Luster metallic

Crystalline silicon has a metallic luster and grayish color. Silicon is a relatively inert element, but it is attacked by halogens and dilute alkali. Most acids, except hydrofluoric, do not affect it. Elemental silicon transmits more than 95% of all wavelengths of infrared, from 1.3 to 6.y... 

Copper is reddish and takes on a bright metallic luster. It is malleable, ductile, and a good conductor of heat and electricity (second only to silver in electrical conductivity). 

Pure silver has a brilliant white metallic luster. It is a little harder than gold and is very ductile and malleable, being exceeded only by gold and perhaps palladium. Pure silver has the highest electrical and thermal conductivity of all metals, and possesses the lowest contact resistance. It is stable in pure air and water, but tarnishes when exposed to ozone, hydrogen sulfide, or air containing sulfur. The alloys of silver are important. 

Yttrium has a silver-metallic luster and is relatively stable in air. Turnings of the metal, however, ignite in air if their temperature exceeds 400oC. Finely divided yttrium is very unstable in air. 

Crystalline tellurium has a silvery-white appearance, and when pure exhibits a metallic luster. It is brittle and easily pulverized. Amorphous tellurium is found by precipitating tellurium from a solution of telluric or tellurous acid. Whether this form is truly amorphous, or made of minute crystals, is open to question. Tellurium is a p-type semiconductor, and shows greater conductivity in certain directions, depending on alignment of the atoms. 

The element is silvery white with a metallic luster its density is exceeded only by that of platinum, iridium, and osmium, and its melting point is exceeded only by that of tungsten and... 

When freshly exposed to air, thallium exhibits a metallic luster, but soon develops a bluish-gray tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydride is formed. The metal is very soft and malleable. It can be cut with a knife. Twenty five isotopic forms of thallium, with atomic masses ranging from 184 to 210 are recognized. Natural thallium is a mixture of two isotopes. A mercury-thallium alloy, which forms a eutectic at 8.5% thallium, is reported to freeze at -60C, some 20 degrees below the freezing point of mercury. 

The metal has a bright silvery metallic luster. Neodymium is one of the more reactive rare-earth metals and quickly tarnishes in air, forming an oxide that spalls off and exposes metal to oxidation. The metal, therefore, should be kept under light mineral oil or sealed in a plastic material. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863oC. 

As with other related rare-earth metals, gadolinium is silvery white, has a metallic luster, and is malleable and ductile. At room temperature, gadolinium crystallizes in the hexagonal, close-packed alpha form. Upon heating to 1235oG, alpha gadolinium transforms into the beta form, which has a body-centered cubic structure. 

The original yams were marketed as silk substitutes for use in apparel, hosiery, lace, home furnishings, ribbons, braids, and in a whole range of fabrics using blends with cotton or wool yams. As the end uses expanded beyond silk replacement, the harsh metallic luster of the yam proved disadvantageous and dull "matt" fibers had to be developed. Oil dulling was invented (11) in 1926, and an improved method using titanium dioxide was developed (12) in 1929. 

Iodine is a bluish black, crystalline soHd having a metallic luster. It is obtained in shiny flakes or prills that can be easily cmshed to powder. Iodine crystallines in rhomboidal plates belonging to the triclinic system. 

In general, the chemistry of inorganic lead compounds is similar to that of the alkaline-earth elements. Thus the carbonate, nitrate, and sulfate of lead are isomorphous with the corresponding compounds of calcium, barium, and strontium. In addition, many inorganic lead compounds possess two or more crystalline forms having different properties. For example, the oxides and the sulfide of bivalent lead are frequendy colored as a result of their state of crystallisation. Pure, tetragonal a-PbO is red pure, orthorhombic P PbO is yeUow and crystals of lead sulfide, PbS, have a black, metallic luster. 

Pyrolusite is a black, opaque mineral with a metallic luster and is frequendy soft enough to soil the fingers. Most varieties contain several percent water. Pyrolusite is usually a secondary mineral formed by the oxidation of other manganese minerals. Romanechite, a newer name for what was once known as psilomelane [12322-95-1] (now a group name) (7), is an oxide of variable composition, usually containing several percent water. It is a hard, black amorphous material with a dull luster and commonly found ia the massive form. When free of other oxide minerals, romanechite can be identified readily by its superior hardness and lack of crystallinity. 

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). 

Selected physical properties of rhenium are summarized ia Table 1. The metal is silvery-white and has a metallic luster. It has a high density (21.02 g/cm ). Only platinum, iridium, and osmium have higher densities. The melting poiat of rhenium is higher than that of all other elements except tungsten (mp 3410°C) and carbon (mp 3550°C). 

Silicon [7440-21-3] Si, from the Latin silex, silicis for flint, is the fourteenth element of the Periodic Table, has atomic wt 28.083, and a room temperature density of 2.3 gm /cm. SiUcon is britde, has a gray, metallic luster, and melts at 1412°C. In 1787 Lavoisier suggested that siUca (qv), of which flint is one form, was the oxide of an unknown element. Gay-Lussac and Thenard apparently produced elemental siUcon in 1811 by reducing siUcon tetrafluoride with potassium but did not recognize it as an element. In 1817 BerzeHus reported evidence of siUcon occurring as a precipitate in cast iron. Elemental siUcon does not occur in nature. As a constituent of various minerals, eg, siUca and siUcates such as the feldspars and kaolins, however, siUcon comprises about 28% of the earth s cmst. There are three stable isotopes that occur naturally and several that can be prepared artificially and are radioactive (Table 1) (1). 

Sodium is a soft, malleable soHd readily cut with a knife or extmded as wire. It is commonly coated with a layer of white sodium monoxide, carbonate, or hydroxide, depending on the degree and kind of atmospheric exposure. In a strictiy anhydrous iaert atmosphere, the freshly cut surface has a faintiy pink, bright metallic luster. Liquid sodium ia such an atmosphere looks much like mercury. Both Hquid and soHd oxidize ia air, but traces of moisture appear to be required for the reaction to proceed. Oxidation of the Hquid is accelerated by an iacrease ia temperature, or by iacreased velocity of sodium through an air or oxygen environment. 

The sulfur nitrides have been the subject of several reviews (206—208). Although no commercial appHcations have as yet been developed for these compounds, some interest was stimulated by the discovery that polythiazyl, a polymeric sulfur nitride, (SN), with metallic luster, is electroconductive (see Inorganic highpolymers) (208,209). Other sulfur nitrides are unstable. Tetrasulfur nitride is explosive and shock-sensitive. 

Properties. Thallium is grayish white, heavy, and soft. When freshly cut, it has a metallic luster that quickly dulls to a bluish gray tinge like that of lead. A heavy oxide cmst forms on the metal surface when in contact with air for several days. The metal has a close-packed hexagonal lattice below 230°C, at which point it is transformed to a body-centered cubic lattice. At high pressures, thallium transforms to a face-centered cubic form. The triple point between the three phases is at 110°C and 3000 MPa (30 kbar). The physical properties of thallium are summarized in Table 1. 

Iron Titanates. Ferrous metatitanate [12168-52-4] FeTiO, mp ca 1470°C, density 472(0), an opaque black soHd having a metallic luster, occurs in nature as the mineral ilmenite. This ore is used extensively as a feedstock for the manufacture of titanium dioxide pigments. Artificial ilmenite may be made by heating a mixture of ferrous oxide and titanium oxide for several hours at 1200°C or by reducing a titanium dioxide/ferric oxide mixture at 450°C. 

Va.na.dium (II) Oxide. Vanadium(II) oxide is a non stoichiometric material with a gray-black color, metallic luster, and metallic-type electrical conductivity. Metal—metal bonding increases as the oxygen content decreases, until an essentially metal phase containing dissolved oxygen is obtained (14). 

The element bismuth [7440-69-9] Bi, found ia Group 15 (VA) of the Periodic Table, has at no. 83, at wt 208.98. Its valences are +5 and +3. Bismuth is a silvery metal having a high metallic luster and exhibits a slightly pink tinge on a cleanly broken surface. The metal itself is britde ia nature and easily broken. 

If pure, the carbides of Groups 1 and 2 are characterized by their transparency and lack of conductivity. The carbides of Group 3, ie. Sc, Y, the lanthanides, and the actinides, ate opaque. Some, depending on composition, show metallic luster and electroconductivity. The cation may exist in the MC2 phases of this group, and the remaining valence electron apparendy imparts pardy metaUic character to these compounds. 

The gouge sites had a bright metallic luster and various shapes (Figs. 11.22 and 11.23). Microstructural examinations of the gouged regions revealed that plastic deformation of the metal had not occurred. 

Highly localized metal loss at the valve seat is apparent in Fig. 11.6. Figure 11.29 shows the same component close up. Wasted surfaces have a bright, metallic luster free of corrosion products or deposits. Metal loss along the edge of the throttling nut is also apparent (Fig. 11.30). 

Several of the welded junctions were removed from the system for metallographic examination (Fig. 15.20). As can be seen from Fig. 15.20, the internal surface was covered with reddish and tan deposits and corrosion products. The metal surface itself retained a bright, metallic luster. 

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Crystalline solid Yellow color, no metallic luster... 

It is worthy of mention that the properties of hauerite are in accordance with the conception that the Mn—S bonds are much weaker than the Fe—8 bonds in pyrite. The hardness of hauerite is 4, as compared with 6—6.5 for pyrite. All members of the pyrite group have a bright metallic luster except hauerite, which is dull. Hauerite is said to have a much smaller electrical conductivity than the others. 

Pure elemental silicon is a hard, dark gray solid with a metallic luster and with a crystalline structure the same as that of the diamond form of carbon. For this reason, silicon shows many chemical and physical similarities. There is also a brown, powdery form of silicon having a microcrystalline form. The element is prepared commercially by reducing the oxide by reacting it with carbon (as coke) in electric furnaces. On a small scale, silicon has been obtained from the oxide by reduction with aluminum meted. 

The interstitial hydrides of transition metals differ from the salt-like hydrides of the alkali and alkaline-earth metals MH and MH2, as can be seen from their densities. While the latter have higher densities than the metals, the transition metal hydrides have expanded metal lattices. Furthermore, the transition metal hydrides exhibit metallic luster and are semiconducting. Alkali metal hydrides have NaCl structure MgH2 has rutile structure. 

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