Uranic oxide

Urano-hydroxyd, n. uranous hydroxide, ura-nium(IV) hydroxide, -reihe, /. uranous series, -salz, n. uranous salt, -uranat, n. uranous uranate, uranium(IV,VI) oxide, UaOa. -verbindung, /. uranous compound, Uran-oxyd, n. uranium oxide, specif, uranic oxide, uranium(VI) oxide, UOa. -ozydhydrat, n. uranium hydroxide, -oxydoxydul, n. = Uranoxyduloxyd. -oxydrot, n. uranium oxide red- -oxydul, n. uranous oxide, ura-nium(IV) oxide, UO2. -oxyduloxyd, n. uranoso-uranic oxide, uranium (I V,VT) oxide, UaOa. -oxydulsalz, n. uranous salt, uranium-(IV) salt, -pechblende, /., -pecherz, n. pitchblende, -phosphat, n, uranium phosphate. -rot, n. uranium red. -salz, n. uranium salt. 

At the end of the eighteenth century, scientists thought that pitchblende was a mixture of iron and zinc compounds. In 1789 Martin Heinrich Klaproth (1743—1817) discovered a new metallic element in a sample of pitchblende, which he named uranus after the recently discovered planet. Although what he actually discovered was the compound uranous oxide (UOj), it was adequate to establish him as the discoverer of uranium. For almost a century, scientists believed that the compound uranous oxide (UO ) was the elemental metal uranium. In 1841 Eugene-Melchoir Pefigot (1811—1890) finally isolated the metal uranium from its compound. Even so, no one knew that both the compounds and metal of uranium were radioactive until 1896, when Henri Becquerel (1852—1908) mistakenly placed apiece of potassium... 

Synonyms uranium oxide uranic oxide urania uranium(IV) oxide... 

In 1823 J. A. Arfwedson reduced the green oxide of uranium (then believed to be the lowest oxide) with hydrogen, and obtained a brown powder which he took to be the metal, but which is now known to be uranous oxide, U02 (25, 30). In 1841 Peligot, on analyzing anhydrous uranous chloride, UC14, found that 100 parts of this chloride apparently yielded about 110 parts of its elements uranium and chlorine. His explanation of this seemingly impossible result was that the uranous chloride reacts with water in the following manner ... 

Since uranous oxide cannot be reduced with hydrogen or carbon, it had always been mistaken for metallic uranium. 

In 1822 Arfwedson published his paper on uranium (18). More than thirty years before, M. H. Klaproth had heated a paste made with uranic oxide and linseed oil, and obtained a brown powder with a metallic luster, which he regarded as metallic uranium. Although others... 

The melting-point of tungsten is higher than that of any other known metal. The metals are stable in air at ordinary temperatures, but when heated they exhibit a remarkable difference in behaviour. Uranium burns briskly at 170° C., producing uranous oxide UO2 molybdenum at a red heat yields the trioxide M0O3 chromium only burns at 2000° C. and forms the sesquioxide CrjOg tungsten is not oxidised at any temperature, except in the vapour form. 

Preparation of Uranium.—The isolation of the metal in a state of purity is accomplished only with difficulty. Three methods of procedure have been suggested, namely, (1) by reduction of urano-uranic oxide, (2) by reduction of uranous chloride, and (3) by electrolysis. The best results have been obtained by the first method, which also possesses an advantage in using as the starting material an oxide which is a commercial product. 

In 1872 Mendeleeft pointed out that there was no place in the Periodic Table for a trivalent element of atomic weight 120, and drew attention to the similarity of uranium to chromium, molybdenum, and tungsten he therefore suggested that the atomic weight should be doubled, so that uranium could be placed below these elements in the table. He also formulated the oxides, by analog with those of the other elements in the group, as follows uranous oxide UOg, urano-... 

Uranium Tetrafluoride, Uranous Fluoride, UF, is the chief product obtained when the metal is acted upon by fluorine. It may be prepared by the action of hydrogen fluoride on urano-uranic oxide or on uranous oxide or by reduction of a solution of uranyl fluoride with stannous chloride. It is also formed with uranium hexafluoride when the pentachloride is acted upon by fluorine at —40° C. thus ... 

Uranous fluoride is a green amorphous powder, insoluble in water, hardly attacked by dilute acids and-only dissolved with difficulty by concentrated acids, except in the case of nitric acid which readily decomposes it. When heated in the air it loses fluorine and leaves a residue of urano-uranic oxide. At ordinary temperatures it is gradually oxidised to the uranyl compound, UOjFj. If heated in absence of air it melts at about 1000° C. ... 

Uranyl Fluoride, UO Fg, is formed with uranous oxyfluoride (see above) by the action of hydrofluoric acid on urano-uranic oxide Us08-f6HF=U0F2-f2U02F2+3H20. 

It is formed in solution by oxidising uranous chloride with nitric acid by dissolving uranic oxide in concentrated hydrochloric acid or by adding barium chloride to a concentrated solution of uranyl sulphate until precipitation is complete. Its aqueous solution on evaporation yields the monohydrate, UOaClj.HaO." The solution is unstable at ordinarj temperatures and slowly deposits uranic hydroxide, which after a time partly redissolves. The uranyl chloride may be reduced in solution to black uranous oxide by the action of magnesium or aluminium powder. The densities of aqueous solutions of uranyl chloride have been determined as follows ... 

Uranyl Bromide, UOgBra.— Wlien uranous oxide is heated in a current of bromine vapour a mixture of uranyl bromide and uranous bromide is formed. The former can be exteacted with ether, and obtained as j-ellou-ish-green fluorescent needles by evaporation of the solution. It is obtained in aqueous solution by the action of bromine water on uranous oxide, or of hydrobromic aeid on uranie oxide yellow needles of the heptahydrate, U03Br2.7H20, separate on concentrating the solution. Uranyl bromide is very deliquescent and is decomposed in moist air to hydrated uranic oxide and hydrobromic... 

The two chief oxides of uranium are the basic uranous oxide UO2 and the acid anhydride UO3. Intermediate between these two is a well-defined green oxide of composition UgOg. Less certain is the existence of a pentoxide UgOj, and a tetroxide, uranium peroxide, UO, though well-defined derivatives of the latter, peruranates, are known. 

Uranous oxide is also obtained in the form of black microscopic crystals when urano-uranic oxide is reduced uith carbon or heated with a little hydrofluoric acid when crystallised uranic hydroxide is heated in hydrogen when uranyl chloride is heated with potassium in a current of hydrogen, or with a mixture of ammonium and sodium... 

A bricli-red variety of uranous oxide has been obtained by ealcining uranyl bromide in the air. It is very stable at high temperatures, and is converted to the black modification by heating in hydrogen without any appreciable loss of oxj gen. 

On a commercial scale uranous oxide is prepared by fusing at red heat a mixture of 35 parts of common salt and 20 parts of sodium uranate with 1 part of powdered charcoal, the heating being continued until the escape of gas ceases. After cooling, the mass is lixiviated with water, and the residue of uranous oxide is washed by decantation. By washing with 5 per cent, hydrochloric acid, any iron, aluminium, or vanadium compounds may be removed, and a commercial product of purity equivalent to 97 per cent. U3O3 is obtained. If the uranous oxide is required for the production of ferro-uranium, the complete removal of iron is not necessary. 

Uranous oxide is only difficultly soluble in hydrochloric and sulphuric acids, even when concentrated. With the latter acid, insoluble uranium sulphate is formed. It readily dissolves, however, in dilute nitric acid forming uranyl nitrate it is also soluble in aqua regia. The amounts of the oxide dissohdng in these acids in a given time vary widely with the mode of preparation of the oxide. 

Colloidal Uranous Oxide.—During the electrolysis of a solution of uranyl chloride a black reduction product is precipitated at the cathode. This precipitate dissolves in water, forming a dark-coloured colloidal solution, which by titration with potassium permanganate, before and after reduction with zinc, has been shown to contain uranous oxide. A similar solution may be obtained by the reduction of uranyl chloride by zinc or copper in dilute acid solution. When very dilute, the solution has a yellow tinge. In an electric field it becomes decolorised at the anode and precipitation takes place at the cathode. It behaves as a typical positive colloid with coagulating agents. 

---