The electrokinetic behaviour of freshly prepared γ‐AlOOH, α‐ and γ‐Al(OH)₃

Abstract

It was shown that the electrokinetic behaviour (especially the isoelectric pH value) of Al-hydroxides depends very strongly on their mode of origin.There is a close connection with the dehydration temperatures, with phosphate-adsorption and with the results of Rontgenographic analysis.

The Isoelectric Points of Solid Oxides, Solid Hydroxides, and Aqueous Hydroxo Complex Systems

“…The hydrous oxides precipitated from metal salt solution are defect structures containing a high concentration of structural defects and excess H20 in addition to coprecipitated ions (124). Schuylenborgh, Arens, and Sanger (110)(111)(112)(113) in a painstaking study of aluminum and iron oxides and hydroxides were able to show that any feature of sample history leading to increased crystal perfection (observed by X-ray diffraction line narrowing) leads to decreased IEPS. As discussed under "Effects of Hydration," substitution of H20 for O2or OHwould be expected to shift the IEPS to a more basic pH.…”

“…Holmes (86) found an intermediate value after an indefinite wateraging time (< 1 day); hence, his value was rejected as failing to represent any equilibrium state of the solid. The observations on natural minerals by Schuylenborgh and Sanger (111,112) have not been reproduced by any other group, hence are questioned but not rejected, because their method is valid (1) and IEPS's for many of their synthetic materials agree with observations by others.…”

Clay-water relationship—theory and application. A review

“…The position of the point of zero charge depends on the crystal structure of the alumina (2). The surface of silica particles may be considered a model for the part of the edge surfaces at which the silica sheets are disrupted.…”