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Inorganic membranes, though more expensive than organic membranes, are heat-resistant and inert and have many applications in a variety of fields. The first applications in isotope separation has led to more recent uses in areas such as liquid filtration, gas separation and high-temperature reactors. Microporous amorphous or crystalline membranes, and dense membranes are the commonly used inorganic membranes. Microporous membranes have zeolite layers grown on microfiltration membranes. Dense membranes are deposited on a support in the form of a plate of active material.

Residual stenosis after recanalization of an acute symptomatic extracranial occlusion of the internal carotid artery (ICA) might be an indication for carotid endarterectomy. We evaluated the proportion of residual high-grade stenosis (≥70, near occlusions not included) on follow-up imaging in a consecutive series of patients with an acute symptomatic occlusion of the extracranial ICA.

The transport behavior of toluene and n-hexane in γ-alumina membranes with different pore diameters was studied. It was shown that the permeability of water-lean hexane and toluene is in agreement with Darcy's law down to membrane pore diameters of 3.5 nm. The presence of molar water fractions of 5−8·10^-4 in these solvents led to a permeability decrease of the γ-alumina layer by a factor of 2−4 depending on pore size. In general, a lower permeability was found for hexane than for toluene. Moreover, in the presence of water a minimum applied pressure of 0.5−1.5 bar was required to induce net liquid flow through the membrane. These phenomena were interpreted in terms of capillary condensation of water in membrane pores with a size below a certain critical diameter. This is thought to lead to substantial blocking of these pores for transport, so that the effective tortuosity of the membrane for transport of hydrophobic solvents increases.

Pervaporation and gas permeation properties of microporous silica membranes made by a sol−gel method are discussed. Defect free molecular sieving membranes are prepared by a dip coating process. The molecular sieving performance was measured and controlled based on gas permeation behavior of the membranes. The apparent activation energy for helium permeation and He/N2 perm-selectivity values were used as the parameters for optimization of the membrane performance. The membranes with very high activation energy for He diffusion were used for pervaporation studies with a methanol/MTBE mixture at 323 K. Separation factor values as high as 260 were measured at a total liquid flux of 0.3 kg/m² hr. Sorption studies performed on corresponding silica gels revealed a separation mechanism based on diffusion of vapor molecules. Permeation of the vapor molecules through the micropores followed an activated diffusion mechanism. The gas permeation data could provide an understanding of the pore size distribution of the membrane, and the vapor sorption and diffusion data on the size and connectivity of the membrane pores.

ZrO2-Y2O3 ceramics with varying Bi2O3 content have been prepared and their microstructure, electrical conductivity and mechanical properties investigated. The sintering rate is strongly increased at low temperatures (1270 to 1420 K) due to the occurrence of a reactive phase the amount of which decreases during the sintering process. The main fluorite phase has an approximately constant composition at 0.85 ZrO2-0.13 Y2O3-0.02 Bi2O3 while the amount of second phase depends on overall composition and sintering procedure. The electrical conductivity is also approximately constant but about a factor of five lower than in ZrO2-Y2O3 ceramics. Typical strength and fracture toughness values are 160 MPa and 1.8 MPa m1/2, respectively. However, the non-reproducibility of the second phase content and morphology seriously influences both mechanical properties.

Alumina films less than 20µm thick are prepared by a process in which a boehmite sol is successively gelled, dried and calcined. The resulting structure has the unique property that only ultra-fine pores with a narrow pore size distribution are present within large crack-free layers. The microstructure can be influenced by the sintering temperature and the acid concentration of the precursor sol. The minimum modal pore size which has been obtained is 2.5 nm. A consistent model of the microstructure of the membranes and an explanation of its uniformity are presented.

Stabilized ZrO2-Y2O3 ceramics have been prepared with varying grain sizes and microstructures with the help of different preparation techniques. Bi2O3 has been added as a sinter aid to some of the samples. This results in a certain amount of a zirconia-rich second phase. For Bi2O3-free samples the fracture toughness (Klc), and therefore the fracture energy, increases with decreasing grain size. A linear relation with the inverse square root of the average grain size is found. The highest value ofKlc amounts to 4.1 MPa m1/2. Fracture toughness values of 1.9±0.2 MPa m1/2 are measured for Bi2O3 containing materials. The fracture surfaces are intergrannular for Bi2O3-containing and transgranular for Bi2O3-free samples, respectively.

Silica sols have been prepared in an alcoholic solution by hydrolysis and condensation of TEOS (tetra-ethyl-ortho-silicate) molecules as a function of water and nitric acid concentration. The polymers are intended as precursors for ceramic, gas separation membranes. These molecules show fractal behavior as determined by SAXS (Small Angle X-ray Scattering). Microporosity of dried and calcined silica polymers is determined by N2-adsorption at 77 K. Fractal dimension and porosity increase with increasing acid concentration. Both the sol structure and the drying kinetics determine the porosity values. N2-adsorption isotherms are not very suitable for the determination of pore size distributions of microporous silica.

For improving chemical and thermal stability of γ -Al2O3membranes boehmite (AlOOH) sol-particles are coated with Zr4+-species with two techniques. These techniques are heterogeneous precipitation (HP-method) and “surface-reaction-followed-by-polycondensation” (SRPC-method). A continuous coating layer is formed at relative low Zr4+-concentration, about one monolayer coverage of boehmite particles, and with the HP-method. For larger concentrations and for the SRPC-method small particles (order 1 nm) of Zr4+-species are formed on the surface of the boehmite particles. After drying and calcination up to 1000°C no continuous layer of a zirconia phase could be detected for all samples. However the thermal stability of the porous structure is improved. Phase transitions of alumina occur at temperatures of 1100°C and the porous structure of the membrane material is then destabilized.

A new method has been developed for the measurement of stresses in thin gel layers during the drying process. The gel layers under investigation consist of boehmite, and are produced during the formation of ?-Al2O3 ceramic membranes. The method is based on the principle of the cantilever beam. Detection of beam deflections is carried out with a laser displacement meter, using a 760 nm infrared laser. Deflections of the beam can be measured continuously during the drying process, making it possible to monitor the stress in the layer also continuously. Examples illustrate that stresses may be as high as 180 MPa. Cracking of gel layers most likely manifests itself by a marked decrease in the stress. Uncracked gel layers may be stressed and subsequently unloaded by slowly lowering and increasing the relative humidity. An increase of temperature at constant air flow and relative humidity leads to an increase of the stress. Lowering the rate of air flow over the sample lowers the stress which is built up. The method which is described here can very probably also be applied to other coating materials, which are dried on rigid supports.

Modification of the internal surface of ?-alumina films was realised by an impregnation method employing an aqueous metal salt-urea solution, followed by drying and reaction at 90 °C. Loads of non-supported films were found to be much lower than those of supported films. The support acts as a reservoir, supplying its metal salt under appropriate conditions to the thin film. This results in high loads. A model analysis identified the ratio of the drying time to the reaction time as the critical parameter. With silver, as well as with magnesia, a long reaction time compared to the drying time proved to be favourable. This is best realised by performing the drying (at 40 °C) and the reaction (at 90 °C) sequentially. Silver loads of 70% of the pore volume were realised. A high degree of dispersion upon heating is maintained only under a reducing atmosphere. Up to 85% of the pore volume could be plugged with magnesia. This does not lead to a considerable pore size decrease however, due to the slit shape of the pores.

An earlier retrograde double-labeling study in cat showed that up to 30% of the corticospinal neurons in the medial and anterior parts of the precruciate motor area represent branching neurons which project to both the spinal cord and the reticular formation of the lower brain stem. These neurons were found to be concentrated in the rostral portion of the motor cortex, from where axial and proximal limb movements can be elicited. In the present study the findings in the macaque monkey are reported. The fluorescent retrograde tracer DY was injected unilaterally in the spinal cord at C2 and the fluorescent tracer FB was injected ipsilaterally in the medial tegmentum of the medulla oblongata. In the contralateral hemisphere large numbers of single DY-labeled corticospinal neurons and single FBlabeled corticobulbar neurons were present. A substantial number of DY-FB double-labeled corticospinal neurons were also found, which must represent branching neurons projecting to both the spinal cord and the bulbar reticular formation. These neurons were present in: 1. The anterior portion of the “cingulate corticospinal area” in the lower bank of the cingulate sulcus; 2. The supplementary motor area (SMA); 3. The rostral part of precentral corticospinal area; 4. The upper portion of the precentral face representation area; 5. The caudal bank of the inferior limb of the arcuate sulcus; 6. The posterior part of the insula. In these areas 10% to 30% of the labeled neurons were double-labeled. The functional implications of the presence of branching corticospinal neurons in these areas is discussed.

Summary: Layer VI of macaque striate cortex contains a number of large solitary neurones called Meynert cells. It has been shown earlier that these Meynert cells project to the posterior bank of the superior temporal sulcus (area V5), but it has also been shown that they project to the superior colliculus. In retrograde fluorescent double-labelling experiments, it was found that Meynert cells represent a class of neurones which distribute divergent axon collaterals to the posterior bank of the superior temporal sulcus and to the superior colliculus, i.e. to a distant cortical and a subcortical structure. This feature appears to be unique among projecting neurones in monkey visual cortex.

The preparation and characterization of porous ceramic membranes is presented. These membranes consist of a macroporous support system, with or without a mesoporous intermediate layer, and a microporous top layer. For the macroporous support membranes two manufacturing routes are described: a conventional and a RBAO (Reaction Bonded Aluminium Oxide) route. The mesoporous γ-Al2O3layer is obtained by means of a sol-gel dipcoating technique. Three microporous top layers are considered: SiO2, Al2O3-pillared montmorillonite and Laponite. These top layers have different pore structures which results in different gas transport properties. A SiO2membrane can be used for H2removal from a gas mixture. Al2O3-pillared montmorillonite and Laponite membranes do not show specific gas separation properties. Dehydration of water/2-propanol mixtures by means of pervaporation also proved a different behavior for these microporous membranes.

A new and simple method for the preparation of MFI zeolite coated activated carbon is presented. Suitable nucleation sites for the growth of zeolites were introduced to the carbon by adding hydrophilic montmorillonite clay to the carbon substrate. A gas tight MFI zeolite coating was obtained on this modified substrate by hydrothermal growth.

Sorption experiments with H2, CO2, CH4 and iso-C4H10 were performed on microporous SiO2 and SiO2/TiO2 (30 mol% TiO2) non-supported membrane top-layers using volumetric and gravimetric techniques.

Gas physisorption is a generally used technique for the characterization of porous solids. Microporous solids, however, need a different approach compared to mesoporous solids due to enhanced adsorption in pores of molecular dimensions. Therefore, conventional theories and models can not be used. The application of physisorption for microporous solids, and the interpretation of the isotherms is elucidated. Some models presented in literature for pore size assessment in the micropore range are discussed. Based on a number of criteria, the Horváth-Kawazoe model, modified for cylindrical pore geometry, is selected. N2 adsorption measurments on zeolites were performed to calibrate the method and to show the applicability and physical justification. Typical data obtained from experiments on non-supported microporous silica membrane top-layers show that the pore size distribution of these materials is bimodal, with a strong maximum at an effective diameter of 0.5 nm, and a weaker maximum at 0.75 nm.

The fluorescent retrograde double-labeling technique has been used to determine whether corticospinal neurons in the cat sensorimotor cortex distribute collaterals to the lower brain stem reticular formation. In this study the fluorescent tracers Nuclear Yellow and Diamidino Yellow 2HCl were used in combination with Fast Blue. One tracer was injected unilaterally in the spinal cord and the other was injected ipsilaterally in the bulbar medial reticular formation. The distribution of the retrogradely labeled neurons was studied in the contralateral hemisphere. In the sensorimotor cortex a large population of neurons was found which were labeled from the spinal cord and were double-labeled from the brain stem. These branching neurons were concentrated in the rostromedial part of area 4 and the adjoining lateral part of area 6. In this region the percentages of corticospinal neurons which were double-labeled from the brain stem ranged from 5% laterally to 30% medially. In two cats it was demonstrated by means of the anterograde transport of HRP that the corticobulbar fibers from this region which must include the corticospinal collaterals are distributed to the reticular formation of the lower brain stem. In view of the fact that the double-labeled neurons are concentrated in the anterior part of the motor cortex, those branching neurons are in all likelihood involved in the control of neck, back and shoulder movements. This control is probably exerted by way of two routes i.e. by way of the direct corticospinal connections to spinal interneurons, and by way of the indirect cortico-reticulospinal connections established by the cortical fibers to the bulbar reticular formation. The present findings suggest that this dual control may be exerted by one and the same cell.

Earlier studies showed that Nuclear Yellow (NY), True Blue (TB) and Fast Blue (FB) are transported retrogradely through axons to their parent cell bodies. NY produces a yellow fluorescent labeling of the neuronal nucleus at 360 nm excitation wavelength, while TB and FB produce a blue fluorescence of the cytoplasm at this same wavelength. Therefore, NY may be combined with TB or FB in double-labeling experiments demonstrating the existence of axon collaterals. However, retrograde neuronal labeling with TB or FB requires a relatively long survival time, while NY requires a short survival time since NY migrates rapidly out of the retrogradely labeled neurons. This complicates double-labeling experiments since TB and FB must be injected first and NY later, a short time before the animal is sacrificed. We report a new yellow fluorescent tracer which labels mainly the nucleus and migrates much more slowly out of the retrogradely labeled neurons than NY. This new tracer can be used instead of NY in combination with TB or FB in double-labeling experiments and unlike NY can be injected at the same time as TB or FB. The new tracer is a diamidino compound (no. 28826) which is commerciallyDistributed by Dr. Illing KG, Warthweg 14-18, Postfach 1150, D-6114 Groß-Umstadt, FRG available. It will be referred to as Diamidino Yellow Dihydrochloride (DY·2HCl). According to the present study DY·2HCl is transported over long distances in rat and cat, and produces a yellow fluorescence of the neuronal nucleus at 360 nm excitation wavelength, resembling that obtained with NY. When combined with TB or FB, DY·2HCl is as effective as NY in double labeling of neurons by way of divergent axon collaterals.

The phase diagram of the Bi2O3-Er2O3 system was investigated. A monophasic f c c structure was stabilized for samples containing 17.5–45.5 mol% Er2O3. Above and below this concentration range polyphasic regions appear. The f c c phase showed high oxygen ion conduction. The ionic transference number is equal to one for specimens containing 30 mol% Er2O3 or less, while an electronic component is introduced at low temperatures for specimens containing 40–60 mol% Er2O3. Between 673 K and 873 K a maximum in the conductivity was found at 20 mol% Er2O3. (Bi2O3)0.8.(Er2O3)0.20 is found to be the best oxygen ion conductor so far known. The conductivity at 773 K and 973 K is 2.3 O-1m-1 and 37 O-1 m-1 respectively. These values are 2–3 times higher than the best oxygen ion conductor reported for substituted Bi2O3 systems and 50–100 times higher than those of stabilized zirconia (ZrO2)0.915(Y2O3)0.085 at corresponding temperatures.

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Microporous SiO2 and SiO2/MO2 (M=Ti, Zr, Al; 10 mol% MOx) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO2 sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1f<2.04.

The synthesis and characterization of supported and non-supported membranes of ?-Al2O3, TiO2 and their binary combinations are described. Non-supported ?-Al2O3 and TiO2 membranes were prepared from colloidal dispersions (sols) of boehmite and titania, respectively. Stable binary sols were also prepared by mixing boehmite and titania sols under appropriate pH conditions, and these were used to prepare binary (?-Al2O3/TiO2) membranes. Supported ?-Al2O3, TiO2 and binary membranes were made by the slip-casting process using the same sols. The membrane layers had, after calcination, a thickness of 3–6 µm depending on the dipping conditions, and an average pore diameter of ~-3–4 nm with a narrow pore-size distribution. The structural transformation of titania from the anatase to the rutile phase was retarded by performing the hydrolysis in the presence of sulphate ions. Polyvinyl alcohol was added to the sols to strengthen the gel network during the drying and calcination process. This resulted in a less critical and more controllable membrane formation process. Multiple dipping (e.g. to repeat the dipping, drying and calcination steps) appeared to be a technique by which (i) defected layers could be repaired; (ii) thick membrane layers could be prepared; and (iii) multilayer membranes consisting of layers of different components could be prepared.

Polymeric SiO2 and binary SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 sols, for ceramic membrane modification applications, have been prepared by acid-catalyzed hydrolysis and condensation of alkoxides in alcohol. The sols were characterized with small angle X-ray scattering, using synchrotron radiation. Directly after synthesis, the sols were found to consist of weakly branched polymeric structures with typical fractal dimensions of around 1.5 and radii of gyration of ≈ 2 nm. The aggregation for silica sols obeys the tip-to-tip cluster-cluster aggregation model in the initial stages. Prehydrolysis of TEOS was found to be the best method to synthesize polymeric binary systems. Based on an analysis of film formation from sols consisting of weakly branched polymers, it is expected that consolidation of these polymers will result in microporous materials.

The fluorescent double-labeling technique has been used to determine whether the corticopontine and the corticotectal fibers in the cat are derived from two different sets of neurons or whether they are derived from branching neurons which distribute collaterals to the pontine grey and the colliculi. After unilateral DY.2HCl injections in the pontine grey and FB injections in the ipsilateral colliculi, large numbers of FB-DY.2HCl double-labeled neurons were present in the cortex of the ipsilateral hemisphere. However, the labeled neurons in its rostral part may have represented pyramidal tract neurons which were labeled retrogradely because their fibers descended through the DY.2HCl injection area. Therefore, also DY.2HCl injections were made in the pyramid (i.e. caudal to the pons) and the cortical pyramidal tract area, containing the retrograde DY.2HCl-labeled neurons, was delineated. In the rest of the experiments only the DY.2HCl-labeled neurons in the caudal two thirds of the hemisphere (outside the pyramidal tract area) were taken into account because only these neurons could, with confidence, be regarded as corticopontine neurons. In some anterograde HRP transport experiments the trajectories of the corticotectal and the corticopontine fibers were visualized. On the basis of the findings the DY.2HCl injections in the pontine grey were placed such that they could not involve any of the corticotectal fibers passing from the cerebral peduncle to the colliculi. Thus artifactual doublelabeling of cortical neurons was avoided. However, also under these circumstances many double-labeled neurons were present in the caudal two thirds of the hemisphere. This led to the conclusion that in the cat a large proportion of the corticopontine neurons in the caudal two thirds of the hemisphere represent branching neurons which also distribute collaterals to the colliculi. The parietal (anterior part of the lateral gyrus, middle and posterior suprasylvian gyri) and the cingulate areas together contained three quarters of all labeled corticopontine neurons outside the pyramidal tract area. In the parietal areas roughly 25% of them were double-labeled and in the cingulate area 14%. However, in the visual areas 18 and 19 a much larger percentage (30–60%) was doublelabeled. In a recent study from our laboratory it was found that in the cat the pyramidal tract fibers distribute an abundance of collaterals to the pontine grey. Therefore, a large proportion of all corticopontine connections in this species appear to be established by branching neurons which also distribute fibers to other cell groups in the brain stem and the spinal cord.

In rare earth oxide (L2 O3) substituted lead titanate Pb1-axLxTiO3+x(1.5-α) within the homogeneity range of the perovskite phase two compositional parameters affect the ferroelectric phase transition (FPT). The parameters are the LO1.5-TiO2 ratio (x) and the PbO-TiO2 ratio (1-αx).An increase of the value of x causes the Curie temperature to decrease and this shift is smaller with a decreasing radius of the rare earth ion. An increase of (1-αx) at a constant value of x increases the Curie temperature to higher values especially if the radius of the rare earth ion is small. At values of x < 0.23 the FPT is not broadened and has a Curie-Weiss behaviour in monophasic, homogeneous, coarse grained materials.For La2O3 substituted PbTiO3 (PLT) with x = 0.30 the FPT is broadened and frequency dependent. A quadratic relation between the reciprocal dielectric constant and the temperature is found.

The defect concentrations in lanthana substituted lead titanate and the effect of sintering temperature on the dielectric constant (e') around the Curie point have been studied. On the basis of our x-ray diffraction results the presence of Ti-site vacancies seems unlikely. This conclusion is in contradiction with Hennings' defect model.A decrease of the sintering temperature leads to a decrease of the maximum value of e' and to a broadening of the peak in the e' vs. temperature curve at the Curie point. Probably, grain size as well as compositional fluctuations contribute to the observed variations.