INVESTIGATION OF THE EVAPORATION AND CRYSTALLIZATION OF A SESSILE DROP OF AMMONIUM SULFATE SOLUTION ON A SMOOTH HEATED SURFACE.

Creation of new composite granular fertilizers with layered structure, which are formed due to the layered mechanism of granulation in the granulator of the fluidized bed is an urgent task. The process of forming these granules is achieved due to the layered granulation mechanism, the basis of which is the formation of a layer of solids on the surface of the granules by mass crystallization. In the production of granular fertilizers based on ammonium sulfate with the addition of organic and inorganic impurities an important place is occupied by the processes of evaporation and mass crystallization, which determine the morphological properties of the obtained granular material. During the experimental study of the evaporation process, it was found that the process consists of three main evaporation periods: the heating period from the initial temperature to equilibrium, the period of equilibrium evaporation and the decreasing drying rate period with crust formation, during which a solid crystal structure is formed. The beginning of each period according to the example of drying droplets in a gas stream during spray drying is described by the nature of the change in droplet temperature. This paper presents the obtained thermograms of the process of evaporation of droplets with a diameter of 3–7 mm 40%, 50% and 60% aqueous solutions of ammonium sulfate with the addition of a mixture of bone meal. The evaporation of 40%, 50% and 60% solutions of ammonium sulfate with the addition of a mixture of bone meal, with a given ratio of AS: BM on a dry residue of 60:40 and 80:20 on a surface temperature of 95°C in the second evaporation period crystalline nuclei appear, and the concentration of solute is close to saturated and almost unchanged, so that the evaporation rate and temperature of the drop, as can be seen from the thermogram, remain constant temperature for all solutions of ammonium sulfate. Increasing the content of bone meal from 8 to 24% to shift the wet thermometer in the kinetics of the evaporation process. The paper also presents the results of morphological analysis of the obtained solid crystallized drops of ammonium sulfate with impurities of bone meal. It was found that the solid crystallized drop of ammonium sulfate with bone meal consists of a framework of microcrystals of ammonium sulfate, with a reduced size of 10 to 80 μm, bone meal in the form of inclusions is placed in the frame, the particle size of bone meal varies up to 100 μm, indicating that the solution is a suspension.

Features of isothermal crystallization of ammonium sulphate

Soil fertility is rapidly decreasing due to irrational land use, erosion and soil pollution and adverse weather conditions. The use of composite granular organic-mineral fertilizers that contain mineral and organic components allows the soil fertility to be increased in the most effective and safe manner for the environment. In the production of granular composite fertilizers in a fluidized bed granulator, the process of isothermal mass crystallization is the main parameter that affects the quality. The effect of impurities on the morphological structure of ammonium sulfate microcrystals during mass crystallization on the surface was investigated by means of microscopic analysis. The influence of temperature and pH of the solution on the structure and shape of the microcrystal layer was studied. The process of mass crystallization depends on the presence of impurities, pH and temperature. Given the fact that there is no analytical or theoretical dependence describing the influence of impurities on the morphological structure, the influence is determined experimentally. The presence of even a small content of surfactants and other impurities in the ammonium sulfate solution has a significant effect on the morphological structure of ammonium sulfate microcrystals, which is revealed as reduction in the concentration of impurities in ammonium sulfate obtained by coke-chemical method. The pH level of the medium affects the structure and shape of microcrystals: smaller crystals with a layered structure are formed in the case of weakly alkaline medium with pH = 8 and smaller microcrystals with a granular structure are formed in the case of pH = 4. Therefore, it is important to maintain the required pH level of the medium during the mass crystallization of ammonium sulfate. In isothermal mass crystallization of saturated aqueous solutions of ammonium sulfate with humic compounds and bone meal proceeding on a surface with temperature 90 °C, small elongated crystals with microcrystal sizes from 10 to 100 μm are formed. Impurities of bone meal and humic compounds in the form of inclusions are placed between the crystals of ammonium sulfate: namely, the endosegregation of impurities in the microcrystalline framework is observed. As the concentration of organic matter in the solution increases, which crystallizes as droplets on the surface, rubble and dendrites are formed outside the initial droplet placement. This phenomenon is explained by the increase of diffusion resistance at the center of the drop; as a result, ammonium sulfate crystallizes in the zone with lower resistance. The process of isothermal mass crystallization of saturated aqueous solutions of ammonium sulfate with admixtures of humic compounds, bone meal and other target components in the specified ratios will create new highly effective fertilizers. The obtained results allow formulating theoretical bases for the formation of solid structures based on ammonium sulfate with admixtures of organic and mineral components.

Specific Mass Growth Rate of Sugar Crystals: Probabilistic Modeling

Introduction. The present research featured industrial sugar crystallization. The article introduces a generalized mathematical model of specific growth rate of sugar crystals depending on temperature, solids, and the purity of solution, as well as on the concentration and average size of crystals. The model includes the probabilistic component of growth rate of monocrystals and the reduced adjustment of the constrained crystal growth depending on the abovementioned as-pects. Study objects and methods. The research focused on mass crystallization of sucrose, including the growth rate of monocrystals and the number of crystals in the fill mass. The obtained experimental data were processed using nonlinear programming. Results and discussion. 421 experiments made it possible to develop a probabilistic mathematical model of specific mass growth rate of sugar monocrystals and its dependence on the solution temperature, purity, and solids content. Model error: ± 11.3%. The model covers the temperature range, concentration of solids, and purity of the solution. The proximity of crystals was calculated according to the dependence of the growth rate on their concentration and the average size (error: ± 1.3%). The adjustment range: concentration of crystals = 5–60%, average size = 0.25–1.50 mm. Conclusion. The present generalized mathematical model of crystallization considered the temperature, as well as the purity and solids content in the fill mass, the concentration of sucrose crystals and their average size. The research compared the effect of linear size and concentration of sugar monocrystals on the calculated and experimental sizes of specific mass growth rate and the dimensionless adjustment of growth rate. The calculated sizes proved to be close to the ex-perimental data, which showed adequacy to the developed crystallization model. The research results can be used to optimize the process of mass sugar crystallization.

CREATION OF GRANULAR COMPOSITE MATERIALS WITH MULTILAYER STRUCTURE

Granular products are widely used in many industries for the production of catalysts in oil refining and organic synthesis, drugs, food products, fertilizer production, etc. The main advantages of granular products are ease of operation and storage. Depending on the morphological structure, the granules obtained as a result of the technological process are divided into one-component, single-layer, composite-coated granule, multilayer granule, frame granule, and combinations thereof. In this paper, we consider, as an example, the technological basis of granulation of aqueous solutions of ammonium sulfate with impurities of humates, calcium carbonate and other substances with the formation of multilayer composite granules in a fluidized bed granulator. The processes of dehydration and mass crystallization during granulation, namely the influence of the drying rate and impurities on the kinetics of the evaporation process of the dispersed heterogeneous solution on solid particles have been studied. In the process of mass crystallization, when the saturation concentration is reached by removing the solvent, the processes of nucleation and crystal growth occur with the formation of a crystalline framework of ammonium sulfate crystals between, which impurities of organic matter and other components are evenly distributed in the volume of the formed micro layer. It was confirmed that the obtained granules of the composite granular fertilizer have a composite multilayer structure with a uniform distribution of suspended particles in the volume of the granule. Bibl. 14, Fig. 4.

Critical phenomena and granatization of water-containing eclogite at P = 3,7-4,0 GPa, T = 1000-1300 °C

The phase relationships have been experimentally studied at eclogitization of basalts and the melting of H2O‑containing eclogite in the basalt-H2O system at P = 3,7-4,0 GPa, T = 1000-1300 C. It is established that the phase relationships depend on temperature. The formation of a supercritical fluid-melt occurs at T = 1000 C, P = 3,7 GPa, conversion eclogite-granatite occurs at T = 1000-1100 C, P = 3,9 GPa, partial melting of eclogite with the formation of Na-alkali silicate melt and clinopyroxenite restite at 1150 C and 1300 C. The supercritical fluid-melt has a high reactivity, resulting in the formation of megacrists of garnet, its enrichment with Ti, the replacement of garnet with clinopyroxene, the formation of ilmenite, K‑containing amphibole, the conversion of eclogite into garnetite as a result of mass crystallization of garnet.

Effect of Rare-Earth Element Oxides on Diamond Crystallization in Mg-Based Systems

Diamond crystallization in Mg-R2O3-C systems (R = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) was studied at 7.8 GPa and 1800 °C. It was found that rare-earth oxide additives in an amount of 10 wt % did not significantly affect both the degree of graphite-to-diamond conversion and crystal morphology relative to the Mg-C system. The effect of higher amounts of rare-earth oxide additives on diamond crystallization was studied for a Mg-Sm2O3-C system with a Sm2O3 content varied from 0 to 50 wt %. It was established that with an increase in the Sm2O3 content in the growth system, the degree of graphite-to-diamond conversion decreased from 80% at 10% Sm2O3 to 0% at 40% Sm2O3. At high Sm2O3 contents (40 and 50 wt %), instead of diamond, mass crystallization of metastable graphite was established. The observed changes in the degree of the graphite-to-diamond conversion, the changeover of diamond crystallization to the crystallization of metastable graphite, and the changes in diamond crystal morphology with increasing the Sm2O3 content attested the inhibiting effect of rare-earth oxides on diamond crystallization processes in the Mg-Sm-O-C system. The crystallized diamonds were studied by a suite of optical spectroscopy techniques, and the major characteristics of their defect and impurity structures were revealed. For diamond crystals produced with 10 wt % and 20 wt % Sm2O3 additives, a specific photoluminescence signal comprising four groups of lines centered at approximately 580, 620, 670, and 725 nm was detected, which was tentatively assigned to emission characteristic of Sm3+ ions.

Релаксация напряжений в кристаллах CrSi-=SUB=-2-=/SUB=-, выращенных в условиях невесомости из расплава Zn системы Cr-Si-Zn

Experimental data and their analysis on the study of Cr〖Si〗_2 microcrystals grown in weightlessness from the melt Zn of Cr-Si-Zn system by mass crystallization and placed in earth conditions are presented. New properties of such crystals are found.