Michael Scheffler

Cellular ceramics : structure, manufacturing, properties and applications

Foreword by David J. Green. Preface. 1 Introduction. 1.1 Cellular Solids - Scaling of Properties. 1.2 Liquid Foams - Precursors for Solid Foams. 2 Manufacturing. 2.1 Ceramic Foams. 2.2 Honeycombs. 2.3 3D Periodic Strutures. 2.4 Connected Fibers: Fiber Felts and Mats. 2.5 Microcellular Ceramics from Wood. 2.6 Carbon Foams. 2.7 Glass Foams. 2.8 Hollow Spheres. 2.9 Cellular Concrete. 3 Structure. 3.1 Characterization of Structure and Morphology. 3.2 Modelling Structure-Property Relationships in Random Cellular Material. 4 Properties. 4.1 Mechanical Properties. 4.2 Permeability. 4.3 Thermal Properties. 4.4 Electrical Properties. 4.5 Acoustic Properties. 5 Applications. 5.1 Liquid Metal Filtration. 5.2 Gas (Particulate) Filtration. 5.3 Kiln Furnitures. 5.4 Heterogeneously Catalysed Processes with Porous Cellular Ceramic Monoliths. 5.5 Porous Burners. 5.6 Acoustic Transfer in Ceramic Surfac Burners. 5.6 Solar Radiation Conversion. 5.7 Biomedical Applications: Tissue Engineering. 5.9 Interpenetrating Composites. 5.10 Porous Media in Internal Combustion Engines. 5.11 Other Developments and Special Applications. Concluding Remarks.

Zeolite covered polymer derived ceramic foams: novel hierarchical pore systems for sorption and catalysis

Abstract Open cell polymer derived ceramic foams were prepared by a self-foaming process of a filler loaded poly(silsesquioxane) and subsequent pyrolysis at 1000°C in nitrogen atmosphere. A 1 : 1 mixture by weight of elemental Si and SiC was introduced as particulate filler. Foam samples without and with addition of a small amount (1.5 wt-%) of Cu2O were prepared. Open cell ceramic foams with average cell diameter of 0.5–1.5 mm, compressive strength of up to 3 MPa and porosity of up to 90% were used as supports for direct crystallisation of MFI type zeolite under partial dissolution/recrystallisation of the ceramic foam. The partial transformation of the Si–O–C based foam material by hydrothermal crystallisation at 150°C for 0–96 h resulted in a well distributed zeolite coating with excellent adhesion on the foam surface. Characterisation of the zeolite/ceramic foam composites was carried out by XRD measurements in order to determine the amount of zeolite in the composite. 29Si MAS NMR experiments were conducted to investigate the influence of Cu2O addition on the crystallisation behaviour.

Polysiloxane-derived ceramic foam for the reinforcement of Mg alloy

Magnesium/ceramic composites with an interpenetrating microstructure were made by pressure infiltrating an open cellular ceramic preform. The low-density ceramic preform with a porosity of 82 % was prepared by foaming a low-viscous polysiloxane/alumina suspension which formed an SiO 2 /Al 2 O 3 microcomposite ceramic foam after thermal treatment in air at 1200°C. Foaming was achieved by an in situ blowing process during curing of the polysiloxane precursor at 200-300°C. The open cellular structure was characterized by a mean strut thickness of 130 μm, an average cell diameter of 800 μm and a high pore connectivity. The ceramic preforms were infiltrated with AZ 31 magnesium alloy by squeeze casting at 680 °C applying a maximum pressure of 86 MPa. Interface bonding was achieved by the formation of spinel and cordierite in a reaction layer at the metal/ceramic interface. The dense metal/ceramic composite possesses significantly higher elastic modulus, yield strength and creep resistance than the monolithic alloy at room temperature and 135 °C. The experimental results suggest that filler-loaded preceramic polymers have a high potential for optimization of lightweight metal cast components.

Zeolite Coatings on Porous Monoliths

Zeolites find various applications in heterogeneous catalysis, microreactor techniques, sorption techniques, ion exchange and more recently in heat pump applications. In common processes zeolites are used as shaped bodies with a size in the millimeter range. Novel processes made it necessary to apply zeolites as coating on inert or reactive bulk or porous substrate materials. In the past fifteen years various methods for zeolite coatings have been developed and adapted to the specific requirements with respect to the process they are to be used and to the specific physical and chemical properties of the support material.

Polymer derived ceramic tapes as substrate and support for zeolites

Abstract Inorganic composite membranes were manufactured by partial zeolitisation of polymer derived ceramic (PDC) tapes. The PDC tapes, which act as mechanical support and chemical source for the zeolite framework builder at the same time, were prepared by tape casting with a slurry composed of polysiloxanes as preceramic polymers, inert (SiC) and reactive (elemental Si) filler particles, and subsequent pyrolysis in argon or nitrogen atmosphere. The tape porosity and the amount of silicon after pyrolysis, available for zeolite crystallisation were controlled by pyrolysis atmosphere and temperature. The partial transformation of the metallic silicon, contained in the tapes, into zeolite crystals was carried out by hydrothermal treatment of the tapes in an aqueous, alkaline solution containing a so called structure directing agent at 150°C with reaction time between 24 and 96 h. The PDC tapes, the PDC tape/zeolite composites and the influence of the thermal history and pyrolysis atmosphere of the PDC tapes on the zeolite layer properties were characterised by means of solid state characterisation, porometry and chemical analysis. With complementary results from the liquid phase after crystallisation (the so called mother liquor) the main parameters affecting the amount and morphology of the zeolite layers on the PDC foams were identified.

Ceramics for Sustainable Energy Technologies with a Focus on Polymer-Derived Ceramics

Due to their high hardness, high temperature stability, and high chemical stability, ceramic materials have significant uses and potential in existing and emerging sustainable technologies . In this paper, we provide a thorough overview of ceramics in a variety of sustainable applications. This is followed by a detailed discussion of an emerging process to make ceramics called polymer (or precursor)-derived ceramics . It is shown that due to the versatility of this process in making a wide range of shapes—fibers, coatings , and porous ceramics, this is an attractive route to make ceramics that will be a critical element in the next generation of sustainable technologies.

Microstructure and Microhardness Changes of 30CrMnSiA Steel Modified Surface Layers by Electrolyte-Plasma Processing

This work is devoted to research of 30CrMnSiA steel structurally modified surface layers and study of electrolyte-plasma treatment parameters influence on changing peculiarities of structural-phase state and also the increase of constructional 30CrMnSi steel operating ability. The chosen technology leads to the formation of stable ferrite-pearlite structures in 30CrMnSi steel surface layers, provides high mechanical properties. As for the basic experimental methods of research in the work we used metallographic analysis applying optical microscope «NEOPHOT-21» and «AXIOPHOT-2», Х-ray analysis on the diffractometer ХPertPRO in monochromatic CuKα-radiation, mechanical tests for microhardness on PMT-3М installation. It is established that microstructure of 30CrMnSi steel modified layers samples while different processing modes, consists of α - phase, iron carbides. Using technology of structural steels electrolytic-plasma cementation under arc discharge terms in the electrolyte, we get diffusive surface layer with increased microhardness parameters and wear resistance providing good operating ability for details often subjected to wear.

Impact of Electrolytic-Plasma Nitriding on 34CrNi1Mo Steel Surface Layer Properties

The present work is devoted to the research into the microstructure and microhardness of structural steel 34CrNi1Mo after electrolytic-plasma nitriding in a cathode heating mode. The technology of electrolyte-plasma hardening provides a reliable quality and the required mechanical properties of the products which are often subjected to wear and temperature-force actions.

Influence of Plasma Carbonitriding and Nitriding on Phase Composition and Mechanical Properties of a X 12 CrNi 18 10 Ti Stainless Steel Surface

Abstract The surface structure of a X 12 CrNi 1810 Ti low-carbon steel after saturation with nitrogen and carbon as a consequence of electrolytic plasma nitriding and carbonitriding was studied in this work. It turned out that the X 12 CrNi 1810 Ti steel surface has a modified martensite structure and high hardness after electrolytic plasma processing. It was determined that carbide and nitride particles are formed in the surface layer during nitriding and carbonitriding followed by tempering. The X 12 CrNi 1810 Ti steel wear resistance after carbonitriding and nitriding was investigated and a decrease of the friction coefficient was observed.

Structured ceramic surfaces by preceramic polymer demixing processes

Polymeric and ceramic coatings with a cellular structure have been manufactured based on demixing processes by the use of two different preceramic polymers and silicon carbide fillers in a dip coating process. The rheological properties of the coating system were adjusted by adding a monomeric silane and methanol, and the crosslinking process was triggered by the addition of catalysts. The surface tension of the coating system was measured and a temperature range for coating and structure formation was identified. The as coated substrates were investigated with respect to an influence of the substrate microstructure and the coating speed on the cellular structure of the coatings. While the substrate microstructure has no influence on the cell structure the coating speed led to a minor change in the cell width. The as received thermoset coatings were pyrolyzed and the structure was intact even after firing at 1100 °C in different atmospheres.