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1. Abstract Worldwide, lithium rich ceramic pebbles are being developed to be used as tritium breeders inside future fusion reactors. Upon irradiation, the pebbles will produce tritium which will be used alongside deuterium to fuel the fusion reaction. It is essential that these pebbles are of sufficient quality to withstand the various forces experienced within the wall of the reactor. Currently, a melt-based process is used at the Karlsruhe Institute of Technology for the production of pebbles composed of lithium orthosilicate with a secondary strengthening phase of lithium metatitanate. Recent studies have focused on incorporating lithium orthogermanate, which forms a solid solution with lithium orthosilicate. Various compositions were used to perform fundamental studies to determine phase transitions as well as melting points for processing. The melt-based KALOS process was then used to produce pebbles with selected compositions. Thereafter the pebbles underwent a series of characterisation tests including microstructure and surface analysis using REM as well as elemental mappings using EDX. XRD was used for determining the crystal structures present in various compositions and the unit cell volumes. The measurements showed that the unit cell volume of each structure linearly depends on the composition. Additionally, pebbles were held at reactor relevant temperatures to determine any changes to the mechanical strength. It was found that pebbles with 30 mol% lithium metatitanate and a lithium orthosilicate/orthogermanate ratio in the range of 1.5–4 showed an increased strength as well as good thermal stability and may have the potential to be used as tritium breeders.

Dynamic models are used to assess the impact of three types of face masks–cloth masks, surgical/procedure masks and respirators–in controlling the COVID-19 pandemic in the United States. We showed that the pandemic would have failed to establish in the US if a nationwide mask mandate, based on using respirators with moderately-high compliance, had been implemented during the first two months of the pandemic. The other mask types would fail to prevent the pandemic from becoming established. When mask usage compliance is low to moderate, respirators are far more effective in reducing disease burden. Using data from the third wave, we showed that the epidemic could be eliminated in the US if at least 40% of the population consistently wore respirators in public. Surgical masks can also lead to elimination, but requires compliance of at least 55%. Daily COVID-19 mortality could be eliminated in the US by June or July 2021 if 95% of the population opted for either respirators or surgical masks from the beginning of the third wave. We showed that the prospect of effective control or elimination of the pandemic using mask-based strategy is greatly enhanced if combined with other nonpharmaceutical interventions (NPIs) that significantly reduce the baseline community transmission. By slightly modifying the model to include the effect of a vaccine against COVID-19 and waning vaccine-derived and natural immunity, this study shows that the waning of such immunity could trigger multiple new waves of the pandemic in the US. The number, severity and duration of the projected waves depend on the quality of mask type used and the level of increase in the baseline levels of other NPIs used in the community during the onset of the third wave of the pandemic in the US. Specifically, no severe fourth or subsequent wave of the pandemic will be recorded in the US if surgical masks or respirators are used, particularly if the mask-use strategy is combined with an increase in the baseline levels of other NPIs. This study further emphasizes the role of human behavior towards masking on COVID-19 burden, and highlights the urgent need to maintain a healthy stockpile of highly-effective respiratory protection, particularly respirators, to be made available to the general public in times of future outbreaks or pandemics of respiratory diseases that inflict severe public health and socio-economic burden on the population.Author summaryWe developed and used dynamic models to assess the role of highly-effective face coverings on the control and mitigation of the COVID-19 pandemic in the US. The study indicates that implementing and sustaining mask mandates is useful in containing diseases like COVID-19. Additionally, the study suggests that prioritizing the use of respirators is more effective in combating the disease than using other mask types. Specifically, the COVID-19 pandemic would have been prevented from being established in the US if four in every five Americans started wearing respirators during the first two months of the pandemic. The study further shows that COVID-19 can be eliminated in the US if a universal masking strategy that emphasizes respirators, requiring only 23% compliance, is combined with other nonpharmaceutical interventions that can reduce community transmission by 20%. Furthermore, the daily COVID-19 death rate can be completely suppressed by June 2021 if 95% of the population consistently use respirators. The elimination will extend to January 2022 if cloth masks were adopted instead. We conclude that stockpiling and distributing highly-efficient face coverings, notably respirators, will be vital in effectively curtailing future epidemics and pandemics of respiratory diseases.

The paper reviews the current status of development and qualification of the HCPB TBM’s functional materials, namely, Li-ceramic breeder and Be multiplier materials. The main functional and performance requirements for both functional materials are overviewed. The main results and outcomes of the post-irradiation examinations (PIE) of Li-ceramic breeder and Be/beryllides materials irradiated in HIDOBE and HICU irradiation campaigns are presented aiming at determination of the materials’ performance, properties and characteristics under neutron irradiation, like e.g. morphology and microstructure, tritium retention/release characteristics, mechanical properties. Fabrication of the advanced ceramic breeder material, containing lithium orthosilicate with addition of lithium metatitanate phase in order to improve its mechanical properties, is described. Results of characterization of this advanced ceramic breeder in terms of mechanical properties, porosity, morphology and effective thermal conductivity of a pebble bed are overviewed. In addition, results of characterization of the reference 1 mm Be pebbles produced by Rotation Electrode Process are presented in terms of their microstructure, tritium release characteristics and interaction with air and steam. A necessity to realize in the future a new irradiation experiment for the functional materials, LIBERTI experiment, is discussed in the conclusions.

Uniaxial compression test (UCT) experiments were conducted along with Discrete Element Method (DEM) simulations. The objective was to investigate the effect of the material properties and of the blanket operational parameters (in terms of packing factor, pebble material/size, compressive load and bed height) on the mechanical response of breeder beds subjected to cyclic loading. UCTs were performed with the EU advanced and reference ceramic breeder materials. To investigate the wall effects on the cyclic response of packed beds, a parametric study was performed varying the bed height to pebble size ratio (H/d). To this end monosized commercial zirconia pebbles with different sizes were also used. The numerical experiments were carried out with the KIT-DEM code on pebble assemblies using mixed boundary conditions (periodic and rigid planes). The influence of the bed height, pebble size and pebble material were systematically evaluated to gain an insight about their influence on the macro and micro response of the beds. Thanks to the microscale numerical modelling the macroscale response is presented together with the micro response at the pebble scale. Good agreement was found between experiments and simulations and thus, the KIT-DEM was confirmed to be a reliable predictive tool for the study breeder bed related problems.

Apparent increases in the size of cerebral metastases after stereotactic radiosurgery (SRS) can be caused by pseudoprogression or true disease progression, which poses a diagnostic challenge at conventional MRI. The purpose of this study was to assess whether interval change in DWI and perfusion MRI parameters can differentiate pseudoprogression from progressive disease after treatment with SRS.Patients with apparent growth of cerebral metastases after SRS treatment who underwent pre- and post-SRS DWI, dynamic susceptibility contrast (DSC)-MRI, and perfusion dynamic contrast-enhanced (DCE)-MRI were retrospectively evaluated. Final assignment of pseudoprogression or progressive disease was determined at 6-month follow-up imaging using the Response Assessment in Neuro-Oncology Brain Metastases criteria. Mean values of apparent diffusion coefficient (ADC), DCE-MRI-derived volume transfer constant (KOf 102 cerebral metastases evaluated, 32 lesions in 29 patients met our inclusion criteria. The mean duration of follow-up was 7.2 months (range, 6-14 months). Twenty-two lesions were determined as pseudoprogression, and 10 lesions were determined as progressive disease using the Response Assessment in Neuro-Oncology Brain Metastases criteria at 6-month follow-up MRI. The interval change pattern of our imaging parameters matched the expected patterns of treatment response for ADC (23/32 lesions; 72%; p = 0.055; odds ratio, 5.1), KPseudoprogression can be distinguished from disease progression in cerebral metastases treated with SRS via an interval decrease in relative CBV and K

The pebble properties of novel two-phase Li 4 SiO 4 pebbles of 1 mm diameter with additions of Li 2 TiO 3 , LiAlO 2 or Li x La y TiO 3 are evaluated in this work as a function of the second phase concentration and the microstructure of the pebbles. The characterization focused on the mechanical strength, microstructure and open as well as closed porosity. Therefore crush load tests, SEM analyses as well as helium pycnometry and optical image analysis were performed, respectively. This work shows that generally additions of a second phase to Li 4 SiO 4 considerably improve the mechanical strength. It also shows that the fabrication processes have to be well-controlled to achieve high mechanical strengths. When Li 2 TiO 3 is added in different concentrations, the determinant for the crush load seems to be the open porosity of the pebbles. The strengthening effect of LiAlO 2 compared to Li 2 TiO 3 is similar, while additions of Li x La y TiO 3 increase the mechanical strength much more. Yet, Li 4 SiO 4 and Li x La y TiO 3 react with each other to a number of different phases upon sintering. In general the pebble properties of all samples are favorable for use within a fusion breeder blanket.

Wet-chemical fabrication processes are highly adaptable to a wide range of raw materials and are therefore well suited for evaluating new material compositions. Here the established emulsion method was modified to fabricate novel two-phase Li 4 SiO 4 pebbles of 1 mm diameter with additions of Li 2 TiO 3 , LiAlO 2 or Li x La y TiO 3 . As the lithium density of the latter two compounds is relatively low, only moderate contents were added. The Li 2 TiO 3 additions, however, cover the full compositional range. The fabrication process was characterized with regard to its constancy and aptness for the anticipated pebble compositions by optical pebble size measurements. Also the phase content and the elemental composition of the fabricated pebbles were analyzed by XRD and ICP-OES combined with XRF, respectively. This work shows that the emulsion method is an appropriate method to produce pebbles with the anticipated Li 2 TiO 3 and LiAlO 2 concentrations in a Li 4 SiO 4 matrix. However, Li 4 SiO 4 and Li x La y TiO 3 react with each other to a number of different phases. To evaluate the activation properties of the pebbles, FISPACT calculations with a DEMO relevant neutron source are applied as well. The addition of aluminum seems to be unfavorable for a fusion application, but moderate concentrations of lanthanum can be tolerated.

All solid breeder concepts considered to be tested in ITER (International Thermonuclear Experimental Reactor), make use of lithium-based ceramics in the form of pebble-packed beds as tritium breeder. A thorough understanding of the thermal and mechanical properties of the ceramic pebble beds under fusion relevant conditions is essential for the design of the breeder blanket modules of future fusion reactors. In this study, the effect of cyclic loading on the mechanical behaviour of pebble bed assemblies was investigated using a Discrete Element Method (DEM) code. The numerical simulations were compared with the experimental outcomes. The results of numerical simulations show that the pebble size distribution affects noticeably the stress-strain behaviour of the assemblies. A good qualitative agreement between experimental and simulation results was found in terms of difference between residual strains of consecutive cycles. An increase of the oedometric modulus with the compressive load was observed for all investigated compositions in both experimental and DEM simulations. The numerical results show an increase of the oedometric modulus (E) with progressive compaction of the assemblies due to the cycling loading, while no significant influence of the pebbles size distribution was observed.

In advanced designs of DEMO breeding blankets with ceramic breeder, the structural material EUROFER is in direct contact with the pebbles of the ceramic breeder (Li4SiO4 + Li2TiO3) that results in a loss of constituent elements in the ceramic and the formation of a corrosion layer on EUROFER under operation relevant conditions. The impact of this corrosion attack on damage mechanisms which are significantly influenced by microstructural changes at the surface, in particular fatigue, needs to be considered in the design of affected components and is therefore investigated within the work reported here. Fatigue specimens made out of EUROFER in unconstrained contact to ceramic breeder pebbles were exposed to purge gas conditions for different durations. The chemical surface attack observed after the exposure is characterized by round stains, partly even round dimples, consisting of concentric diffusion zones which meet in case of the long exposure time forming an almost closed corrosion multi-layer. The impact of this attack on the fatigue behavior was subsequently investigated by performing strain-controlled low cycle fatigue (LCF) tests at 550 °C. To cover the scatter expected for the fatigue lifetime, a sufficient number of LCF experiments were conducted. The results show significant reduction of the fatigue lifetime, which quantitatively depends on the level of the attack/exposure time as well as the level of the applied load/strain amplitude.

The former EU reference lithium orthosilicate based breeder pebbles were exposed to neutron irradiation in the HICU (High neutron fluence Irradiation of pebble staCks for fUsion) experiment to test their stability and tritium release properties under DEMO relevant conditions. The samples, varying by three different Li-6 contents, were exposed to irradiation at two different temperatures and the pebbles were either pre-compacted or not. This second part of the post-irradiation examination is focussing on the tritium release behaviour of the ceramic breeder pebbles. The irradiation temperature has the strongest influence on the tritium release behaviour. The tritium inventory is significantly higher for samples that were irradiated at low temperatures. A clear trend regarding higher release rates with increasing Li-6 content was not observed. Tritium is released in a multi-staged process as HTO, HT or corresponding fragments. Fits based on the Wigner-Polanyi equation suggest that recombination reactions of tritium with adsorbed species on the pebble’s surface play the dominant role in the release process. However, the probability for the recombination of two adsorbed T-species on the surface seems to be too low, as no reliable signal for T2 was detected.

The HICU (High neutron fluence Irradiation of pebble staCks for fUsion) experiment was performed in the High Flux Reactor (HFR) in Petten, NL, in order to irradiate candidate tritium breeder materials in a fusion relevant environment. The presented work focuses on the post-irradiation examination of the irradiated lithium orthosilicate based breeder pebbles. The pebble samples showed three different contents of Li-6 and were irradiated at two different temperatures and in mechanically constrained and unconstrained state. In this particular publication, the influences of the irradiation conditions on the pebble morphology, microstructure, porosity, and mechanical strength are addressed. The results indicate that in general a high irradiation temperature seems to be advantageous for maintaining the mechanical strength of the irradiated pebbles. A higher mechanical strength and a significantly lower closer porosity is observed for samples that were irradiated at high temperatures in comparison to pebbles that were irradiated at low temperatures. The effects on the pebble properties with respect to the Li-6 content are small in contrast to effects of the irradiation temperature. With an increased Li-6 content, no deterioration of the material properties was observed, especially for samples irradiated at high temperatures.

The long-term thermal stability of advanced ceramic breeder pebbles consisting of lithium orthosilicate (Li4SiO4) and additions of lithium metatitanate (Li2TiO3) was tested in an annealing experiment at 900 °C for up to 128 days. Different gas atmospheres were used to test the influence of moisture in the purge gas. Li4SiO4 pebbles including nominally 25, 30, and 35 mol% Li2TiO3 were investigated with regard to their chemical composition, microstructure, porosity, and mechanical properties after predetermined time intervals and at the end of the experiment. No lithium loss and no secondary phases were detected. The microstructures, porosities and mechanical stabilities did not show significant changes over time. Moreover, moisture in the purge gas atmosphere has no negative influence on the material properties.

Worldwide research and development has been performed on solid breeder materials as a tritium source for future fusion power reactors. These ceramic materials will be used in the International Thermonuclear Experimental Reactor (ITER) to check their performance and screen their applicability for use in fusion blankets. While all members of the ITER project are engaged in the development of solid breeder blanket concepts, five are actively involved in the fabrication of tritium breeding ceramics for the different test blanket modules to be tested in ITER. All solid breeder concepts proposed for ITER are based on the use of ceramics in the form of pebble beds with pebble diameters of about 1 mm or smaller. Although alternative materials are still under investigation, the main candidates for tritium breeding ceramics are lithium metatitanate and lithium orthosilicate. Recent developments and preparatory work for ITER are presented.

Background and Purpose— Patients with acute ischemic stroke are at increased risk of developing parenchymal hemorrhage (PH), particularly in the setting of reperfusion therapies. We have developed a predictive model to examine the risk of PH using combined magnetic resonance perfusion and diffusion parameters, including cerebral blood volume (CBV), apparent diffusion coefficient, and microvascular permeability (K2). Methods— Voxel-based values of CBV, K2, and apparent diffusion coefficient from the ischemic core were obtained using pretreatment magnetic resonance imaging data from patients enrolled in the MR RESCUE clinical trial (Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy). The associations between PH and extreme values of imaging parameters were assessed in univariate and multivariate analyses. Receiver-operating characteristic curve analysis was performed to determine the optimal parameter(s) and threshold for predicting PH. Results— In 83 patients included in this analysis, 20 developed PH. Univariate analysis showed significantly lower 10th percentile CBV and 10th percentile apparent diffusion coefficient values and significantly higher 90th percentile K2 values within the infarction core of patients with PH. Using classification tree analysis, the 10th percentile CBV at threshold of 0.47 and 90th percentile K2 at threshold of 0.28 resulted in overall predictive accuracy of 88.7%, sensitivity of 90.0%, and specificity of 87.3%, which was superior to any individual or combination of other classifiers. Conclusions— Our results suggest that combined 10th percentile CBV and 90th percentile K2 is an independent predictor of PH in patients with acute ischemic stroke with diagnostic accuracy superior to individual classifiers alone. This approach may allow risk stratification for patients undergoing reperfusion therapies. Clinical Trial Registration— URL: https://www.clinicaltrials.gov . Unique identifier: NCT00389467.

Purpose: Collateral flow is an independent predictor of reperfusion and infarct size in patients with acute ischemic stroke (AIS). MR perfusion time-maps show delayed perfusion but unable to differentiate antegrade from collateral flow if used alone. Using a multiparametric approach, we aimed to identify a perfusion biomarker that can represent the extent of collaterals in comparison to angiographic findings. Methods: AIS patients with MCA proximal occlusion who had baseline MRI and cerebral angiography included. MR perfusion data were processed by Bayesian method to generate arterial tissue delay (ATD) maps at thresholds of 2 & 6 seconds. The volume of delayed perfusion (Vol-ATD 2sec ), critical hypoperfusion (Vol-ATD 6sec ), and hypoperfusion (Vol-ATD 2sec-6sec ) in addition to corresponding rCBV and rCBF were calculated. Baseline angiography collaterals were dichotomized to poor (TICI ≤2a) or good collaterals (TICI≥ 2b). The association of perfusion biomarkers and status of collaterals was assessed by repeated measure of analyses and receiver operating characteristic (ROC) to determine the optimal parameters for predicting the status of collaterals. Results: In 37 patients included, 20 had good collaterals on cerebral angiography. After controlling for age, baseline NIHSS and infarct volume, multivariate logistic regression analysis identified rCBV (p=0.001) and hypoperfused volume (Vol-ATD 2sec-6sec ), but not rCBF, Vol-ATD 2sec or Vol-ATD 6sec , as independent predictors of good collaterals. ROC analysis showed AUC of 0.89 (sensitivity/specificity: 85%90%) for rCBV and AUC of 0.78 (sensitivity/specificity: 70%82%) for Vol-ATD 2sec-6sec . Hypoperfused tissue volume (Vol-ATD 2sec-6sec ) x its rCBV, termed hypoperfused tissue collateral index , remained an independent predictor of good collaterals with improved diagnostic accuracy over each measure alone (AUC: 0.96, sensitivity/specificity: 91%100%). Conclusions: Multiparametric MR perfusion can be used to assess the status of collaterals in patients with AIS. Hypoperfused tissue collateral index defined as hypoperfused volume (Vol-ATD 2sec-6sec ) x rCBV is a new perfusion index with diagnostic accuracy of 96% compared to angiographic findings to predict status of collaterals.

One of the technological problems of a fusion reactor is the change in composition and structure of ceramic breeders (Li 4 SiO 4 or Li 2 TiO 3 pebbles) during long-term operation. In this study changes in the composition and microstructure of Li 4 SiO 4 pebbles with 2.5 wt% silicon dioxide additions, fabricated by a melt-spraying process, were investigated after fast electron irradiation ( E = 5 MeV, dose rate up to 88 MGy h −1 ) with high absorbed dose from 1.3 to 10.6 GGy at high temperature (543–573 K) in air and argon atmosphere. Three types of pebbles with different diameters and grain sizes were investigated. Products of radiolysis were studied by means of FTIR and XRD. TSL and ESR spectroscopy were used to detect radiation defects. SEM was used to investigate structure of pebbles. Experiments showed that Li 4 SiO 4 pebbles with a diameter of 500 μm had similar radiation stability as pebbles with diameter α 10.56 of the lithium orthosilicate pebbles at an absorbed dose of 10.56 GGy in air atmosphere is 1.5% and 0.15% at irradiation in dry argon. It has been suggested that changes of radiation stability of lithium orthosilicate pebbles in air atmosphere comparing with irradiated pebbles in argon atmosphere is effect of chemical reaction of lithium orthosilicate surface with air containing – H 2 O and CO 2 in irradiation process. As well as it has been suggested that silicon dioxide – lithium metasilicate admixtures do not affect formation mechanism of radiation defect and products of radiolysis in lithium orthosilicate pebbles.

Within the European Union, slightly hyperstoichiometric lithium orthosilicate has evolved as one of the candidate solid breeder materials for the helium cooled pebble bed blanket, which will be tested in ITER. In the past, several long-term irradiation experiments proved that lithium orthosilicate shows excellent tritium release behavior when purged with helium with 0.1% hydrogen. In this work, short-term irradiation experiments at the High Flux Reactor in Petten with two standard pebble qualities, as-received and heat-treated lithium orthosilicate were carried out to investigate possible differences in tritium release. Since the surface of the pebbles may play a significant role, especially for short-term irradiation, and the mechanism of desorption from the surface determines the chemical form and very likely the release rate of tritium, the aim of this work is to link the chemical composition of the surface to the Thermal Programmed Desorption (TPD) tritium release experiments. Therefore X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were applied to characterize the surface of the unirradiated pebbles and to obtain sputter depth profiles of up to 800 nm. In addition, X-ray diffractometry was used to determine the composition of phases of the samples before and after irradiation.

For the fabrication of Li-6 enriched ceramic breeder materials for ITER, the availability of Li-6 enriched compounds is limited, and metallic Li-6 is the most widely available compound. As metallic lithium cannot be used directly in ceramic fabrication processes, we investigated different syntheses to obtain lithium orthosilicate or lithium metatitanate directly from molten lithium. In exothermic reactions of molten lithium with silicon, silica, or titania, several intermediate or precursor phases were observed under argon that could easily be transformed to the desired ceramic phases by a subsequent heat treatment under air. The reaction steps and the resulting phases were studied by differential scanning calorimetry and X-ray diffractometry. The synthesis from lithium and silicon seems to be especially suited for the production of larger quantities and has the advantage that silicon is available with a very high grade of purity.

Europe has developed two reference tritium breeder blankets concepts for a DEMO fusion reactor: the Helium-Cooled Lithium–Lead and the Helium-Cooled Pebble-Bed. Both will be tested in ITER under the form of Test Blanket Modules (TBMs). The paper reviews the current status of development and qualification of the EU TBMs functional materials; i.e. ceramic solid breeder materials, beryllium/beryllides multiplier materials and Lithium–Lead liquid metal breeder material Pb–15.7Li. For each functional material the main functional/performance requirements with key qualification issues, current status of the R&D activities and the EU development strategy are presented. In the development strategy major steps considered are listed pointing out importance of the ‘Development/qualification/procurement plan’, currently under elaboration, for definition of a roadmap of further activities aiming at delivery of qualified functional materials to be used in the European TBMs in ITER.

In the breeder units (BUs) of the HCPB TBM, the lithium orthosilicate (OSi) pebbles are contained by cooling plates which are made of Eurofer. The assembly of the TBM box and BUs is based on welding processes which require post welding heat treatment (PWHT). According to the proposed TBM manufacture strategy, the BUs will be packed with the OSi pebbles during the TBM assembly; consequently the pebbles and the Eurofer plates will undergo the PWHT. Therefore the objective of this study is to investigate the effect of the PWHT on both Eurofer and OSi and their interaction. The test unit is a Eurofer box packed with OSi pebbles and Eurofer specimens. This test unit and all Eurofer specimens were heat treated inside a furnace which is capable of providing the required heating and cooling rates under a controlled atmosphere of vacuum or argon. Charpy impact and tensile tests of the Eurofer specimens and crush load tests of the OSi pebbles were performed after the heat treatment to investigate any changes in their mechanical properties. The results of these mechanical tests revealed that both materials did not suffer any significant degradation in their mechanical properties or chemical compatibility problems. The metallurgical analyses of both materials showed minimum chemical interaction.

Industrial use of micro components is determined by the availability of efficient manufacturing techniques. While micro injection moulding of plastic is common practice, metal and ceramic powder injection moulding (PIM) still is under development. High-pressure and low-pressure injection moulding methods complement each other ideally, covering the entire spectrum from prototype to large-scale production. With high-pressure PIM, micro gear wheels with diameters

Within the framework of the Collaborative Research Center 499 (SFB 499) of the German Research Foundation (DFG), one task was the development of a zirconia micro turbine as a demonstrator tool to enhance the interaction of the participating workgroups. This case study describes the evolution of the demonstrator and experiences gained with the design and the manufacturing of a micro device. Although it was not the aim of this basic research project to develop a commercial product, the experiences are valuable for improving the performance of industrial product development processes for ceramic micro devices. The various parts of the zirconia micro turbine were prepared by a rapid prototyping process chain (RPPC) that allows for a fast and inexpensive manufacturing of ceramic parts with details down to the micron range. A first design concept was made to mainly demonstrate the shaping feasibility of the process in the micro range. However, some features affected the performance due to their low loading capacity. Thus, a modified design was improved for power output and durability. After optimization of the process chain, dense and homogenous ceramic micro parts could be manufactured. These parts were used for the assembling of a functional micro turbine demonstrator, which was powered by compressed air.

Functional materials should play an important role not only in ITER but also in fusion machines beyond ITER, though it is occasionally claimed that future fusion plants should have much more simple structures and they should be free from auxiliary systems such as diagnostics. Studies on test blanket modules (TBM) clearly show the importance of functional materials there. The paper will review the present status of studies and developments of functional ceramics for nuclear fusion applications, with a perspective on their application in electric-power generating fusion power plant, namely DEMO.

Ceramic microstructure devices in form of counterflow and crossflow microchannel heat exchangers have been manufactured to be used in thermal and chemical process engineering. The performance has been tested using water as a test fluid with maximum flow rates of 120 kg/h. The results of the measurements are compared with global estimations using standard correlations for heat exchangers and a more detailed simulation using a local porous body approach of the micro structured region. The devices show stronger heat transfer and pressure loss than predicted by theoretical considerations. This result is mainly explained by effects of channel blockages arising from the joining process.

Diamond powders were attempted to be consolidated at elevated temperature using an explosive compaction technique employing a cylindrical configuration. A compacted diamond sample recovered from the center of a cylinder, close to the end plug made of stainless steel showed high hardness and tight interparticle bonding between the diamond powders. The sample was characterized on the basis of X-ray diffraction patterns. No graphitization was observed due to heating or compaction, and the hot compacted sample was highly strained by intensive deformation at elevated temperature.

The main line of ceramic breeder materials research and development is based on the use of the breeder material in the form of pebble beds. At present, there are three candidate pebble materials (Li4SiO4, and two forms of Li2TiO3) for DEMO reactors that will be used for testing in ITER. This paper reviews the R&D of as-fabricated pebble materials against the blanket performance requirements and makes recommendations on necessary steps toward the qualification of these materials for testing in ITER.

Worldwide research and development has been performed on solid breeder materials as a tritium source for future fusion power reactors. These ceramic materials will be used in the International Thermonuclear Experimental Reactor (ITER) to check their performance and screen their applicability for use in fusion blankets. While all members of the ITER project are engaged in the development of solid breeder blanket concepts, five are actively involved in the fabrication of tritium breeding ceramics for the different test blanket modules to be tested in ITER. All solid breeder concepts proposed for ITER are based on the use of ceramics in the form of pebble beds with pebble diameters of about 1 mm or smaller. Although alternative materials are still under investigation, the main candidates for tritium breeding ceramics are lithium metatitanate and lithium orthosilicate. Recent developments and preparatory work for ITER are presented.

A method is developed to electrophoretically deposit homogeneous zirconia layers with a thickness of about 5 μm on microstructured steel substrates. To realize layers in this range of thickness, the use of fine to submicron zirconia powder is necessary. To determine the electrokinetic behavior of the powder particles during electrophoresis, their electrophoretic mobility (EM) is measured. Special attention is drawn to the dependence of the mobility on particle size, where Henry theory can be applied. After depositing the layer on the substrate, it is sintered at 1000 °C and investigated by optical microscopy and SEM.

Fabrication of micropatterned ceramics or ceramic microparts make high demands on the precision and resolution of the moulding process. As finishing of miniaturised or micropatterned ceramic components is nearly impossible, shaping has to be done by a replication step in the green, unfired state. To avoid high tooling costs in product development, a rapid prototyping process chain has been established that enables rapid manufacturing of ceramic microcomponents from functional models to small lot series within a short time. This process chain combines the fast and inexpensive supply of master models by rapid prototyping with accurate and flexible ceramic manufacturing by low-pressure injection moulding. Besides proper feedstock preparation and sufficient small grain size, the quality of the final components is mainly influenced by the quality of the master model. Hence, the rapid prototyping method must be carefully selected to meet the requirements of the component to be fabricated.

Most shaping processes for ceramics are based on a powder technological moulding process using a negative mould and subsequent thermal compaction. Especially for prototypes and small-lot series of microcomponents, the outlay for moulds is the major costing factor. Therefore the use of rapid prototyping (RP) processes can decisively reduce the costs and time in product development of ceramic microcomponents. By combining the high resolution of, for example, stereolithography as an inexpensive and fast supply for master models with the high flexibility of low-pressure injection moulding, a rapid prototyping process chain (RPPC) has been established for the fabrication of micropatterned ceramic components as functional models or pre-production lots. This RPPC proved to have a very high moulding precision and accuracy in the submillimetre range, but also enables the fabrication of components with outer dimensions of several centimetres. Different RP techniques were investigated with regard to their suitability to be used as master models in the replication chain. The quality of the master models turned out to be of decisive significance for the quality and reproducibility of the ceramic mouldings.

In the European helium cooled pebble bed (HCPB) blanket slightly hyperstoichiometric lithium orthosilicate (Li 4 SiO 4 +SiO 2 ) and lithium metatitanate (Li 2 TiO 3 +TiO 2 ) pebbles are considered as candidate ceramic breeder materials. Such ceramic breeder pebbles and pebble beds were investigated in different types of experiments carried out at Forschungszentrum Karlsruhe. In longterm annealing experiments (96 days at 970 °C in He+0.1% H 2 atmosphere) the behaviour of the pebbles under DEMO blanket relevant conditions was investigated. Mechanical uniaxial and triaxial compression tests at temperatures up to about 850 °C were performed to determine the mechanical behaviour of pebble beds as a function of temperature (stress–strain dependence, thermal creep behaviour, friction coefficients). Thermal conductivity measurements up to about 800 °C were carried out with the aim to study the effect of creep on the pebble bed heat conduction. An overview of the experimental activities on ceramic breeder materials is given.

Most processes for the manufacturing of ceramic components have in common that they are based on a powder-technological shaping process using a negative mold and subsequent thermal compaction. For microcomponents these processes require special adjustments especially when high aspect ratio structures have to be fabricated. Shaping methods that allow the application of silicone rubber molds, like low-pressure injection molding (LPIM) or centrifugal casting, not only have the potential to fabricate ceramic components with high aspect ratios but also offer a possibility for the rapid manufacturing of ceramic microcomponents.

Cost-intensive and time-consuming manufacturing of new miniaturized or micropatterned ceramic components may profit decisively from the use of rapid prototyping processes. However most known generative processes do not provide a sufficient resolution for the fabrication of microdimensional or micropatterned components or are restricted to polymer materials. In contrast to this, a rapid prototyping process chain (RPPC), which combines e.g., micro stereolithography and a low-pressure shaping method using soft molds, allows the rapid manufacturing of ceramic microcomponents from functional models to preliminary or small lot series.

In the development of the European Helium Cooled Pebble Bed (HCPB) blanket the reference material is slightly overstoichiometric lithium orthosilicate (Li 4 SiO 4 + SiO 2 ) pebbles, fabricated by the melting-spraying method. Slightly overstoichiometric lithium metatitanate (Li 2 TiO 3 + TiO 2 ) and lithium metazirconate (Li 2 ZrO 3 + ZrO 2 ) pebbles, fabricated using a extrusion-spheronization-sintering process, are considered as alternative candidates for the ceramic breeder material. In order to compare the long-term behaviour of the three materials at HCPB-blanket relevant temperature and atmosphere (He + 0.1% H 2 ), a campaign of three long time annealing experiments were carried out at Forschungszentrum Karlsruhe (FZK). Pebbles of each ceramic breeder material (Li 4 SiO 4 + SiO 2 from FZK, Li 2 TiO 3 + TiO 2 and Li 2 ZrO 3 + ZrO 2 from CEA) were annealed for 96 days at 970 °C. During this period the change of the mechanical characteristics, the microstructure, and the chemical composition of the pebbles was analysed. After the end of the annealing experiment, uniaxial compression tests of pebble beds were performed additionally. In the present paper the results from the second experimental campaign are reported and discussed.

Ceramic microreactors can be used for applications that cannot be covered by metal or polymer systems, because special material properties, such as high thermal and chemical resistance are required. However, application of ceramic microcomponents often fails due to the time-consuming and costly manufacturing of components with patterning details in the micrometer range. A promising solution to this problem is a rapid prototyping process chain. It offers a fast and precise fabrication of ceramic components down to the micrometer range by combining stereolithography and low-pressure ceramic injection molding. Its fast and flexible tooling allows rapid product development and manufacturing of ceramic components as functional models or in small series. For use in chemical microreaction technology, a modular ceramic microreactor with inner dimensions in the sub-millimeter range has now been developed by means of this process chain.

Time-intensive and cost-consuming manufacturing of new ceramic components may be improved significantly by the use of rapid prototyping processes especially in the development of miniaturized or micropatterned components. Their molding is generally very expensive and finishing is difficult to the point of impossibility. Most known generative ceramic molding processes do not provide a sufficient resolution for the fabrication of microstructured components. In contrast to this, a rapid prototyping process chain that combines micro-stereolithography and low-pressure injection molding, for example, allows the rapid manufacturing of ceramic microcomponents from functional models to preliminary or small-lot series, microcomponents from functional models to preliminary or small-lot series.

Preparation, crystal structure and some basic properties of a new fullerene-containing molecular solid, C60S8CS2, comprising C60 fullerene molecules, S8 rings and linear CS2 groups are described. The orthorhombic structure ( a = 9.973(1) A , b = 13.356(2) A , c = 28.654(4) A , space group Pnma, z = 4), as determined from single crystal X-ray data collected at room temperature, has been refined to a resolution of about 1.8 A. The structure is built up of six-membered zig-zag rings of C60 molecules in the b-c plane which share common edges and are stacked closely upon each other along a. In this way they form a 3D framework with large 1D channels along a containing the S8 and CS2 molecules. Within the resolution of the experiment the fullerene molecules in C60S8CS2 appear to be orientationally disordered while the S8 and the CS2 molecules are well ordered. The compound is an insulator with a reddish-brown colour and almost isotropic light absorption.

The crystal structure and some basic properties of RESrGaCuO{sub 5}(RE: La, Pr, Nd, space group Ima2, z = 4, a = 16.277(1) {angstrom}, b = 5.5191(3) {angstrom}, c = 5.3342(3) {angstrom} for RE = Nd) has been studied by powder and single-crystal X-ray methods, electrical resistivity and magnetic susceptibility measurements, DSC, TG, and optical microscopy. The structure consists of almost planar nets of distorted corner sharing Cu-O{sub 6} octahedra connected along the longest axis via Ga-O{sub 4} tetrahedral chains with RE and Sr ions filling the large voids between planes and chains. It is isotypic to the structure of the mineral Brownmillerite (Ca{sub 2}(Al,Fe){sub 2}O{sub 5}). Together with its recently described double Cu-O{sub n} layer counterpart RESr{sub 2}GaCu{sub 2}O{sub 7} it forms a homologous series of new gallate-cuprates which closely resemble the corresponding Ga-free superconducting cuprates with single and double Cu-O{sub n} layers. Stoichiometric RESrGaCuO{sub 5} has a fixed oxygen content and is semiconducting with a strong anisotropy of the optical absorption, indicating a pronounced 2-dimensional character of the electronic properties. P-doping of these materials by partial substitution of RE by additional Sr has not been successful up to now.

Rapid prototyping techniques allow the rapid and flexible generation of single design models as well as fabrication tools for the replication of small scale series, at present mainly in the macroworld. A current internet search using one of the established search engines reveals the following typical results: 445000 links for “rapid prototyping” 55000 links for “rapid” and “prototyping” and “micro” 5100 links for “micro” and “stereolithography” 70 links for “microstereolithography” 50 links for “rapid” and “nano” and “prototyping” links for “nanostereolithography”.