Sample size and geometry

Lack of standards in testing for refractories becomes apparent when one realizes that factors such as sample size and geometry, state of stress in the lining, thermal gradient, thermal cycling and duration are difficult to scale down to a laboratory scale to simulate service conditions. Accelerated tests involving severe conditions do not always conform to realistic conditions and may lead to unrealistic results. 

Two concerns surround toxic gas tests. The first is over how the gases are generated. Eactors such as sample size and geometry as well as test procedures can affect not only the concentration of the gases generated but possibly even the types of compounds produced. 

None of the tests can be guaranteed to give an accurate representation of what happens in a fire, because the flammability of plastics formulations is a very complex matter, and factors like sample size and geometry, proximity of other combustible materials, prevailing temperatures, wind speed and direction, and the scope for rapid heat dissipation vary with the circumstances. 

In practice, correction factors should generally be avoided whenever possible, i.e. the sample size and geometry and the probe head should be chosen in such a way that the sample can either be treated as a bulk material (t > 55), or a thin film (/ < 0.55), and the lateral dimensions exceed the conditions ofD> 40r (for circular or rectangular samples). Based on the above conditions for the correction factor F2, the distance d between the outer probes and the sample edges (Fig. 23-1) should be at least 5s, to keep the error in the resistance below 5%. 

Sublimation drying was performed in a custom-built dryer consisting of an eight liter vacuum chamber mounted in a commercial chest freezer, a dry ice cold trap, solvent filter, and rotary vane vacuum pump (Fig 2). This system has an ultimate vacuum pressure of approximately 2x10 Torr, and the ability to control chamber temperatures between 0 C and -25 C. This dryer allows for greater possibilities in sample size and geometry, at a lower cost than commercially available fteeze dryers. 

It was shown that the sample size and geometry were important factors in microwave processes. For example, changing the sample size from 5 to 15 g caused a temperature increase of 32 °C in 10 min at the same power level. Essentially, no coupling occurred between a sample of 5g... 

In addition, the Raman technique has proved to be particularly valuable in the study of single crystals where the infrared technique has greater limitations on sample size and geometry. Polarization data obtained from Raman spectra allow unambiguous classification of fundamentals and lattice modes into the various symmetry classes. Although Raman spectroscopy will never challenge X-ray diffraction as a tool for quantitative structural analysis, it is the preferred technique when qualitative information is sufficient because it is faster and less expensive. 

Effect of Catalyst Loading. In another set of experiments, two extruded monoliths of identical size and geometry were coated with Pt. One sample was... 

How do sample size and sample form (geometry or packing) affect the profile of the decomposition ... 

Microdialysis probes come in several sizes and geometries they can be much smaller than ultrafiltration probes because the volume of sample collected does not depend on the membrane surface area (Fig. 3A). Therefore, small microdialysis probes are used when precise spatial resolution is desired. When less spatial resolution is needed and higher recoveries are desirable, longer loop-type probes can be used (Fig. 3B). 

Some studies have addressed the possible interplay between sample size and degradation of aliphatic polyesters. Sample size is commonly interchanged with sample geometry. Production of variously shaped devices introduces a variety of proeessing routes, which results in further changes to polymer degradation. 

Flexibility is particularly important in mechanical analysis for testing many different sizes and geometries of polymer samples over a wide temperature and modulus range. 

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