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Jason A. Smith - One of the best experts on this subject based on the ideXlab platform.
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Knorr-Rabe Partial Reduction of pyrroles: application to the synthesis of indolizidine alkaloids.
Beilstein journal of organic chemistry, 2008Co-Authors: Brendon S. Gourlay, John H. Ryan, Jason A. SmithAbstract:The Birch Reduction of electron rich pyrroles does not occur readily. However, dissolving metal Reduction with zinc under acidic conditions gives 3-pyrrolines (2,5-dihydropyrroles) in reasonable yield. This dissolving metal Reduction was first reported by Knorr and Rabe in 1901 but since then has only been reported for the Reduction of electron rich pyrroles.
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Clinical outcome of trans-sacral interbody fusion after Partial Reduction for high-grade l5-s1 spondylolisthesis.
Spine, 2001Co-Authors: Jason A. Smith, Vedat Deviren, Sigurd Berven, Frank S. Kleinstueck, David S. BradfordAbstract:A clinical retrospective study was conducted. To evaluate the clinical and radiographic outcome of Reduction followed by trans-sacral interbody fusion for high-grade spondylolisthesis. In situ posterior interbody fusion with fibula allograft has improved the fusion rates for patients with high-grade spondylolisthesis. The use of this technique in conjunction with Partial Reduction has not been reported. Nine consecutive patients underwent treatment of high-grade (Grade 3 or 4) spondylolisthesis with Partial Reduction followed by posterior interbody fusion using cortical allograft. The average age at the time of surgery was 27 years (range, 8-51 years), and the average follow-up period was 43 months (range, 24-72 months). Before surgery, eight patients had low back pain, seven patients had radiating leg pain, and five patients had hamstring tightness. The average grade of spondylolisthesis by Meyerding grading was 3.9 (range, 3-5). Charts and radiographs were evaluated, and outcomes were collected by use of the modified SRS outcomes instrument. Radiographic indexes demonstrated significant improvement with Partial Reduction and fusion. The slip angle, as measured from the inferior endplate of L5, improved from 41.2 degrees (range, 24-82 degrees ) before surgery to 21 degrees (range, 5-40 degrees ) after surgery. All the patients were extremely or somewhat satisfied with surgery. The two patients who underwent this operation without initial instrumentation experienced fractures of their interbody grafts. Both of these patients underwent repair of the pseudarthrosis with placement of trans-sacral pedicle screw instrumentation and subsequent fusion. Partial Reduction followed by posterior interbody fusion is an effective technique for the management of high-grade spondylolisthesis in pediatric and adult patient populations, as assessed by radiographic and clinical criteria. Pedicle screw instrumentation with the sacral screws capturing L5 is recommended when this technique is used for the treatment of high-grade spondylolisthesis. According to the clinical and radiographic results from this study, Partial Reduction and posterior fibula interbody fusion supplemented with pedicle screw instrumentation is an effective technique for select patients with high-grade spondylolisthesis at L5-S1.
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clinical outcome of trans sacral interbody fusion after Partial Reduction for high grade l5 s1 spondylolisthesis
Spine, 2001Co-Authors: Jason A. Smith, Vedat Deviren, Sigurd Berven, Frank S. Kleinstueck, David S. BradfordAbstract:Study design A clinical retrospective study was conducted. Objective To evaluate the clinical and radiographic outcome of Reduction followed by trans-sacral interbody fusion for high-grade spondylolisthesis. Summary of background data In situ posterior interbody fusion with fibula allograft has improved the fusion rates for patients with high-grade spondylolisthesis. The use of this technique in conjunction with Partial Reduction has not been reported. Methods Nine consecutive patients underwent treatment of high-grade (Grade 3 or 4) spondylolisthesis with Partial Reduction followed by posterior interbody fusion using cortical allograft. The average age at the time of surgery was 27 years (range, 8-51 years), and the average follow-up period was 43 months (range, 24-72 months). Before surgery, eight patients had low back pain, seven patients had radiating leg pain, and five patients had hamstring tightness. The average grade of spondylolisthesis by Meyerding grading was 3.9 (range, 3-5). Charts and radiographs were evaluated, and outcomes were collected by use of the modified SRS outcomes instrument. Results Radiographic indexes demonstrated significant improvement with Partial Reduction and fusion. The slip angle, as measured from the inferior endplate of L5, improved from 41.2 degrees (range, 24-82 degrees ) before surgery to 21 degrees (range, 5-40 degrees ) after surgery. All the patients were extremely or somewhat satisfied with surgery. The two patients who underwent this operation without initial instrumentation experienced fractures of their interbody grafts. Both of these patients underwent repair of the pseudarthrosis with placement of trans-sacral pedicle screw instrumentation and subsequent fusion. Conclusions Partial Reduction followed by posterior interbody fusion is an effective technique for the management of high-grade spondylolisthesis in pediatric and adult patient populations, as assessed by radiographic and clinical criteria. Pedicle screw instrumentation with the sacral screws capturing L5 is recommended when this technique is used for the treatment of high-grade spondylolisthesis. According to the clinical and radiographic results from this study, Partial Reduction and posterior fibula interbody fusion supplemented with pedicle screw instrumentation is an effective technique for select patients with high-grade spondylolisthesis at L5-S1.
David S. Bradford - One of the best experts on this subject based on the ideXlab platform.
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Clinical outcome of trans-sacral interbody fusion after Partial Reduction for high-grade l5-s1 spondylolisthesis.
Spine, 2001Co-Authors: Jason A. Smith, Vedat Deviren, Sigurd Berven, Frank S. Kleinstueck, David S. BradfordAbstract:A clinical retrospective study was conducted. To evaluate the clinical and radiographic outcome of Reduction followed by trans-sacral interbody fusion for high-grade spondylolisthesis. In situ posterior interbody fusion with fibula allograft has improved the fusion rates for patients with high-grade spondylolisthesis. The use of this technique in conjunction with Partial Reduction has not been reported. Nine consecutive patients underwent treatment of high-grade (Grade 3 or 4) spondylolisthesis with Partial Reduction followed by posterior interbody fusion using cortical allograft. The average age at the time of surgery was 27 years (range, 8-51 years), and the average follow-up period was 43 months (range, 24-72 months). Before surgery, eight patients had low back pain, seven patients had radiating leg pain, and five patients had hamstring tightness. The average grade of spondylolisthesis by Meyerding grading was 3.9 (range, 3-5). Charts and radiographs were evaluated, and outcomes were collected by use of the modified SRS outcomes instrument. Radiographic indexes demonstrated significant improvement with Partial Reduction and fusion. The slip angle, as measured from the inferior endplate of L5, improved from 41.2 degrees (range, 24-82 degrees ) before surgery to 21 degrees (range, 5-40 degrees ) after surgery. All the patients were extremely or somewhat satisfied with surgery. The two patients who underwent this operation without initial instrumentation experienced fractures of their interbody grafts. Both of these patients underwent repair of the pseudarthrosis with placement of trans-sacral pedicle screw instrumentation and subsequent fusion. Partial Reduction followed by posterior interbody fusion is an effective technique for the management of high-grade spondylolisthesis in pediatric and adult patient populations, as assessed by radiographic and clinical criteria. Pedicle screw instrumentation with the sacral screws capturing L5 is recommended when this technique is used for the treatment of high-grade spondylolisthesis. According to the clinical and radiographic results from this study, Partial Reduction and posterior fibula interbody fusion supplemented with pedicle screw instrumentation is an effective technique for select patients with high-grade spondylolisthesis at L5-S1.
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clinical outcome of trans sacral interbody fusion after Partial Reduction for high grade l5 s1 spondylolisthesis
Spine, 2001Co-Authors: Jason A. Smith, Vedat Deviren, Sigurd Berven, Frank S. Kleinstueck, David S. BradfordAbstract:Study design A clinical retrospective study was conducted. Objective To evaluate the clinical and radiographic outcome of Reduction followed by trans-sacral interbody fusion for high-grade spondylolisthesis. Summary of background data In situ posterior interbody fusion with fibula allograft has improved the fusion rates for patients with high-grade spondylolisthesis. The use of this technique in conjunction with Partial Reduction has not been reported. Methods Nine consecutive patients underwent treatment of high-grade (Grade 3 or 4) spondylolisthesis with Partial Reduction followed by posterior interbody fusion using cortical allograft. The average age at the time of surgery was 27 years (range, 8-51 years), and the average follow-up period was 43 months (range, 24-72 months). Before surgery, eight patients had low back pain, seven patients had radiating leg pain, and five patients had hamstring tightness. The average grade of spondylolisthesis by Meyerding grading was 3.9 (range, 3-5). Charts and radiographs were evaluated, and outcomes were collected by use of the modified SRS outcomes instrument. Results Radiographic indexes demonstrated significant improvement with Partial Reduction and fusion. The slip angle, as measured from the inferior endplate of L5, improved from 41.2 degrees (range, 24-82 degrees ) before surgery to 21 degrees (range, 5-40 degrees ) after surgery. All the patients were extremely or somewhat satisfied with surgery. The two patients who underwent this operation without initial instrumentation experienced fractures of their interbody grafts. Both of these patients underwent repair of the pseudarthrosis with placement of trans-sacral pedicle screw instrumentation and subsequent fusion. Conclusions Partial Reduction followed by posterior interbody fusion is an effective technique for the management of high-grade spondylolisthesis in pediatric and adult patient populations, as assessed by radiographic and clinical criteria. Pedicle screw instrumentation with the sacral screws capturing L5 is recommended when this technique is used for the treatment of high-grade spondylolisthesis. According to the clinical and radiographic results from this study, Partial Reduction and posterior fibula interbody fusion supplemented with pedicle screw instrumentation is an effective technique for select patients with high-grade spondylolisthesis at L5-S1.
Timothy J. Donohoe - One of the best experts on this subject based on the ideXlab platform.
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The Partial Reduction of electron-deficient pyrroles: procedures describing both Birch (Li/NH3) and ammonia-free (Li/DBB) conditions.
Nature protocols, 2007Co-Authors: Timothy J. Donohoe, Rhian E. ThomasAbstract:The Partial Reduction of electron-deficient pyrroles using either Birch (Li/NH(3)) or ammonia-free (Li/di-tert-butyl biphenyl) conditions allows formation of pyrroline compounds in good yield and, when combined with a reductive alkylation or similar approach, leads to highly functionalized, synthetically useful compounds. This methodology has been proven in the syntheses of several complex natural products, all of which show interesting biological activity. This protocol describes in detail the following stages of the Partial Reduction procedure: formation of the reducing solution, Partial Reduction of the pyrrole compound and finally quench of the resulting anion/dianion using either protonating agents or an aldehyde. The ammonia-free conditions described herein are particularly useful for reactions requiring the use of reactive electrophiles, such as acid chlorides or enolizable aldehydes, which are incompatible with the standard Birch Reduction conditions. The reaction procedure for the ammonia Birch Reduction (procedure A) takes about 9.5 h to complete. Those described for the ammonia-free Reductions, procedure B and procedure C, can be expected to take approximately 33 and 8 h, respectively.
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Partial Reduction of pyrroles: application to natural product synthesis
Chemical record (New York N.Y.), 2007Co-Authors: Timothy J. Donohoe, Rhian E. ThomasAbstract:The Partial Reduction of N-Boc pyrroles has been explored giving stereoselective routes to disubstituted pyrrolines in good yields and with excellent diastereoselectivities. A novel methodology has been developed to carry out reductive aldol reactions on 2-substituted N-Boc pyrroles; use of aldehydes under reductive aldol conditions gave the anti aldol product in good selectivity. This chemistry was used as the key transformation in a synthesis of omuralide, which was achieved in 13 steps and 14% overall yield. We also report a methodology for selectively forming either cis or trans 2,5-disubstituted pyrrolines via a Partial Reduction of an electron-deficient N-Boc pyrrole. The trans pyrroline formed using this route was utilized in the syntheses of the polyhydroxylated pyrrolizidine natural products hyacinthacine A1 and 1-epiaustraline. Further investigation has led to the development of routes to enantiopure substituted pyrroline compounds. This has been achieved via a chiral protonation approach using easily accessible chiral acids, such as ephedrine and oxazolidinones, to quench enolates formed during the Partial Reduction process. Alternatively, enzymatic desymmetrization of symmetrical diol compounds formed from the Partial Reduction products of substituted pyrroles is also reported. This leads to formation of both enantiomers of 2,2- and 2,5-disubstituted N-Boc pyrrolines in excellent ee and yields.
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Partial Reduction of pyrroles application to natural product synthesis
Chemical Record, 2007Co-Authors: Timothy J. Donohoe, Rhian E. ThomasAbstract:The Partial Reduction of N-Boc pyrroles has been explored giving stereoselective routes to disubstituted pyrrolines in good yields and with excellent diastereoselectivities. A novel methodology has been developed to carry out reductive aldol reactions on 2-substituted N-Boc pyrroles; use of aldehydes under reductive aldol conditions gave the anti aldol product in good selectivity. This chemistry was used as the key transformation in a synthesis of omuralide, which was achieved in 13 steps and 14% overall yield. We also report a methodology for selectively forming either cis or trans 2,5-disubstituted pyrrolines via a Partial Reduction of an electron-deficient N-Boc pyrrole. The trans pyrroline formed using this route was utilized in the syntheses of the polyhydroxylated pyrrolizidine natural products hyacinthacine A1 and 1-epiaustraline. Further investigation has led to the development of routes to enantiopure substituted pyrroline compounds. This has been achieved via a chiral protonation approach using easily accessible chiral acids, such as ephedrine and oxazolidinones, to quench enolates formed during the Partial Reduction process. Alternatively, enzymatic desymmetrization of symmetrical diol compounds formed from the Partial Reduction products of substituted pyrroles is also reported. This leads to formation of both enantiomers of 2,2- and 2,5-disubstituted N-Boc pyrrolines in excellent ee and yields. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 180–190; 2007: Published online in Wiley Inter-Science (www.interscience.wiley.com) DOI 10.1002/tcr.20115
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The ammonia-free Partial Reduction of substituted pyridinium salts
Organic & biomolecular chemistry, 2006Co-Authors: Timothy J. Donohoe, Rhian E. Thomas, Dale J. Johnson, Laura H. Mace, Jessica Y. K. Chiu, Jason S. Rodrigues, Richard G. Compton, Craig E. Banks, Peter Tomčík, Mark J. BamfordAbstract:This paper reports a study into the Partial Reduction of N-alkylpyridinium salts together with subsequent elaboration of the intermediates thus produced. Activation of a pyridinium salt by placing an ester group at C-2, allows the addition of two electrons to give a synthetically versatile enolate intermediate which can be trapped with a variety of electrophiles. Furthermore, the presence of a 4-methoxy substituent on the pyridine nucleus enhances the stability of the enolate reaction products, and hydrolysis in situ gives stable dihydropyridone derivatives in good yields. These versatile compounds are prepared in just three steps from picolinic acid and can be derivatised at any position on the ring, including nitrogen when a p-methoxybenzyl group is used as the N-activating group on the pyridinium salt. This publication describes our exploration of the optimum reducing conditions, the most appropriate N-alkyl protecting group, as well as the best position on the ring for the methoxy group. Electrochemical techniques which mimic the synthetic reducing conditions are utilised and they give clear support for our proposed mechanism of Reduction in which there is a stepwise addition of two electrons to the heterocycle, mediated by di-tert-butylbiphenyl (DBB). Moreover, there is a correlation between the viability of Reduction of a given heterocycle under synthetic conditions and its electrochemical response; this offers the potential for use of electrochemistry in predicting the outcome of such reactions.
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Partial Reduction of pyridinium salts as a versatile route to dihydropyridones.
Organic letters, 2005Co-Authors: Timothy J. Donohoe, Dale J. Johnson, Laura H. Mace, Mark J. Bamford, Osamu IchiharaAbstract:The addition of two electrons to a pyridinium salt turns it into a nucleophile. The intermediate generated by the Reduction of such salts can be reacted successfully with a range of different electrophiles (acids, alkyl halides, and carbonyl compounds) and the intermediate hydrolyzed in situ to provide a wide range of dihydropyridones. Each position on the dihydropyridone ring is then accessible using standard synthetic manipulations.
M. Ricci - One of the best experts on this subject based on the ideXlab platform.
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One-stage Posterior Decompression-Stabilization and Trans-sacral Interbody Fusion after Partial Reduction for Severe L5-S1 Spondylolisthesis
Spine, 2003Co-Authors: Pietro Bartolozzi, Andrea Sandri, Marco Cassini, M. RicciAbstract:A retrospective clinical study was conducted. To evaluate the clinical and radiologic outcomes of one-stage posterior decompression-stabilization after Partial Reduction and trans-sacral interbody fusion with a titanium cage for severe L5-S1 spondylolisthesis. Trans-sacral interbody fusion for the management of severe L5-S1 spondylolisthesis with or without Partial Reduction and pedicular fixation has been previously described. The use of a trans-sacral titanium cage has not been previously reported. Fifteen patients with severe L5-S1 spondylolisthesis were treated consecutively with posterior decompression, Partial Reduction, pedicular fixation, and posterior lumbar interbody fusion using a trans-sacral titanium cage. The mean age at the time of surgery was 22.4 years (range, 11-37 years). The mean follow-up period was 31.4 months (range, 12-58 months). Nine patients had severe back pain and six patients radicular pain. Three patients had a Partial unilateral L5 motor deficit and two an L5 sensory deficit. Five patients had extremely tight hamstrings. The mean preoperative percentage of slipping was 69.3% (range, 53-91%). Patients were evaluated for complications and fusions, and outcomes were collected using the modified Scoliosis Research Society Outcomes Instrument. At follow-up, all patients, except one with major vascular complications, were extremely or reasonably satisfied with the surgery. All patients showed improvements in radiologic indexes and stable fusion at the final follow-up examination. Posterior decompression and Partial Reduction followed by circumferential stabilization performed in one stage combining pedicle fixation with trans-sacral titanium cage interbody fusion is an effective and safe technique for the management of severe spondylolisthesis.
Stephen L. Sass - One of the best experts on this subject based on the ideXlab platform.
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Magneto-optical properties of nanocomposite films obtained by Partial Reduction of (Ni,Mg)O and (Co,Mg)O solid solutions
Journal of Applied Physics, 1998Co-Authors: J. A. Smith, P. Limthongkul, L. Hartsuyker, S. Y. Kim, Stephen L. SassAbstract:Metal-ceramic nanocomposite films consisting of either Ni or Co particles embedded in a MgO matrix were produced by two techniques involving the Partial Reduction of a mixed oxide solid solution. Transmission electron microscopy, Rutherford backscattering spectrometry, x-ray diffraction, and magneto-optical Faraday and Kerr rotation measurements were used to characterize the films. The metallic particles were well dispersed in the films, resistant to subsequent re-oxidation, with their size controlled by choice of processing conditions. The coercive field of the samples is influenced by the residual strain arising from the coefficient of thermal expansion difference between the film and the substrate upon which it is deposited. Large magneto-optical Faraday and Kerr rotations are achieved for relatively thick nanocomposite samples as compared to pure metallic films.
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Microstructures and mechanical properties of NiMgO composites formed by displacement and Partial Reduction reactions
Acta Materialia, 1997Co-Authors: J. A. Smith, P. Limthongkul, Stephen L. SassAbstract:Metal-ceramic microstructures were produced by two different approaches: a displacement reaction between Mg and NiO and a Partial Reduction reaction starting with a solid solution of (Mg,Ni)O. In both cases Ni-rich particles were embedded in a Mg-rich (Mg,Ni)O ceramic phase. For the displacement reaction, the two phase structure is produced during hot pressing. For the Partial Reduction reaction, individual ceramic grains are first reduced to a two phase mixture and then hot pressed to form a monolithic solid. The resultant microstructures contain different distributions of Ni in the MgO matrix. The fracture toughness measured by the chevron notch technique was related to the morphologies of the different microstructures. The presence of chromium ions as a dopant in the Partial Reduction reaction was found to have a significant beneficial effect on the bend strength and fracture toughness of the composites produced by this method.
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Influence of residual stresses on the evolution of micro-structure during the Partial Reduction of NiAl2O4
Materials Science and Engineering: A, 1997Co-Authors: Ersan Üstündag, Z. Zhang, M.l. Stocker, P. Rangaswamy, Mark A.m. Bourke, Shanthi Subramanian, Kurt E. Sickafus, J.a. Roberts, Stephen L. SassAbstract:Abstract Metal-ceramic microstructures were formed in situ by the Partial Reduction (i.e. the Reduction of only one of the metallic elements) of the spinel compound NiAl 2 O 4 . Depending on Reduction conditions, these microstructures consist of Ni particles embedded in an α-Al 2 O 3 or a multiphase matrix called ‘defect spinel’. The volume shrinkage that accompanies the reaction generates residual stresses which profoundly affect the microstructure evolution. Conversely, formation of metastable, intermediate phases, generation of porosity and cracking are all observed and may act to relax the residual stresses. Electron microscopy observations as well as both neutron and X-ray diffraction residual stress measurements are used to study the influence of residual stresses on the microstructure evolution during the Reduction process.
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Metal-ceramic microstructure control in Partial Reduction reactions in the model system FeMnO by doping
Materials Science and Engineering: A, 1995Co-Authors: R. Subramanian, Stephen L. Sass, E. Üstünda, Rüdiger DieckmannAbstract:Abstract The formation of metal-ceramic multi-phase microstructures by Partial Reduction of ternary or higher ceramic oxides was investigated experimentally in the model system FeMnO by changing the oxygen Partial pressure at constant temperature and total pressure. The addition of dopants such as BaO, CaO, MgO, SrO, Al 2 O 3 , Cr 2 O 3 or ZrO 2 to the initial, polycrystalline oxide solid solution (Fe 1− x Mn x ) 1−Δ O strongly influences the location of metal precipitation during Reduction. Electron microscopic studies were performed for microstructural characterization, phase identification and chemical analysis. The experimental observations are discussed based on solubility limits and the segregation of dopants.
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In-situ formation of metal-ceramic microstructures by Partial Reduction reactions
Solid State Ionics, 1995Co-Authors: R. Subramanian, Stephen L. Sass, E. Üstündagˇ, Rüdiger DieckmannAbstract:The formation of metal-ceramic multi-phase microstructures by Partial Reduction of ternary or higher ceramic oxides has been experimentally investigated in the model system Fe-Mn-O and in the more practical system Al-Ni-O by changing the oxygen Partial pressure at constant temperature and total pressure. In the Fe-Mn-O system the addition of impurities such as Al 2 O 3 , CaO, Cr 2 O 3 and ZrO 2 to the initial, polycrystalline oxide solid solution (Fe 1-x Mn x )O strongly influences the location of the metal precipitation during Reduction. The experimental observations are discussed based on solubility limits and segregation of impurities. In the Al-Ni-O system, depending on the Reduction temperature, two different morphologies of nearly pure Ni particles, equiaxed and rod-like, form within an oxide matrix. Equiaxed Ni particles (0.02 to 0.5 μm in diameter) embedded in α-Al 2 O 3 were formed at 1350°C, while rod-like Ni particles (∼5 μm in length and 0.1 μm in diameter) in a metastable «defect spinel» phase, containing much less Ni than NiAl 2 O 4 , were formed at 1100°C. Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis
