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Featured researches published by Tongsan D. Xiao.


Journal of Materials Science | 1992

Synthesis of Si(C, N) nanoparticles by rapid laser polycondensation/crosslinking reactions of an organosilazane precursor

Kenneth E. Gonsalves; Peter R. Strutt; Tongsan D. Xiao; P. G. Klemens

A study has been made of basic mechanisms involved in the rapid synthesis of pre-ceramic and ceramic nanoparticle powders. In this process an aerosol, formed from an ultrasonically atomized liquid organosilazane monomer, [CH3SiHNH]n, is injected into the beam of an industrial CW CO2 laser. One critical feature examined was the rapid condensation of molecular species from the laser plume, in a process involving three-dimensional crosslinking polycondensation reactions. In accompanying studies, a model has been formulated to determine the laser plume temperature, the cooling rate of condensing species and the particle diameter. These are obtained by analytical solution of heat conduction, momentum and mass conservation equations that consider heat loss by gas conduction, radiation, evaporation and convection.


Journal of Materials Science | 1993

Synthesis of Si(N,C) nanostructured powders from an organometallic aerosol using a hot-wall reactor

Tongsan D. Xiao; Kenneth E. Gonsalves; Peter R. Strutt; P. G. Klemens

Current studies show that nanostructured Si(N,C) powders are readily synthesized by rapid condensation of a pyrolytically decomposed silazane precursor, namely [CH3SiHNH]n,n−3 or 4. Basically, the process involves ultrasonic conversion of the liquid-phase precursor to an aerosol, followed by thermal decomposition in a hot reactor. This was followed by the rapid condensation of the gaseous product exiting the reactor, to form ceramic particles of nanoscale dimension. Thermal decomposition was performed at a temperature of 1000 °C, near ambient pressure with a flow rate of ∼ 150 standard cm3 min−1 for NH3. One critical feature examined in this process was the rapidity of the powder synthesis, in a reaction which involves (i) elimination of ligand groups, (ii) formation of ceramic species, and (iii) condensation of ceramic species into ultrafine ceramic particles. These features have been studied using Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photo-electron and nuclear magnetic resonance spectroscopies. Additionally, a model is formulated to determine the effect of process parameters on particle size.


Nanostructured Materials | 1994

Synthesis and processing of nanostructured M50 type steel

Kenneth E. Gonsalves; Tongsan D. Xiao; G. M. Chow; C.C. Law

Abstract A nanostructured FeCrMoVM50 type steel was prepared via a chemical route. The process involved the thermal decomposition of organometallic precursors Fe(CO)5, Cr(CO)6, Mo(CO)6 and V(CO)6, at 150°C for the formation of nanostructured M50 type steel powders. In addition to the thermal decomposition of these carbonyls, the results of the reduction of respective metal halides for the production of the same steel are also presented. The nanostructured steel powders obtained were also consolidated samples, were characterized using x-ray synthesized powders, as well as the consolidated samples, were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution electron microscopy (HRTEM). Possible mechanisms for the formation of nanostructured particles are also discussed.


Acta Materialia | 1997

Microstructural characteristics of chemically processed manganese oxide nanofibres

Tongsan D. Xiao; Bokhimi; M. Benaissa; R. Pérez; Peter R. Strutt; Miguel José Yacamán

Nanostructured fibrous manganese oxide cryptomelane-type hollandite powders were prepared via a chemical route. Powders were obtained by the chemical reaction of the aqueous solutions of potassium permanganate and manganese sulfate in the presence of a strong acid, followed by crystalline growth at elevated temperatures. These powders were characterized by powder X-ray diffraction (XRD), Rietveld refinement, analytical scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with micro-micro diffraction (μμd), and high resolution transmission electron microscopy (HRTEM). The crystalline structure, morphology, crystallite size, fibre growth direction, and structural defects are discussed.


Nanostructured Materials | 1996

Synthesis of nanostructured NiCr and Ni-Cr3C2 powders by an organic solution reaction method

Tongsan D. Xiao; S. Torban; Peter R. Strutt; Bernard H. Kear

Nanostructured nickel/chromium (NiCr) and nickel-chromium carbide (NiCr3C2) powders were prepared via a chemical route. The technique involves reductive decomposition of an organic solution of metal chloride precursors using sodium triethylborohydride. After co-precipitation of a nanoscale mixed metal (Ni+Cr) powder, low temperature annealing is used to form nanostructured NiCr alloy powder, or low temperature gas phase carburization to form nanostructured Ni-Cr3C2 cermet powder. These powders were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and chemical analysis. The mechanisms of halide reduction and phase formation are discussed.


Nanostructured Materials | 1992

Synthesis of polymerized preceramic nanoparticle powders by laser irradiation of metalorganic precursors

Peter R. Strutt; Kenneth E. Gonsalves; Tongsan D. Xiao

1,583,333 5/1926 Bigum ....................................... 165/91 2,118,438 5/1938 Lawrence et al. .......................... 71/69 3,642,521 2/1972 Moltzam et al. ... 117/105.2 4,014,980 3/1977 Fujimaki et al. ... 423/448 4,108,964 8/1978 Kratel et al. ..... ... 423/336 4,221,825 9/1980 Guerder et al. ... 427/34 4,891,339 1/1990 Calcote et al. ... 501/87 4,900,483 2/1990 Witzke et al. ... ... 264/29.2 5,128,081 7/1992 Siegel et al. ......... ... 264/81 5,186.872 2/1993 Nishiwaki et al. ... 264/5 5,268,337 12/1993 Katz et al. ....... ... 501/94 5,514,350 5/1996 Keer et al. .............................. 422/198


Materials Science and Engineering B-advanced Functional Solid-state Materials | 1993

Synthesis of chromium silicide-silicon carbide composite powders

Ping Luo; Peter R. Strutt; Tongsan D. Xiao

Abstract A special class of materials of interests to the electronic industry are the intermatallic matrix composites, containing phases such as chromium silicide and silicon carbide. Our studies address this need by investigating a low cost method for synthesizing a chromium silicide-silicon carbide composite using a chemical processing technique. The precursor used in this synthesis route is a homogeneous aqueous solution of chromium chloride and sodium methylsiliconate. This solution may be either processed in bulk or spray dried, to form an intermediate precursor powder. Subsequent thermochemical treatment was carried out at temperatures of 900, 1100 and 1300°C, in a dynamic argon gas environment. Characterization of the chromium silicide-silicon carbide composite was performed using electron microscopy and X-ray analysis. A submicron spherical composite crystalline material was obtained using spray-dried precursor powders. Irregularly shaped particles were obtained when the precursor powder was made by chemical precipitation of the bulk solution. The relative Cr-to-Si concentration distribution of the composite particles has been studied and homogeneous composite particles were produced using the spray-drying process to produce the precursor powder. Structural analysis of the composite powder indicated the presence of two chromium silicide phases, namely CrSi2 and Cr5Si3. Glocuse had a significant effect in reducing the oxide impurities.


MRS Proceedings | 1989

Silicon Nitride Synthesis by Laser Pyrolysis of an Aerosol-Dispersed Precursor

Tongsan D. Xiao; Peter R. Strutt; Kenneth E. Gonsalves

Surface layers of ultrafine Si 3 N 4 particles (30–100 nm. diameter) have been synthesized by laser-pyrolysis of a liquid precursor, dispersed as an aerosol. This aerosol was formed in a nitrogen environment (at near ambient pressure) using an ultrasonically activated nozzle. The organosilazane precursor, which was specially designed for CO 2 laser pyrolysis, was of the type (CH 3 SiHNH) x , with x = 3 or 4. In the current experiments deposition was performed on Ni substrates using a (i) 7 cm/s. substrate translational velocity, and (ii) ˜2.8 × 10 2 w/cm 2 power density.


Journal of Magnetism and Magnetic Materials | 1995

Nitrogen location in R2Fe17 compounds: an NMR study

Y. D. Zhang; J. I. Budnick; W. A. Hines; N. X. Shen; Tongsan D. Xiao; Tariq Manzur

Abstract 14 N, 89 Y and 1 H spin-echo NMR experiments have been carried out in order to study the nitrogen location in the R 2 Fe 17 lattice with R = Gd, Lu and Y. The observed 14 N spectrum for the Gd-compound indicates that essentially all of the N atoms occupy the octahedral interstitial sites. However, the ‘two-peak’ 14 N spectra for the Y-compounds and, to a lesser degree the Lu-compound, indicate that some of the N atoms enter the tetrahedral interstitial sites in addition to the octahedral sites. A consideration of both 14 N and 89 Y spectra indicates that the probability for a N atom to enter a tetrahedral site in the Y 2 Fe 17 lattice is much smaller than that for octahedral site occupation. This study reveals that the local structure of Y 2 Fe 17 N x may change with the nitrogenation conditions.


Nanostructured Materials | 1993

Chemical synthesis of an aluminum nitride/ boron nitride nanostructured composite material

Peter R. Strutt; Tongsan D. Xiao; Kenneth E. Gonsalves; R. Boland

Abstract Aluminum nitride/boron nitride composite material is of interest becuase the constituent phases posses (i) high thermal conductivity combined with optical transparency over a wide spectral range, (ii) excellent dielectric properties and (iii) high mechanical strength. As a consequence of these attributes, a chemical processing route has been developed to produce nanostructured AlN/BN material. The method involves low temperature conversion of an aqueous solution of simple aluminum, boron, and nitrogen containing compounds to form intermediate precursor material. This material is essentially a gel, and subsequent high temperature conversion produces AlN/BN composite. Characterization studies reveal the material to be nanoporous and contain a distribution on AlN and BN nanoparticles. Details of the process, together with structural and microscopic features of the nanostructured material are discussed.

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Peter R. Strutt

University of Connecticut

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G. M. Chow

National University of Singapore

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Bernard H. Kear

University of Connecticut

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Donald M. Wang

University of Connecticut

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Huimin Chen

University of Connecticut

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J. I. Budnick

University of Connecticut

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P. G. Klemens

University of Connecticut

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Xiaohe Chen

University of Connecticut

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N. X. Shen

University of Connecticut

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