Carbon nanotube reinforced aluminum based nanocomposite fabricated by thermal spray forming

The present research concentrates on the fabrication of bulk aluminum matrix nanocomposite structures with carbon nanotube reinforcement. The objective of the work was to fabricate and characterize multi-walled carbon nanotube (MWCNT) reinforced hypereutectic Al-Si (23 wt% Si, 2 wt% Ni, 1 wt% Cu, rest Al) nanocomposite bulk structure with nanocrystalline matrix through thermal spray forming techniques viz. plasma spray forming (PSF) and high velocity oxy-fuel (HVOF) spray forming. This is the first research study, which has shown that thermal spray forming can be successfully used to synthesize carbon nanotube reinforced nanocomposites. Microstructural characterization based on quantitative microscopy, scanning and transmission electron microscopy (SEM and TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and X ray photoelectron spectroscopy (XPS) confirms (i) retention and macro/sub-macro level homogenous distribution of multiwalled carbon nanotubes in the Al-Si matrix and (ii) evolution of nanostructured grains in the matrix. Formation of ultrathin β-SiC layer on MWCNT surface, due to chemical reaction of Si atoms diffusing from Al-Si alloy and C atoms from the outer walls of MWCNTs has been confirmed theoretically and experimentally. The presence of SiC layer at the interface improves the wettability and the interfacial adhesion between the MWCNT reinforcement and the Al-Si matrix. Sintering of the as-sprayed nanocomposites was carried out in an inert environment for further densification. As-sprayed PSF nanocomposite showed lower microhardness compared to HVOF, due to the higher porosity content and lower residual stress. The hardness of the nanocomposites increased with sintering time due to effective pore removal. Uniaxial tensile test on CNT-bulk nanocomposite was carried out, which is the first ever study of such nature. The tensile test results showed inconsistency in the data attributed to inhomogeneous microstructure and limitation of the test samples geometry. The elastic moduli of nanocomposites were computed using different micromechanics models and compared with experimentally measured values. The elastic moduli of nanocomposites measured by nanoindentation technique, increased gradually with sintering attributed to porosity removal. The experimentally measured values conformed better with theoretically predicted values, particularly in the case of Hashin-Shtrikman bound method.

Tin oxide based composites derived using electrostatic spray deposition technique as anodes for lithium-ion batteries

Recent advances in the electric & hybrid electric vehicles and rapid developments in the electronic devices have increased the demand for high power and high energy density lithium ion batteries. Graphite (theoretical specific capacity: 372 mAh/g) used in commercial anodes cannot meet these demands. Amorphous SnO2 anodes (theoretical specific capacity: 781 mAh/g) have been proposed as alternative anode materials. But these materials have poor conductivity, undergo a large volume change during charging and discharging, large irreversible capacity loss leading to poor cycle performances. To solve the issues related to SnO2 anodes, we propose to synthesize porous SnO2 composites using electrostatic spray deposition technique. First, porous SnO2/CNT composites were fabricated and the effects of the deposition temperature (200, 250, 300 °C) & CNT content (10, 20, 30, 40 wt %) on the electrochemical performance of the anodes were studied. Compared to pure SnO2 and pure CNT, the composite materials as anodes showed better discharge capacity and cyclability. 30 wt% CNT content and 250 °C deposition temperature were found to be the optimal conditions with regard to energy capacity whereas the sample with 20% CNT deposited at 250 °C exhibited good capacity retention. This can be ascribed to the porous nature of the anodes and the improvement in the conductivity by the addition of CNT. Electrochemical impedance spectroscopy studies were carried out to study in detail the change in the surface film resistance with cycling. By fitting EIS data to an equivalent circuit model, the values of the circuit components, which represent surface film resistance, were obtained. The higher the CNT content in the composite, lower the change in surface film resistance at certain voltage upon cycling. The surface resistance increased with the depth of discharge and decreased slightly at fully lithiated state. Graphene was also added to improve the performance of pure SnO2 anodes. The composites heated at 280 °C showed better energy capacity and energy density. The specific capacities of as deposited and post heat-treated samples were 534 and 737 mAh/g after 70 cycles. At the 70th cycle, the energy density of the composites at 195 °C and 280 °C were 1240 and 1760 Wh/kg, respectively, which are much higher than the commercially used graphite electrodes (37.2–74.4 Wh/kg). Both SnO2/CNTand SnO2/grapheme based composites with improved energy densities and capacities than pure SnO2 can make a significant impact on the development of new batteries for electric vehicles and portable electronics applications.

The response to an ESL population boom in the Beaufort County, South Carolina school system: A case study

The purpose of this case study was to examine the why the English language learners (ELLs) in the Beaufort County, South Carolina school system have been so successful. This school system has recently experienced a boom in its ESL student population, and this population has performed very well on standardized tests. This study used critical theory as its theoretical framework and examined why the students have been successful rather than marginalized in Beaufort County schools. This phenomenon was investigated using semi-structured interviews with the ESOL Coordinator for Beaufort County, 4 ESL-lead teachers, and 6 mainstream teachers.^ Data were collected using semi-structured interviews with Sarah Owen, the Beaufort County ESOL, Gifted and Talented, and World Languages coordinator. Based on the results of her interview, 4 themes emerged that were used for the semi-structured interviews with ESOL and mainstream teachers. The interviews centered on the themes of ESL policy, ESL leadership, and teacher training. The ESL and mainstream teacher interviews also revealed several subthemes that included teacher attitude, why Beaufort County has been successful with the ELLs, and the teachers' recommendations for other schools systems trying to successfully accommodate a large ESL student population in mainstream classrooms. ^ The findings from the teachers' interviews revealed that additional training for the teachers without ESL experience helped them become comfortable instructing ELLs. This training should be conducted by the ESOL teachers for those without ESOL certification or endorsement. As the teachers had more training, they had better attitudes about teaching ESOL students in their classes. Finally, those who utilized the additional ESOL training and ESOL accommodations saw better student achievement in their classes.^ Based on the finding of this study, the researcher proposed a model for other school systems to follow in order to replicate the success of Beaufort County's ELLs. The implications of this study focus on other schools systems and why ELLs are not obtaining the same level of success as those in Beaufort County's schools. Finally, recommendations for further research are provided.^

The Response to an ESL Population Boom in the Beaufort County, South Carolina School System: A Case Study

The purpose of this case study was to examine the why the English language learners (ELLs) in the Beaufort County, South Carolina school system have been so successful. This school system has recently experienced a boom in its ESL student population, and this population has performed very well on standardized tests. This study used critical theory as its theoretical framework and examined why the students have been successful rather than marginalized in Beaufort County schools. This phenomenon was investigated using semi-structured interviews with the ESOL Coordinator for Beaufort County, 4 ESL-lead teachers, and 6 mainstream teachers. Data were collected using semi-structured interviews with Sarah Owen, the Beaufort County ESOL, Gifted and Talented, and World Languages coordinator. Based on the results of her interview, 4 themes emerged that were used for the semi-structured interviews with ESOL and mainstream teachers. The interviews centered on the themes of ESL policy, ESL leadership, and teacher training. The ESL and mainstream teacher interviews also revealed several subthemes that included teacher attitude, why Beaufort County has been successful with the ELLs, and the teachers’ recommendations for other schools systems trying to successfully accommodate a large ESL student population in mainstream classrooms. The findings from the teachers’ interviews revealed that additional training for the teachers without ESL experience helped them become comfortable instructing ELLs. This training should be conducted by the ESOL teachers for those without ESOL certification or endorsement. As the teachers had more training, they had better attitudes about teaching ESOL students in their classes. Finally, those who utilized the additional ESOL training and ESOL accommodations saw better student achievement in their classes. Based on the finding of this study, the researcher proposed a model for other school systems to follow in order to replicate the success of Beaufort County’s ELLs. The implications of this study focus on other schools systems and why ELLs are not obtaining the same level of success as those in Beaufort County’s schools. Finally, recommendations for further research are provided.

Tin Oxide Based Composites Derived Using Electrostatic Spray Deposition Technique as Anodes for Li-Ion Batteries

Recent advances in the electric & hybrid electric vehicles and rapid developments in the electronic devices have increased the demand for high power and high energy density lithium ion batteries. Graphite (theoretical specific capacity: 372 mAh/g) used in commercial anodes cannot meet these demands. Amorphous SnO2 anodes (theoretical specific capacity: 781 mAh/g) have been proposed as alternative anode materials. But these materials have poor conductivity, undergo a large volume change during charging and discharging, large irreversible capacity loss leading to poor cycle performances. To solve the issues related to SnO2 anodes, we propose to synthesize porous SnO2 composites using electrostatic spray deposition technique. First, porous SnO2/CNT composites were fabricated and the effects of the deposition temperature (200,250, 300 oC) & CNT content (10, 20, 30, 40 wt %) on the electrochemical performance of the anodes were studied. Compared to pure SnO2 and pure CNT, the composite materials as anodes showed better discharge capacity and cyclability. 30 wt% CNT content and 250 oC deposition temperature were found to be the optimal conditions with regard to energy capacity whereas the sample with 20% CNT deposited at 250 oC exhibited good capacity retention. This can be ascribed to the porous nature of the anodes and the improvement in the conductivity by the addition of CNT. Electrochemical impedance spectroscopy studies were carried out to study in detail the change in the surface film resistance with cycling. By fitting EIS data to an equivalent circuit model, the values of the circuit components, which represent surface film resistance, were obtained. The higher the CNT content in the composite, lower the change in surface film resistance at certain voltage upon cycling. The surface resistance increased with the depth of discharge and decreased slightly at fully lithiated state. Graphene was also added to improve the performance of pure SnO2 anodes. The composites heated at 280 oC showed better energy capacity and energy density. The specific capacities of as deposited and post heat-treated samples were 534 and 737 mAh/g after 70 cycles. At the 70th cycle, the energy density of the composites at 195 °C and 280 °C were 1240 and 1760 Wh/kg, respectively, which are much higher than the commercially used graphite electrodes (37.2-74.4 Wh/kg). Both SnO2/CNTand SnO2/grapheme based composites with improved energy densities and capacities than pure SnO2 can make a significant impact on the development of new batteries for electric vehicles and portable electronics applications.