Synthesis and stabilities of the basic copper(II) chlorides atacamite, paratacamite and botallackite

Abstract

Strictly reproducible syntheses of the trimorphs of composition Cu2CI(OH)3 , atacamite, paratacamite, and botallackite, have been developed. In syntheses involving direct precipitation, or reaction of aqueous solutions with solid phases, reliable results are obtained only if the temperature and time of reaction are carefully controlled. Botallackite, the rarest of the naturally occurring trimorphs, is a key intermediate and crystallizes first under most conditions; subsequent recrystallization of this phase to atacamite or paratacamite, or of the latter from the former, depends upon the precise nature of the reaction medium. The crystallization sequence indicates that paratacamite, as has long been suspected, is the thermodynamically stable phase at ambient temperatures. Spertiniite, Cu(OH)2 , can be reproducibly synthesized via one route in the non-commutative titration of aqueous copper chloride with aqueous sodium hydroxide solutions.

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…It is however not stable in acidic conditions (oxalic acid, for example), which promotes the formation of mooloite (CuC 2 O 4 ·nH 2 O) [127]. Also, among the polymorphs, different stabilities are observed, botallackite being the first formed and more unstable, while paratacamite seems the favoured species at ambient temperature [167]. The polymorph paratacamite has so far been identified as degradation product on other Cucontaining pigments [64,117,119,123,129].…”

Near-field/altered-zone models report

“…Some products of these human-made materials rarely occur naturally and are therefore not necessarily predictable from a geochemical database. For example, botallackite, a rare copper hydroxy-chloride, has been observed associated with the corrosion of a copper object exposed to chloride ion (Pollard et al, 1989). Stability fields and reactive sequences of the basic copper (II) chlorides have only recently been proposed (Pollard et al, 1989), on the basis of this and other historical data, as a complement to experimental data, where experimental data alone have previously failed.…”

“…For example, botallackite, a rare copper hydroxy-chloride, has been observed associated with the corrosion of a copper object exposed to chloride ion (Pollard et al, 1989). Stability fields and reactive sequences of the basic copper (II) chlorides have only recently been proposed (Pollard et al, 1989), on the basis of this and other historical data, as a complement to experimental data, where experimental data alone have previously failed. That diffusion-controlled phenomena should be expected over time periods of at least 2000Êyr is apparent from investigations of corrosion phenomena in ancient bronzes (Scott, 1985).…”

Engineered materials characterization report, volume 3 - corrosion data and modeling update for viability assessments

“…Some products of these man-made materials rarely occur naturally and are therefore not necessarily predictable from a geochemical data base. Botallackite, a rare hydroxide of copper chloride, for example, has been observed associated with the corrosion of a copper object exposed to chloride ion (Pollard et al, 1989). Stability fields and reactive sequences of the basic copper (II) chlorides have only recently been proposed (Pollard et al, 19891, extrapolated from this and other historical data as a complement to experimental data, where experimental data alone has previously failed.…”