Powders water adsorption

We developed another dispersant presenting properties for a special application. In some cases when an ultra fine calcium carbonate slurry is spray dried, a re-agglomeration of the powder often occurs, due to high water adsorption. This powder aggregation is detrimental to the quality of the final product. 

Chemical analyses and physical property measurements made on the starting materials and the products of the ammonium fluotitanate reactions are shown in Table 2. The analytical data for the products of the iron ammonium fluoride reaction are shown in Table 3. Following treatment, the various zeolite products contained up to 16.1 wt.% Ti02 in the zeolites treated with ammonium fluotitanate, and up to 16.9 wt.% Fe203 in the zeolites treated with ammonium Iron fluoride. X-ray powder diffraction intensity is decreased in the substituted products, but retention of oxygen and water adsorption capacity indicates that pore volume has been retained. No extraneous peaks due to other crystalline phases were observed in the X-ray powder diffraction patterns of well washed products. 

Dilute fluorine gas (0-20%) can be used to treat zeolites at near-ambient temperature and pressure. Most of the resulting materials retain very high crystallinity even after 600°C postcalcination for two hours. Both framework infrared spectra and X-ray powder diffraction patterns clearly show structural dealumination and stabilization. The hydrophobic nature of the fluorine-treated and 600sC-calcined material is shown by a low water adsorption capacity and selective adsorption of n-butanol from a 1 vol.% n-butanol-water solution. Fluorination also changes the catalytic activity of the zeolite as measured by an n-butane cracking method. 

The Impact of Water Adsorption on the Energetics of Surface Interactions of Powders of Different Crystal Forms... 

Chemical Modification of Alumina The commercial grade alumina (AD-101) produced by Indian Petrochemicals Corporation Limited, CATAD Division, Bombay is used as the starting alumina in the present study. This alumina is treated with mild alkali(NaOH) and with mild acid (HCl). About 25 gms of AD-101 is exactlty weighed and taken in a round bottomed flask and to it requisite concentration of NaOH/HCl is added and heated at required temperature for 4-15 hrs. After treatment it is thoroughly washed with double distilled water to remove excess of acid / alkali by monitoring the pH of the extract. A commercial alumina adsorbent available in the market which is specifically used for removal of tert-butyl catechol from styrene is used as a reference. The commercial sample was in the form of a finely divided powder (<120 mesh size) with a water adsorption capacity of 13% at 60% RH. 

The surface hydration-hydroxylation structure of titania, proved previously mainly by IR studies using dry titania powders, also seems to hold when these powders are dispersed in water. An interesting approach, therefore, is to probe directly the uptake of water from the gas phase by DS-coated rutile surfaces (42). Water adsorption isotherms are presented in Figure 14. The dual nature of titania surface sites, a property not seen... 

To account for the apparent strong adsorption of electrolyte ions at the ceramic powder/water interface, Yates et al. [10,21] proposed the formation of ion pairs at charged surface sites (the site-binding model for the metal oxide/aqueous solution interface). This model and its modifications have been successfully applied to many oxide/aqueous solution interfaces in the presence of simple monovalent inorganic ions [21-23]. For a ceramic powder surface in a simple electrolyte solution (e.g., KNO3 and NaCl), the formation of ion pairs can be represented as... 

To correlate the adsorption and diffusion properties to the cation distribution in the structure of CaNaA zeolites, temperature programmed desorption, anomalous X-ray powder diffraction and quasi elastic neutron scattering experiments were performed. It is shown that water adsorption and diffusion behaviour differs with the calcium content. Fourier maps obtained from anomalous diffraction experiments near the Ca K-edge allow to identify the calcium crystallographic sites unambiguously. 

The surface hydration-hydroxylation structure of titania, proved previously mainly by IR studies using dry titania powders, also seems to hold when these powders are dispersed in water. An interesting approach, therefore, is to probe directly the uptake of water from the gas phase by DS-coated rutile surfaces [42]. Water adsorption isotherms are presented in Figure 52.14. The dual nature of titania surface sites, a property not seen with other common oxides such as silica and alumina, leads to an unusual type of water adsorption isotherm for titania. The isotherm shows two distinct knees (Figure 52.14) connected by a region where adsorption increases linearly with the partial vapor pressure of water. The explanation for this adsorption behavior is rather complex [42] and beyond the scope of this chapter. This behavior is believed to be due to the presence of hydrated surface cation sites. 

FIGURE 2.33 DTF IPSDs with respect to (a) the pore volume and (b) the specific surface area calculated on the basis of the water adsorption isotherms for nanooxides. (Adapted from Powder TechnoL, 195, Gun ko, V.M., Zarko, V.L, Turov, V.V. et al.. Morphological and structural features of individual and composite nanooxides with alumina, silica, and titania in powders and aqueous suspensions, 245-258, 2009g, Copyright 2009, with permission from Elsevier.)... 

Figure 4.4 Effect of lauric acid coating (from iso-propyl alcohol) on the water adsorption and resistivity of a chalk powder.

Rennukka and AmiruP reported fabrication of P(3HB-co-4HB)/chitosan blends by adding chitosan powder (5, 10,15 and 20 wt%) to P(3HB-co-4HB) with various 4HB molar fractions (10,18 and 28 mol%). Since P(3HB-co-4HB) copolymer is hydrophobic in nature, it did not show any hydrophilicity regardless of various compositions of 4HB monomer. However, there was a significant improvement of the water adsorption capability when the chitosan content in the blends was increased from 5 to 20 wt%. Water uptake was influenced by the presence of the free hydrophilic groups in the blend films. The presence of chitosan induced the intra or/and inter-molecular network between the components in the blend films. Therefore, the hydrophilicity of the blend films increased. 

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