Copper and its alloys have good electrical and thermal conductivity as well as good resistance to corrosion [1] but it has a low mechanical strength. However, its mechanical strength can be improved by adding alloying elements by means of Mechanical Alloying (MA) and powder metallurgy [2][3][4][5].In this work we report the results of the Cu10Mo alloy, synthesized during 10 h by MA. The microstructural characterization was carried out by X-Ray Diffraction to identify the phases formed after MA process, the crystals size was determined by Rietveld method using the MAUD software [6]. This results were obtained with a value of chi 2 : 1.33 and Rwp = 8.28 respectively. Finally, analysis of Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) were used to determine the morphology and chemical composition of the particles formed. Figure 1 shows the X-Ray results of the alloy. It is possible to observe the presence of different peaks, which correspond to the Cu and Mo elements. By other hand the Rietveld analysis showed a crystal size of 13 and 24 nm and a microdeformation of 38.5 x 10 -4 and 3.6 x 10 -6 R.M.S., for the Co and Mo respectively. Figure 2a shows the morphology of the particles analyzed by SEM. It can be observed a different morphology of the particles, the average size is ranking between 5-30 nm. The chemical composition of the particles can be observed in figure 2b where Cu and Mo peaks are observed. It is possible to observe that ther is not a presence a other peak, which can indicate contamination from the steel balls used during the milling, the quantification of the elements indicated that the particles are composed of 94.56% wt and 5.46% wt of Cu and Mo respectively.
The high energy ball milling is an easy and low cost technique that has been highly used in the processing of powder materials. This technique has demonstrated to be effective in the synthesis of new compounds, formation of solid solutions, production of nanostructured materials, activation of powders and homogenization of phases [1]. In this study we report the use of the SPEX mechanical milling to synthesize α-Al 2 O 3 from γ-Al 2 O 3 . The γ-Al 2 O 3 was obtained by the calcination of pseudoboehmite at 500 ºC for 2 h. The pseudoboehmite was synthesized from aluminum sulfate hydrated (Al 2 (SO 4 ) 3 • xH 2 O) and anhydrous ammonia (NH 3 ). The powders of γ-Al 2 O 3 were poured into a steel stainless jar in batches of 10 gr and milled for times of 5 and 10 h. No control agent or any other additional component was added during the milling process. The mechanical treatment was performed at room temperature and under atmospheric conditions. The as milled powders were analyzed by XRD and SEM. Figure 1(a, b and c) shows the effect of the mechanical milling in the particle size and distribution. Figure 1a displays the raw powders of γ-Al 2 O 3 that are composed by big particles of irregular shape. The particles after 5 h (1b) adopted a round shape and a light decrease of particle size in comparison to the raw powder. Short times of milling demonstrated to be effective in the reduction and homogenization of the particle size. The Figure 2 shows the XRD analysis of the powders before and after milling treatment. These analyses show that the SPEX mechanical milling supplies enough energy to achieve the beginning of the transformation from γ to α-Al 2 O 3 . After 10 h of milling, new reflections were detected and assigned to the reflections (-216), (-224), (-213), (-114) and (-112) in good agreement to the XRD pattern COD 1000032. No evidence of contamination generated during the mechanical milling was observed. Moreover, the presence of the intermediate phases δ and θ was not detected. Therefore, it appears that the transformation from γ to α-Al 2 O 3 occurred with the absence of these transitional changes as showed previously by A. Tonejc [2]. Recently, other researchers have shown similar results in the milling of commercial powders of γ-Al 2 O 3 and boehmite by means of planetary ball milling [3][4]. The results reported in our work show that SPEX mechanical milling is highly effective in the reduction and homogenization of particle size. Moreover, it has been demonstrated that SPEX milling is successful to achieve the transformation from γ-Al 2 O 3 to α-Al 2 O 3 at room temperature without producing any significant level of contamination.
In recent years, the notorious importance of the study of nanomaterials has been appreciated. Nanotechnology is a relevant field that studies the synthesis, development and practical implementation of nanoparticles and nanomaterials, whose dimensions fall within the range of 1 to 100 nm. In this size range, the physical and biological properties change entirely concerning the features of the particles above this scale [1]. Among the wide variety of studies carried out in the area of synthesis, gold nanoparticles standout due to their catalytic properties and their ease of their obtainment by green methods [2]. Green synthesis employs antioxidant and surfactants biomolecules taken from the plant's extracts, which can be used for the nanoparticles synthesis, considering it as a novel and sustainable method. This method has been used mostly to synthesize gold and silver nanoparticles with suitable size and shape control [3].In this work, Loeselia Mexicana (Lam.) Brandegee plant extract was used. Fresh Loeselia Mexicana leaves were separated from the stems to be dried, milled and washed with distilled water using magnetic stirring. The extraction of biomolecules was carried out by mixing the milled leaves with 100 ml of distilled water at 70°C for 10 minutes using magnetic stirring. The extract was filtered and cooled to room temperature. Gold nanoparticles synthesis was carried out by mixing the leaf extract with 2mM HAuCl 4 in a 1:1 volume ratio. A sample was left under sunlight for 20 minutes, and another one was heated in an oven at 40°C for 20 minutes. Synthesized samples showed a color change from pale yellow to violet, indicating that gold nanoparticles were synthesized. Nanoparticles growth and stabilization were monitored by UV-Vis spectroscopy (OceanOptics USB 4000). The XRD pattern was obtained (Bruker D8 Advance, DAVINCI Lynx eye) using CuKα radiation (λ = 1.5406 A°), angular range from 20° to 90° and 0.02° / second step. SEM images were obtained by backscattered electron technique (JEOL JSM-7600F). Figure 1 shows the gold nanoparticles UV-Vis spectra, the peak is located between 500-600 nm in both samples, and it is characteristic of the gold nanoparticles [4]. It is noted that the specimen exposed to sunlight has a higher absorbance. However, the peak is broader, which indicates that a greater quantity of nanoparticles was obtained with a more extensive size distribution than the sample heated at 40°C. Thus, the results showed that Loeselia Mexicana (Lam.) Brandegee biomolecules can reduce the HAuCl 4 solution and stabilize the gold nanoparticles. Figure 2 corresponds to the XRD pattern, wherein the gold crystallographic phase formation can be seen. Figures 3a-b correspond to the sample heated at 40°C, therein an appreciable amount of spherical gold nanoparticles are observed between 50-60 nm accompanied by tetrahedral and icosahedral nanoparticles. Figures 3c-d corresponds to the sample under sunlight showing a reduced formation of nanoparticles around large particles greater than 300 nm. The sunlight...
Hardfacing is a widely used method to service life extensión of the surfaces in continuous caster rolls subjected to severe wear, corrosion or oxidation. Martensitic stainless steels within the 12 % chromium alloys are the most used steels to hardfacing, nitrogen can be added to for cladding applications as an to carbon sustitute to increase hardness and form austenite at elevated temperatures [1,2]. The Heat input (HI) is one of the important variables refers to quality of the welding. Due to the heat input and the slow cooling rate occurs after welding, detrimental residual stresses are generated to the mechanical properties and / or corrosion in service. The leading steel companies in the world are located in coastal areas, where the continuous caster rolls are subject to corrosive environments as seawater. This work studies electrochemical corrosion behavior of martensitic stainless steels in synthetic seawater deposited as hardfacing, weldment have been obtained using an automatic flux-cored arc welding process (FCAW). The rolls were surfaced with a 414N-O tubular wire, a nitrogen-bearing, low-carbon wire that produces a martensitic deposit with a composition optimized for corrosion resistance. Figure 1, shows EDS result after the electrochemical test in seawater, can be seen of product obtained has concentrations of oxygen, chromium and iron. Figure 2, shows XPS result of corrosión products, where can see shape and composition of O 1s core-level spectra, presence of oxide, (oxy)-hydroxide, and water can be deduced from O 1s peak fit. Peaks at ~540 eV originate from molecular oxygen (O2) due to ambient air. Shape of Fe 2p core-level spectra, where presence of oxide, (oxy)-hydroxide, and metallic iron can be deduced from Fe 2p3/2. Shape of Cr 2p core-level spectra, where presence of oxide, hydroxide, and metallic Cr 0 can be deduced from Cr 2p3/2 [3]. Can be concluded that Fe is found as oxide while oxy-hydroxides appear combined with Cr and Fe.References:[1] Agustín Gualco et al, Materials and Design 31
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