Effect of Al2O3 and CaF2 additives on the viscosity of conventional cryolite melts

The viscosity of cryolite melts of conventional composition NaF–AlF3–CaF2–Al2O3 was studied by rotational viscometry using the FRS 1600 high-temperature rheometer. The cryolite ratio of the NaF–AlF3 melt was 2.1, 2.3, and 2.5; the Al2O3 content varied from 2 to 6.6, and CaF2 – from 0 to 8 wt%. The measurements were carried out in the temperature range from liquidus to 1200 °C. The conditions for the laminar flow of the investigated melts were determined, based on the measurements of the cryolite melts viscosity as a function of the shear rate at a constant temperature. A shear rate of 12 ± 1 s–1 was chosen for studying the viscosity temperature dependence for all samples. The viscosity temperature dependence of cryolite melts is described by a linear equation. The temperature coefficient b in this equation has negative values and varies in the range of (–0.01)–(–0.06) mPa·s/deg. It was found that the viscosity of cryolite melts of conventional composition in the range of operating temperatures of aluminum electrolysis (950–970 °C) varies from 2.5 to 3.7 mPa·s (depending on the composition and temperature). The viscosity of cryolite-alumina melts increases with the rise of alumina content: 1 wt% Al2O3 increases the viscosity, on average, by 1%. However, the influence of CaF2 is more significant: the addition of 1 wt% CaF2 leads to an increase in viscosity by 3%. A decrease in the CR of the melt by 0.1 (in the range of 2.1–2.5) leads to a decrease in the viscosity of cryolite melts by 2.3%. A viscosity regression equation for the cryolite melts of conventional composition as a function of several independent parameters (temperature, CR, CaF2 and Al2O3 content) is obtained by the multivariable approximation of experimental data. The equation satisfactorily (within 1.5%) describes the viscosity of conventional industrial electrolytes and can be used for estimation of their viscosity.

Development of methodical approaches to assessing the formation of rennet-induced milk gels using the method of rotational viscometry

Формирование структуры сычужно-индуцированных молочных гелей, имеющее первостепенное значение в производстве целого ряда продуктов, наиболее объективно может быть охарактеризовано исключительно посредством инструментального измерения реологических параметров. В статье представлены результаты эксперимента по определению способности молочных систем с различной концентрацией сухих веществ к сычужному свертыванию с использованием ротационной вискозиметрии. Метод базируется на анализе изменений динамических показателей вязкости в процессе коагуляции молока, а также его УФ- и НФ-ретентатов с использованием вискозиметра Brookfield с последующей сравнительной графической оценкой кинетики гелеобразования и пиковой вязкости образующихся сгустков. Полученные данные подтвердили эффективность предлагаемых методических подходов для сравнительной оценки способности к сычужной коагуляции молока и его концентратов, полученных разными способами баромембранной обработки, и выявили перспективные направления исследований по изучению активности и дозировок молокосвертывающих препаратов, а также по выбору оптимальных температурно-временных режимов сычужной коагуляции молочных систем с прогнозированием их структурно-механических параметров. Rennet-induced milk gels are crucial for the production of a number of products. The formation of their structure can be objectively characterized only with the use of instrumental measurements of rheological parameters. The article presents the results of the experiment on determining the ability of milk systems with different dry substances concentration to rennet clot using rotational viscometry. This method is based on the analysis of changes in the dynamic viscosity indicators during the milk coagulation and its UV and NF retentates, followed by a comparative graphical assessment of the gelation kinetics and maximum clots viscosity. In our experiment, we used Brookfield viscometer. The presented data confirmed the effectiveness of the proposed methodological approaches for the comparative assessment of the ability to rennet coagulation of milk and its concentrates obtained by different methods of baromembrane treatment. A great prospect has been obtained in studies on the study of the activity and doses of milk-clotting enzymes and, the selection of the optimal temperature-time regimes of rennet clotting of milk systems with the prediction of their structural and mechanical parameters.

The Curing Rheokinetics of Epoxyphosphazene Binders

The influence of epoxyphosphazene-modifying additives on the features of the hot curing process of epoxy-amine composition was studied by the rotational viscometry method. The modification caused an acceleration of the curing process, changed rheokinetics of viscosity increase, especially the stage molecular mass growth of linear chains became almost twice shorter for composition with 30% modifier than for unmodified one. We suggest the reason for these changes is the polyfunctionality of epoxyphosphazene, which finally results in high-density network formation. In cold curing process the bulkiness of epoxyphosphazene molecule and the lack of heat for its motion results in incomplete cure. Thus, in order to cope with these difficulties hot curing systems were proposed and studied.

The Influence of Molecular Weight Hydroxypropylcellulose on Rheological Properties of Aqua-Ethanol-Coal Suspensions

The rheological properties of aqua-ethanol-coal of varying degrees coal metamorphism, stabilized by macromolecular surfactants was studied by rotational viscometry. It was found that including of hydroxypropylcellulose as a stabilizer for dispersions of coal and water-ethanol mixtures, increasing their stability. It is shown that with increasing molecular weight of hydroxypropylcellulose viscosity of disperse systems increases, regardless of the degree of coal metamorphism. With increasing concentrations of the polymer injected more than 0.01 % of coal the viscosity of the systems increases sharply.