The formation of ice between hydrotalcite particles measured by thermoporometry
| Autor: | M.K. Titulaer, Herre Talsma, J. B. H. Jansen, J.W. Geus |
|---|---|
| Rok vydání: | 1996 |
| Předmět: |
Thermogravimetric analysis
Hydrotalcite Chemistry Sorption 02 engineering and technology 010502 geochemistry & geophysics 021001 nanoscience & nanotechnology Molecular sieve 01 natural sciences Chloride law.invention Crystallography Adsorption Chemical engineering Geochemistry and Petrology law Specific surface area medicine Calcination 0210 nano-technology 0105 earth and related environmental sciences medicine.drug |
| Zdroj: | Clay Minerals. 31:263-277 |
| ISSN: | 1471-8030 0009-8558 |
| DOI: | 10.1180/claymin.1996.031.2.12 |
| Popis: | Thermoporometry (TPM) was applied to hydrotalcite precipitates prepared with carbonate, bicarboxylic acids and chloride. It was used to measure the formation of an ice body between the hydrotalcite particles. Before TPM could be applied, the dried hydrotalcite precipitate had to be soaked for two weeks in water. The mean value of a factor F measured by TPM, which described the shape of the ice body in hydrotalcite, was 1.7. This value was between those of a purely cylindrical (F = 2) and a purely spherical ice body (F = 1), indicating the formation of ice lenses. From the radius of the ice body, Rn, ice volume, V,, and shape factor F, the corresponding specific surface area of the hydrotalcite particles could be assessed. The TPM indicated that the distance between the separate hydrotalcite crystals in water, which is equal to 2(Rn+0.9) nm, was a function of the type of anion incorporated at the interlayer, such as chloride and bicarboxylic acid. The pore volume and surface area of the hydrotalcite particles measured by TPM were compared with those determined by the traditional nitrogen sorption technique on dried hydrotalcite. It appeared that sorption of N2 yielded much lower values than TPM. This difference was interpreted as being due to slow penetration of N2 through the dried hydrotalcite samples to the interparticle voids. Hydrotalcites can be used as shape-selective heterogeneous catalysts, adsorbents, detergents, and molecular sieves in the chemical industry. The performance as a catalyst is highly dependent on the mobility of gaseous reactants or products through the porous structure. A rapid penetration of reactants in hydrotalcite is required for the desired reactivity. Hydrotalcites can be produced at a low temperature which keeps the precipitated particles at the lowest size and their surface area and reactivity to a maximum. Natural samples of hydrotalcites are not suitable because of the presence of impurities. The hydrotalcite catalyst can also be used intact, with intercalation of various catalytic active (in)organic molecules (Tatsumi et al., 1992), or used in calcined form (Reichle, 1985). Hydrotalcite minerals |
| Databáze: | OpenAIRE |
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