Zahoor Ahmad

Degradation of PVC: Effect of zinc chloride on the concentration of polyenes

Abstract The thermal degradation of Polyvinylchloride (PVC) and PVC in the presence of ZnCl 2 was studied using UV-visible spectroscopy. Formation of a charge transfer complex, H + ZnCl 3 − , with the conjugated chain was observed. The results are compared with the previous studies at low temperature. Time dependence of concentration of polyene sequences in the presence of different amounts of ZnCl 2 was also studied. A critical analysis of the measurement of polyene sequences and the effect of ZnCl 2 on their formation has been given.

Cadmium chloride catalyzed degradation of PVC: UV-visible spectrophotometric and thermogravimetric studies

The kinetic parameters of the dehydrochlorination (DHCl) process of PVC mixed with different amounts of cadmium chloride have been determined using thermogravimetric analysis. UV-visible spectrophotometric analysis has been carried out on the samples degraded for different intervals of time. Formation of a stable complex with polyene linkages by cadmium chloride and its effect on the degradation process has been discussed. The values of kinetic parameters have been compared with that reported for catalyzed degradation of PVC using zinc chloride.

Physical, electrical and magnetic properties of nano-sized Co-Cr substituted magnesium ferrites

Co-Cr substituted magnesium ferrite nanomaterials (Mg1−xCoxCrxFe2−xO4 with xu2009=u20090.0−0.5) have been prepared by the polyethylene glycol assisted micro emulsion method. X-ray diffraction analysis confirms the single-phase cubic close-packed lattice formation of synthesized materials. Hysteresis loops are measured up to field of 4 MA/m and high field region of these loops are modeled using the Law of Approach to saturation to calculate the magnetocrystalline anisotropy constant. The saturation magnetization of the samples increases initially from 148 kA/m for xu2009=u20090.0 to 299 kA/m (xu2009=u20090.3) and then decreases to 187 kA/m (xu2009=u20090.5). Curie temperature for this series is found to be in the range of 618-766 K. Room temperature resistivity increases gradually from 7.5u2009×u2009108 Ωu2009cm (xu2009=u20090.0) to 3.47u2009×u2009109 Ωu2009cm (xu2009=u20090.5). Additionally, dielectric measurements are carried out at room temperature in a frequency range of 100 Hz to 3 MHz. With improvement in the values of the above-mentioned properties, the synthesized materials could be suitable for potential application in some magnetic and microwave devices.

Generalized dispersion relation for electron Bernstein waves in a non-Maxwellian magnetized anisotropic plasma

A generalized dielectric constant for the electron Bernstein waves using non-Maxwellian distribution functions is derived in a collisionless, uniform magnetized plasma. Using the Neumann series expansion for the products of Bessel functions, we can derive the dispersion relations for both kappa and the generalized (r,q) distributions in a straightforward manner. The dispersion relations now become dependent upon the spectral indices κ and (r,q) for the kappa and the generalized (r,q) distribution, respectively. Our results show how the non-Maxwellian dispersion curves deviate from the Maxwellian depending upon the values of the spectral indices chosen. It may be noted that the (r,q) dispersion relation is reduced to the kappa distribution for r=0 and q=κ+1, which, in turn, is further reducible to the Maxwellian distribution for κ→∞.

Electrostatic potentials and energy loss due to a projectile propagating through a non-Maxwellian dusty plasma

The electrostatic potentials (Debye and wake) and energy loss due to a charged projectile propagating through an unmagnetized collisionless dusty plasma are derived employing kappa and generalized (r,q) velocity distributions for the dust acoustic wave. It is found that these quantities in general differ from their Maxwellian counterparts and are sensitive to the values of spectral index, κ in the case of kappa distribution and to r, q in the case of generalized (r,q) distribution. The amplitudes of these quantities are less for small values of the spectral index (κ, r=0, q) but approach the Maxwellian in the limit κ→∞ (for kappa distribution) and for r=0, q→∞ [for generalized (r,q) distribution]. For any nonzero value of r, the potential and the energy loss grow beyond the Maxwellian results. The effect of kappa and generalized (r,q) distributions on potential and energy loss is also studied numerically and the results are compared with those of the Maxwellian distribution.

Electrical Behavior of Tb-Mn Substituted Y-Type Hexa-ferrites for High-Frequency Applications

Single phase nanostructured Tb-Mn substituted Y-type hexaferrites with composition Sr2Co2−xMnx TbyFe12−yO22 (xxa0=xa00.0–1, yxa0=xa00.0–0.1) have been synthesized by the normal microemulsion technique. X-ray diffraction patterns reveal the formation of Y-type hexagonal single phase. The crystallite size, calculated by Scherer’s formula, is found in the range of 30–48xa0nm, which is well suitable for obtaining good signal-to-noise ratio in high density recording media. The enhancement in direct current resistivity has been attributed to the reduction in Fe3+ ions at octahedral sites. The Arrhenius plots show that there are two conduction mechanisms operating in the synthesized materials: in the ferri-region, the conduction is due to electrons, whereas in the para-region, it is due to polaron hopping phenomena. The calculated values of activation energy in the para-region are greater than 0.40xa0eV, which clearly suggests that the conduction phenomenon is due to hopping of polarons. Variation of dielectric constant with frequency depicts that the dielectric constant initially decreases with increase in frequency, while at higher frequency it decreases slowly. The dielectric results are in agreement with the Maxwell–Wagner model. Both the resonance and relaxation peaks at high frequency have been observed in dielectric loss and tan δ data. It has been noted that such types of peaks appear when hopping frequency becomes equal to that of the external applied field. The high values of resistivity and low dielectric loss make these materials best candidates for high frequency applications.

Dispersion relation for pure dust Bernstein waves in a non-Maxwellian magnetized dusty plasma

Pure dust Bernstein waves are investigated using non-Maxwellian kappa and (r,q) distribution functions in a collisionless, uniform magnetized dusty plasma. Dispersion relations for both the distributions are derived by considering waves whose frequency is of the order of dust cyclotron frequency, and dispersion curves are plotted. It is observed that the propagation band for dust Bernstein waves is rather narrow as compared with that of the electron Bernstein waves. However, the band width increases for higher harmonics, for both kappa and (r,q) distributions. Effect of dust charge on dispersion curves is also studied, and one observes that with increasing dust charge, the dispersion curves shift toward the lower frequencies. Increasing the dust to ion density ratio (nd0ni0) causes the dispersion curve to shift toward the higher frequencies. It is also found that for large values of spectral index kappa (κ), the dispersion curves approach to the Maxwellian curves. The (r,q) distribution approaches the kap...

Optimization and characterization of a Pilot-psi cascaded arc with non-LTE numerical simulation of Ar, H2 gases

A numerical simulation code, PLASIMO, is used to model non-LTE plasmas in the cascaded arc for hydrogen and argon. The purpose of these simulations is to optimize the cascaded arc plasma source, which is used to produce a high density plasma column in Pilot-psi, a linear device to study plasma surface interaction processes. Results are compared with the experimental findings to validate the model. The effect of a change in the arc channel geometry on the ionization degree is studied. It is found that for the hydrogen arc an increase in length beyond 30?mm will not increase the ionization degree, in contrast to widening the arc. With an increase in radius from 2?mm to 5?mm for a 30?mm long arc the degree of ionization of hydrogen increases from 5.4 to 38. For the argon arc an increase both in the length and in the width increases the ionization degree. With an increase in length from 30?mm to 40?mm for a 2?mm wide arc the degree of ionization of argon increases from 14.5 to 17.1, whereas with an increase in radius from 2?mm to 5?mm for 30?mm long arc the same increases from 14.5 to 37.5. To simulate the influence of the wall material, the effect of hydrogen wall association on the degree of ionization and dissociation is studied. Wall association in the nozzle section, where heating is absent, significantly reduces the degree of dissociation, in agreement with the experimental data. In Pilot-psi, the arc is operated in a high magnetic field, so the effect of a magnetic field on the yield of Ar+ and H+ ions leaving the arc is also studied. It is found that with a 3?T magnetic field the Ar+ yield increases from 1.6 ? 1020 to 2.1 ? 1020 (25% increase) while the H+ yield increases from 1.4 ? 1020 to 2.9 ? 1020 (100% increase).

Numerical simulation of a cascaded arc source with different Ar–H2 mixtures of nonlocal thermal equilibrium plasmas

Cascaded arc of Pilot-PSI is modeled using numerical simulation code PLASIMO [G. M. Janssen, Ph.D. thesis, Eindhoven University of Technology (2000), http://plasimo.phys.tue.nl]. Pilot-PSI is a linear device used to produce a high density plasma column for the study of plasma surface interaction processes. In this modeling effort nonlocal thermal equilibrium plasma of Ar–H2 mixture is used. The purpose of these simulations is to optimize the cascaded arc for a higher yield of H+ ions and to investigate the role of Ar–H2 mixture ratios. The associative charge exchange reaction followed by dissociative recombination plays a very important role in the dissociation of H2 molecules and as a consequence the yield of H+ increases and of Ar+ decreases. The Ar+ density also decreases in the arc when H2 concentration is increased beyond certain value. With a mixture of 2.5 standard liters per minute Ar and 0.5 SLM H2 the H+ ion flux exceeds the flux obtained in pure H2 gas, at a reduced expenditure of energy per ion.

Response to “Comment on ‘Generalized dispersion relation for electron Bernstein waves in a non-Maxwellian magnetized anisotropic plasma’” [Phys. Plasmas 22, 024701 (2015)]

Sharifi and Parvazian have presented comments on our paper by questioning the validity of the results. The plots of different curves of kappa and (r, q) distributions produced by them are incorrect. They pretended as if we have made claim that our results are valid for large arguments of product of Bessel Function, whereas Neumanns series expansion is valid only for small arguments. In our paper, no claim is made that the results are valid for all values of b. Our results are valid only for b ≪ 1. The results plotted by the commenters are incorrect and in this response we are presenting correct plots of dispersion curves.