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- Title
Determination of food additive zinc-cobalt(II) phosphate form resistant to high temperatures.
- Authors
Antraptseva, Nadiia; Podobii, Olena; Bila, Galyna
- Abstract
Introduction. The aim of the research was to study the process of dehydration of zinc-cobalt(II) phosphates during heat treatment. Materials and methods. Zinc-cobalt(II) phosphate tetrahydrates were used as the main research objects. The content of ingredients in the composition of phosphates was as follows, % mass.: Zn, 41.8-23.5; Co, 2.3-12.8; P, 13.6-13.8; H2O, 16.1-16.3. Spectral methods were used to study the process and products of dehydration. Infrared absorption spectra were recorded at 20 ℃ and -190 ℃, as well as in the process of heating phosphates. X-ray phase analysis was performed. Results and discussion. In the structure of zinc-cobalt(II) phosphates there are two types of crystallographically nonidentical water molecules, the OH groups of which form a rigid system of hydrogen bonds of different strength and directionality (from 29.35-30.48 kJ·mol-1 in the OH···ОРО3 group to 12.48-13.31 kJ·mol-1 in the OH···H2O group). The energy of H-bonds, cation-water bonds and the asymmetry of water molecules increase with an increase in the cobalt content from 2.3 to 12.8 % mass., which is associated with a stronger polarizing effect of cobalt on water molecules that make up the nearest coordination environment of the cation. Zinc-cobalt(II) phosphates are thermally stable up to 85-90 °С. Upon further increase of temperature, their dehydration occurs with the pairwise removal of four water molecules and the formation of one hydrated form as an intermediate product - zinc-cobalt phosphate dihydrate. The temperature regimes of the process of dehydration of phosphates of different cationic composition correlate with the energy state of water molecules and are maximal in phosphate containing 12.8 % mass. cobalt. It is stable during heat treatment up to 90 °C. In the interval from 90 to125°C two water molecules are removed with the formation of zinc-cobalt (II) phosphate dihydrate. This compound is stable in the temperature interval from 125 to 250 °C. A further increase in temperature is accompanied by the release of the last two moles of water and the formation of completely dihydrated zinc-cobalt(II) phosphate. Temperature intervals of thermal stability of zinc-cobalt(II) phosphates and products of their dehydration are by 15-20 °С higher than phosphates with a higher cobalt content. Conclusions. Zinc-cobalt(II) phosphate, containing the maximum amount of cobalt, is the most termostable form. Zinccobalt(II) phosphate dihydrate formed as a result of the release of two water molecules at 90-125 °C is the only stable product.
- Subjects
FOOD additives; HIGH temperatures; PHOSPHATES; COBALT; ABSORPTION spectra; HEAT treatment; INFRARED absorption
- Publication
Ukrainian Food Journal, 2023, Vol 12, Issue 2, p285
- ISSN
2304-974X
- Publication type
Article
- DOI
10.24263/2304-974X-2023-12-2-10