Upper-limit Temperature Research Articles

Rapid metabolism fosters microbial survival in the deep, hot subseafloor biosphere

A fourth of the global seabed sediment volume is buried at depths where temperatures exceed 80 °C, a previously proposed thermal barrier for life in the subsurface. Here, we demonstrate, utilizing an extensive suite of radiotracer experiments, the prevalence of active methanogenic and sulfate-reducing populations in deeply buried marine sediment from the Nankai Trough subduction zone, heated to extreme temperature (up to ~120 °C). The small microbial community subsisted with high potential cell-specific rates of energy metabolism, which approach the rates of active surface sediments and laboratory cultures. Our discovery is in stark contrast to the extremely low metabolic rates otherwise observed in the deep subseafloor. As cells appear to invest most of their energy to repair thermal cell damage in the hot sediment, they are forced to balance delicately between subsistence near the upper temperature limit for life and a rich supply of substrates and energy from thermally driven reactions of the sedimentary organic matter.

Fabrication of multilayer Graphene-coated Copper nanoparticles for application as a thermal interface material

A process to fabricate a thermal interface material (TIM) was developed to coat graphene, which is chemically stable and thermally conductive, on the surface of copper nanoparticles (CNPs) to prevent their oxidation while promoting heat dissipation. The CNPs were synthesized using the polyol method to convert polyvinylpyrrolidone (PVP) into multilayer graphene (MLG) via chemical vapor deposition (CVD). For optimization, CVD temperature, the amount of additional PVP solution, and PVP molecular weight (MW) in polyol process were varied. The results showed that thermal properties degraded with increasing residual PVP, and an increasing ID/IG ratio confirmed improved MLG quality. The optimal MLG coating conditions were found to be a CVD temperature of 880℃, 50 wt% additional PVP solution and using K30 PVP in polyol process (MW: 45,000). These conditions provided the highest thermal conductivity of 19.66 W/m∙K. Thermogravimetric analysis established that oxidation began at 150℃, which is higher than the upper temperature limit of electronic components. Therefore, MLG-coated CNPs would be suitable as TIM.

Nucleation kinetics of the [formula omitted] precipitate in dilute Mg–Y alloys: A kinetic Monte Carlo study

The β″ precipitate is a primary strengthening precipitate in Mg–Y alloys. It nucleates as localized zigzag- and hexagonal-shaped clusters. Studies on the nucleation kinetics of β″ precipitate are scarce. In this study, we applied the kinetic Monte Carlo (KMC) approach to explore the nucleation kinetics of the β″ precipitates in the Mg–3.0 at.%Y system using a density functional theory-based interatomic potential. The time evolution of nucleation of the β″ precipitates was characterized based on the KMC results. Using these results, we predicted the existence of an optimum temperature for the formation of the β″ precipitates to be 550 K, at which the time necessary for nucleation is the shortest. Moreover, an upper temperature limit, above which the β″ precipitates cannot nucleate, was computed as 700 K. This study explains precipitate nucleation in Mg–Y alloys at an atomic level and provides the theory for obtaining an optimal age-hardening response.

Effect of cyclic heat treatment on microstructure and mechanical properties of laser aided additive manufacturing Ti–6Al–2Sn–4Zr–2Mo alloy

Globular α phases can significantly improve the ductility of titanium alloys. Cyclic heat treatment (CHT) has been proved to be an effective way to induce the formation of globular α phases in α+β titanium alloy Ti–6Al–4V fabricated by laser aided additive manufacturing (LAAM). However, there is no prior research reporting methods for obtaining globular α phases in LAAM-built near-α titanium alloys. This work investigated the cyclic heat treatment (CHT) procedures suitable for the LAAM-built near-α titanium alloy Ti–6Al–2Sn–4Zr–2Mo (Ti6242) to attain the globular α phases. The results show that 980 ​°C is the most suitable upper temperature limit for CHT. However, it is difficult to achieve a high volume fraction of the globular α phases in the LAAM-built Ti6242 alloys through CHT, which is ascribed to the low composition gradient caused by more α-stabilizing elements and fewer β-stabilizing elements. The as-built sample demonstrated elongation of 6.3%, which is lower than the AMS 4919J standard (elongation ≥10%). After 980 ​°C CHT and 980 ​°C CHT with solution heat-treatment, the formation of the globular α phases significantly increased the elongation to 13.5% and 12.9%, respectively. Although the mechanical strength is reduced after heat-treatment, the room-temperature tensile properties still exceed the AMS 4919J standard. Fractography examination showed that the as-built sample exhibited a mixed brittle and ductile fracture behavior, while the 980 ​°C CHT and 980 ​°C CHT with solution heat-treated samples displayed ductile fracture.

Deep-branching ANME-1c archaea grow at the upper temperature limit of anaerobic oxidation of methane

Deep-branching ANME-1c archaea grow at the upper temperature limit of anaerobic oxidation of methane

Hot ductility improvement of copper-arsenic steel by rare earth cerium

The effect of Ce on hot ductility of Cu-As bearing steel in the temperature ranging from 700 to 1100 °C was investigated using Gleeble-3800 thermal-mechanical simulator. The hot ductility evaluation and fracture morphology observation showed that the hot ductility was obviously improved as Ce content increased from 0 to 0.0290 wt%. Detailed, the upper limit temperature of the ductility trough was decreased from 1057 to 765 °C, and the temperature corresponding to the minimum reduction of area was decreased from 850 to 750 °C. The fracture morphology was overall transformed from the dominantly intergraular brittle failure to the ductile failure characterized by the large and deep dimples. Analysis of metallographic, inclusions and grain boundary elements suggested that increasing Ce content inhibited the proeutectoid ferrite formation, which enhanced hot ductility of the steel bearing Cu and As. Moreover, the competitive grain boundary segregation of the solute Ce and As in steel with 0.0022 wt% Ce without arsenious rare earth inclusions decreased the quantity of As distributed at grain boundaries and thereby improved the hot ductility. When the Ce content reached 0.0290 wt%, a large number of arsenious rare earth inclusions were formed, and the grain boundary segregation of As was further decreased As, which was more beneficial to hot ductility than that with the lower Ce content in austenite single phase region.

Performance Investigation of PCM/Pin Fin Coupled Battery Thermal Management System

The low thermal conductivity of phase-change materials (PCMs) hampers the commercialization of PCM cooling battery thermal management systems. Further reduction of the thermal resistance between the PCM and batteries is still a challenging problem. In this study, a PCM / pin fin design is proposed. ANSYS Fluent was used to construct the model of PCM / pin fin design. The SIMPLE algorithm and the second-order upwind scheme were used to solve the momentum and energy equations. Compared with the traditional pure PCM and PCM/plate fin designs, the maximum temperature of the battery (<I>T</I>_max) was lower for the PCM/pin fin design because the heat transport from the batteries to the PCM was enhanced owing to the pin fin with a larger heat-transfer area. <I>T</I>_max for the pure PCM configuration reached 55.76°C after discharge, exceeding the upper-limit temperature of 55°C. In contrast, for the PCM/pin fin design, <I>T</I>_max was only 53.44°C. This indicates that the PCM/pin fin design effectively alleviates the heat accumulation of the battery and successfully maintains the battery temperature within a safe range. The effects of PCM thickness and fin section area on thermal behavior were investigated. It was found that the decrease of fin cross-sectional area can significantly reduce <I>T</I>_max. When the fin cross-sectional area is 1 mm², the <I>T</I>_max is only 51.07°C. In addition to control <I>T</I>_max under 55°C, the minimum PCM thicknesses were 3.71, 2.89, and 2.38 mm for pure PCM, PCM/plate fin, and PCM/pin fin, respectively. Thus, compared with the other designs, in the PCM/pin fin design, fewer materials are required, the weight of the modules is reduced, and the energy density is improved.

Deformation of Poly-l-lactid acid (PLLA) under Uniaxial Tension and Plane-Strain Compression.

The ability of PLLA, either amorphous or semicrystalline, to plastic deformation to large strain was investigated in a wide temperature range (Td = 70–140 °C). Active deformation mechanisms have been identified and compared for two different deformation modes—uniaxial drawing and plane-strain compression. The initially amorphous PLLA was capable of significant deformation in both tension and plane-strain compression. In contrast, the samples of crystallized PLLA were found brittle in tensile, whereas they proved to be ductile and capable of high-strain deformation when deformed in plane-strain compression. The main deformation mechanism identified in amorphous PLLA was the orientation of chains due to plastic flow, followed by strain-induced crystallization occurring at the true strain above e = 0.5. The oriented chains in amorphous phase were then transformed into oriented mesophase and/or oriented crystals. An upper temperature limit for mesophase formation was found below Td = 90 °C. The amount of mesophase formed in this process did not exceed 5 wt.%. An additional mesophase fraction was generated at high strains from crystals damaged by severe deformation. After the formation of the crystalline phase, further deformation followed the mechanisms characteristic for the semicrystalline polymer. Interlamellar slip supported by crystallographic chain slip has been identified as the major deformation mechanism in semicrystalline PLLA. It was found that the contribution of crystallographic slip increased notably with the increase in the deformation temperature. The most probable active crystallographic slip systems were (010)[001], (100)[001] or (110)[001] slip systems operating along the chain direction. At high temperatures (Td = 115–140 °C), the α→β crystal transformation was additionally observed, leading to the formation of a small fraction of β crystals.

Testing the cooling system of the helicopter internal combustion engine in hot climates

The article discusses the need to solve the problem of increasing the temperature limits of the operation of the cooling system of the internal combustion engine (ICE) of the helicopter. This issue arose from the fact that during the operation of the helicopter on the territory of African countries with a hot climate, the engine overheated. The use of helicopters in these conditions was due to the demand in the aviation market. To solve the problem, new elements of the cooling system were selected, i.e. radiator and two types of fans. The research was aimed at increasing the heat transfer from the radiators of the cooling system by increasing the size of the radiator and increasing the air flow rate through the radiator. 3D modeling, design of a new cooling system (CO), and then design of CO in two versions with TEMIC and SPAL fans were done. First, ground and flight tests for two prototypes in a temperate climate were done, as a result of which a prototype with the best performance parameters was determined. During the tests the equipment and measuring instruments were used: voltmeter, ammeter, voltmeter; shunt; motor tester with the ability to transfer data via Bluetooth; smartphone with OpenDiag software installed, which is included and connected to the motor tester via Bluetooth, helicopter objective control system, flight data registration system, equipment and devices normally installed on the helicopter. For flight tests in hot climates, a new cooling system with a SPAL fan was used, these tests lasted three days. This article describes the final stage of a series of tests for the effectiveness of the cooling system of a helicopter and an analysis of the results obtained with confirmation of the final achievement of the set goals, i.e. raising the upper temperature limit of the outside air for the safe operation of the helicopter.

Chemical Evolution of the Exceptional Arctic Stratospheric Winter 2019/2020 Compared to Previous Arctic and Antarctic Winters

AbstractThe winter 2019/2020 showed the lowest ozone mixing ratios ever observed in the Arctic winter stratosphere. It was the coldest Arctic stratospheric winter on record and was characterized by an unusually strong and long‐lasting polar vortex. We study the chemical evolution and ozone depletion in the winter 2019/2020 using the global Chemistry and Transport Model ATLAS. We examine whether the chemical processes in 2019/2020 are more characteristic of typical conditions in Antarctic winters or in average Arctic winters. Model runs for the winter 2019/2020 are compared to simulations of the Arctic winters 2004/2005, 2009/2010, and 2010/2011 and of the Antarctic winters 2006 and 2011, to assess differences in chemical evolution in winters with different meteorological conditions. In some respects, the winter 2019/2020 (and also the winter 2010/2011) was a hybrid between Arctic and Antarctic conditions, for example, with respect to the fraction of chlorine deactivation into HCl versus ClONO2, the amount of denitrification, and the importance of the heterogeneous HOCl + HCl reaction for chlorine activation. The pronounced ozone minimum of less than 0.2 ppm at about 450 K potential temperature that was observed in about 20% of the polar vortex area in 2019/2020 was caused by exceptionally long periods in the history of these air masses with low temperatures in sunlight. Based on a simple extrapolation of observed loss rates, only an additional 21–46 h spent below the upper temperature limit for polar stratospheric cloud formation and in sunlight would have been necessary to reduce ozone to near zero values (0.05 ppm) in these parts of the vortex.

Asymmetric Character of the Ferroelectric Phase Transition and Charged Domain Walls in a Hybrid Improper Ferroelectric

AbstractIn improper ferroelectrics, the spontaneous ordering is typically driven by a structural distortion or a magnetic spin alignment. The induced electric polarization is only a secondary effect. This dependence is a rich source for unusual phenomena and ferroelectric domain configurations for proper, polarization‐driven ferroelectrics. This study focuses on the polar domain structure and the hysteretic behavior at the ferroelectric phase transition in Ca3Mn1.9Ti0.1O7 as a representative of the recently discovered hybrid improper ferroelectric class of multiferroics. Combining optical second harmonic generation and Raman spectroscopy gives access to the spontaneous structural distortion and the resulting improper electric polarization. This study shows that hybrid improper ferroelectrics contrast proper and improper ferroelectrics in several ways. Most intriguingly, adjacent ferroelectric domains favor head‐to‐head and tail‐to‐tail domain walls over charge‐neutral configurations. Furthermore, the phase transition occurs in an asymmetric fashion. The regime of phase coexistence of the nonpolar and polar phases shows a clear and abrupt upper temperature limit. In contrast, the coexistence toward low temperatures is best described as a fade‐out process, where 100‐nm‐sized islands of the nonpolar phase expand deep into the polar phase.

Drag Reduction in Pipelines by Cationic Surfactant Additives.(Dept.P0

This work is concerned with the drag reduction using cationic surfactants. (quaternary ammonium amine-sodium salicylate)dissolved in water. Drag reduction measurements were carried out in 6.17 and 2.69 mm diameter tubes, for Reynolds numbers from 101 to 106 and for temperature range of 30o to 120o C. The influence of surfactant composition. Temperature, mechanical shear, concentration and sodium salicylate concentration on the dragreduction were investigated. Trimethyl amine salts are most effective drag reducing agents. While alkyl dimethyl ammonium amine salts are not affective. Length of alkyl group has a major affect on the upper temperature limit for drag reduction. Appreciable amount of shorter chain reduces the maximum temperature. Concentrations of 1500 ppm of quaternary ammonium amine and 1500ppm of sodium salicylate are needed for affective drag reduction for Czz amines. Cationic surfactants of this type was found to produce higher drag reduction values in the larger tube than that for non-ionic surfactants or for high polymer solutions.

Effect on the thermal resistance and thermal decomposition properties of thermally cross-linkable polyimide films obtained from a reactive acetylene

Homopolyimides are prepared by 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as dianhydride monomer and several diamine monomers. The copolyimides are prepared with 4,4′-oxydianiline as an amine monomer， 3,3′,4,4′-oxydiphthalic anhydride as an anhydride monomer with the addition of 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as another anhydride monomer. The structure of polyimides is characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Thermogravimetric analysis, thermomechanical analysis and thermo-oxidative degradation kinetics analysis are used to investigate the properties of polyimides. The homopolyimide show the best thermal stability in both nitrogen and air atmosphere by 4,4′-oxydianiline and 4,4′-(ethyne-1,2-diyl)diphthalic anhydride. The results also indicate that the thermally cross-linkable copolyimide films not only enhance the thermal stability behaviors of polyimide by controlling the addition of dianhydride, but also improve substantially the upper limit temperature of thermal aging by undergoing chemical cross-linking reaction of the diphenylethynylene structures and providing multifarious naphthalene ring groups and biphenyl structures. Diphenylacetylene crosslinking merging to the long-chain of polyimide is a useful conversion for enhancing the thermal stability and the thermal degradation stability of aromatic polymers.

Highly Water Durable Solid Electrolyte Type Ammonia Gas Sensor with Ammonium Lanthanum Niobate As an Auxiliary Sensing Electrode

Ammonia (NH3) gas is one of the toxic gases causing a serious health damage, while NH3 is a useful chemical in industrial field. Therefore, for preventing unexpected accidents caused by inhalation, rapid, continuous, and reliable NH3 detection is greatly required by applying smart gas sensor which can put every NH3 emitting site. Among the various kinds of NH3 gas detection tool, the solid electrolyte type sensor is regarded to be a promising candidate for on time monitoring tool due to its selective and quantitative gas detection, thermal stability, and compactness in size, if both the low-temperature sensor operation and satisfactory water durability are realized.In 2011, we have reported a solid electrolyte type NH3 gas sensor showing high water durability at 230°C by using Al3+ ion conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte and water durable NH4 +-β-gallate auxiliary sensing electrode. However, the operation temperature of this sensor (230°C) at which the high sensitivity without electrical noise was obtained are still high for expecting a long-term sensor operation, and it is required to lower the operation temperature. Because a main reason for preventing the low-temperature operation is high electrical resistance of NH4 +-β-gallate, we can expect to lower the operation temperature by newly designing an auxiliary sensing electrode.In this study, we focused on NH4LaNb2O7 in which NH4 + ions existed stably in the layered structure, similar to the NH4 +-β-gallate solid, and fabricated the highly water durable NH3 gas sensor which can operate even at 180°C, by combining with (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte.The NH4LaNb2O7 solid was obtained by the ion-exchange of RbLaNb2O7, which was synthesized by conventional solid-state reaction, in NH4NO3 eutectic solution. Similar to our previous sensor, the sensor element was devised by the combination of (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte, NH4LaNb2O7 auxiliary sensing electrode, and Al metal reference electrode. The NH3 gas sensing performances were investigated at 180°C in atmospheres whose water content was varied from 0 to 4.2 vol.%.From the thermal analysis of the synthesized NH4LaNb2O7 solid, it was found that NH4 + ions stably existed in (NH4)LaNb2O7 solid up to 200°C. Therefore, we decided the sensor operation temperature at 180°C which is slightly lower than the upper temperature limit of NH4LaNb2O7 solid for holding NH4 + ions in its structure. The present sensor exhibited a stable and continuous sensor response to NH3 gas concentration change with a 90% response time of 6 minutes (Response time includes substitution time of test gas in the gas flow line) at 180°C even under humid atmosphere containing 4.2 vol% H2O. Furthermore, the sensor EMF outputs for each NH3 gas concentration were almost same even for varying humidity from 0 to 4.2 vol%, and the EMF changes by changing NH3 gas concentration obeyed a theoretical Nernst relationship over three months, indicating that the present sensor with NH4LaNb2O7 solid as an auxiliary sensing electrode showed the theoretical response for NH3 gas at 180°C with long term stability even in humid atmosphere.

Evidence of taxonomic non-equilibrium effects in the clumped isotope composition of modern cephalopod carbonate

The stable oxygen isotope composition (δ18O) of ammonites and belemnites is a common proxy for Jurassic and Cretaceous sea temperatures. The challenges and uncertainties associated with cephalopod δ18O and other proxy based paleotemperature reconstructions make cephalopods such as ammonites and belemnites a favourable target for carbonate clumped isotope paleothermometry. Our measurements of the clumped isotopic composition of modern cephalopods (Nautilus pompilius, Nautilus macromphalus, Nautilus belauensis and Sepia officianalis), however, confirm significant “vital effects” in clumped isotopic of cephalopod aragonite.We present the first intra-shell measurements of clumped isotopic composition of nautilus demonstrating that clumped isotope composition (∆47) is correlated with δ18O shell carbonate. We observe a decrease in ∆47 from juvenile to adult septa, which does not correspond with changes in surface seawater temperature or temperature variation on vertical migration of the nautilus within the water column. The clumped isotope composition of juvenile septa yield temperatures that are within error of growth temperature while most recently formed septa reflect growth temperatures 3–8 °C above the upper temperature limit of survival of the organism (27 °C). Non-equilibrium effects observed in the ∆47 of modern nautilus comprise up to a 29 °C overestimate in shell formation temperature.Combined δ18O and ∆47 measurements are used to differentiate between potential mechanisms that may generate non-equilibrium signatures observed. Non-equilibrium clumped isotope signatures may result from variations in the salinity of cameral fluid within nautilus chambers, dehydration of HCO3− and/or isotopic fractionation during CO2 diffusion across cell walls. The inter-skeletally variable non-equilibrium offsets in ∆47 of nautili aragonite observed in this study suggest that care must be taken when using the clumped isotope composition of cephalopod carbonate, in particular ammonite aragonite, as a paleotemperature proxy. Belemnite calcite and ontogenetically early septa of aragonitic ammonites may be feasible targets for paleotemperature reconstruction by carbonate clumped isotope thermometry.

A Data-Driven Predictive Machine Learning Model for Efficiently Storing Temperature-Sensitive Medical Products, Such as Vaccines: Case Study: Pharmacies in Rwanda.

Temperature control is the key element during medicine storage. Pharmacies sell some medical products which are kept in fridges. The opening and closing of the fridge while taking some medicine makes the outside hot air enter the fridge, which will increase the inner fridge temperature. When the frequency of opening and closing of the fridge is increased, the temperature may go beyond the allowed storage temperature range. In this paper, we are proposing a model with the help of machine learning that will be used in multiple chambers fridges to keep indicating the time remaining for the inner temperature to go beyond the allowed range, and if the time is short, the system will propose to the pharmacist not to open that particular room and proposes a room that has enough time slots (time to reach the upper limit temperature). By using training data got from a thermoelectric cooler-based fridge, we constructed a multiple linear regression model that can predict the required time for a given room to reach the cut-off temperature in case that room is opened. The built model was evaluated using the coefficient of determination R2 and is found to be 77%, and then it can be used to develop a multiple room smart fridge for efficiently storing highly sensitive medical products.

Survey of subrange inconsistency of long-stem standard platinum resistance thermometers

The subrange inconsistency (SRI) of a large ensemble of long-stem standard platinum resistance thermometers (SPRTs), representative of worldwide production, has been investigated for all pairs of ITS-90 overlapping subranges between 83.8058 K and 933.473 K. The results are reported in terms of various statistical parameters to facilitate their comparison with the results of different authors, although a statistical test, applied to one specific pair of subranges, supported a Gaussian distribution of the results and justified the subsequent use of the mean and standard deviation as statistical parameters. Depending on the pair of overlapping subranges, the mean SRI as calculated varied from −1.23 mK to +0.21 mK and the SRI standard deviation varied from 0.04 mK to 0.62 mK. These numbers generally increased with the upper temperature limit of the pair of subranges, especially where the lower subrange requires a point which is not included in the upper subrange. The contribution to SRI from the fixed-point uncertainty propagation (PoU) was evaluated. The results showed that, although the effect of PoU on SRI largely cancels out for points common to both subranges, PoU still amounts to 59% to 130% of the differences between overlapping pairs of subranges. This means that the differences as calculated are probably a substantial overestimate of the true SRI. It is suggested that this effect is taken into account in making recommendations for typical uncertainties due to non-uniqueness.

OBTAINING AND PROPERTIES OF COMPOSITIONS OF UREA GREASES AND THEIR COMPONENTS ON THE BASIS OF VEGETABLE OILS

Background. In recent years, requirements for the properties of lubricants and their components are increasing. Attention is paid to the impact of lubricants on the environment. Urea greases fully meet the high requirements for the properties of lubricants. The development of greases of this class and vegetable oil-based additives should solve the environmental problems of their use. Objective. The purpose of the paper is development of urea greases and their components using raw materials of plant origin. Methods. A number of protective additives to lubricants were obtained by epoxidation of vegetable oils and introduction of nitrogen-containing fragments on the carbonyl group and epoxy ring. Amidation of triacylglycerides of vegetable oils with ethylenediamine synthesized monoaminoamides of fatty acids of linear structure. Urea thixotropic systems are synthesized by the interaction of polyisocyanate with fatty acid monoaminoamides in petroleum oil. Synthesized additives in various quantities were introduced into the composition of the investigated products in order to check the operational properties of the finished greases. Results. The obtained greases are characterized by a high level of mechanical and colloidal stability. Their composition and chemical structure were established by a set of spectrometric methods of analysis. The upper temperature limit of application of the synthesized urea in the range of 150–200 °С is established by the method of derivatographic analysis. It is established that the combination of urea thickener and vegetable oil-based additives allows obtaining urea greases with high thermal stability, improved protective and antioxidant characteristics. The use of environmentally friendly oleochemical products in the composition of the thickener and lubricant additives improves the biodegradability of the developed grease composition. Conclusions. It is shown that the proposed series of vegetable oil transformations allows obtaining ready-made compositions of urea greases and their components using raw materials of natural origin. The obtained products have satisfactory operational properties and according to some indicators industrial analogues prevail. This allows us to recommend the developed urea oils as substitutes for commercial products.

Investigation of the parameters of carbon nanotube growth on zirconium diboride supported Ni catalyst via CVD

Carbon nanotubes (CNTs) were synthesized on zirconium diboride (ZrB2) through CVD using a Ni catalyst. The influences of the synthesis temperature, time and catalyst amount on the quality and quantity of grown CNTs were studied. The catalyst content determined the temperature at which the CNTs began to grow. When the Ni catalyst content was low, the temperature at which the CNTs began to grow should be higher, and was 1050 °C for 5 wt% Ni content, but was 950 °C for 15 wt% Ni content. Meanwhile, agglomeration of metal atoms was observed if the synthesis temperature was increased until reaching the upper limit temperature for CNT synthesis, which was 1100 °C for 5 wt% and 10 wt% Ni content, but was 1000 °C for 15 wt% Ni content. Increased Ni catalyst content also led to higher catalytic activity as long as the Ni catalyst content did not exceed 15 wt%. Meanwhile, prolonged synthesis time extended the reaction time for the decomposition of C2H2, but resulted in the agglomeration of carbon atoms when the synthesis time was 150 min. The results showed that the uniform distribution of CNTs can be obtained in ZrB2 powder and there was no reaction between ZrB2 and Ni catalyst. The suitable synthesis conditions for obtained uniform size of CNTs grown with a higher degree of graphitization on ZrB2 that identified in this work were: Ni catalyst content of 10 wt%, synthesis temperature of 1050 °C, and synthesis time of 120 min.

Superconducting fluctuations above T c in (Li1− x Fe x )OHFeSe single crystal

The magnetization and resistivity measurements have been done to investigate the superconducting fluctuations effect above the superconducting transition temperature (T c) in (Li1−x Fe x )OHFeSe single crystal. These measurements were performed with applying the external magnetic fields in the ab plane of (Li1−x Fe x )OHFeSe single crystal. By analyzing the diamagnetism response and excess conductivity, the behavior of superconducting fluctuations in the normal state is studied. The upper limit temperature of superconducting fluctuation is determined to be around 1.2 times larger than T c, suggesting that the superconducting fluctuation of (Li1−x Fe x )OHFeSe is a large one. This exceeding value is obviously higher than the conventional superconductors. In addition, the superconductivity of (Li1−x Fe x )OHFeSe coexists with the magnetism rooted in the (Li, Fe)OH layer and induced by magnetic field at low temperature.