Filtern
Dokumenttyp
Schlagworte
- Gamma irradiation (3)
- Polyethylene (3)
- Crosslinking (2)
- HMW (2)
- HMW-PE (2)
- UHMW-PE (2)
- (U)HMW-PE (1)
- ATH (1)
- Absorption (1)
- Aluminium trihydroxide (1)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (8)
High and ultra-high molecular weight polyethylenes were gamma-irradiated with doses up to 600 kGy. The changes in the material properties were analysed using DSC, DMA, IR spectroscopy, as well as measurements of density and insoluble content. The irradiation led to an increase of the degree of crystallinity because of chain scissions during irradiation, leading to shorter and thus more mobile chains. Both the plateau value of the shear modulus G′ and the insoluble content increased with Irradiation dose, indicating the formation of additional crosslinks. Furthermore, IR spectroscopy revealed irradiation induced oxidation and the formation of double bonds, indicating that some of the hydrogen atoms responsible for the neutron shielding capability have been released.
Elastomers are widely used as the main sealing materials for containers for low and intermediate level radioactive waste and as an additional component to metal seals in spent fuel and high active waste containers. The safe encapsulation of the radioactive container inventory has to be guaranteed according to regulation and appropriate guidelines for long term storage periods as well as for temperatures as low as -40°C during transport. Therefore, the understanding of failure mechanisms that lead to leakage at low temperatures is of high importance. It is known that the material properties of elastomers are strongly temperature dependent. At low temperatures, this is caused by the rubber-glass transition (abbreviated: glass transition). During continuous cooling, the material changes from a rubber-like entropy elastic to a stiff energy elastic behaviour, which allows nearly no strain or retraction. Hence, rubbers are normally used above their glass transition, but the minimum working temperature limit is not defined precisely; this can cause problems during the above noted applications. Therefore, the lower operation temperature limit of elastomer seals must be determined in dependence of the material properties. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are combined with standardised measurements to determine the compression set according to ISO 815. To reduce the test time of the standard tests, a faster technique than normally used was developed. Additionally, the breakdown temperature of the sealing function of complete O ring seals was measured in a component test set-up to compare it with the results of the other tests. The experimental set-up is capable of measuring the leakage rate at low temperatures by the pressure rise method. A fluorocarbon rubber (FKM) was selected for this investigation as it is often used for radioactive waste containers. The materials (seals and test sheets) were purchased from a commercial seal producer.
Rubbers are widely used as main sealing materials for containers for low and intermediate level radioactive waste and as additional component to metal seals in spent fuel and high active waste containers. The save encapsulation of the radioactive container inventory has to be guaranteed according to legislation and appropriate guidelines for long term storage periods as well as down to temperatures of -40 °C during transport.
Therefore the understanding of failure mechanisms that lead to leakage at low temperatures is of high importance.
It is known that the material properties of rubbers are strongly temperature dependent. At low temperatures this is caused by the rubber-glass transition (abbr. glass transition). During continuous cooling the material changes from rubber-like entropy-elastic to stiff energy-elastic behaviour, that allows nearly no strain or retraction, due to the glass transition. Hence rubbers are normally used above their glass transition but the minimum working temperature limit is not defined precisely, what can cause problems during application. Therefore the lower operation temperature limit of rubber seals should be determined in dependence of the material properties.
The results of Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) are combined with the results of standardized measurements as the compression set according to ISO 815. To reduce the test time of the standard tests a faster technique was developed.
Additionally, the breakdown temperature of the sealing function of complete O-ring seals is measured in a component test setup to compare it with the results of the other tests. The experimental setup is capable of measuring the leakage rate at low temperatures by the pressure rise method.
A fluorocarbon rubber (FKM) was selected for this investigation as it is often used for radioactive waste containers. Some materials (seals and test sheets) were purchased from a commercial seal producer and some materials were compounded and cured at BAM in form of rubber sheets.
Effect of well dispersed amorphous silicon dioxide in flame retarded styrene butadiene rubber
(2013)
Spherically shaped amorphous silicon dioxide with broad size particle distribution was used in combination with aluminium trihydroxide (ATH) in styrene butadiene rubber composites. The pyrolysis, flammability, fire properties, flame spread and gas diffusion were investigated. The kind and amount of ATH, but in particular the fine silicon dioxide chosen as an additive, influenced the thermal decomposition and fire behaviour of styrene butadiene rubber composites. Gravimetric gas sorption measurements showed that the gas diffusion was systematically lower with silicon dioxide. The initial pyrolysis gas release was hindered, increasing the temperature at which decomposition begins as well as the ignition time in fire tests. During combustion, ATH and silicon dioxide accumulate on the surface of the specimen, forming a residual protective layer. A reduced peak heat release rate and fire spread were observed. The addition of a special kind of silicon dioxide is proposed to play a key role in optimising fire retardancy.