Now showing 1 - 10 of 54
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    Metal matrix composites by friction stir processing
    (12-08-2017) ;
    Yadav, Devinder
    Metal Matrix Composites by Friction Stir Processing discusses the capabilities of utilizing friction stir processing (FSP) as a tool to manufacture new materials, such as composites. FSP is considered a tool for grain refinement. However, this work illustrates how FSP has a wider capability due to the material flow and mixing the process offers. This book highlights such aspects by demonstrating the ability of the process to incorporate a second phase and make metal matrix composites (MMCs). The book covers the current research on processing MMCs by FSP, and presents a novel approach of making ductile MMCs by FSP using metal particle reinforcements.
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    Phase stability and conductivity of rare earth co-doped nanocrystalline zirconia electrolytes for solid oxide fuel cells
    (25-08-2020)
    Kumar, C. N.Shyam
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    Reddy, G. Srinivas
    Solid oxide fuel cell (SOFC) is a green energy technology that directly coverts chemical energy into electricity. Scandia stabilized zirconia (SSZ) shows the highest conductivity among zirconia based electrolytes for SOFCs. However, the stability of the cubic phase, which is the desirable phase for high conductivity, can be an issue in SSZ electrolytes due to its transformation to other low-conducting phases at higher temperatures. In the present investigation, SSZ electrolyte was co-doped with ytterbia, gadolinia and ceria with an objective of improving the high-temperature phase stability. Both the doped and co-doped compositions exhibited a single cubic phase in the as-processed condition. The phase stability at high temperature was studied by aging the sintered pellets at 900 °C for 500 h in air. X-ray diffraction and transmission electron microscopy analysis revealed formation of small amount of the low-conducting tetragonal phase in 1 mol % ytterbia and gadolinia co-doped compositions on ageing which resulted in conductivity degradation. Increasing the doping level to 2 mol% prevented the formation of the tetragonal phase. The ceria co-doped composition (1 mol%), on the other hand, was clean without any sign of the secondary phases even after high-temperature ageing. The rhombohedral ‘β’ phase formed in the binary composition (SSZ) after sintering but was absent in all the co-doped compositions. The conductivity of the co-doped samples was higher than the binary SSZ. Thus, it can be said that rare earth co-doping is an effective way of improving the phase stability and conductivity of SSZ electrolytes.
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    A novel spark plasma sintering route to process high-strength Ti–4Al–2Fe/TiB nano-composite
    (02-11-2018)
    Chaudhari, Rajesh
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    Ti–4Al–2Fe alloy and Ti–4Al–2Fe/TiB nano-composite were processed by a novel spark plasma sintering route. KBF4 was used as an alternative and inexpensive boron precursor to form TiB reinforcement in situ during sintering. Fe was used as an alternative to vanadium to make the (α + β) Ti matrix. The processed Ti–4Al–2Fe alloy exhibited excellent mechanical properties (CS = 1798 MPa). The TiB whiskers were distributed homogeneously and were fine (widths 130 nm and lengths from 100 nm to 3 µm). No residual TiB2 was found in the composite, in contrast with other methods. The TiB homogenised and refined the microstructure, while the hardness (710 HV), compressive strength (2414 MPa) and elastic modulus (140 GPa) all increased significantly when compared to the unreinforced alloy.
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    A facile method of resource recovery from bauxite residue by phosphoric acid treatment
    (01-07-2023)
    Mayuranathan, Kishore Kumar
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    Bauxite residue (BR) is an industrial waste from alumina refineries. Despite being comprised of valuable secondary materials, utilization of BR is limited owing to its high alkalinity and presence of some toxic constituents. Acid neutralization is widely used as a pre-treatment step to mitigate the problems caused by the alkalinity of BR. In this work, BR was treated with various concentrations of phosphoric acid (1 M, 3 M, 5 M, 8 M) followed by thermal treatment to recover the valuables (metals) in terms of metal phosphates. Phosphates of Al and Si were the main constituents of the residue while the supernatant contained mainly Fe and Al. The supernatant solution was acidic (pH between 1.5 and 1.9) and hence can be used to treat BR in place of phosphoric acid to obtain the metal phosphates as before. The 1 M sample residue showed presence of P2O5 like superphosphate fertilizer. The water leaching test showed insignificant levels of metal dissolution in the 8 M sample, thus exhibiting its ability toward immobilizing the constituents of BR. Additionally, the phosphates can be melted at 1000–1100 °C indicating their suitability for glass forming. Thus, phosphoric acid treatment of BR can result in phosphates that can be used in a range of applications.
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    Effects of ball milling and particle size on microstructure and properties 5083 Al-Ni composites fabricated by friction stir processing
    (01-10-2015)
    Shyam Kumar, C. N.
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    Yadav, Devinder
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    Janaki Ram, G. D.
    Ni particles were incorporated in a 5083 Al alloy matrix by friction stir processing (FSP) to fabricate metal particle reinforced composite. During the optimization of the process parameters for uniform particle distribution, it was found that ball-milled finer particles (10. μm) were dispersed more uniformly in the matrix compared to as-received coarse particles (70. μm). Hence, the particles were ball-milled before incorporating into 5083 Al matrix. The finer ball-milled particles were dispersed uniformly, however a thin intermetallic layer was formed at the particle-matrix interface. The layer was found to be Al-Ni intermetallic. When as-received fine particles of similar size (10. μm) were incorporated using the same FSP parameters no such layer was observed in the processed composite. Hence, ball milling of particles influenced the microstructure of the composite. The high-energy state of the ball-milled particles can be attributed to the formation of the interfacial layer. The strength of both the composite was higher compared to the unreinforced 5083 Al alloy. FSP also refined the grain size of the aluminum matrix from 25. μm to 3.5. μm and this also contributed to the strength enhancement of the composites. The strength and ductility of the ball-milled composite were lower as expected compared to the composite with as-received fine Ni particles due to the presence of the interfacial reaction layer.
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    Processing and compressive strength of Al-Li-SiCp composites fabricated by a compound billet technique
    (19-02-2009) ;
    Surappa, M. K.
    Al-Li-SiCp composites were fabricated by a simple and cost effective stir casting technique. A compound billet technique has been developed to overcome the problems encountered during hot extrusion of these composites. After successful fabrication hardness measurement and room temperature compressive test were carried out on 8090 Al and its composites reinforced with 8, 12 and 18 vol.% SiC particles in as extruded and peak aged conditions. The addition of SiC increases the hardness. 0.2% proof stress and compressive strength of Al-Li-8%SiC and Al-Li-12%SiC composites are higher than the unreinforced alloy. In case of the Al-Li-18%SiC composite, the 0.2% proof stress and compressive strength were higher than the unreinforced alloy but lower than those of Al-Li-8%SiC and Al-Li-12%SiC composites. This is attributed to clustering of particles and poor interfacial bonding. © 2008 Elsevier B.V. All rights reserved.
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    Synthesis and photoelectrochemical catalytic properties of polyoxometalate supported on zeolitic imidazolate Framework, ZIF-9–PMo12
    (01-05-2023)
    Augustine, Chippy Alphons
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    Khatun, Nasima
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    Development of photocatalysts for hydrogen generation is highly imperative in the current scenario for resolving the worldwide energy crisis. Continuous efforts are being made to find low-cost and durable photocatalysts with better light absorption capacity to mitigate energy issues. Herein, a new p-n heterojunction photocatalyst has been synthesized successfully using a polyoxometalate (POM), phosphomolybdic acid (PMo12), and zeolitic imidazolate framework (ZIF-9). Photoelectrochemical studies under visible-light irradiation revealed that ZIF-9–PMo12 exhibits a higher photocurrent density than pure ZIF-9. The support of ZIF-9 prevented the instability of PMo12 in aqueous solutions and improved the photoresponse ability of ZIF-9. The p-n junction formation impedes the recombination of electrons and holes, resulting in the improved photocatalytic property. Photoelectrochemical experiments confirmed the photocatalytic features, and thus this work paves the way for the development of an efficient, stable, and low-cost photocatalyst for green H2 generation.
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    Effect of friction stir processing (FSP) on microstructure and properties of Al-TiC in situ composite
    (25-05-2011) ;
    Yadav, Devinder
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    Suhas, G.
    Aluminium based in situ composites have many advantages over their conventional counterparts. However, a major problem in such composites is the segregation of the in situ formed particles at the grain boundaries. In this study, it has been shown for the first time that friction stir processing (FSP) can be used effectively to homogenise the particle distribution in Al based in situ composites. An Al-5wt.% TiC composite was processed in situ using a mixture of K2TiF6 and graphite powders in aluminium melt. Friction stir processing was employed on the as-cast composite to uniformly distribute the TiC particles in the Al matrix. The composite was subjected to single and double pass FSP and its effect on the microstructure and properties was evaluated. A single pass of FSP was enough to break the particle segregation from the grain boundaries and improve the distribution. Two passes of FSP resulted in complete homogenization and elimination of casting defects. The grain size was also refined after each FSP pass. This led to significant improvement in the mechanical properties. The novel feature of the composite is that while the strength and hardness improved substantially after FSP, the ductility was not compromised. © 2011 Elsevier B.V.
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    Synthesis of Al-TiC in-situ composites: Effect of processing temperature and Ti:C ratio
    (01-10-2009)
    Al-TiC insitu composites are gaining increasing importance because of good wettability of TiC with Al melt and its favourable properties. However, incomplete reaction between the released Ti and C in Al melt leads to formation of undesirable phases like Al3Ti which is detrimental to the properties. In this investigation, Al-TiC composites are processed at different temperatures from 700 °C to 1200 °C and with different Ti:C ratios to asses the effect of these two parameters on the formation of TiC particles. Microstructural features and X-ray diffraction results show that at temperatures below 1000 °C blocky type Al3Ti forms. As the temperature is increased the blocky nature of Al3Ti changes to needle like indicating release of Ti to a greater extent and as a result more and more TiC particles form. At 1200 °C there is no evidence of Al3Ti formation after a reaction time of 30 minutes. Increasing the carbon content (Ti:C ratio) to two fold of the stoichimetric amount does not show any significant effect. Though a four fold increase in carbon content showed some promise, however, some amount of free carbon was found to remain. © 2009 TIIM, India.
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    Processing and properties of Al-Li-SiCp composites
    (01-09-2007) ;
    Surappa, M. K.
    Al-Li-SiCp composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 μm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al-Li-8%SiC and Al-Li-12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al-Li-8%SiC and Al-Li-12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al-Li-18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macro- and microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ′ (Al3Li) and S′ (Al2CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al-Li-12%SiC, which shows marginally lower UTS and compressive strength than the Al-Li-8%SiC composite in extruded condition, exhibits higher strength than Al-Li-8%SiC in peak-aged condition. © 2007 NIMS and Elsevier Ltd.