Pressure jump applications

The simplest experiment we can visualise performing is the very rapid application of a small strain which is then maintained at a constant level. This is simply a strain-jump experiment and can be treated in an analogous fashion to a temperature or a pressure-jump experiment. The stress will follow the strain and increase to a maximum value. For an... 

Conductivity and Optical Detection Using p-Jump Relaxation 75 Evaluation of p-Jump Measurements 76 Commercially Available p-Jump Units 78 Application of Pressure-Jump Relaxation Techniques to Soil Constituents 81 Stopped-Flow Techniques 91 Introduction 91... 

A sudden pressure release or application of pressure can be employed to cause the pressure jump. Ljunggren and Lamm (1958) described the first pressure-jump apparatus, which consisted of a sample cell connected to a nitrogen tank. With this apparatus, a pressure increase to 15.2 MPa could be obtained in 50 ms by quickly opening the valve. Chemical relaxation was monitored conductometrically. 

Application of Pressure-Jump Relaxation Techniques to Soil Constituents... 

Gruenewald, B., and Knoche, W. (1979). Recent developments and applications of pressure jump methods. In Techniques and Applications of Fast Reactions in Solutions (W. J. Gettins and E. Wyn-Jones, eds.), pp. 87-94. Reidel Publ., Dordrecht, The Netherlands. 

The perturbation of the equilibrium normally is a change in temperature, pressure or concentration of one of the reagents and the methods are known as temperature jump, pressure jump and concentration jump, respectively. The advantage of these methods is that the perturbation, especially of temperature and pressure, can be applied very quickly and reactions with half-times in the microsecond range can be observed. The major limitation is that the equilibrium position of the reaction must involve significant concentrations of both reactants and products. Thus relaxation methods are not applicable to essentially irreversible reactions. 

A number of soil chemical phenomena are characterized by rapid reaction rates that occur on millisecond and microsecond time scales. Batch and flow techniques cannot be used to measure such reaction rates. Moreover, kinetic studies that are conducted using these methods yield apparent rate coefficients and apparent rate laws since mass transfer and transport processes usually predominate. Relaxation methods enable one to measure reaction rates on millisecond and microsecond time scales and 10 determine mechanistic rate laws. In this chapter, theoretical aspects of chemical relaxation are presented. Transient relaxation methods such as temperature-jump, pressure-jump, concentration-jump, and electric field pulse techniques will be discussed and their application to the study of cation and anion adsorption/desorption phenomena, ion-exchange processes, and hydrolysis and complexation reactions will he covered. 

The objective of this chapter is to discuss the theory of chemical relaxation and its application to the study of soil chemical reaction rates. Transient relaxation techniques including temperature-jump (t-jump), pressure-jump (p-jump), concentration-jump (c-jump) and electric-field pulse will be discussed both as to their theoretical basis and experimental design and application. Application of these techniques to the study of several soil chemical phenomena will be discussed including anion and cation adsorp-tion/desorption reactions, ion-exchange processes, hydrolysis of soil minerals, and complexation reactions. 

Gruenewald, B., and W. Knoche. 1979. Recent developments and applications of pressure jump... 

Of the relaxation methods only the temperature-jump and pressure-jump methods have been adapted for high pressure application, and of these two only the former (hptj) has been used in many systems for volume of activation determinations. Despite the flurry of activity in developing hptj,84 88 the method has not found application in organometallic chemistry, although in principle it could be employed if the system properties and solvent were suitable. 

Details of a standard pressure-jump instrument89 and high-pressure pressure-jump cells can be obtained from appropriate literature.90 93 The method has found very limited application and not at all in organometallic chemistry. Commercial units or modules for high pressure relaxation methods are not available. 

These were developed initially by Eigen and depend on the application of a small disturbance to a chemical system at equilibrium, normally by the dissipation of a pulse of energy in the temperature-jump method but also on occasion by a sudden change in pressure (pressure-jump) or electric field. The system then adapts (Fig. 11) to its new situation, normally a slightly higher temperature and hence a changed equilibrium constant, at a rate that can be measured either optically or conductimetrically. The... 

RECENT DEVELOPMENTS AND APPLICATIONS OF PRESSURE JUMP METHODS... 

The time resolution of rapid-flow methods is limited by the rate at which two reactants are mixed, which is restricted to about 1 ms. To measure faster reactions, alternative methods are required. A generally applicable method is the measurement of system adjustment following a relatively small perturbation. A system at equilibrium is perturbed by a sudden temperature or pressure jump, applied as a single rapid change or as a periodic oscillation. Changes in the concentration of reactants and products are subsequently monitored. From the patterns observed, individual rate constants can be obtained. 

Over a macroscopic filter area these incoherent jumps would average out each other leading to a smooth evolution of the pressure drop as that in Fig. 14. The type of simulation shown in Fig. 19 is expected to be largely applicable in the near future for industrial use exploiting grid-computing environments (http //www.unizar.es/flowgrid/). 

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