The
crystallization of ciprofloxacinan antibacterial fluoroquinolone
compoundwith salicylic acid resulted in the isolation of five
distinct solid forms of the drug, namely, an anhydrous salt, two polymorphic
forms of the salt monohydrate, methanol and acetonitrile solvates,
and the salt-cocrystal hydrate. The salicylate salts were investigated
by different analytical techniques ranging from powder and single
crystal X-ray diffractometry, differential scanning calorimetry, thermogravimetric
analysis, variable temperature powder X-ray diffraction, dynamic vapor
sorption analysis, dissolution, and solubility investigations. Real-time in situ Raman spectroscopy was used to investigate the mechanochemical
formation pathways of the different solid polymorphs of ciprofloxacin
salicylate. The mechanism of the phase transformation between the
crystalline forms was evaluated under mechanochemical conditions.
It was found that the formation pathway and kinetics of the grinding
process depend on the form of the starting material and reaction conditions.
The analysis of the solid-state thermal evolution of the hydrated
salts revealed the two-step mechanism of dehydration process, which
proceeds through a formation of the distinct intermediate crystalline
products.
Here, we report on
a first mechanochemical synthesis of ettringite,
an important cement hydrate phase. The mineral compound ettringite
([Ca
3
Al(OH)
6
]
2
·(SO
4
)
3
·26H
2
O) occurs rarely in nature, but
is common for cement-based materials. Ettringite has wide technical
application in the ceramic and paper industry. However, its typical
wet-chemical synthesis is cumbersome and produces waste water and
CO
2
emissions. Here, we investigate the first mechanochemical
synthesis of ettringite for developing an easy and sustainable alternative
for industrial application. The mechanosynthesis was monitored in
situ by coupled synchrotron X-ray diffraction (XRD) and infrared thermography
(IRT). The consumption of the reactants and the formation of the reaction
product were monitored with time-resolved XRD. IRT showed the temperature
increase based on the exothermic reaction. The reaction conversion
was significantly improved changing the strategy of the mechanosynthesis
from a one- to a two-step process. The latter included neat pregrinding
of solid reactants followed by a delayed addition of the stoichiometric
amount of water. Thus, an increase of reaction conversion from 34
to 94% of ettringite could be achieved.
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