Calcium alloyability

FLAVORCHARACTERIZATION] (Volll) -lead-calcium alloys in READ ALOYS] (Vol 15)... 

Goldbeater Gold-beryUium Gold bronzes Gold-cadmium alloys Gold-calcium alloy... 

FoUowing the removal of the enriched dross, the required quantities of calcium, as a lead—calcium alloy and magnesium in the form of metal ingots, are added. The bath is stirred about 30 min to incorporate the reagents and hasten the reaction. The molten lead is cooled gradually to 380°C to permit the precipitate to grow and soHdify. The dross is skimmed for use with the next lot of lead to be treated. 

Fig. 6. Large columnar as-cast grain stmcture of lead—calcium alloys at a magnification of 80>...

Fig. 7. Grain stmcture of lead—0.07 wt % calcium alloy aged for seven days showing serrated grain boundaries at a magnification of 320x.

Rea.ctivity ofLea.d—Ca.lcium Alloys. Precise control of the calcium content is required to control the grain stmcture, corrosion resistance, and mechanical properties of lead—calcium alloys. Calcium reacts readily with air and other elements such as antimony, arsenic, and sulfur to produce oxides or intermetaUic compounds (see Calciumand calciumalloys). In these reactions, calcium is lost and suspended soHds reduce fluidity and castibiUty. The very thin grids that are required for automotive batteries are difficult to cast from lead—calcium alloys. 

Lead—Calcium—Aluminum Alloys. Lead—calcium alloys can be protected against loss of calcium by addition of aluminum. Aluminum provides a protective oxide skin on molten lead—calcium alloys. Even when scrap is remelted, calcium content is maintained by the presence of 0.02 wt % aluminum. Alloys without aluminum rapidly lose calcium, whereas those that contain 0.03 wt % aluminum exhibit negligible calcium losses, as shown in Figure 8 (10). Even with less than optimum aluminum levels, the rate of oxidation is lower than that of aluminum-free alloys. 

Lead—copper alloys are specified because of superior mechanical properties, creep resistance, corrosion resistance, and high temperature stabiUty compared to pure lead. The mechanical properties of lead—copper alloys are compared to pure lead, and to lead—antimony and lead—calcium alloys in Tables 4 and 5. 

Tia is also used as an ahoyiag element ia lead—antimony alloys to improve fluidity and to prevent drossiag, ia lead—calcium alloys to improve mechanical properties and enhance electrochemical performance, ia lead—arsenic alloys to maintain a stable composition, and as an additive to low melting alloys. 

These reactions are thermodynamically unfavorable at temperatures below ca 1500°C. However, at temperatures in the range from 1000 to 1200°C a small but finite equiUbrium pressure of barium vapor is formed at the reaction site. By means of a vacuum pump, the barium vapor can be transported to a cooled region of the reactor where condensation takes place. This destroys the equiUbrium at the reaction site and allows more barium vapor to be formed. The process is completely analogous to that used in the thermal reduction of CaO with aluminum to produce metallic calcium (see Calcium AND CALCIUM alloys). 

Barium is a member of the aLkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely aUied series in which the chemical and physical properties of the elements and thek compounds vary systematically with increa sing size, the ionic and electropositive nature being greatest for barium (see Calcium AND CALCIUM ALLOYS Calcium compounds Strontium and STRONTIUM compounds). As size increases, hydration tendencies of the crystalline salts increase solubiUties of sulfates, nitrates, chlorides, etc, decrease (except duorides) solubiUties of haUdes in ethanol decrease thermal stabiUties of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

U.S. imports of calcium metals fluctuate greatiy. Since the mid-1980s, the avadabiHty of very low priced calcium metal from China and the CIS has led to substantial reductions in calcium production by Western producers. This has been compensated to a certain extent by an increase in sales of processed materials, ie, alloys and particulates, by the Western companies. In 1991, more than 700 tons of calcium metal were imported to the United States from the People s RepubHc of China. Significant quantities of calcium alloys and particulates have also been imported from France and Canada. 

Sealed batteries have made little entry into this market with heavy cycling service, since the lead-calcium alloys required for these versions tend towards premature capacity loss, a phenomenon intensively investigated in recent years and possibly close to a solution. 

For the separation of such batteries, gel construction and microfiber glass fleece separators again compete because of the deep discharge cycles, the gel construction with its lower tendency to acid stratification and to penetration shorts has advantages for the required power peaks, microfiber glass fleece construction would be the preferred solution. The work on reduction of premature capacity loss with lead-calcium alloys has shown that considerable pressure (e.g., 1 bar) on the positive electrode is able to achieve a significantly better cycle life [31-36], Pressure on the electrodes produces counter pressure on the separators, which is not unproblematic for both separation systems. New separator developments have been presented with... 

Calcium alginate gels, 4 728 Calcium alloys, 4 530 Calcium aluminate, 2 345t Calcium aluminate cement, 2 415-416 5 500t, 502... 

Corrosion reactions, 21 845 Corrosion resistance, 9 710 10 441 of copper wrought alloys, 7 742-744 of lead-calcium alloys, 14 774 of materials used with fluorine, 11 839 of platinum-group metals, 19 600, 601t of silver, 22 639... 

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