Thermodynamics of the system NaF-AIF3: Part VI. revision

Literature data are reviewed to derive enthalpies and entropies of Na₃AlF₆ and NaF, and they are combined with electrochemical and equilibrium data to yield free energies of formation of Na₃AlF₆ from the constituent fluorides. Liquidus data and measurements of the Na content of Al in equilibrium with the melts then enable the calculation of the free energy of formation, enthalpy, and entropy of all mixtures liquid at 1293 K. In stoichiometric Na₃AlF₆ at 1293 K, a_NaF =0.37 and a_{AlF 3} = 4.9 × 10⁻⁴. The activity coefficient of Na in dilute solution in Al is given byRT ln γ_Na = (40 967 + 9.480 T) J. At 1293 K the partial pressure of NaAlF₄ is given by pNaA1F₄/bar = 27a_NaF . a_{Aif 3}- A heavier species— suggested to be NaAl₃F₁₀—is present in the vapor above AlF₃-rich melts.     

Geometric approach to VLSI layout compaction

We present a new geometric approach to VLSI layout compaction in this paper. In contrast to existing compaction algorithms, we rely on the geometric method and bypass both compaction grids and constraint graphs during the entire compaction process. A systematic and efficient way is introduced to enumerate all possible jogs. For the given layout topology we prove that the geometric algorithm yields the minimum-area layout in one-dimensional compaction with automatic jog insertion. In the final output, only necessary jogs are inserted and the total wire length is minimized as a secondary goal. Furthermore, the integration of local compaction tools into a layout CAD system and the practical extensions of our algorithm are addressed.     

Loss of current efficiency in aluminum electrolysis cells

Consideration of the mechanism of loss of current efficiency (CE) leads to a form of equation which is simple, likely to give reasonable extrapolation beyond the range where experimental data are available, and convenient for responding to practical questions. With coefficients generated from plant experiments (performed by others), the equation is log (pct loss of efficiency) = 0.0095 (superheat) -−0.019 (pct A1F₂) − 0.060 (pct LiF) + const where superheat is the difference (in °C) between cell temperature and the pseudo-binary eutectic temperature with A1₂O₃, and pct A1F₃ is excess A1F₃. The coefficient for CaF₂ is zero. The constant is characteristic of the cell design. The question of reconciling the values of the coefficients with literature data on the solubility of Al in cryolite melts and current theories of loss of efficiency is discussed. Formerly Principal Scientist, Kingston Laboratory, Alcan International Ltd., Kingston, ON K7L 5L9, Canada, is retired.     

Amplitude-modulating periodicities in global and regional heat/temperature variations

Being one of the major factors influencing global heat energy content in the surface-atmosphere system, global air temperature is studied and the dominating periodicities therein obtained. It is established that since 1856, variations in global air temperature have been dominantly amplitude-modulated by an oscillation whose period is about 105 years. This oscillation, which is of solar origin, is apparently largely responsible for the ongoing warming trend at global level. Analysis of air temperature records from individual regions yields different dominant periodicities for the two hemispheres. While temperature variations in many parts of the northern hemisphere are dominantly amplitude-modulated by an oscillation at a period of ≈ 180 years, corresponding variations in many parts of the southern hemisphere are dominantly amplitude-modulated by an oscillation at a period of ≈ 55 years. Both of these oscillations are apparently of solar origin.     

Determination of mass density, dielectric, elastic, and piezoelectric constants of bulk GaN crystal

Mass density, dielectric, elastic, and piezoelectric constants of bulk GaN crystal were determined. Mass density was obtained from the measured ratio of mass to volume of a cuboid. The dielectric constants were determined from the measured capacitances of an interdigital transducer (IDT) deposited on a Z-cut plate and from a parallel plate capacitor fabricated from this plate. The elastic and piezoelectric constants were determined by comparing the measured and calculated SAW velocities and electromechanical coupling coefficients on the Z- and X-cut plates. The following new constants were obtained: mass density p = 5986 kg/m(3); relative dielectric constants (at constant strain S) ε(S)(11)/ε(0) = 8.6 and ε(S)(11)/ε(0) = 10.5, where ε(0) is a dielectric constant of free space; elastic constants (at constant electric field E) C(E)(11) = 349.7, C(E)(12) = 128.1, C(E)(13) = 129.4, C(E)(33) = 430.3, and C(E)(44) = 96.5 GPa; and piezoelectric constants e(33) = 0.84, e(31) = -0.47, and e(15) = -0.41 C/m(2).     

Arsenic removal from aqueous solutions by adsorption on magnetite nanoparticles

Magnetite nanoparticles were used to treat arsenic‐contaminated water. Because of their large surface area, these particles have an affinity for heavy metals by adsorbing them from a liquid phase. The results of the study showed that the maximum arsenic adsorption occurred at pH 2, with a value of approximately 3.70 mg/g for both As(III) and As(V) when the initial concentration of both arsenic species was maintained at 2 mg/L. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on the contact time, the initial concentration of arsenic, the phosphate concentration in the water and the adsorbent concentration. The results suggest that arsenic adsorption involved the formation of weak arsenic–iron oxide complexes at the magnetite surface. At a fixed adsorbent (magnetite nanoparticles) concentration of 0.4 g/L, percent arsenic removal decreased with increasing phosphate concentration. Magnetite nanoparticles removed <50% of arsenic from water containing >6 mg/L phosphate. In this case, an optimum design for achieving high arsenic removal by magnetite nanoparticles may be required.