Tungsten density

Spectra of ZrC>2-supported WOx species were recorded by Baertsch et al. (2002) after 1 h under 2-butanol dehydration conditions (0.5 kPa reactant, 323 K). The relative abundance of reduced centers was estimated from the Kubelka-Munk function in the range 1.5-3.2 eV (824—388 nm). Dehydration rates were obtained in a separate quartz reactor at 373 K. UV-vis band area and rate increased with the tungsten density up to a particular loading. Equivalent experiments with WOx/ A1203 were performed by Macht et al. (2004). A parallel increase of the initial dehydration rate at 373 K and the relative abundance of reduced centers at 423 K were pointed out. 

On a typical product wafer, the tungsten density is usually low, that is, about 20% or less. The remaining surface is covered mainly by oxide or other dielectric materials. This leaves four times more chances to have the scratch on the oxide or dielectric material than on tungsten. Furthermore, the tungsten structures are usually very small and a scratch is typically less visible. On a very small structure, a scratch on the W will look more like a pit. In addition, W is one of the hardest metals that is more difficult to scratch than other softer materials such as copper or aluminum. For all these reasons, after W CMP, it is more likely to see scratches on the dielectric materials than on the W structures (Fig. 17.18). 

Besides the material based characteristics, the difference of density of the used particle/substrate combination is a very important criterion. The difference of density influences the contrast of the radiographic tests. Tungsten carbides were used as mechanically resistant particles and titanium based alloys as substrate. The substrate material is marked by an advantageous relation of strength to density. This material is often used in aeronautics, astronautics, and for modification of boundary layers. The density of tungsten carbide (15.7 g/cm ) is about 3.5 times higher than the density of titanium (4.45-4.6 g/cm ). 

In all spent researches the received ratio signal / noise and sensitivity for revealed defects, distribution of material density and the weights of high density components (tungsten, lead, uranium) are well agreed with results of alternate physics-chemical methods of analyses... 

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... 

Specifications. The use of tungsten hexafluoride in CVD appHcations in the manufacture of high density siUcon chips requires a high purity product, essentially free of all metallic contaminants. Several grades of WF are available. Table 2 shows the specifications for three grades of WF. ... 

Density is a particularly important characteristic of alloys used in rotating machinery, because centrifugal stresses increase with density. Densities of the various metals in Table 1 range from 6.1 to 19.3 g/cm. Those of iron, nickel, and cobalt-base superaHoys fall in the range 7-8.5 g/cm. Those alloys which contain the heavier elements, ie, molybdenum, tantalum, or tungsten, have correspondingly high densities. 

Space Applications. The growth of powder metahurgy in space technology has arisen from the difficulty of handling many materials in conventional fusion-metahurgy techniques, the need for controhed porosity, and the requirement of many special and unique properties (60,61). Powder metahurgy is applied in low density components with emphasis on porous tungsten for W—Ag stmctures, beryhium compounds, titanium and... 

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). 

High density tungsten alloy machine chips are recovered by oxidation at about 850°C, foUowed by reduction in hydrogen at 700—900°C. Typically, the resultant powders are about 3-p.m grain size and resinter readily. There can be some pickup of refractory materials used in furnace constmction, which must be controUed. This process is important commercially. Eor materials that may be contaminated with other metals or impurities, the preferred recovery process is the wet chemical conversion process used for recovery of tungsten from ores and process wastes. Materials can always be considered for use as additions in alloy steel melting. 

Iron carbide (3 1), Fe C mol wt 179.56 carbon 6.69 wt % density 7.64 g/cm mp 1650°C is obtained from high carbon iron melts as a dark gray air-sensitive powder by anodic isolation with hydrochloric acid. In the microstmcture of steels, cementite appears in the form of etch-resistant grain borders, needles, or lamellae. Fe C powder cannot be sintered with binder metals to produce cemented carbides because Fe C reacts with the binder phase. The hard components in alloy steels, such as chromium steels, are double carbides of the formulas (Cr,Fe)23Cg, (Fe,Cr)2C3, or (Fe,Cr)3C2, that derive from the binary chromium carbides, and can also contain tungsten or molybdenum. These double carbides are related to Tj-carbides, ternary compounds of the general formula M M C where M = iron metal M = refractory transition metal. 

Tungsten Highest melting point nonvolatile oxide to at least 2500 F Highest density oxidizing rapidly brittle at low temperatures... 

Diphosphate tungsten bronzes (DTB) Cs Hg (P 04)4(W03)gai e chai ge-density wave (CDW) conductors. The framework of Cs contains columns of corner-sharing WO octahedra internked through P O group. Properties of Cs can be tuned via out-of-... 

Calculations of this type are carried out for fee, bcc, rock salt, and hep crystal structures and applied to precursor decay in single-crystal copper, tungsten, NaCl, and LiF [17]. The calculations show that the initial mobile dislocation densities necessary to obtain the measured rapid precursor decay in all cases are two or three orders of magnitude greater than initially present in the crystals. Herrmann et al. [18] show how dislocation multiplication combined with nonlinear elastic response can give some explanation for this effect. 

Figure 3.13. Simple relationships between properties and microstriictural geometry (a) hardness of some metals as a function of grain-boundary density (b) coercivity of the cobalt phase in tungsten earbide/coball hard metals as a function of interface density (after Exner 1996).

Select a tungsten carbide bit with high offset and chisel inserts if the shale content of the formation increases and/or the mud density is high. Use bit type 5-2 or 5-3. 

Metals with bcc structures, such as tungsten, are not close packed. Therefore, their densities would be greater if they were to change to a ccp structure (under pressure, for instance). 

What would the density of tungsten he if its structure were ccp rather than bcc Its actual density is 19.3 g-cm J. 

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