Zinc electrode shape change I. In situ monitoring

Zinc electrode shape change, the redistribution of zinc material over the electrode during repeated cycling, has beenidentified as one of the main life-limiting factors for alkaline nickel oxide/zinc secondary batteries. To investigate this phenomenon in situ, a radiotracer, 65Zn, is incorporated in the battery and its movement monitored during repeated cycling ofthe battery. The changes in the distribution of 65Zn over the electrode during battery operation are attributed to the displacement of radioactive zincate ions via the battery electrolyte. It is shown that the spatial distribution of 65Zn offers areliable indication for the zinc material distribution over the electrode, provided an electrode with uniformly specific radioactivity is used in the measurements. Radiotracer experiments using zinc electrodes containing 2 weight percent HgOas an additive and uniformly labeled with 203Hg, have revealed that during battery cycling no substantial net transport ofmercury species occurs. It is concluded that it is highly unlikely that the mercury additive detaches from or moves overthe zinc electrode surface during the cycling process. Also, these experiments show that zinc material transport as a resultof detachment of electrode mass did not occur

Zinc electrode shape change II. Process and mechanism

The process and mechanism of zinc electrode shape change is investigated with the radiotracer technique. It is shownthat during repeated cycling of the nickel oxide/zinc battery zinc material is transported over the zinc electrode via the battery electrolyte. During charge as well as during discharge zinc material is transported over the electrode. The direction ofthe zinc material transport during charge is opposite its direction during discharge. The amount of zinc material displacedover the electrode during charge is smaller than during discharge, so that after one charge-discharge cycle the net zinc material transport is observed in the direction as found during discharge. A new model for shape change is presented: thedensity gradient model. The model is based on the occurrence of an electrolyte flow during repeated charge-discharge cycling of the zinc secondary battery, which transports zinc material over the electrode. During battery cycling this electrolyte flow arises as a result of density gradients in the solution layer adjacent to the zinc electrode and of volume variationsof the battery electrolyte

A BGO detector for catalysis studies with positron emitters

A detector for measurement of the activity distribution of positron emitters in a catalyst reactor has been designed and built. The detector consists of two banks of each ten BGO scintillation crystals. The activity distribution is measured as a function of time and position along the reactor. The attainable position resolution along the reactor is 3 mm and the minimum sampling time for the measurement of an activity profile is 1 second. The detector has a high sensitivity and the flexibility to be used with catalyst reactors of different types and size

A BGO Detector for Positron Emission Profiling in catalysis

As part of a project to study the reaction kinetics in catalysts, a detector system has been designed and built. The detector will measure in one dimension the activity distribution of positron emitters in catalyst reactors under operational conditions as a function of time. The detector consists of two arrays of ten EGO crystals each and has the flexibility to measure with high sensitivity the activity profile in various reactor sizes; the position resolution that can be reached is 3 m

Nuclear, physical and chemical aspects in cyclotron production of radionuclides

The cyclotron has developed into an indispensable machine for production of a variety of radionuclides. Several nuclear, physical and chemical aspects are treated, with emphasis on their interdependencies, which are illustrated with examples. Attention is also given to production of short-lived positron emitters. These are of increasing interest, not only for clinical investigations, but also for technological research. Finally, the cyclotron as a production machine is compared to the nuclear reactor

Nuclear analytical methods in the life sciences

A survey is given of various nuclear analytical methods. The type of analytical information obtainable and advantageous features for application in the life sciences are briefly indicated. These features are: physically different basis of the analytical method, isotopic rather than elemental determination, no interfering effect of electrons and molecular structure, and penetrating character of nuclear radiation. Suggestions are given for exploitation of the sometimes unique potentials of nuclear analytical methods, particularly when requiring considerable investment for equipment, supporting facilities, and specialized staff