On-site monitoring for better selection of stone repairs: a case study

Weathering of clay-bearing sandstones does not only depend on material properties but also on the environmental conditions they are exposed to. The same is true for repaired stones, in which the compatibility of the repair mortar should be studied not only in terms of material properties, but also in terms of the climatic conditions it will be sub- jected, in order to maximize this compatibility. This paper proposes a methodology to quantify the thermal and hygric stresses in clay-bearing sandstones and their repair, based on the measurement of temperature and relative humidity at the surface and at several depths in a repaired and a non-repaired stone, as well as wind-driven rain and absorbed water. This is illustrated by a case study in an historical building. The data are used to quantify the stresses in the mate- rials and to propose possible degradation mechanisms.ISSN:2050-744

Effective Copper Diffusion Coefficients in CuSO₄—H₂SO₄ Electrowinning Electrolytes

Mass transport is an important factor in the deposit quality of copper electrowinning. Presently, there is limited diffusivity data available at commercially relevant concentrations between 25 and 40 °C. Linear sweep voltammetry at a rotating disk electrode was used to measure effective diffusion coefficients of cupric ion for a wide range of copper concentrations (10-50 g/L), sulfuric acid concentrations (120-240 g/L), and temperatures (25-60 °C). The results were well correlated by the equation: D, m2/s = 2.977 x 10-10 -5.462 x 10-13 [Cu]-1.212 x 10-12 [H2SO4] + 1.688 x 10-11 x T, where [Cu] and [H2O4] are in g/L, and T is °C. Addition of 20 mg/L Cl- slightly increased effective diffusivity. Other common commercial organic smoothing agents were found to have no effect. The measured diffusivities were used to calculate the maximum permissible current density that can produce smooth dense cathodes as a function of copper concentration and temperature