Media immersion tests

Test medium (immersed for 72 h) Tensile strength (MPa) at at 50% at 100% cohesion elongation elongation loss Maximum elongation (%) Adhesion after test Judgement ... 

Test medium (immersed for 72 h at 23°C) Volume change (%) Mass change %) Volume change after drying (%)... 

Chemical corrosion tests focus primarily on resistance to surface and selective corrosion. In general, the effect of material and corrosive medium variables can be understood with these methods. The variable potential, on the other hand, is more or less undefined and can experience time changes depending on the properties of the various partial reactions involved in corrosion. The fluctuation range of the potentials found in practice cannot be taken into account in the immersion test. Often, therefore, the results obtained in chemical corrosion testing using electrochemical methods must be further differentiated to take account of the variable potential. If the corrosion rate determined in chemical corrosion testing depends heavily on the potential, and has little to offer, but if there is only a little potential dependence it is more reliable. 

For the corrosion of ceramics by ordinary liquid media, the testing is usually done by immersion tests the sample is placed in a heated retort or autoclave inside a stirred excess of corrosive medium. Common test conditions are at the boiling point of the medium (e.g. 10% H2SO4, 30% NaOH) for a week. 

Before a pollutant molecule can diffuse in the geomembrane, it must first penetrate from the surrounding medium into the geomembrane. If one submerges a geomembrane in an aqueous solution of a chemical (immersion test), the molecules of the chemical can potentially become dissolved in the plastic. Depending on the extent of their enrichment, molecules may also leave the geomembrane. At a specified temperature T and specified pressure p an equilibrium state is established where a certain mole fraction X of the chemical in the plastic is in equilibrium with a certain mole fraction xo in the aqueous solution. The partition coefficient a is defined as the ratio of the two mole fractions ... 

The constant phase element can be found for electrochemical behavior in both electrolytes. The unique identification came from the depressed semicircle in Nyquist plots [45]. The existence of a Warburg impedance in the 3.5% NaCl immersion test indicated diffusion control (mass transfer) in that medium. The signature of Warburg impedance is found in Nyquist plots exhibiting a 45° curve in the low frequency region (see Fig. 31.5). Clearly, the polarization resistance did not decrease much for zk/s in 0.1 M HCl even after 8 weeks of immersion. However, there was a significant decrease in 3.5% NaCl. The double layer capacitance for the sample containing a polyaniline film on mild steel was always smaller in 0.1 M HCl environments than in 3.5% NaCl. 

Simple immersion tests. Basically, small sections of the candidate material are exposed to the test medium for a period of time and the loss of weight of the material is measured. Immersion testing... 

The bubble point test is based on the fact that, for a porous filter medium, immersed in and thoroughly wetted by a specific liquid, the pressure required to force a gas bubble through a pore is inversely proportional to the diameter of the pore. In practice, this means that the pore size of a filter element can be established by wetting the element completely with the liquid and measuring the pressure at... 

The Champ-Sons model is a most effieient tool allowing quantitative predictions of the field radiated by arbitrary transducers and possibly complex interfaces. It allows one to easily define the complete set of transducer characteristics (shape of the piezoelectric element, planar or focused lens, contact or immersion, single or multi-element), the excitation pulse (possibly an experimentally measured signal), to define the characteristics of the testing configuration (geometry of the piece, transducer position relatively to the piece, characteristics of both the coupling medium and the piece), and finally to define the calculation to run (field-points position, acoustical quantity considered). 

Static Tests Ideally, a static test would consist of immersing a test sample in the liquid medium held in an inert container under isothermal conditions. 

Figure 4.50. Cumulative dissolution results. Two experimental tablet formulations were tested against each other in a dissolution test in which tablets are immersed in a stirred aqueous medium (number of tablets, constructional details and operation of apparatus, and amount of medium are givens). Eighty or more percent of the drug in either formulation is set free within 10 minutes. The slow terminal release displayed by formulation B could point towards an unwanted drug/excipient interaction. The vertical bars indicate ymean - with Sy 3%. A simple linear/exponential model was used to approximate the data for the strength 2 formulation. Strengths I and 3 are not depicted but look very similar.

A slurry is to be filtered with a rotary drum filter that is 5 ft in diameter and 8 ft long, rotates once every 10 s, and has 20% of its surface immersed in the slurry. The drum operates with a vacuum of 20 in.Hg. A lab test was run on a sample of the slurry using 1/4 ft2 of the filter medium at a constant flow rate of 40 cm3/s. After 20 s the pressure drop was 30 psi across the lab filter, and after 40 s it was 35 psi. How many gallons of filtrate can be filtered per day in the rotary drum ... 

To evaluate its capability for refractive index measurement, the fiber FPI device was tested using various liquids including methanol, acetone, and 2-propanol at room temperature. The interference spectra of the device immersed in various liquids are shown in Fig. 7.12 for comparison. The signal intensity dropped when the device was immersed in liquids as a result of the reduced refractive index contrast and thus lowered Fresnel reflections from the cavity endfaces. However, the interference fringes maintained a similar visibility. The spectral distance between the two adjacent valleys also decreased, indicating the increase of refractive index of the medium inside the cavity. Using (7.4), the refractive indices of the liquids were calculated to be nmethanoi = 1 -3283, acetone = 1 -3577, and n2-propanoi = 1.3739, which was close to the commonly accepted values. 

In the pharmaceutical industry, it is important that aU products are properly tested and vahdated prior to release for sale. One of the most important tests is the determination of tablet dissolution rate. In this procedure tablets are immersed in a suitable medium to mimic the action of the stomach and the release of the active ingredients monitored over a period of time. Automation of these procedures is obviously important for various reasons including cost, accuracy of analysis and for validation of the results according to good laboratory practice. 

On in vitro testing when the pulsed release system is immersed in the dissolution medium, the following can be observed ... 

BECKE TEST. A microscope of moderate or high magnification is used to compare the indices of refraction of two contiguous minerals for of a mineral and a mounting medium or immersion liquid), in a thin section or other mount. When the two substances differ substantially in refractive index, they are separated by a bright line, called the Becke line. The line moves toward the less refractive of two materials when the tube of the microscope is lowered. 

The bubble point test is a popular single-point physical integrity test for disc filter membranes based on Eq. (21). A fdter medium is wetted with a liquid, and test gas pressure is slowly raised until a steady stream of bubbles appears from a tube or hose attached to the downstream side of the filter and immersed in water (Fig. 9). The pressure at which the bubbles first appear is recorded as the bubble point and is related to the largest pores in the fdter medium. A pore size can be calculated from Eq. (21) however, it must be realized that the bubble point test does not measure the actual pore size, but only allows correla-... 

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