In Situ Ultrasonic Spectroscopy Study of the Nucleation and Growth of Copper Sulfate Pentahydrate Batch Crystallized from Supersaturated Aqueous Solutions

Abstract

In situ ultrasonic attenuation spectroscopy is applied to the challenging case of monitoring the nucleation and growth of copper sulfate pentahydrate crystallized from supersaturated aqueous solutions, a system not readily amenable to analysis via optical methods due to the intense blue color of the saturated crystallizing solution. In experiments in the 2.8-L rectilinear reactor of a spectrometer, crystallization and dissolution points are reliably detected from the measured attenuation spectra. There are minor differences between data taken at 10 and 50 MHz, notably the lower frequency data appearing to be more sensitive to the particle formation/dissolution process. The nucleation data reveal that the material crystallizes fairly easily as characterized by a metastable zone width of ca. 3-4°C and a significantly cooling-rate-dependent nucleation order of reaction of ca. 1.7 reflecting the fact that for high cooling rates the nucleation rate is less than that associated with supersaturation generation. The evolving crystal size distribution following nucleation, calculated from ultrasonic attenuation spectroscopy measurements, reveals well-defined oscillations in the observed crystal sizes consistent with the break-up of crystals larger than ca. 250 µm in this crystallizer. From dynamic measurements of changing particle size and concentration during the crystallization process, apparent crystal mass growth rates are calculated to be between 2.3 × 10 -3 kg/m 2 ‚s at the maximum cooling rate of 0.55°C/min and 2.02 × 10 -4 kg/m 2 ‚s at the minimum cooling rate of 0.2°C/min. On the basis of these data and assuming a spherical particle model, the linear crystal growth rates are estimated to be between 2.0 × 10 -6 m/s at the maximum cooling rate of 0.55°C/min and 1.8 × 10 -7 m/s at the minimum cooling rate of 0.2°C/min.

Perspective on the Use of Ultrasonic Monitoring for In Situ Diagnostics of Zeolite and MOF Crystallization

“…Comparison with SEM especially revealed that US spectroscopy reflects reality the best. The importance of the crystallization mechanism can be emphasized with regard to a study by Wilkinson et al . who investigated the crystallization of copper sulfate pentahydrate in a similar way as Tebbutt et al , Their results showed that the crystal size was strongly influenced by the cooling rate; however, at a size of roughly 300 μm the crystals break resulting in a similar PSD independent of the cooling rate.…”

Applications of ultrasonics in food science - novel control of fat crystallization and structuring

“…For example, we have sized whole milk, separately sizing the protein particle size distribution and that of the milk fat globules [31] [32]. Attempts to use this technique to size crystals during growth have not been overly successful despite considerable effort [33][34][35][36][37][38][39][40][41]because the phase transition itself introduces an additional attenuation term, over and above the scattering terms [30] [42](thermal and visco-inertial) currently included in the inversion models. As a result, empirical methods of analysis were resorted to which suffered from the complicated and variable interaction between the ultrasound field and the crystallising material, we now know that the quasi-continuous acoustic fields can modify the crystal nucleation process [43] and Section 4.3.1 below, An advantage that ultrasound attenuation spectroscopy enjoys over light scattering techniques is its ability to measure concentrated systems and in stirred conditions, so that the emergence of structure can be followed over time.…”

Solid–Liquid Equilibrium and Process Design of CuSO4 + NaCl + (H2O or H2SO4/H2O) Systems at 298.15 K

“…Several studies have investigated the solid–liquid equilibrium and crystallization of the copper sulfate pentahydrate (CuSO 4 ·5H 2 O). − Giulietti et al presented a study of batch cooling experiments, from 70 to 30 °C, some of which included 2% free acid. They concluded that programmed cooling produced larger crystals than linear cooling.…”