Concave Nozzle Burner for CVD Reactant Penetration
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Solution Overview
Problem
Conventional burners for chemical vapor deposition processes, such as those used in optical fiber preform manufacturing, face limitations in precursor transformation due to inadequate penetration of reactants like H2O into the SiCl4 stream and heat penetration into the precursor stream, leading to reduced process yield, especially at high deposition rates.
Innovation Solution
A burner design featuring a central nozzle with a concave cross-section, surrounded by a crown of nozzles and an innershield gas nozzle, which increases the contact surface area between the precursor and reactants, enhancing both reactant penetration and heat penetration, thereby improving the deposition yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the reactant nozzle cross-section is increased to increase the reactant flow rate without excessively increasing the exit speed, then the deposition rate can be increased, but the penetration of H2O into the SiCl4 stream and heat penetration into the precursor stream are thwarted, leading to low process efficiency
Solution Approach 1:
The patent applies curvature by designing the central nozzle with a concave cross-sectional shape instead of a conventional circular or flat geometry. This concave curvature increases the surface area of the precursor stream exposed to reactants and flame, enhancing both mass transfer (H2O penetration) and heat transfer without requiring an increase in nozzle cross-section or exit velocity. The curved surface geometry allows better interaction between the precursor and reactive species, resolving the contradiction between deposition rate and process efficiency.
2Productivity
If the burner dimensions are increased to accommodate higher reactant flow rates, then the deposition rate can be increased, but the intense flows produced would reduce the penetration phenomena, leading to low-efficient processes
Solution Approach 1:
The patent applies local quality by modifying only the local geometry of the central nozzle (the precursor injection point) with a concave cross-section, while keeping the overall burner structure and other components relatively simple. This localized geometric modification creates favorable conditions for reactant penetration and heat transfer precisely where needed - at the interface between the precursor stream and the flame - without requiring a complete redesign of the entire burner system or increasing overall dimensions.
3Manufacturing precision
If the reactant nozzle cross-section is increased to improve precursor transformation, then the contact surface between precursor and reactants is increased, but the exit speed of reactants is reduced excessively
Solution Approach 1:
The patent applies dimensionality change by transitioning from a two-dimensional circular nozzle cross-section to a three-dimensional concave cross-sectional geometry. This additional geometric dimension allows the nozzle to provide a larger surface area for reactant-precursor contact while maintaining a compact overall size and preserving high exit velocities. The concave shape creates multiple surfaces at different orientations, maximizing exposure to flame gases without increasing the projected cross-sectional area that would restrict flow speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The concave nozzle design increases the precursor stream's surface area exposed to flame gases, leading to higher transformation efficiency, faster reaction kinetics, improved particle coalescence, and reduced turbulence, resulting in increased deposition rates and lower consumption of reactants and flame gases.
Implementation Method 1
a main process of diffusive hydrolysis between the precursor and the combustion product (H2O) by the reaction SiCl4+2H2O→SiO2+4HCl
Implementation Method 2
heat penetration into the stream of precursor and forming soot
Implementation Method 3
the burner is fed with a silica precursor (such as SiCl4, optionally together with dopants materials, such as GeCl4), combusting gases (e.g. oxygen and hydrogen or methane)
Implementation Method 4
a main process of diffusive hydrolysis between the precursor and the combustion product (H2O) by the reaction SiCl4+2H2O→SiO2+4HCl
Implementation Method 5
Reduced heat penetration results, in particular, in a reduced particle heating and in a reduced thermophoretic effect
Data Source
AI summary
A burner for a vapour deposition process has a central nozzle for ejecting a glass precursor material, at least a crown of nozzles surrounding said central nozzle for ejecting a flame reactant, and a circular nozzle between said central nozzle and said crown of nozzles for ejecting an innershield gas, wherein the central nozzle has a concave shape in a cross section in the axial plane and, preferably, a symmetry about an axial plane.