Black oxide

Addition of an alkali metal hydroxide solution to an aqueous solution of a nickel(II) salt precipitates a finely-divided green powder. nickel(II) hydroxide NilOHfj on heating this gives the black oxide. NiO. which is also obtained by heating nickel(II) carbonate or the hydrated nitrate. Black nickel(II) sulphide, NiS, is obtained by passing hydrogen sulphide into a solution of a nickel(II) salt. 

It is readily dehydrated on warming, to give the black oxide CuO. It dissolves in excess of concentrated alkali to form blue hydroxo-cuprate(II) ions, of variable composition it is therefore slightly amphoteric. If aqueous ammonia is used to precipitate the hydroxide, the latter dissolves in excess ammonia to give the deep blue ammino complexes, for example [Cu(NH3)4(H20)2] ... 

Iron Oxide Reds. From a chemical point of view, red iron oxides are based on the stmcture of hematite, a-Fe202, and can be prepared in various shades, from orange through pure red to violet. Different shades are controlled primarily by the oxide s particle si2e, shape, and surface properties. Production. Four methods are commercially used in the preparation of iron oxide reds two-stage calcination of FeS047H2 O precipitation from an aqueous solution thermal dehydration of yellow goethite, a-FeO(OH) and oxidation of synthetic black oxide, Fe O. ... 

Silver in the +3 oxidation state, including silver peroxide, ie, black oxide, marketed as AgO, is obtained by the action of the vigorous oxidising agent S20 g on Ag20 or other Ag compounds. X-ray and neutron diffraction analyses show the nominal AgO unit cell to be Ag20 Ag202- Both Ag" and Ag " are present. Another compound of potentially important commercial value is Ag O, which has a unit cell of two Ag and two Ag ions. Its preparation is as follows ... 

Properties. Uranium metal is a dense, bright silvery, ductile, and malleable metal. Uranium is highly electropositive, resembling magnesium, and tarnishes rapidly on exposure to air. Even a poHshed surface becomes coated with a dark-colored oxide layer in a short time upon exposure to air. At elevated temperatures, uranium metal reacts with most common metals and refractories. Finely divided uranium reacts, even at room temperature, with all components of the atmosphere except the noble gases. The silvery luster of freshly cleaned uranium metal is rapidly converted first to a golden yellow, and then to a black oxide—nitride film within three to four days. Powdered uranium is usually pyrophoric, an important safety consideration in the machining of uranium parts. The corrosion characteristics of uranium have been discussed in detail (28). 

Brown oxides are manufactured either by blending mixtures of the red, yellow, and black oxides or by precipitation of an iron salt with alkaU followed by partial oxidation of the precipitate. The result is a mixture of red Fe202 [1309-37-1] and black Fe O [1309-38-2] FeO Fe202-... 

The black oxides are prepared by the controlled precipitation of Fe O (treat FeSO -7H2 O with NaOH and O2) to form a mixture of ferrous and ferric oxides. 

Pits are more numerous and deeper on the apparent bottom of the pipe. Surfaces between pits are covered with a tenacious, black oxide layer. 

When a copper wire is exposed to air at room temperature, it becomes coated with a black oxide, CuO. If the wire is heated above a certain temperature, the black oxide is converted to a red oxide, Cu20. At a still higher temperature, the oxide coating disappears. Explain these observations in terms of the thermodynamics of the reactions... 

The presence of red ferric oxide usually indicates an inactive pit but black oxide infers active pitting. Condensate receivers are common points for oxygen infiltration (especially in smaller boiler plants). 

All pipes and fittings are transported to the pickling process in which an overhead crane is used to lower them into an acidic pickle liquor solution that chemically cleans and etches the black oxide surface layer resulting in a clean, rust-resistant pipe. 

Thorium is a radioactive, silvery-white metal when freshly cut. It takes a month or more for it to tarnish in air, at which point it forms a coating of black oxide. Although it is heavy, it is also a soft and malleable actinide metal. The metal has a rather low melting point, but its oxide has a very high melting point of about 3,300°C. Thorium reacts slowly with water but reacts more vigorously with hydrochloric acid (HCl). 

Elemental arsenic is stable in dry air but exposure to moist air tarnishes its surface to a golden bronze color which converts to a black oxide on further exposure. Arsenic vapors react with oxygen to form arsenic trioxide (sesquiox-ide) ... 

Heating above 800°C converts copper(lI) oxide into copper(l) oxide. Also, when the black oxide is heated with copper metal, copper(l) oxide is formed ... 

Green cubic crystals transforms to a grayish black octahedral form, known as black oxide, when strongly ignited black oxide has a metallic luster density of green oxide is 6.72 g/cm Mohs hardness 5.5 melts at 1955°C insoluble in water soluble in acids at ordinary temperatures black form dissolves in hot acids. 

Oxidation of silver gives a black oxide, which probably is the AgO ... 

If 100 parts of this carbonate, dissolved in nitric acid and separated by the alkaline carbonates, gives us 100 parts of artificial carbonate, and if the base of these two combinations is the black oxide, we must recognize that invisible hand which holds the balance for us in the formulation of compounds and fashions properties according to its will. We must conclude that nature operates not otherwise in the depths of the world than at its surface or in the hands of man. These ever-invariable proportions, these constant attributes, which characterize true compounds of art or of nature, in a word, this pondus naturae so well seen by Stahl all this, I say, is no more at the power of the chemist than the law of election which presides at all combinations. From these considerations is it not right to believe that the native carbonate of copper... 

Thallous halides do not absorb ammonia at ordinary temperature, but in liquid ammonia these salts form triannnino-thallous halides of composition [T1(NH3)3]C1, [Tl(NH3)3]Br.1 The triammino-deriva-tives formed are somewhat soluble in liquid ammonia, and the solubility increases with rise of temperature and increase in atomic weight of the halogens. No lower ammino-derivatives are known. Tliallic halides absorb ammonia gas readily. If ammonia gas is passed into an alcoholic solution of thallic chloride, or if dry ammonia gas is passed over dry thallic chloride, the gas is absorbed and a white crystalline substance is formed of composition [T1(NH3)3]C13. The crystals may be washed with alcohol containing ammonia and then with absolute alcohol, and finally dried in vacuo. On coming in contact with water the triammine is decomposed with precipitation of violet-black oxide thus ... 

Solutions of the fixed alkalies convert it into black oxide, and by ammonia it is changed into the double salt, 2 (Mg KHa), Hg, 01, which is also black. This amide compound is different from that which is formed when calomel and dry ammonia are brought in contact the last has, according to Kane, the formula 2 Hgs C1,H NH ... 

Manganese —Binoxide of Afawymiese—MnOj.—One of the commonest ores of mangoncse is found in a state of great purity in Sweden and other parts. The purest variety is that known in commerce under the term of pyrolusits, or black oxide of manganese. 

---