Effect Of Heating Mode Research Articles

Self-Assembly of Au Nanoclusters into Helical Ribbons by Manipulating the Flexibility of Capping Ligands.

Self-assembly is a powerful technology to construct nanomaterials with helical structures. However, using metal nanoclusters (NCs) as the building blocks for the construction of helical architectures is still rarely reported. In this paper, Au NC assembled helical ribbons (Au NCHRs) are successfully constructed by using Au NCs as the building blocks. Effects of heating mode, solvent polarity and ligand length on the self-assembly process of Au NCs are discussed. The results indicate that the lengths of overlapped and nonoverlapped ligands between adjacent Au NCs play the dominated role on adjusting the morphologies of the resulting assemblies. Ligands with appropriate overlap can provide sufficient flexibility for the helical assembly of Au NCs without losing the stability. If the length of the overlapped parts is too long, the assemblies are usually rigid without the helical structure. Instead, the overlength of nonoverlapped ligands will boost the flexibility but damage the structural stability of the assemblies. Since everything in the world is assembled by atoms and molecules, recognizing the self-assembly mechanism of NCs may promote our understanding on the bountiful complexity of life and nature.

Effect of Heating Mode on Thermal Stability of Nanocrystalline Hydroxyapatite

This study reports the effect of heating mode on the thermal stability of nanocrystalline hydroxyapatite (HA) by comparing conventional electric resistance heating and microwave heating of HA to 1100°C under the same experimental conditions. It was found that, compared with conventional heating, microwave heating of HA resulted in less hydroxyapatite decomposition and a higher Ca/P molar ratio of the product (1.42 versus 1.37) in association with a smaller lattice contraction of the phase probably caused by the selective thermal effect of microwave radiation. It also produced smaller grains (56.54 nm versus 64.32 nm) along with a higher specific surface area and larger total pore volume, featured by the differences of 36.80% and 79.29%, respectively. Moreover, it led to more homogeneous pore distribution. These physicochemical features are expected to contribute to superior mechanical and biologic properties of the final product.

Effects of Heating Mode and Temperature on the Microstructures, Electrical and Optical Properties of Molybdenum Thin Films.

In this paper, molybdenum (Mo) thin films are deposited on soda-lime glass (SLG) substrates by direct current magnetron sputtering and heated in three different modes at different temperatures, including substrate heating, annealing treatment, and both substrate heating and annealing treatment. The effects of heating temperature and heating mode on the structures, morphology, optical and electrical properties of Mo thin films were systematically investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), atomic force microscope (AFM) and UV-visible spectrophotometer (UV-vis spectra). It is shown that as the substrate and annealing temperature increase, the crystallinity of Mo thin films is improved, and the grain sizes become bigger. Especially in the mode of both substrate heating and annealing treatment at higher temperature, the obtained Mo thin films show higher crystallinity and conductivity. Moreover, with the increase of substrate and annealing temperature in different heating modes, both the surface compactness of Mo films and the optical reflectance increase correspondingly. Furthermore, the Mo film, prepared at the substrate heating temperature of 400 °C and annealed at 400 °C, showed excellent comprehensive performance, and the resistivity is as low as 1.36 × 10−5 Ω·cm. Using this optimized Mo thin film as an electrode, copper indium gallium selenium (CIGS) solar cells have a maximum photo-conversion efficiency of 12.8%.

Effect of Heating Mode on Sinterability of YSZ+CeO2 Ceramics

In the current research work, a comparative study on densification and microstructural evolution of CeO2 particle reinforced 8 mol % yttria stabilized zirconia (YSZ) sintered ceramics has been carried out. The ceramic compacts were fabricated via microwave and conventional sintering methods. The sintering conditions that were used for microwave and conventional methods are 1400 °C for 20 min and 1400 °C for 5 h, respectively. The sintered samples were characterized for densification, microstructural behavior, and hardness. Microwave sintering method of sintering resulted in high sintered densities as compared to the conventional counter parts. Microwave sintered samples exhibited finer grains as compared to conventionally sintered specimens. The grain size of the 8YSZ+CeO2 sintered ceramics was found to decrease with CeO2 addition. The X-ray diffraction (XRD) results showed no phase change because of CeO2 addition. The Vickers hardness was found to increase with increasing amount of CeO2.

The effects of external physical fields on the isothermal kinetics of fullerol formation

The isothermal kinetics of fullerol formation under different heating modes: conventional (CH), ultrasonic (USH) and microwave (MWH) was investigated. The isothermal kinetic curves of fullerol formation at different temperatures (293, 298, 303, 308 and 313 K) were measured. The kinetic model of the reaction was determined on the basis of the shape of the dependencies of reaction rate on fullerene concentration and on method of initial rates. The values of isothermal rate constants under different heating conditions and temperatures and their kinetic parameters were calculated. The effect of heating mode on the values of the kinetic parameters was established. The possibility of an existence of overheating and hot spots on the rate of fullerol formation was evaluated and discussed. The model of impact of USH and MWH on the reaction kinetics that is based on the model of selective energy transfer is suggested. The established effects of USH and MWH on the reaction of fullerol formation are successfully explained by that model.

An investigation on effect of heating mode and temperature on sintering of Fe-P alloys

The present study examines the effect of sintering temperature and heating mode on densification, microstructure and mechanical properties of Fe-P alloys. The green compacts were heated conventionally and in microwave under 95%N2–5%H2 (forming gas) at 1120°C and 1250°C for 60min. Both the compositions (Fe-1.5P and Fe-3P in wt%) were found to couple well in microwave field with rapid heating (~40°Cmin−1) and resulted in reduction of overall processing time by about 90% in comparison of conventional heating. Microwave sintering resulted in higher densification in case of Fe-P alloys. Moreover, an important feature of microwave and conventionally sintered samples was that their microstructures exhibited distinctly rounded pores. This resulted into improved corrosion and mechanical properties in general.

Impact of heating mode in synthesis of monodisperse iron-oxide nanoparticles via oleate decomposition

The present work introduces the optimization of a synthetic procedure for oleate-coated iron-oxide nanoparticles by the thermal decomposition of Fe oleate dried at 30 and 70 °C in high-boiling organic solvents. The attention is focused on the temperature of the thermal decomposition, the nature of organic solvent, heating rate and the mode of the heating. In particular, heating on Wood alloy with simultaneous bubbling of argon through the reaction mixture versus the heating on mantel with magnetic stirring is highlighted as a route to improve the monodispersity of the nanoparticles. The effect of heating mode and rate on the nanoparticles size is estimated. The obtained tendencies point to the heating mode and rate as additional factors affecting the kinetic separation between nucleation and nanoparticle growth processes.

Effect of Microwave and Conventional Heating on Sintering Behavior of Cu-10vol.%SiC Nanocomposites

Effect of heating mode and sintering temperature on sinterability of ex-situ Cu-10vol.%SiC composites was investigated. The Cu and SiC powder mixture were mechanically alloyed for 5 hours at 100 rpm in a planetary ball mill under argon atmosphere. The as-milled powders of Cu-10vol.%SiC were compacted and sintered in conventional tube furnace and microwave furnace at 700°C, 800°C, and 900°C. Microwave reduces the processing time significantly along with higher heating rates when compared to conventional tube furnace. Based on XRD result, the average Cu crystallite size is 80.49 nm after milling and its value remained under 100 nm after sintering. Microwave gave relatively smaller crystallite size than tube furnace. SEM revealed the homogeneous distribution of SiC particles in the Cu matrix in both heating mode. Relatively higher densification parameter was obtained by microwave furnace sintered at 900°C. This temperature was defined as an optimum sintering temperature and microwave sintering was claimed to exhibit much better sinterability than conventional tube furnace sintering.

Effect of heating mode and electrochemical response on austenitic and ferritic stainless steels

Powder metallurgical (P/M) processing has the main advantage of making near net shape products. Nowadays, in automobile industries, stainless steels have become the most promising material owing to their good corrosion resistance. In the current study, 316L and 434L stainless steel powders were sintered using microwave and conventional methods through powder metallurgy route. The effects of sintering modes on the microstructure, mechanical properties and corrosion responses of 316L and 434L stainless steel composites are investigated in detail. The results showed that the sample prepared through microwave sintering route exhibited significantly superior densification, higher hardness and better corrosion resistance as compared to the conventionally processed counterpart. On the whole, 316L composites showed better corrosion resistance than 434L stainless steels.

Kinetic analysis of nicotine desorption from silicon dioxide under non-isothermal conditions

Abstract The non-isothermal kinetics of nicotine desorption from precipitated silicon dioxide was investigated. The non-isothermal thermogravimetric curves of nicotine desorption at different heating rates (β = 5, 10 and 20 K/min) were recorded. The kinetics model of non-isothermal kinetics of nicotine desorption was determined by using the model-fitting and master-plot methods. It was found that non-isothermal nicotine desorption can mathematically describe by the theoretical kinetics model of phase – boundary controlled reaction (contracting volume, i.e., three dimensional shape) – R3. By applying the method of Kissinger and method of invariant kinetic parameters the values of kinetic parameters were determined. It was established that both applied method give almost identical kinetic parameters regardless their theoretical limitations. The dependence of activation energy on the degree of nicotine desorption was determined using the KAS method. It was found that the value of activation energy is independent on the degree of nicotine desorption. The effect of heating mode on the kinetic of nicotine desorption was analyzed. It was established that the type of heating mode (isothermal and non-isothermal) does not influence the mechanism of the formation of the activation complex nor the kinetics model of desorption. The increase in the values of kinetic parameters obtained for non-isothermal heating in comparison to the isothermal ones are explained with the Larson's model of selective transfer of energy.

Effect of heating mode and Y2O3 addition on electrochemical response on austenitic and ferritic stainless steels

The present study compares the effect of Y2O3 addition and heating mode on the electrochemical response on austenitic (316L) and ferritic (434L) stainless steel during solid state sintering. Up to 12 vol.-%Y2O3 was added to 316L and 434L stainless steel. The compacts were sintered at 1350°C for 60 min. The sintered samples were characterised for their density and hardness. The effect of heating mode and Y2O3 addition on the microstructural evolution and electrochemical (corrosion) response for the microwave sintered samples are compared with conventionally sintered samples. The density of stainless steel samples sintered through the microwave sintering was higher than that of conventional sintering.

Unique effects of microwave heating on polymerization kinetics of poly(methyl methacrylate) composites

The effects of heating mode (conventional and microwave) on the kinetics of isothermal polymerization of MMA composite materials were investigated. Isothermal kinetics curves at temperature range from 343 K to 363 K for both conventional (CH) and microwave heating (MWH) were determined. It was found that the polymerization of MMA composite materials was kinetically elementary reaction for both CH and MWH. The kinetics of CH polymerization can be described by the model of phase-boundary controlled process (contracting volume), whereas the kinetics of MWH polymerization can be described by the model of first-order chemical reaction. The kinetics parameters (Ea and ln A) of the polymerization under microwave heating are lower than for conventional heating. The established decreases in the activation energy and pre-exponential factor under the MWH compared to the CH is explained with the increase in the energy of ground vibrational level of the C–O valence vibrations (ν = 987 cm−1) in methyl methacrylate molecule and with the decrease in its anharmonicity factor which is caused with the selective resonant transfer of energy from the energetic reservoir to the oscillators in methyl methacrylate molecules.

Effect of heating mode on sinterability of carbonyl iron compacts

In recent years, microwave processing has gained wide acceptance as a novel method for sintering metal powders. As compared to conventional sintering, microwave sintering provides rapid and volumetric heating involving conversion of electromagnetic energy into thermal energy within the material. This results in finer microstructures, thereby providing improved mechanical properties and quality of the products. This study examines the dependence of densification, microstructure and mechanical properties on the heating mode of Fe–2%Cu and Fe–2%Cu–0·8%C. The powdered compacts were sintered in conventional (radiation mode) and microwave (2·45 GHz, multimode) furnaces at 1120°C in 90N2–10H2 atmosphere, and comparative analysis of the properties was investigated.

Effect of heating mode on sintering of ferrous compacts through powder metallurgy route

Microwave heating is recognised for its various advantages, such as time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved properties. The present paper focuses on preliminary work carried out with the use of microwave radiation applied to sintering of ferrous compacts. The ferrous alloy compacts were sintered in a multimode microwave furnace of 2·45 GHz and 6 kW nominal power at 1120°C for 60 min in forming gas. Results of densification, mechanical properties and microstructural evaluation of the microwave sintered samples are reported and compared with conventionally sintered ones. In general, it is observed that the microwave radiation generally enhances the properties of the sintered material when compared with conventionally sintered material.

Effect of microwave and conventional heating on sintering behavior and properties of Al–Mg–Si–Cu alloy

Effect of heating mode and sintering temperature on sinterability and properties of the 6711 (Al–1Mg–0.8Si–0.25Cu) alloy was investigated. Alloy compacts were consolidated in conventional and microwave furnace at 570, 590, 610 and 630 °C under vacuum (10 −6 torr). Microwaves coupled with the compacts and resulted in ∼58% reduction in processing time along with higher heating rates when compared to conventional sintering. However rapid heating rate resulted in inhomogeneous microstructure with larger melt fraction at grain boundaries. XRD analysis showed absence of intermetallics due to insufficient time for diffusion. With increasing sintering temperature, all compacts did undergo supersolidus liquid phase sintering (SLPS), accordingly higher densification and shrinkage was observed. The electrical conductivity and hardness followed similar trend as sintered density in both modes. Alloy compact sintered at 630 °C resulted in significant improvement of mechanical properties (TRS: 57%↑; UTS: 27%↑and ductility: 41%↑) in conventional mode. Age hardening treatment under T6 temper enhanced the tensile strength by 136% with drastic reduction in ductility as compared with sintered compacts.

Effect of Heating Mode on Sinterability of Fe-Ni Steels

The present study examines the effect of heating mode on the densification, microstructure, and mechanical properties of iron-nickel steel with graphite and phosphorus addition. The compacts were sintered in conventional (radiatively-heated) and microwave (2.45 GHz, multimode) furnaces at 1120°C for 1 hour in forming gas (dissociated ammonia atmosphere, 95% N2-5% H2). The experimental results show that microwave sintered alloy has better properties compared with the conventionally sintered counterparts. Detailed analyses by using optical microscopy and scanning electron microscopy (SEM) reveal that microwave sintered sample has finer microstructure. SEM examination of the fractured surfaces indicate that a mixed mode fracture containing both, ductile and brittle types, is present in microwave sintered alloy, in contrast with the brittle fracture only in conventional sintered counterpart.

Influence of microwave heating on the polymerization kinetics and application properties of the PMMA dental materials

AbstractThe effects of heating mode (conventional isothermal heating (CIH) and microwave isothermal heating (MWIH) on the kinetics of polymerization and the properties important for the application (residual monomer, hardness, and water absorption) of three commercial poly(methyl methacrylate) (PMMA) base dental materials were investigated. The degree of monomer conversion was determined by infrared spectrometry. The hardness of the polymerized samples was measured by shore D method, whereas the water absorption was measured gravimetrically. Kinetics models for polymerizations using different heating modes were determined by model fitting method. The rate of the MWIH polymerization was eight times higher compared with the CIH polymerization. The CIH polymerization is found to be the phase–boundary controlled reaction for which the rate of contracting volume is the rate limiting step, whereas MWIH polymerization is found to be the first‐order reaction and the monomer concentration in the polymerization mixture is the rate limiting step. The samples of PMMA base dental materials synthesized by MWIH polymerization exhibit better application properties (hardness and water absorption). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of heating mode and sintering temperature on the consolidation of 90W–7Ni–3Fe alloys

The present study compares the sintering response of 90W–7Ni–3Fe alloys consolidated in a 2.45 GHz microwave furnace and a conventional furnace. The W–Ni–Fe compacts were sintered in a temperature range of 1200–1500 °C corresponding to solid-state as well as liquid phase sintering. The compacts were successfully sintered in a microwave furnace with about 80% reduction in the overall processing time. For both the heating modes, the W–Ni–Fe alloys exhibited significant densification prior to melt formation through solid-state sintering. The in situ dilatometric studies revealed that the contribution to densification from solid-state sintering is higher at lower heating rates. In comparison to conventional sintering, microwave sintered compacts showed relatively refined microstructure and higher hardness and flexural strength.

Effect of heating mode on sintering of tungsten

Microwave heating is recognized for its various advantages, such as time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved properties. The present paper investigates the feasibility of consolidating tungsten powders through microwave sintering. A comparative analysis has also been attempted between the sintering response of pure tungsten powder compact in a microwave and conventional furnace.

Effects of a silica spin-on interlayer and heating mode on the joining of zirconia and MaCor™

Transmission electron microscopy (TEM) has been used to assess the role of thin spin-on interlayers and the effects of heating mode, joining temperature, and time on microstructure development in the process of joining zirconia and MaCor™. Sintered polycrystalline partially stabilized zirconia (PSZ) specimens and commercial machinable glass ceramic (MaCor™) have been joined with or without a thin (∼400 nm) amorphous silica interlayer. After joining at different temperatures, times, and with and without the silica interlayer, the interface between zirconia and MaCor™ showed similar interfacial microstructures, with all of the interfaces showing intimate bonding between the zirconia and MaCor™, without any additional interfacial phases. Experiments indicate that joining requires higher nominal temperatures when carried out using conventional heating rather than microwave heating.