M. A. Shaz

High yield synthesis of electrolyte heating assisted electrochemically exfoliated graphene for electromagnetic interference shielding applications

Herein, we demonstrate a facile one pot synthesis of graphene nanosheets by electrochemical exfoliation of graphite. In the present study, we report a significant increase in the yield of graphene by electrolyte heating assisted electrochemical exfoliation method. The obtained results of heating assisted electrochemically exfoliated graphene (utilizing H2SO4 + KOH + DW) synthesis clearly exhibit that the yield increases ∼4.5 times i.e. from ∼17% (room temperature) to ∼77% (at 80 °C). A plausible mechanism for the enhanced yield based on lattice expansion and vibration of intercalated ions has been put forward and discussed in details. The quality of graphene was examined by Raman, XPS, FTIR, AFM, SEM, TEM/HRTEM and TGA techniques. The Raman as well as morphogenesis results confirm the quality of the graphene nanosheets. We have used this graphene as electromagnetic interference shielding material where a comparatively large quantity of graphene is required. This graphene exhibits enhanced shielding effectiveness (46 dB at 1 mm thickness of stacked graphene sheets in frequency region 12.4 to 18 GHz) as compared to conventional electromagnetic interference shielding materials, which is greater than the recommended limit (∼30 dB) for techno-commercial applications. Thus the present work is suggestive for future studies on enhancement of yield of high quality graphene by proposed method and the use of synthesized graphene in electromagnetic interference shielding and other possible applications.

Synthesis and microhardness measurement of Ti–Zr–Ni nanoquasicrystalline phase

Abstract The Ti–Zr–Ni forms one of the interesting systems of quasicrystals and related structures. It is the only system in Ti-based quasicrystalline phases which belongs to Bergman class and at the same time gives rise to a stable quasicrystalline structure. We report the formation of nanoquasicrystalline phase directly from melt spinning of molten Ti 53 Zr 27 Ni 20 alloy. Such a phase has been obtained at an optimum copper wheel speed (40 m/s) and jet pressure of 90 atm. We have also measured the mechanical response of this material by the microhardness technique. It shows much better ductility, strength and fracture toughness than the usual alloy having micron-sized quasicrystalline phase. Even at higher load (200 g) no crack seems to appear. We do observe shear bands suggesting the better toughness of bulk material containing nanoquasicrystalline/nanocrystalline phase.

Nanocrystallization and structural correlation in quasicrystalline and crystalline phases during mechanical milling

Abstract The main objective of the proposed work is to investigate the formation of nanoquasicrystalline and related nanocrystalline phases in Al—Cu—Fe system during mechanical milling at the initial stage of milling. The mechanical milling of a quasicrystalline Al65Cu20Fe15 alloy was performed in a high-energy ball mill (Szegvari attritor) by varying milling time from 2.5 min to 60 min under liquid hexane medium at the speed of 400 rpm with a ball to powder ratio of 40 : 1. X-ray diffraction was carried out for evaluating the lattice strain, lattice parameters and crystallite sizes of the milled sample. It was found that the evolution of monoclinic Al13Fe4 phase from Al65Cu20Fe15 quasicrystalline phase occurred after 2.5 min of milling, which was further confirmed by transmission electron microscopy. After 5 min of ball milling nano size disordered B2 phase (bcc, a = 0.29 nm) was also found. The systematic analysis of the XRD patterns for evolving lattice parameter, sequential strain suggests that the lattice strain during milling has been quite considerable.

Phase transformations in Al70Ni24Fe6 decagonal system during high energy ball milling

In the present investigation, the decagonal phase in Al70Ni24Fe6 alloy was used for studying the structural and microstructural stability during ball milling in an attritor mill for 1, 2, 4, 8, and 12u2009h under hexane medium with a powder to ball ratio of 1:100. The milled powder was annealed in an argon atmosphere for durations ranging from 1 to 40u2009h at 500°C. The as-cast alloy was found to consist of micron size decagonal phase as a major one along with minor amount of Al3Ni and Al13(Fe,Ni)4 crystalline phases. Powders milled for more than 8h contained predominantly the B2 phase. The crystallite size of the B2 phase was estimated to be around 17u2009nm after 12u2009h of milling. A lamellar like microstructure exhibiting the presence of nano-phase embedded in the grain of B2 phase has been found to evolve after 8u2009h of ball milling. Subsequent annealing treatment at 500°C for 10, 20 and 40u2009h of mechanically milled powder for 12u2009h has led to the transformation of B2 phase to the τ3 type vacancy ordered phase. The implications of these phase transformations and the evolution of corresponding microstructures will be discussed.

Formation of quasicrystalline phase in Al70−x Ga x Pd17Mn13 alloys

In the present investigation, the formation and stability of icosahedral phase in Al70− x Ga x Pd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with xu2009=u20092.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x ≥5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ξ′ crystalline (orthorhombic structure with unit cell au2009=u200923.5u2009Å, bu2009=u200916.6u2009Å and cu2009=u200912.4u2009Å) phases. In the case of the melt spun ribbon for xu2009=u20095 at% Ga, only an icosahedral phase has been found, but for 15u2009>u2009xu2009>u20095 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For xu2009=u200915 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. However, for xu2009=u200920, only a hexagonal Al3Pd2 phase results.

Formation and stability of icosahedral phase in Al65Ga5Pd17Mn13 alloy

The formation and characterization are described of a quaternary (pseudo-ternary) icosahedral quasicrystal in Al65Ga5Pd17Mn13 alloy. X-ray diffraction and transmission electron microscopy observations confirmed the formation of icosahedral, B2 type and ξ′ crystalline (orthorhombic structure with unit cell au2009=u200923.5 Å, bu2009=u200916.6 Å and cu2009=u200912.4 Å) phases in as-cast alloy. The icosahedral phase is formed after annealing at 800°C for 60 h. This is the first report of the formation of an icosahedral phase in an Al–Ga–Pd–Mn quaternary alloy by present technique. The energy dispersive X-ray analysis investigations suggest the presence of Ga (∼5 at.%) in the alloy. Icosahedral Al–Ga–Pd–Mn provides a new opportunity to investigate various characteristics, including surface characteristics. Attempts are made to discuss the micromechanisms for the formation of the quasicrystalline phase in Al–Ga–Pd–Mn alloys.

Investigation of transition from decagonal to vacancy ordered phase on replacement of Co by Cu in Al70Co15–xCuxNi15

Abstract The alloy with composition Al70Co15Ni15 forms one of the important quasicrystalline phase exhibiting formation of decagonal variants [1, 2]. In the present investigation, copper has been substituted in place of cobalt i.e. the phases corresponding to Al70Co15–xCuxNi15, have been investigated. It is found that when copper concentration reaches to a value of 10 atomic percent with the composition corresponding to Al70Co5Cu10Ni15, the decagonal phase starts yielding to give rise to vacancy ordered phase. When all cobalt is replaced by copper i.e. when the composition corresponds to Al70Cu15Ni15, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. It can thus be said that copper substitution brings in decagonal to vacancy ordered (VOP) phase transition. It has also been observed that gradual increase in concentration of Cu in Al70Co15–xCuxNi15 leads to cellular to dendritic transition in morphology.

On the formation of nano-sized quasicrystals in Ti53Zr27Ni20 alloy

Abstract We report here the formation of a nano-quasicrystalline (qc) phase in the melt spun ribbons of Ti53Zr27Ni20 alloy based on the results of transmission electron microscopy (TEM). Such a phase was formed by employing melt spinning of the alloy, at a wheel speed of 40xa0m/s. The nano-qc phase (30–40xa0nm) was detected through diffraction monitored by 30xa0nm electron probe using TEM. Together with this crystalline phases were found to coexist. These crystalline phases were found to be belonging to cubic crystal system (a=3.40 A ) and a hexagonal phase (a=5.21 A , c=8.53 A ) .

Highly efficient field emission properties of radially aligned carbon nanotubes

Here, we report extraordinary field emission properties from one pot synthesized aligned carbon nanotubes endowed with related Fe nanoparticles (NPs). The CNT configuration is in the form of a carbon hollow cylinder (CHC) with CNTs radially aligned towards the CHC axis. The structure generates electron field emission properties such as an ultralow turn on field (0.35 V μm−1 at 10 μA cm−2), a low threshold field (0.41 V μm−1 at 100 μA cm−2) and a high field emission current density (7.71 mA cm−2 at 0.78 V μm−1). It also exhibits multi-fold improvement in the field enhancement factor (1.34 × 104) with highly stable current emission at 100 μA measured for 14 h. No post synthesis treatment is required for enhanced field emission characteristics. The growth related Fe NPs assist in lowering the work function and hence enhancing the field emission properties. The possibility of assembling nano-structured field emitters into macroscale architectures suggests new prospects for next generation three dimensional electron sources.

Structural analysis of nanocrystalline spinel synthesized by quasicrystalline precursor

The cations Co2+/Ni2+ and Al3+ distribution in nanocrystalline (Co,Ni)Al2O4 spinel have been investigated using X-ray and transmission electron microscopy. The novel nanocrystalline (Co,Ni)Al2O4 spinel has been synthesized by mechanically milling of Al70Co15Ni15 decagonal quasicrystalline precursor with further annealing at 873 K under a controlled oxygen atmosphere for 20 hours. The x-ray diffraction data has been refined by the Rietveld method using JANA2006 and subsequently, the corresponding structure has been constructed using software Diamond 4.1. The phase structure has also been confirmed by analysis of transmission electron microscopy. Selected area diffraction (SAED) pattern obtained by TEM has been linearized by diffraction ring profiler software, which is analogues to XRD pattern of (Co,Ni)Al2O4 confirms the dvalues and corresponding plane. This is new software where data extracted from SAED is used for probable refinement. These analyses indicate that the cations Co2+ and Ni2+ distributed in the tetrahedral coordinated sites are the dominant species in the normal spinel phase. Harshit et al. (2016) Ceramics International 42, 19429–19432.