Ferroic Halide Perovskite Optoelectronics

Metal halide perovskites (MHPs) as one of the most active materials gained tremendous attention in the past decade because of their outstanding performance in optoelectronics. Owing to their perovskite structure, ferroelectricity is anticipated in this class of materials. However, whether MHPs are ferroelectric or not remains elusive. Recently, discussion regarding ferroelasticity in MHPs has been also raised. In addition, ionic motion and structural dynamics are well known in MHPs. The interplay of these phenomena including electric polarization, strain, ionic motion, and structural dynamics can have a significant impact on optoelectronics. Therefore, understanding the mechanism behind these phenomena and their interactions is critical in addressing the controversy about ferroicity of MHPs and developing functional devices. Here, the current findings about MHP's ferroicity are summarized and evaluated and a perspective for the future is provided. It is suggested that ionic motion and associated phenomena, coupled with ferroic behavior, are the main drivers behind MHPs functionality. The challenges are also discussed in probing MHPs’ ferroicity and what new measurement modalities are needed to fully understand and characterize MHP behavior. Finally, it is discussed how ferroic and strain can affect the optoelectronic performance of MHPs and how they can be used for engineering of higher performance devices.     

Effect of Al Antioxidant on the Rate of Oxidation of Carbon in MgO–C Refractory

Kinetics of air oxidation of MgO–C–Al refractory at 600°–1300°C were investigated using the software based on the modified shrinking core model (KDA). Commercial bricks containing 88.5% MgO, 10% residual carbon, and 1.5% aluminum anti-oxidant were oxidized isothermally with air. Combination of experimental data with model calculations indicated gas diffusion through solid material and pores as a major controlling step. Previously observed chemisorption process was eliminated from the rate-controlling mechanism with addition of aluminum antioxidant. Comprehensive rate equations were devised for MgO–C–Al and MgO–C oxidation reactions. Overall activation energies of Q _id (internal diffusion)=139.15 kJ/mol at T ≤800°C and Q _pd (pore diffusion)=25.48 kJ/mol at T >800°C were obtained for MgO–C–Al oxidation reactions. Corresponding values were determined to be Q _id=134.85 kJ/mol and Q _ca (chemical adsorption)=66.69 kJ/mol at T ≤800°C and Q _pd=18.95 kJ/mol and Q _ca=66.69 kJ/mol at T >800°C for MgO–C oxidation reactions. Addition of aluminum anti-oxidant indicated a reducing effect on oxidation of MgO–C bricks at 800°C≤ T ≤1250°C. Reverse behavior was observed at T ≤700°C.     

Prediction of CO<Subscript>2</Subscript> mass transfer parameters to light oil in presence of surfactants and silica nanoparticles synthesized in cationic reverse micellar system

CO₂ miscible injection method combined with surfactants and silica nanoparticles was studied to investigate the effect of these additives on CO₂ mass transfer parameters to the light oil, including diffusion coefficient, mass transfer coefficient and solubility. Silica nanoparticles with controlled size distribution were synthesized in isooctane/1-hexanol/CTAB/ammonium hydroxide, a highly-stable reverse micellar system with w _o =5. The presence of Si-O-Si and Si-O-H bonds in FTIR spectra of the system revealed that silica nanoparticles are formed by partial hydrolysis of TEOS. Results of DLS indicated that the average size and size distribution of the synthesized nanoparticles were 27.6 nm and 13-76 nm, respectively. Diffusion tests were carried out using CO₂ gas and three liquid systems: isooctane/1-hexanol, isooctane/1-hexanol/CTAB reverse micellar system without nanoparticles, and isooctane/1-hexanol/CTAB reverse micellar system with nanoparticles. Results of modeling and optimization of the gas-liquid systems under nonequilibrium interface condition, using pressure decay data show that the presence of surfactants and nanoparticles leads to decreased gas diffusion coefficient; while increased interface mass transfer resistance due to presence of aqueous droplets and nanoparticles as well as lower solubility of CO₂ in the light oil are the results of applying these additives, which limits their application. The obtained CO₂ diffusion coefficients for isooctane/1-hexanol, reverse micellar system without nanoparticles, and reverse micellar system with nanoparticles are 8.5550×10^?8, 8.2216×10^?8, and 8.1114×10^?8 m²/s, respectively.     

Spontaneous Imbibition Experiments of Enhanced Oil Recovery with Surfactants and Complex Nano-Fluids

Two types of porous media were analyzed with the intention of exploring alternative enhanced oil recovery methods. Core samples were taken from the Tensleep Formation of the Black Mountain Field in Hot Springs County, WY. The lithology is mainly sandstone and dolomite. The measured effective porosity values ranged from 13.0 to 18.0%, and permeabilities from 19 to 68 md. Production from the Tensleep and Phosphoria formations using conventional methods has resulted in a low secondary recovery factor, possibly due to high capillary forces and an oil-wet formation. Different surfactants were investigated to determine the viability of a possible enhanced oil recovery process using a spontaneous imbibition process in Amott cells. A very high enhanced recovery factor of more than 89% was achieved using a complex nano-fluid that consists of a mixture of surfactant, solvent, co-solvent and water. These recovery factors compared with 13% by brine imbibition and up to 21% using commercial surfactants. At the other end of the scale, very high porosity volcanic pumice was also subjected to the same tests. For this rock the porosity values ranged from 65 to 90% and permeabilities were 2.0–2.7 d. Secondary recovery showed values up to 81% on spontaneous imbibition and up to 91% when surfactants were employed. These experimental results indicate that pumice has favorable reservoir characteristics, but, due to its weak brittle nature, it would not be expected that it could withstand the overburden stress at any significant depth. However, it does represent a useful laboratory specimen.     

Development of a semi-quantitative food frequency questionnaire for use in United Arab Emirates and Kuwait based on local foods

Background  

The Food Frequency Questionnaire (FFQ) is one of the most commonly used tools in epidemiologic studies to assess long-term nutritional exposure. The purpose of this study is to describe the development of a culture specific FFQ for Arab populations in the United Arab Emirates (UAE) and Kuwait.     

Reactivity stabilization and capacity study of fabricated alumina and zirconia-supported CaO-based sorbents for high-temperature CO2 capture in a fixed-bed reactor

Calcium looping process is a promising approach for CO₂ capture from the flue gas of fossil fuel power plants and the cement industry. Even though the advantages of calcium-based sorbents are low cost and high uptake capacity, they suffer from low durability during cycles. Modified sorbents were fabricated by adding alumina and zirconia and the mixture of alumina and zirconia to calcium oxide via the co-precipitation method. The performance of synthesized sorbents in terms of stability and CO₂ capture capacity were evaluated using a fixed bed reactor in various CO₂ sorption/desorption cycles. The sorbents were fabricated by a co-precipitation methodology using 10% binders (alumina and/or silica). X-ray diffraction (XRD), BET/BJH, and scanning electron microscopy (SEM) were conducted for characterization of synthesized sorbents. CaO-10% ZrO₂ showed the best performance among the fabricated sorbents in terms of stability during 5 cycles and CO₂ capacity (14 mmol CO₂/g sorbent). The formation of CaZrO₃ with a perovskite structure and high-temperature resistance could be attributed to well performance of zirconia-supported sorbent. On the other hand, no sign of aluminum zirconate formation was approved in XRD analysis for the fabricated sorbent using mixed binders of zirconia and alumina to enhance its stability during cycles.     

Antioxidant Activities of Free and Liposome-Encapsulated Green tea extracts on canola oil oxidation stability

In the present study, green tea extract was encapsulated in liposomes based on the Mozafari method (with no organic solvents) and characterized for its physicochemical properties (encapsulation efficiency, particle size, and Z-potential). Encapsulation efficiency, particles size, and Z-potential were determined to be 51.34, 419 nm, and -57 mV, respectively. Total polyphenol content of the green tea by Folin-Ciocalteu's phenol reagent was measured as 164.2 mg gallic acid/g extract. Free radical scavenging activities of free and liposomal extracts were 90.6 and 93.4%, respectively, using the DPPH method. Antioxidant activity of the ethanolic extract of green tea in free and liposomal forms with concentrations of 200, 600, and 1000 mg L⁻¹ were assessed on oxidative stability of the canola oil at 60 °C for 0, 4, 8, 12, 16, 20, 24, 28, and 32 days. Results were compared to results of synthetic antioxidant butylated hydroxytoluene at 200 mg L⁻¹. To assess antioxidant activity on canola oil stability, peroxide, thiobarbitoric acid, and anisidine values were assessed as well as the total oxidation value and rancimat test. Results showed that the liposomal green tea extract was more effective than the free extract. Furthermore, a 600 mg L⁻¹ concentration of the green tea extract showed a significant antioxidant activity, compared to other extract concentrations. Increasing storage time and various concentrations of the ethanolic green tea extracts included significant effects on canola oil stability (P ≤ 0.05). Results demonstrated that the green tea extract could be used as an effective antioxidant. Free and liposomal extract (at 600 mg L⁻¹) resulted in stronger functionality than the synthetic antioxidant butylated hydroxytoluene.     

Dynamics and control of a thermally self-sustaining energy storage system using integrated solid oxide cells for an islanded building

A solid oxide cell-based energy system is proposed for a solar-powered stand-alone building. The system is comprised of a 5 kW_el solid oxide fuel cell (SOFC), a 9.5 kW_el solid oxide electrolysis cell (SOEC), and the required balance of plant. The SOFC supplies: 1- building demand in the absence of sufficient solar power, 2- heat for SOEC in endothermic and standby modes. Thermal integration of SOFC and SOEC is implemented through a network of heat exchangers, combined with set of control algorithms. Two control strategies were implemented to actuate the SOFC in response to endothermic heat demands of SOEC by manipulating: 1- electric power, 2- fuel utilization. The results of dynamic simulation of system for two scenarios (sunny day and cloudy day) showed successful compliance of temperature constraints with both methods. Manipulation of fuel utilization, however, resulted in better system performance in terms of efficiency and H₂ balance.