrator. Using this combination, concentrations of organic volatiles in the ppb range can be detected and positively identified.     

FTIR-PAS analysis of silica gel modified with amines for the treatment of natural gases contaminated with sulphur compounds

The quantitative analysis of organic microsamples [vinylite (PVC-PVA) cellulose-nitrate and polyamide] on Al-foils was performed with good precision (rel. standard deviation 1.04% to 12.1%) after calibration of their main IR-bands with relative conductometric techniques. It was shown that the lower detection limit using the 15×Cassegrain objective was 1m and that the linear range of the calibration curves was limited by a deviation of Beer's law atA>1.2 due to the reststrahlen-effect.     

Synthesis, spectroscopy and catalysis of

Chromium acetyl acetonate [Cr(acac)3] complexes have been grafted onto the surface of two mesoporous crystalline materials; pure silica MCM-41 (SiMCM-41) and Al-containing silica MCM-41 with an Si:Al ratio of 27 (AlMCM-41). The materials were characterized with X-ray diffraction, N2 adsorption, thermogravimetrical analysis, diffuse reflectance spectroscopy in the UV-Vis-NIR region (DRS), electron spin resonance (ESR) and Fourier transform infrared spectroscopy. Hydrogen bonding between surface hydroxyls and the acetylacetonate (acac) ligands is the only type of interaction between [Cr(acac)3] complexes and SiMCM-41, while the deposition of [Cr(acac)3] onto the surface of AlMCM-41 takes place through either a ligand exchange reaction or a hydrogen-bonding mechanism. In the as-synthesized materials, Cr3+ is present as a surface species in pseudo-octahedral coordination. This species is characterized by high zero-field ESR parameters D and E, indicating a strong distortion from O(h), symmetry. After calcination, Cr3+ is almost completely oxidized to Cr6+, which is anchored onto the surface as dichromate, some chromate and traces of small amorphous Cr2O3 clusters and square pyramidal Cr5+ ions. These materials are active in the gas-phase and slurry-phase polymerization of ethylene at 100 degrees C. The polymerization activity is dependent on the Cr loading, precalcination temperature and the support characteristics: a 1 wt % [Cr(acac)3]-AlMCM-41 catalyst pretreated at high temperatures was found to be the most active material with a polymerization rate of 14000 g polyethylene per gram of Cr per hour. Combined DRS-ESR spectroscopies were used to monitor the reduction process of Cr(6+/5+) and the oxidation and coordination environment of Cr(n+) species during catalytic action. It will be shown that the polymer chains initially produced within the mesopores of the Cr-MCM-41 material form nanofibres of polyethylene with a length of several microns and a diameter of 50 to 100 nanometers. These nanofibres (partially) cover the outer surface of the MCM-41 material. The catalyst particles also gradually break up during ethylene polymerization resulting in the formation of crystalline and amorphous polyethylene with a low bulk density and a melt flow index between 0.56 and 1.38g per 10 min; this indicates the very high molecular weight of the polymer.     

Post-synthesis deposition of V-zeolitic nanoparticles in SBA-15

A post-synthesis deposition of vanadium silicalite-1 zeolite nanoparticles in the pores of SBA-15 results in a highly ordered hexagonal templated silica material with V-silicalite zeolitic plugs, giving rise to an increased crystallinity of the amorphous mesoporous walls.     

Investigation of the morphology of the mesoporous SBA-16 and SBA-15 materials

Mesoporous SBA-16 and SBA-15 were studied in order to control their possible morphologies. SBA-16 is synthesized using a silicon source (tetraethoxysilane, TEOS) and a ternary system consisting of surfactant F127 (EO106PO70EO106), water, and butanol. The same ternary system, with higher butanol concentration, is used to form SBA-15 material as well. An increase of the TEOS concentration results in a morphology shift of SBA-16 from micron-sized spheres, over randomly shaped aggregated particles, to macrospheres with a size of 15 mm. An identical increase in TEOS concentration also results in the formation of SBA-15 macrospheres, which can be controlled in size. Micron-sized spheres of SBA-15 were formed using a quaternary system of surfactant P123 (EO20PO70EO20), cetyltrimethylammonium bromide (CTAB), ethanol, and water. All mesoporous silica materials were characterized using SEM, XRD, and N2 sorption techniques.     

Laser microprobe mass analysis of o-phenylenediamine on asbestos fibres

The adsorption behaviour of o-phenylenediamine and its catalytically formed oxidation products such as 2,3,-diaminophenazine and higher-molecular-weight compounds on different varieties of asbestos is studied by using laser desorption mass spectrometry. The results prove that amosite adsorbs the product more easily than do crocidolite and anthophyllite, whereas U.I.C.C. chrysotile A does not give rise to detectable adsorption, and the adsorption observed for U.I.C.C. chrysotile B is only fair. The method shows potential for the investigation of the surface reactivity of pure and industrially transformed asbestos and other fibrous materials.     

Vibrational analysis of arsenic acid and its anions: I. Description of the Raman spectra

The Raman spectra of arsenic acid and its anions have been recorded. For some regions in the spectra, where overlapping bands arise, a band profile analysis has been performed using the damped least square procedure. The vibrational assignments for the observed frequencies have been proposed and discussed.     

The synthesis,spectroscopic and thermal study of oxamic acid compounds of some metal(II) ions

Summary The preparation of oxamic acid complexes of general formula M(H₂NCOCOO)₂·xH₂O (M = Mn^II, Co^II, Ni^II, Cu^II or Zn^II; x = 1 for Cu^II, x = 2 for the other metals) is reported. The i.r. and Raman spectra are discussed considering a trans-octahedral structure, formed by five-membered chelate rings with the amide oxygen and one carboxylic oxygen as donor atoms. The apical positions are occupied by water molecules. The thermal degradation process is very similar for the different complexes, first losing H₂O in one or different steps, then the fragments of the organic ligand to give the metal oxide as residue. The thermal degradation of the Cu^II and Zn^II compounds results in the formation of a new polymeric compound by deprotonation of the primary amide function in an endothermic process, the polymer further decomposes to form the metal oxide.