K. Nestler

Thermogravimetric and differential scanning calorimetric analysis of natural fibres and polypropylene

The thermal behaviour of variably separated flax and hemp fibres was characterised by means of thermogravimetric and differential scanning calorimetric analyses. Reference measurements of cellulose served to describe the degradation behaviour. Furthermore, thermoanalytic investigations on polypropylene were carried out to evaluate the thermal stability and the respective activation energy of the materials. The results prove the thermal stability necessary for the consolidation process of composite materials.

Production and characterization of C and SiC layers on C fibres

SummaryThe construction, testing and operation of a semi-technical system for the multi-stage coating of endless fibres by means of thermally-activated CVD is described. One objective of this is to apply layer systems under conditions similar to those used in production with long-term reproducibility. Rovings coated in this way, for example, are made of high-tensile carbon fibres, and used as reinforcing components in the manufacture of modern composite materials. Research programs and laboratory test batches are characterized extensively by methods of surface and solid state analysis such as SEM, TEM, AES, XPS and RAMAN. Analytical investigations are supplemented by strength measurements made at several sites on the fibre coating and on the later application.

Thermochemistry of hydride and phenyl groups on the surface of amorphous silicon dioxide

The thermodynamic properties of hydride and phenyl groups on the surface of amorphous silicon dioxide are investigated in the presented work. The characteristics of the surface silane centers (SiH) are determined from the data obtained by infrared spectroscopy and caloric measurements. The conversions of hydrogen and benzene with the surface are described by thermodynamic calculations at reactions take place in the gaseous phase. To model the reaction between hydrogen and the surface the thermodynamic data for (OH)4−nSin (n=0–4) in the gaseous phase are used. The surface groups and the model molecules are comparable because the thermodynamic characteristics depend only from the local environment. The thermodynamic properties of (OH)3SiC6H5 in the gaseous phase are determined to describe the reaction between benzene and the surface. The predications of these calculations are confirmed by the spectroscopic results. The properties of the surface phenyl groups (SiC6H5) are concluded from these data.

Thermoanalytische Charakterisierung von Adsorbatstrukturen am Beispiel von amorphem Siliciumdioxid

Abstract The present work concentrates on the thermoanalytic characterization of hydride and phenyl groups chemisorbed at the surface of Aerosil 300. Reaction enthalpies for the oxidation of the hydride and phenyl groups are computed from DTA measurements in DSC mode. Linear relations are received between enthalpy and surface concentrations of the species. The molar reaction enthalpy for the hydride groups is classified into elementary steps in a cyclic process and is compared with theoretically expected molar reaction enthalpies for the oxidation of the possible hydride species at the surface. IR-spectroscopic investigations to the silane absorption band illustrate the existence of different hydride species and support the thermodynamic statements. Thermal stability of the phenyl groups is investigated by TG–MS measurements. Pyrolysis of the groups runs in several steps. Investigations to the isotope exchange lead to conceptions across possible dismantling ways.

Thermoanalytic and spectroscopic investigations of hydride structures on the surface of amorphous silicon dioxide

The surface of amorphous silicon dioxide is hydrogenated and the hydride structures obtained are investigated by means of thermoanalytic and infrared spectroscopic measurements. Different hydride groups are found by IR spectroscopy. The results are confirmed by thermal measurements. The experimentally determined bond parameters of the surface silane centers document the differences in comparison with the Si–H bonds of other silanes. Model structures with comparable characteristics of the silicon–hydrogen bond lead to conclusions concerning the surface texture of the adsorbent.