Hypothesis: The electrical charges that develop on the surface of the ceramic particles upon contact with water, due to the interaction with ions in solution, result in a liquid-solid interface, which utterly modifies the properties of individual particles and the way they interact with each other to form a structure. This work explores a new approach to the relationships between structure and stability of suspensions. Experiments: For this purpose, suspensions with a constant 0.35 volume fraction of alpha-alumina particles, neither spherical nor smooth, and controlled ionic strength (0-90 mM KCl) were prepared and characterized in terms of flow behaviour, electrical conductivity and particle's electrokinetic mobility. Findings: Electrical conductivity (132 mu S/cm < conductivity < 5730 mu S/cm) and rheology measurements (10(-2) Pa s < viscosity < 10(4) Pa s) were found to complement each other to produce a more accurate picture of the suspension's structure. Deviations of experimental data from well-accepted behavioural models were elucidated when the surface area equivalent particle size was used. With the electrical double layer thickness obtained from electrical conductivity measurements, this enabled the interpretation of the relationship between the suspension's viscosity and the particles electrical conductivity, which provides a criterion for the stability of concentrated colloidal suspensions. (C) 2020 Elsevier Inc. All rights reserved.

Probably the most decisive benefit of Powder Injection Molding (PIM) is the wide range of materials. As a logical consequence current R+D activities target on the adaptation of new metal and ceramic materials.

The slightly attractive inter-particle equilibrium potential associated with electrostatically stabilized suspensions of minimum viscosity is described by the DLVO theory and commonly gauged by static zeta-potential measurements, plagued with experimental uncertainties. In this work, the electrokinetic mobility of alumina particles was measured in suspensions prepared with selected solids content and ionic strength, as well as was the electrical conductivity of each suspension and suspending liquid. Particles electrical conductivity was then calculated and related to the colloidal stability described by the DLVO theory, enabling the identification of a processing window for the stability control of concentrated suspensions. The maximum repulsive potential and distance between particles (similar to 46 nm) corresponds to the particles maximum conductivity. When the particles conductivity is zero, the diffuse layer is fully collapsed and they stand at the minimum reversible distance (similar to 7 nm). At the equilibrium conductivity, a potential" curve is produced with a secondary attractive minimum of similar to 1.5 kT at an inter-particle distance of similar to 17 nm, as suggested by the DLVO theory and the Equipartition of Energy theorem. The condition for accurate measurement of static zeta-potential occurs at the isoconductivity point between particles and suspending liquid. 2017 Elsevier B.V. All rights reserved.

In this study, it was tried to develop a process chain for ceramic injection molding of Al 2 O 3 -chopped-fiber reinforced oxide-ceramic-matrix-composite. The feedstocks are compounded at 50 Vol. % filling degree of solid (Al 2 O 3 μ-powder (Taimei Chemicals Co. Ltd.) and 3,2 mm chopped fibers (3M)), in which fiber content varies from 0 Vol. % to 100 Vol. %. As binder system, PE + Paraffin Wax + Stearic Acid are used. The ingredients are compounded in a kneader (Brabender) at 125°C and after the viscosity measurement in the high pressure capillary rheometer at 160°C and certain shear rates, the feedstock is injection molded (Battenfeld) at 160°C, which is followed by debinding process, including chemical (in n-Hexane) and thermal steps, and 2h sintering at different temperatures. Flow paths in the machinery parts, rheological properties of binding system, fiber content and the fiber orientation have significant effect on the flow behavior of the feedstock, fiber -orientation, -distribution & -length, which are crucial to understand the properties of end-parts like mechanical reinforcement of the fibers. The fibers in the sintered parts are ca. 200 μm in average length. The fibers in the feedstock show different orientations depending on the part-geometry and the green bodies have different densities depending on sintering temperature, amount of dispersant and fiber orientation.

In this study precursor derived SiOC/MoSi2 composites were evaluated with respect to their potential for the application as glow plug material. In a first step, fully dense composite materials with different fractions of electrical conductive MoSi2 were fabricated by field-assisted sintering technique (FAST). The percolation threshold, where the electrical properties change from insulating to a suitable level of conduction depends on the microstructure, which can be controlled by the initial particle size of the used SiOC particles. It becomes principally possible to fabricate both, the insulating part and the heater material with the same MoSi2 content and therefore without thermal mismatch. Room temperature properties, high temperature strength, oxidation and creep behaviour depend strongly on the MoSi2 volume fraction. MoSi2 contents beyond the percolation threshold lead to significantly enhanced creep rates. At high temperatures, reactions between SiOC and MoSi2 can be observed, which differ at the air exposed surface and in the interior of the samples. From these findings, an upper limit for the application temperature can be derived. (C) 2016 The Ceramic Society of Japan. All rights reserved.

Additive Manufacturing (AM), also known as 3D printing, is a relatively new technology which enables the toolless production of components and entire assemblies directly from a CAD file. Today, the technology is still not widely used in industrial production. It is mainly limited to special applications, although it shows great potential. In this paper, first approaches are shown to apply AM to the production of rotors for permanent magnet synchronous machines (PMSM). The possibilities of a lightweight design with a low moment of inertia as well as the influence on the magnetic anisotropy for an improved sensorless control of PMSM are pointed out. The results clearly demonstrate the great potential of additive manufacturing in electrical engineering applications.

Ceramic rolls for wire hot rolling at multi-line rolling mills may fail bycontact overloading. The present paper deals with a refinement of first publications onthis topic. In the first part the relations for stress intensity factor computation via theweight function method are compiled. Then it is shown whether the mixed-mode stressintensity factors of the curved cracks can be applied for the prediction of crack path viathe condition of local symmetry.

The residual stress intensity factors at the surface and at the deepest point of the semi-elliptical Knoop indentation crack is determined from the stresses in the damaged zone below the indenter. For this purpose, the weight function approach by Cruse and Besuner was used and wide-range expressions of the geometric function are given. The solution is then applied to a commercial silicon nitride for which all relevant geometrical data are available.

A method to manufacture unique interpenetrating 50 vol% nickel–chromium/alumina composites, namely NiCr8020/Al2O3/50pp, is reported. Key process is a high temperature squeeze casting procedure at temperatures above 1500 °C used to infiltrate alloy NiCr8020 into porous alumina preforms exhibiting a bimodal pore structure. Microstructure and mechanical properties of this new composite material are presented. Bending creep tests at 1000 and 1150 °C are performed. The obtained results are discussed in comparison to a nickel based superalloy. It is shown, that particle preform reinforcement is a promising method to improve creep resistance of nickel based alloys significantly. Due to its outstanding creep resistance, the composite material has a high potential for structural and tribological applications at high temperatures in oxidizing atmospheres.

Transparent glass sponges are a new class of materials that can potentially be used for effective light dispersion in photobioreactors. In this work, transparent glass sponges are prepared by the polymer replica technique employing polyurethane sponges with cell sizes of 20 pores per inch as templates and commercially available nanoscaled SiO2 powders. Necessary conditions for obtaining transparent open-celled glass sponges are presented. Topics such as slurry stabilization, temperature for burning-out the polymer and subsequent sintering of the remaining SiO2 structure to transparent cellular bodies are discussed. It was found, that concentrated suspensions at around pH 10 offer suitable properties for both, bringing enough particles onto the polymer template for the formation of a stable and self-supporting SiO2 shell and for successful sintering of the particulate framework to transparent bodies. Therefore, an adjusted burning-out process and an adequate sintering regime is presented. Furthermore, the resulting sponge structure is characterized employing X-Ray diffractometry, light, and scanning electron microscopy. In addition, volume image analysis was performed using magnetic resonance imaging. This method allows the calculation of geometrical parameters like cell-size and specific surface area of the resulting structure, required for application of the new material.

The structure formation in water based ceramic suspensions during unidirectional freezing was experimentally investigated over a wide range of solidification velocities. Supplementary experiments with polystyrene suspensions were carried out to extend the range of particle sizes. Depending on particle size, solids loading and solidification velocity, planar, lamellar or isotropic growth of the ice crystals leads to different types of microstructure. The results are summarized in a microstructure map as a first estimate for the role of the process parameters in microstructure formation.

Accurate measurements of the intrinsic crack-tip toughness, K(I0), are essential to understanding the strength and toughness of bridging ceramics. Furthermore, even the most carefully made R-curve measurements cannot accurately assess this initial toughness point. In this manuscript, both rigorous and approximate methods are proposed for determining K(I0) from crack-tip opening displacement (COD) measurements on Vickers indent cracks for materials with steeply rising R-curves. Such approaches are attractive because of the relative ease of producing indentation cracks and analyzing the CODs; further, the latter method is of particular interest because it saves considerable computational effort. Both the advantages and limitations of the proposed methods are discussed. Finally, based on applying the above methods to three Si(3)N(4) ceramics, it was concluded that there is a common crack-tip toughness of K(I0)approximate to 2.2 +/- 0.3 MPa center dot root m.

High‐toughness, high‐strength ceramics, such as self‐reinforced Si3N4, derive their superior mechanical properties from microstructures that promote very steeply rising R curves. Furthermore, accurately evaluating the R curve at the earliest stages of crack growth is necessary for correctly understanding, and predicting, the mechanical behavior. Compliance‐ and optical‐based methods for evaluating the crack length, and R curve, at the early stages of crack extension from machined notches are discussed. The earliest stages of crack growth are missed during measurements of the crack length by optical observations due to the nonuniform extension of the crack front during initial crack extension. The most accurate method of evaluating the crack length over all amounts of crack extension is from compliance measurements analyzed by solving a system of equations that incorporates both the effects of the notch and the changes in compliance with the development of bridging tractions. Such a method is computationally expensive, but for materials with steeply rising R curves, simply applying the linear‐elastic compliance evaluation, which only accounts for the notch, but not the bridging tractions, gives a result within about 1%. At longer crack extensions, such an approximation method will incur significant errors; however, at this stage, optical measurements can provide accurate assessments of crack length and enable an accurate assessment of the R curve.