Oxidation behavior of U-10 at% Zr alloy in air at 300–500 ‡c

The oxidation behavior of U-10 at% Zr alloy was studied using an X-Ray Diffractometer (XRD) and a thermogravimetric analyzer in the temperature range from 300 to 500 ‡C in air. From XRD, Infrared Spectroscopy (IR) and chemical analysis studies it was found that U-Zr alloy after complete oxidation was converted to U₃O₈ and ZrO₂ broken into several pieces of thin plates and some blocks. From the slope value (l/n=0.562-0.872) of the log-log plots of the weight gain against time, the oxidation kinetics was analyzed by a paralinear equation. The activation energy of 20 % conversion of U-Zr alloy to U₃O₈ and ZrO₂ was 57.02 kJ/mol and the oxidation rate per unit time and area was obtained to be :

Adsorption Behavior of Trimethylolpropane-Dehydroabietic Acid Ester at the Air–water Interface

A novel amphipathic trimethylolpropane-dehydroabietic acid ester was successfully prepared with acyl chloride method. Various analytical techniques such as liquid chromatography–mass spectrometry, Fourier transform infrared spectrometry, proton and carbon nuclear magnetic resonance spectroscopy were employed to evaluate the chemical structure of the ester. The surface properties of the ester were investigated by surface tension and resonance light-scattering techniques. The surfactant molecules are adsorbed at the water–air interface in different adsorption states, i.e., state 1 and 2. The dynamic adsorption behavior was studied by combining experimental results and a reorientation model. The molar fraction of solvent decreased, while the molar fraction of surfactant molecules increased with increasing ester concentration at the surface layer. The adsorption value of state 1 presented a unimodal shape and the adsorption value of state 2 presented an s-shape with the increase in surface pressure. The free energy of adsorption is ?36.06 kJ mol^?1, more negative than the free energy of micellization (?29.69 kJ mol^?1), it is actually easier for surfactant molecules to adsorb on the air–water interface.     

Investigation on hydrate growth at the oil–water interface: In the presence of asphaltene

Natural gas hydrates can readily form in deep-water oil production processes and pose a great threat to the oil industry. Moreover, the coexistence of hydrate and asphaltene can result in more severe challenges to subsea flow assurance. In order to study the effects of asphaltene on hydrate growth at the oil–water interface, a series of micro-experiments were conducted in a self-made reactor, where hydrates nucleated and grew on the surface of a water droplet immersed in asphaltene-containing oil. Based on the micro-observations, the shape and growth rate of the hydrate shell formed at the oil–water interface were mainly investigated and the effects of asphaltene on hydrate growth were analyzed. According to the experimental results, the shape of the water droplet and the interfacial area changed significantly after the formation of the hydrate shell when the asphaltene concentration was higher than a certain value. A mechanism related to the reduction of the interfacial tension caused by the absorption of asphaltenes on the interface was proposed for illustration. Moreover, the growth rate of the hydrate shell decreased significantly with the increasing asphaltene concentration under experimental conditions. The conclusions of this paper could provide preliminary insight how asphaltene affect hydrate growth at the oil–water interface.     

Thermodynamic parameters of amitriptyline hydrochloride–additives at cloud point: effects of the ethanol–water mixed media

Abstract

Addition of organic solvents is known to change the properties of amphiphiles through modification of bulk phase. Amitriptyline hydrochloride (AMT) is a tricyclic amphiphilic drug which is usually used as an antidepressant. In drug delivery, the cloud point (CP) of the drug is an important parameter. This article discusses the effects of ethanol–water (EtOH–WR) compositions on the energetic parameters, such as changes in Gibbs energy of clouding (Δ_sG⁰), enthalpy of clouding (Δ_sH⁰), and entropy of clouding (TΔ_sS⁰) of AMT-additive systems. Monovalent alkali halide salts, cationic conventional surfactants, and gemini surfactants were used as additives in the EtOH–WR mixed media whose compositions were varied between 0 and 15% (w/w). The Δ_sG⁰ values are positive for all the additives and the values decrease with the rise in mole fractions of the additives. The Δ_sH⁰ and TΔ_sS⁰ were noted to be positive except for KF in 15% EtOH–WR mixed media.     

Role of microstructure in the grinding and polishing of α-sialon ceramics

The grinding and polishing behaviour of three tailored α-sialon microstructures made of the same chemical composition: fine-grained, bimodal and large elongated-grained, were determined. The fine-grained microstructure was characterised by extensive lateral cracks in the grinding process and widespread grain pullout during the mechanical polishing; in contrast, the large elongated-grained microstructure exhibited high grinding damage resistance, and a defect-free, mirror-like surface after mechanical polishing. The bimodal microstructure showed an intermediate behaviour during both processes. The material removal mechanisms during grinding and polishing were analysed and modelled as a function of grain size and aspect ratio.     

Evolution mechanism of the microstructure and mechanical properties of plasma-sprayed yttria-stabilized hafnia thermal barrier coating at 1400 °C

Yttria stabilized hafnia (Hf_0.84Y_0.16O_1.92, YSH16) coatings were sprayed by atmospheric plasma spraying (APS). The effects of thermal aging at 1400 °C on the microstructures, mechanical properties and thermal conductivity of the coatings were studied. The results show that the as-sprayed coating was composed of the cubic phase, and the nano-sized monoclinic (M) phase was precipitated in the annealed coating. The presence of M phase effectively constrained the sintering of the coating due to its superior sintering-resistance. The Young's modulus kept at a nearly same level of ~78 GPa even after annealing, and the coating annealed for 6 h yielded a maximum value of hardness but revealed a declining tendency in the Vicker's hardness with prolonged sintering time. The thermal conductivity increased from 0.8-0.95 W m^-1 K^-1 at as-sprayed state to 1.6 W m^-1 K^-1 after annealing at 1400 °C for 96 h. The dual-phase coating is promising to serve at temperatures above 1400 °C due to its excellent thermal stability and mechanical properties.     

Investigation on the microstructure of self-reinforced Nd-α-sialon ceramics

α-Sialon ceramics doped with Nd₂O₃ were prepared by hot-pressing sintering at 1900 °C holding for 1 h with a heat preservation for 1 h at 1500 °C. Microscopic observations indicate that elongated α-sialon grains appear and are embedded in the fine equiaxed-grain matrix. A small amount of β-sialon phases and secondary crystallized phases M′ (Nd₂Si_3−xAl_xO_3+xN_4−x) also exist in the Nd-α-sialon ceramic. A core/shell structure can be found in the elongated α-sialon and β-sialon grains with a high aspect ratio, in which some misfit dislocations surround the core. The 21R AlN-polytype was observed by transmission electron microscopy (TEM), which could not be detected by X-ray diffraction (XRD) due to its trace amount. Different nucleation and growth modes of sialon grains were also discussed.     

First-principles calculations of the effects of the interface microstructure on the wettability of a Cu–Ti/AlN system

The active element Ti is always added to Cu-, Ag-, or Sn-based fillers used to join ceramics, because it promotes the wetting of the fillers on ceramics. However, different mechanisms have been proposed on the mode of action of the active element Ti in promoting the wetting of the filler alloy. In this study, in order to gain a better understanding of the two controversial wetting mechanisms, which are based on adsorption and interfacial reaction, density functional theory (DFT) calculations were performed to investigate the role of the active element on the interfacial properties of the Cu–Ti/AlN wetting system. The following three typical wetting interface models were constructed: (1) the original interface of Cu/AlN, (2) adsorption interface of Cu/AlN(Ti), and (3) reaction interface of Cu/TiN. First, according to the convergence of the surface energy, a four-atom-layer Cu (111) slab, an eight-atom-layer AlN (001) slab, and a five-atom-layer TiN (001) slab were used to represent the Cu bulk, AlN bulk, and TiN bulk, respectively. Then, interface models were constructed and the work of adhesion, Bader charges, differential charge density, and density of states were analyzed, and the theoretical contact angles were calculated. The results indicate that both the adsorption of Ti at the interface and its reaction with AlN to form a TiN layer remarkably improve the wetting of Cu on AlN, and the contact angle decreased from 173° to 74° and then to 119°. This study constitutes a modest step toward clarifying the wetting mechanism of Ti-added active fillers on ceramics.     

Clarifying the effect of sintering conditions on the microstructure and mechanical properties of β-tricalcium phosphate

The effect of the sintering conditions (temperature and time) on the microstructure (density and grain size) and mechanical properties (hardness, elastic modulus, and strength) of β-tricalcium phosphate (β-TCP) bioceramics fabricated from Ca-deficient commercial powders is analyzed. Contrary to current general opinion, it is demonstrated that the optimal sintering temperature to maximize the mechanical performance of this β-TCP material is not necessarily below the β ? α transformation temperature (1125 °C). In particular, optimal performance was achieved in samples sintered at 1200 °C for 3 h, since it was not until higher temperatures or longer sintering times that microcracking develops and mechanical properties are degraded. It is argued that the residual stresses developed during this reversible transformation do not lead to microcrack propagation until sufficiently large starting flaws develop in the microstructure as a consequence of grain growth. Implications of these findings for the processing routes to improve sintering of this important bioceramic are discussed.     

Assessment of early age properties of cementitious system through isopropanol–water replacement in the mixing water

In this study, a new method to assess early properties of cementitious materials by water-solvent replacement is investigated. Isopropanol was used to replace a part of mixing water of binder paste, limiting the maximum degree of hydration it can achieve. Results of four independent methods (calorimetry, thermo-gravimetric analysis, back-scattered electron imaging and mechanical strength) confirmed that the hydration reactions of the cement have been effectively delayed and suppressed due to the presence of isopropanol. A set of curves is obtained to identify the appropriate combination of i) the extent of water–isopropanol replacement and ii) time for achieving the targeted degree of hydration. This allows assessing material properties at low and/or desired degree of hydration with less time limitation during sample manipulation, achieving a better preserved and homogeneous microstructure. It has however to be noted that this method has limits with respect to direct moisture-transport related studies.     

Hydration of calcium aluminates at 60°C – Development paths of C2AHx in dependence on the content of free water

The influence of water loss during the hydration of calcium aluminates on the phase development is investigated at 60°C. This is relevant for applications in which calcium aluminate cement (CAC) based formulations are exposed to quick drying during hydration. The presented results provide new insights into the well-known conversion processes occurring in CAC pastes. Using in situ XRD two different routes of the development of initially formed C₂AH₈ are determined: (a) transformation to C₃AH₆ + AH₃ in the presence of sufficient free water and (b) dehydration to C₂AH₅ at a lack of free water. Moreover, the influence of precuring of the pastes at 23°C before heating to 60°C is investigated. The increasing loss of free water with increasing precuring time resulting from both, precipitation of hydrate phases and evaporation, causes incomplete hydration of CA or CA₂ as well as dehydration of C₂AH₈ instead of conversion into C₃AH₆. Comparative investigations of sealed samples always revealed complete hydration of CA and CA₂ as well as complete conversion of C₂AH₈.     

Aggregation behavior of a polystyrene–b-poly(phenylsilsesquioxane) H-type copolymer at the air/water interface

A comprehensive Langmuir film balance/atomic force microscope study of the surface aggregation behavior of an H-type block copolymer having four branches of polystyrene (PS) blocks (number average molar mass (M_n) = 5000 Da per each branch) and poly(phenylsilsesquioxane) (PPSQ) (M_n = 40,000 Da) has been performed. Temperature dependent surface pressure isotherms and hysteresis experiments were combined with molecules aggregation number per surface micelle, leading to a self-consistent picture of the surface morphology and aggregation phenomena. In spite of the ladder structure of the PPSQ segment, the micelles mostly exist as spherical aggregates because of strong interaction between PS blocks.     

Hydrate formation in oil–water systems: Investigations of the influences of water cut and anti-agglomerant

To investigate the characteristics of hydrate formation in oil–water systems, a high-pressure cell equipped with visual windows was used where a series of hydrate formation experiments were performed from natural gas + diesel oil + water systems at different water cuts and anti-agglomerant concentrations. According to the temperature and pressure profiles in test experiments, the processes of hydrate formation under two kinds of experimental procedures were analyzed first. Then, based on the experimental phenomena observed through the visual windows, the influences of water cut and anti-agglomerant on the places of hydrate formation and distribution, hydrate morphologies and hydrate morphological evolvements were investigated. Hydrate agglomeration, hydrate deposition and hydrate film growth on the wall were observed in experiments. Furthermore, three different mechanisms for hydrate film growth on the wall were identified. In addition, the influences of water cut and anti-agglomerant on the induction time of hydrate formation were also studied.     

Influence of the temperature dependence of the thermophysical properties of coal–water fuel on the conditions and characteristics of ignition

The results of an experimental study and mathematical simulation of the ignition of coal–water fuel (CWF) particles, the main thermophysical characteristics of which (thermal conductivity (λ), heat capacity (C), and density (ρ)) depend on temperature, are reported. Based on the results of the numerical study, the influence of changes in the thermophysical properties upon the heating of the main bed of fuel on the conditions and characteristics of its ignition was analyzed. The ignition delay times (t _i) of CWF particles were determined under the typical furnace conditions of boiler aggregates. As a result of the mathematical simulation of the process of CWF ignition, it was established that the temperature dependence of thermophysical characteristics can exert a considerable effect on the characteristics and conditions of ignition. In this case, it was found that the ignition of coal–water drops is possible under the conditions of their incomplete dehydration. A good agreement of the theoretical ignition delay times of the CWF particles and the experimental values of t _i was established.     

Effect of the fractional composition of the solid components of coal–water fuel on the characteristics of ignition and combustion

The experimental results of studies of the ignition and subsequent combustion processes of the single drops of organic coal–water fuels (OCWFs) arranged on the junction of a quick-response thermocouple (thermal inertia, <1 s) in an atmosphere of heated (600–1000 K) air are presented. The particles of 2B brown coal and D coal, water, and oils of different types (turbine, motor, and transformer oils) were used as the main OCWF components. The effect of the degree of grinding (fineness) of the solid fuel components of OCWFs on the following integral characteristics of the ignition and combustion of prepared fuel compositions was established: the delay times of ignition and complete combustion. A decrease in the delay times of ignition and complete combustion with decreasing the degree of grinding was detected (in a range of 40–200 μm used as an example). The reasons and special features of the influence of this factor on the integral characteristics of the test processes were recognized.     

Emission control in the combustion of coal–water and organic coal–water fuels

Promising methods for decreasing anthropogenic emissions due to the combustion of coals of different ranks and coal–water fuel (CWF) and organic coal–water fuel (OCWF) slurries on their basis are considered. The maximum concentrations of the main anthropogenic emissions of sulfur, nitrogen, and carbon oxides (SO _x , NO _x , and CO _x ) formed upon the combustion of solid fuels in a powdered state and as the components of CWF and OCWF slurries were determined. The concentrations of the most hazardous oxides formed upon the combustion of coals of different ranks (brown and black coals) and CWF and OCWF slurries were compared. The experimental results substantiated the use of CWF and OCWF slurries for emission control in coal-burning power engineering. The addition of a combustible liquid component to a CWF slurry (the production of an OCWF slurry) makes it possible to ensure acceptable environmental and energy characteristics.