Phase Transformations in Third Generation Gamma Titanium Aluminides: Ti-45Al-(5, 10) Nb-0.2B-0.2C

Third generation γ-titanium aluminides with nominal compositions Ti–45Al–5Nb–0.2B–0.2C and Ti–45Al–10Nb–0.2B–0.2C were investigated to identify the phase transformation and their morphological stability with temperature. Electron microscopy and differential scanning calorimetry were employed for the characterization of phases and for recording the corresponding transformations, respectively. It has been inferred that the order–disorder transformation temperatures α₂ → α increased with increasing Niobium (Nb), while the α-transus temperature decreases. The stability of the microstructure for both alloys with temperature were also investigated. Mass change measured for the heating rates 20 °C s⁻¹ and 30 °C s⁻¹ reveals that the alloy Ti–45Al–10Nb–0.2–0.2C shows stability up to 1100 °C, and the alloy Ti–45Al–5Nb–0.2B–0.2C is stable up to 900 °C. The orientation relationship between the phases indicates that with the change in shape of the α phase from lamellar to equiaxed, it deviates from the Blackburn orientation relationship.

     

Conjugated polymer mediated synthesis of nanoparticle clusters and core/shell nanoparticles

Two water soluble conjugated polymers, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and ammonium ion stabilized poly(phenylene vinylene) (P2), are found to be able to reduce noble metal ions to zero-valent metals via a direct chemical deposition technique. Au nanoparticle clusters can be obtained through reduction of Au³⁺ ions by PEDOT:PSS and the electronic coupling between them can be controlled by HAuCl₄ concentration. Core/shell Ag/polymer nanostructures are prepared from reduction of Ag⁺ ions by P2, which have a ppb detection limit for 4-MBA using surface-enhanced Raman spectroscopy (SERS). This conjugated polymer mediated synthesis of metal nanoparticles may open a new avenue for fabricating nanomaterials and nanocomposites with tunable optical properties that are dominated by their structure and electronic coupling between nanoparticles.     

Room temperature hydrogen gas sensors of functionalized carbon nanotubes based hybrid nanostructure: Role of Pt sputtered nanoparticles

Fast detection of H₂ gas at room temperature has constantly remained a challenge. The metal-oxide based gas sensors have shown excellent sensing properties for gases like H₂, NO, CO and NH₃. In the present work, the H₂ gas sensing characteristics of multiwalled carbon nanotubes based hybrid sensor (F-MWCNTs/TiO₂/Pt) has been reported. The fabricated sensor shows 3.9% sensitivity for low concentration i.e. 0.05% of H₂ with good repeatability and stability at room temperature. The sensing response of F-MWCNTs/TiO₂/Pt is interrelated to change in their resistance on the introduction of H₂ gas and this phenomenon is required for deep understanding the effect of H₂ adsorption on their electronic conduction. The improvement in sensitivity of F-MWCNTs/TiO₂/Pt as compared to MWCNTs/TiO₂ towards H₂ is because of the catalytic role of dispersed Pt nanoparticles deposited by sputtering.     

Comparative analysis of mechanical properties of size films

The advent of very high speed shuttleless looms has increased the importance of sizing. Starch has been the most popular and economic size material. Synthetic binders are also being blended with starch to improve weaving loom efficiency. Some synthetic size materials have got restrictions in use mainly because of ecological reasons. In the recent years, many modifications have come up in the starch as a sizing agent. Different modifications give different properties, which can be suited for particular application. In the present study, a comparative analysis of different varieties of natural starch, modified starch and synthetic size materials have been carried out for their cohesion power, adhesion power, abrasion resistance and bending rigidity. Comparison is made between various varieties and also among different blends to see the effect of blending on different mechanical properties of size film. The effect of lubricant on properties of size film is also examined. In general, it is observed that paste characteristics and film properties of synthetic and modified starch are better than the natural starch.     

Electrochemical,Morphological and Anti-corrosive Characteristics of Pyrazine Derivatives for Mild Steel Corrosion in Aggressive Medium: A Comparative Study

The anti-corrosive characteristics of 2,5-dimethylpyrazine (2,5-DMP) and 2,6-dimethylpyrazine (2,6-DMP) on the corrosion of mild steel in 0.5 M sulfuric acid have been studied by gravimetric method and electrochemical techniques (potentiodynamic polarization, linear polarization resistance and electrochemical impedance measurement) to observe the adsorption of these pyrazine derivatives at the metal/solution interface. The results obtained have revealed that 2,5-DMP performs more efficiently in comparison with 2,6-DMP showing an efficiency of 97.12% at a concentration of 10^?2 M. The polarization curves clearly indicate that both chemicals act as a mixed-type inhibitors showing a predominance toward the cathodic reaction. Langmuir’s isotherm model was found to adequately describe the adsorption of both these inhibitors onto the mild steel surface. The calculated value of the free energy for the adsorption process, \(\Delta G^\circ_{\text{ads}}\), reveals a strong chemisorbed bond as well as a spontaneous adsorption process between the tested inhibitors and the mild steel surface. Surface morphological analysis of the MS specimens treated with these inhibitors has been conducted using energy-sispersive atomic X-ray spectroscopy. The results obtained have shown a good agreement with the results obtained from electrochemical techniques. Quantum chemical calculations have also been performed using hyperchem 8.0.6 package to supplement the findings from the preceding techniques.     

Ion implantation effects of negative oxygen on copper nanowires

Copper nanowires of diameter 80 nm were synthesized in polycarbonate membrane using template technique. Samples were then implanted with 160 keV O^?1 ion beam with varying particle fluence of 1?×?10¹², 5?×?10¹² and 1?×?10¹³ ions/cm². The SRIM (Stopping and range of ions in matter) software was used to study the processes involved. Compositional analysis confirms implantation of oxygen ions and the stoichiometry of Cu:O was found to be 6:1 by weight % when implanted at 1?×?10¹³ ions/cm². Scanning electron microscopy reveals no changes in morphology of nanowires on implantation. X-ray diffraction analysis showed no shifting in the ‘2θ’ position of diffraction peaks however some new diffraction peaks of oxygen were seen. Implantation with oxygen ion led to the increased crystallite size and reduced strain. The conductivity of the nanowires was found to increase linearly with the ion fluence presenting constructive effect of negative ion implantation on copper nanowires.     

Study of surface activation of PET by low energy (keV) Ni and N ion implantation

Polyethyleneterephthalate (PET) has been modified by 100 keV Ni⁺ and N⁺ ions using metal ion from volatile compound (MIVOC) ion source to fluence ranging from 1 × 10¹⁴ to 1 × 10¹⁶ ions/cm². The increasing application of polymeric material in technological and scientific field has motivated the use of surface treatment to modify the physical and chemical properties of polymer surfaces. When a material is exposed to ionization radiation, it suffers damage leading to surface activation depending on the type. The surface morphology was observed by atomic force microscopy (AFM). That show the roughness increases with fluence in both the cases. The Ni particles as precipitation in PET were observed by cross-section transmission electron microscopy (XTEM). The optical band gap (E_g) deduced from absorption spectra; was calculated by Tau’c relation. Raman spectroscopy shows quantitatively the chemical nature at the damage caused by the Ni⁺ and N⁺ bombardment. The ration of I_D/I_G shows graphite-like structure is formed on the surface. A layer of hydrogenated amorphous carbon is formed on the surface, which has confirmed by XPS results also.     

Conduction nature of conical pores in PET membrane

Summary The preparation of conical pores in polyethylene terepthlate (PET) membrane is described. The conical pores prepared in PET by track etching technique. For this purpose, Cl⁹⁺ ion irradiated film was placed into an electrolytic cell and etched from one side while other side of membrane was protected by a stopping medium. During etching, current was recorded as a function of time, which shows a sudden change, indicating the pores breakthrough. After breakthrough, the etch process is interrupted by replacing the etching solution. After etching, the current voltage characteristics were determined under symmetric bath conditions. The resulting conical pores show non ohmic behavior, similar to that of an electronic diode.     

Parameter convergence in adaptive feedback linearizing control of limit cycling systems with input saturation

Adaptive feedback linearizing control schemes are used to suppress limit cycle oscillations in nonlinear systems where the system parameters are either unknown or uncertain. Parameter convergence is desirable in these schemes as it provides a measure of robustness of the scheme and also permits the unknown/uncertain system parameters to be estimated. In recent work, we have shown how using a persistently exciting forcing it is possible to achieve parameter convergence in nonlinear limit cycling systems. In practice, however, limits on the control input to the plant due to saturation must be considered, and the main goal of this work is to analyze the effect of input saturation on parameter convergence in an adaptive feedback linearization framework. In particular, a technique known as control hedging is incorporated and the effectiveness of this method for very severe saturation constraints has been evaluated. Results are presented for a single degree-of-freedom wing rock dynamics model and a multi degree-of-freedom combustion acoustics model showing successful parameter convergence even in the presence of input saturation.