Colloidal vanadium pentoxide

Colloidal Vanadium Pentoxide.11—When a soluble vanadate is treated with mineral acids, a red, curdy form of vanadium pentoxide is precipitated, which, on being shaken with water, appears to dissolve to a red liquid. This reaction gives rise to the following usual method for making a colloidal solution Ammonium metavanadate, NH4V03, is made into a paste with 10 per cent, hydrochloric acid of 10 per cent, concentration, and the resulting gel of vanadium pentoxide is washed repeatedly on the filter with distilled water until it assumes the colloidal form, i.e. until it is peptised, and in consequence passes through the... 

Colloidal vanadium pentoxide is negatively charged and according to Biltz can be made by treating ammonium vanadate Avith HCl. The precipitate is washed until it goes into solution and then it is dialyzed. The hydrosol is colored yellow. Concentrated solutions coagulate easily. 

The vanadium pentoxide catalyst Is prepared as follows Suspend 5 g. of pure ammonium vanadate in 50 ml. of water and add slowly 7 5 ml. of pure concentrated hydrochloric acid. Allow the reddish-brown, semi-colloidal precipitate to settle (preferably overnight), decant the supernatant solution, and wash the precipitate several times by decantation. Finally, suspend the precipitate in 76 ml. of water and allow it to stand for 3 days. This treatment renders the precipitate granular and easy to 6lter. Filter the precipitate with suction, wash it several times with cold 5 p>er cent, sodium chloride solution to remove hydrochloric acid. Dry the product at 120° for 12 hours, grind it in a mortar to a fine powder, and heat again at 120° for 12 hours. The yield of catalyst is about 3 - 5 g. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

A colloidal suspension of conductive vanadium pentoxide [130] can be used to perform intercalation, adsorption or encapsulation of electroactive molecules or biomolecules for electrodes or biosensor realization [131]. Encapsulation of glucose oxidase in nanocomposite films made with polyvinyl alcohol and V205 sol-gel matrix or in ferrocene intercalated V2Os sol-gel [132] were envisaged to prepare glucose biosensors. 

Vanadium pentoxide sols can be employed to bring about coagulation of positively charged colloids for example, ferric hydroxide and aluminium hydroxide. The amount necessary for the coagulation of a given quantity of the positive colloid is very small in comparison with the required quantities of arsenic trisulphide, antimony trisulphide, and other negative colloids. It appears, therefore, that the colloidal... 

The preparation of lyophilic sols is easy and most of the time a mixture of the dispersion medium and the substance to be dispersed need only be stirred. Gelatine, for example, disperses almost spontaneously in water. The hydroxides of iron, aluminium, chromium and zirconium as well as vanadium pentoxide and silicic acids all belong to the group of hydrophilic colloids. 

J. J. Legendre and J. Livage, Vanadium pentoxide gels I. Structural study by electron diffraction, J. Colloid Interface Set, 94, 75-83 (1983). 

Furthermore it appears that the thixotropic state can best (or perhaps only) be obtained with sols containing disc-shaped or rod-shaped particles, such as bentonite (a colloidal clay), ferric oxide, vanadium pentoxide, etc. 

S. D. Desai and E. L. Cussler, Microporous vanadium pentoxide. 2. Making solids from colloidal... 

Flow birefringence can be understood properly with the help of a commonplace example. A curious thing happens when an aged colloidal dispersion of vanadium pentoxide is stirred slowly the path of the stirnng rod lights up since the colloidal particles orient themselves along the stream lines. This effect is observed because of the difference in the amount of light reflected by the symmetrically oriented particles as compared to the randomly oriented ones. In a similar... 

The diameters of atoms and molecules of classical chemistry lie below one half mfjL. The region of colloids has usually been chosen to begin at a dimension of 1 mp. and to end upwards at about 1 (jl, where the region of emulsions and suspensions begins. In the mean time there are objections of various kinds against the choice of these limits. In the first place there is as the basis of this old subdivision the supposition that one is always dealing with practically spherical particles, which has proved frequently not to be the case. Particles which have these small sizes in one dimension (e.g. discshaped particles) or in two dimensions (e.g. needle-shaped particles) but which arc otherwise much larger, behave as colloids both when the small sizes correspond with those of small molecules (e.g. in linear macromolecules) and when the latter He within the colloid limits (e.g. in vanadium pentoxide sol). 

Several colloidal systems containing anisodimensional particles may under certain circumstances show a reversible separation into two phases. The oldest example is the iron hydroxide sol described by Cotton and Mouton The same phenomenon has been studied more extensively on iron hydroxide, vanadium pentoxide, tungsten trioxi-de, benzopurpurin and other dyes by Zocher % Szegvari Heller and recently on tobacco mosaic virus by BerNal and Fankuchen and cn cucumber virus by Bawden and Pterie ... 

---