Magnetite black

Magnetite black with metallic luster Fe304 Ti, Mg, Ni, Mn, AI, V, Cr Occurs in context with limestone, hematite, pyrite other sulfides New York, Pennsylvania and Arkansas... 

Magnetite Black Fe3O4 Common ceramic pigment. 

Magnetite black mag-n3- tlt blak (1851) n. Fe304. Magnetic iron oxide. 

SPR property, for example, gold, silver, copper, tin, lead, mercury, cadmium, indium including the alkali metals. The SPR varies with the nanoparticle form and thereby every nanocomposite tends to have a characterislic color, for example, gold ruby red, silver brown, cadmium yellow, magnetite black platinum, brownish red. UV-Visible spectra in the present study were recorded on a Spectra Max 190 plate reader (Molecular Devices, Sunnyvale, USA) which was operated at a resolution of 1 nm. The SPR for silver nanoparticles, of sizes 24 2.5 nm, showed an intense band centered at 430 nm, which is due to the excitation of SPR in the metal nanoparticles, as can be seen in Fig. 3b, and suggests the presence of silver nanoparticles. 

The mixed oxide Fc304 (tri-iron tetroxide) is a black solid, which occurs naturally as magnetite it is formed when iron(III) oxide is strongly heated, and its structure is effectively made up of oxide (O ) and iron(II) and iron(III) ions. 

Idiochromatic examples of this are black magnetite [1309-38-2] Fe O otherwise written as Fe(II)0 Fe2(111)02 and the analogous red Mn O and the pigments Pmssian blue [14038-43-8] and Turnbull s blue [25869-98-17, both Fe4(III)[Fe(II)(CN)2]2. Allochromatic examples are widespread in the mineral field, with Fe + + Fe + being involved in blue and green tourmaline [1317-93-7] blue iolite (cordierite) [12182-53-5] etc. 

Figure 3.6 Tubercle cross section shows black magnetite-rich shell beneath deposit and hematite cap. Note the core material below the magnetite shell. (Magnification 7.5x.) (Courtesy of National Association of Corrosion Engineers, Corrosion 89 Paper No. 197 by H. M. Herro.)...

Tubercles consisted of hard, hlack oxide shells overlaid with friable carbonate-containing deposits. In places, several laminate black magnetite shells existed. The outer crust could be crushed by gentle pressure with a finger. Tubercles were riddled with white crystalline fibers. Other detritus was incorporated into the tubercle core and crust. Metal loss was less than 0.030 in. (0.076 cm) below each tubercle. Wall thickness was almost 0.25 in. (0.64 cm). 

Long-term overheating may cause thermal oxidation on both the external and the internal superheater surfaces, resulting in a gradual buildup of coarse black magnetite. Corrosion fatigue may also occur. 

The presence of corrosion products is not always a negative event some small degree of surface corrosion of all steel heat exchanger surfaces is generally beneficial. Under the reducing conditions normally found on the surfaces of pre-boiler FW heaters, FW lines, and boiler surfaces, black magnetite naturally forms by the direct thermal reaction of water with steel. The development of this self-limited magnetite film is most desirable, and optimum formation is achieved at pH levels of 10.5 to 11.5. 

Under the hot deaerated (reducing) conditions normally found on the surfaces of pre-boiler FW heaters, FW lines, and boiler surfaces, a dense, passive, black, iron oxide film of magnetite (Fe304) naturally forms. 

Sludge in the boiler is typically red to brown (hematite) but becomes black with age (coarse magnetite). 

Copper salts usually are the result of corrosion in the post-boiler section and may be present as red cuprous oxide (Cu20), black cupric oxide (CuO), or blue-green copper sulfate (CuSO ). Mostly, copper salts are mixed with hematite and magnetite and take on a black color. 

The most abundant titanium sand deposits are black sands in streams and on beaches of volcanic regions. The principal black minerals are magnetite, titanoferous magnetite and black silicates, chiefly angite and homblend. It is quite difficult to produce an ilmenite suitable for pigment product from black sand, but other sand deposits that contain rutile, ilmenite and often monazite are found in Australia, USA, India and Africa. These deposits are either alluvial or marine in origin. 

Fe(OH)2 does not exist as a mineral. The Fe is divalent and the structure which is based on a hep anion array, is similar to that of brucite. Pure Fe(OH)2 is white. It is, however, readily oxidized, upon which it develops into greenish-blue, so-called, green rust or, on further oxidation, into black magnetite. 

To the naked eye, goethite and akaganeite appear yellow-brown, lepidocrocite orange and hematite usually red (Plate 6.1). Feroxyhyte and ferrihydrite are dark reddish brown, maghemite brown to brownish red and magnetite and wiistite are black. 

In the dry state magnetite is readily oxidized to maghemite by air. Ultrafme crystals of magnetite change (over years) from black to the brown of maghemite even at room temperature (Murad Schwertmann, 1993). At temperatures >300°C, the transformation proceeds further to hematite (see section 14.2.7). 

Rust formed by atmospheric corrosion is often voluminous (Fig. 18.4) and visually appears as loose orange-brown or black masses. This type of rust is always a mixture of phases and frequently consists of two layers - magnetite at the iron/rust interface (as a result of reduced oxygen supply) with an outer layer of loose lepidocrocite and/ or goethite. Hematite is formed during high temperature aqueous corrosion and is also found in the passive layer (which forms at room temperature). 

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