Adhesion-Induced Interactions between Micron-Sized Zirconia or Carbon Spheres and Melamine-Cross-Linked Polyester Surfaces

The thermodynamic work of adhesion between micron-sized zirconia or carbon spheres and polyester-melamine surfaces was determined using the Johnson-Kendall-Roberts (JKR) relationship, after first validating the JKR approach for this system. The calculated works of adhesion for both zirconia and carbon were similar for any given substrate composition and were found to be approximately 35 mJ/m² at low melamine concentrations, close to theoretical predictions. The apparent work of adhesion decreased with increasing melamine concentration, most likely due to the presence of a glassy melamine-rich surface layer, which is not representative of the bulk. The value found for low melamine concentration was assumed to be a true value for cocondensed polyester-melamine, and this was used to estimate surface modulus and the amount of excess melamine in the surface as a function of bulk composition.     

Chemical stability of some poly(amide imide) type polymers

The stability of some heterocyclic poly(amide imide)s in acidic and alkaline medium was compared to the structurally related polyimide and poly(amide imide)s without other heterocyclic groups. All the polymers have high stability in acidic medium. The introduction of additional heterocycles such as 1,3,4-0xadiazole or phenylquinoxaline into the macromolecular chain of a poly(amide imide) increases substantially the resistance to alkaline medium. Polyamides containing imide rings only in the side chain are more stable to hydrolysis than related polyamide having imide units in the main chain.     

Thermomechanical and thermodilatometric analysis of green alumina porcelain

A modulated force thermomechanical analysis (mf-TMA) and thermodilatometric analysis (TDA) of the green ceramic mixture of kaolin (27 wt.%), Al₂O₃ (50 wt.%) and feldspar (23 wt.%) up to 1000 °C is presented. The mf-TMA reflects changes during heating the green ceramics with higher sensitivity than TDA. Discrepancies between mf-TMA and TDA revealed that the elastic behavior of the green porcelain samples is determined most importantly by processes on the crystal boundaries (escaping of the water molecules at the low temperatures up to 150 °C and solid state sintering at the temperatures above 450 °C). Processes in the crystal interiors (e.g. dehydroxylation) have a lesser function. Thermodilatometric results depend more on the processes which take place inside the crystals than on the processes on the crystal surfaces.     

Isotactic and syndiotactic polypropylene/multi-wall carbon nanotube composites: synthesis and properties

Isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) nanocomposites containing 0.1–3.5 wt.% multi-wall carbon nanotubes (MWCNTs) have been synthesized via in situ polymerization method with the use of C₂- and C_s- symmetry zirconocenes activated by methylaluminoxane (MAO) in liquid propylene medium. Fracture morphology studies by SEM reveal different MWCNT dispersion efficiency in various polymer matrices, which arises from the catalytic peculiarities of the composite synthesis. Considerable Young’s modulus enhancement of iPP and sPP (25–66%) takes place even at low MWCNT loadings (below 0.5 wt.%). The obtained nanocomposites can find use as efficient electromagnetic shielding materials and microwave absorbing filters due to relatively low permittivity values and considerable dielectric losses in microwave range. Calorimetry data demonstrate that MWCNTs exert evident influence as nucleating agents causing the rise of iPP and sPP crystallization temperature. Considerable retardation effect on iPP thermal oxidative degradation has been observed: the temperature of maximal weight loss rate rises by ~52 °C upon incorporating only 1.4 wt.% MWCNTs.     

Transient accident analysis of a supercritical carbon dioxide Brayton cycle energy converter coupled to an autonomous lead-cooled fast reactor

The supercritical carbon dioxide (S-CO₂) Brayton cycle is a promising advanced alternative to the Rankine steam cycle and recuperated gas Brayton cycle for the energy converters of specific reactor concepts belonging to the U.S. Department of Energy Generation IV Nuclear Energy Systems Initiative. A new plant dynamics analysis computer code has been developed for simulation of the S-CO₂ Brayton cycle coupled to an autonomous, natural circulation lead-cooled fast reactor (LFR). The plant dynamics code was used to simulate the whole-plant response to accident conditions. The specific design features of the reactor concept influencing passive safety are discussed and accident scenarios are identified for analysis. Results of calculations of the whole-plant response to loss-of-heat sink, loss-of-load, and pipe break accidents are demonstrated. The passive safety performance of the reactor concept is confirmed by the results of the plant dynamics code calculations for the selected accident scenarios.     

Prof. Dr.-Ing. Dr. h. c. Franz Kollmann Zum 65. Geburtstag

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