A Novel Method of Synthesis of Nanostructured Aluminum Nitride Through Sol‐Gel Route by In Situ Generation of Nitrogen

Nanostructured Aluminum Nitride (AlN) has been prepared by carbothermal reduction followed by nitridation (CTRN) of alumina gel over a temperature range 1200°C–1350°C and time period of 30 min to 3 h. Before heat treatment the gel is repeatedly evacuated and purged with ammonia. The nanopores of the gel are filled with ammonia which acts as a source of in situ nitrogen at heat‐treatment temperature. Dextrose also decomposes at the reduction temperature and generates ultrafine carbon. The stability diagram of the carbon saturated Al–N–O system is constructed and it shows that extremely low partial pressure of oxygen is required for the stability of AlN. The ultrafine carbon as well as hydrogen from the cracking of ammonia is not sufficient to create the extremely low partial pressure of oxygen required for the stabilization of AlN. So the sample is heat treated in charcoal boat in nitrogen atmosphere to achieve an extremely low partial pressure of oxygen required for the formation of AlN. The material has been characterized through XRD, FESEM, and HRTEM analyses. The spherical particle size of AlN is obtained ～21 nm.     

Low-frequency Raman scattering of light by silver nanoparticles

Silver nanoparticles sprayed onto a crystalline quartz substrate are characterized by means of the low-frequency Raman scattering. Contributions of silver nanoparticles of different sizes to the Raman scattering spectrum are estimated. Data of scanning electron microscopy are used to verify the validity of the results obtained.     

Deuterium thermal desorption from Ni-rich deuterated Mg thin films

Mg–Ni multilayers and Ni-rich Mg thin films were deposited by electron gun and pulsed laser deposition, respectively. Samples were submitted to thermal treatment in deuterium or hydrogen atmosphere at 423 K and 10⁵ Pa pressure to promote the metal to hydride phase transition.The H chemical bonding in the multilayer samples, after annealing in H₂ atmosphere, was examined by Fourier transform infrared spectroscopy: the obtained spectra suggest that the samples with the Mg:Ni=2:1 atomic ratio contain the Mg₂NiH₄ phase while the samples with lower Ni concentration contain both the MgH₂ and the Mg₂NiH₄ phases.The effect of the Ni additive on the stability of the deuteride phase was studied by thermal desorption spectroscopy (TDS). The TDS spectra of the single-phase Mg₂NiD₄ samples show a TDS peak at 400 K. The TDS spectra of the two-phase samples show both the D₂ desorption peak at 400 K and a second peak at higher temperature that we attributed to the dissociation of the MgD₂ phase. The high-temperature peak shifts to lower temperatures by increasing the Ni content.It is suggested that in the two-phase samples, the lattice volumes having the Mg₂Ni structure resulting from the dissociation of the Mg₂NiD₄ phase reduce the thermodynamic stability of the MgD₂ phase.     

Temperature dependence of electromechanical properties of PLZT <Emphasis Type="Italic">x</Emphasis>/57/43 ceramics

The compositions of lead lanthanum zirconate titanate PLZT [Pb(Zr_0.57Ti_0.43)O₃ + x at% of La, where x = 3, 5, 6, 10 and 12] have been synthesized using mixed oxide route. The temperature dependent electromechanical parameters have been determined using vector impedance spectroscopy (VIS). The charge constant d ₃₁ and elastic compliance s ₁₁ ^E show a peak in all the samples at a temperature T _mt much below the ferroelectric — paraelectric transition temperature, whereas the series resonance frequency f _s shows a dip at these temperatures. The Poisson’s ratio σ ^E increases with temperature T showing a broad peak at a temperature higher than T _mt . The voltage constant g ₃₁ decreases and the planar coupling coefficient K _p remains constant up to half of the T _mt and then falls sharply with T. Half of the T _mt can, therefore, be used for specifying the working temperature limit of the piezoceramics for the device applications.     

Oberflächenenergetische Charakterisierung

Surface Energetic Characterization of Nanoscale Fillers and Elastomers Almost any technically used rubber material is filled with particles in nanometer size, by which the properties of the material can be specific controlled. In modern car tires the used fillers have crucial influence on driving security (wet grip and ice grip), on fuel consumption (rolling resistance) and on the cost‐effectiveness (life time of the tire) [1].The first fillers used in rubber application were carbon blacks; actually in passenger car tires mostly surface modified silica is applied. The implementation of novel filler systems like organophilic modified layered silicates (organo‐clays) or carbon nanotubes is subject of intense research [2,3]. Surface energy and –polarity of the filler surface is a crucial, but often underestimated determining factor. All surface properties of rubber and filler have to be well balanced to get the nanoscale filler particles finely dispersed in the rubber matrix and also to obtain a good adhesion between polymer and filler surface.     

Enhanced corrugated QWIP performance using dielectric coverage

We report here the effect of dielectric/metal coverage on the performance of the corrugated quantum well infrared photodetectors (C-QWIP) in two wavelength regimes. We found that with proper dielectrics, both the detector dark current and the spectral responsivity can he improved upon the monitoring 45° edge coupled QWIP. In the 8 μm regime, the normalized responsivity of a Si₃ N₄ covered C-QWIP was found to be improved by 3.3 times. In the 14 μm regime, the improvement is a factor of 1.8 using Si₃N₄ coverage and a factor of 2.5 using SiO₂ coverage     

Effect of austempering treatment on microstructure and mechanical properties of high-Si steel

In the present investigation, the influence of austempering treatment on the microstructure and mechanical properties of silicon alloyed cast steel has been evaluated. The experimental results show that an ausferrite structure consisting of bainitic ferrite and retained austenite can be obtained by austempering the silicon alloyed cast steel at different austempering temperature. TEM observation and X-ray analysis confirmed the presence of retained austenite in the microstructure after austempering at 400 °C. The austempered steel has higher strength and ductility compared to as-cast steel. With increasing austempering temperature, the hardness and strength decreased but the percentage of elongation increased. A good combination of strength and ductility has been obtained at an austempering temperature of 400 °C.     

Investigation on microwave absorption capacity of nanocomposites based on metal oxides and graphene

Graphene and its nanocomposites were prepared via solution mixing process. Graphene based polymer nanocomposites were prepared by two step process. Firstly, graphene/poly(3-methyl thiophene)(PMT)/BaTiO₃ nanocomposite was prepared by in situ chemical oxidation polymerization technique. In the second step these nanocomposites were dispersed in thermoplastic polyurethane (TPU) matrix by solution blending process. All the four nanocomposites in TPU [30 % modified graphene (P1), 30 % Poly(3-methyl thiophene) (P2), 30 % graphene/PMT/BaTiO₃ (P3) and 15 % graphene/PMT/BaTiO₃ + 15 % Fe₃O₄ (P4)] were analyzed by different analytical techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Microwave absorbing property was measured by Agilent vector network analyzer (ENA E5071C) in the X-band region (8–12 GHz). Microwave absorption result was interpreted with the help of complex permittivity and permeability of the prepared materials. Matching of both dielectric loss and magnetic loss is essential for an effective radar absorbing material (RAM). P1, P2, P3 and P4 showed the maximum return loss of ?14.37, ?9.3, ?30.02 and ?47.59 dB respectively. Thermal stability of the RAMs was determined by the help of thermogravimetric analysis (TGA) instrument. Among the all, P4 showed better thermal property. All results support their use as RAM in different field.     

Pinch Roller Failure Analysis and Resulting Enhancement of Rebar Mechanical Properties

Reinforcing bars, popularly termed “rebars,” are used to impart tensile strength to concrete structures. Concrete has high resistance to weathering and fire and high compressive strength but almost no tensile strength, hence rebars are used to provide the latter to concrete. Property consistency along the length of rebars is an important prerequisite. When the finished product is subjected to thermomechanical treatment (TMT), proper control of rolling and water box parameters and efficient pinch rolling are needed to achieve acceptable properties. Variation of yield strength (YS) along TMT bars from the front to back end has been observed within the same heat treatment. In the presented investigation, it was observed that pinch rolling ineffectiveness is the main reason for the poor mechanical properties at the back end. The pinch roller was unable to support the back end of the TMT bars properly to maintain the speed and tension of the bars, resulting in nonuniform cooling of the back end through the water box and subsequent mechanical property failure. Due to the substandard material of the pinch roller, it was unable to hold the back end of the bar properly. Based on analysis of the roller it was concluded that it failed due to improper microstructure, resulting in inadequate hardness and toughness for the stringent operating conditions. AISI H13 is a better material to use in such high-service-temperature conditions. Moreover, proper heat treatment is needed to achieve adequate hardness and microstructure properties. After proper heat treatment of pinch rollers, their service life was increased twofold, minimizing the YS variation along the rebars.