71 research outputs found
Superfunctional high-entropy alloys and ceramics by severe plastic deformation
High-entropy alloys and ceramics containing at least five principal elements
have received high attention in recent years for various mechanical and
functional applications. The application of severe plastic deformation (SPD),
particularly the high-pressure torsion (HPT) method combined with the CALPHAD
and first-principles calculations, resulted in the development of numerous
superfunctional high-entropy materials with superior properties compared to the
normal functions of engineering materials. This article reviews the recent
advances in the application of SPD to achieving superfunctional high-entropy
materials. These superfunctional properties include (i) ultrahigh hardness
levels in high-entropy alloys which are comparable to ceramics, (ii) high yield
strength and good hydrogen embrittlement resistance in high-entropy alloys;
(iii) high strength, low elastic modulus, and high biocompatibility in
high-entropy alloys, (iv) fast and reversible hydrogen storage in high-entropy
alloys and corresponding hydrides, (v) photovoltaic performance and
photocurrent generation on high-entropy semiconductors, (vi) photocatalytic
oxygen and hydrogen production on high-entropy oxides and oxynitrides from
water splitting, and (vii) CO2 photoreduction on high-entropy ceramics. These
findings introduce SPD as not only a processing tool to improve the properties
of existing high-entropy materials but also as a synthesis tool to synthesize
novel high-entropy materials with superior properties compared with
conventional engineering materials
Active photocatalysts for CO2 conversion by severe plastic deformation (SPD)
Excessive CO2 emission from fossil fuel usage has resulted in global warming
and environmental crises. To solve this problem, photocatalytic conversion of
CO2 to CO or useful components is a new strategy that has received significant
attention. The main challenge in this regard is exploring photocatalysts with
high activity for CO2 photoreduction. Severe plastic deformation (SPD) through
the high-pressure torsion (HPT) process has been effectively used in recent
years to develop novel active catalysts for CO2 conversion. These active
photocatalysts have been designed based on four main strategies (i) oxygen
vacancy and strain engineering, (ii) stabilization of high-pressure phases,
(iii) synthesis of defective high-entropy oxides, and (iv) synthesis of
low-bandgap high-entropy oxynitrides. These strategies can enhance the
photocatalytic efficiency compared to conventional and benchmark photocatalysts
by improving CO2 adsorption, increasing light absorbance, aligning the band
structure, narrowing the bandgap, accelerating the charge carrier migration,
suppressing the recombination rate of electrons and holes, and providing active
sites for photocatalytic reactions. This article reviews recent progress in the
application of SPD to develop functional ceramics for photocatalytic CO2
conversion
Black brookite rich in oxygen vacancies as an active photocatalyst for CO2 conversion: experiments and first-principles calculations
Photocatalytic CO2 conversion is a clean technology to deal with CO2
emissions, and titanium oxide (TiO2) polymorphs are the most investigated
photocatalysts for such an application. In this study, black TiO2 brookite is
produced by a high-pressure torsion (HPT) method and employed as an active
photocatalyst for CO2 conversion. Black brookite with a large concentration of
lattice defects (vacancies, dislocations and grain boundaries) showed enhanced
light absorbance, narrowed optical bandgap and diminished recombination rate of
electrons and holes. The photocatalytic activity of the black oxide for CO2
conversion was higher compared to commercial brookite and benchmark P25
catalyst powders. First-principles calculations suggested that the presence of
oxygen vacancies in black brookite is effective not only for reducing optical
bandgap but also for providing active sites for the adsorption of CO2 on the
surface of TiO2
Impact of TiO2-II phase stabilized in anatase matrix by high-pressure torsion on electrocatalytic hydrogen production
Electrocatalysis using renewable energy sources provides a clean technology to produce hydrogen from water. Titanium oxide is considered as a potential electrocatalyst not only for hydrogen production but also for CO2 conversion. In this study, to enhance the cathodic electrocatalytic activity of TiO2, the phase composition on TiO2 surface is modified by inclusion of high-pressure TiO2-II phase using high-pressure torsion (HPT) straining. Detailed spectroscopic studies revealed that the energy band gap is reduced and the valence band energy increased with increasing the TiO2-II fraction. The highest electrocatalytic activity for hydrogen production was achieved on an anatase-rich nanocomposite containing TiO2-II nanograins
Nanomaterials by severe plastic deformation: review of historical developments and recent advances
International audienceSevere plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity
Synthesis and Applications of Hollow Particles
Hollow particle is a promising material with the special properties of low densities, thermal insulation and distinct optical activity. Due to their potential promising applications in the fields of drug delivery, catalysis and optics, a great effort has been devoted to develop new preparation methods which are collected and reviewed in this paper. All these methods are classified into three groups, namely sacrificed template method, in-situ template method and device-based method based on the characteristics of the methods. The advantage and disadvantage of each method are compared and the trends for preparation are pointed out. In light of the wide applications of hollow particles, the later part of this paper focuses on their potential applications in industry. Their applications are not limited in the fields of papermaking, rubber processing and plastic improvement, but also expanded to electronic, catalytic and biological areas
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