The K2ZrF6 wetting process: Effect of surface chemistry on the ability of a SiC-Fiber preform to be impregnated by aluminum

SiC-ceramic materials, either as flat substrates or porous fiber preforms, are spontaneously wetted by aluminum at 700 °C to 800 °C when they have been pretreated with an aqueous solution of K₂ZrF₆. The wetting enhancement effect results from exothermic chemical reactions occurring at the SiC/Al interface. The first phenomenon thought to occur is a disruption of the alumina film covering liquid aluminum due to a reaction of A1₂O₃ with K₂ZrF₆. Then alumina is totally dissolved at low temperatures by potassium/aluminum mixed fluorides, giving rise to a very fluid cryolitic liquid spreading out on the surface of liquid aluminum and to the true SiC/Al interface. Simultaneously, a large evolution of heat occurs, mainly due to the reduction of K₂ZrF₆ by aluminum and the formation of Al₃Zr. The impregnation of 2D-SiC/SiC preforms by aluminum is modeled, and the effect of both the contact angle decrease and local temperature rise on the impregnation of the preforms, e.g., by gravity casting, is established. Formerly Researcher with the Laboratoire de Chimie du Solide du CNRS Formerly Researcher with the Laboratoire de Chimie du Solide du CNRS Formerly Researcher with the Laboratoire de Chimie du Solide du CNRS Formerly Professor with the Laboratoire de Chimie du Solide du CNRS Université de Bordeaux I, F-33405, Talence, France,     

Errata: Planar to equiaxed transition in the presence of an external wetting surface

The online version of the original article can be found at     

Planar to equiaxed transition in the presence of an external wetting surface

First time experimental evidence is presented for the steady-state growth of equiaxed grains during directional solidification in the presence of a positive temperature gradient. The evidence is shown for transparent grains in the succinonitrile-acetone system, which are induced to grow on wetting surfaces (restraints). The conditions for equiaxed to dendrite transitions on the restraint are recorded, and a simple model is developed to explain this effect.     

Mechanism of brittle-ductile transition of a glass-ceramic rigid substrate

The hardness, elastic modulus, and scratch resistance of a glass-ceramic rigid substrate were measured by nanoindentation and nanoscratch, and the fracture toughness was measured by indentation using a Vickers indenter. The results show that the hardness and elastic modulus at a peak indentation depth of 200 nm are 9.04 and 94.70 GPa, respectively. These values reflect the properties of the glass-ceramic seen to be directly related to normal force on the tip. The critical load and scratch depth estimated fiom the scratch depth profile after scratching and the friction profile are 268.60 mN and 335.10 nm, respectively. If the load and scratch depth are under the critical values, the glass-ceramic rigid substrate will undergo plastic flow rather than fracture. The formula of critical depth of cut described by Bifnao et al. is modified based on the difference of critical scratch depth     

Movement (flow) of a wetting liquid in a porous ceramic under the action of capillary forces

Translated from Poroshkovaya Metallurgiya, No. 4(328), pp. 39–43, April, 1990.     

The interplay between language, gesture, and affect during communicative transition: A dynamic systems approach.

From a dynamic systems perspective, transition points in development are times of increased instability, during which behavioral patterns are susceptible to temporary decoupling. This study investigated the impact of the vocabulary spurt on existing patterns of communicative coordination. Eighteen typically developing infants were videotaped at home 1 month before, at, and after the vocabulary spurt. Infants were identified as spurters if they underwent a discrete phase transition in vocabulary development (marked by an inflection point), and compared with a group of nonspurters whose word-learning rates followed a trajectory of continuous change. Relative to surrounding sessions, there were significant reductions in overall coordination of communicative behaviors and in words produced in coordination at the vocabulary spurt session for infants who experienced more dramatic vocabulary growth. In contrast, nonspurters demonstrated little change across sessions. Findings underscore the importance of transitions as opportunities for observing processes of developmental change. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The wetting of aluminum oxide by chromium-nickel melts

Summary A study was made of the effect of time, temperature, and concentration on the angle of contact between aluminum oxide and chromium-nickel melts. The wetting isotherm has a minimum. The presence of the minimum is attributed to reaction between the melt and solid aluminum oxide. The best adhesion to aluminum oxide is exhibited by nickel-chromium alloys containing up to 30 at.% chromium.