Thermodynamic activities in silicon binary melts

The thermodynamic activities in the silicon binary melts with Al, Ca, Mg, Fe, Ti, Zn, Cu, Ag, Au, Sn, Pb, Bi, Sb, Ga, In, Pt, Ni, Mn and Rh are studied. The silicon activities along the liquidus are calculated through a quasi-regular solution model using the recently determined liquidus constants for the silicon binary systems. The silicon activities at its melting point are calculated considering regular solution approximation. The activities of the other melt component at the silicon melting point are also calculated through the graphical integration of the Gibbs–Duhem equation for the activity coefficient, which are further utilized to determine the corresponding activities along the liquidus. The calculated activities are presented graphically, and it is indicated that the results are consistent with the reported activity data in the literature. The activities in the dilute solutions are also calculated graphically. Moreover, the activities of particular dilute solute elements in silicon are calculated through a simple formula, which is a function of the liquidus constants.     

Quantifying the uncertainty of on-line sensors at WWTPs during field operation

It remains an ongoing task to quantify the uncertainty of continuous measuring systems at WWTPs during field operation. The commonly used methods are based on lab experiments under standardized conditions and are only suitable for characterizing the measuring device itself. For measuring devices under field conditions, a knowledge of the response time, trueness and precision is equally important.

A method is proposed which can be used to characterize newly installed on-line sensors or to evaluate monitoring data which may contain systematic errors. The concept is based on comparative measurements between the sensor and a reference. A linear regression is used to differentiate between trueness and precision. Various statistical tests are conducted to validate the preconditions of linear regression. The information about the trueness and precision of the measuring system under field conditions helps to adapt control strategies more effectively to the relevant processes and permits sophisticated control concepts. Moreover, the concept can help to define guidelines for evaluating the uncertainties of effluent quality monitoring to overcome the concerns about on-line sensors, improve the trust in these systems and to allow the use of continuously measuring systems for legislative purposes.

The approach is discussed in detail in this paper and all statistical tests and formulas are listed in the Appendix.     

Update on the Equilibrium between Liquid Fe‐Ti‐O Slags and Metallic Iron

The current work is an update on the equilibrium between a synthetic high titania slag and metallic iron at temperatures above the slag melting point. The experimental setup is essentially the same as previously shown in the literature, thus employing a cold crucible in a high frequency induction furnace. A new addition to the experimental setup is the temperature measurement by a spectropyrometer. The temperature measurements will give the liquidus temperature for the slags. This temperature shows a decreasing trend as the FeO content in the slag increases. 24 slags have been successfully produced with iron saturation with a FeO content ranging from 6 to 33 wt%. The slags show a clear trend and provide a solid foundation to the location of the slag‐metal equilibrium line in the investigated area. The experiments are in agreement with previously published experimental data but not with previously calculated results using thermodynamical software.     

Characteristics of Calcium-Aluminate Slags and Pig Iron Produced from Smelting-Reduction of Low-Grade Bauxites

Metallurgical and Materials Transactions B - Low-grade bauxite ores are not favorable in the conventional Bayer process for alumina production, as they are producing more bauxite residue (red mud)...     

Degenerate onset of convection in vertical porous cylinders

In this work we analyze the performance of a novel conceptual design for water-wave energy converters. The model system in question consists of a water tank with two hinged side walls that oscillate when the water surface within the tank is subjected to a temporally periodic, spatially distributed pressure variation. Then, through transmissions, the two oscillating walls are connected to electric generators. A linearized two-dimensional potential flow problem is formulated for this model system, and the steady periodic system response is solved for analytically. A comprehensive parameter study then is carried out so as to clarify how the system’s performance is affected by its design and operation parameters. It is found that, in addition to a series of resonant forcing frequencies that produce large electric power output, there also exist certain anti-resonant forcing frequencies that generate zero power. Moreover, with optimally tuned parameters, the maximized electric power output of the model system studied in this work is comparable with, and even higher than, that of preexisting systems of similar nominal size.     

Modelling nitrite in wastewater treatment systems: a discussion of different modelling concepts

Originally presented at the 1st IWA/WEF Wastewater Treatment Modelling Seminar (WWTmod 2008), this contribution has been updated to also include the valuable feedback that was received during the Modelling Seminar. This paper addresses a number of basic issues concerning the modelling of nitrite in key processes involved in biological wastewater water treatment. To this end, we review different model concepts (together with model structures and corresponding parameter sets) proposed for processes such as two-step nitrification/denitrification, anaerobic ammonium oxidation and phosphorus uptake processes. After critically discussing these models with respect to their assumptions and parameter sets, common points of agreement as well as disagreement were elucidated. From this discussion a general picture of the state-of-the-art in the modelling of nitrite is provided. Taking this into account, a number of recommendations are provided to focus further research and development on nitrite modelling in biological wastewater treatment.     

Reduction of Norwegian and Indian ilmenite with carbon monoxide and hydrogen gas blends

Synthesis gas, produced from natural gas, can be used to minimise coal consumption and carbon dioxide emissions during the processing of ilmenite. Two different ilmenite ores have been reduced with carbon monoxide and hydrogen mixtures to investigate the effects of temperature and gas composition on the final product. Thermogravimetric analysis was used to observe the reaction progress. Experimental work revealed that between 900 and 1000?°C the hydrogen content in the gas has an equally significant effect as the temperature. Statistical analysis determined that the source of the ore did not have a significant effect on the reaction rate. Armalcolite is one of the main products of pre-reduction in addition to metallic iron and rutile from these ilmenite concentrates. There is also some indication that titanium dioxide is reduced. Optical microscope images revealed that increasing amounts of hydrogen resulted in smaller more uniformly distributed metallic iron particles.