Abstract
In this study, crystallization phenomena were investigated by real-time in situ observation of seeded droplets under evaporation using a self-developed hot-stage platform. Ternary solutions at eutonic conditions at 25 °C were investigated for the following systems: NaCl–KCl–H2O, NaCl–CaSO4–H2O, and NaCl–Na2SO4–H2O. Evidence of epitaxial growth was found for aqueous NaCl–KCl and aqueous NaCl–Na2SO4. Sodium chloride nucleated and grew epitaxially upon the other substrates in a larger proportion compared with the inverse. This observation could be related to the higher solubility, and consequently higher residual supersaturation of NaCl regarding the other components. Hopper-like NaCl crystals developed in almost all systems. The results may help devise strategies to control particle morphologies and purity in industrial crystallization from complex systems.
Highlights
Crystallization processes are well established for the production of a wide range of particulate products as well as for purification and separation processes [1]
Our previous studies on batch evaporative simultaneous crystallization have shown that epitaxial growth is an important phenomenon affecting the morphology and composition of the crystals in the NaCl–KCl–H2O system, while it was not observed in the NaCl–CaSO4–H2O system [4,5,6,7]
CaSO4 was not seeded here, evidence of its seeds serving as nuclei for the formation of NaCl seeds were found in previous studies [7]. Epitaxial growth develops both in the aqueous NaCl–KCl and the aqueous NaCl– Na2SO4 systems, with NaCl growth upon the other substrates being more prominent than the inverse
Summary
Crystallization processes are well established for the production of a wide range of particulate products as well as for purification and separation processes [1]. In cases of high epitaxial fit between phases with very similar lattice constants, the nucleating phase tends to grow as a thin film on the substrate, covering its entire surface [25,26], in a process known as Frank van der Merwe growth mechanism. The Stranski–Krastanov mechanism starts with the nucleation of a thin layer of a stressed structure that, beyond a critical thickness, is followed by 3D crystal-islands [27] In this case, the sum of the energy of the epitaxial layer and the energy of the interface between the crystals is larger than the surface energy of the substrate (γE + γi > γs), and three-. TThhee ssaallttssaannddddisitsitlilleldedwwataetrewr ewreerweewigehigedheadndanmdixmedixiendaninEarlnenEmrleeynemrecyoevrerceodvwerietdh awliitdh.aTlhide. sTuhsepesnussipoennswioans wplaascepdlaicneda ihneaathinegatipnlgatpelaatte5a0t°5C0 ◦wCitwh imthamgnaegtnicetsitcirsrtiinrgri,ntgo, etonseunrseurfue lfludllisdsioslsuotliuotnio. nT.hTehseasltasltws wereeredidriercetclytlywweiegihgehdedfofor raalllltthhee ssyysstteemmss eexxcceepptt ffoorr (oC(oaNNfnfl−CdaaCiCCaoaC2lln2+––l+s−CCaawnaainodSSednOOrSesSO44–Osw–4HuH−4eb2i−r2OoteOrni)aos).sc.unAtwAbessdteswrtratfheehrceroetoeemdbddotiisabtsfshisrtnooaoeelimlunnduteetitbicdohoyenenbsdsoynoaifesfrdsCcyCioesaaalssSvSsmoOiaOlnorv44gyuiinisnCasgtmeaexoCCxotftarlur2NeCenammaltn2CeodealllfynyNtNodssalalbo2NoCSewwOala,2,t4dStot.hhdOTbeeeh4edrr.eeea.TaqqdAhduudrediioerreaeuedddddn. ddNAaaemmra5do+0oouNauumnnnanddL+tt o5f0 emaLchofsoelaucthiosnolwutaiosnpwreapsaprerdepaanreddsatnordedstohreerdmheetricmaleltyiccallolysecdlo. sBeedf.oBreefporeerfpoermrfoinrmg itnhge ethxepeerxipmeernimtse,nstosl,ustoioluntsiownesrwe perree-phreea-theedatteod2t5o°2C5. ◦C
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