Jan Luyten

Alumina and titania multilayer membranes for nanofiltration: preparation, characterization and chemical stability

Abstract The preparation and characterization of porous ceramic multilayer nanofiltration (NF) membranes is described. During preparation, special care was given to each sub-layer that forms a part of the multilayer configuration: the macroporous substrate, the membrane interlayers and the NF toplayers. High-quality macroporous supports are prepared from α-Al 2 O 3 . Three types of colloidal sol–gel derived mesoporous interlayers are considered: Al 2 O 3 , TiO 2 and mixed Al 2 O 3 –TiO 2 . The active NF toplayer is a very thin and fine textured polymeric TiO 2 toplayer. Optimized α-Al 2 O 3 /γ-Al 2 O 3 /anatase and α-Al 2 O 3 /anatase/anatase multilayer configurations show high retentions for relatively small organic molecules (molecular weight cut-off 2 O 3 layers is restricted to mild aqueous media (pH 3–11) or non-aqueous media (organic solvents). For NF applications in aqueous media with a lower or higher pH, the multilayer membrane composed of anatase on a α-Al 2 O 3 support is to be preferred.

Aqueous tape casting of yttria stabilised zirconia using natural product binder

Abstract A new and simple tape cast process has been developed for e.g. the fabrication of YSZ-electrolyte for solid oxide fuel cells (SOFCs). The method is environmentally friendly since it is water-based and uses a natural compound as a binder. The tape cast suspension was formulated taking into account a maximal solids loading, a minimum of organic compounds, colloidal stability, rheological and wetting properties. Green sheets of variable thickness (50–400 μm) have been prepared. After sintering, dense and defect-free electrolyte material, as required for SOFCs, was obtained. The microstructure and the surface of the sintered sheet material were characterised with FESEM.

Porous Ceramic Membranes: Preparation, Transport Properties and Applications

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-Al2O3 layer 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 SiO2 membrane can be used for H2 removal 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.

Quantitative Screening of Engineered Implants in a Long Bone Defect Model in Rabbits

We have standardized a long bone defect model in rabbits to quantitatively compare the bone healing performance of engineered biological implants and have tested the bone healing efficiency of porous cylindrical scaffolds (ø-h, 6-20 mm [diameter 6 mm, height 20 mm] porosity, 70%) that were produced from hydroxyapatite (HA), titanium (Ti), and a novel biodegradable polymer-bioceramic composite (PH70alphaTCP). Scaffolds were perfused with or without 20 x 10(6) rabbit periosteal cells (RPCs) in a bioreactor and implanted in a standardized 2 cm defect in rabbit tibiae. X-rays revealed that new bone had formed at 3 weeks after creation of the defects. At sacrifice after 10 weeks, bone corticalization was observed in the majority of animals. Although PH70alphaTCP scaffolds did not inhibit callus formation, histomorphometric analysis revealed that there was no bone within the biomaterial, in contrast to HA and Ti scaffolds (bone volume ranging from 10% to 25%). We found that Ti and HA scaffold had good osteoconductive properties, but only HA scaffolds seeded with RPCs contributed to long bone mechanical functionality, with the maximum energy and angle being 308% and 155% greater than in control defects without scaffold.

Vancomycin release from poly(d,l-lactic acid) spray-coated hydroxyapatite fibers

The influence of the poly(D,L-lactic acid) (PDLLA) coating thickness on the in vitro vancomycin release from a hydroxyapatite (HA) carrier was studied. Microporous HA fibers with a porosity of 51 v% and an average pore diameter of 1.0 μm were fabricated by a diffusion-induced phase separation technique. They were loaded with 38 mg vancomycin hydrochloride (VH)/gHA, and their cylindrical shape enabled the application of the spray coating technique for the deposition of uniform PDLLA coating thicknesses, varying from 6.5 μm to 28 μm. The resulting in vitro VH release varied from a complete release within 14 days for 6.5 μm coatings to a release of 23% after 28 days for 28 μm coatings. It was clear that the VH release rate from a HA fiber can be adjusted by varying the PDLLA coating thickness. Microbiological tests of these fibers against a methicillin-resistant Staphylococcus aureus (MRSA) isolate pointed to the importance of the initial burst release and confirmed that the released antibiotics had the potential to interfere with S. aureus biofilm formation.

Implantable (Bio)Polymer Coated Titanium Scaffolds: A Review

In the current review we aim to give an overview of the state of the art of the research on (bio)polymer functionalised titanium implants for bone tissue engineering applications. After a short introduction on bone tissue engineering and the requirements the applied materials have to meet, an extensive discussion on titanium in bone tissue engineering will be given. Starting with a short description of both the titanium bulk and surface properties, the requirement for surface modified titanium will be highlighted. The discussion will encompass inorganic and organic chemical modifications and a combination thereof with a focus on the organic modifications. Within the latter type of modification, physical adsorption, physical incorporation and covalent immobilisation will be compared. In the final part of the review an overview will be given of the fabrication and characterisation of three-dimensional titanium scaffolds.

Ion Transport and Thermomechanical Properties of SrFe ( Al ) O3 − δ – SrAl2O4 Composite Membranes

Moderate additions of monoclinic SrAl 2 O 4 to perovskite-type SrFe(Al)O 3-δ mixed conductors improve the sinterability and thermomechanical properties, including the thermal shock resistance, Vickers hardness, and fracture toughness, and decrease thermal expansion. The iron solubility in SrAl 2 O 4 , a mixed ionic and n-type electronic conductor with insulating properties, is lower than 5%. The total conductivity of SrAl 2 O 4 ceramics in air varies in the range 10 -7 -10 -5 S/cm at 973-1223 K. The transport properties and phase stability of dual-phase (SrFe) 1-x (SrAl 2 ) x O 2 (x = 0.3-0.7) composite membranes, where the partial dissolution of strontium aluminate in the ferrite phase leads to formation of A-site-deficient Sr 1-y Fe 1-2y Al 2y O 3-δ (y ≈ 0.08-0.12), are determined by the perovskite component. The total conductivity and Seebeck coefficient oxygen partial pressure dependencies exhibit general trends typical for SrFeO 3 -based solid solutions. Although the conductivity and oxygen permeability of (SrFe) 1-x (SrAl 2 ) x O z composites decrease with increasing x, the permeation fluxes through (SrFe)o.7(SrAl 2 ) 0.3 O z ceramics are comparable to those through single-phase SrFe 0.7 Al 0.3 O 3-δ . Under high p O2 gradients such as air/(H 2 -H 2 O), the oxygen transport is limited by surface-related processes, enabling stable operation of (SrFe) 0.7 (SrAl 2 ) 0.3 O 2 membranes. This composition was selected for fabrication of tubular membranes by the cold isostatic pressing. Surface modification of (SrFe) 0.7 (SrAl 2 ) 0.3 O z in order to enhance the exchange kinetics was found inappropriate from a stability point of view.

Synthesis and characterization of a pillared clay membrane

Abstract Ceramic multilayer membranes with a top layer of Al2O3-pillared montmorillonite were prepared. To deposit the top layer, a γ-alumina membrane was first dipped in a montmorillonite suspension followed by a pillaring of the deposited clay layer. SEM analysis showed that very thin top layers were formed. The layer thickness increased with dipping time but could be limited to a few tenths of a micrometer. Although the top layer was very thin, gas permeation measurements indicated a high flow resistance. X-ray diffraction indicated that the low permeation was possibly due to an incomplete pillaring of the clay layer.

Catalyst design with porous functional structures

The chemical industry is experiencing important changes. The driving force for these changes is a growing need to improve competitiveness and consolidate market positions while complying with the regulations for safeguarding human health, and the environment. Currently, what is known as “green chemistry” or “sustainable technology” is at the heart of the changes the chemical industry is undergoing. Catalysis and materials science will play an important role in this new approach. One domain with specific relevance is porous ceramics and metals, substrates with pores sizes ranging from vacancies at the atomic level to macro pores with sizes of millimeters. There are plenty of emerging applications for porous functional components. Each application will specify the window of properties of the porous material. A technology assessment of the developed porous materials and powder processing techniques for their use as catalyst or membrane system will be presented, limited to inorganic porous materials which can be synthesized by dry and wet powder processing methods. The applications overview for porous materials is focused on macroporous components with a designed functional coating.

1.11 – Basic Aspects in Inorganic Membrane Preparation

Nowadays, a large variety of inorganic membranes exist, which include ceramic as well as metal membranes. The earliest developments involved membranes with pores in the micrometer range. The latest developments include microporous and dense membranes on the one hand and macroporous foams on the other hand. Despite this wide pore-size range, the synthesis of inorganic membranes shows some common aspects. All synthesis starts from suitable powder preparation from precursor material. Subsequently, these powder particles are packed in a green product with a certain shape. After shaping, the synthesis of all inorganic membranes involves one or more heat treatments, leading to the final porous or dense microstructure of the membrane. To make dense or fine-porous membranes suitable for real applications, these membranes consist of a multilayer composition with a coarse-porous support providing the necessary mechanical strength, and the fine-porous or dense top layer responsible for the separation aimed at. In this manner, the membranes can combine a high flux and a high separation factor. In specific cases, the inorganic membranes are further functionalized in order to change the affinity of the membrane surface, or to obtain catalytically active membranes. This chapter gives a concise but broad overview of all synthesis methods used, with emphasis on new trends and recent developments in this highly evolving field.