Mittal V.,The Petroleum Institute
Applied Clay Science | Year: 2012
Alkylammonium montmorillonites have onset temperature of degradation in the same temperature range used for compounding of thermoplastics, thus, requiring more thermally stable organic cations. In the current study, phosphonium, imidazolium and pyridinium ions differing in their chemical architecture (length of alkyl chains, number of phenyl groups etc.) were exchanged on the surface of montmorillonites. The montmorillonites with two different cation exchange capacities (CECs) were used. The thermal behavior of the modified montmorillonites was analyzed by thermogravimetric analysis. To achieve quantitative insights into the onset of degradation, temperatures to reach 5% and 10% mass loss and peak degradation temperatures were compared. Time to reach 1% mass loss was also calculated in the dynamic TGA. The surfactants used in the study were more thermally stable than the conventional alkylammonium cations due to their delayed onset as well as peak degradation temperatures. The time required to attain certain extent of degradation was also much higher in the case of phosphonium montmorillonites, thus, confirming their better thermal resistance. Though the degradation temperatures as well as profiles of the modified montmorillonites with different CECs were similar, the dynamic TGA revealed better thermal behavior of the higher CEC montmorillonite. The X-ray diffraction studies also concluded that optimal modification of the montmorillonite surface could be attained, thus, confirming the high potential of phosphonium montmorillonites for nanocomposites. © 2011 Elsevier B.V.
Beig A.R.,The Petroleum Institute
IEEE Transactions on Industrial Electronics | Year: 2012
In high-power applications, the output voltage of a voltage source inverter (VSI) must be synchronized with its fundamental component in order to eliminate subharmonics. With proper selection of switching states, it is possible to obtain synchronization and symmetry in the space vector pulse width modulation (SVPWM) algorithm. This paper presents an improved three-level SVPWM algorithm for the overmodulation region, which guarantees synchronization, half-wave symmetry, quarter-wave symmetry, and three-phase symmetry for all integer values of the pulse number. The proposed synchronized SVPWM algorithm is experimentally verified. The performance of the proposed algorithm is compared with other conventional algorithms. The comparative results prove that the consideration of synchronization and various symmetry results in better performance of the VSI. © 2012 IEEE.
Mittal V.,The Petroleum Institute
Macromolecular Materials and Engineering | Year: 2014
Polymer/graphene based nanomaterials have attracted significant scientific interest in the recent years due to marked enhancement in the polymer properties at low filler fractions. The property enhancements are attributed commonly to high aspect ratio of graphene platelets, filler-polymer interactions at the interface, as well as uniform dispersion of the platelets in the polymer matrices. Graphene also provides opportunities to tune its surface in order to achieve compatibility with the polymer matrices. Occasionally, chemical binding of the polymer matrix to the graphene surface has also been achieved. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Kim H.,University of Minnesota |
Abdala A.A.,The Petroleum Institute |
MacOsko C.W.,University of Minnesota
Macromolecules | Year: 2010
Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent-and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives for this new class of nanocomposites. © 2010 American Chemical Society.
Bassioni G.,The Petroleum Institute
Applied Energy | Year: 2012
The manufacture of cements with several main constituents is of particular importance with regard to reducing climatically relevant CO2 emissions in the cement industry. This ecological aspect is not the only argument in favor of Portland composite cements; they are also viable alternatives to Portland cement from the technical point of view. Substitution of ordinary Portland cement (CEM I) by Portland composite cements (CEM II) and (CEM III), which clearly possess different chemical and mineralogical compositions, results in changes of their reaction behavior with additives like superplasticizers. A common admixture to CEM I in that sense is limestone (industrial CaCO3); its interaction with polycarboxylates is ignored and its inertness is taken for granted. This study provides a systematic approach in order to better understand the interaction of these polymeric superplasticizers with CaCO3 by adsorption and zeta potential measurements. The results give some fundamental understanding in how far the cement industry can reduce the production of cement clinker by replacing it with limestone as admixture and consequently the CO2 emission is reduced, which is of high political and environmental interest. © 2010 Elsevier Ltd.