Preparation of a CeO2–ZrO2 based nano-composite with enhanced thermal stability by a novel chelating precipitation method

In this study, a chelating agent is introduced to prepare CeO₂–ZrO₂ nano-composite through a precipitation process. The physicochemical properties of the oxide precursors, nano composite materials are strongly dependent on the preparation method and whether a chelating agent is used. Adding an appropriate quantity of chelating agent SO₄²⁻ can facilitate thermal stability and phase structure uniformity of CeO₂–ZrO₂ mixed oxides. The calculation results showed that the Gibbs free energy of chelating complex of [ZrSO₄]²⁺ (ΔG = −127.2469 kJ/mol) is higher than the [Ce(III)SO₄]⁺ (ΔG = -29.8279 kJ/mol). The precipitation chemical potential of Zr⁴⁺ moves close to the precipitation chemical potential of Ce³⁺. The novel and low-cost chelating precipitation method can modify the homogeneity of the compounds at the atomic scale, which can offer a powerful opportunity for, and provide direction in, the design of materials with exceptional properties.     

Thermal stability of CVI and MI SiC/SiC composites with Hi-Nicalon™-S fibers

The influence of high-temperature argon heat-treatment on the microstructure and room- temperature in-plane tensile properties of 2D woven CVI and 2D unidirectional MI SiC/SiC composites with Hi-Nicalon?-S SiC fibers was investigated. The 2D woven CVI SiC/SiC composites were heat-treated between 1200 and 1600 °C for 1- and 100-hr, and the 2D unidirectional MI SiC/SiC composites between 1315 and 1400 °C for up to 2000 hr. In addition, the influence of temperature on fast fracture tensile strengths of these composites was also measured in air. Both composites exhibited different degradation behaviors. In 2D woven CVI SiC/SiC composites, the CVI BN interface coating reacted with Hi-Nicalon?-S SiC fibers causing a loss in fast fracture ultimate tensile strengths between 1200 and 1600 °C as well as after 100-hr isothermal heat treatment at temperatures > 1100 °C. In contrast, 2D unidirectional MI SiC/SiC composites showed no significant loss in in-plane tensile properties after the fast fracture tensile tests at 1315 °C. However, after isothermal exposure conditions from 1315° to 1400°C, the in-plane proportional limit stress decreased, and the ultimate tensile fracture strain increased with an increase in exposure time. The mechanisms of strength degradation in both composites are discussed.     

Thermal analysis of a diesel engine operating with diesel–biodiesel blends

In this paper we study the transient heat conduction in a piston of a diesel engine, subjected to a periodic boundary condition on the surface in contact with the combustion gases. The heat transfer coefficient at the top surface was modeled taking into account the temperature and pressure inside the combustion chamber. Such instantaneous pressure was measured using a special probe for an engine operating with several blends of diesel and biodiesel, and the temperature was obtained through a First Law analysis. The physical properties, including the cetane number were evaluated experimentally for all diesel/biodiesel blends used in this work. An elliptic scheme of numerical grid generation was used, so that the irregular shaped piston in the physical domain was transformed into a cylinder in a computational domain. The timewise variations of the temperature of several points in the piston were examined for different piston materials and various load conditions.     

Preparation of SiO2–SiC composites with a precursor method

SiO₂–SiC composite particles were prepared through a hybrid sol–gel precursor process. Compacts were prepared by using a conventional sintering process. The techniques of DSC–TG, SEM and XRD were use to characterize the composite particles and the sintered compacts. It was found that a core–shell structure was constructed in the composite particles with cores of SiC and shells of amorphous SiO₂. Nucleation of SiO₂ occurred at about 1200 °C. The optimized sintering temperature for 30SiO₂–70SiC (vol.%) composites was about 1400 °C with a relatively homogeneous microstructure. The maximum density was about 2.03 g cm^?3.     

Filtering surface water with a polyurethane-based hollow fiber membrane: effects of operating pressure on membrane fouling

Membrane fouling seriously restricts applications of membrane technology. A novel strategy was ap-plied in this study to retard membrane fouling by changing operating pressure with the pressure responsibility membrane. A polyurethane-based hollow fiber membrane was used to treat surface water for evaluating the effect of operating pressure on membrane fouling. Some bench-scale tests in dead-end mode were carried out. In the experi-ments without backwashing, as operating pressure increased, severe membrane fouling occurred on membrane sur-face, while the permeate quality was improved obviously, which is considered to be due to shrinkage deformation. The total resistance, irreversible resistance and reversible resistance under different backwash pressures were de-termined in filtration/backwashing test. With the increase of backwash pressure, the total resistance decreased, and more importantly, the irreversible resistance also decreased, which implies that small particles deposited inside membrane pores and cake layers on membrane surface are effectively removed. Similar results could be obtained in mass balance tests. The results of the present study indicate that the application of pressure responsibility membrane in surface water treatment may be an effective strategy for reducing membrane fouling.     

Evaluation of insect residue resistant coatings – Correlation of a screening method with a conventional assessment technique

Laminar flow technologies such as laminar flow control (LFC) and hybrid laminar flow control (HLFC) are drag reduction techniques that allow the stabilization of the boundary layer and therefore permit an extended region of laminar flow to be achieved. The laminar flow region is, however, easily disturbed by surface contamination caused by insect debris, ice or dust particles. This causes a transition of the flow, and results in a turbulent boundary layer. Mitigation of surface contamination through the use of low surface energy coatings is thus of great interest. In this paper, the use of a screening method (utilizing a wet abrasion scrub test) to determine the effectiveness of candidate coatings against insect contamination has been employed. The method was compared to a conventional assessment technique, namely an insect delivery device. It was demonstrated that both approaches have merit; both methods provide useful means of directly quantifying the adhesion of insect debris to aircraft wing surfaces. An analogue, which can be used as a substitute to live insect testing, was also evaluated. The effect of humidity and water on the adhesive properties of insect haemolymph has been investigated.     

Effect of corona discharge on the stability of the adhesion of thin silicone-organic coating to polyamide fiber surface made by the sol–gel method

This paper presents the effect of pretreatment of polyamide (PA6) nonwoven with corona discharge on the stability of the adhesion of thin hydrophobic silicone-organic coating based on vinyltriethoxysilane, made by the sol–gel method. This pretreatment with corona discharge causes a change in the physicochemical properties of the PA6 fiber surface. These changes include, among others, an increase in the fiber surface roughness, wettability, and surface free energy. At the same time, XPS and EDS investigations have shown an increase in the degree of oxidation and the formation of functional polar groups on the fiber surface (C–O–, C–OH, and O=C–O–). As a result of the changes in the surface properties of pretreated PA6 fibers, a higher degree of the sol deposition was obtained compared with that for untreated nonwoven surface. The assessment of the stability of the adhesion of thin hydrophobic coating to the fiber surface was carried out on the basis of changes in the content of silica deposited on fibers and the kinetics of water contact angle after washing and abrasion processes. In the end, the PA6 nonwoven, pretreated with corona discharge, shows a higher stability of the adherence of the thin silicone-organic coating and a higher degree of hydrophobicity than the untreated nonwoven.     

WGS activity of a novel Cu–ZrO2 catalyst prepared by a reflux method. Comparison with a conventional impregnation method

The activity in the WGS reaction of Cu/ZrO₂ catalysts prepared by a method of refluxing in an aqueous NH₄OH solution is studied. It is shown that at 3% Cu load the methods of impregnation over monoclinic or tetragonal ZrO₂ do not produce active catalysts for the WGS reaction. However, the method of refluxing generates highly active catalysts with Cu loads of 3% (w/w) or higher. The activity of the catalysts prepared by refluxing is associated with the formation of small Cu clusters, which would allow the regrouping of the H atoms to generate molecular H₂ in the presence of the crystalline tetragonal ZrO₂.     

Thermal batteries with ceramic felt separators – Part 1: Wetting,loading behavior and chemical stability

The use of a thermally and chemically stable ceramic felt separator for thermal batteries is believed to enhance the reliability by minimizing the sudden failure of an electrolyte upon shock compared to the conventional pellet-pressed one. To achieve desirable electrochemical properties for applications in thermal batteries, the separator should hold a sufficient amount of molten electrolyte with a minimal leakage to prevent physical contact between the cathode and anode. In addition, the chemical stability of the separator materials should be maintained under a very reactive molten Li-salt electrolyte environment to confer high ionic conductivity and reliability. To assess the feasibility of 3 types of ceramic felt as a separator for thermal batteries, 2 types of Al₂O₃ felt with different porosity and one ZrO₂ felt are examined using binary LiCl-KCl and ternary LiF-LiCl-LiBr as the electrolytes. This Part 1 explains the wetting, loading and leakage behaviors of the ceramic felts for molten electrolytes along with the chemical stability. The ionic conductivity of the electrolytes and electrochemical properties of the resulting thermal batteries will be presented in Part 2.     

Thermoanalytical evaluation of the thermal stability of petroleum distillates: Distillates with a boiling range of 250–425 °C

The thermal stabilities of petroleum distillates with boiling point (b.p.) in the range 250–425 °C produced from a medium Iraqi crude oil were evaluated using different thermoanalytical techniques: differential scanning calorimetry; thermogravimetry; and differential thermogravimetry. Results obtained from these methods were correlated with some of the physico-chemical properties of the distillates studied. It was shown by differential scanning calorimetry that the stability of the distillates increased with increase in their total aromatic constituents, but was not related to the total content of sulphur compounds present. Thermogravimetry indicated that the thermal stabilities of the distillates increased with increase in their corresponding average molecular weights.     

Application of ATR–FTIR spectroscopy combined with sputter etching for depth profiling of a chemical additive within a pulp fiber

Attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy in combination with the sputter etching technique was applied to the determination of the depth distribution of a chemical additive within a pulp fiber. After etching successively, the surface additive content was determined by ATR–FTIR spectroscopy. Sputter etching until 5 min was homogeneous and proportional to obtain precise depth profile. From the relationship between etching time and the thickness of removed surface layer, it is possible to follow the partial concentration profiles of the additive as a function of distance from the original surface. The obtained profile is compared qualitatively with that of variable-angle ATR–FTIR depth profiling method. The profile shows that most of the additive is located at the fiber surface; however, some of it is broadly distributed toward the inside of the fiber. The present method can be used to clarify the distribution of other paper additives within a pulp fiber, and, moreover, it can be applied to depth profiling of a minor component within a solid material. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 461–468, 1998     

Thermal pyrolysis and kinetic analysis of a ZnxCo1−x ZiF-8 metal–organic framework for recent applications

Zeolitic imidazolate frameworks (ZIFs) are interesting materials for use in several aspects: energy storage material, gas sensing, and photocatalysis. The thermal stability and pyrolysis process are crucial to determine the active phase of the material. A deep understanding of the pyrolysis mechanism is in demand. So, the thermodynamics and combustion process with different heating rates were examined, and the kinetic parameters were computed employing thermogravimetric tests. Based on the TG analysis of combustion, pyrolysis moves to the high-temperature region with an increase in heating rate. The decomposition process can be separated into dehydration (300–503 K) and pyrolysis reaction (703–1100 K). Three points of the decomposition process are performed by dynamical analysis owing to shifts of slopes, but the combustion process has only one stage. Dynamical parameters, for instance, the possible mechanism, the pre-exponential factor, and the apparent activation energy were obtained through comparison using the Kissinger formula. The thermodynamics analysis of the Zn_1?xCo_x ZIF-8 materials is an effective way to explore the temperature influence on the process of pyrolysis, which can benefit in several recent applications.

     

Fabrication of adsorbents with enhanced CuⅠ stability: Creating a superhydrophobic microenvironment through grafting octadecylamine

In atmospheric conditions, Cu^Ⅰ is easily oxidized to Cu^Ⅱ due to the coexistence of moisture and oxygen.The poor oxidation inhibition of Cu^Ⅰ restricts the practical application of Cu^Ⅰ -containing materials.Herein we introduce an approach to construct a superhydrophobic microenvironment in Cu^Ⅰ functionalized metal–organic frameworks by coordinatedly grafting organic amine compounds onto open metal sites(OMSs), which can hinder the accessibilit...     

Improving the interfacial properties of carbon fiber–epoxy resin composites with a graphene-modified sizing agent

We successfully prepared a graphene-modified carbon fiber (CF) sizing agent with good dispersity and stability by dispersing reduced graphene oxide (RGO) into an emulsion-type sizing agent. RGO was obtained by the reduction of graphene oxide (GO) with the help of gallic acid. The influence of the graphene-modified sizing agent on the interfacial properties of the CF–epoxy resin composites was investigated with microbond testing and the three-point bending method. The results show that optimized interfacial properties were achieved when the size of the modified graphene was less than 1 μm, the content of RGO was 20 ppm, and the pH value of the sizing agent was 10.5. The interfacial shear strength of the composites reached 92.3 MPa, which was 29.6% higher than that of the composites with unmodified CFs. Compared with commercial-CF-fabric-reinforced composites, the interlaminar shear strength of the composites treated with the RGO-modified sizing agent increased by 21.5%. Both the interfacial and interlaminar failure morphologies of the composites were examined with scanning electron microscopy (SEM). The results show that a large amount of residual resin adhered to the surfaces of the CFs treated with the RGO-modified sizing agent; this indicated good interfacial properties between the CFs and the resin matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47122.     

Gasification of Brazilian coal-chars with CO2: effect of samples’ properties on reactivity and kinetic modeling

The gasification of coals obtained from important coalfields in Brazil was investigated in 1.0?bar of CO₂ using a thermogravimetric analyzer. Tests were carried out in two sequential steps: pyrolysis under N₂ at 1213 K and isothermal gasification under CO₂ in the temperature range of 1113–1213 K. The kinetic study was performed in the kinetically controlled regime and three gas-solid models were fitted to the experimental data. According to the results, subbituminous coal-chars presented higher reactivities than bituminous types, with maceral and ash compositions playing a key role in the overall process. The reaction rates increased with increasing temperature, with maximum values found in the conversion range of 10–60%. The random pore model that predicts a maximum point of reactivity over the reaction course suitably described the gasification kinetics. Values of activation energy between 146.63(±0.03) kJ/mol and 215.09(±0.05) kJ/mol were found, which are consistent to literature data of coals gasified worldwide. Despite the relatively high ash content (32–45%), the Brazilian coals appeared to be sufficiently reactive to be gasified, thus indicating the significance of this study to the development of gasification process in Brazil.     

Thermal Decomposition of Potassium Titanium Hexacyanoferrate（Ⅱ） Loaded with Cesium in a Fixed Bed Calciner

The thermal decomposition of potassium titanium hexacyanoferrate（ Ⅱ ） （KTiFC） loaded with cesium （referred to as Used Exchanger,or UE） was-studied at different flow rate of air in a fixed bed calciner. The calcina t ign processconsisted of four stages：ambient temperature- 180℃ （stageⅠ ）, 180-250℃（stage Ⅱ）, 250-400℃ （stage Ⅲ）, and constant 400℃ （stage Ⅳ）.The most intense reaction occurred in stage .Ⅱ. The rate of thermal decomposition was controlled, depending on the O2 flux, by O2 or CN concentration in ditterent stages. Results from differential thermal analysis （DTA） showed that the calcination reaction of the anhydrous UE was exothermic, with an approximate heat output of 4.6kJ·g^-1, which was so large to cause the possible agglomeration of calcined residues. The agglomeration could be avoided by enhancing heat transfer and controlling the O2 flux. It was found that there was no cyanides in the calcined residues and no CN-bearing gases such as HCN and （CN）2 in the off-gas. It seemed that the catalytic oxidation furnace behind the fixed bed calciner could be cancelled.     

Synthesis of a novel lipopeptide with α-melanocyte-stimulating hormone peptide ligand and its effect on liposome stability

Introduction of liposomes into target cells is important for drug delivery systems. For this purpose, the surface of the liposome is equipped with ligand peptides, which may bind to specific receptors on the cell membrane. An artificial novel lipopeptide (MSH-C4A2) containing the α-melanocyte-stimulating hormone (α-MSH) sequence and two long alkyl chains was designed and synthesized, and the liposome, composed of egg phosphatidylcholine (EPC) and MSH-C4A2, was prepared. The stability of the liposome was estimated by measuring calcein leakage from the liposome inner phase. The stability of the liposome decreased upon addition of MSH-A4C2, which seemed to be attributable to the amphiphilic property of the peptide moiety (α-MSH) of MSH-A2C4. The stability was, however, recovered fairly well upon addition of cholesterol (Ch) or phosphatidylglycerol (PG). It was concluded therefore that the ternary system, MSH-C4A2/Ch/EPC or MSH-C4A2/PG/EPC, is suitable for preparing the functional liposome.     

Thermal Conductivity of a Glass: I. Measurement by the Glass–Metal Contact

The thermal (phonon) conductivity of glass has been measured by contacting the sample with a metal at a different uniform initial temperature. The subsequent temperature response in the metal is measured by a tiny thermocouple just underneath the (contact) surface. The coefficient of heat penetration c _p follows directly from the fitted asymptotic temperature jump or drop for long times. Division by the separately measured heat capacity c _p yields the thermal conductivity . The conductivity measurement reproducibility was = 3%. The standard deviation between validation measurements and round robin test results on Pyrex glass was = 5.8%, somewhat more than the accuracy = 5.2% of the round robin test results. The measurement method is insensible for slight imperfections of the thermal contact and infrared radiation diffusion (photon conductivity) in a hot glass. The method has been used with minor modifications for solid and molten samples at temperatures of 50–850°C and conductivities of 0.1–25 W/(m K). The thermal (phonon) conductivity of the investigated soda-lime silicate glasses increases slightly (27–30%) with temperature from ambient up to around the glass transition.     

Thermal stability of NO 2 ⋅ and NO⋅ radicals formed in an Al23 catalyst during its preparation from a nitrate precursor

During the preparation of alumina as a catalyst support from aluminium nitrates by precipitation with a NH₄OH base, NO ₂ ^⋅ radicals have been formed in the catalyst after calcination under air in the solid at different temperatures. These radicals remained stable until a calcination temperature of 800°C. When the calcined catalyst was degassed under vacuum above 300 °C, the NO ₂ ^⋅ was reduced to give NO^⋅ and O^- species which were both tightly trapped in the solid. These latter species remained stable until vacuum treatment at 800 °C. This revised version was published online in July 2006 with corrections to the Cover Date.