Transportní procesy v reaktivních systémech

Transport processes i reactive systems

habilitation thesis

Czech

C-C kompozity a huminové látky jsou vzájemně srovnány na základě v nich probíhajících přenosových jevů.

This work deals with reaction and transport processes in two various reactive systems: carbon-carbon composites and humic acids. Carbon-carbon composites are progressive synthetic materials for special applications. Humic acids are nature substances, which occur in soils, coals, peat and water sediments. Although these two systems are really different, the processes in their preparation or function can be characterized generally as a chemical reaction coupled with transport phenomena. In first part the liquid impregnation of carbon-carbon composites is studied in detail. The most important process in liquid impregnation is momentum transfer. Its velocity and efficiency is dependent on precursor and composite properties and impregnation conditions. This process is very sensitive to concentration and temperature. Viscosity of heated precursor is generally low but high temperature causes its cross-linking and viscosity can increase. Low concentrated precursor flows well but the amount of added matrix after following re-curing and re-carbonization is not sufficient. To decrease precursor cross-linking rate during infiltration and fill effectively composite porous structure the optimal impregnation conditions are proposed on the basis of viscosity measurement. The influence of impregnation conditions on rheological behaviour of polymer precursor and impregnation efficiency is discussed. Porous structure of carbon-carbon composite is analyzed by means of optical microscopy. Pores, voids and cracks are divided into three groups according their size and shape and described using simple models. Humic acids and their interactions with metal ions are studied in three various colloidal systems: suspensions, sols and gels. Diffusion is main transport process in mixing systems. In contrast to polymer precursor high chemical affinity is one of the most important properties of humic acids. They play the significant role in natural systems where they can immobilize toxic heavy metals. New model which includes production of hydrogen ions from carboxylic and phenolic groups is derived for mathematical description of adsorption of metal ions on solid humic acids. Probable mechanism of interactions of metal ions with humic sols is proposed and discussed. Humic gel is used as model system for study of diffusion because it can be prepared with defined size and shape. This fact is very important for choice of initial and boundary conditions and mathematical description of whole process. Final part of habilitation thesis takes heed of similarities between both studied systems. Transport processes in both systems can be described using similar mathematical equations. But requirements for their applications are different. While polymer precursor infiltrates in composite porous structure and then it converts to carbon matrix during composite preparation, the final product should be inert in its applications. All these processes proceed in material history. On the other hand humic acids can function in nature because of their unique chemical structure, conformation variability and chemical reactivity. But also humic acids have their own history which they were formed during...

C-C kompozity, huminové kyseliny, transportní jevy

C-C composite, humic acids, transport phenomena

KLUČÁKOVÁ, M.

1. 1. 2004

Brno

142