Experimental pool boiling investigations of FC-72 on silicon with artificial cavities and integrated temperature microsensors

In this experimental study, fluorinert FC-72 is boiled on a silicon chip with artificial cavities and integrated microsensors. The horizontal silicon chip with dimensions of 39.5 × 19 × 0.38 mm is completely immersed in FC-72. The integrated nickel–titanium temperature microsensors on the back of the chip are calibrated individually and exhibit a near-linear increase of electrical resistance with temperature. The applied heat fluxes and the resulting wall superheat at the boiling surface are varied by means of an integral thin-film resistance heater (95% Al, 4% Cu and 1% Si), also on the back of the silicon chip. Artificial cylindrical cavities with a mouth diameter of 10 μm and depths of 40, 80 or 100 μm situated above the microthermometers serve as artificial nucleation sites, due to trapped vapour. Bubble growth rates, frequencies, departure diameters of bubbles and waiting times between bubbles from an isolated cavity for different wall superheats and pressures were obtained by analysing high-speed video images and the simultaneously measured temperature below the artificial cavity.     

Important aspects in the formulation of solid–fluid debris-flow models. Part I. Thermodynamic implications

This article points at some critical issues which are connected with the theoretical formulation of the thermodynamics of solid–fluid mixtures of frictional materials. It is our view that a complete thermodynamic exploitation of the second law of thermodynamics is necessary to obtain the proper parameterizations of the constitutive quantities in such theories. These issues are explained in detail in a recently published book by Schneider and Hutter (Solid–Fluid Mixtures of Frictional Materials in Geophysical and Geotechnical Context, 2009), which we wish to advertize with these notes. The model is a saturated mixture of an arbitrary number of solid and fluid constituents which may be compressible or density preserving, which exhibit visco-frictional (visco-hypoplastic) behavior, but are all subject to the same temperature. Mass exchange between the constituents may account for particle size separation and phase changes due to fragmentation and abrasion. Destabilization of a saturated soil mass from the pre- and the post-critical phases of a catastrophic motion from initiation to deposition is modeled by symmetric tensorial variables which are related to the rate independent parts of the constituent stress tensors.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5 μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Investigations on the Thermal Cycling Stability of SiFeCr Coated NbtZr

 Refractory metal alloys play an important role as highly thermostable materials. Due to their lack of oxidation stability under elevated temperatures it is necessary to protect them with coatings. The thermal cycling stability of Si20Cr20Fe-coatings on Nb10W2.5Zr was investigated by means of imaging secondary ion mass spectrometry showing the inward-diffusion of oxygen and subsequent preferential precipitation of zirconium oxides at the grain boundaries in the bulk. An unintentional interface layer of high boron content that most likely plays a major role in oxidation protection was found. EDX measurements have been performed to investigate on the phases formed in this complex system.     

SIMS Characterisation of Aluminum-Alloyed Hot Isostatic Pressed Steel

 Recently, interest in steel alloyed with∼1% Al increased. These materials are expected to show a higher resistance against oxidation at high temperatures which will improve their performance when used as high-speed-steels. Furthermore, efforts have been made to combine the advantages of Al-steels with those of powder-metallurgic methods like hotisostatic-pressing (hip). This should result in a better macro- and microscopic homogeneity of the distribution of all compounds, yielding less waste-production and a longer life-time of products. In order to gain deeper insights in the process of “hipping” of the considered material and to see the distribution of both main as well as trace components, 2D and 3D-SIMS measurements of the material were performed before and after having undergone the hip process. The measurements showed enrichments of Na, K, Mg, Ca, and S at the particle boundaries before as well as after the hip-process. In the hipped material, the enrichments are significantly stronger in the spatial domains in-between larger particles. They also reveal, that the concentration of C is not equal in all particles and that the particles are covered with an Al₂O₃-layer which is not dispersed by the hip-process. There were also found small (∼50–100 nm) nitride-precipitates before as well as after the hip-process.     

Debris flow modeling: A review

A debris flow represents a mixture of sediment particles of various sizes and water flowing down a confined, channel-shaped region (e.g., gully, ravine or valley) down to its end, at which point it becomes unconfined and spreads out into a fan-shaped mass. This review begins with a survey of the literature on the physical-mathematical modeling of debris flows. Next, we discuss the basic aspects of their phenomenology, such as dilatancy, internal friction, fluidization, and particle segregation. The basic characterization of a debris flow as a mixture motivates the application of the continuum thermodynamical theory of mixtures to formulate a model for a debris flow as a viscous fluid-granular solid mixture. A major advantage of such a formulation, which goes beyond the most general models in the literature, e.g., Takahashi (1991), is that it can be used to expose and better understand the assumptions underlying existing models, as well as to derive new, more sophisticated models. Finally, we delve into the issue of how such models have been or can be implemented numerically, as well as general boundary conditions for debris flows.Dedicated to Professor Reint de Boer upon the occasion of his 60^th birthday     

Similarity solutions for granular avalanches of finite mass with variable bed friction

This paper continues a series of studies on the plane flow of a pile of cohesionless granular material down a rough inclined plane. Internal and basal friction laws are assumed to obey the Mohr-Coulomb yield criterion but in contrast to previous investigations the angle of friction at the bottom of the pile is considered to depend on the position or on the velocity or on both. Similarity, i.e. shape preserving solutions are constructed. The depth of the pile and the profile of the total minus the centre of mass velocity are determined analytically, but the total length and the position of the centre of mass are calculated numerically. If the basal friction angle is constant, the centre of mass moves with constant acceleration and the length of the pile extends monotonically. These motions change, when the angle of friction varies along the pile — the length of the pile may extend, contract or remain stationary and the centre of mass motion may decelerate or even reach steady state. Eight special cases are exhibited which demonstrate the influence of the friction law on the speed and spread of the pile.     

Pattern formation in granular avalanches

Three new experiments are described which exhibit strong pattern formation in the deposits left by successive granular avalanches. At low flow rates continuous deposition, erosion or rotation gives rise to intermittent avalanche release. Once in motion kinetic sieving of a bi-disperse granular mixture creates a two-layer shear band in which the larger particles overlie the smaller particles. When this is brought abruptly to rest by the upslope propagation of a shock wave a pair of str ipes is “frozen” into the deposited material. Successive releases create a large scale pattern, which strongly reflects the history of the granular flow. At faster deposition, erosion and rotation rates a new flow regime is entered in which intermittency and shock formation ceases, and the associated patterns change. Received Aug. 25, 1997     

A dynamic theory for magnetizable elastic solids with thermal and electrical conduction

A general dynamical theory of magnetizable, electrically and thermally conducting media is developed for soft ferromagnetic or paramagnetic materials in external electromagnetic fields. The general equations are linearized by assuming infinitesimal strains, linear constitutive equations and that all field variables may be divided into two parts: a "rigid body state" and a "perturbation state". The former is the same as the one in rigid body electrodynamics, and the latter which accounts for electromagnetic interaction with the deformable continuum is coupled with stress and strain through linearized field equations. The theory is developed for general anisotropy but specialized for materials with uniaxial, or higher, symmetry.