Identifying parameters on genesis of coronal phases at olivine-plagioclase contact: A comparison from different geological terrane

<p>Corona texture between olivine-plagioclase is a common phenomenon in metabasic rocks and has been reported from different geological terrane of the world. However, the documented coronal phases from these terrane show significant variation in terms of number and composition. In this study, we have tried to explore the effect of different parameters like pressure, temperature, reactant bulk composition, availability of fluid, chemical potential gradient etc. on the genesis of such distinct coronal minerals. To address this question, we have compared three coronal assemblages developed between olivine and plagioclase from published literature (Gallien et al. 2012; Banerjee et al. 2019; Adak & Dutta, 2020). These three samples represent different terrane and have distinctly separate geological evolutionary history that led in formation of the texture. The samples are – i) #CGGC, a mafic intrusive from Chotanagpur Granite Gneissic Complex, India (Adak & Dutta, 2020); ii) #GTSI, an olivine bearing mafic dyke from Granulite Terrane of South India (Banerjee et al. 2019); and iii) #VFH, a troctolitic gabbro from Valle Fértil and La Huerta range, Argentina (Gallien et al. 2012). The layers in coronae of #CGGC and #GTSI are defined by three phases of separate composition; orthopyroxene and amphibole are common, but #CGGC contains spinel and #GTSI contains magnetite. Whereas, #VFH contains four phases, clinopyroxene in addition to orthopyroxene, spinel and amphibole. Besides evaluation of reactant composition and their effect, our methodology also incorporates Schrienemaker’s analysis through P-T and chemical potential diagrams. Considering the chemistry of both the reactant and product phases we have used a simplified CMASH system and calculated μCaO–μH<sub>2</sub>O, μMgO–μH<sub>2</sub>O, μCaO–μMgO diagram along with petrogenetic grid for each sample. The results show that along with change in P-T, factors like initial composition of the reactant minerals, behaviour of the system during reaction (open/closed) and P-T-t path of evolution also play significant role in determining the products in coronae formed from the reactant olivine and plagioclase.</p><p> </p>

Surface Microenvironment Optimization Induced Robust Oxygen Reduction for Neutral Zinc-Air Batteries

Neutral zinc-air batteries (ZABs) are promising candidates for the next-generation power devices with considerably elongated lifetime comparing to conventional alkaline ZABs. However, neutral cathodic oxygen reduction reaction is seriously limited by the mass transfer efficiency of hydroxyl due to insufficient interfacial chemical potential-gradient between catalytic layer and electrolyte. Herein, we highlight that electrochemical oxidation induced surface microenvironment optimization could realize optimal chemical potential-gradient around catalytic sites and bring outstanding neutral ORR activity. The electro-deposited sub-nano Pt decorated surface-microenvironment-optimized Co2N samples (denoted as Pt-SMO-Co2N NWs) possessed 92 mV and 365 mV lower overpotential than commercial Pt/C and pristine Co2N in 0.2 M PBS. As for neutral ZABs, Pt-SMO-Co2N NWs cathode delivers a power density of 67.9 mW*cm−2 and displays negligible decay after nearly 80 hours stability test at 20 mA*cm-2. In depth characterization proposes that remarkable performance improvement originates from optimized microenvironment which increases the surface chemical potential gradient and facilitates proton coupled electron transfer during ORR. We anticipated that such synergetic optimization of microenvironment and intrinsic activity of active sites is an effective strategy which may be extended the catalytic reactions beyond ORR.

Thermodynamic Interpretation on the Rheology of Aqueous Bentonite Suspensions

Since their exceptional rheological behavior, bentonite suspensions are widely used in engineering, industrial, agricultural, and drilling applications. So, the aim of the present study is to investigate the rheological properties of three types aqueous suspensions prepared with calcium bentonite (CaB), sodium bentonite (NaB) obtained from that by Na2CO3 activation, and NaB with the excess soda. The CaB taken from Giresun/Turkey region contains calcium smectite (CaxS) as clay mineral and opal CT (SiO2.nH2O) as impurity which is paracrystalline silica. Soda content by the activation and bentonite content in the suspension were changed in the interval of 2.5-15.0% and 5-20% by mass, respectively. CaxS completely converted to sodium smectite (Na2xS) by the activation with the soda content of 2.5% and then Na2xS+Na2CO3 mixtures formed. Rheological properties of these aqueous suspensions were measured using a Fann Viscometer. These properties reached their maxima by the most thixotropic Na2xS suspensions and greatly increased with the increasing of smectite content. Rheological plots drawn of the shear rate vs. shear stress in the interval of 170-1020 s-1 showed that the suspensions flow as a Bingham Plastic. Change in rheological properties depending on the smectite type and content as well as excess soda content was explained thermodynamically based on the chemical potential gradient between interlayer and dispenser waters.

A Mathematical Model of a Direct Propane Fuel Cell

A rigorous mathematical model for direct propane fuel cells (DPFCs) was developed. Compared to previous models, it provides better values for the current density and the propane concentration at the exit from the anode. This is the first DPFC model to correctly account for proton transport based on the combination of the chemical potential gradient and the electrical potential gradient. The force per unit charge from the chemical potential gradient (concentration gradient) that pushes protons from the anode to the cathode is greater than that from the electrical potential gradient that pushes them in the opposite direction. By including the chemical potential gradient, we learn that the proton concentration gradient is really much different than that predicted using the previous models that neglected the chemical potential gradient. Also inclusion of the chemical potential gradient made this model the first one having an overpotential gradient (calculated from the electrical potential gradient) with the correct slope. That is important because the overpotential is exponentially related to the reaction rate (current density). The model described here provides a relationship between the conditions inside the fuel cell (proton concentration, overpotential) and its performance as measured externally by current density and propane concentration.