Key Engineering Materials Vol. 904

Abstract: In this research we investigated the contact angle of commercial SnAgCu solder paste mixing with some carbon allotropes such as graphite, graphene quantum dots, and fullerene of varying concentrations with melting temperature, wettability, interfacial microstructure. The wettability was assessed in terms of the contact angle. The in-line digital holography was used for determining the contact angle and morphological of samples at each temperature which the samples have been heating from room temperature until the melting temperature. In the experiment, only one beam was used as the object and reference beams which recorded by a CMOS camera. The recorded image was reconstructed by the angular spectrum digital holography numerical programing. Using the reconstructed images of our results, the shape and contact angle of solder pastes can be investigated.

Abstract: An electrosparking experiment of ASP30 powder metallurgical steel was carried out through tool electrode forced cooling based on micro heat pipe bundle by using the semiconductor encapsulation mould. Results demonstrate that the micro groove formed among sintered copper fibers based on wick of micro heat pipe and the unique composite structure of the surface chopped morphology can not only increase capillary pressure of the wick, but also strengthen evaporation/condensation process at two ends of the micro heat pipe, and improve cooling effect of micro heat pipe to tool electrode significantly. Compared with traditional electrosparking, electrosparking of tool electrode forced cooling based on micro heat pipe bundle increases the inter-electrode cooling, chip removal and deionization of electrosparking and further lowers tool electrode loss by strengthening heat dissipation of tool electrode. Hence, it can improve stability of electrosparking, increase pulse utilization and increase the processing speed and processing surface quality significantly.

Abstract: This research studies effects of the brazing time on interfacial microstructure of brazed joint between the porous copper foam (PCF) and Cu substrate using CuNiSnP amorphous filler metal. To examine the interfacial microstructure and its properties, an assessment of PCF/CuNiSnP/Cu brazed joints was conducted after electric furnace brazing under hydrogen (H₂) atmosphere. The results showed that the interfacial microstructure was thick for short brazing time specimens and thin for prolonged brazing time specimens. The interfacial microstructures consisted of Cu-rich solid solution, (Cu, Ni)₃P, and Cu₃P as a eutectic structure discovered in the brazing region at different brazing times of 5, 10, and 20 min. Only the Cu-rich solid solution and (Cu, Ni)₃P were found in the specimen with brazing time of 30 min. indicating that different brazing times affected interfacial microstructures and therefore reliability of the brazed joints.

Abstract: The calcined clay bricks are the second most used materials in construction that, after the demolition processes, tends to become rubble, generating a negative visual and environmental impact, in addition to the fact that the brick-making process has not been industrialized in Ecuador, for that, its properties are deficient; in this way, the present research aims to study the physical, chemical and mineralogical characteristics of brick waste from the Southern part of ​​this country, for the elaboration of ecological bricks through geopolymerization processes, using as alkaline activator Sodium Hydroxide at temperature ranged between 90 °C and 200 °C, obtaining an optimal mixture at the combination 12.5 M, 26 wt% Cs, 150 °C. The mechanical properties of bricks as simple compression and flexural strength, respectively, applying the experimental Griffith criterion method by finite element simulation method. These ecological bricks obtained are suitable for use in construction.

Abstract: Ultrasonic-assisted soldering welding is widely applied for joining difficult materials. The cavitation phenomenon in liquid always occurs during the ultrasonic excitation. Base metals are striked by ultrasonic cavitation, creating erosion on the surface. The soft solder materials are penetrated on the rough surface, generated inter-metallic compounds. This work expresses the design of ultrasonic soldering machine using 20 kHz source and steel sonotrode. The curvature of reflecting plates with specific radius and their location are also condidered. The major technological parameters of ultrasonic soldering welding such as ultrasonic exciting time, power and curvature radii of reflecting plate are discussed. Tin soldering material is utilized for joining copper wires and plates are investigated. SEM images on the surface of tin soldering on cooper plates and tensile strength are investigated.

Abstract: Acid mine drainage is characterized by low pH value, many types of heavy metals, high concentration of heavy metals and great environmental damage. Copper precipitation by sulfate reducing bacteria is a common method. In this experiment, the AMD after iron removal was treated by an upflow anaerobic bioreactor. The effects of HRT, carbon source type, carbon source dosage and reactor temperature on the operation of the reactor were studied. The optimum process parameters were determined: HRT was 12h, formic acid was used as carbon source and the dosage was 0.5g/L, and the temperature was 30 °C. Under the process conditions, the Cu concentration in the reactor effluent decreased to 0.043mg/L, and the recovery rate of Cu metal was 99.9%. The mechanism of copper deposition in the reactor was studied by characterization of the structure and morphology of the precipitated product and the analysis of the microbial community structure in the effluent of the reactor.

Abstract: Activated carbons (ACs) are a versatile group of adsorbents for water pollution control, especially organic dyes. Harsh chemicals and high temperatures are required for the activation process of ACs, which becomes a significant concern due to their toxicity and harmful effects on human health and the environment. Gamma irradiation, an alternative green technique, is a promising strategy for pretreatment and escalates the nitrogen or oxygen functional group of ACs. The current study provides the modification of ACs by the gamma irradiation in the various pH (5-11) of urea solution. The modified ACs were characterized by scanning electron microscopy (SEM), nitrogen gas adsorption-desorption analysts (BET), temperature program desorption (TPD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction spectroscopy (XRD). The point of zero charges and dye adsorption capacities were determined. This finding demonstrates that the ACs can be modified by gamma irradiation at 25 kGy in the urea solution media. The degree of graphitization enhanced significantly at pH 11(AC-pH11). The oxygen-rich functional groups created by radiation assists could enhance the electrostatic attraction between acid gases or cationic dyes. AC-pH11 also was able to adsorb methylene blue (160.73 ± 1.70 mg/g) greater than methyl orange (127.57 ± 2.22 mg/g).

Abstract: Coal fly ash (CFA) and bottom ash (BA) obtained from coal fired power plants in Thailand and local supplier were characterized using XRF, XRD and N₂ adsorption-desorption techniques. Their possibilities for conversion of palm oil into biodiesel were investigated. Selected CFA was also modified with lanthanum (La) at different La loading and the influence of La loading on biodiesel conversion was evaluated. The resulted showed that the Class C CFA as contained large amount of CaO (free lime) could catalyze the transesterification to achieve the highest FAME content of 89% under the operation conditions; the reaction temperature of 200 °C, the reaction pressure of 39 bars, the catalyst loading of 5 wt% of oil, the molar of oil to methanol of 1:30 and the stirring speed of 600 rpm for 5 h. The addition of La on the Class C CFA had a negative effect on conversion of palm oil. The FAME content decreased gradually from 89 to 62% with increasing La loading from 0 to 1 wt%.

Abstract: Quick lime or calcium oxide has attracted significant attention as a sustainable material to be used as fillers and catalysts in a broad range of industries. The quick lime derived from calcination of eggshell waste in a laboratory-scale rotary furnace is reported in this study. The eggshell waste was prepared by washing several times, drying in the sun, grinding and sieving through a 250 micrometers sieve size. Calcination of the sieved eggshells waste was conducted in a single zone rotary tube furnace at 800 °C with 5 degree slope and at 1 rpm. Both physical and chemical properties of the calcium oxide derived from the calcination of eggshell waste were systematically investigated by various scientific instruments. The results from powder X-Ray Diffraction (PXRD) and X-Ray Fluorescence: (XRF) showed that most of the calcium carbonate in the eggshell waste was thermally transformed to nano-calcium oxide with mean crystallite size of 47.5 nm and with a purity of 97.8%. The results from this study indicated the optimum conditions and the possibility for mass production of nano-calcium oxide via rotary furnace and have shown that the obtained nano-calcium oxide is comparable to the commercial chemical.

Abstract: The development of new environmentally friendly binder from calcium carbide residue and fly ash wastes were investigated in this study. The key point of this work is difference to several previous investigations in that the optimized mixture proportion of the raw materials were calculated based on their chemical composition and their reaction. The compressive strength development over the curing age was also compared with reference mortar created with OPC binder. Mortar cubes were cast from the mix containing the calcium carbide residue and fly ash, at the optimized ratio. The compressive strength of the mortar was then monitored over an extended period: at 56 days it was 10.66 MPa, which is approximately 47% of the reference mortar. The morphologies and chemical compositions of the developed mortar showed the presence of spherically shaped of unreacted fly ash powder particles embedded in a cement C–S–H gel resulting from the pozzolanic reaction of raw materials.