The first interpretation should be factors s. The best fit was obtained with 0. Above this concentration a Waller factors for the two tin shells at short and negative surface charge is observed in all the pH long distance are equal to 0. This result indicates that the crystal- an iep.
These features evidence the increase of the lite size for the sample containing 7. The inset shows the typical hydrodynamic with the XRPD results since no remarkable change size distribution of diluted 1 vol. A Fig. The value of pH 3. This indicates Fig. The vertical dot line displays the pHiep of unmodified SnO2 particles. The lines drawn through the points are guides to the eyes.
The inset displays the hydrodynamic diameter distribution of particles prepared with 7. Increas- resulting in isolated fragments that peel with ing the powder content a new family of particles is relative facility. In this case the absence of crack apparent in the size distribution function, which was verified only when the thickness of the become bimodal.
The intensity, the mean hydro- supported layer is lower than 0. The increasing difference fired at 8C, is displayed in Fig. These results evidence that the presence SEM micrographs of the dried supported SnO2 of fully dispersed particles in the sol leads to a membranes with 0. SEM micrographs of the dried supported SnO2 membranes with 0. The hydro- dynamic diameter estimated for these MW are 1. This evidences that the pore entrance sieving effects act in the separation process.
At low pH the enolic form Our experimental data Table 1 show that the left part of a is stable whereas at high pH, the primary particle size crystallite size in the dried quinone form right part of a is the equilibrium powder is practically unaffected by the presence of form.
This evidences that the initial steps of the middle part of a could act as a chelating agent formation and growth of SnO2 nanoparticles are with respect to the tin oxide surface, roughly not modified by this complexing agent and this is schematized in Scheme 1 b , resulting to the sur- fully consistent with the acid condition of the face schematized in part c.
So, the surface Scheme 1. The evaporation until 11 vol. This feature allows the towards the deprotonated chelating form and the deposition of gel layer with high particle concen- grafting power of this molecule at the surface of tration and controlled sizes.
The drying shrinkage SnO2 nanoparticles is highly improved. The surface ing process. Comparing the z values at pHiep of unmodified particles vertical doted line in Fig.
Conclusion 7. This results from pH conditions, which do pH range. Never- higher than 7. The results reported for moieties are bonded to tin atoms in a chelate form.
This value is in nanoscale level, with solid contents up to 7 vol. This feature results of crack-free SnO2 supported membranes and from the increase of sol stability towards gelation.
Sainctavit, J. Petiau, A. Manceau, R. Rivallant, M. Belakhovsky, G. Renaud, Nucl. A The authors acknowledge the collaboration of [11] F. Villain, V. Briois, I. Castro, C. Helary, M. Briois, C. Santilli, S. Pulcinelli, G. Brito, J. Solids Gurman, J. Zabinsky, J. Rehr, A. Ankudinov, R. Albers, M.
Eller, Phys. B 52 Briois, S. Pulcinelli, C. A sol of sulphur can also be prepared when H 2 S gas is bubbled through an aqueous solution of SO 2. A number of metals like silver, gold, platinum, mercury lead can be obtained in the colloidal state by the reduction of their salt solutions dilute using suitable reducing agents like hydrogen sulphide, formaldehyde, stannous chloride, tannic acid etc. A colloidal solution of ferric hydroxide is obtained by boiling a dilute solution of ferric chloride.
By hydrolysis of a dilute solution of sodium silicate with a hydrochloric acid, the colloidal solution of silicic acid is obtained. Arsenious sulphide, As 2 S 3 is a lyophobic colloid. It is obtained by the hydrolysis of arsenious oxide AS 2 0 3 with boiling distilled water, followed by passing H 2 S gas through solution obtained. In the colloidal solution of arsenious sulphide, each particle is surrounded by HS- ions, produced by the dissociation of H 2 S.
By Exchange Solvent Method:. There are a number of substances whose colloidal solutions can be prepared by taking a solution of the substance in one solvent and pouring it into another solvent in which the substance is relatively less soluble. If a solution of sulphur or phosphorus prepared in alcohol is poured into water, a colloidal solution of sulphur or phosphorus is obtained due to the low solubility of sulphur or phosphorus in water.
By change of physical state:. A colloidal solution of certain elements such as mercury and sulphur are obtained by passing their vapours through cold water containing a stabilizer an ammonium salt or a citrate. Excessive Cooling Method:. A colloidal solution of ice in an organic solvent like ether or chloroform can be prepared by freezing a solution of water in the solvent.
The molecules of water which can no longer be held in solution, separately combine to form particles of colloidal size. Purification of Colloidal Solution. The process of separating the particles of colloid from those of crystalloid, by means of diffusion through a suitable membrane animal membrane or parchment paper is called dialysis.
The apparatus used for the performing dialysis is called dialyser. The colloidal particles can not pass through a parchment or cellophane membrane while the ions of the electrolyte crystalloids can pass through it.
A bag made up of suitable semipermeable membrane containing the colloidal solution is suspended in a vessel through which fresh water is continuously flown. The molecules and ions of crystalloids diffuse through the membrane into the water and are washed away.
Thus the sol in the bag is purified. The ordinary process of dialysis is slow. This process is called electrodialysis. The ions present in the colloidal solution migrate towards oppositely charged electrodes. The important application of electrodialysis process in the artificial kidney machine used for the purification of the blood of the patients whose kidneys have failed to work.
The pores of ordinary filter paper are large, hence colloidal particles pass through them easily. The treated filter paper may retain colloidal particles and allow the true solution particles to escape. Such filter paper is known as ultrafilter and the process of separating colloids by using ultrafilters is known as ultrafiltration. The colloidal particles left on ultrafilter paper are then washed with a fresh dispersion medium to get a pure colloidal solution.
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