Laser-Induced Thermophoresis and Particulate Deposition Efficiency

1985 ◽  
Vol 107 (1) ◽  
pp. 155-160 ◽  
Author(s):  
T. F. Morse ◽  
C. Y. Wang ◽  
J. W. Cipolla
Keyword(s):  
Laser Radiation ◽  
Particle Concentration ◽  
Energy Equation ◽  
Numerical Solutions ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Deposition Efficiency ◽  
Particulate Deposition ◽  
Dependent Absorption ◽  
Fiber Preforms

The interaction of laser radiation and an absorbing aerosol in a tube flow has been considered. The aerosol is produced by external heating of reactants as in the MCVD (Modified Chemical Vapor Deposition) process to produce submicron size particles in the manufacture of optical fiber preforms. These particles are deposited by thermophoretic forces on the inner wall of the tube as they are convected by a Poiseuille velocity profile. Axial laser radiation in the tube interacts with the absorbing particles, and the laser heating of the gas induces additional thermophoretic forces that markedly increase the efficiency of particulate deposition. A particle concentration dependent absorption coefficient that appears in the energy equation couples the energy equation to the equation of particle conservation, so that a nonlinear set of coupled partial integro-differential equations must be solved. Numerical solutions for aerosol particle trajectories, and thus deposition efficiencies, have been obtained. It is shown that laser enhanced thermophoresis markedly improves the deposition efficiency.

Process Improvement Using In-Situ Particle Detection

1993 ◽  
Vol 36 (3) ◽  
pp. 21-24
Author(s):  
Jin Wu ◽  
James Miller ◽  
Mark Tinker
Keyword(s):  
Process Improvement ◽  
Vapor Deposition ◽  
Particle Deposition ◽  
Particle Concentration ◽  
Particle Distribution ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Particle Detection ◽  
Particle Level

An engineering criterion is derived to determine when the particle level detected in exhaust flow can be treated as a representiative measure of particle concentration in the reactor. It is established when gravitation sedimentation is the dominant phenomenon affecting particle deposition and when the particle distribution in the reactor is well-mixed. An example of using this technology to improve a plasma-en-hanced chemical vapor deposition process is presented.

scholarly journals Fabrication of Alumina-Doped Optical Fiber Preforms by an MCVD-Metal Chelate Doping Method

2020 ◽  
Vol 10 (20) ◽  
pp. 7231
Author(s):  
K. A. Mat Sharif ◽  
N. Y. M. Omar ◽  
M. I. Zulkifli ◽  
S. Z. Muhamad Yassin ◽  
H. A. Abdul-Rashid
Keyword(s):  
Refractive Index ◽  
Metal Chelate ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Process Efficiency ◽  
Mole Percent ◽  
High Uniformity ◽  
Deposition Direction ◽  
Two Parameters ◽  
Fiber Preforms

This paper reports on the fabrication of alumina-doped preforms using a modified chemical vapor deposition (MCVD)-vapor phase chelate delivery system with Al(acac)3 as the precursor. The objectives of this work are to study the deposition process, the efficiency of the fabrication process, and the quality of the fabricated fiber preforms. Two parameters are studied, the Al(acac)3 sublimator temperature (TAl °C) and the deposition direction (i.e., downstream and upstream). Other parameters such as the oxygen flow and deposition temperature are fixed. The results show that high uniformity of the refractive index difference (%RSD < 2%) and core size (%RSD < 2.4%) was obtained along the preform length using downstream deposition, while for the combined upstream and downstream deposition, the uniformity deteriorated. The process efficiency was found to be about 21% for TAl °C of 185 °C and downstream deposition. From the EDX elemental analysis, the refractive index was found to increase by 0.0025 per mole percent of alumina.

Reaction couples of ceramic thin films prepared by CVD

1988 ◽  
Vol 46 ◽  
pp. 798-799
Author(s):  
D.W. Susnitzky ◽  
S.R. Summerfelt ◽  
C.B. Carter
Keyword(s):  
Thin Film ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Solid State Reactions ◽  
Spatial Distributions ◽  
Diffusion Couples ◽  
Kinetics Studies ◽  
Ceramic Thin Films ◽  
Initial Stage

Solid-state reactions have traditionally been studied in the form of diffusion couples. This ‘bulk’ approach has been modified, for the specific case of the reaction between NiO and Al2O3, by growing NiAl2O4 (spinel) from electron-transparent Al2O3 TEM foils which had been exposed to NiO vapor at 1415°C. This latter ‘thin-film’ approach has been used to characterize the initial stage of spinel formation and to produce clean phase boundaries since further TEM preparation is not required after the reaction is completed. The present study demonstrates that chemical-vapor deposition (CVD) can be used to deposit NiO particles, with controlled size and spatial distributions, onto Al2O3 TEM specimens. Chemical reactions do not occur during the deposition process, since CVD is a relatively low-temperature technique, and thus the NiO-Al2O3 interface can be characterized. Moreover, a series of annealing treatments can be performed on the same sample which allows both Ni0-NiAl2O4 and NiAl2O4-Al2O3 interfaces to be characterized and which therefore makes this technique amenable to kinetics studies of thin-film reactions.

Chemical Vapor Deposition of Sr1−xBaxNb2O6 Thin Films Using Metal Alkoxide Precursors

2000 ◽  
Vol 15 (8) ◽  
pp. 1702-1708
Author(s):  
Ruichao Zhang ◽  
Ren Xu
Keyword(s):  
Thin Films ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Single Phase ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Thin Layers ◽  
Metal Alkoxide ◽  
Stoichiometry Control ◽  
Alkoxide Precursors

A novel two-step metalorganic chemical vapor deposition process was used in this study to prepare Sr1−xBaxNb2O6 (SBN) thin films. Two thin layers of single-phase SrNb2O6 and BaNb2O6 were deposited alternately on a silicon substrate, and the solid solution of SBN was obtained by high-temperature annealing. The stoichiometry control of the SrNb2O6 and the BaNb2O6 thin films was achieved through deposition process control, according to the evaporation characteristics of double metal alkoxide. The evaporation behavior of double metal alkoxide precursors SrNb2(1-OC4H9)12 and BaNb2(1-OC4H9)12 was studied, and the results were compared with the evaporation of single alkoxide Nb(1-OC4H9)5.

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