Copper-rich precipitate

Steels for WWER-type RPVs are of low-alloyed type, mostly with bainitic microstructure, and thus their radiation damage nature is, in principle, identical with all other RPV steels, with matrix damage, formation of copper-rich precipitates and solute segregation in grain boundaries. Additionally, in materials with a high nickel content, the existence of a late blooming phase is not excluded. 

Cadmium also may be recovered from zinc ores and separated from other metals present as impurities by fractional distillation. Alternatively, the cadmium dust obtained from the roasting of zinc ore is mixed with sulfuric acid. Zinc dust is added in small quantities to precipitate out copper and other impurities. The metal impurities are removed by filtration. An excess amount of zinc dust is added to the solution. A spongy cadmium-rich precipitate is formed which may he oxidized and dissolved in dilute sulfuric acid. Cadmium sulfate solution is then electrolyzed using aluminum cathodes and lead anodes. The metal is deposited at the cathode, stripped out regularly, washed and melted in an iron retort in the presence of caustic soda, and drawn into desired shapes. More than half of the world s production of cadmium is obtained by elecrolytic processes. 

Figure 2. Transverse section of sample from inside neck of the Anahita Rhyton (CM A 62-294). Structure illustrates darker etching grains (muddy), indicating precipitation of copper-rich phase (X55).

A final method of strengthening Fe->12Ni-0.5Al involved precipitate strengthening. Copper was chosen as the precipitate material, since it has very low solubility in Fe and precipitates as a copper-rich terminal solid solution containing a small amount of iron. Thus, copper would not be expected to form an embrittling intermetallic compound. Copper additions ranging from 0.5 to 3.0at.% were... 

The dressing operations at the Herculaneum smelter are conducted entirely in kettles. The dross plant uses four 250-ton capacity kettles. The lead bullion is received from the furnaces, and is allowed to cool. This cooling causes the copper, sulfur, and trace amounts of other impurities to precipitate and rise to the surface of the bullion, producing a copper-rich dross. This dross is skimmed off and put through a wet screw classifier and sold as a byproduct to copper smelters. The drossed bullion is transferred to another kettle where it is further cooled and fluxed with sulfur for final decopperizing. This dross is skimmed and recycled to the blast furnace. The decopperized lead bullion is then pumped to the refinery. Maintenance in the dross plant is minimal and is managed on an as needed basis. 

Bems et al. [37] tried to formulate the solid-formation steps of copper-rich precursors based on their results obtained by thermogravimetry (TG). Similar solid-formation steps were proposed by Li etal. [42] for Cu precipitation. Accordingly, when Na2C03 is added under pH control to an aqueous solution of Cu(N03)2 and Zn(N03)2, the sohd formation starts with the initial precipitation of amorphous copper hydroxide, that is, this initial solid formation is not... 

Figure 3. Microstructure of T-II86, observed with optical microscope after I micron polishing of a cross-section. Grey phases are the tin oxide grains, white spots are copper-rich phases that precipitated at grain boundaries, and dark grey areas are porosity.

Figure 12. Microstructure of T-1186 in area C observed with optical microscope after polishing. There is no major change in the grains or pores but large quantities of copper-rich phases have precipitated at grain boundaries. These larges precipitated phases are believed to induce cracking observed on the electrode in Figure 9.

Ferric iron will oxidise tin to Sn", which will precipitate in the leaching stage as metastannic acid (1148004) and is hence separated with the leach residue. It is therefore possible to process smelter bulhon directly without softening, although decopperising will still be beneficial to provide a separate copper-rich stream, to reduce the quantity of mixed leach residue for further processing and to minimise interference with subsequent silver recovery. 

Figure 6.46(a) shows part of the phase diagram of the Al-Cu system. One prerequisite for precipitation hardening is the existence of a two-phase region where the matrix phase (in the example, aluminium with copper in solid solution) is in equilibrium with the precipitation phase (a copper-rich phase in the example), a so-called miscibility gap (see section C.3). 

Schematic of grain boundary region in a 2XXX alloy. Precipitation of the very-high-copper-content precipitates on the boundary causes a copper-depleted zone on either side of the boundary. The difference in the electrochemical potentials of the copper-depleted zone and the copper-rich matrix form a strong galvanic cell with a potential difference of about 0.12 V. Furthermore, the anodic copper-depleted zone is small in area compared with the area of the cathodic grain matrix, resulting in a high driving force for rapid intergranular corrosion. (Courtesy of Alcoa Technical Center, Edward L. Colvin.)...

However, at ageing condition, Cu atoms segregate by diffusion to form Copper rich zones called Guinner -Preston (GP Zone 1). This increased with further growth at 165"C to produce a GP zone 2 where a p. precipitate phase was formed. This produced a stronger effect as the precipitates generate stresses that helped in preventing dislocation movement... 

D14 Copper-rich copper-beryllium alloys are precipitation hardenable. After consulting the portion of the phase diagram shown in Figure 11.31, do the following ... 

Figures 2a and b report the XRD powder patterns of the precipitates heated at 653K in air and in a reducing atmosphere (H2 N2= 10 90 v/v), respectively. Calcined samples (Fig. 2a) show the presence only of spinel-type phases, whose XRD patterns become more and more broad as the copper content increases. IR spectra confirm the presence, for all calcined samples, of spinel phases, and also show he presence of dichromate-type phases (25), the amounts of which increase with increasing copper content. In previous papers it was shown that non-stoichiometric Zn/Cr spinel-type phases formed by decomposition of amorphous chromates and that some amounts of residual Cr ions are present in these phases (8,15). Taking into account that copper and zinc may form mixed spinel-type phases (with cubic symmetry for high zinc contents) (20,24), we may hypothesize the formation up to a ratio Cu/Cu-i-Zn= 0.5 of cubic non-stoichiometric spinel-type phases, containing both elements and characterized by an excess of bivalent ions. On the other hand, on the basis of the XRD spectra of Figure 2a, we cannot speculate about the number and/or nature of the phases present in the copper-rich catalysts.

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