Volumetric Change Methods

6 Gas Adsorption on Solid Measurement Methods 1.6.6.1 Volumetric Change Methods 

The change in volume of gas during adsorption is measured directly in principle, and the apparatus is comparatively simple. One can use a mercury (other suitable liquids) reservoir beneath the 

FIGURE 5.6 Plot of (relative volume) vgas versus (relative pressure) Pgas (schematic) (types (a) I and II, (b) III, and (c) IV and V). 

Different gases (such as nitrogen) are normally used as the adsorbate if the surface area of a solid needs to be examined. The gas is cooled by liquid nitrogen. The tap to the sample bulb is opened, and the drop in pressure is determined. In the surface area calculations, a value of 0.162 nm2 is used for the area of an adsorbed nitrogen molecule. 

Because of the toxic properties of Hg, modern apparatus use a combination of valves to measure the change in the volume of gas adsorbed. Commercially available instruments are designed with such modem detectors. 

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The Watts shrinkage test method measures shrinkage of a test sample in terms of volumetric change after curing. The sample preparation consisted of using 90 mg of an... 

ASTM D1434 [25] provides for a second method of measuring the gas transmission rate of plastics, namely that at constant pressure. This technique also forms the basis of a rubber test standard [29], In this case the pressure is kept constant in the low-pressure chamber and the volumetric change in the permeated gas is measured. Equation 11 reduces to... 

Adsorption capacity Calculation method of adsorption capacity is through the measurement of volumetric change to calculate the adsorption capacity. The formula of... 

In a drop-on-demand inkjet printer, the fluid is maintained at ambient pressure and a transducer is used to create a drop only when needed. The transducer creates a volumetric change in the fluid which creates pressure waves. The pressure waves travel to an orifice, and are converted to fluid velocity, which results in a drop being ejected from the orifice. Figure 8 shows a schematic of a drop-on-demand type inkjet system which can generate 60 xm diameter drops of butyl carbitol (an organic solvent) from a device with a 50 [xm orifice at 4000 drops per second. Therefore, various molds for microfluidic applications could be created by this method. 

TMA is a method for measuring linear or volumetric changes in polymers as a function of temperature, time or force and is often used in conjimction with DSC to investigate the structure and properties of polymers. This combination is often found in commercial microthermal analysers (see Section 6.4.9). While the DSC is concerned with the energetics of physical and chemical changes, TMA measures the dimensional effects associated with these changes and so it can be used to obtain the coefficient of thermal expansion for polymer samples. 

Before discussing the problems of control laboratories, it is important to have a clear picture of the revolutionary changes which have been, and still are, taking place in the field of analytical chemistry. One has only to observe the recent issues of Analytical Chemistry, noting especially the editorials of Murphy (14) and the articles of Muller (13), to recognize the trend away from the classical gravimetric and volumetric methods of 20 years ago. 

Gal-Or and Hoelscher (G5) have recently developed a fast and simple transient-response method for the measurement of concentration and volumetric mass-transfer coefficients in gas-liquid dispersions. The method involves the use of a transient response to a step change in the composition of the feed gas. The resulting change in the composition of the liquid phase of the dispersion is measured by means of a Clark electrode, which permits the rapid and accurate analysis of oxygen or carbon dioxide concentrations in a gas, in blood, or in any liquid mixture. 

Attention is finally focused on the advantages of conductometric titrations, which include (i) colored solutions where no indicator is found to function satisfactorily can be successfully titrated by this method (ii) the method is useful for titrating weak acids against weak bases, which does not produce a sharp change in color with indications in ordinary volumetric analysis and (iii) more accurate results are obtained because of the graphical determination of the end-point. 

TITRATION. A method of determining volumetrically the concentration of a substance in solution by adding a standard solution of known volume and strength until a change in an indicator is noted or by electrical measurements. 

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