Phase Relations in the Na2CO3–ZrO2–SiO2–H2O System at 0.1 and 0.05 GPa and 450°C

The phase relations in the Na₂CO₃–ZrO₂–SiO₂–H₂O system were studied at 0.1 and 0.05 GPa and 450°C using large-particle-size and nanocrystalline zirconias. Four silicates were obtained when use was made of readily soluble ZrO₂(nanocr): ZrSiO₄, Na₂ZrSi₆O₁₅ · 3H₂O, Na₂ZrSi₃O₉ · 2H₂O, and Na₄Zr₂Si₅O₁₆ · H₂O. In the system containing poorly soluble ZrO₂(cr), only Na₂ZrSi₆O₁₅ · 3H₂O was found to crystallize. It is shown that the structures of all the Na–Zr silicates contain invariant six-polyhedron structural precursors, each made up of two ZrO₆ octahedra and four SiO₄ tetrahedra, and belong to a homologous series of structures based on the silicate Na₂ZrSi₂O₇, which forms via direct packing of cyclic subpolyhedral precursors.     

Fundamental Understanding of Nonaqueous and Hybrid Na–CO2 Batteries: Challenges and Perspectives

Alkali metal–CO₂ batteries, which combine CO₂ recycling with energy conversion and storage, are a promising way to address the energy crisis and global warming. Unfortunately, the limited cycle life, poor reversibility, and low energy efficiency of these batteries have hindered their commercialization. Li–CO₂ battery systems have been intensively researched in these aspects over the past few years, however, the exploration of Na–CO₂ batteries is still in its infancy. To improve the development of Na–CO₂ batteries, one must have a full picture of the chemistry and electrochemistry controlling the operation of Na–CO₂ batteries and a full understanding of the correlation between cell configurations and functionality therein. Here, recent advances in CO₂ chemical and electrochemical mechanisms on nonaqueous Na–CO₂ batteries and hybrid Na–CO₂ batteries (including O₂-involved Na–O₂/CO₂ batteries) are reviewed in-depth and comprehensively. Following this, the primary issues and challenges in various battery components are identified, and the design strategies for the interfacial structure of Na anodes, electrolyte properties, and cathode materials are explored, along with the correlations between cell configurations, functional materials, and comprehensive performances are established. Finally, the prospects and directions for rationally constructing Na–CO₂ battery materials are foreseen.     

Thermodynamic analysis and optimization of a novel N2O–CO2 cascade system for refrigeration and heating

In this study, a natural refrigerant based cascaded system, with nitrous oxide as the low temperature fluid and carbon dioxide as the high temperature fluid, is analyzed for simultaneous cooling and heating applications. Effects of significant design and operating parameters on system performance are studied. Optimization of intermediate pressure for maximum COP for various design and operating parameters are presented as well. Results show that use of internal heat exchanger has marginal influence on system performance. Due to similar thermodynamic properties of nitrous oxide and carbon dioxide, the optimized intermediate temperature turns out to be independent of the performance of gas cooler and evaporator for a given operating condition. Due to the same reason, N₂O as low temperature fluid and CO₂ as high temperature fluid in a cascade arrangement exhibit similar behavioural trends in a system where the fluids are swapped.     

Regulating the Electronic Structure of Bismuth Nanosheets by Titanium Doping to Boost CO2 Electroreduction and Zn–CO2 Batteries

The electrochemical carbon dioxide reduction reaction (E-CO₂RR) to formate is a promising strategy for mitigating greenhouse gas emissions and addressing the global energy crisis. Developing low-cost and environmentally friendly electrocatalysts with high selectivity and industrial current densities for formate production is an ideal but challenging goal in the field of electrocatalysis. Herein, novel titanium-doped bismuth nanosheets (Ti Bi NSs) with enhanced E-CO₂RR performance are synthesized through one-step electrochemical reduction of bismuth titanate (Bi₄Ti₃O₁₂). We comprehensively evaluated Ti Bi NSs using in situ Raman spectra, finite element method, and density functional theory. The results indicate that the ultrathin nanosheet structure of Ti Bi NSs can accelerate mass transfer, while the electron-rich properties can accelerate the production of *CO₂⁻ and enhance the adsorption strength of *OCHO intermediate. The Ti Bi NSs deliver a high formate Faradaic efficiency (FE_formate) of 96.3% and a formate production rate of 4032 µmol h⁻¹ cm⁻² at −1.01 V versus RHE. An ultra-high current density of −338.3 mA cm⁻² is achieved at −1.25 versus RHE, and simultaneously FE_formate still reaches more than 90%. Furthermore, the rechargeable Zn–CO₂ battery using Ti Bi NSs as a cathode catalyst achieves a maximum power density of 1.05 mW cm⁻² and excellent charging/discharging stability of 27 h.     

Achieving Tunable Selectivity and Activity of CO2 Electroreduction to CO via Bimetallic Silver–Copper Electronic Engineering

Limited comprehension of the reaction mechanism has hindered the development of catalysts for CO₂ reduction reactions (CO₂RR). Here, the bimetallic AgCu nanocatalyst platform is employed to understand the effect of the electronic structure of catalysts on the selectivity and activity for CO₂ electroreduction to CO. The atomic arrangement and electronic state structure vary with the atomic ratio of Ag and Cu, enabling tunable d-band centers to optimize the binding strength of key intermediates. Density functional theory calculations confirm that the variation of Cu content greatly affects the free energy of *COOH, *CO (intermediate of CO), and *H (intermediates of H₂), which leads to the change of the rate-determining step. Specifically, Ag₉₆Cu₄ reduces the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction(HER), thus achieving the best CO selectivity. While Ag₇₀Cu₃₀ shows relatively low formation energy of both *COOH and *H, the compromised thermodynamic barrier and product selectivity allows Ag₇₀Cu₃₀ the best CO partial current density. This study realizes the regulation of the selectivity and activity of electrocatalytic CO₂ to CO, which provides a promising way to improve the intrinsic performance of CO₂RR on bimetallic AgCu.     

A Carbon-Free and Free-Standing Cathode From Mixed-Phase TiO2 for Photo-Assisted Li–CO2 Battery

Li–CO₂ battery provides a new strategy to simultaneously solve the problems of energy storage and greenhouse effect. However, the severe polarization of CO₂ reduction and CO₂ evolution reaction impede the practical application. Herein, anodic TiO₂ nanotube arrays are first introduced as carbon-free and free-standing cathode for photo-assisted Li–CO₂ battery, and the photo-assisted charge and discharge mechanism is first clarified from the perspective of photocatalysis. Mixed-phase TiO₂ exhibits a long cycling life of 580 h (52 cycles) at 0.025 mA cm⁻² and delivers a high discharge specific capacity of 3001 µAh cm⁻² under UV illumination. The charge voltage dramatically reduces from 4.53 to 3.03 V under UV illumination. The improvement of photo-assisted Li–CO₂ battery performance relies on the synergistic effect of the hierarchical porous structure, strong UV absorption, efficient separation, and transfer of photo-generated electrons and holes at hetero-phase junction, and the facilitation of photo-generated electrons and holes on CO₂ reduction and CO₂ evolution reaction. This work can provide useful guidance for designing efficient photocathode for photo-assisted Li–CO₂ battery and other metal–air batteries.     

A novel CO2 refrigeration system achieved by CO2 solid–gas two-phase fluid and its basic study on system performance

In this report, a new CO₂ refrigeration system is introduced, which can achieve a refrigeration capability below the CO₂ triple point of ?56.6 °C. The proposed CO₂ refrigeration system consists of two thermodynamic cycles arranged in cascade, where one is a CO₂ trans-critical cycle and another is a trans-triple-point cycle. An experimental set-up is constructed and tested in order to obtain a basic knowledge about this CO₂ system. Based on the measured data, it is concluded that the built CO₂ refrigeration system can operate continuously and stably, although dry ice particles exist in the closed CO₂ loops. An average COP (a ratio of cooling energy to the compressor power consumption) is measured at 2.45 in the present experiment range for the low-pressure system of the experimental set-up. In addition, the influence of the condensation temperature on the refrigeration cycle is investigated and more studies are needed for the future optimization work.     

Preparation of MgH2–Ni, MgH2–Ni–Si and MgH2–Ni–Ni2Si composites by mechanochemical method and their hydrogen absorption and desorption properties

To improve kinetics for hydrogen absorption of Mg and hydrogen desorption of MgH₂, ternary composites were prepared from MgH₂, Ni and Si or Ni₂Si by a mechanochemical technique. The X-ray diffraction spectra of the resultant ternary composites after the initial hydrogen desorption treatment at 400 °C in vacuum suggested that in all composites the nanocrystalline Mg₂Ni would be formed in the intergrain region between Mg and Ni components, while in the MgH₂–Ni–Si composite the nanocrystalline Mg₂Si would also be formed in the intergrain region between Mg and Si components. However, Ni₂Si did not form any alloys with Mg. The hydrogen absorption rate at 250 °C for the MgH₂–Ni–Ni₂Si composite was comparable to that for the MgH₂–Ni and MgH₂–Ni–Si composites, while the hydrogen desorption rate at 250 °C decreased in the order of MgH₂–Ni > MgH₂–Ni–Ni₂Si > MgH₂–Ni–Si. In contrast, the hydrogen desorption rate at 220 °C for the MgH₂–Ni–Ni₂Si composite was faster than that for the MgH₂–Ni composite, suggesting that Ni₂Si was a key material in the improvement of hydrogen desorbability at lower temperatures. Moreover, the most plausible reaction model and the rate-determining process for hydrogen absorption and desorption at 250 °C were determined.     

Corrosion and stress corrosion cracking behavior of 316L austenitic stainless steel in high H2S–CO2–Cl− environment

In oil and gas production environments, H₂S and Cl^? can coordinate to cause pitting or stress corrosion cracking (SCC) of stainless steels. There has been limited work conducted on corrosion and SCC of autenitic stainless steels in high H₂S–CO₂–Cl^? environments. In this paper, by four-point bending test method and scanning electron microscopy analysis, SCC of 316L steel was investigated under high H₂S–CO₂ pressures with 150,000 ppm Cl^? at 60 °C. The effect of high H₂S–CO₂ pressure was discussed. The results indicated that the higher H₂S–CO₂ pressure can accelerate anodic dissolution process, deteriorate passive films, and aggravate SCC sensitivity. Using cyclic potentiodynamic polarization measurements, the corrosion behavior of 316L steel was studied in high H₂S–CO₂–Cl^? environments. The effect of pH on pitting corrosion was discussed. Lower pH can promote both cathodic and anodic actions on 316L steel and facilitate passive film breakdown.     

Porous Host–Guest MOF-Semiconductor Hybrid with Multisites Heterojunctions and Modulable Electronic Band for Selective Photocatalytic CO2 Conversion and H2 Evolution

Optimizing catalysts for competitive photocatalytic reactions demand individually tailored band structure as well as intertwined interactions of light absorption, reaction activity, mass, and charge transport.  Here, a nanoparticulate host–guest structure is rationally designed that can exclusively fulfil and ideally control the aforestated uncompromising requisites for catalytic reactions. The all-inclusive model catalyst consists of porous Co₃O₄ host and Zn_xCd_1-xS guest with controllable physicochemical properties enabled by self-assembled hybrid structure and continuously amenable band gap. The effective porous topology nanoassembly, both at the exterior and the interior pores of a porous metal–organic framework (MOF), maximizes spatially immobilized semiconductor nanoparticles toward high utilization of particulate heterojunctions for vital charge and reactant transfer. In conjunction, the zinc constituent band engineering is found to regulate the light/molecules absorption, band structure, and specific reaction intermediates energy to attain high photocatalytic CO₂ reduction selectivity. The optimal catalyst exhibits a H₂-generation rate up to 6720 µmol g⁻¹ h⁻¹ and a CO production rate of 19.3 µmol g⁻¹ h⁻¹. These findings provide insight into the design of discrete host–guest MOF-semiconductor hybrid system with readily modulated band structures and well-constructed heterojunctions for selective solar-to-chemical conversion.     

Photoluminescence and scintillation properties of Eu2O3–BaO–Nb2O5–TeO2 glass and glass ceramics

Journal of Materials Science: Materials in Electronics - 1Eu2O3–3BaO–20Nb2O5–76TeO2 glass and the corresponding glass-ceramics were synthesized with the aim to investigate the...     

A comparative study of microstructure and mechanical behavior of CO2 and diode laser deposited Cu–38Ni alloy

Cu–38Ni alloy was deposited on C71500 (Cu–30Ni) substrates by a laser-aided direct metal deposition technique using CO₂ and diode lasers. Structure–property relationships of deposited specimens were investigated by optical microscopy, electron microscopy, X-ray diffraction techniques, and microhardness and tensile measurements. Laser-deposited specimens’ microstructures were primarily dendritic, forming columnar grains growing epitaxially from the substrate and subsequent layers along the preferred crystallographic growth. The grain growth pattern and grain size distribution was significantly different in both specimens. The lattice parameter of the solid solution phase was relatively larger in diode laser-formed specimen; CO₂ laser-formed specimens showed relatively higher but non-uniform hardness distribution whereas a very uniform hardness distribution was observed in diode laser formed specimens. Diode laser formed specimens showed higher tensile properties compared to CO₂ laser formed specimens which were comparable to C71500 substrates. Microstructure and mechanical behavior were explained based on laser processing parameters.     

Phase Relations in the Systems LiOH–GeO2–H2O and LiOH–SiO2–H2O at 500°C and 0.1 GPa

Crystallization in the LiOH–GeO₂–H₂O and LiOH–SiO₂–H₂O hydrothermal systems was studied at 500°C and 0.1 GPa. The systems were shown to contain both the isostructural compounds Li₂SiO₃ and Li₂GeO₃ and phases differing in crystal chemistry: Li₂Si₂O₅, Li₂Ge₃O₆(OH)₂, and Li₃HGe₇O₁₆ · 4H₂O (containing Ge in different oxygen coordinations). The crystallization fields revealed in the germanate system are (in order of increasing LiOH concentration) GeO₂ GeO₂+ Li₂Ge₃O₆(OH)₂ Li₂Ge₃O₆(OH)₂ + Li₂GeO₃ Li₃HGe₇O₁₆ · 4H₂O + Li₂GeO₃; those in the silicate system are -SiO₂ -SiO₂+ Li₂Si₂O₅ Li₂Si₂O₆ + Li₂SiO₃ Li₂SiO₃. Increasing the LiOH concentration increases the number of Li atoms per tetrahedrally coordinated Si or Ge atom in the crystallizing compounds. The high stability of Li₂Ge₃O₆(OH)₂ is interpreted in terms of the matrix assembly of the structure from cyclic invariant subpolyhedral structural units.     

CO2-laser-induced vapor-phase synthesis of Hn-diamond nanoparticles at 0.6–2 bar

Recently, a novel reaction route to synthesize diamond nano- and microparticles in the size range of 6 – 18,000 nm was discovered. Homogeneously nucleated diamond nanoparticles have unique properties, such as very high radial growth rates (3 mm/s), spherical and faceted morphology and very high purity. A broad range of potential applications for spherical diamond nanoparticles is suggested, e.g. in the fields of polishing of ultra-high-purity materials, ceramics, tribology, micromechanics, monoisotopic C-12 and C-13 diamond technology.     

Sintered porous cermets based on TiB2 and TiB2–TiC–Mo2C

TiB₂ powder, with different binders (Ni and Ni/Mn), after milling were cold compacted (300 MPa) and sintered in H₂ at 1300 and 1350°C for 1 h. To improve the sintering behaviour, TiC/Mo₂C alloy carbide was added and the milled charge along with the same binders (Ni and Ni/Mn) was cold compacted and sintered under similar conditions. Sintered density, porosity, transverse rupture strength (TRS), grain size and lattice parameter of binder and hard phases were measured. Better densification was observed with Ni/Mn binder as compared to Ni binder for either hard phase based systems. Maximum value of TRS was noted for TiB₂–TiC–Mo₂C–40 wt.% Ni/Mn cermet. Melt exudation was observed for either hard phase based systems with Ni binder.     

Single-Site Metal–Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2H4

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO₂ reduction reaction (CO₂RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal–organic framework (MOF), named as Cu–MOF–CF, to realize improved electrochemical CO₂RR performance, is reported. The Cu–MOF–CF shows suppression of CH₄, great increase in C₂H₄ selectivity (48.6%), and partial current density of C₂H₄ at −1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu–MOF–CF for CO₂RR results from the improved microenvironment of the Cu active sites that inhibits CH₄ production, more CO intermediate produced by single-site Cu–MOF in situ for CF, and the enlarged active surface area by porous Cu–MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO₂RR.     

Obtaining of Ni–P–TiO2 Composite Coatings with TiO2 Sol and Surfactants and Their Properties

The influence of surfactants and TiO₂ sol on mechanical, catalytic, and corrosive properties of electroless Ni–P coatings was investigated. Additives of the surfactants caused the decrease of internal stresses in the Ni–P coatings and smoothing of their surfaces. Incorporation of the TiO₂ particles facilitated the rise of microhardness of the Ni–P coatings from 545 ± 11 Hv up to 614 ± 17 Hv. Additives of the surfactants accelerated hydrogen evolution reaction on the composite Ni–P–TiO₂ coatings in acid and alkaline media, and increased photocatalytic activity in methylene blue decomposition. Incorporation of the TiO₂ particles and application of the surfactants resulted in an improvement in the corrosion resistance of original Ni–P coatings in 0.5 M H₂SO₄.     

Properties and microstructure of WC–TiC–Co and WC–TiC–MO2C–Co(Ni) cemented carbides

Abstract

The present study is an attempt to observe the changes in microstructure and properties of modified WC–10Co cemented carbides from the viewpoint of the distinctive role played by modified binder phase. Introduction of TiC into WC–10Co cemented carbide results in microstructural non-uniformity, i.e. a wide range of grain size distribution, which in turn gives rise to a drastic drop in values of transverse rupture strength and toughness. The modification of binder and carbide phases by incorporating, respectively, nickel and M02C improves the microstructural uniformity, which ensures better mechanical properties. The present findings have been interpreted in terms of various quantitative microstructural parameters, with particular attention being given to the wettability factor.

MST/1363     

Structural verification and optical characterization of SiO2–Au–Cu2O nanoparticles

In this paper, SiO₂–Au–Cu₂O core/shell/shell nanoparticles were synthesized by reducing gold chloride on 3-amino-propyl-triethoxysilane molecules attached silica nanoparticle cores for several stages. Cu₂O nanoparticles were synthesized readily with the size of 4–5 nm using a simple route of sol–gel method Then, they were clung to the surface of Au seeds. The morphology of the resultant particles was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Transmission electron microscopy images demonstrate growth of monodispersed gold seeds and Cu₂O nanoparticles in narrow size up to 10 nm and 5 nm, respectively. The presence of gold and Cu₂O coating was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. Absorption spectroscopy shows considerably 40 nm blue shift in absorption edge for SiO₂–Au–Cu₂O nanostructure rather than SiO₂–Au core/shell nanoparticles.