Alok Srivastava

Panjab University, Chandigarh, Chandīgarh, India

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Publications (19)34.33 Total impact

  • Journal of Radioanalytical and Nuclear Chemistry 01/2014; 300(1). · 1.42 Impact Factor
  • Arjun Singh, P. K. Soni, T. Shekharam, Alok Srivastava
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    ABSTRACT: This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N2 atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N2 atmosphere. In the derivative curve, there was single maximum degradation peak (T max) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (T g ) and degradation temperature (T d ) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
    Journal of Applied Polymer Science 02/2013; 127(3). · 1.64 Impact Factor
  • Arjun Singh, P.K. Soni, Manjit Singh, Alok Srivastava
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    ABSTRACT: In this paper, thermal degradation and degradation kinetic of a poly(vinylidene fluoride–chlorotrifluoroethylene) (poly(VDF–CFTE)) copolymers are investigated by thermogravimetry (TG) under non-isothermal conditions. Thermal degradation of poly(VDF–CFTE) copolymers namely FKM1, FKM2, FKM3 and FMK4 samples is carried out at different heating rate under nitrogen atmosphere. The activation energies of poly(VDF–CFTE) samples are calculated from Kissinger–Akahira–Sunose (KAS) and Friedman kinetic methods. To investigate the kinetic model of thermal degradation for poly(VDF–CTFE) copolymers, Criado method is employed. The results showed that the probable model for the degradation of poly(VDF–CTFE) copolymers agreed with a power law and diffusion (D1) model. The activation energies of FKM1, FKM2, FKM3 and FKM4 samples are found to be 196, 197, 198 and 207 kJ mol−1, respectively.
    Thermochimica Acta 11/2012; 548:88–92. · 2.11 Impact Factor
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    ABSTRACT: In northern part of Indian sub-continent, As related environmental and health issues receive attention from all over the world. Forty-eight sediment samples were collected from the Ganga Alluvial Plain (GAP) and its weathering products (from the Gomati River) for the study of As distribution and mobilization. These sediment samples were analyzed by Instrumental Neutron Activation Analysis (INAA) method using Cirus Research Reacter of Bhabha Atomic Research Centre, Mumbai. Average As concentrations in the GAP sediments (10.44 mg kg−1), the Gomati River bed sediments (1.36 mg kg−1) and the Gomati River suspended sediments (5.30 mg kg−1) were reported. Significant decrease of As content from the alluvial sediments to the river sediments is a clear indication of its mobilization by chemical weathering processes of mineral biotite. Present study demonstrates the importance of INAA for quantification and mobilization of As and improves our understanding related to As related environmental issues in northern India and elsewhere.
    Journal of Radioanalytical and Nuclear Chemistry 11/2012; 294(2). · 1.42 Impact Factor
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    ABSTRACT: Thin films of poly(ethyleneterephthalate) (PET) were exposed to different radiation dose brought about by 80 MeV carbon and 98 MeV silicon ion beam. The UV–vis absorption studies reveal that there is decrease in optical band gap energy to the extent of ∼29.3 and 42.1%. The X-ray diffraction analyses have shown that crystallite size decreased by ∼18.6 and 52.6%, indicating amorphization of PET. The colour of PET films change from colourless to light yellowish followed by light brown as radiation dose is increased. The colour formation has been ascribed to an increase in conjugation in the carbon chain. In the case of PET irradiated with carbon ion, the electrical conductivity increased with frequency beyond a threshold value of 1 kHz. The increase in conductivity of PET films on irradiation is due to formation of defects and carbon clusters as a result of polymer chain scission. The thermal study further confirmed the increase in amorphous nature with increase in radiation dose. The results indicate that radiation dose brings about significant physicochemical transformations in PET.
    Radiation Physics and Chemistry 03/2012; 81(3):284–289. · 1.19 Impact Factor
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    ABSTRACT: Kidney stones obtained from six patients belonging to the stone belt region of India (Punjab) were analyzed for inorganic constituents using instrumental neutron activation analysis (INAA) and energy dispersive X-ray fluorescence (EDXRF) techniques. For INAA, samples were irradiated along with IAEA RM Soil 7 as reference standard in CIRUS reactor, BARC, Mumbai. Gamma activity of irradiated samples was measured using a 45% relative efficiency HPGe detector coupled to 8 k channel analyzer. EDXRF method was used for determination of concentration of Ca. The concentrations of ten elements namely Ca, Na, K, Mn, Co, Cr, Zn, Br, Sm and Cl, are reported and discussed.
    Journal of Radioanalytical and Nuclear Chemistry 12/2011; 294(3). · 1.42 Impact Factor
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    ABSTRACT: The phyto-accumulation efficacy of selenium (Se) from soil by chickpea plant is reported. Chickpea plants were grown in soil having different concentrations (1–4 mg kg−1) of Se. Samples of soil and different parts of chickpea plants in Se rich soil were analyzed for determination of Se concentrations by instrumental neutron activation analysis (INAA). Samples were irradiated in self-serve facility of CIRUS reactor, BARC, Mumbai at a neutron flux of the order of 1013 cm−2 s−1. The gamma activity at 264.7 keV of 75Se (119.8 d) was measured using a 45% relative efficiency HPGe detector coupled to MCA. Dependence of Se distribution in soil and plants on its spiking concentration was evaluated in this work. The Se concentrations determined in plant parts grown in control soil and in soil spiked with Se (4 mg kg−1) are in the range of 0.6–0.8 and 65–68 mg kg−1 respectively.
    Journal of Radioanalytical and Nuclear Chemistry 11/2011; 294(2). · 1.42 Impact Factor
  • Sajeela Awasthi, Alok Srivastava, M. L. Singla
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    ABSTRACT: Cyclic voltammetry was used to investigate the electrochemical behavior of citric acid (CA) and quinine hydrochloride (QH) at a polypyrrole-pentacyanoferrate/Platinum (PPY–PCNFe/Pt) electrode in aqueous medium. The analytical plots obtained were found to be linear in the concentration range between 1.0 and 9.0mM for both the analyte solutions. The detection limits (3δ) were found to be 1.17×10−4M and 1.08×10−5M for CA and QH analyte solutions, respectively. It was further observed that the diffusion of ionic species into and out of the polymeric film made the PPY–PCNFe/Pt electrode highly electroactive thereby enabling it to efficiently detect the analyte solutions having concentration as low as 1mM.
    Synthetic Metals 08/2011; 161(15):1707-1712. · 2.22 Impact Factor
  • Alok Srivastava, G S Bains, R Acharya, A V R Reddy
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    ABSTRACT: Soil samples from the seleniferous region of Punjab State in India were analyzed by instrumental neutron activation analysis (INAA) using reactor neutrons and high resolution γ-ray spectrometry. Samples were collected from three different depths namely surface, root and geological bed zones. Concentrations of 15 elements including selenium and arsenic were determined by relative method. For comparison purposes, soil samples collected from a non-seleniferous region were also analyzed.
    Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 02/2011; 69(5):818-21. · 1.09 Impact Factor
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    ABSTRACT: The mungbean plants were grown hydroponically in the absence (control) or presence of 0.1, 0.25, 0.50 and 0.75 ppm selenium (as sodium selenate) for 10 days. The growth of shoots and roots increased with application of selenium with greater extent in shoots. With 0.5 and 0.75 ppm Se levels, the shoot growth was stimulated by 24% to 27% over control, respectively, while the roots showed a corresponding increase of 18-19%, respectively. The shoot-to-root ratio was enhanced significantly with Se application and maximum effects occurred at 0.75 ppm Se. A significant increase was observed in chlorophyll and cellular respiration ability with 0.5 and 0.75 ppm selenium. The increase in growth by selenium was accompanied by elevation of starch, sucrose and reducing sugars. The activity of starch hydrolysing enzymes--amylases and sucrose hydrolysing enzyme--invertase was stimulated significantly with selenium. This was associated with elevation of activities of sucrose synthesising enzymes--sucrose synthase and sucrose phosphate synthase. It was concluded that increase in growth of shoots and roots by application of Se was possibly the result of up-regulation of enzymes of carbohydrate metabolism thus providing energy substrates for enhanced growth.
    Biological trace element research 10/2010; 143(1):530-9. · 1.92 Impact Factor
  • Sajeela Awasthi, Alok Srivastava, M.L. Singla
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    ABSTRACT: With a view to develop conducting polymer film of high electroactivity, pentacyanonitrosylferrate (PCNFe) doped polypyrrole (PPY) composite films are prepared using cyclic voltammetry deposition method. The PPY–PCNFe composite is characterized by FTIR, TEM and TGA analysis. The electroactivity of PPY–PCNFe composite film is studied in 3 mM KCl (common electrolyte) solution. Two redox pairs at E1/2 = −0.59 V and 0.02 V due to redox behavior of polymer and dopant anions respectively are observed. The electroactivity study reveals the existence of two types of PCNFe dopant anions in the polymeric film: one form is loosely held and prone to easy removal from the polymer matrix whereas the other form is strongly bound to polymer backbone and prone to electrochemical redox reaction by movements of electrons. The high electroactivity of the film is attributed to the movements of ionic species into and out of the polymeric film as well as movements of electron.
    Synthetic Metals 07/2010; 160:1401-1404. · 2.22 Impact Factor
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    ABSTRACT: Bean (Phaseolus vulgaris L.) seedlings were subjected to varying selenium levels (1, 2, 4, and 6 ppm) in a hydroponic culture. The germination reached 100% in 48 h in all Se levels except 6 ppm, where it took 72 h. The root and shoot growth was stimulated at 1 and 2 ppm Se levels that was commensurate with increase in chlorophyll content, leaf water content, and cellular respiration. At 4 and 6 ppm Se levels, the growth was inhibited appreciably, which was associated with increase in stress injury measured as damage to membranes and decrease in cellular respiration, chlorophyll, and leaf water content. The oxidative injury as elevation of lipid peroxidation was larger compared to hydrogen peroxide accompanied by reduced levels of enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) and non-enzymatic (ascorbic acid and glutathione) antioxidants. Proline content was significantly higher at 1 and 2 ppm Se but diminished considerably at 4 and 6 ppm levels concomitant with the reduced growth. Exogenous application of proline (50 µM) resulted in substantiation of its endogenous levels that antagonised the toxic effects of Se by improving the growth of seedlings. The stress injury was reduced significantly with simultaneous increase in enzymatic and non-enzymatic antioxidants. Especially the components of ascorbate-glutathione cycle showed larger stimulation with proline application. The role of proline in mitigating the toxic effects of Se is discussed.
    Biological trace element research 05/2010; 140(3):354-67. · 1.92 Impact Factor
  • M. L. Singla, Sajeela Awasthi, Alok Srivastava
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    ABSTRACT: The polyaniline/Mn3O4 composite doped with perchloric acid, sulphuric acid, ortho-phosphoric acid, acetic acid and acrylic acid have been characterized as sensing materials to determine relative humidity in the range of 20–90%. Each composite sample has been used in the form of pellet. Relative humidity measurement has been related with the change in resistance of doped composite samples. Each acid doped polyaniline/Mn3O4 showed an increase in resistance as relative humidity increases, however the sensitivity is found to dependent on the type of dopant anions. The response of each composite is found to be almost linear with the humidity but the composites doped with organic acids have found to be more sensitive than those with inorganic dopants. However polyaniline samples doped with these acids under similar conditions showed reverse behaviour that is the resistance decreases with the increase in relative humidity but with lower sensitivity. The anomalous behaviour of the acid doped composite samples may be due to lowering of p-type nature of the polymer chains in the composites with an increase of humidity. Due to the linear increase in resistance of composites doped with organic acids can act as humidity sensor.
    Sensors and Actuators B Chemical 11/2007; 127(2):580-585. · 3.84 Impact Factor
  • Amit L. Sharma, Alok Srivastava
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    ABSTRACT: The effects of ion beam irradiation on optical, chemical and electrical properties of nitroso substituted polyaniline, polynitrosoaniline (N-PANI) have been investigated. N-PANI was irradiated with 100 MeV 28Si ions at different ion-fluences. The pristine and irradiated polymer samples were characterized by FT-IR, UV–visible spectroscopic techniques. The electrical conductivity studies were conducted on polymer samples. A significant change in optical band gap and room temperature electrical conductivity was observed in polymer samples after irradiation. The solubility of the polymer samples has also been tested in 1-methyl-2-pyrrolidone (NMP).
    Current Applied Physics 09/2007; · 2.03 Impact Factor
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    ABSTRACT: The paper deals with the study of TCR and conductivity behaviour of the PANI/Mn3O4 composite in its emeraldine salt state doped with different acids like H3PO4, H2SO4, HClO4, CH3COOH and CH2CHCOOH. The conductivity results have also been compared with pure emeraldine salt doped with same acid. The characterisation of each composite sample and emeraldine salt was done using XRD, FT-IR, and TGA. From the TCR studies it has been observed that PANI/Mn3O4 composite doped with acetic acid and acrylic acid have negative temperature co-efficient (NTC) behaviour in the temperature range 20–110 and 20–160°C, respectively. Thermistors constant (B) values calculated from the data are 3625K−1 for composite doped with acetic acid and 3745K−1 for acrylic acid. Composite samples doped with H3PO4, H2SO4 and HClO4 acid did not show NTC behaviour, as the thermistor constant values in these composites are found to be on lower side. The results of the conductivity behaviour for the composite doped with CH3COOH and HClO4 are of the same order as that of doped emeraldine salt, whereas in other three composite samples the conductivity is much lower in comparison to emeraldine salt samples. XRD studies reveal that crystalline PANI/Mn3O4 composite has been transformed into amorphous phase during doping.From FT-IR spectra, it can be concluded that adsorbed acids anion on the oxide surface work as the charge compensator for positive charge on PANI. TG curves of composite suggest that the thermal degradation process of PANI/Mn3O4 composite proceeds in three steps and thermal stability of the composite depend on the dopant acid. The improvement in the thermal stability of composite is attributed to the interaction between a specific acid and PANI/Mn3O4 composite which may restrict the thermal motion of the PANI chain and shield the degradation of PANI in the composite. From the above study it can be concluded that the PANI/Mn3O4 composite doped with organic acids has the potential to act as NTC material for thermistor applications. Due to variation in the conductivity behaviour of doped composites and PANI, it may find application as sensing material.
    Sensors and Actuators A Physical 05/2007; 136(2):604-612. · 1.94 Impact Factor
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    ABSTRACT: The physico-chemical changes brought about by swift heavy ions of silicon and nickel in polyvinyl chloride (PVC) are discussed in terms of optical, electrical and chemical modifications. The electrical conductivity of the polyvinyl chloride, both in independent form as well as in blended form, increases with the increase in the ion fluence and the mass of the swift heavy ions. It was further observed that under the present experimental conditions, PVC did not have any significant influence on the electrical conductivity of PVC–PANI blend. The present work shows that swift heavy ion modification technique under limited conditions could be utilized for increasing the conductivity of insulating polymer conducting polymer (IPCP) blends.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 04/2006; · 1.19 Impact Factor
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    ABSTRACT: Films of 12μm thickness of the polymer polyethylene terephthalate (PET) were exposed to swift heavy ions of silicon with energies ranging from 44MeV to 120MeV and total ion fluence ranging between 1011 and 1013ions/cm2. The structural properties were investigated using Fourier transform infra red (FT-IR) and X-ray diffraction (XRD) techniques whereas the thermal studies were carried out employing differential scanning calorimetry (DSC). It was noticed that in general irradiation of PET by swift heavy ions of silicon led to the transformation of the polymer into a disordered amorphous state. However, at low fluence, some degree of ordering was noticed as reflected from new peak appearing in the XRD pattern. Around 35% decrease in the crystallite size was observed at the highest fluence. The observation of a mixture of different endotherms arising due to series of melting points at lower temperatures gave further evidence to the observation stated above. The results obtained in the present work are discussed in the light of similar studies reported in literature on other polymers irradiated with low and high energy radiations.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 03/2006; 244(1):243-247. · 1.19 Impact Factor
  • Alok Srivastava
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    ABSTRACT: This paper reports on radon concentrations in dwellings from fifty different locations of India. The incorporated data were obtained using the passive solid state nuclear track detector technique. The estimated geometric mean value for India is 67.1 Bq m(-3). Chuadanga in Bangladesh had the lowest observed indoor radon concentration of 27.3 Bq m(-3) and Una in the northern part of India had the highest concentration of 281.5 Bq m(-3). This paper discusses the national geometrical mean value in terms of the national geometric mean values of other countries and also in terms of the geological influence. The estimated indoor radon levels are compared with the indoor radon levels as recommended by the International Commission on Radiation Protection (ICRP). It was observed that there are several locations in India where dwellings have higher indoor radon levels than the ICRP recommended value and requires some sort of intervention from regulating authorities. The mean value for indoor radon level given in the report of UNSCEAR 2000 for India needs to be revised.
    Journal of Environmental Radioactivity 02/2005; 78(1):113-21. · 3.57 Impact Factor
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    ABSTRACT: The commercially available solid state nuclear track detector CR-39 was bombarded with 100 MeV Si8+ ions. The Fourier transformed infrared (FTIR) spectroscopic technique was employed for studying the changes in chemical properties whereas differential scanning calorimetry was used for studying the changes in the thermal properties. It was observed that there were substantial chemical modifications in the sample such as the breaking of C-O single bonds and the formation of phenolic O-H bonds. It was further observed that CR-39 is amorphous and rigid and shows no glass transition temperature.
    Radiation Effects and Defects in Solids 07/2003; 158(8):561-566. · 0.60 Impact Factor