In this work, we investigate the flame aerosol deposition of TiO2 nanoparticles in a well-defined premixed stagnation flame based on two-dimensional phase-selective laser-induced breakdown ...spectroscopy (PS-LIBS). The deposited nanoparticles are in anatase phase with an average size of ∼10 nm. In PS-LIBS measurement, atomic emissions of titanium near the wavelength of 500 nm are extracted by spectral filter lenses and imaged for demonstrating the particle volume fraction distributions. The PS-LIBS signals can well depict the whole process of particle formation and transport, including the rapid gas-to-particle conversion near the flame front, dilution and concentrating of the nanoparticles induced by gas density variations, and dropping of particle volume fractions near the substrate. A quantitative model has been proposed to describe convection, thermophoresis, and diffusion of the nanoparticles. Combining the PS-LIBS measurement and the numerical simulation, it is found that, the nanoparticles concentrate outside the boundary layer at low substrate temperatures due to a joint effect of gas compression and thermophoresis. Further parametric analysis indicates that substrate temperatures and precursor loading rates can strongly affect the particle concentration boundary layer and the particle deposition rate.
This work examines the effect of temperature-time history on the flame synthesis of titania nanoparticles using a specially designed swirl-stabilized tubular burner with two kinds of precursor ...feeding modes, the tangential inlet and the central jet inlet. When the Damköhler number is less than unity, a rapidly mixed type tubular flame is well-formed, which is chosen to be the condition for flame synthesis. The ex situ characterization of the synthesized TiO2 nanoparticles shows that the particle samples from the tangential inlet feeding mode are mainly anatase (up to 84.3%) with a mean primary particle size of 13.0 ± 3.2 nm, whereas those from the central jet inlet feeding mode are large polydisperse rutile (up to 74%) nanoparticles with a mean size of 16.9 ± 8.8 nm. The significant differences in particle size and crystal phase are attributed to the varied temperature-time histories of two feeding modes, as the residence time of nanoparticles in high-temperature zone of the central jet inlet mode is much longer with larger variation than that of the tangential inlet feeding mode. Finally, the well-dispersed Pd/TiO2 nanocatalysts are generated by elaborately feeding palladium acetate through the central jet inlet and titanium tetraisopropoxide through the tangential inlets, respectively, to better match the temperature-time histories with the decomposition properties of two different precursors. The study demonstrates the potential of this swirl-stabilized burner for producing tailored single- and multi-component nanomaterials for a variety of applications.
•The precursor feeding modes of tangential inlet and central jet inlet are demonstrated in a swirl-stabilized flame reactor.•The different residence time in high-temperature zone of two feeding modes control nanoparticle morphologies.•The unique temperature-time characteristics of two feeding modes are utilized for doping synthesis of Pd/TiO2 nanocatalyst.
Using molecular dynamics (MD) simulations in conjunction with a reactive force field method, the chemical kinetics of the hydrolysis of titanium tetraisopropoxide (Ti(OC3H7)4, TTIP) at ...high-temperature conditions is investigated. The MD simulations allow for presenting the complete dynamic process of the TTIP conversion at the atomic level. The rate constant of TTIP hydrolysis at 1 atm is estimated to be k=1.23×1014×exp(−11,323/T(K))mol−1cm3s−1 using a second-order reaction model. On the basis of Ti-containing intermediate species profiles, the evolutions of the main decomposition products during the TTIP hydrolysis are identified and key reaction pathways are elucidated. The results show that the clusters are formed before TiO2 molecules are observed. During the decomposition, Ti-containing species with one or two CO bonds and carbon-free species with more than two TiO bonds are formed and undergo two separate pathways. One is the combination via the formation of TiOTi bridges, forming early clusters that serve as precursors for large TiO2 nanoparticles. The other is the further decomposition to smaller molecules such as TiO2 that participate in the subsequent cluster formation. Interactions between Ti and O atoms in the cluster stabilize the large structure through the abstraction of water and –CxHy groups.
Display omitted
•Formation pathways of incipient titanium clusters from TTIP are elucidated.•A new Ti/C/H/O reactive force field is developed.•Temperature has a non-linear effect on the formation of ...incipient titanium clusters.•O2 in the ambient promotes the inception and quantity of TiO2 significantly.
We performed ReaxFF reactive molecular dynamics simulations to investigate the inception mechanism of TTIP precursor droplet conversion to Ti-containing clusters in 1000 K–2500 K with or without gaseous O2 molecules. A new Ti/C/H/O ReaxFF force field has been developed. Key intermediate titanium species and the initial decomposition pathways of TTIP are identified. The effects of temperature, O2 concentration and high-temperature residence time on the conversion of TTIP to incipient titanium clusters are investigated. Results suggest that high pyrolysis temperature does not necessarily promote the formation of incipient Ti-containing clusters, due to less stable TiO bonds at high temperatures. Ti2OxCyHz species appear earlier than TiO2 during TTIP pyrolysis, while TiO2 forms earlier than Ti2OxCyHz species and has much higher concentration with ambient O2. Decreasing high-temperature residence time boosts the formation of Ti-containing clusters by facilitating the condensation of TiO2 vapors. The growth pattern of the incipient titanium clusters is elucidated as formation of TiO bond with TiOxCyHz species or titanium clusters followed by continuous breakage of TiO or CO bonds to release hydrocarbon moieties.
Key effects of solvent formulations on the structure and morphology of optical-quality yttrium-aluminum nanocomposites using liquid-fed aerosol flame synthesis are investigated. Employing a ...temperature-controlled flat flame burner with inexpensive nitrates as multi-component precursors, three different solvent formulations, i.e., ethanol, ethanol/2-ethylhexanoic acid (EHA), and butanol, are studied. Adding EHA into ethanol in a 1:1 volume ratio dramatically changes the flame-made yttrium-aluminum oxides from hollow inhomogeneous powders that contain non-uniform large particles to homogeneous nanopowders around 10 nm. As characterized by in-situ phase Doppler anemometry, droplet size with increasing burner height for the EHA/ethanol case remains constant at the beginning, whereas those for both ethanol and butanol cases reduce immediately. EHA likely causes a shift from the droplet-to-particle precipitation route to the gas-to-particle route because of the formed low-boiling-point 2-ethylhexanoates from nitrates via ligand exchange. By replacing ethanol with butanol, hollow particles are produced with better crystallinity because of its high calorific value that helps to heat precursors at the droplet surface. In-situ diagnostics using phase-selective laser-induced breakdown spectroscopy, which tracks only atomic emission from the nanoparticle phase. The result shows that the Al atomic emissions in the EHA/ethanol mixture case gradually increase along the burner height, while those for both ethanol and butanol cases fluctuate, further verifying the favoring of the gas-to-particle route for producing uniform, ultrafine solid multi-oxide particles by adding EHA in solvents.
Graphene has been subjected to widespread attention, and its highly extraordinary properties have led to abundant scientific researches. The present study shows that fluffy graphene can ignite in a ...fairly short time upon exposure to a conventional flash light, even in an extremely low temperature environment. The ignition process is fierce and multi-points are distributed with temperatures as high as 1840K with few residues. This kind of ignition can be attributed to the graphene nanostructure efficiently converting light to heat and causing a large amount of heat to accumulate within a very short flash time with the temperature quickly exceeding the ignition point. It is further demonstrated that graphene can ignite in an environment as low as about −50 °C. When fluffy graphene was added to extremely lean methane/oxygen/nitrogen mixtures, ignition of the mixtures was successfully triggered by flash light. The ignition characteristics make graphene a promising alternative for ignition fields in harsh environment.
•Fluffy graphene can ignite by flash within a short exposure time even at −50 °C.•Ignition temperatures can reach as high as 1840K.•Flash ignition can be attributed to nanostructure photo-thermal effects.•Very lean-fuel can be successfully ignited by fluffy graphene using flash.
This study aimed to detect the difference in resting cerebral activities between ischemic stroke pa- tients and healthy participants, define the abnormal site, and provide new evidence for ...pathological mechanisms, clinical diagnosis, prognosis prediction and efficacy evaluation of ischemic stroke. At present, the majority of functional magnetic resonance imaging studies focus on the motor dysfunc- tion and the acute stage of ischemic stroke. This study recruited 15 right-handed ischemic stroke patients at subacute stage （15 days to 11.5 weeks） and 15 age-matched healthy participants. A rest- ing-state functional magnetic resonance imaging scan was performed on each subject to detect cerebral activity. Regional homogeneity analysis was used to investigate the difference in cerebral activities between ischemic stroke patients and healthy participants. The results showed that the ischemic stroke patients had lower regional homogeneity in anterior cingulate and left cerebrum and higher regional homogeneity in cerebellum, left precuneus and left frontal lobe, compared with healthy participants. The experimental findings demonstrate that the areas in which regional homogeneity was different between ischemic stroke patients and healthy participants are in the cerebellum, left precuneus, left triangle inferior frontal gyrus, left inferior temporal gyrus and anterior cingulate. These locations, related to the motor, sensory and emotion areas, are likely po- tential targets for the neural regeneration of subacute ischemic stroke patients.
The automatic control of Heating, ventilation and Air Conditioning (HVAC) systems aims to achieve the thermal comfort requirements of occupants with minimum energy consumption. The automatic control ...strategy of existing HVAC systems determines a set value for creating a thermal environment in accordance with relevant design principles and/or occupants’ preferences. An overly-cooled indoor environment may reduce the occupant's thermal comfort and result in excessive energy consumption. In order to improve thermal comfort and save energy, this study proposes an indoor thermal environment optimal control method based on the online monitoring of thermal sensation. First, a smart wristband collects the human physiological data, including wrist skin temperature and heart rate. This is for predicting human thermal sensation, where a fuzzy comprehensive evaluation method is employed to determine the integrated thermal sensation of multi occupants. Then, a linear adjustment algorithm is developed to optimize the indoor temperature set point. In order to evaluate the performance of the thermal sensation-based control method, a series of experiments were conducted using the thermal sensation-based control and set point-based control. The results show that the thermal sensation-based control can adjust the temperature setting in a timely fashion according to the occupants’ integrated thermal sensations, although they do not necessarily state their subjective perception. It is also revealed that the thermal sensation-based control can achieve a more comfortable thermal environment than the set point-based control. Furthermore, the thermal sensation-based control saves 13.8% in daily energy consumption compared to the set point-based control method.
Display omitted
•Green supercapacitor assisted photocatalytic fuel cell system was constructed.•Continuous hydrogen production was obtained under light and dark in the system.•Hydrogen production, ...electricity generation and waste degradation in the system.•Enhanced photoelectrocatalysis conversion and increased total energy gain.
Photocatalysis for hydrogen production and pollution degradation is of significance for energy recovery and environment protection. However, hydrogen production can not be maintained due to intermittent illumination during a full-day. To solve this issue, in this paper, we herein developed a green supercapacitor assisted photocatalytic fuel cell system with a chemical bias, which aimed for storing photoelectrons by supercapacitors (2 mg/cm2) under light irradiation and discharging for hydrogen production under dark to enable continuous hydrogen production. The results suggested that the system can achieve a sustainable hydrogen production under illumination (32 μmol/L) and in dark (13 μmol/L), and an improved efficiency of the photoelectrocatalysis conversion with the chemical bias. In addition, the system exhibited a good degradation capacity of ethylene glycol under illumination with the generation of electricity. This paper provided an alternative approach to achieve continuous hydrogen production, electricity generation and waste degradation using the supercapacitor assisted photocatalytic fuel cell system.
In this study, we investigate coal matrix swelling during the process of gas diffusion from cleats and its impact on the evolution of strain. We inject helium into both jacketed and unjacketed coal ...samples within a pressurized core holder. In the unjacketed experiment, the coal sample was exposed to hydrostatic gas pressure. In the jacketed experiment, the coal sample was constrained by fixed displacement at the two ends and by constant confining pressure laterally. In both experiments, strains were measured continuously both parallel/perpendicular to the bedding plane of the coal as internal pressure of helium is increased. For the unjacketed test the initial rapid compactive deformation of the sample rebounds to dilative at long term — attributed to the gas diffusion-induced swelling of the coal matrix. For the jacketed test both axial and circumferential coal strains are first dilative due to the decrease in effective stress with subsequent changes of coal strain induced by the gas diffusion closely associated with the specific boundary conditions. For a constant stress boundary, the circumferential strain first remains unchanged for some time and then gradually increases to steady state. Such a phenomenon suggests that when gas diffuses from the cleat to the matrix, the coal matrix-cleat system probably undergoes a transition from local swelling to macroswelling. In contrast, for a fixed displacement boundary, the axial strain first decreases and then reaches a steady state. It also indicates that the swelling of the matrix not only decreases the aperture of the fracture, but also expands the circumferential profile of the coal sample due to the Poisson effect. In addition, helium diffusion in the matrix is estimated by using the bidisperse diffusion model. The calculated effective diffusivity increases with pore pressure. This suggested that the gas diffusion coefficient is a pore pressure-dependent parameter. These results demonstrate that gas diffusion from the cleat to the matrix can cause the swelling of the coal matrix, change the aperture of the cleat, and in turn impact the evolution of the coal permeability.
•A set of experiments were conducted to investigate how the coal matrix swells due to gas diffusion from fracture to matrix.•The relation between coal matrix swelling and the process of gas diffusion from fracture to matrix was observed.•The interaction between coal fracture and matrix induced by gas transport was observed.•A transition from local interaction to macro interaction was observed and explained.
PDF
