The Migration of High Angle Grain Boundaries during Recrystallization

When plastically deformed metallic materials are annealed, new strain free grains emerge from the microstructure and grow by means of grain boundary migration until the deformation microstructure is eliminated. This process is called recrystallization. In this paper the various methods by which grain boundary migration rates are measured stereologically in order to characterize the growth process are described and compared using illustrations from recrystallization experiments on commercial AA1050 aluminum. It seems abundantly clear that during recrystallization of cold-deformed materials, isothermal grain boundary migration rates decrease with time and reasons for such a decrease are discussed. A new methodology whereby migration rates of the individual recrystallization texture components may be quantified by combining stereology and orientation imaging by the electron back scattered pattern analysis is outlined. By illustration, recent experiments on aluminum and copper are summarized documenting the slight growth rate advantage the cube texture component (001)[100] possesses during recrystallization of cold rolled material. The role of orientation pinning effects on grain boundary migration is described briefly. It appears that such pinning effects allow recrystallized grains emerging from the weaker deformation texture components to enjoy an average growth rate advantage over those emerging from the stronger deformation texture components.     

Thermal stability and crystallization kinetics of Ge13In8Se79 chalcogenide glass

Ge-In-Se system, similar to many other chalcogenide glasses, has attracted much attention due to its interesting physical properties and applications. This article reports thermal analysis and estimation of activation energies of the glass transition and amorphous-crystallization transformation of Ge₁₃In₈Se₇₉ chalcogenide glass. The kinetic parameters were investigated under a non-isothermal condition at different heating rates (7–40?K/min) using differential scanning calorimetric (DSC) technique. The amorphous nature of the samples was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The activation energy was calculated from DSC data using five isoconversional methods: Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang, Starink, and Vyazovkin. The results confirm that the activation energy of crystallization varies and depends on the degree of crystallization as well as temperature. It was also observed that the transformation from amorphous to the crystalline structure is complex involving different mechanisms of nucleation, diffusion, and growth.     

Electroless copper plating on 3-mercaptopropyltriethoxysilane modified PET fabric challenged by ultrasonic washing

Electroless deposition of Cu on poly(ethylene terephthalate) (PET) fabric modified with 3-mercaptopropyltriethoxysilane was investigated. Morphology, composition, structure, thermal decomposing behavior of copper coating PET fabric after ultrasonic washing in water for 1 h were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), Raman spectrometer, X-ray diffraction (XRD), and thermogravimetric analysis (TG), respectively. Copper plating on modified fabric has good adherence stability and high electric conductivity before and after ultrasonic washing, while copper coating fabric without modification is easily destroyed during the washing process, which leads to the textile changing from conductor to dielectric. As the copper weight on the treated fabric is 28 g/m², the shielding effectiveness (SE) is more than 54 dB at frequency ranging from 0.01 MHz to 18 GHz.     

The kinetics of precipitation in Al-2.4 wt% Cu alloy by Kissinger, Ozawa, Bosswel and Matusita methods

The isothermal and non-isothermal ageing of an Al-2.4 wt% Cu alloy have been studied using X-ray diffraction analysis and differential scanning calorimetry (DSC) at different heating rates. Quantitative metallography methods have been applied to measure the corresponding transformed volume fractions at various temperatures and times of precipitation. The variation of the heating rate using DSC technique has allowed us to calculate two kinetics parameters of precipitation which are the Avrami exponent and the activation energy of the process using Kissinger, Ozawa and Bosswell methods. These parameters are similar to those found for the precipitation reaction of θ′ and θ (Al₂Cu) phases.     

Evaluating the use of laser radiation in cleaning of copper embroidery threads on archaeological Egyptian textiles

Cleaning of copper embroidery threads on archaeological textiles is still a complicated conservation process, as most textile conservators believe that the advantages of using traditional cleaning techniques are less than their disadvantages. In this study, the uses of laser cleaning method and two modified recipes of wet cleaning methods were evaluated for cleaning of the corroded archaeological Egyptian copper embroidery threads on an archaeological Egyptian textile fabric. Some corroded copper thread samples were cleaned using modified recipes of wet cleaning method; other corroded copper thread samples were cleaned with Q-switched Nd:YAG laser radiation of wavelength 532 nm. All tested metal thread samples before and after cleaning were investigated using a light microscope and a scanning electron microscope with an energy dispersive X-ray analysis unit. Also the laser-induced breakdown spectroscopy (LIBS) technique was used for the elemental analysis of laser-cleaned samples to follow up the laser cleaning procedure. The results show that laser cleaning is the most effective method among all tested methods in the cleaning of corroded copper threads. It can be used safely in removing the corrosion products without any damage to both metal strips and fibrous core. The tested laser cleaning technique has solved the problems caused by other traditional cleaning techniques that are commonly used in the cleaning of metal threads on museum textiles.     

Phase Behavior of Poly(Ethylene Oxide) Studied by Modulated‐Temperature DSC—Influence of the Molecular Weight

Abstract

Melting and crystallization behavior of poly(ethylene oxide) (PEO) with different molecular weight was investigated by modulated‐temperature differential scanning calorimetry (MT‐DSC)—step‐scan alternating DSC. It was found that by separating the reversing and nonreversing components of the (total) heat flow, PEO 10000, which exhibits the highest degree of crystallinity, shows the smallest nonreversing signal during crystallization. This effect can be attributed to the favorable structural features associated with spacial alignment. On the other hand, the crystallization process of PEO with molecular weight of 3400 is hindered by a relatively high content of end groups that may cause defects in the crystal lattice. For PEO 35000, low segmental mobility and chain entanglements lower the rate of crystallization. The area of the reversing component of PEO melting for different molecular weight fractions confirms that for PEO 10000, recrystallization is less intensive than for both the lower and higher molecular weight analogues.     

Synthesis process of nanowired Al/CuO thermite

Al/CuO nanothermites were fabricated by thermal oxidation of copper layer at 450 °C for 5 h and by aluminum thermal evaporation: thermal evaporation allows producing thin layer less than 2 μm in size. The copper has been deposited by electroplating or thermal evaporation depending on the required thickness. The obtained diameter of Al/CuO nanowires is 150-250 nm. Al/CuO nanowires composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Two distinct exothermic reactions occurred at 515 and 667 °C and total energy release of this thermite is 10 kJ/cm³.     

Peroxide-based route assisted with inverse microemulsion process to well-dispersed Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> nanocrystals

Well-dispersed bismuth titanate (BIT) nanocrystals with an average size ranged from 3 to 60 nm were synthesized via a peroxide-based route assisted with an inverse microemulsion process. The crystallite size and lattice parameter of BIT upon variable-temperature were determined by X-ray diffraction (XRD). The particle size was confirmed by transmission electron microscopy (TEM). Thermal decomposition behaviour of Ti-peroxy and BIT gel and crystallization kinetics of BIT nanocrystals were investigated by differential scanning calorimetry/thermogravimetry (DSC/TG) and Fourier-Transform infrared spectroscopy (FTIR). Analysis of nonisothermal DSC data yielded a value of 220.84 ± 2.73 KJ/mol and 2.25 ± 0.26 for the activation energy of crystallization (E _a) and the Avrami exponent (n), respectively.     

Miscibility,Morphology, and Thermal Properties of Poly(Trimethylene Terephthalate)/Polycarbonate

Abstract

Poly(trimethylene terephthalate)/polycarbonate (PTT/PC) blends were prepared by melt blending and rapid quenching in ice water. The miscibility and thermal properties were investigated using differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA). The blend's morphologies were investigated using scanning and transmission electron microscopies. Both DSC and DMA results suggested that PTT and PC were very limited, partially miscible pairs. The melting point, melt crystallization, and cold crystallization exotherms in the blends of PTT were depressed by the presence and amount of PC. When the PC content was <50 wt%, PC spherical particles were found to distribute evenly in the PTT matrix; at 50–60 wt%, the two‐phase structures were close to being bicontinuous. At higher PC content, PTT formed a string‐like texture in the PC matrix. The PTT spherulitic morphologies in PTT/PC blends were found to be very sensitive to PC and PC content. When the PC content was ≥60 wt%, the blends crystallized as an agglomeration of tiny PTT crystals.     

Preignition characteristics of nano- and micrometer-scale aluminum particles in Al–CO2 oxidation systems

The objective of this study was to gain understanding of the preignition oxidation of Al powders in CO₂. The thermal behavior and reaction energy was studied using simultaneous thermogravimetric analysis and differential scanning calorimetry (TG–DSC). The particle morphology was examined at different stages of the process using field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM). The corresponding chemical changes were analyzed by X-ray diffraction spectrometry (XRD) and energy dispersion X-ray spectrometry (EDS). Dimensional properties of Al particles have a significant influence on the oxidation processes. Distinctly different properties were shown between nm-Al and μm-Al, where the reactions are found to occur at different temperature ranges. The powder behavior is controlled by the oxide layer that coats each particle and prevents exposure of the metal core to the reactive CO₂ gas. The properties of the oxide layer are related to the particle size. Carbon has been shown to play an important role in the reacting Al–CO₂ system. A new mechanism of nano-Al particle oxidation in CO₂ under gradually increasing temperature was proposed.     

磷对冷轧纯铜再结晶的影响

本文研究了微量磷对冷轧纯铜再结晶的影响。当磷原子主要是溶解在铜中时,大大提高了再结晶温度,增加了再结晶激活能,阻止了立方结构的形成,改变了再结晶结构;但出氧化磷状态存在于铜中时,对以上各方面的影响就不很明显。所有样品的再结晶结构,都与加工结构中的某一种取向相同或接近,并且与主要加工结构间存在着沿<111>相差20—45°的几何关系。分析从金相及X光研究后得到的结果,认为在这种情况下,同位再结晶和选择性生长是再结晶结构形成的过程。 关键词：     

Rapid treatment of CIGS particles by intense pulsed light

Intense pulsed light (IPL) technique has been proposed to make large grains Cu(In_0.7Ga_0.3)Se₂ (CIGS) film using CIGS particles. The proposed process is non-vacuum based and performed at room temperature without selenization treatment. Melting and recrystallization of CIGS particles to larger grains without structural deformation and phase transformation are proved with adequate characterization evidences. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion analysis (EDS) were used to characterize the prepared films. Melting of the CIGS particles and recrystallization to larger grains by light energy in 20 ms short reaction time could be the reason for no structural deformation and secondary phase generation during the process. The CIGS film prepared from its constituent nanoparticles by IPL treatment has great potential for use as absorber layer for solar cell application and is expected to have large impact on cell fabrication process in terms of cost reduction and simplified processing.     

Synthesis and characterization of monodisperse copper nanoparticles using gum acacia

A simple method was put forward in this paper for preparing colloidal copper nanoparticles in aqueous solutions using copper sulfate, gum acacia and hydrazine hydrate as copper precursor, capping agents and reducing agents, respectively, without any inert gas. The formation of nanosized copper was confirmed by its characteristic surface plasmon absorption peak at 604 nm in UV–vis spectra. The transmission electron microscopic (TEM) and scanning electron microscope (SEM) images show that the as-synthesized copper fine spherical particles are distributed uniformly with a narrow distribution from 3 nm to 9 nm. The X-ray diffraction (XRD) and high resolution transmission electron microscopic (HRTEM) demonstrated that the obtained metallic nanoparticles are single crystalline copper nanoparticles. Fourier transform infra-red (FT-IR) spectroscopic data suggested that the copper nanoparticles are coated with gum acacia. The effects of the quantity of gum acacia on the particle size were investigated by the UV–vis spectra and TEM images. The growth process of the nanoparticles was monitored by the UV–vis spectra. The mechanism of the formation copper nanoparticles was discussed. The process raised in this study can be served as an excellent candidate for the preparation of copper nanoparticles in a large scale production.     

Crystallization kinetics study of Pb4.3Se95.7 chalcogenide glass using DSC technique

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Pb_4.3Se_95.7 chalcogenide glass. Non-isothermal measurements were performed at different heating rates (5-60 K/min). The activation energy of crystallization was determined by analyzing the data using Matusita et al. method. A strong heating rate dependence of the activation energy was observed. The isoconversional methods of Kissinger-Akahira-Sunose (KAS) and Vyazovkin confirm that the activation energy of crystallization is not constant but varies with the degree of crystallization and hence with temperature. This variation indicates that the transformation from amorphous to crystalline phase in Pb_4.3Se_95.7 is a complex process involving different mechanisms of nucleation and growth.     

Morphology,Nonisothermal Crystallization Behavior and Mechanical Properties of Polypropylene Modified by Ionomers

The morphology and nonisothermal crystallization behavior of polypropylene modified by ionomers based on ethylene copolymers (Surlyn 8920 and 9320) were investigated by using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The crystallization rate of polypropylene was accelerated by the ionomers which initiated heterogeneous nucleation of the polypropylene. At low ionomers content (0.25 wt%), Surlyn 8920, neutralized by sodium, was more efficient to enhance the crystallization rate of polypropylene than Surlyn 9320 (neutralized by zinc). The crystallization process of polypropylene modified by the ionomers was analyzed by different kinetics models. The study showed that the Mo approach was applicable for this system, whereas the Avrami, Jeziorny, and Ozawa methods were not. Furthermore, the notched impact strength of polypropylene modified by the ionomers was increased without any reduction of tensile strength and flexural modulus.     

Sonochemical synthesis of cobalt aluminate nanoparticles under various preparation parameters

Cobalt aluminate (CoAl₂O₄) nanoparticles were synthesized using a precursor method with the aid of ultrasound irradiation under various preparation parameters. The effects of the preparation parameters, such as the sonochemical reaction time and temperature, precipitation agents, calcination temperature and time on the formation of CoAl₂O₄ were investigated. The precursor on heating yields nanosized CoAl₂O₄ particles and both these nanoparticles and the precursor were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The use of ultrasound irradiation during the homogeneous precipitation of the precursor reduces the duration of the precipitation reaction. The mechanism of the formation of cobalt aluminate was investigated by means of Fourier transformation infrared spectroscopy (FT-IR) and EDX (energy dispersive X-ray). The thermal decomposition process and kinetics of the precursor of nanosized CoAl₂O₄ were investigated by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energy (E) and the pre-exponential constant (A) were 304.26 kJ/mol and 6.441 × 10¹⁴ s^?1, respectively. Specific surface area was investigated by means of Brunauer Emmett Teller (BET) surface area measurements.     

Effect of laser energy on the deformation behavior in microscale laser bulge forming

Microscale laser bulge forming is a high strain rate microforming method using high-amplitude shock wave pressure induced by pulsed laser irradiation. The process can serve as a rapidly established and high precision technique to impress microfeatures on thin sheet metals and holds promise of manufacturing complex miniaturized devices. The present paper investigated the forming process using both numerical and experimental methods. The effect of laser energy on microformability of pure copper was discussed in detail. A 3D measuring laser microscope was adopted to measure deformed regions under different laser energy levels. The deformation measurements showed that the experimental and numerical results were in good agreement. With the verified simulation model, the residual stress distribution at different laser energy was predicted and analyzed. The springback was found as a key factor to determine the distribution and magnitude of the compressive residual stress. In addition, the absorbent coating and the surface morphology of the formed samples were observed through the scanning electron microscope. The observation confirmed that the shock forming process was non-thermal attributed to the protection of the absorbent coating.     

Study of crystallization kinetics of Se77.5Te15Sb7.5 glass using isoconversional models

The crystallization process of Se_77.5Te₁₅Sb_7.5 glass is studied by differential scanning calorimetry (DSC) technique under non-isothermal conditions at various heating rates. The crystallization parameters are deduced using different models. The validity of the Johnson–Mehl–Avrami (JMA) model to describe the crystallization process for the studied composition is investigated. Comparing experimental and calculated DSC curves indicate that the crystallization process of Se_77.5Te₁₅Sb_7.5 glass cannot satisfactorily be described by the JMA model. In general, simulation results indicate that the Sestak–Berggren model is more suitable to describe the crystallization kinetics. The crystalline phases are identified using the X-ray diffraction technique and scanning electron microscopy.     

Surface impurity diffusion-induced recrystallization of ultrafine-grained molybdenum

Methods of scanning and transmission electron microscopy are used to perform a comparative analysis of the structur evolution of ultrafine-grained molybdenum subjected to nickel-free annealing and to diffusion annealing accompanied by nickel penetration from the surface into the bulk of Mo(Ni) specimens. The kinetics of nickel diffusion-induced recrystallization of ultrafine-grained molybdenum in the temperature interval 1123–1223 K is investigated and the recrystallization activation energy is determined. Plausible reasons for a decrease in the nickel diffusion-induced recrystallization temperature of ultrafine-grained molybdenum as compared to its fine-grained cousin are discussed. The nickel diffusivity in ultrafine-grained molybdenum along grain boundaries is estimated on the basis of the results obtained. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 37–42, May, 2007.     

Swelling assisted photografting of itaconic acid onto sodium alginate membranes

Grafting of itaconic acid (IA) was achieved onto sodium alginate (NaAlg) membranes by using UV-radiation. Process was performed under nitrogen atmosphere and benzophenone (BP) was used as a photoinitiator. Membranes were preswelled before the polymerization process and ethanol was determined as the best swelling agent among the studied solvents. The effect of polymerization time, initiator and monomer concentrations on the grafting efficiency were investigated. The best conditions for optimum grafting were obtained with IA concentration of 1.0 M, a BP concentration of 0.1 M and a reaction time of 4 h at 25 °C. Under these conditions grafting efficiency for NaAlg-g-IA membranes was found to be 14% (w/w). To obtain further increase in grafting efficiency membranes were also preswelled in IA and BP solutions and polymerization was carried out at different temperatures after UV polymerization. Grafted membranes were characterized by using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Effect of grafting on membrane properties such as intrinsic viscosity and swelling percentage were also determined.