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A. Zvirgzdiņš, K. Veldre and A. Actiņš

Structures of Mildronate Polymorphic and Pseudopolymorphic Forms

Structures of mildronate polymorphic and pseudopolymorphic forms were determined using powder X-ray diffractometry data. Mildronate di-hydrate structure was determined for the verification of methodology, which was applied for mildronate monohydrate and anhydrous form structure determination. All mildronate forms crystallize in primitive latti-ces - anhydrous form in P21/n, monohydrate in P1 and dihydrate in P21/c. The structures of mildronate forms show similarities to carnitine and its derivatives.

Open access

K. Krūkle-Bērziņa, A. Actiņš and A. Bērziņš

Hydration of Xylazine Hydrochloride Polymorphic Forms A, Z and M

In this work, the hydration of Xylazine hydrochloride polymorphic forms A, Z and M was monitored by gravimetry. A solid state kinetic model of hydration was defined, and rate constants were calculated for different temperatures and humidity conditions. Activation energy values were obtained from the Arrhenius plots of the rate constants in the co-ordinates ln k - T -1.

Open access

J. Kostjukovs, I. Sarceviča and A. Actiņš

Thermal Regeneration Model for Spent Montmorillonite Sorbent

The regeneration possibilities of montmorillonite after repeated heating in the temperature range of 300 °C - 450 °C were investigated. A simple technique for thermal regeneration of spent montmorillonite sorbent was developed. Powder X-ray diffraction (PXRD), thermogravimetry/differential thermal analysis (TG/DTA), wavelength dispersion X-ray fluorescence spectrometry (WDXRF) and visible light spectrometry were employed for sample characterization. Heating at 300 °C allowed successful repeating of regeneration, at which the montmorillonite structure could be restored after several heating cycles. However, regeneration at about 450 °C resulted only in partial regeneration of montmorillonite structure. After three regeneration cycles at 450 °C the pseudo-illitization was irreversible.

Open access

A. Bērziņš and A. Actiņš

Simulations of solid-state transformation kinetics were carried out calculating temperature and conversion degree for non-isothermal experiments with different heating rates. Simulations were divided in two parts: with constant and with variable activation energy. Simulations were analyzed with widely used model-based and model-free activation energy determination methods, frequency factor and kinetic model determination methods. Much of the attention was devoted to the calculation of kinetic models and frequency factors, as a more difficult and less developed step. For simulations where activation energy did not change all activation energy determination methods were found to give correct results. However, much attention should be devoted to frequency factor determination, because incorrect results would lead to problems in determination of kinetic models. For simulations where activation energy changes, correct activation energy can be determined only by differential methods or integral methods using numerical integration over small intervals. Isokinetic relationship coefficients b and c were more accurately determined with the average linear integral method. Correct kinetic model determination was possible only when coefficients b and c were accurate, and only by analyzing results of all available methods.

Open access

J. Karasa, J. Kostjukovs, A. Palaša and A. Actiņš

A procedure of smectite containing clay enrichment has been optimized, and the process of sedimentation has been studied. The new enrichment based method for quantitative determination of clay fraction in smectite containing sediment was developed. A new method for obtaining organoclays from enriched smectite clays has been investigated. The method is based on solid-state reaction between smectite and organic compounds, where organic molecules can be intercalated in dried clay mineral (montmorillonite) by solid-state reactions, without or with use of solvents. The enriched clay and the obtained organoclay samples were characterized with X-ray powder diffraction (PXRD).

Open access

A. Kons, A. Bērziņš, K. Krūkle-Bērziņa and A. Actiņš

Abstract

The paper reports the investigation of three umifenovir molecular complexes with dicarboxylic acids, prepared to improve the bioavailability of this drug. All three molecular complexes were investigated by powder X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. The solubility and thermal properties were determined as well. Polymorph and solvate screening of umifenovir molecular complexes were performed by recrystallization from various solvents, as well as neat and solvent-drop grinding