Interruption test

Hoinkins et al., (1967) glued the ion exchange particles to a cylinder that rotated in the solution and could be easily removed and reimmersed. Bunzl (1974b) attached peat particles to a polyvinylchloride (PVC) cylinder with self-adhesive tape. The cylinder, which had a small propeller at its lower end, was rotated at 470 rpm in an H solution to saturate the peat. Then the cylinder was dipped in Pb(N03)2 and removed at certain times. Interruption tests showed that FD was rate-limiting for Pb-H exchange on peat. 

The development of damage in the form of matrix cracks within 1-D CMCs subject to tensile loading has been traced by direct optical observations on specimens with carefully polished surfaces, and by acoustic emission detection,7 9 62,79-81 as well as by ultrasonic velocity measurements.82 Interrupted tests, in conjunction with sectioning and SEM observations, have also been used. Analysis of the matrix damage found in 1-D CMCs provides the... 

Client Interrupt Testing The system was tested to determine what would happen in the case of a sudden breakdown of a client s Personal Computer (PC). The acceptance criterion was that the database would not be corrupted. Data not saved properly should thus be rolled back automatically to the latest secure version of the data. 

Several methods are available to ascertain whether film diffusion is rate determining for a given system (e.g., interruption test, determination of the Helfferich number) but will not be discussed here in more detail. 

All the previously described mechanism criteria rely in some way or another upon comparing the predictions of rate theory with the observations. The interruption test , first described by Kressman, is a favoured means of differentiating between film and particle diffusion rate control since it places no reliance upon theoretical boundary conditions or exchanger properties. 

The actual rate determining step cannot be infered from the course of the kinetic curves, but some assessment is possible by means of specially arranged experiment. Interruption test makes it possible to assess the role intraparticle diffusion (diffusion in pores of the adsorbent) as potential rate determining step. The isotope exchange experiment is started in usual way vide infra), and k kinetic data points are collected (equilibration times t, . .., ft), but at the time ijj the solid is separated from the liquid, then both phases are stored separately for a time much... 

Interruption test, 536, 537 Ionic radius, correlation with PZC, 211 Ionic strength, effect on specific adsorption, 322... 

Interruption test suggests particle diffusion control. Even Na distribution between the particle and solution after 5 ntin. 

Many experimental criteria have been suggested for identification of the rate-controlling step. The majority are based on curve fitting to idealized rate laws and are unreliable. The two best methods are the so-called interruption test and the determination of the dependence of (he rate on particle. size. 

Particle size (r ) Solution concentration (O Separation factor (ocy) Stirring rate (rpm) Exchanger capacity (Q Interruption test Temperature (7) Proportional to l/r° Proportional to C See text Sensitive Proportional to 1/C Not sensitive Kinetic increment 4%/ K Proportional to l/r Independent Independent Independent Independent Sensitive Kinetic increment 6%/°K... 

In the interruption test (Kressman and Kitchener, 1949), the ion exchanger is temporarily separated from the liquid. If the rate is controlled by mass transfer in the liquid, the rate upon reimmersion is the same as at the time of separation, the quasi-stationary state in the film is very quickly re-established. If the rate is controlled by intraparticle diffusion, concentration gradients within the particle have time to relax, and the rate is faster upon reimmersion. This comparison is independent of specific mechanisms and algebraic forms of rate laws. 

Interruption tests indicated that diffusion of the ions across a liquid layer (film) of unstirred solution surrounding the peat particles is the ratecontrolling step (Bunzl, 1974a). Accordingly, rate equations for film diffusion-controlled, ion-exchange processes for the boundary and initial conditions of our experiments are derived and compared to experimental results. 

The above theory will of course not hold, if film diffusion is not the rate-determining step. This can be the case if e.g., the desorption process is very slow or even almost irreversible (e.g., as a result of conformational changes of the polydispersed molecular aggregates). Therefore, before any rate equations are applied, the rate-determining step should be confirmed (e.g., by interruption tests). 

Combustion test, including burner, combustion air failure and power interruption tests... 

Fig. 4.7 Stress-strain curves for polymer PU3 (DBDI-PEA-BDO) at nominal strain-rate 3.1x10 s (a) interrupted test, with 10 min. stress relaxation at intervals of 50% elongation (b) continuous test [61]...

By doing this study, a quantitative correlation was found by us, between the magnitude of the Mullins effect and the fractional energy dissipation by hysteresis under cyclic straining, giving a common relation that was approached by all the materials studied. Stress relaxation in interrupted tests also increased with hysteretic energy loss [175]. 

Fig. 4.45 Loading and unloading of a DBDI material (DBDI EG PEA). Interrupted test with 100 s waiting time during loading [127]...

Fig. 8.81 Relationship between time-to -failure and steady-state creep rate for the monolithic (filled square box) and composite (filled circle) materials. The downward arrows indicate tests with large accelerated creep (tests at 1350 °C). The upward arrows indicate interrupted tests [40]. With kind permission of John Wiley and Sons...

The bulk of the results obtained in this study were obtained by analytical transmission electron microscopy. Observations were made on both grades of material in the as-received, untested condition and after tensile testing at 1250°C. Test samples selected for examination covered the range of observed creep behavior, and included samples that failed after times ranging from -10 to -200 hours depending on applied stress and also samples from interrupted tests that survived for up to 2000 hours under lower applied stresses. In addition, a comparison was made of non-reinforced samples tested with and without a 500 hour pre-anneal at the test temperature. In all cases, the gauge sections of crept samples were cut parallel to the stress axis to obtain both near-surface and raid-plane sections. Prior to final TEM specimen preparation, these sections were examined optically for evidence of distributed creep cavitation or crack damage. 

The current interrupt test is particularly easy to perform with single cells and small fuel cell stacks. With larger cells the switching of the higher currents can be problematic. Current interrupts and electrical impedance spectroscopy give us two powerful methods of finding the causes of fuel cell irreversibihties, and both methods are widely used. 

Typical results from three current interrupt tests are shown in Figures 3.10, 3.11, and 3.12. These three examples are shown because of the clear qualitative indication they give of the importance of the different types of voltage drop we have been describing. Because oscilloscopes do not show vertical Unes, the appearance is slightly different... 

Figure 3.10 Current interrupt test for a low-temperature, ambient pressure, hydrogen fuel cell. The ohmic and activation voltage drops are similar. (Time scale 0.2s/div , i = lOOmAcm . )...

Figure 3.11 Current interrupt test for a direct methanol fuel cell. There is a large activation overvoltage at both electrodes. As a result, the activation overvoltage is much greater than the ohmic, which is barely discernible. (Time scale 2s/div. / = 10mAcm. )...

Fuel cell circuit for current interrupt test consisting of load, on/off switch, and a transient recording device such as oscilloscope of data acquisition system (DAS). 

Thompson, Wadsworth e Louat [52] testing mirror-polished specimens of polycrystalline high purity copper, found that if they would interrupt tests, from time to time, and electro polish a surface layer 2 pm depth, most of slip lines and bands would disappear with the exception of some that, instead, would persist. This was the sign of a surface damage that, though microscopic, was deeper than 2 pm. 

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