Semi-colloids

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. 

Halb-kochen, n. partial boiling, parboiUng. -koks, m. semicoke. -kokung,/. semieoking, partial carbonization. -koUoid, n. semi-colloid. 

Another type of nitrocellulose powder used for some time which eventually disappeared from the market was a semi-colloidal nitrocellulose powder containing inorganic salts such as potassium or barium nitrate (e.g. Poudre T in France, with 2% potassium nitrate) or with dichromates (e.g. Poudre J in France with 14% ammonium dichromate and 3% potassium dichromate). The dichromate powder was very sensitive to friction and its dust contained toxic dichromates. 

Nitroglycerine powders can be classified into two groups with and without a volatile solvent. Semi-colloidal nitrocellulose powders and nitroglycerine solventless powders are the most important types of smokeless powder. 

The semi-colloidal powders are designated in every country according to the purpose for which they are intended. In the U.S.S.R. (Gorst [1]) rifle powders were formerly given the letter B (Russian Y from the word vintovka i.e. rifle) followed by another letter denoting the type of projectile to be used, thus BA (Russian VL) for powder for light projectiles, BT (Russian YT), for powder for heavy projectiles. 

The catalyst is prepared by suspending 20 g. of c.p. ammonium metavanadate in 200 cc. of water and adding slowly 30 cc. of concentrated hydrochloric acid (sp. gr. 1.19). The reddish-brown semi-colloidal precipitate is washed several times with water by decantation and finally suspended in 300 cc. of water and allowed to stand at room temperature for three days. This treatment makes the precipitate granular and easy to filter. The precipitate is collected on a filter using a pump and washed several times with water to free it from hydrochloric acid. It is then dried at 120° for twelve hours, finely powdered and again dried for twelve hours at 120°. 

Maitra S., RahamaA. n, SarkaA. r, Tarafdar A.. Zirconia-mullite materials prepared from semi-colloidal route derived precursors. Ceramics International, 2006,32 201-206... 

Features Solventless produces light-stable films low VOC Properties Disp. char, odor semi-colloidal (< 0.2p) particle size sp.gr. 1.03 dens. 8.75 Ib/gal vise. < 100 cps flash pt. (TCC) > 100 C pH 7-9 surf. tens. 46 dynes/cm VOC 33.5 g/l Film props. tens. str. 7400 psi tens, elong. 150% (ultimate) anionic 35% solids Witcobond W-213 [UniroyaQ Chem. Descrip. PU aq. disp. 

Hardened cement paste mainly consists of a porous, semi-colloid phase of calcium sihcate hydrates physically incorporating crystalline calcium aluminate sulphate hydrates, the so-called cement gel. The cement gel has a very large active internal surface area that can adsorb water molecules it has been found through measurements that the specific surface S of hardened cement paste is of the magnitude of 200000 m /kg of the material. The specific surface is a measure of the internal, free surface in m per kg of the material. 

---