Torranin Chairuangsri

Realization of Interlinked ZnO Tetrapod Networks for UV Sensor and Room-Temperature Gas Sensor.

Here, interlinked ZnO tetrapod networks (ITN-ZnO) have been realized by using microwave-assisted thermal oxidation. With this simple and fast process, a nanostructured ZnO morphology having tetrapodlike features with leg-to-leg linking is obtained. The electrical and ethanol-sensing properties related to the morphology of ITN-ZnO compared with those of other ZnO morphologies have also been investigated. It has been found that ITN-ZnO unexpectedly exhibits superior electrical and gas-sensing properties in terms of providing pathways for electron transport to the electrode. A UV sensor and a room-temperature gas sensor with improved performance are achieved. Therefore, ITN-ZnO is an attractive morphology of ZnO that is applicable for many new applications because of its novel properties. The novel properties of ITN-ZnO are beneficial for electronic, photonic, optoelectronic, and sensing applications. ITN-ZnO may provide a means to improve the devices based on ITN-ZnO.

The precipitation of copper in abnormal ferrite and pearlite in hyper-eutectoid steels

Abstract The precipitation of copper within abnormal ferrite and pearlitic phases in hyper-eutectoid Fe-C-Cu and Fe-C-Mn-Cu experimental steels has been examined, principally by transmission electron microscopy, in terms of morphology, mechanism and crystallography. Interphase precipitation of copper during austenite decomposition was found to be a primary precipitation mechanism. However, precipitation due to ageing was also observed in both abnormal and pearlitic ferrite. The latter case appeared either as uniformly distributed precipitates within the ferrite or in association with dislocations. Copper precipitates adopted either the Kurdjumov–Sachs or the Nishiyama–Wasserman orientation relationship with respect to the ferrite. Disc-shaped precipitates thought to form by ageing within abnormal and pearlitic ferrite develop on {001}ferrite habit planes. Twinning observed within copper precipitates formed by interphase precipitation was attributed to a requirement to accommodate the growth of precipitates at the interphase boundary. Multi-twinned precipitates were found in pearlitic ferrite and may be evidence for an intermediate transitional state between b.c.c. and f.c.c. structure.

Abnormal ferrite in hyper-eutectoid steels

Abstract The microstructural characteristics of ultra-high carbon hyper-eutectoid Fe–C and Fe–C–Cu experimental steels have been examined after isothermal transformation in a range just beneath the eutectoid temperature. Particular attention was paid to the formation of so-called “abnormal ferrite”, which refers to coarse ferrite grains which can form, in hyper-eutectoid compositions, on the pro-eutectoid cementite before the pearlite reaction occurs. Thus it is confirmed that the abnormal ferrite is not a result of pearlite coarsening, but of austenite decomposition before the conditions for coupled growth of pearlite are established. The abnormal ferrite formed on both allotriomorphic and Widmanstatten forms of pro-eutectoid cementite, and, significantly, it was observed that the pro-eutectoid cementite continued to grow, despite being enclosed by the abnormal ferrite. Under certain conditions this could lead to the eventual formation of substantially reduced amounts of pearlite. Thus, a model for carbon redistribution that allows the pro-eutectoid cementite to thicken concurrently with the abnormal ferrite is presented. The orientation relationships between the abnormal ferrite and pro-eutectoid cementite were also determined and found to be close to those which have been reported between pearlitic ferrite and pearlitic cementite.

Fine structure of wing scales of butterflies, Euploea mulciber and Troides aeacus.

Wing scales of male Euploea mulciber (E. mulciber) and Troides aeacus (T. aeacus) butterflies were investigated from interest in photonic crystal by scanning electron microscopy and optical reflectance measurement. On the basis of the structural observation, the colouration in different areas in their wings was discussed. It was particularly deduced that a violet-green iridescence characteristic of E. mulcibers forewing is caused only in a wavelength range from ∼380 to ∼510nm by multiple interference from a highly tilted, triple-layered cuticle arrangement on the brown scales. It was also found that T. aeacus does not produce a blue-green sheen such as observed by Troides magellanus because its scales have no multiple cuticle layers but microrib layers unable to produce any backscattering diffraction.

Quantitative analysis of a complex metal carbide formed during furnace cooling of cast duplex stainless steel using EELS and EDS in the TEM

In this work, a method to determine the atomic ratio of Mo and C within complex metal carbides using EELS in the TEM has been developed. The method is based on the determination of k-factors for given experimental conditions from the EEL spectra of Mo(2)C and MoO(3) standards, which had been independently checked by XRD and EPMA. Factors affecting the k(Mo/C) value of the Mo(2)C standard were also investigated and the value was shown to be insensitive to background subtraction window width but sensitive to prolonged irradiation and specimen thicknesses above a critical value. The method and k-factor obtained from the Mo(2)C standard was applied to spectra from a complex metal carbide precipitate formed during furnace cooling of a cast duplex stainless steel. Using EELS and EDS in the TEM, the composition was estimated to be (Cr(1.52)Fe(2.33)Mo(1.25)Ni(0.17)Si(0.46))C, which is close to M(6)C stoichiometry, and the structure was confirmed by electron diffraction.

Preparation of Nanoparticles by Laser Ablation on Copper Target in Distilled Water

Preparation of nanoparticles by pulsed Nd:YAG (1064 nm) laser ablation on copper target submerged in distilled water has been studied. Effects of pulse power and liquid height were investigated. Colloidal nanoparticles were characterized by UV-Vis spectroscopy, Raman dynamic light scattering and transmission electron microscopy. The concentration of nanoparticles was increased with the pulse power at a particular liquid height or volume. The size of nanoparticles related complicatedly to both parameters. The optimum conditions were the pulse power of 80 W and the liquid height of 3-4 mm. The obtained mean particle size was 20-37 nm, having the maximum UV-Vis absorption wavelength at 617-630 nm. The colloids contained mainly copper oxide nanoparticles.

Effects of Destabilisation Heat Treatment on Microstructure, Hardness and Corrosion Behaviour of 18wt.%Cr and 25wt.%Cr Cast Irons

Effects of destabilisation heat treatment on microstructure, hardness and corrosion resistance of 18wt.%Cr and 25wt.%Cr irons have been investigated. The as-cast samples were heat-treated by destabilisation at 1000°C for 4 hour and then air cooling. The microstructure was investigated by light microscopy and scanning electron microscopy. The results show that the as-cast microstructure in 18wt.%Cr iron consists of pearlite, formed by decomposition of primary dendritic austenite, plus eutectic structure. In the 25wt.%Cr iron with lower hardness, the microstructure consists of primary dendritic austenite plus eutectic structure. The austenite had partly transformed to martensite, especially at areas adjacent to eutectic carbides. After destabilisation, the microstructure of both irons consists of eutectic and secondary carbides in a martensite matrix giving increased hardness. It was found that corrosion resistance of the irons was improved after destabilisation. The 25wt.%Cr showed superior corrosion resistance than the 18wt.%Cr iron due to greater residual Cr in the matrix to encourage passivity.

Microstructural and Mechanical Development of As-Cast and Heat-Treated 935AgCu Alloys

Microstructural and mechanical development of the various heat-treated 935 Ag-Cu alloys were explored. The heat-treatment processes were applied viz. holding before quenching for 2 and 15 min, homogenization at 750 °C for 60 min followed by water quenching, and aging at 350 °C for 15 to 60 min followed by water quench. It was found that the specimens with copper addition gave a high resiliency in all heat treatment conditions however the effect of homogenization with aging treatment fostered deep blemish or fire scale on its surface. The amplifications of resiliency of 935 heat-treated AgCuSn and AgCuBe alloy were increased but elongation values were slightly reduced. The 935 AgCuBeSn specimens produced adequate resiliency and elongation after aging at 350 °C for 15 to 60 min followed by water quenching. Partial dissolution and spheroidization of eutectic phase were occurred by homogenization treatment at 750 °C. Aging treatment promoted precipitation of 3-20 nm fcc (Cu,Sn)–rich precipitates and engendered an improvement of hardness, yield strength and the modulus of resilience or resiliency.

Challenges and strategies of surface modification of electrogalvanized coatings for electron microscopy analysis

Despite wide usage of electrogalvanized coatings in various applications, characterization studies on their micro/crystal structure, and the understanding of how they correspondingly affect the properties, such as corrosion, are rather limited. This is mainly attributed to some difficulties in preparing and examining the zinc coating layers, owing to their intrinsically low corrosion resistance and refined nano-scaled crystallite size. This study aims to examine such challenges systematically and propose some mitigation strategies. Particularly, sample preparation processes, including surface finishing for metallography and sample thinning processes are explored. Furthermore, a range of electron microscopy techniques, including scanning electron microscopy (SEM), electron back scattered diffractometry (EBSD), and transmission electron microscopy (TEM) are investigated in relation to the achievable clarity of microstructural details of electrogalvanized coatings.

Oxidation Behavior of 30wt.%Cr-3.75wt.%V High Chromium Cast Iron

This work focuses on the oxidation behavior of 2.4wt.%C-30wt.%Cr-3.75wt.%V cast iron in air at 1000 °C for 1-48 h with weight gain measurements taken at different times. The oxidized surfaces and cross sections were characterized by XRD, OM, SEM and EDS. It was found that the as-cast microstructure consisted of a ferritic matrix and M7C3 carbide. The surface oxide scale consisted of multi-oxides and the grain size of the oxides increased with increasing holding times. XRD and SEM-EDS results revealed that the multi-oxide layer can be Cr2O3, (Fe,Cr,V)2O3 and SiO2. After about 48 h, a continuous SiO2 inner-layer was observed and the oxide scale tended to swell, contained pores, and became detached from the surface because of its poor adherence.