Bruno G.,Corning Inc. |
Garlea V.O.,Oak Ridge National Laboratory |
Muth J.,Oak Ridge National Laboratory |
Efremov A.M.,Corning SNG |
And 2 more authors.
Acta Materialia | Year: 2012
Mechanisms of microcracking and stress release in β-eucryptite ceramics were investigated by applying a combination of neutron diffraction (ND), dilatometry and the Integrity Factor Model (IFM). It was observed that the macroscopic thermal expansion of solid samples closely follows the lattice thermal expansion as a function of temperature, and both are dominated by microcracks closing (during heating) and opening (during cooling). Analogous experiments on powders showed that the stresses that manifest peak shift are indeed relieved by comminution, and that the resulting lattice thermal expansion can be considered as unconstrained. By means of Rietveld refinement of the ND data, the evolution with temperature of peak width parameters linked to strain distributions along the basal, pyramidal and axial planes could also be extracted. The peak width parameters S HKL correlated well with the strains calculated by peak shift and with the model results. Furthermore, while the peak shifts showed that the powders are basically stress free, the S HKL showed a strong evolution of the peak width. Powders carry, therefore, a measurable strain distribution inside the particles, owing to the thermal expansion anisotropy of the crystallites. The IFM allowed this behavior to be rationalized, and the effect of microcracking on thermal expansion to be quantified. Experimental data allowed accurate numerical prediction of microcracking on cooling and of the evolution of microstresses. They also allowed the derivation of the material elastic modulus from bulk thermal expansion curves through the IFM concept. Ultrasound resonance measurements of the elastic modulus strongly support these theoretical predictions. © 2012 Acta Materialia Inc. Published by Elsevier Ltd.
Bruno G.,Corning Inc. |
Efremov A.M.,Corning SNG |
An C.,Corning Inc. |
Nickerson S.,Corning Inc.
Ceramic Engineering and Science Proceedings | Year: 2011
Porous microcracked ceramic materials present interesting peculiarities such as very low thermal expansion and very high strain tolerance. Those make them excellent thermal shock resistant materials. Microcracking is generally generated during cooling from the firing/ceramming temperature, due to a large crystal thermal expansion anisotropy. We have investigated some of the peculiar properties of porous ceramics such as the (partly negative) thermal expansion, the hysteresis of the Young's modulus as a function of temperature, and its non-linearity as a function of applied uniaxial compressive load. Microcracked porous ceramics, such as β-eucryptite, cordierite and aluminum titanate have been taken as examples, and we have compared them with non-microcracked porous ceramics such as silicon carbide and alumina. We have observed that the Young's modulus and the thermal expansion of microcracked ceramics cycle as a function of temperature, following the same curve; moreover, the Young's modulus has a strong variation (different for each material) as a function of applied load. This, linked to the observation that thermally-induced microcracks have a particular crystallographic orientation, has led us to distinguish two kinds of microcracks: thermal and mechanical. The latter are generated during loading, as extension of existing ones, or fresh, and may not be reversible as the former. Indeed, the time-dependence analysis of the stress-strain curves has allowed us to produce further evidence that the two phenomena coexist in porous microcracked ceramics. Most of the non-linear phenomena do not appear in non-microcracked ceramics. Finally, the integrity factor modeling work has allowed rationalizing the phenomenon.
Chivilikhin M.S.,Corning SNG |
Soboleva V.,Corning SNG |
Kuandykov L.,Corning SNG |
Woehl P.,Corning Inc. |
Lavric E.D.,Corning Inc.
Chemical Engineering Transactions | Year: 2010
Corning® Advanced-Flow™ glass reactors are continuous flow reactors with hydraulic diameter in the range of millimetres. These devices make possible the switch of chemical reactions from batch mode to continuous processing through more efficient, more economical and safer processes. In addition, these reactors provide a platform for developing innovative chemistries that have never been considered industrially practical, either for hazard or yield reasons. Corning proprietary apparatuses are compact, adaptable and scalable, optimizing overall production cost and quality of high-value specialty, fine, and pharmaceutical chemicals. Corning Advanced-Flow™ glass reactors are composed of multiple inter-connected glass devices having different designs, offering the advantages of process intensification and glass-specific qualities like transparency and very good chemical resistance. This paper presents the comparison between experimental and CFD modelling results of a family of Corning glass devices aiming at achieving and maintaining very efficient mixing along the dwell time path. Numerical results are compared to experimental data: velocity profiles measured by micro-PIV means, pressure drop and heat transfer coefficient. The satisfactory agreement between experimental results and CFD modelling proved the utility of numerical simulations in the development of new designs. Therefore, CFD tools help on one hand to predict the performance of new devices and on the other hand to optimize their design in order to improve their behaviour. Thus, CFD simulation facilitates the design and reduces time and cost for the investigation. Copyright © 2010, AIDIC Servizi S.r.l.