Consequence of Damage in Silica on Young’s Modulus

Water diffusion into silica glass results in a thin zone near the surface of the glass. In this zone the water reacts with the SiO₂ structure and “damages” the originally intact SiO₂ rings. The consequence is a reduced Young’s module. This effect can be described by use of continuum damage mechanics according to Kachanov and Lemaitre. The amount of damage can be estimated from literature data on sound velocity measurements

Mass transfer coefficients for water at silica surfaces : Additional results

Monotonously increasing water concentrations at silica surfaces can be described by a mass transfer surface condition for diffusion that hinders free water penetration from a water vapour environment into silica. So far, the related mass transfer coefficient has been determined predominantly from water uptake measurements. In this report, the data basis will be extended by taking into consideration further literature results on measurements of surface water concentrations and by evaluation of disk curvature measurements

Water diffusion in cracked surface layers : Unloaded cracks

Water diffusion at the surface of a silica glass is increased when surface cracks are present which were inadvertently introduced by the surface treatment of samples. Due to the larger true surface exposed to the humid environment, an apparently increased diffusion constant must occur. With the help of a simple model the influence of the cracks for small water penetration depths is described. Simplified approximations are given which allow a continuous interpolation of two limit solutions over greater penetration depths or diffusion times. In the present report we restrict our considerations on unloaded cracks

Analytical solutions of the diffusion differential equation

The water diffusivity in silica is affected by swelling stresses in the surface region which are caused by the silica/water reaction. Since the diffusivity is a function of stress, the consequence is a diffusivity that depends on the local water concentration. Then the solution of the diffusion equation is complicated and makes numerical computations necessary. Disadvantage of numerical computations is the fact that the used extend of the depth range must be finite and, consequently, the semiinfiite body can only be approximated. In the following considerations we will give exact and semi-analytical solutions for diffusion problems in the half-space

'Flying Plasmons': Fabry-P\`erot Resonances in Levitated Silver Nanowires

Plasmonic nano structures such as wire waveguides or antennas are key building blocks for novel highly integrated photonics. A quantitative understanding of the optical material properties of individual structures on the nanoscale is thus indispensable for predicting and designing the functionality of complex composite elements. In this letter we study propagating surface plasmon polaritons in single silver nanowires isolated from its environment by levitation in a linear Paul trap. Symmetry-breaking effects, e.g., from supporting substrates are completely eliminated in this way. Illuminated with white light from a supercontinuum source, Fabry-P\`erot-like resonances are observed in the scattering spectra obtained from the ends of the nanowires. The plasmonic nature of the signal is verified by local excitation and photon collection corresponding to a clean transmission measurement through a Fabry-P\`erot resonator. A numerical simulation is used to compute the complex effective refractive indices of the nanowires as input parameter for a simple Fabry-P\`erot model, which nicely reproduces the measured spectra despite the highly dispersive nature of the system. Our studies pave the way for quantitative characterization of nearly any trappable plasmonic nano object, even of fragile ones such as droplets of liquids or molten metal and of nearly any nanoresonator based on a finite waveguide with implications for modeling of complex hybrid structures featuring strong coupling or lasing. Moreover, the configuration has the potential to be complemented by gas sensors to study the impact of hot electrons on catalytic reactions nearby plasmonic particles

Damage in silica by hydroxyl generation described by Wang\u27s theoretical data

Water diffusion into silica glass results in a thin zone near the surface of the glass. In this zone the water reacts with the SiO₂ structure and "damages" the originally intact SiO₂ rings. The consequence is a reduced Young’s module. This effect can be described by use of continuum damage mechanics according to Kachanov and Lemaitre. In this report the dependency between hydroxyl concentration and damage will be described for large water concentrations by using the Wang-model. In addition the implications on strength of pre-damaged materials, deformation behavior and crack-tip stress intensity factor are addressed

Korrosionsschutzschichten für Dieselpartikelfilter aus Cordierit zur Erhöhung der thermochemischen Belastbarkeit

Ein im normalen Betrieb geeignetes Material für Dieselrußpartikelfilter stellt Cordierit dar. Bei der Filterregeneration, die nötig ist um die im Betrieb akkumulierten Rußpartikel abzubrennen, kann es zu Reaktionen mit Aschebestandteilen kommen, wodurch der Filter geschädigt wird. Um dies zu verhindern, wird ein Schutzschichtmaterial identifiziert und ein Verfahren etabliert, womit die Porenkanäle des Filters beschichtet werden, um die durch Ölaschen hervorgerufenen Schädigungen zu minimieren

Interpretation of irregular water profiles at silica surfaces

In the present Report, we will discuss the irregular water distributions at silica surfaces as were reported by the measured data from Zouine et al. [1], especially those at room temperature. The question was whether the deviations from the usually found erfc-shaped water pro- files can be understood by competing diffusion and surface dissolution and whether back-diffusion after water or air storage, may affect the type of water profile. We will come to the conclusion that the irregular distributions of the measured data by Zouine et al. [1], especially those at room tem- perature, can be understood by back-diffusion after water or air storage, respectively

Mass-transfer coefficient for water at silica surfaces: Effect of surface dissolution?

In earlier evaluations of literature results, it was found that the mass transfer when storing silica in liquid water was significantly greater than in tests in a steam atmosphere under saturation vapor pressure. In the literature, different glass qualities were compared and it is conceivable that small material differences may lead to the observed results. On the other hand, it can be shown qualitatively that there is also the possibility of mass removal through dissolution, which is different for liquid water and saturated steam. This is the subject to be addressed in this report

Mass transfer coefficient for silica in liquid water at 200°C

In previous reports on the mass transfer coefficient of quartz glass in water, we were able to determine that this is significantly larger in liquid water than in saturated water vapor as the surrounding medium. From literature results by Zouine et al. (2007) a lower limit value of the time parameter h/√D in eq.(4) of >10$^{-6}$ h$^{-1/2}$, could be deduced for 200°C and liquid water. One explanation for this result could be, among other things, an increased roughness due to the dissolution of the surface layers of the glass in water than is to be expected for water vapour