Material In Ambient Air Research Articles

Mössbauer study of iron oxide nanoparticles

AbstractMagnetic nanoparticles have recently attracted attention for biochemical and medical applications like drug delivery and hyperthermia for a variety of reasons with most important being their stability, chemical compatibility, and suitable magnetic properties like moderate specific mass magnetization. Cobalt ferrites are a well‐studied family of materials and the partial substitution of Fe3+ cations by rare earth (RE) ones may be used to tune the magnetic properties. In the present work pure and substituted Co ferrite nanoparticles with nominal stoichiometry CoFe2−xRxO4 (R = Yb, Gd; x = 0.05, 0.1, 0.3) synthesized by the co‐precipitation method are studied with 57Fe Mössbauer spectroscopy to determine the incorporation of RE ions in the spinel lattice. The fitting procedure was based on the standard spinel model using two sextets for the octahedral and the tetrahedral coordinated positions of Fe atoms. All isomer shift values were found within the typical range of high spin ferric ions while quadrupole splitting values strongly suggest that there is a substitution preference; RE ions replace iron ones in octahedral sites. The inversion parameter was found to decrease with RE content (lowest value about 0.534 for CoFe1.90Yb0.10O4) and thermal treatment always results in changing the material toward normal spinel, while pure CoFe2O4 was inverse. Thermal treatment of substituted materials in ambient air at temperature range 1500–1700 K for 12 h increase crystallite size and changes the degree of inversion.

Origin of environmentally structural susceptibility of nickel-based layered oxide cathodes

Environmental susceptibility is an intrinsic property associated with the handling and storage process of nickel-based layered oxide materials in ambient air, which combines with electrochemical factors to determine the cathode performance. Nonetheless, the mechanism underlying such environmental effect has not been well elucidated yet. In this work, using atomic-resolution imaging and spectroscopy, we discover that chemical desodification of Ni-based sodium oxides upon air-exposure triggers extensive initiation and propagation of intragranular cracks along the a-b plane in the lattice, which is distinct from the dense interphase layer for chemically delithiated Ni-based lithium oxides. We rationalize that the diverse environmental susceptibility of Ni-based layered oxides is dictated by Li/Na chemical reaction-diffusion-induced structural evolution or failure, based on the ab initio calculation and numerical kinetic modeling. The established correlation between reaction-diffusion-induced stress fields and structural changes provides new visions for developing high energy and high stability Ni-based layered cathode materials.

Synthesis and characterization by co-precipitation under an inert atmosphere of lamellar Fe/Al double hydroxides and comparison with samples co-precipitated under an ambient atmosphere

Aluminum-iron layered double hydroxides were prepared by low saturation co-precipitation under ambient atmosphere and under nitrogen using various molar ratios. These materials were characterized using different analysis techniques such as X-ray diffraction, differential thermal analysis, thermogravimetric analysis, Fourier transform infrared and Nitrogen gas adsorption-desorption at the temperature −196 ​°C (BET, BJH, NLDFT).The synthesis of these materials in ambient air always gives rise to the appearance of impurities for all the molar ratios used. However, under nitrogen, the impurities start appearing as of the molar ratio equal to 3. It is worth indicating that the atmosphere used and the amount of iron added both have an impact on the formation of impurities. Four methods were used to study the textural parameters of the materials prepared under ambient conditions. The results obtained showed that the synthesized compounds are microporous, and the pore size does not exceed 2 ​nm. It was therefore concluded that the materials prepared under nitrogen atmosphere are of mesoporous-type.

Superior All‐Solid‐State Batteries Enabled by a Gas‐Phase‐Synthesized Sulfide Electrolyte with Ultrahigh Moisture Stability and Ionic Conductivity

AbstractSulfide solid electrolytes (SEs) are recognized as one of the most promising candidates for all‐solid‐state batteries (ASSBs), due to their superior ionic conductivity and remarkable ductility. However, poor air stability, complex synthesis process, low yield, and high production cost obstruct the large‐scale application of sulfide SEs. Herein, a one‐step gas‐phase synthesis method for sulfide SEs with oxide raw materials in ambient air, completely getting rid of the glovebox and thus making large‐scale production possible, is reported. By adjusting substituted elements and concentrations, the ionic conductivity of Li4‐xSn1‐xMxS4 can reach 2.45 mS cm−1, which represents the highest value among all reported moist‐air‐stable and recoverable lithium‐ion sulfide SEs reported. Furthermore, ASSBs with air/water‐exposed and moderate‐temperature‐treated Li3.875Sn0.875As0.125S4 even maintains superior performances with the highest reversible capacity (188.4 mAh g−1) and the longest cycle life (210 cycles), which also breaks the record. Therefore, it may become one of the most critical breakthroughs during the development of sulfide ASSBs toward its practical application and commercialization.

High-performance fully-ambient air processed perovskite solar cells using solvent additive

Incredible progress in the efficiency of hybrid perovskite solar cells (PSCs) has nominated perovskites as a promising light-harvesting for new-generation photovoltaic devices. Additive engineering in PSCs is a valid and straightforward method to increase the surface quality of perovskite films. Herein, we prepared mixed cation of cesium (Cs)/formamidinium (FA)/methylammonium (MA) PSCs via an air-processed sequential deposition method. Acetonitrile (ACN) was used as an effective additive to improve the surface properties of perovskite layer. Our measurements demonstrated that with the incorporation of ACN in the FAI/MABr/MACl precursor surface defects on the perovskite film well passivated, and consequently, crystal grain size increased. A PCE of 15.64% was achieved for ACN-based PSCs higher than of 13.06% one for without additive devices. Additionally, ACN-containing devices showed a lower hysteresis effect as compared to the control devices. Most importantly, ACN additive based PSCs showed more stable behavior in ambient air, thermal, and humidity stability tests. This work introduces a simple approach for the fabrication of high-performance perovskite materials in ambient air.

Low-Thermal-Budget Doping of 2D Materials in Ambient Air Exemplified by Synthesis of Boron-Doped Reduced Graphene Oxide.

Graphene oxide (GO) doping and reduction allow for physicochemical property modification to suit practical application needs. Herein, the challenge of simultaneous low‐thermal‐budget heteroatom doping of GO and its reduction in ambient air is addressed through the synthesis of B‐doped reduced GO (B@rGO) by flash irradiation of boric acid loaded onto a GO support with intense pulsed light (IPL). The effects of light power and number of shots on the in‐depth sequential doping and reduction mechanisms are investigated by ex situ X‐ray photoelectron spectroscopy and direct millisecond‐scale temperature measurements (temperature >1600 °C, < 10‐millisecond duration, ramping rate of 5.3 × 105 °C s−1). Single‐flash IPL allows the large‐scale synthesis of substantially doped B@rGO (≈3.60 at% B) to be realized with a thermal budget 106‐fold lower than that of conventional thermal methods, and the prepared material with abundant B active sites is employed for highly sensitive and selective room‐temperature NO2 sensing. Thus, this work showcases the great potential of optical annealing for millisecond‐scale ultrafast reduction and heteroatom doping of GO in ambient air, which allows the tuning of multiple physicochemical GO properties.

Ambient Air Stable Ni-Rich Layered Oxides Enabled by Hydrophobic Self-Assembled Monolayer.

Ni-rich layered oxides, such as LiNi0.8Co0.1Mn0.1O2 (NCM811), are considered as promising cathode materials for lithium-ion batteries due to their high energy density. However, Ni-rich layered oxides are prone to react with water and carbon dioxide in ambient air forming residual lithium compounds, resulting in deterioration of electrochemical performance and bringing a challenge to the cathode electrode preparation. In this work, we have, for the first time, demonstrated that the chemical stability of the NCM811 material in ambient air can be significantly enhanced by passivating the surface with a hydrophobic self-assembled monolayer (SAM) of octadecyl phosphate (OPA). As a result, the degradation reaction between the NCM811 material and ambient air and thus the electrochemical performance deterioration were significantly suppressed during ambient air exposure. Specifically, the 5C-rate capacity retention deterioration of the NCM811 sample during 14-day ambient air exposure has been decreased from 12 to 2% by OPA passivation. Furthermore, the 200-cycle capacity retention deterioration of the NCM811 sample after 7-day ambient air exposure has been improved from 23 to 0.7% by OPA passivation. These results are very important for the practical application of Ni-rich oxide since no need for controlling of humidity is required on the cathode manufacture; thus, the cost can be reduced. The concept of molecular self-assembly on the NCM811 material also open vast possibilities to design reagents for surface passivation of Ni-rich layered oxides.

Effect of Humidity on Friction and Wear—A Critical Review

The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity on macro- and nano-scale friction and wear of various types of materials. The materials included in this review are graphite and graphene, diamond-like carbon (DLC) films, ultrananocrystalline diamond (UNCD), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), boric acid, silicon, silicon oxide, silicates, advanced ceramics, and metals. Details of underlying mechanisms governing friction and wear behaviors vary depending on materials and humidity; nonetheless, a comparison of various material cases revealed an overarching trend. Tribochemical reactions between the tribo-materials and the adsorbed water molecules play significant roles; such reactions can occur at defect sites in the case of two-dimensionally layered materials and carbon-based materials, or even on low energy surfaces in the case of metals and oxide materials. It is extremely important to consider the effects of adsorbed water layer thickness and structure for a full understanding of tribological properties of materials in ambient air.

Highly Stable All‐Inorganic Perovskite Solar Cells Processed at Low Temperature

All‐inorganic perovskites such as cesium lead bromide (CsPbBr3) can show much better stability than organic–inorganic hybrid perovskite materials in ambient air. However, fabricating a high‐quality CsPbBr3 perovskite film normally requires a high annealing temperature, leading to the difficulty of preparing CsPbBr3 solar cells with low‐temperature solution process. In this work, we demonstrated a pyridine‐vapor treatment in two‐step fabrication of CsPbBr3 perovskite films that can reduce the annealing temperature to about 160 °C. The mechanism is attributed to the reaction of pyridine with lead bromide, which forms an intermediate phase and leads to a low activation energy in the formation of CsPbBr3 perovskite films during thermal annealing. The devices without encapsulation show excellent stability in ambient air with the humidity up to 70%. This work provides a novel approach for preparing inorganic perovskite solar cells at low temperature.

The processing and heterostructuring of silk withlight.

Spider silk is a tough, elastic and lightweight biomaterial, although there is a lack of tools available for non-invasive processing of silk structures. Here we show that nonlinear multiphoton interactions of silk with few-cycle femtosecond pulses allow the processing and heterostructuring of the material in ambient air. Two qualitatively different responses, bulging by multiphoton absorption and plasma-assisted ablation, are observed for low- and high-peak intensities, respectively. Plasma ablation allows us to make localized nanocuts, microrods, nanotips and periodic patterns with minimal damage while preserving molecular structure. The bulging regime facilitates confined bending and microwelding of silk with materials such as metal, glass and Kevlar with strengths comparable to pristine silk. Moreover, analysis of Raman bands of microwelded joints reveals that the polypeptide backbone remains intact while perturbing its weak hydrogen bonds. Using this approach, we fabricate silk-based functional topological microstructures, such as Mobiüs strips, chiral helices and silk-based sensors.

Near-threshold fatigue propagation of physically through-thickness short and long cracks in a low alloy steel

In this paper, the near-threshold fatigue behavior of physically through-thickness short cracks and of long cracks in a low alloy steel is investigated by experiments in ambient air. Physically through-thickness short fatigue cracks are created by gradually removing the plastic wake of long cracks in compact tension specimens. The crack closure is systematically measured using the compliance variation technique with numerical data acquisition and filtering for accurate detection of the stress intensity factor (SIF) at the crack opening. Based on the experimental results, the nominal threshold SIF range is shown to be dependent on the crack length and the characteristic of the crack wake which is strongly dependent on the loading history. The effective threshold SIF range and the relation between the crack propagation rate and the effective SIF range after the crack closure correction are shown to be independent on crack length and loading history. The shielding effect of the crack closure is shown to be related to the wake length and load history. The effective threshold SIF range and the relationship between the crack growth rate and the effective SIF range appear to be unique for this material in ambient air. These properties can be considered as specific fatigue properties of the couple material/ambient air environment.

Thermo-mechanical stability of a cellular assembly of carbon nanotubes in air

Carbon nanotubes (CNT) in bulk form offer outstanding structural and functional properties, and are shown to remain viscoelastic over a wide temperature range (77–1273K) under inert conditions. We examine the quasi-static and dynamic compressive mechanical response of these cellular CNT materials in ambient air up to a temperature of 773K. In uniaxial quasi-static compression, several displacement bursts are noted at large strains. These are results of the slippage and zipping of the CNT, and lead to significant mechanical energy absorption. Results of the dynamic mechanical analysis experiments show no degradation in storage modulus and loss coefficient for up to 20h at 673K. Hence, these stable cellular CNT structures can be utilized up to a maximum temperature of 673K in air, which is much higher than the best polymers.

Glass-ceramic LiFePO 4 for lithium-ion rechargeable battery

Glass-ceramic LiFePO 4 was synthesized through the crystallization of glass powder prepared by melting low-cost raw materials in ambient air. To obtain the homogeneous precursor glass, the addition of a small amount of Nb 2O 5 was effective. Ferric ions in the precursor glass were reduced and precipitated as LiFePO 4 through the heat treatment of a mixture of the glass powder and a carbon source. The obtained glass-ceramic particles contained a LiFePO 4 crystalline phase and a carbon-containing surface amorphous layer with a thickness of about 20 nm. A lithium-ion rechargeable battery fabricated with the glass-ceramic powder showed better high-rate performance than that of a battery made using commercial LiFePO 4 ceramic powder. The better performance of the battery with the glass-ceramic is attributed to the existence of the surface amorphous layer. This synthesis process, consisting of glass melting in air and the subsequent crystallization of glass powder, has the potential to be used for the large-scale continuous production of high-performance LiFePO 4.

Gas–particle partitioning of persistent organic pollutants in the Western Balkan countries affected by war conflicts

Bombing and destruction of the industrial and military targets accompanied by complete or incomplete combustion during the war conflict and NATO operation in former Yugoslavia caused the emission of persistent organic pollutants into the atmosphere, water, and soil. A total of 129 ambient air samples from 24 background, urban, and industrial sites, including hot spots, were collected to assess a gas-particle partitioning behavior of various persistent organic pollutants. High volume sampling technique was applied with quartz filters that collect the atmospheric particles and polyurethane foam filters (PUF) that retain the gaseous compounds. Three to ten samples were taken at each site. GFs and PUFs were analyzed separately for their content of polychlorinated biphenyls, organochlorine pesticides, and polyaromatic hydrocarbons. Gas phase and particle phase concentrations of selected persistent organic pollutants (POPs) in all samples were converted into the particle-bound fractions Phi. These fractions were found to be highly variable, but generally highest in Bosnia and Herzegovina due to the elevated levels of total suspended material in ambient air. Experimental values of particle-associated fraction were compared to the Junge-Pankow model. Interestingly, a model for urban/industrial environments provided a better prediction of partitioning behavior than a model for background and rural background sites. That is probably because the total amount of atmospheric particles is higher in the Balkan region than found in the previously published studies. Even though it has been stated in previous studies that less than 5% of polychlorinated biphenyls (PCBs) are bound to the particles, up to 67% of PCBs were particle associated at several sampling sites in this study. PCB-contaminated soils are probably still one of the strong sources of particles to the atmosphere. Information on the particle-bound fractions of POPs is important not only for prediction of their fate but also for an estimation of risks they can pose to the environment as well as to humans. When assessing such hazards, it has to be considered that modeled values of the particle-bound fractions can be seriously underestimated at sites with elevated levels of suspended atmospheric matter or at sites with heavily contaminated soils.

UV laser photolytic solution deposition of a-Fe/polyoxocarbosilane/carbon nanocomposite and evolution to α-Fe 2O 3/polyoxocarbosilane/carbon nanocomposite

KrF laser-induced photolysis of Fe(II) acetylacetonate in 2-propanol leads to (i) formation of nanosized iron and (ii) etching of the silica reactor by carbonaceous photolytic products, yielding amorphous polyoxocarbosilane. These reactions allow chemical solution deposition of Fe/polyoxocarbosilane/carbon nanocomposite possessing rare amorphous Fe phase. The material in ambient air undergoes slow oxidative passivation of the Fe constituent forming a discontinuous a-Fe 2O 3 shell and when heated it transforms to nanosized crystalline α-Fe 2O 3/polyoxocarbosilane/carbon nanocomposite. Its magnetic moment is a superposition of ferromagnetic contribution from large particles and superantiferromagnetic contribution from the thin passivating shell.

Impact of the Circulating Fluidized Bed Riser on the Performance of a Loopseal Nonmechanical Valve

Most advanced coal-fuel power systems require the transfer and control of solids between two or more vessels. In many instances, the key to a successful process operation is how well the solids transfer and control system has been designed. This is particularly true in a transport gasifier and circulating fluidized bed (CFB) combustors, which are dependent upon the rapid and reliable circulation of solids to maintain a constant solids concentration in the CFB. Proper design and operation of solids returning systems are essential to the performance and operation of CFB combustion systems. An experimental investigation was conducted at the National Energy Technology Laboratory (NETL) of the U.S. Department of Energy (DOE) to study the flow and control of a light material (cork), which has a particle density of 189 kg/m3 and a mean diameter of 812 μm, through a nonmechanical valve, or loopseal, in a 0.3 m diameter CFB cold model. Fluidizing this material in ambient air approximates the same gas:solids density ratio as coal and coal char in a pressurized gasifier. The loopseal is composed of the lower section of the standpipe, an upward-flowing fluidized-bed section, and a downwardly angled overflow tube which is connected to the desired return point at the bottom of the riser. In the nonmechanical valve, both the standpipe and the fluidized-bed up-flow section of the loopseal were aerated and fluidized with air, respectively. The objective of this study was to investigate the effects of standpipe aeration, loopseal aeration, solids inventory, and superficial gas velocity through the riser on the flow rate of circulating solids. A correlation that predicts the solids flow rate as a function of these variables was developed. Comparison of the correlation with the experimental data is discussed. Pressure drop across the fluidized-bed up-flow section of the loopseal was found to increase slightly with the solid flow rates.

Flow Regime Study of a Light Material in an Industrial Scale Cold Flow Circulating Fluidized Bed

A series of experiments was conducted in the 0.3meter diameter circulating fluidized bed test facility at the National Energy Technology Laboratory (NETL) of the U. S. Department of Energy. The particle used in this study was a coarse, light material, cork, which has a particle density of 189kg∕m3 and a mean diameter of 812μm. Fluidizing this material in ambient air approximates the same gas-solids density ratio as coal and coal char in a pressurized gasifier. The purpose of this study is twofold. First, this study is to provide a better understanding on the fundamentals of flow regimes and their transitions. The second purpose of this study is to generate reliable data to validate the mathematical models, which are currently under development at NETL. Utilization of such coarse, light material can greatly facilitate the computation of these mathematical models. Furthermore, the ratio of density of cork to air under ambient conditions is similar to the density ratio of coal to gas at the gasification and pressurized fluidized bed combustion environment. This paper presents and discusses the data, which covered operating flow regime from dilute phase, fast fluidization, and to dense phase transport by varying the solid flux, Gs at a constant gas velocity, Ug. Data are presented by mapping the flow regime for coarse cork particles in a ΔP∕ΔL‐Gs‐Ug plot. The coarse cork particles exhibited different behavior than the published literature measurements on heavier materials such as alumina, sand, FCC, silica gel, etc. A stable operation can be obtained at a fixed riser gas velocity higher than the transport velocity, e.g., at Ug=3.2m∕s, even though the riser is operated within the fast fluidization flow regime. Depending upon the solids influx, the riser can also be operated at dilute phase or dense phase flow regimes. Experimental data were compared to empirical correlations in published literature for flow regime boundaries as well as solids fractions in the upper dilute and the lower dense regions for fast fluidization flow regime. Comparisons of measured data with these empirical correlations show rather poor agreements. These discrepancies, however, are not surprising since the correlations for these transitions were derived from experimental data of comparative heavier materials such as sands, FCC, iron ore, alumina, etc.

Time-Dependent Behavior of Cementless Concrete-Like Material Based on Oil Shale Fly Ash Binders in Ambient Air

The time-dependent behavior of cementless concrete-like materials inambient air was assessed by checking long-term strength of laboratoryspecimens on the basis of high calcium oil shale (HCOSFA) binders aswell as X-Ray Diffraction and Scanning Electron Microscopy, studyingcomposition and microstructure of cured binder material. It wasestablished that there are two distinct stages in the strengthdevelopment of specimens containing only HCOSFA as a binder: An increaseof compressive strength for the first month and the continuous dropuntil the 60th month of exposure. In specimens prepared with usingHCOSFA and low calcium coal fly ash (LCCFA) binder, three stages ofstrength change were identified: An increase of compressive strength forthe first month, a sharp drop thereafter until the third to sixth monthfollowed by a gradual loss or stabilization over a period of 60 months.It was resolved that binder hydration results in the formation ofettringite and gypsum together with other compounds. It was found thatettringite is not stable in ambient air and over time the amount ofettringite was diminished. This disintegration resulted in a continuousloss of strength in specimens containing only HCOSFA. The addition ofLCCFA to HCOSFA generated an additional amount of high-strength, stablesecondary CSH in the hardened system. The secondary CSH helped toneutralize consequences of ettringite transformation and improved theperformance of cementless concrete-like materials in ambient air.

Assessment of the effect of air pollution on material damages in Northeast Asia

Material exposure tests have been carried out to evaluate the relationship between air pollution and material damage, with the cooperation of researchers in Japan, China and Korea, since 1993. Test materials such as bronze, copper, marble, and steel have been exposed to both unsheltered and rain-sheltered outdoor conditions, with the simultaneous passive sampler measurement of SO2 and NO2 concentrations, at 17 separate sampling sites in East Asia. Meteorological data were gathered from the AWS in each country, and the chemical compositions of wet deposition analyzed by bulk sampling of the monthly rainfall. As a result, the corrosion rates of the test materials in ambient air were found to be in the order: carbon steel >marble >bronze ⩾copper. The corrosion rates of test materials in the unsheltered outdoor conditions were 2.28–6.24 times larger than those under the rain-sheltered conditions. The rates of corrosion were also found to be the highest in the heavily polluted areas of China, with these rates for the metal pieces generally being proportional to the SO2 concentration. With the two Korean sites, the test pieces at the Daegu site displayed higher rates of corrosion, possibly due to the higher SO2 concentration.

Characterization of Fine Particle Material in Ambient Air and Personal Samples from an Underground Mine

Personal samplers representing 4 job classifications and stationary samplers at 2 locations in an underground mine were deployed to measure fine particle carbon (organic/elemental), ions (sulfate plus nitrate), elements (metals and others), and speciated organic compounds including polycyclic aromatic hydrocarbons (PAH), oxygenated PAH, and hopanes/steranes. Chemically segregated size distribution was investigated after collection with a multistage impactor placed at 1 sampling site. All samples exceeded the currently proposed mine air standard of 160 w g/m 3 total carbon, and most exceeded the interim standard of 400 w g/m 3 . Carbon accounted for about 70% of the fine particle mass (described as a reconstructed mass of all measured chemical species); sulfate and ore/waste rock-derived metals constituted most of the remainder. Most of the personal samples were more concentrated than the ambient samples; 1 sample exceeded 2.5 mg/m 3 total mass. The PAH consisted mostly of gas-phase/semivolatile compounds and minor amounts of the particle-phase species, which is consistent with the composition of diesel exhaust, the major source of fine particle material in the mine. Size-segregated chemistry showed that the majority of the material below 1 w m of aerodynamic diameter was carbon, with the largest amount at approximately 0.2 w m. Metals, derived primarily from resuspended ore/waste rock, comprised the majority of the material above 1 w m. Results are placed in context of current mine-monitoring techniques that aim to regulate diesel particulate material.