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Manoj Gupta - One of the best experts on this subject based on the ideXlab platform.

  • Processing, microstructure, and properties of Mg–SiC composites synthesised using fluxless casting process
    Materials Science and Technology, 2013
    Co-Authors: Manoj Gupta, Li Lu
    Abstract:

    AbstractIn the present study, Elemental Magnesium and Magnesium–silicon carbide composites were synthesised using the methodology of fluxless casting followed by hot extrusion. Microstructural characterisation studies revealed low porosity and a completely recrystallised matrix in every material. The average size of the recrystallised grains was found to decrease with an increasing presence of SiC particulates. For the reinforced Magnesium, fairly uniform distribution of SiC particulates and good SiC–Mg interfacial integrity was realised. The results of X-ray diffraction studies indicated the absence of oxide phases and no evidence of interfacial reaction products except in the case of Mg–26.0 wt-%SiC sample. Results of physical and mechanical properties characterisation revealed that an increase in the amount of SiC particulates incorporated leads to an increase in macrohardness and elastic modulus, which does not affect the 0.2% yield strength and reduces the ultimate tensile strength, ductility, and co...

  • Enhancing damping of pure Magnesium using nano-size alumina particulates
    Materials Letters, 2005
    Co-Authors: Narasimalu Srikanth, X L Zhong, Manoj Gupta
    Abstract:

    Abstract In the present study, Elemental Magnesium was reinforced with nano-size alumina particulates. Synthesis of materials was accomplished using the powder metallurgy route. Energy dissipation in the form of damping capacity was determined using free–free type suspended beam arrangement coupled with circle-fit approach. This technique is based on classical vibration theory, by which the geometry and material properties of the metallic specimen are related to measured resonant frequency and structural damping. Using the fact that the ratio of the vibration response to the applied force fits to a circle in the Argand plane for each resonant frequency of the test specimen, the damping factor and natural frequency is predicted accurately for the test specimen. The results revealed that an increase in the alumina content up to 0.4% volume percentage lead to an increase in the damping capacity up to 34%. Attempt is made to correlate the increase in damping with the various microstructural changes arising due to the presence of the nano-size alumina particulates in the composite sample.

  • effect of presence of nano size alumina particles on the properties of Elemental Magnesium
    Journal of Metastable and Nanocrystalline Materials, 2005
    Co-Authors: X L Zhong, Manoj Gupta
    Abstract:

    In present study, Elemental Magnesium was reinforced with nano-size alumina particles (50-nm). The composite samples were synthesized using the technique of powder metallurgy and the effect of extrusion temperature and sintering on the end properties was particularly investigated. The results of microstructural characterization studies confirmed the presence and reasonably uniform distribution of alumina particles. Results obtained from extruded unsintered samples revealed that the hardness and dimensional stability of Magnesium increases with an increasing presence of alumina particles while the 0.2%YS, UTS and ductility deteriorated. Results further revealed that including sintering step and extruding at higher temperature lead to an increase in dimensional stability, hardness, 0.2%YS, UTS and ductility for an alumina content as low as one percent by weight.

  • Application of a model for the work hardening behavior to Mg/SiC composites synthesized using a fluxless casting process
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002
    Co-Authors: M. Manoharan, Manoj Gupta
    Abstract:

    Abstract An understanding of the work hardening behavior of particulate reinforced metal-matrix composites is crucial in optimizing the parameters for deformation processing of these materials. In the present study, Elemental Magnesium and Magnesium–silicon carbide composites were synthesized using the methodology of fluxless casting followed by hot extrusion. The microstructures of the composites were characterized and the mechanical properties were determined. The results of ambient temperature tensile testing on the extruded Mg and Mg/SiC samples revealed that an increase in the weight percentage of SiC particulates in pure Magnesium increases the elastic modulus, did not affect the 0.2% yield strength, and reduced the ultimate tensile strength and ductility. A modified continuum model was applied to relate the work hardening behavior of the composites to microstructural parameters and to predict the fracture strain of the composites. The model is shown to predict the fracture strain of the composites quite accurately for all the three weight fractions of reinforcements evaluated in this study.

Ulrich S Schubert - One of the best experts on this subject based on the ideXlab platform.

A K Bhandari - One of the best experts on this subject based on the ideXlab platform.

  • Prospective evaluation of parenteral Magnesium sulfate in the treatment of patients with reentrant AV supraventricular tachycardia.
    American heart journal, 1990
    Co-Authors: P T Sager, J Widerhorn, R Petersen, C Leon, E Ryzen, R Rude, S H Rahimtoola, A K Bhandari
    Abstract:

    This study prospectively assessed the electrophysiologic effects of parenteral Magnesium sulfate administration on paroxysmal atrioventricular (AV) reentrant supraventricular tachycardia and the efficacy of Magnesium to terminate these arrhythmias. Eleven normomagnesemic patients, seven with orthodromic reentrant supraventricular tachycardia that used an accessory AV pathway, and four with typical AV nodal reentry were examined. All patients had a history of sustained supraventricular tachycardia requiring pharmacologic therapy or electrical cardioversion for termination of tachycardia. After baseline electrophysiologic study, including documentation of sustained supraventricular tachycardia that was reproducibly induced, parenteral Magnesium sulfate (a bolus of 0.3 mEq/kg of Elemental Magnesium infused over a 10-minute period followed by a maintenance infusion of 0.2 mEq/kg/hr) was administered during sustained supraventricular tachycardia. The serum Magnesium concentration increased from (mean +/- standard deviation) 1.9 +/- 0.2 mg/dl to 4.0 +/- 0.6 mg/dl (p = 0.0001). Except for flushing and mild diaphoresis during infusion of the Magnesium sulfate bolus, and dry heaves in one patient, there were no untoward effects or significant changes in systolic blood pressure. During administration of Magnesium, the tachycardia cycle length increased from 319 +/- 39 msec to 348 +/- 43 msec (p = 0.0001). Slowing of the tachycardia occurred predominantly in the antegrade limb of the circuit at the level of the AV node with the AH interval increasing from 171 +/- 66 msec to 197 +/- 68 msec (p = 0.0001), whereas there was no significant change in the HV interval (43 +/- 3 msec to 43 +/- 4 msec, p = NS) or the VA interval (106 +/- 43 msec to 110 +/- 47 msec, p = NS) during tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

  • Prospective evaluation of parenteral Magnesium sulfate in the treatment of patients with reentrant AV supraventricular tachycardia
    American Heart Journal, 1990
    Co-Authors: P T Sager, J Widerhorn, R Petersen, C Leon, E Ryzen, R Rude, S H Rahimtoola, A K Bhandari
    Abstract:

    This study prospectively assessed the electrophysiologic effects of parenteral Magnesium sulfate administration on paroxysmal atrioventricular (AV) reentrant supraventricular tachycardia and the efficacy of Magnesium to terminate these arrhythmias. Eleven normomagnesemic patients, seven with orthodromic reentrant supraventricular tachycardia that used an accessory AV pathway, and four with typical AV nodal reentry were examined. All patients had a history of sustained supraventricular tachycardia requiring pharmacologic therapy or electrical cardioversion for termination of tachycardia. After baseline electrophysiologic study, including documentation of sustained supraventricular tachycardia that was reproducibly induced, parenteral Magnesium sulfate (a bolus of 0.3 mEq/kg of Elemental Magnesium infused over a 10-minute period followed by a maintenance infusion of 0.2 mEq/kg/hr) was administered during sustained supraventricular tachycardia. The serum Magnesium concentration increased from (mean±standard deviation) 1.9±0.2 mg/dl to 4.0±0.6 mg/dl ( p =0.0001). Except for flushing and mild diaphoresis during infusion of the Magnesium sulfate bolus, and dry heaves in one patient, there were no untoward effects or significant changes in systolic blood pressure. During administration of Magnesium, the tachycardia cycle length increased from 319±39 msec to 348±43 msec ( p =0.0001). Slowing of the tachycardia occurred predominantly in the antegrade limb of the circuit at the level of the AV node with the AH interval increasing from 171±66 msec to 197±68 msec ( p =0.0001), whereas there was no significant change in the HV interval (43±3 msec to 43±4 msec, p =NS) or the VA interval (106±43 msec to 110±47 msec, p =NS) during tachycardia. In two patients the tachycardia terminated spontaneously. However, termination of supraventricular tachycardia in these patients was the result of three- and four-beat runs of spontaneous nonsustained ventricular tachycardia. Administration of Magnesium did not suppress the inducibility of supraventricular tachycardia in any patient or significantly influence the effective refractory periods of the right atrium, AV node, accessory pathway, or right ventricle. Thus in normomagnesemic patients with reentrant paroxysmal supraventricular tachycardia, parenterally administered Magnesium sulfate increases the tachycardia cycle length by slowing the antegrade limb of the reentrant circuit at the level of the AV node. Although it slows the tachycardia, Magnesium sulfate is only rarely effective in terminating supraventricular tachycardia.

Mojtaba Bahrami-karkevandi - One of the best experts on this subject based on the ideXlab platform.

  • Effect of excess boron oxide on the formation of tungsten boride nanocomposites by mechanically induced self-sustaining reaction
    Ceramics International, 2014
    Co-Authors: Bahman Nasiri-tabrizi, Reza Ebrahimi-kahrizsangi, Mojtaba Bahrami-karkevandi
    Abstract:

    Abstract The influence of the type of reducing agent, milling time and excess boron oxide on the formation of tungsten boride nanocomposites by mechanically induced self-sustaining reaction was studied. The powder mixtures were mechanically activated using a high-energy planetary ball mill under two distinct experimental conditions. In the first manner, a mixture of tungsten trioxide, boron oxide and graphite with the stoichiometric composition was milled for different times. In the second approach, a mixture of tungsten trioxide, boron oxide and Elemental Magnesium with a molar ratio of 2: x : y (with x =2.5–6.25 and y =13.5–24.75) was activated for 1 and 30 h. In the presence of 30–50 wt% excess boron oxide, WB was formed during milling. Further increasing the boron oxide content to 150 wt% led to a significant change in the mechanochemical behavior of the system so that WB and W 2 B 5 became more dominant after 1 h of milling. During leaching in 18% HCl aqueous solution, MgO was completely removed and consequently tungsten boride nanocomposites with high phase purity were obtained. According to microscopic observations, the 30 h milled sample showed an average particle size of about 95 nm after the leaching process.

  • Formation and stability of tungsten boride nanocomposites in WO3–B2O3–Mg ternary system: Mechanochemical effects
    International Journal of Refractory Metals & Hard Materials, 2014
    Co-Authors: Mojtaba Bahrami-karkevandi, Reza Ebrahimi-kahrizsangi, Bahman Nasiri-tabrizi
    Abstract:

    Abstract Mechanochemical behavior of WO3–B2O3–Mg ternary system to produce tungsten boride-based nanocomposites was investigated in terms of milling duration. To provide essential conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR), a mixture of tungsten trioxide, boron oxide and Elemental Magnesium with the stoichiometric composition was activated using a high-energy planetary ball mill. Based on the obtained data, the adiabatic temperature was around 3659 K which confirmed that the reaction mode was MSR. Due to the occurrence of a combustion reaction at the beginning of milling, the phase compositions were W, WB, W2B, and MgO. After 60 min of milling, WB disappeared completely and a ternary nanocomposite with the phase constituents of W2B, W and MgO was obtained. With increasing the milling time to 1800 min, no phase transformation was observed and thus a nanocomposite powder with similar phase compositions was produced. However, the percentage of the detected phases fluctuated in terms of milling time. During the leaching process, MgO (unwanted phase) was completely removed and consequently a nanocomposite powder with the phase compositions of W2B and W was formed. From the microscopic observations, the size of the composite particles was varied from 38 to 500 nm.

Bahman Nasiri-tabrizi - One of the best experts on this subject based on the ideXlab platform.

  • Effect of excess boron oxide on the formation of tungsten boride nanocomposites by mechanically induced self-sustaining reaction
    Ceramics International, 2014
    Co-Authors: Bahman Nasiri-tabrizi, Reza Ebrahimi-kahrizsangi, Mojtaba Bahrami-karkevandi
    Abstract:

    Abstract The influence of the type of reducing agent, milling time and excess boron oxide on the formation of tungsten boride nanocomposites by mechanically induced self-sustaining reaction was studied. The powder mixtures were mechanically activated using a high-energy planetary ball mill under two distinct experimental conditions. In the first manner, a mixture of tungsten trioxide, boron oxide and graphite with the stoichiometric composition was milled for different times. In the second approach, a mixture of tungsten trioxide, boron oxide and Elemental Magnesium with a molar ratio of 2: x : y (with x =2.5–6.25 and y =13.5–24.75) was activated for 1 and 30 h. In the presence of 30–50 wt% excess boron oxide, WB was formed during milling. Further increasing the boron oxide content to 150 wt% led to a significant change in the mechanochemical behavior of the system so that WB and W 2 B 5 became more dominant after 1 h of milling. During leaching in 18% HCl aqueous solution, MgO was completely removed and consequently tungsten boride nanocomposites with high phase purity were obtained. According to microscopic observations, the 30 h milled sample showed an average particle size of about 95 nm after the leaching process.

  • Formation and stability of tungsten boride nanocomposites in WO3–B2O3–Mg ternary system: Mechanochemical effects
    International Journal of Refractory Metals & Hard Materials, 2014
    Co-Authors: Mojtaba Bahrami-karkevandi, Reza Ebrahimi-kahrizsangi, Bahman Nasiri-tabrizi
    Abstract:

    Abstract Mechanochemical behavior of WO3–B2O3–Mg ternary system to produce tungsten boride-based nanocomposites was investigated in terms of milling duration. To provide essential conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR), a mixture of tungsten trioxide, boron oxide and Elemental Magnesium with the stoichiometric composition was activated using a high-energy planetary ball mill. Based on the obtained data, the adiabatic temperature was around 3659 K which confirmed that the reaction mode was MSR. Due to the occurrence of a combustion reaction at the beginning of milling, the phase compositions were W, WB, W2B, and MgO. After 60 min of milling, WB disappeared completely and a ternary nanocomposite with the phase constituents of W2B, W and MgO was obtained. With increasing the milling time to 1800 min, no phase transformation was observed and thus a nanocomposite powder with similar phase compositions was produced. However, the percentage of the detected phases fluctuated in terms of milling time. During the leaching process, MgO (unwanted phase) was completely removed and consequently a nanocomposite powder with the phase compositions of W2B and W was formed. From the microscopic observations, the size of the composite particles was varied from 38 to 500 nm.