Effects of Different Calcium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

Andalusite containing low-cement castables (LCCs) have been used in aluminum casthouses for several decades. CaF₂ is commonly added to the refractory to improve its corrosion resistance mainly because of its role in the formation of anorthite (CaAl₂Si₂O₈); the latter has been reported to decrease the penetration of molten aluminum alloys into refractories. This article investigates the effect of the addition of different calcium containing compounds (CaO, CaCO₃, CaSO₄, CaF₂, Clinker white cement, calcia feldspar, wollastonite, and Ca₃(PO₄)₂) on reactions with the refractory constituents to form anorthite as well as the effect of the additives on both the subsequent physical properties and the corrosion resistance of andalusite LCC refractories. Corrosion tests using the Alcoa cup test at temperatures (1123 K [850 °C] for 150 hours and 1433 K [1160 °C] for 72 hours) were conducted to determine the extent of penetration, whereas immersion tests in boiling water were conducted to determine the extent of open porosity in the material. Scanning electron microscopy coupled with energy dispersive spectrometer, optical microscopy, and X-ray diffraction techniques were employed to characterize the phase formations in the materials after the tests. The study demonstrated that both calcia feldspar and clinker white cement had the potential to be used as new additives for decreasing the penetration of molten Al-alloy into the refractory materials. Anorthite formation (in the refractory matrix), along with the absence of glassy phases, were responsible for the improvement in the corrosion resistance of the castables containing calcia feldspar. However, in the sample containing cement, the presence of calcium silicate phases were observed to resist reactions with molten aluminum. The observed results were validated using thermodynamic calculations, which indicated that tricalcium silicates (3CaO.SiO₂) and dicalcium silicate (2CaO.SiO₂) phases were more resistant than wollastonite (CaSiO₃) for applications involving contact with molten aluminum.     

Study of Creep–Fatigue Crack Growth Behavior in a Gas Turbine Casing

Journal of Failure Analysis and Prevention - A creep–fatigue crack growth on the outer surfaces of a turbine casing was assessed, and the turbine casing’s overall lifetime was...     

Adaptive Markov-based approach for dynamic virtual machine consolidation in cloud data centers with quality-of-service constraints

Dynamic virtual machine (VM) consolidation is one of the emerging technologies that has been considered for low-cost computing in cloud data centers. Quality-of-service (QoS) assurance is one of the challenging issues in the VM consolidation problem since it is directly affected by the increase of resource utilization due to the consolidations. In this paper, we take advantage of Markov chain models to propose a novel approach for VM consolidation that can be used to explicitly set a desired level of QoS constraint in a data center to ensure the QoS goals while improving system utilization. For this purpose, an energy-efficient and QoS-aware best fit decreasing algorithm for VM placement is proposed, which considers QoS objective when determining the location of a migrating VM. This algorithm employs an online transition matrix estimator method to deal with the nonstationary nature of real workload data. We also propose new policies for detecting overloaded and underloaded hosts. The performance of our proposed algorithms is evaluated through simulations. The results show that the proposed VM consolidation algorithms in this paper outperforms the benchmark algorithms in terms of energy consumption, service-level agreement violations, and other cost factors.     

Study of graphene device electronic properties with horizontal and vertical double vacancy defects

Abstract

Graphene device electronic properties with double vacancy (DV) defects for two cases, along the direction and perpendicular to the current pathways graphene device, were investigated by using the first principles calculations in combination with density functional theory. The bond lengths, density of states, transmission probability, and current-voltage curves are computed. For relaxed pristine graphene the bond length is around 1.43?Å. However, the bond lengths near the defects for relaxed graphene for DV case are modified to 1.40-1.49?Å. It is also observed that I???V graph is nonlinear based on the current-voltage curve of graphene device which contain DV defects. Furthermore, it has been shown that having the DV defects lead to reduce the current relative to the case of perfect graphene device. Moreover, we noted that when the voltage is increased from zero to one volt new peaks are created near Fermi level in the transmission spectrum graphs. In addition, we noted that the current for the vertical DV defect is smaller than the pristine and horizontal DV device because the number of blocked electrons current pathways in vertical DV defect is larger than the two other cases, namely the pristine and horizontal DV defect cases The obtained results can be useful for the construction of new nanoelectronic devices and may have practical applications.     

Effect of alumina content and heat treatment on microstructure and upconversion emission of Er3+ions in oxyfluoride glass-ceramics

The effect of alumina content and heat treatment temperature and time, on microstructure and Er3+ (0.5 mol.%) emission of oxy-fluoride glass-ceramics were investigated in this research. Two values of 1.8 (SA1.8Er0.5) and 2.18 (SA2.18Er0.5) were selected in this re-search for SiO2/Al2O3 ratio. According to DTA results, precursor glasses were heat treated at 630, 660 and 690 °C for 4 h and some glasses were also heat treated at 630 °C for 48 and 72 h. The results indicated that alumina content had significant effect on phase separation and vis-cosity of the glasses. Therefore the size, size distribution, and volume concentration of nano CaF2 crystals which precipitated during the heat treatment depended on alumina content of the glass. Due to the much smaller size of the precipitated CaF2 crystals in the glasses of low alumina content, these samples maintained excellent transparency and had narrower crystal size distribution than the high alumina glasses. The crystal size was increased markedly with the temperature increasing from 630 to 690 °C. On the other hand a slight increase was observed in the crystal size by raising the heat treatment time in both glasses. Results indicated that in low alumina content glass (SA2.18Er0.5) the size of CaF2 nanocrystals was controlled in one order of magnitude. The increase of heat treatment time and temperature led to the incorporation of Er3+ ions into CaF2 crystalline phase, increasing significantly the upconversion intensity. After heat treatment at 690 ℃ for 4 h, atomic force microscope (AFM) re-vealed the development of small crystals with an average size of 80 and 30 nm in SA1.8Er0.5 and SA2.18Er0.5 samples, respectively.     

Effect of heat treatment and solution preparation procedure on colloidal stability of whey protein sour cherry beverage

In this study, a whey protein sour cherry beverage was prepared using whey protein concentrate, sour cherry concentrate, Angum gum, water and sugar as initial ingredients. Whey protein concentrate and gum solutions were prepared by four methods. Heat treatment of the solutions led to denaturation of proteins, a change in the solubility of proteins and sediment formation. Our results showed that denaturation of proteins made the peptide fragments of the proteins to bind the gum, thus preventing the separation of the serum.     

Designing dual-mode luminescence in Er3+ doped Y2WO6 microparticles for anticounterfeiting and temperature measurement

In recent years, rare earth ions doped optical materials have been extensively utilized in anticounterfeiting, temperature measurement, and other fields. However, it is difficult for single-mode photoluminescence to meet the increasingly complex anticounterfeiting needs in practice. In this article, Yb³⁺/Er³⁺ codoped Y₂WO₆ multifunctional microparticles have been designed and prepared, which can emit multimode luminescence and are used for anticounterfeiting and temperature measurement. Under excitation at 254, 365, and 980 nm, Y₂WO₆:Yb³⁺/Er³⁺ microparticles can emit blue, green, and yellow-green luminescence, respectively. The multicolor emission is helpful to improve the security of anticounterfeiting in multimode. In addition, the upconversion, downconversion luminescence, and downconversion lifetime attenuation of this material can be used for fast responsive and noncontact temperature measurement. Among the three temperature measurement methods, the material has the highest sensitivity under the downconversion temperature measurement method, which is 1.25 × 10^–2 K^–1 (at 303 K). The results suggest that the Y₂WO₆:Yb³⁺/Er³⁺ microparticles have excellent applications in the domain of multimode anticounterfeiting and temperature measurement.     

A novel zero dead zone PFD and efficient CP for PLL applications

This paper presents a high dynamic range programmable gain amplifier (PGA) with linear-in-dB and digital to analog converter (DAC) gain control using a BiCMOS process. The proposed PGA is composed of a folded Gilbert variable gain amplifier cell, a DC offset cancellation circuitry, two inductorless fixed gain amplifiers with bandwidth extension, a symmetrical exponential voltage generator, a novel buffer amplifier with active inductive peaking for testing purposes and a 10 bit R-2R DAC. The linear-in-dB and DAC gain control scheme facilitate the analog baseband gain tuning accuracy and stability, which also provides an efficient way for digital baseband automatic gain control. The PGA chip is fabricated using 0.13 μm SiGe BiCMOS technology. With a power consumption of 80 mA@1.2 V supply voltage, the fabricated circuit exhibits a tunable gain range of ? 30–27 dB (DAC linear gain step guaranteed), a 3 dB bandwidth of around 3.5 GHz and a gain resolution of better than 0.07 dB.     

Fabrication and characterization of chitosan/kefiran electrospun nanofibers for tissue engineering applications

Chitosan (CS)-based nanofibrous scaffolds are very promising in tissue engineering applications. However, electrospinning of CS is not possible unless using toxic solvents such as trifluoroacetic acid or by blending with other polymers. In the present study, we investigated CS-based nanofibers' fabrication by blending it with kefiran as a natural polysaccharide. A series of solutions with various CS to kefiran ratios were prepared and underwent electrospinning. The effects of main process parameters, including applied voltage and needle tip-to-collector distance on nanofibers' diameter and morphology, were also studied. Nanofibers containing 80% CS and 20% Kefiran with an average diameter of 81 ± 17 nm were successfully electrospun. Thermogravimetric analysis indicated the presence of both polymers in blend nanofibers. The diameter of CS/kefiran nanofibers increased with enhanced applied voltage, while needle tip-to-collector distance did not significantly affect the mean diameters. Appropriate viability of l929 cells on the obtained scaffolds was demonstrated utilizing Alamar blue assay. Also, cell attachment onto the fiber surface was confirmed by scanning electron microscopy. Results indicated that CS/kefiran nanofibrous scaffolds would be promising for tissue engineering applications.