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We report the synthesis of nanocrystalline calcium carbonate with varying particle sizes by precipitation techniques from an aqueous solution of calcium nitrate and sodium carbonate at controlled pH. The particle size of the carbonate powder was precisely controlled by changing the precursor concentration. The synthesized carbonate powders were characterized by using scanning electron microscopy, X-ray diffraction technique, and transmission electron microscopy. The particle size, along with the crystallite size of as-synthesized carbonate powder, decreases with increasing precursor concentration. The non-isothermal decomposition kinetics of the carbonate powder was also evaluated by using near to the modified Arrhenius equation's exact solution. The experimental results were best fitted at n = 0.5, and the one-dimensional diffusion-controlled transport process mechanism (D 1) and one-dimensional phase boundary movement mechanism (R 1) was found to be very close fit of the corresponding evaluated g(α) value. The apparent activation energy of the nano calcium carbonate decomposition was found in the range of 120–175 kJ/mol, which is also inherently functioning with the average particle size. The apparent activation energy of decomposition of CaCO 3 found to be decreased with decreasing average particle size of nanocrystalline calcium carbonate. [ABSTRACT FROM AUTHOR]

Sintering of alumina from 1500°C to 1650°C and tribo‐mechanical properties at room temperature had been investigated using nano CuO as a sintering aid. Bulk density gradually increases with sintering temperature from 1500°C to 1600°C and is optimized at 1600°C, beyond this, bulk density does not significantly increase at 1650°C. The addition of 2 wt% CuO showed the best result on densification. Densification of about 97.74% was attained at 1600°C with the incorporation of 2 wt% CuO. Nano CuO at grain boundaries forms CuAl2O4 liquid which modifies the morphology of the grain and improves mechanical properties. The formation of self‐lubricating tribo‐film on the wear track results in a low coefficient of friction <0.2 and reduces specific wear rate. 4 wt% CuO addition increases contact tensile stress (σmax) by 51.2% and high Hertzian contact pressure (Pmax≈1.51 GPa) causes plastic deformation of wear track. The re‐solidified strengthening bond phase on the wear track simultaneously increases in friction coefficient and wear resistance with CuO addition. The optimizing effect of CuO addition shows that 2 wt% significantly decreases wear rate, and increases hardness and fracture toughness. [ABSTRACT FROM AUTHOR]

In this article, it is shown that in a linear induction machine (LIM), the force ripple that arises due to the magnetic asymmetry does not depend on whether the LIM is being fed from a voltage source or a current source. When the LIM is fed from a three-phase balanced voltage source, the primary voltage is balanced but the LIM draws an unbalanced current from the supply. When the LIM is fed from a three-phase balanced current source, the primary current is balanced but an unbalanced voltage appears across the LIM terminals. In both these cases, the unbalance creates a ripple in the propulsive force of the LIM. This force ripple increases with the increase in the speed of the LIM. This article shows that at any given speed, the percentage of the ripple component in the propulsive force remains constant irrespective of all operating conditions. The variation of the force ripple with the speed can be represented by a curve, which is unique for one LIM. This curve neither depends on the value of the primary voltage or primary current, nor does it depend on the nature of the energy source from which the LIM is being supplied. The force ripple arises from the flux distortion due to end effects and can, therefore, be instrumental in estimating the amount of end effects existing in an LIM. [ABSTRACT FROM AUTHOR]

A power transformer, when energized at no-load, may have transient currents up to 100 times that of the steady state magnetizing current. This inrush current has several detrimental effects on power quality and may damage sensitive equipment connected to the system. In this paper, a power electronic based control circuit is developed, which estimates the last remnant and, utilizing this data, it controls the next re-energization instant to achieve inrush free switching. An equivalent circuit model of a transformer is also presented to simulate the transient dynamic performance of a transformer for any arbitrary switching operation. [ABSTRACT FROM AUTHOR]

This paper proposes a simplified analytical averaged model of a thyristorized commutatorless series motor. The motor operation is generally complicated due to the complexities present in the three-phase synchronous machine used and the nonlinearities introduced by the switching operation of the power electronic converter that is feeding the electrical machine. The simple analytical model is formulated in light of a conventional dc series motor and is found to be approaching the simplicity of a conventional dc series motor both in dynamic condition and steady state. The developed simplified model is found to yield results closely tallying with those obtained from a ‘detailed numerical model’ developed earlier, which is totally numerical in nature. The results are also validated experimentally on a small laboratory-built prototype. The developed model lays the foundation of controlling the motor for different industrial loading applications. One such application, viz., constant torque loading, is considered to show that the control strategy adopted on the basis of the discussed model works satisfactorily to develop a constant torque according to a given torque reference irrespective of load disturbances. [ABSTRACT FROM AUTHOR]

Assesses the steady-state model of a silicon-controlled-rectifier based load-commuted commutatorless series motor. Influence of harmonics in the production of steady torque; Computation of the harmonic torque; Component of the armature current and level field current.

In this paper, an image processing technique is introduced to measure the grain size and their distributions from the SEM image of copper oxide (CuO) and titanium dioxide (TiO2) doped sintered alumina ceramics accurately. The noise present in SEM image is removed by applying low pass Gaussian filter followed by suppression of regional minima over a threshold. The clarity of individual grains and grain boundaries have been done by applying Watershed transform to this preprocessed SEM image. Morphological operations like dilation and erosion are used to make the grain‐boundary edges clear and continuous. The individual grain size in µm scale is measured from the pixel length of the rectangular bounding box drawn around the segmented grain. The normal Gaussian type distribution of grain size is observed in both CuO‐ and TiO2‐doped grains in SEM image. The average grain size of CuO‐doped alumina grains (2.24 µm) is very close to G50 value (2.17 µm), but G50 value of TiO2‐doped grains (8.59 µm) is slightly higher than its average grain size (7.96 µm). The proposed algorithm is compared with linear intercept method and the grain sizes obtained are very close to each other. [ABSTRACT FROM AUTHOR]

This investigation reports the adsorption effect of Cobalt and Zinc ions on the antibacterial properties of Silicon Carbide (SiC) added fired Porcelain based ceramics against Escherichia coli and Staphylococcus aureus. Incorporation of SiC in porcelain composition shows decrease in bulk density and increase in apparent porosity gradually upto 15 weight percent addition. The bulk density and apparent porosity of 15 wt% SiC added porcelain are 2.01 g/cm3 and 24.03%, respectively. Phase and microstructural charecterization reveals that fine grained interlocked mullite network with little unconverted quartz and carborandum are uniformly distributed in the microstructure. Co+2 and Zn+2 adsorption on exposed surface is calculated to be ~0.42 mg/cm2 and Inductively coupled mass plasma spectroscopy (ICP‐MS) shows that 1641.41 ppm of Co+2 and 1936.37 ppm of Zn+2 are leached in water from adsorbed surface. This is the first report where, transition metal specific antibacterial efficacy of SiC added porcelain‐based ceramics are investigated. This report reveals that both Co+2 and Zn+2 adsorption results in antibacterial efficacy against E coli and S aureus and Co+2 adsorption is superior to (zone of inhibition is ~1.3 cm more depending on bacteria and sample specifications) Zn+2 adsorption. [ABSTRACT FROM AUTHOR]

The present investigation is focused on the in-situ synthesis of Graphene oxide (GO)-ferrite nanoparticle hybrid framework by gel-combustion method followed by fabrication of homogeneous, structurally stable thin (~100–120 μm) hybrid-polyurethane coating on a metallic aluminum substrate and its application on the properties of broadband absorption over the microwave frequency region. Microstructure studies of hybrid materials illustrated that small sized ferrite nanoparticles (~17 nm) are grafted on and through the graphene layers, which forms a homogeneous coating thereby. The hybrid-nanocomposite coating demonstrated superior broadband absorption properties with absorptivity higher than 90% throughout a bandwidth of ~6 GHz, and moreover, it was found that with increased loading of GO in the nanocomposite, the bandwidth range of absorption frequency increases with enhanced absorptivity. The real part and imaginary part of the surface impedance values of the coating was obtained as 377 Ω and 0 Ω, respectively, which imply that the free-space impedance of the hybrid-nanocomposite coating is matching correctly. The nanocomposite coating showed ultra-high absorptivity over the frequency band of 8–12 GHz, which has numerous practical applications as radar absorbing materials (RAM), stealth technology, electromagnetic shielding, and radiated electromagnetic interference (EMI) management in onboard spacecraft and many more. [ABSTRACT FROM AUTHOR]