Sintering of Particulate Composites under a Uniaxial Stress

The sintering of particulate composites consisting of a finegrained zinc oxide matrix and <10 vol% of coarse silicon carbide inclusions was investigated at 725°C under a uniaxial stress of ⋍250 kPa. Data for the densification and creep rates of the composite were compared with those for the unreinforced matrix. The inclusions cause a drastic reduction in the measured densification and creep rates. They have a greater effect on the densification process, however; the ratio of the densification rate to the creep rate of the composite is approximately half that of the unreinforced compact. The factors that cause the reduction in this ratio are present from the very early stage of sintering.     

Influence of Nd2O3 Doping on the Reaction Process and Sintering Behavior of BaCeO3 Ceramics

The influence of Nd₂O₃ doping on the reaction process and sintering behavior of BaCeO₃ is investigated. Formation of BaCeO₃ is initiated at 800°C and completed at 1000°C. When Nd₂O₃ is added to the starting materials, the formation of BaCe_1–xNd_xO_3–δ is delayed and the temperature for complete reaction is increased to 1100°C. Only a BaCe_1-xNd_xO_3–δ solid solution with an orthorhombic crystal structure is present in the specimens for x ≤ 0.1. A secondary phase rich in Ce and Nd is formed within grains and at grain boundaries, when the Nd₂O₃ content is greater than the solubility limit (x ≥ 0.2). Pure BaCeO₃ is difficult to sinter, even at 1500°C, and only a porous microstructure could be obtained. However, doping BaCeO₃ with Nd₂O₃ markedly enhances its sinterability. The enhancement of the sinterability of Nd₂O₃-doped specimens at x ≤ 0.1 is attributed to the increase in the concentration of oxygen ion vacancies, which increases the diffusion rate. At x ≥ 0.2, the grain size is abnormally coarsened, which is caused by the formation of a liquid phase. While this liquid phase accelerates sintering, its beneficial effect on densification is counteracted by the segregation of the secondary grain-boundary phase which inhibits sintering.     

Interactions between measures for the support of electricity from renewable energy sources and CO2 mitigation

As Europe wants to move towards a secure, sustainable and competitive energy market, it has taken action, amongst other, to support electricity from renewable energy sources (RES-E) and to mitigate CO₂ emissions. This paper first qualitatively discusses price- and quantity-based measures for RES-E deployment as well as CO₂ mitigation. Next, a simulation model is developed to quantitatively discuss the effects of a tradable green certificate system, a premium mechanism, a tradable CO₂ allowance system and a CO₂ tax on both RES-E deployment and CO₂ mitigation. A three-regional model implementation representing the Benelux, France and Germany is used. In a first step of simulations, all measures are implemented separately. In a second step, combinations of both RES-E supporting and CO₂ mitigating measures are simulated and discussed. Significant indirect effects are demonstrated, especially for RES-E supporting measures on the reduction of CO₂ emissions. Interactions between different measures show that the price level of quantity-based measures can be strongly influenced.     

Co-continuous metal-ceramic nanocomposites

A room temperature technique was developed to produce continuous metal nanowires embedded in random nanoporous ceramic skeletons. The synthesis involves preparation of uniform, nanoporous ceramic pre-forms and subsequent electrochemical metal infiltration at room temperature, so to avoid material incompatibilities frequently encountered in traditional high-temperature liquid metal infiltration. Structure and preliminary evaluations of mechanical and electronic properties of copper/alumina nanocomposites are reported.     

Mutation analysis of the nerve specific promoter of the peripheral myelin protein 22 gene in CMT1 disease and HNPP

We analysed the nerve specific promoter of the peripheral myelin protein 22 gene (PMP22) in a set of 15 unrelated patients with Charcot-Marie-Tooth type 1 disease (CMT1) and 16 unrelated patients with hereditary neuropathy with liability to pressure palsies (HNPP). In these patients no duplication/deletion nor a mutation in the coding region of the CMT1/ HNPP genes was detected. In one autosomal dominant CMT1 patient, we identified a base change in the non-coding exon 1A of PMP22 which, however, did not cosegregate with the disease in the family. This study indicates that mutations in the nerve specific PMP22 promoter and 5' untranslated exon will not be a common genetic cause of CMT1A and HNPP.     

Spinel formation in sodium-β″-alumina

Transmission electron microscopy of sodium-beta″-alumina shows that during observation, a large amount of intergrowth defects form rapidly along the 00.1 planes. These defects are identified as spinel intergrowths formed resulting from loss of Na₂O constituting the conduction plane in sodium-β″-alumina. These artifacts complicate significantly the detailed interpretation of non-stoichiometry in β″-aluminas.     

Some geometrical aspects of breakdown of sodium beta alumina

The breakdown of single and polycrystalline sodium beta alumina was studied at 300°C and at room temperature. The breakdown in polycrystals involves a propagation of a highly-branched sodium-filled crack network. In single crystals the fracture surface could be studied directly. It was found that the crack network is filled with sodium from the crack faces rather than the crack tip.