Journal of Thermal Spray Technology

, Volume 17, Issue 4, pp 564–573

Particles Spreading Phenomena in the Case of Glass Thermal Spraying

  • Thierry Poirier
  • Marie Pierre Planche
  • Olivier Landemarre
  • Christian Coddet
Peer Reviewed

The spreading phenomena of particles during thermal spraying are quite difficult to observe given the kinetics of the process. In this work, the splat formation of glass and alumina is theoretically compared, showing that glass transition and low-thermal conductivity yield a higher ratio between cooling and flattening times, which strongly modifies their spreading behavior. Wipe tests show that splash—splat transition temperature can be modified by the glass composition and its subsequent hydrodynamic properties. The detection of peculiar remaining objects, such as fibers and wavelets shows the possibility of “freezing” some phenomena that are totally unobservable with crystalline oxides, except with high-velocity observations.

Keywords

cooling fragmentation glass splat substrate temperature wavelets 

Nomenclature

a,b

Empirical flattening coefficients, dimensionless

c

Wavelets speed, m/s

Cp

Heat capacity of the particle in the liquid phase, J/kg.K

D

Initial diameter of the particle, m

Dsplat

Splat diameter, m

e

Flattened film thickness, m

f

Frequency of wavelets, s−1

F

Degree of fragmentation, dimensionless

g

Gravity constant, m/s2

K

Sommerfeld number, dimensionless

l

Wavelength, m

lC

Critical wavelength value before obtaining gravitational predominance, m

L

Latent heat of transformation, J/kg

\( {\cal L}\)

Travel distance of wavelets, m

\( \ifmmode\expandafter\dot\else\expandafter\.\fi{m} \)

Particles mass flow rate, kg/s

N

Number of impinging particles during ttransf

Nu

Nusselt number, dimensionless

P

Probability, dimensionless

Re

Reynolds number, dimensionless

Ssplat

Surface area of splat, m2

Sexposed

Substrate surface area exposed to impinging particles, m2

Tg

Glass transition temperature, °C

Ts

Substrate temperature, °C

Tglazing

Typical glazing temperature, °C

Tparticle

Particle temperature, °C

Ttransformation

Change of state temperature, °C

\( {\cal T}\)

Period between wavelets, s

ttransf

Cooling time, s

tsplat

Flattening time, s

U

Spreading velocity, m/s

V

Particle velocity, m/s

Vi

Volume of a size class of particles, m3

Vtotal

Total volume of particles, m3

We

Weber number, dimensionless

Greek symbols

ΔT

Temperature gap between particle and transformation temperatures, °C

ξ

Spreading factor, dimensionless

ρ

Particle density, kg/m3

λ

Thermal conductivity, W/m K

μ

Particle viscosity, Pa.s

σ

Surface tension, N/m

Ξ

Ratio between cooling and flattening time, dimensionless

Ψ

Feedstock intrinsic prefactor for Ξ and ttransf

Ω

Wavelet pulsation, rad/s

Copyright information

© ASM International 2008

Authors and Affiliations

  • Thierry Poirier
    • 1
  • Marie Pierre Planche
    • 2
  • Olivier Landemarre
    • 2
  • Christian Coddet
    • 2
  1. 1.Grupo de Ingeniería de SuperficiesUniversidad Simón BolívarCaracas Venezuela
  2. 2.LERMPSUTBMBelfort cedexFrance

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