S. Ahuja

Argonne National Laboratory, Lemont, Illinois, United States

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Publications (5)5.93 Total impact

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    ABSTRACT: The method of gelcasting requires making a mixture of a slurry of ceramic powder in a solution of organic monomers and casting it in a mold. Gelcasting is different from injection molding in that it separates mold filling from setting during conversion of the ceramic slurry to a formed green part. In this work, nuclear magnetic resonance (NMR) spectroscopy and imaging has been used for in-situ monitoring of the gelation process and gelcasting of alumina. 1H NMR spectra and images are obtained during polymerization of a mixture of soluble reactive acrylamide monomers. Polymerization was initiated by adding an initiator and an accelerator to form long-chain, cross-linked polymers. Multidimensional NMR imaging was utilized for in-situ monitoring of the process and for verification of homogeneous polymerization. Comparison of the modeled intensities with acquired images shows a direct extraction of T1 data from the images.
    03/2008: pages 247 - 254; , ISBN: 9780470314821
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    ABSTRACT: Surface acoustic wave (SAW) sensors must be specifically designed for each application because many variables directly affect the acoustic wave velocity. In the present work, we have designed, fabricated, and tested a SAW sensor for detection of metastable states of He. The sensor consists of two sets of micromachined interdigitated transducers (IDTs) and delay lines fabricated by photolithography on a single Y-cut LiNbO <sub>3</sub> substrate oriented for Z-propagation of the SAWs. One set is used as a reference and the other set employs a delay line coated with a titanium-based thin film sensitive to electrical conductivity changes when exposed to metastable states of He. The reference sensor is used to obtain a true frequency translation in relation to a voltage controlled oscillator. An operating frequency of 109 MHz has been used, and the MT finger width is 8 μm. Variation in electrical conductivity of the thin film at the delay line due to exposure to He is detected as a frequency shift in the assembly, which is then used as a measure of the amount of metastable He exposed to the sensing film on the SAW delay line. A variation in the He pressure versus frequency shifts indicates the extent of the metastable He interaction
    Ultrasonics Symposium, 1996. Proceedings., 1996 IEEE; 12/1996
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    ABSTRACT: 1H nuclear magnetic resonance spectra and images have been acquired during polymerization of a mixture of soluble reactive methacrylamide (monomer) and N,N‘-methylenebisacrylamide (cross-linking molecule). The mixture was polymerized by adding ammonium persulfate (initiator) and tetramethylethylenediamine (accelerator) to form long-chain, cross-linked polymers. Study of the time-varying spin−lattice relaxation times (T1) during the polymerization was conducted at 25 and 35 °C and the variation of spectra and T1 with respect to the extent of polymerization was determined. To verify homogeneous polymerization, multidimensional 1H NMR imaging was utilized for in-situ monitoring of the process. The intensities from the images are modeled and the correspondence shows a direct extraction of T1 data from the images.
    Macromolecules 01/1996; 29(16):5356-5360. · 5.93 Impact Factor
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    ABSTRACT: In the gelcasting process, a slurry of ceramic powder in a solution of organic monomers is cast in a mold. The process is different from injection molding in that it separates mold-filling from setting during conversion of the ceramic slurry to a formed green part. In this work, NMR spectroscopy and imaging have been conducted for in-situ monitoring of the gelation process and for mapping the polymerization. ¹H nuclear magnetic resonance spectra have been obtained during polymerization of a premix of soluble reactive methacrylamide (monomer) and N, N`-methylene bisacrylamide (cross-linking molecules). The premix was polymerized by adding ammonium persulfate (initiator) and tetramethyl-ethylene-diamine (accelerator) to form long-chain, cross-linked polymers. The time-varying spin-lattice relaxation times T⁠during polymerization have been studied at 25 and 35°C, and the variation of spectra and T⁠with respect to extent of polymerization has been determined. To verify homogeneous polymerization, multidimensional NMR imaging was utilized for in-situ monitoring of the process. The intensities from the images are modeled and the correspondence shows a direct extraction of T⁠data from the images.
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    ABSTRACT: Argonne National Laboratory, with support from DOE`s Office of Nonproliferation and National Security, is currently developing an intelligent hand-portable sensor system. This system is designed specifically to support the intelligence community with the task of in-field sensing of nuclear proliferation and related activities. Based upon pulsed laser photo-ionization time-of-flight mass spectrometry technology, this novel sensing system is capable of quickly providing a molecular or atomic analysis of specimens. The system is capable of analyzing virtually any gas phase molecule, or molecule that can be induced into the gas phase by (for example) sample heating. This system has the unique advantages of providing unprecedented portability, excellent sensitivity, tremendous fieldability, and a high performance/cost ratio. The system will be capable of operating in a highly automated manner for on-site inspections, and easily modified for other applications such as perimeter monitoring aboard a plane or drone. The paper describes the sensing system.