Ceramic accommodation-controlling

Superplasticity in Ceramics Accommodation-Controlling Mechanisms Revisited... 

As can be inferred from the equations outlined above, none of the different models can adjust the creep parameters for all the different ceramics, especially in the case of YTZP,7 explaining why there is still controversy over the accommodation process controlling superplasticity. The same conclusions can be outlined for ceramic composites, although more experimental work should be done.20,31... 

For ceramics with secondary glassy phases, the accommodation processes are governed by these phases. Although diffusion may occur, the glassy phase viscosity controls accommodation mainly in different ways ... 

A version of our apparatus for the study of gas uptake and the measurement of mass accommodation coefficients is shown m Figure 1. The apparatus consists of three chambers. A highly controlled stream of droplets is produced in the first chamber with a nozzle vibrated by a piezoelectric ceramic oscillator. About 100,000 droplets are produced per second. The radius of the droplets is typically 60 microns and the droplets travel at about 3000 centimeters per second. 

Two types of transformations can be very broadly distinguished. The first is the formation of a solid solution, in which solute atoms are inserted into vacancies (lattice sites or interstitial sites) or substitute for a solvent atom on a particular sublattice. Many types of synthetic processes can result in this type of transformation, including ion-exchange reactions, intercalation reactions, alloy solidification processes, and the high-temperature ceramic method. Of these, ion exchange, intercalation, and other so-called soft chemical (chimie douce) reactions produce no stmctural changes except, perhaps, an expansion or contraction of the lattice to accommodate the new species. They are said to be under topotactic, or topochemical, control. 

A lapping system equipped with a 15 in. copper lap plate and an electronically controlled diamond slurry dispenser was used in this research. A 3 xm diamond slurry was employed, which produced higher and more stable material removal rate than a 1 pm diamond slurry. The slurry was applied at a rate of 3 sec of spray every 30 sec. The lapping pressure on each ceramic test bar was 35,700 Pa. A sample carrier accommodated five test bars arranged aroimd the outer perimeter of the carrier. 

The accommodation processes are responsible for the rate-control of superplasticity, and no single mechanism exists to accommodate GBS, even with regards to a particular ceramic system. As noted above, several factors can affect the different mechanisms, among which should be included the nature of the impurities present in the grain boundaries, the secondary phases, and the testing conditions. The different mechanisms for accommodation will be analyzed in the following sections. 

In the simplest case, the lead source is simply removed from the home. A ceramic mug or traditional remedy responsible for lead poisoning can be handled in this way. If the source is water, the child can be given filtered water rather than drinking straight from the tap. In the case of lead paint in a day-care facility or babysitter s house, the family could find alternative accommodations for child care. Measures you can take to control various sources of lead poisoning are discussed in detail in Chapters 13-16. 

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