Thermodynamics of Nitric Acid Extraction with Iso-Butanol. I. Water Activity In Iso-Butanol

A numerical procedure was employed to evaluate hydrated water attached to the extractable nitric acid/iso-butanol complex. The hydratation number was found to be 11, a value favourable in comparison to the hydratation numbers published for straight chain alcohols extractants. Of several tested approaches, the fourth order interaction Scatchard equation offers water activity coefficients in the alcohol phase which are in close agreement with the measured ones.     

The influence of structure order on the kinetics of dehydroxylation of kaolinite

The structural order of kaolinite is an important factor that shows a substantial effect on the processes which take place during the thermal treatment of kaolin. The influence of structural order on the dehydroxylation process was investigated by simultaneous thermogravimetry and differential thermal analysis (TG-DTA). The thermal analysis was performed on the samples with gradually decreasing structural order prepared by milling procedure. The apparent activation energy of dehydroxylation process decreases with decreasing structural order according to the exponential function. The extrapolation of experimental data leads to the estimation of apparent activation energy of 76.6 kJ mol^?1 and of frequency factor of 0.12 × 10⁴ s^?1 related to completely disordered form of kaolinite, while the ordered form shows the apparent activation energy of 216.17 kJ mol^?1 and the frequency factor of 9.26 × 10⁴ s^?1. The relationships between features such as the infrared pattern of treated material, the degree of structural order and the apparent activation energy were established.     

Structural Study of the Partially Disordered Full‐Length δ Subunit of RNA Polymerase from Bacillus subtilis

The partially disordered δ subunit of RNA polymerase was studied by various NMR techniques. The structure of the well‐folded N‐terminal domain was determined based on inter‐proton distances in NOESY spectra. The obtained structural model was compared to the previously determined structure of a truncated construct (lacking the C‐terminal domain). Only marginal differences were identified, thus indicating that the first structural model was not significantly compromised by the absence of the C‐terminal domain. Various ¹⁵N relaxation experiments were employed to describe the flexibility of both domains. The relaxation data revealed that the C‐terminal domain is more flexible, but its flexibility is not uniform. By using paramagnetic labels, transient contacts of the C‐terminal tail with the N‐terminal domain and with itself were identified. A propensity of the C‐terminal domain to form β‐type structures was obtained by chemical shift analysis. Comparison with the paramagnetic relaxation enhancement indicated a well‐balanced interplay of repulsive and attractive electrostatic interactions governing the conformational behavior of the C‐terminal domain. The results showed that the δ subunit consists of a well‐ordered N‐terminal domain and a flexible C‐terminal domain that exhibits a complex hierarchy of partial ordering.     

Implementation of Artificial Neural Networks in Modeling the Water-Air Temperature Relationship of the River Drava

Water temperature directly affects the physical, biological and chemical characteristics of the river and determines the fitness and life of all aquatic organisms. It has direct and indirect effects on nearly all aspects of stream ecology. Accurately estimating water temperature is a complex problem. The purpose of this article is to analyze the relationship between the air and water temperature of the River Drava by constructing an artificial neural network (ANN) model and choosing appropriate network architectures for the River Drava’s daily river water temperature as well as demonstrating its application in improving the interpretation of the results. A linear regression model, as well as a stochastic model are also constructed and compared to ANN models consisting of a multilayer perceptron neural network and a radial basis function network. The results indicate that the ANN models are much better models and that ANNs are powerful tools that can be used for the estimation of daily mean river temperature.     

Preparation of dehydroxylated and delaminated talc: Meta-talc

The roentgen-amorphous delaminated and dehydroxylated phase was prepared applying intensive milling procedure and subsequent thermal treatment of talc. Due to the similarity in properties and in thermal behavior of this material with roentgen-amorphous delaminated and dehydroxylated kaolinite phase, i.e. meta-kaolinite, the name meta-talc was suggested for this material. The properties and the behavior during thermal treatment were investigated using thermal analysis, x-ray diffraction analysis, infrared spectroscopy and scanning electron microscopy. The suggested procedure changes the activation energy of dehydroxylation, the behavior during thermal treatment and the phase composition of the product. The kinetics and thermodynamics of the thermal transition were evaluated using Kissinger equation and Eyering law.     

Magnetic behavior of nickel–bismuth ferrite synthesized by a combined sol–gel/thermal method

The bulk NiFe_2?xBi_xO₄ ferrites with various Bi³⁺ concentration (x=0, 0.1, 0.15) were synthesized via sol–gel procedure, starting from nickel, bismuth and iron nitrate powders, followed by the conventional thermal treatment. The structural and magnetic properties of the as-prepared ferrites were studied by means of X-ray diffraction, alternating gradient force magnetometry and Faraday balance. The anisotropy constant was determined by the law of approach to saturation (LAS) model. An increasing Bi³⁺ concentration in NiFe_2?xBi_xO₄ leads to a decrease in the saturation magnetization, Néel temperature and the anisotropy constant of the material.     

The Nondestructive Determination of the Aluminum Content in Pressed Skulls of Aluminum Dross

During production of primary and secondary aluminum, various amounts (in some cases up to 200 kg) of aluminum dross, a mixture consisting of molten aluminum metal and different oxide compounds (the nonmetallic phase), are skimmed per tonne of molten metal. To preserve the maximum aluminum content in hot dross for further extraction, it is necessary to cool the dross immediately after skimming. One way to do this is to press the skimmed hot dross in a press. In this process, the skimmed dross is transformed into so-called pressed skulls, with characteristic geometry convenient for storage, transport, or further in-house processing. Because of its high aluminum content—usually between 30% and 70%—pressed skulls represent a valuable source of aluminum and hence are in great demand in the aluminum recycling industry. Because pressed skulls are generally valued on a free-metal recovery basis, which is influenced by the yield of recovery, or in other words, by the quality of the recycling process, it was recognized as important and useful to develop a method of fast and cost-effective nondestructive measurement of the free aluminum content in pressed skulls, independent of the technology of pressed skulls recycling. In the model developed in this work, the aluminum content in pressed skulls was expressed as a function of the pressed skulls density, the density of the nonmetallic phase, and the volume fraction of closed pores. In addition, the model demonstrated that under precisely defined conditions (i.e., skulls from the dross of the same aluminum alloy and skimmed, transported, cooled, and pressed in the same way and under the same processing conditions), when other parameters except the pressed skulls density remain constant, the aluminum content in pressed skulls can be expressed as a linear function of the pressed skulls density. Following the theoretical considerations presented in this work, a practical industrial methodology was developed for nondestructive prediction of the amount of free aluminum in pressed skulls w _Al, based on nondestructive measurement of the density ρ of the pressed skulls. The pressed skulls density is measured by a fully automatic gas displacement pyknometer with a working volume large enough to enable the insertion of the whole pressed skull sample. An additional integral part of this methodology is the set of experimentally determined linear graphs w _Al-ρ, plotted in advance for all classes of pressed skulls existing in the plant, from the experimentally collected data on pressed skulls density and aluminum recovery by melting. After selecting the proper graph w _Al-ρ, which is usually performed on an aluminum alloy basis, the pyknometric measured density of the pressed skulls can be routinely related to the aluminum content sought, within a relative error of ±5%.