Entwicklung von Siliciumcarbid-Verbundwerkstoffen

Development of silicon carbide composites . This paper describes the production of fibre-reinforced SiC composites applying the methods of chemical vapour impregnation (CVI), reaction bonding by liquid silicon impregnation (RB-SiC), and impregnation with subsequent polymerisation and thermal decomposition of organosilicon compounds. The chemical and physical fundamentals of these processes are discussed. Composites of different fibre/matrix combinations are introduced; the most promising combinations can be selected from the experimental results presented.     

Entwicklung von Kristallisatoren

Development of crystallizers . The control of the crystallization kinetics and the spatial variation of the crystal mass are of decisive importance for the operation of industrial crystallizers. The influence of micro- and macro-attrition is demonstrated with particular reference to collisions with impeller blades and to breakage of crystals between impeller and draft tube. Spatial variations of supersaturation and crystal mass within the crystallizer have been shown to influence crystal size distribution. These variations are described by physical and mathematical models. Crystal size distributions measured in both pilot and industrial crystallizers show that simulation with the proposed models is very reliable. A model approach provides valuable support for the development of industrial crystallizers and also for the development of control using microprocessors.     

Theorie des Ultraschallabbaus auf der Grundlage des Perlschnurmolekül-Modells

The progress of ultrasonic degradation of polymers in solution can be described theoretically by the aid of the model of pearlstring molecules. According to this molecular model macromolecules are built up like a pearl necklace of so-called tertiary structural units. There is correlation between molecular weight of structural units to be obtained by measuring electron micrographs and limiting molecular weight after ultrasonic degradation. Experimental results suggest that molecules resembling a string of pearls are broken at the chain between its spherical units. Two imaginable ways of degradation mechanism are discussed: fragmentary and stepless depolymerization. In the first case the chain is broken between its structural units in several steps; in the second case the pearlstring molecule is broken to all its units in one step. Mathematical consideration has provided an equation for the stepless mechanism. By the aid of this equation the complete progress of depolymerization can be calculated if the limiting molecular weight after ultrasonic degradation is known. On the other hand the limiting molecular weight may be calculated if the beginning of degradation is known. Stepless and fragmentary degradation can be distinguished by comparing the experimentally determined depolymerization with the calculated one.     

Zur optimierung der Polymerfraktionierung auf der Grundlage von Lösungsgleichgewichten in Lösungsmittel-Fällungsmittel-Systemen

The phase separation behavior of dilute polydisperse polymer solutions primarily depends on the partial concentration of each polymer component. So the equilibrium data obtained by turbidimetric titration with “calibration” fractions and their mixtures can be used for the construction of a solubility diagram (Claesson-diagram) which generally allows to describe fractionation processes. It can be shown that the characteristic features of precipitation fractionations can well be derived from the solubility diagram. This diagram then offers the possibility for a complete discussion of parameter variation (concentration, step of γ-variation, process-scheme, temperature, solvent/nonsolvent-system) on the efficiency of a fractionation step. On one hand these results correspond – as for the concentration variation – to well known experimentell experiences. On the other hand it is possible for the first time to give definite predictions for the influence of temperature and the solvent/nonsolvent system. The temperature selection can be shown to be inconsiderable for the separation effect. The usual characterization of solvents and nonsolvents as “good” or “poor” is absolutely insufficient, if not misleading, for there is no connection between these properties and the shape of the solubility diagram. Based on the analysis of the single parameters the optimum conditions for the preparation of narrow preparation of narrow precipitation fractions can be derived.     

Entwicklung von Biopolymermembranen mit funktionellen Eigenschaften

The manifold possibilities to apply coatings made from biopolymers require the design of such membranes with functional properties. The influence of different additives and process parameters on the mechanical stability and penetrability of biopolymer membranes, especially of films based on alginates, is given in this work. Spheres of alginates made by the falling droplet method were used as model system. Besides different effects of additives it turned out that the mechanical stability and the penetrability could be influenced independently.     

Entwicklung und Projektierung von Anlagen zur Hochdruck-Extraktion von Naturstoffen

Development and planning of plant for the high-pressure extraction of natural products . Important criteria in the designing of plant for the recovery of carrier or extract are reviewed, especially for the extraction of natural products with supercritical CO₂. The quantities to be determined in the planning of a large-scale plant are outlined and a typical process, the extraction of spices, is discussed in detail. The plant components and assemblies are presented together with their particular process engineering and construction characteristics. Finally, the thermodynamic aspects are dealt with in more detail and ways of optimizing a large-scale plant and reducing the power consumption are outlined. Particular attention is paid to the question of optimization regarding the most economic method of operation of such a plant in the future.