Possible Negative Value of the Grüneisen Coefficient of Hydrogen in the Area of Pressures from 40 to 75 GPa and Temperatures from 3500 to 7500 K

Experimental data on single and double shock compression of initially liquid and gaseous (compressed by initial pressure) hydrogen isotopes (protium and deuterium) at pressures of ≈10–180 GPa and temperatures of ≈3000–20 000 K are considered. The mean values of the measured variables (pressure, density, internal energy, and temperature) show that hydrogen at a pressure of ≈41 GPa in the temperature interval of ≈3500–5700 K and at a pressure of ≈74 GPa in the temperature interval of ≈5000–7500 K is characterized by a negative value of the Grüneisen coefficient. Such an anomaly may play a key role in some processes, including those proceeding in the Jupiter gas envelope, which mainly consists of protium (≈90%) and helium (≈10%). In the range of pressures (depths) of its manifestation, convection in the protium envelope is forbidden with an increase in temperature in the envelope with increasing pressure. Possibly, a comparatively low fraction of helium does not suppress the anomaly, and it serves as a barrier for large-scale convection in the Jupiter envelope. Additional refining experiments are required to confirm this anomaly.     

Size distribution of exhaled particles in the range from 0.01 to 2.0 μm

This study investigates the number size distribution of endogenously produced exhaled particles during tidal breathing and breathing with airway closure. This is the first time that the region below 0.4 μm has been investigated. The particle concentration was generally lower for tidal breathing than for airway closure, although the inter-individual variation was large. During tidal breathing, the size distribution peaks at around 0.07 μm. This peak is still present during the airway closure manoeuvre, but an additional broad and strong peak is found between 0.2 and 0.5 μm. This suggests that different mechanisms govern the generation of particles in the two cases. The particles produced from airway closure may be attributed to formation of film droplets in the distal bronchioles during inhalation. It is speculated that the very small particles are film droplets originating from the alveolar region.     

Effects of the preparation methods on the performance of the Cu–Cr–Fe/γ-Al2O3 catalysts for the synthesis of 2-methylpiperazine

Co-precipitation, impregnation and ultrasonic sol–gel (USG) methods have been used to prepare Cu–Cr–Fe/γ-Al₂O₃ catalysts, which were further used to synthesize 2-methylpiperazine. The catalysts were characterized by XRD, XPS, TG/DSC, BET, TPR, AAS and TEM. It is found that preparation method can greatly impact the catalytic performance of the catalysts, the Cu–Cr–Fe/γ-Al₂O₃ catalyst prepared by the ultrasonic sol–gel method proved to be the most active and stable for this reaction. The dispersion and stabilization of Cu⁰ in the reduced catalysts are attributed to the existence of CuCr₂O₄ and Fe₂O₃. A surprising copper migration was detected by XPS analysis for the Cu–Cr–Fe/γ-Al₂O₃-USG catalyst after the calcination process, which may be crucial to the high activity and stability of this catalyst.     

Tuning the crystallite size of monoclinic ZrO_2 to reveal critical roles of surface defects on m–ZrO_2 catalyst for direct synthesis of isobutene from syngas

The effects of crystallite size on the physicochemical properties and surface defects of pure monoclinic ZrO_2 catalysts for isobutene synthesis were studied. We prepared a series of monoclinic ZrO_2 catalysts with different crystallite size by changing calcination temperature and evaluated their catalytic performance for isobutene synthesis from syngas. ZrO_2 with small crystalline size showed higher CO conversion and isobutene selectivity, while samples with large crystalline size preferred to form dimethyl ether(DME) instead of hydrocarbons, much less to isobutene. Oxygen defects(ODefects) analyzed by X-ray photoelectron spectroscopy(XPS) provided evidence that more ODefectsoccupied on the surface of ZrO_2 catalysts with smaller crystalline size. Electron paramagnetic resonance(EPR) and ultraviolet–visible diffuse reflectance(UV–vis DRS) confirmed the presence of high concentration of surface defects and Zr~(3+) on mZrO_2-5.9 sample, respectively. In situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS) analysis indicated that the adsorption strength of formed formate species on catalyst reduced as the crystalline size decreased. These results suggested that surface defects were responsible for CO activation and further influenced the adsorption strength of surface species, and thus the products distribution changed. This study provides an in-depth insight for active sites regulation of ZrO_2 catalyst in CO hydrogenation reaction.     

Characterization of Steric Field-Flow Fractionation Using Particles to 100 μm Diameter

Abstract

Steric field-flow fractionation has been applied to a larger range of particle sizes than heretofore studied, thus expanding the upper diameter limit to approximately 100 μm. The large size range investigated (6–100 μm), combined with velocity-dependent studies, provided the parameters for two simple empirical retention equations. The implication of these equations to selectivity and plate height were investigated theoretically. The experimental results, combined with the theory, showed that the diameter-based selectivity was less than unity and decreased somewhat with increasing velocity. Calculated polydispersity contributions appeared to constitute a major part of peak broadening, but observed plate heights increased with flow velocity whereas the polydispersity contribution was predicted to decrease with velocity. The theoretical and practical implications of the results are summarized.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.     

Effect of preparation methods on the structure and catalytic performance of Fe–Zn/K catalysts for CO_2 hydrogenation to light olefins

Potassium promoted iron–zinc catalysts prepared by co-precipitation method(C–Fe–Zn/K),solvothermal method(S–Fe–Zn/K)and hydrothermal method(H–Fe–Zn/K)could selectively convert CO_2to light olefins,respectively.The physicochemical properties of the obtained catalysts were determined by SEM,N_2physisorption,XRD,H_2-TPR,CO_2-TPD and XPS measurements.The results demonstrated that preparation methods had great influences on the morphology,phase structures,reduction and adsorption behavior,and hence the catalytic performance of the catalysts.The samples prepared by hydrothermal and co-precipitation method generated small uniform particles and led to lower specific surface area.In contrast,microspheres with larger specific surface area were formed by self-assembly of nanosheets using solvothermal method.ZnFe_2O_4was the only detectable phase in the fresh C–2Fe–1Zn/K,S–3Fe–1Zn/K and S–2Fe–1Zn/K samples.ZnFe_2O_4and ZnO co-existed with increasing Zncontent in S–1Fe–1Zn/K sample,while ZnO and Fe_2O_3could be observed over H–2Fe–1Zn/K sample.All the used samples contained Fe_3O_4,ZnO and Fe_5C_2.The peak intensity of ZnO was strong in the AR-H–2Fe–1Zn/K sample while it was the lowest in the AR-C–2Fe–1Zn/K sample after reaction.The formation of ZnFe_2O_4increased the interaction between iron and zinc for C–2Fe–1Zn/K and S–Fe–Zn/K samples,causing easier reduction of Fe_2O_3to Fe_3O_4.The surface basicity of the sample prepared by co-precipitation method was much more than that of the other two methods.During CO_2hydrogenation,all the catalysts showed good activity and olefin selectivity.The CO selectivity was increased with increasing Zncontent over S–Fe–Zn/K samples.H–2Fe–1Zn/K catalyst preferred to the production of C_5~+hydrocarbons.CO_2conversion of 54.76%and C_2~=–C_4~=contents of 57.38%were obtained on C–2Fe–1Zn/K sample,respectively.     

A Study on the Change in the Dielectric Properties of CR-39 Polymer Track Detector Due to α-Irradiation in the Frequency Range from 100 Hz to 100 kHz

The dielectric properties in the frequency range from 100 Hz to 100 kHz of polyallyldiglycol carbonate “CR-39” samples before and after irradiations have been investigated. The irradiations were verified with 4.84 MeV α-particles at different irradiation times. The dependence of the dielectric properties of unirradiated and irradiated samples at room temperature (25°C) and constant frequency (10 kHz) on the total number of α-particles have been studied. It was found that the CR-39 can be used as a detector for high α-particles fluxes.     

High temperature thermal physical performance of SiC/UO2 composites up to 1600 °C

SiC was introduced to UO₂ matrix by spark plasma sintering (SPS) to improve the thermal conductivity. The microstructure evolution and thermal physical properties up to 1600?°C were firstly reported. The grain growth and the formation of equiaxed grain structure were inhibited by the addition of SiC. The critical SPS sintering temperature, above which SiC was positive on improving thermal conductivity, was discovered to be 1300?°C. Two equations were proposed to calculate the thermal diffusivity and thermal conductivity of SiC/UO₂ sintering at 1500?°C. Each percent of SiC fraction brought about 3% increment in thermal conductivity. The coefficient of thermal expansion (CTE) was decreased after SiC addition. Such improvement in thermal conductivity and decrease in CTE were beneficial to the fuel safety in accident condition.     

Effect of CsxH3?xPW12O40 addition on the catalytic performance of ZnFe2O4 in the oxidative dehydrogenation of n-butene to 1,3-butadiene

Oxidative dehydrogenation of n-butene to 1,3-butadiene over ZnFe₂O₄ catalyst mixed with Cs _x H_3−x PW₁₂O₄₀ heteropolyacid (HPA) was performed in a continuous flow fixed-bed reactor. The effect of Cs _x H_3−x PW₁₂O₄₀ addition on the catalytic performance of ZnFe₂O₄ was investigated. Cs _x H_3−x PW₁₂O₄₀ itself showed very low catalytic performance in the oxidative dehydrogenation of n-butene. However, addition of small amount of Cs _x H_3−x PW₁₂O₄₀ into ZnFe₂O₄ enhanced the catalytic performance of ZnFe₂O₄ catalyst. The catalytic performance of ZnFe₂O₄-Cs _x H_3−x PW₁₂O₄₀ mixed catalysts was closely related to the surface acidity of Cs _x H_3−x PW₁₂O₄₀. Among the catalysts tested, ZnFe₂O₄-Cs_2.5H_0.5 PW₁₂O₄₀ mixed catalyst showed the best catalytic performance. Strong acid strength and large surface acidity of Cs_2.5H_0.5PW₁₂O₄₀ was responsible for high catalytic performance of ZnFe₂O₄-Cs_2.5H_0.5PW₁₂O₄₀ mixed catalyst. Thus, Cs_2.5H_0.5PW₁₂O₄₀ could be utilized as an efficient promoter and diluent in formulating ZnFe₂O₄ catalyst for the oxidative dehydrogenation of n-butene.     

Effect of the Cu vacancy on the thermoelectric performance of p-type Cu1−xInTe2 compounds

In this study, the effect of Cu vacancy on the thermoelectric performance of Cu_1-xInTe₂ is reported, where x is 0, 0.04, 0.06, 0.08 and 0.10. Cu vacancy can yield excess holes lifting the carrier density of CuInTe₂, which is an intrinsic p-type semiconductor. Meanwhile, the mass fluctuation caused by Cu vacancy attributes to the enhanced point defects phonon scattering, resulting in a reduced lattice thermal conductivity. The optimum Cu vacancy content is found to be 0.04, attaining a maximum zT value of 0.83 at 820 K. Meanwhile, there is a 50% enhancement compared to that of pure sample which arises from the large power factor and the relatively low thermal conductivity. Our result indicates the great potential of Cu_1-xInTe₂ for thermoelectric application at middle-temperature.     

Mechanochemical synthesis of NbC–NbB2 nanocomposite from the Mg/B2O3/Nb/C powder mixtures

An experimental study was conducted on the preparation and characterization of nanocrystalline niobium boride and carbide composite (NbB₂–NbC) in the Mg–B₂O₃–Nb–C system via mechanochemical method. The thermodynamic appraisal indicated that the reduction and synthesis reactions were highly exothermic and should be self-sustaining. According to the differential thermal analysis (DTA) results, a pre-milling treatment of powder mixture up to 2 h not only reduced the reaction temperature, but also induced a different reaction path. In addition, the amount of Mg₃(BO₃)₂, as a major by-product of the thermal synthesis, was significantly decreased by applying adequate mechanical activation. The phase analysis revealed that the NbB₂ phase was achieved after 3 h high energy ball milling in self-stunning mode; meanwhile, the formation of NbC was progressively completed after a longer period of milling up to 7 h. According to the morphological evolutions, the range of particle size was within 100 nm.     

Effects of pretreatment atmospheres on the catalytic performance of Pd/γ-Al2O3 catalyst in benzene degradation

In the current paper, a strategy for catalytic degradation of benzene over Pd/γ-Al₂O₃ catalysts via different atmospheres (H₂, N₂, He and air) pretreatment was carried out in a fixed bed reactor. The experimental results indicated that H₂, N₂, and He pretreatments have a significant positive effect on the initial activity of the catalyst compared to air. We have also investigated the effects of pretreatment atmospheres on the catalytic performance for benzene degradation through the information on the chemical state and crystal structure of the catalysts using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and CO chemisorption measurements techniques. The chemical state of Pd species decreased via H₂ pretreatment, leading to the increase of the initial catalytic activity, while chemical state increased accompanying with a decrease in degradation benzene via air pretreatment. There is no change in the chemical state of Pd species using inert atmosphere (N₂ and/or He) pretreatment, but the initial activity of the catalyst improved significantly due to the modified crystal structure of Pd species in the catalysts, with the crystalline PdO being transformed to amorphous state.     

Microstructure and mechanical performance of SiCf/BN/SiC mini-composites oxidized at elevated temperature from ambient temperature to 1500 °C in air

SiC_f/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapour deposited (CVD) BN interface layers were fabricated. The mechanical performance and binding strength of the composites and the fibre/interface for the oxidized SiC_f/BN/SiC mini-composite samples (oxidation at 1000, 1200, 1300, 1400 and 1500 °C in air for two hours) were investigated by tensile tests and fibre push-out tests, respectively. The value of oxidation mass change was also measured. Some unusual phenomena for the SiC_f/BN/SiC mini-composites oxidized at 1000 °C were discovered in this work. The tensile strength reached a maximum value, and the mass gain rate showed as a singular negative value, while the shear strength between the fibre and the matrix was moderate. Scanning electron microscopy, energy dispersive spectrometry, infrared spectroscopy and X-ray diffraction characterization methods were used to reveal the microstructural evolution and investigate the unusual phenomenon during oxidation procedures. This work will provide guidance for predicting the service life of SiC_f/BN/SiC composite materials and may enable these materials to become a backbone for thermal structure systems in aerospace applications.     

The effect of the addition of Y2O3 to Ni/α-Al2O3 catalysts on the autothermal reforming of methane

The addition of Y₂O₃ to Ni/α-Al₂O₃ catalysts was investigated by BET surface area measurements, hydrogen chemisorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, temperature programmed reduction, temperature programmed oxidation and cyclohexane dehydrogenation. Autothermal reforming experiments were performed in order to evaluate the methane conversion and proceeded through an indirect mechanism consisting of total combustion of methane followed by CO₂ and steam reforming generating the synthesis gas. The Y₂O₃·Al₂O₃ supported catalysts presented better activity and stability in autothermal reforming reaction. Temperature programmed oxidation analysis demonstrated that the addition of Y₂O₃ resulted in a change of the type or the location of coke formed during reaction. None of the prepared catalyst presented deactivation by sintering under the tested conditions. The improved stability of supported catalysts Y₂O₃·Al₂O₃ was the result of minimizing the formation of coke on the surface of nickel particles.     

Use of the 15?N gas flux method to measure the source and level of N2O and N2 emissions from grazed grassland

Understanding the contribution of nitrification and denitrification to production of nitrous oxide (N₂O), a potent greenhouse gas, is important in devising effective mitigation strategies to reduce emissions. In this study the ¹⁵N gas flux method was used to investigate N₂O and N₂ emissions following an application of ¹⁵N labelled ammonium nitrate (0.71?mol?N?m^?2) to intensive grassland swards (grazed at 2.74 or 2.05 livestock units ha^?1 year^?1) at a site in Southern Ireland. The ¹⁵N labelled fertiliser (NO₃ moiety ¹⁵N labelled at 60 at. %) was applied to designated soil areas in the field, enclosed by static chambers, in June 2009, September 2009 and March 2010. Fluxes of N₂O and N₂ were determined over 12?days on each occasion. N₂O and N₂ emissions were significantly (P?<?0.001) lower in March 2010 than in June or September 2009. There was little difference between the two swards grazed at different stocking rates on N₂O or N₂ emissions. Mean cumulative N₂O emissions over 103?h were 212.9, 279.5 and 62.06?mg?m^?2 for June 2009, September 2009 and March 2010, respectively. Mean cumulative N₂ emissions for the three time periods were 818.8, 893.8 and 87?mg?m^?2, respectively. The N₂O mole fraction averaged 0.21 and 0.23 in June 2009 and September 2009, respectively, but increased to 0.41 in March 2010 which may have been due to changes in denitrifier community composition or due to N₂O reductase being sensitive to low soil temperatures. The results point to denitrification of nitrate as the major source of N₂O at this site which may have implications for choice of fertiliser in moist temperate climates.     

Investigation of the effect of branched structure on the performances of the copolymers synthesized from ethylene and α-olefin with rac-Et(Ind)2ZrCl2/MMAO catalyst system

The branched copolymers prepared from ethylene and α-olefins using rac-Et(Ind)₂ZrCl₂/MMAO catalyst system were studied. Both the absolute molecular weight and the molecular size (radius of gyration, R_g) of the polymers eluting from gel permeation chromatography (GPC) columns were obtained simultaneously via a high temperature GPC coupled with a two-angle laser light scattering (TALLS) detector. The branched structures and performances of the copolymers display approximate molecular weight and molecular sizes were investigated. Wide angle X-ray diffraction analyses indicate that 16-carbon side branch could co-crystallize effectively with backbone chain at low α-olefin incorporation. The melt behaviors of the copolymers were studied by dynamic rheological measurements. Both branch length and comonomer content affect considerably the loss modulus, storage modulus and complex viscosity of the copolymers. The relationship between the dynamic-mechanical behavior and the comonomer content of the copolymers was also examined by dynamic-mechanical experiments. It is found that the intensity of β-transition raise with comonomer content increasing.     

Catalytic performance of Co-Mo-Ce-K/γ-Al2O3 catalyst for the shift reaction of CO in coke oven gas

The catalytic performance of Co-Mo-Ce-K/γ-Al₂O₃ catalyst for the shift reaction of CO in coke oven gas is investigated using X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The results indicate that Ce and K have a synergistic effect on promoting the catalytic activity, and the Co-Mo-Ce-K/γ-Al₂O₃ catalyst with 3.0 wt-% CeO₂ and 6.0 wt-% K₂O exhibits the highest activity. CeO₂ favors Co dispersion and mainly produces an electronic effect. TPR characterization results indicate that the addition of CeO₂-K₂O in the Co-Mo-Ce-K/γ-Al₂O₃ catalyst decreases the reduction temperature of active components, and part of octahedrally coordinated Mo⁶⁺ transforms into tetrahedrally coordinated Mo⁶⁺, which has a close relationship with the catalytic activity.