Thematic bibliography of mercury porosimetry

Frequency-domain Photoacoustic Spectroscopy (PAS) was used with a He-Ne laser exciting beam to probe commercially available, powdered and pressed nickel electrodes with dual-porosity profiles. The frequency response of the electrodes was shown to be capable of providing quantitative information about the thermal conductivity and diffusivity of each of the two porous layers, provided the depth of the porosity junction in the electrode bulk is known. The reasonable agreement of the experimental data with a one-dimensional mathematical model of the photoacoustic response from a two-layer, photoacoustically saturated, continuous system indicates that powdered and pressed nickel electrodes behave photoacoustically approximately like a simple continuous composite-layer solid. This conclusion, together with experimental PAS results from uniporous electrodes, emphasizes the high potential of photoacoustic spectroscopy as a nondestructive, depth profiling, analytical technique for the determination of complex porosity profiles in electrodes manufactured for use in electrochemical energy conversion devices, such as fuel cells.

Quantitative Depth Profiling of Biporous Nickel Electrodes by Frequency-Domain Laser-Induced Photoacoustic Spectroscopy

Together with porous metals produced by conventional power metallurgy techniques (whose porosity varies from 20 to 60%), today materials of high porosity, ranging from 70 to 9597%, play an increasingly important role in many branches of engineering. These materials offer a combination of such properties as low density, high permeability to gases and liquids, good filtering ability, a large open surface, ability to retain liquids by capillary action, and low electrical and thermal conductivities.*

Properties of high-porosity metals

1.

For a porous material with a bidisperse structure, the conditions bringing about the “opening” of the structure depend primarily on the amount of the pore-forming addition. On passing from a round to an acicular particle shape, the amount of the pore-forming addition necessary for the “opening” of the bidisperse structure falls.




2.

The strength of a porous material with a bidisperse structure is determined chiefly by its total porosity, and is practically unaffected by the properties of the pore-forming addition.

Effect of pore-forming additions on some characteristics of sintered permeable nickel materials with a “bidisperse” structure

The structure of porous nickel plaques produced by the following routes has been examined using scanning electron microscopy: (a) pressure-less sintering of nickel powder; (b) slurry sintering of powder; (c) roll-compaction and sintering of powder; (d) pyrolysis of cloth impregnated with nickel chloride. The observations show that measurements of pore-size distribution with a mercury porosimeter can be misleading, and also reveal the existence of fine closed porosity in plaques made from impregnated cloth. The relation of the observed porosity characteristics and inter-particle bond diameters to the mechanical and electrical properties of the plaques is discussed.

D. J. Burr

Papers

The structure and properties of porous nickel plaques