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1. SPRAY PYROLYSIS
To
Dr. Harpreet Singh
Assistant Professor (SMMEE)
Prepared By
Patel A. R.
Research Scholar
SCHOOL OF MATERIALS, MECHANICAL AND ENERGY ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY ROPAR
Nangal Road, RUPNAGAR-140001
PUNJAB

2. Technique basically consist of atomization of a salt-containing
liquid, the transport of spray droplets, and pyrolysis of the
salt on the substrate to form the Oxide coating, ceramic
coating and powder production.
VARIOUS TECHNIQUES
CLASSIFICATION
atomic layer epitaxy
2

3. • Technique to prepare dense and porous oxide films, ceramic coatings, and n-m
sized powders.
• Spray pyrolysis represents a very simple and relatively cost-effective method,
especially regarding equipment cost.
• Spray pyrolysis does not require high quality substrates or chemicals.
• The method has been employed for the deposition of dense films, porous films,
and for powder production.
• Even multi-layered films can be easily prepared using this versatile technique.
• Spray pyrolysis has been used for several decades in the glass industry [1] and
in solar cell production to deposit electrically conducting electrodes [2].
SALIENT FEATURES
EQUIPMENT REQUIRED
• An atomizer,
• Precursor solution,
• Substrate heater, and
• Temperature controller.
3

4. • Precursor solution prepared
• Slurry of solution and powder made
• Atomization of slurry
• Heating of substrates,
• Spraying of atomized particles over the surface
• Pyrolysis of salt in the solution
• Formation of the thin oxide layers
• Post processing of the surface layer
STEPS
APPLICATIONS
• Solar cells, (thin film deposition)
• Anti-reflection coatings,
• Solid oxide fuel cells,
• Powder production
• Gas sensors,
• Humidity sensors, etc.
4

5. THIN FILM DEPOSITION
• Spraying a metal + salt solution onto a heated substrate
• Droplets impact on the substrate surface,
• Spread into a disk shaped structure, and
• undergo thermal decomposition
• (The shape and size of the disk depends on the momentum and volume of the
droplet and substrate temperature. The film is usually composed of overlapping disks
of metal salt being converted to oxide on the heated substrate).
Production of transparent and conducting oxide films as windows in solar cells by spray
pyrolysis. 5

6. • MgO thin films are commonly used as buffer layers. Thin, uniform, and homogeneous
layers of MgO were deposited on Si (100), fused silica and sapphire [3]. These thin films
(0.1 to 0.5 urn thick) are used as buffer layers for depositing films of YBa2Cu307 .
• Kim et al. have studied the influence of additives on the properties of MgO films
deposited by electrostatic spray deposition [4]. A large number of separated particles
were observed on the surface of MgO films when pure tetrahydrofuran (THF) was used
as a solvent. However, smooth and particle free MgO films were deposited when 1-
butyl alcohol or 1-octyl alcohol was added to THF. i.e. the alcohols effectively restrain
MgO nucleation resulting from the vaporization of droplets.
• De Sisto et al. deposited 0.2 pm thin alumina films by spray pyrolysis using aqueous
acetic acid solution of Al acetylacetone [5], AI2O3 is used in electronic devices as a thin
insulating layer. There was no voltage breakdown observed up to 10 V of applied
potential. Films obtained by thermal decomposition of aluminium isopropoxide led to
voltage breakdowns at 4 V. It was concluded that AI203 films deposited using spray
pyrolysis exhibit high quality and higher breakdown voltages than those prepared by
other technique.
THIN FILM PRODUCTION
Applications
6

7. • Even better quality insulating a-Cr203 layers with breakdown voltages higher than 20
V were formed on silicon substrates [6].
• Yttria-stabilized zirconia (YSZ) is the most commonly used electrolyte material in solid
oxide fuel cells. Thin YSZ films have already been deposited by spray pyrolysis on glass
[7, 8], aluminium [9], steel [10], porous La(Sr)Mn03 cathode [11, 12], and porous
La(Sr)Co03 cathode [13] as substrate.
• Terbia-doped yttria-stabilized zirconia thin films have been deposited using
electrostatic spray deposition [14]. This material exhibits mixed electronic-ionic
conductivity at high oxygen partial pressures and therefore, can be used as SOFC
electrode.
• Dense cell containing the YSZ-coated ceria electrolyte with cracks exhibits a higher
open circuit voltage than those with ceria alone [15].
• Titania films have been deposited on steel to prevent corrosion using titanium
isopropoxide as the precursor [16].
THIN FILM PRODUCTION
Applications
7

8. POWDER PRODUCTION
• During synthesis the solution is atomized to droplets .
• Using carrier gas the droplets are passed through a diffusion dryer for solvent
evaporation, precursor precipitation, and drying.
• After this thermolysis reactor where dry particles decomposes and form in to a
micro-porous particle.
• Finally particles send to a calcination furnace for getting sintered.
(Properties of the solution and the precursor can strongly influence the particle
morphology, spray pyrolysis results in particles with morphologies from solid, to
hollow and porous, and even fibers can be obtained)
Entrapped salt
Messing et al. have reviewed the spray pyrolysis techniques in terms of process parameters
that control the formation of powders [17]. 8

9. GAS SENSORS
• Some semiconducting metal oxides that changes their electrical conductance in the
presence of carbon monoxide e.g. hydrocarbons.
• Such sensors typically consists of an thin oxide semiconductor film on an insulating
substrate with two metal electrodes attached.
• Thin oxide films on glass substrates as sensors for CH2CI2 in oxygen [18].
• SnÜ2 films for NO2 sensors using the spray pyrolysis technique [19].
• LaOCl-Sn02 films produced by spray deposition technique for sensing CO2 in air [20].
• Porous Sn02 and Sn02–Mn203 films for H2 sensor by spray deposition technique [21,22].
The Sn02-Mn2Û3 (10:1) mixed oxide films showed a sensitivity to hydrogen.
• Some metal oxide sensors show sensitivity to humidity. The Sn02-Fe203 films has been
investigated for this application [23].
The nature of the iron salt influenced the humidity sensitivity of the samples. The films
deposited from an alcohol solution containing Fe2(C204)3 exhibit higher sensitivity than a
solution containing Fe(NH4)(S04)2. This is due to the higher porosity of the structure
obtained from iron oxalate, because during the oxalate pyrolysis a lot more gaseous
decomposition products are released compared to the sulphate precursors.
9

10. • The spreading behavior of droplets is due to surface tension and roughness of the
coated substrate, porosity of substrate also influences the morphology of a film [25].
• Films with low porosity were produced when using a solvent with a high boiling point.
[24, 25, 26]. Due to slower evaporation of solvent during the droplet transport and
spreading.
• By adding acetic acid to the precursor solution, the morphology of Ti02 films change
from a cracked to a crack-free reticular structure [27].
• Metal-organic compounds are more favorable compared to nitrates, due to their
volatility and lower decomposition temperatures [28].
FILM MORPHOLOGY
I) dense, II) dense with incorporated particles, III) porous top layer with dense bottom layer,
and IV) fractal-like porous. Substrate temperature is the main parameter governing film
morphology. Followed by concentration of the precursor solution, but only at high salt
concentrations, which produces rough films. [24].
With Increase in Temperature
10

11. Electrostatic atomizer
• Strong, local electric forces at a charged liquid-gas interface to generate fine droplets.
• Various spraying modes can be formed depending on the electric potential applied, the
liquid flow rate, the electrical conductivity and the surface tension of the liquid [3].
• The cone-jet mode provides a spray with fine monosized droplets. A broad droplet size
distribution can be expected from multi-jet mode operation.
Air blast atomizers
• High speed air to produce the aerosol [1].
• The liquid is introduced into an air stream and atomized into drops by the energy of the
gas stream.
ATOMIZER
ELECTROSTATIC V/S AIR BLAST
Preferred droplet impact fashion
onto a heated substrate. 11

12. ESD APPARATUS
a high DC voltage power supply (30 kV), a
hollow metal needle, and a substrate holder.
The liquid feeding unit or syringe pump, a
glass syringe, and a flexible tube of Viton
material.
Heating plate and either an IR pyrometer and
a contact thermo element. (IR for contactless
and thermo element for metallic substrates
temperature measurement .
Technical specifications of Equipments
This spraying unit includes
Tip to heating plate
temperature distribution
12

13. Disks of 35 mm in diameter and 75 µm in thickness of Inconel 600 (Goodfellow, UK) were
considered as substrates for experimentation. This nickel alloy (Ni72/Crl6/Fe8) was chosen as
substrate material due to its oxidation resistance and has a shiny appearance with a typical
surface roughness that observed in a rolling operation.
Surface morphology of the uncoated Inconel 600 substrate. [31]
BASIC SURFACE
13

14. SUBSTRATE TEMPERATURE
Surface morphologies of YSZ films deposited using the ESD technique at different
temperatures (for 1 hour), 200°C; 250°C; 300°C; and 350°C (from left). Precursor solution:
0.085 mol/l Zr(C5H702)4 + 0.015 mol/l YCl3XH2O ethanol (50 vol%) + butyl carbitol (50 vol%).
At 200C droplet still reach in solvent, thin wet layer.
At 250C just dry surface and some chances of trace of wet layer.
At 300C fast drying, results in stresses and subsequent cracking.
At 350C droplets are dry, discrete particles on surface and production of rough surface.
280 C + 50 C is best
for dense films
In case of PSD film was cracked at 200°C and dense. At 250C hardly any particles on the
surface. While morphology of the film at 350°C still of type I.
Hence it follows that better quality films can be deposited using the PSD setup. 14

15. SOLUTION FLOW RATE
Surface morphologies of YSZ films
deposited using ESD setup at 325°C
for 2 h with different flow rates 1.4
and 4.2 ml/h (from left). Precursor
solution: 0.17 mol/l ZrCU + 0.03
mol/l YCI3XH2O ethanol (50 vol%) +
butyl carbitol (50 vol%) solution.
films deposited with the low precursor flow rate contain less agglomerates and look
denser than that deposited with the high flow rate using ESD.
In case of PSD has higher flow rates around 30 ml/h to 120 ml/h. Within this range of
flow rates no significant change in the morphology is observed.
However, it should be noted that the probability of film cracking is much higher when
the precursor solution is supplied at a flow rate of 120 ml/h.
15

16. Surface morphology of YSZ films
deposited using ESD setup at 325°C for
2 h with solutions of different chloride
concentrations: (a) 0.2 mol/l and (b)
0.1 mol/l. Precursor solution: ZrCl4 +
YCl3-XH20 ethanol (50 vol%) + butyl
carbitol (50 vol%) solution.
Morphology --> Type II for both
TYPE OF SALT - Chloride
Advantages: high solubility in ethanol (more than 0.5 mol/l) and low price.
Disadvantage: extremely chemically aggressive cause corrosion of the setup.
chlorine impurities hinder the crystallization of the initially amorphous thin film.
More agglomerates and slightly larger particles are present in the film deposited using the
0.2 mol/l solution compared to the 0.1 mol/l solution.
Spreading of droplets and increase in particle size, responsible for this.
Result in more roughness.
Qualitatively, the spreading rate decreases with increasing viscosity (0.2 ml/l). This result in
more rough surface
Roughness also increases with increase in salt concentration in the precursor solution.
16

17. Surface morphology (two magnifications) of
an YSZ film deposited using ESD setup at
325°C for 2 h and nitrate solution of 0.1
mol/l nitrate. Precursor solution:
ZrO(N03)2aq + Y(N03)3-6H20 ethanol (50
vol%) + butyl carbitol (50 vol%) solution.
TYPE OF SALT - Nitrates
Result to a porous type III film or a fractal-like type IV morphology, It seems that landing
droplets already contain precipitated particles.
At low temperature, the film was
cracked. At higher temperature the
film was crack-free and was of type I
morphology. No solid particles are
present on the film surface.
This is because air blast atomizer generates larger droplets. Large droplets evaporate slowly,
and consequently precipitation of the solute is hindered during aerosol transport. Therefore
droplets arriving at the substrate did not contain any precipitates.
PSD
ESD
PSD
ESD
17

18. Influence of the deposition time for the
film deposition using the PSD set-up.
Film morphology after 60 min (a) and
300 min (b). The influence of the
deposition time on the film morphology
deposited at 250°C . Both films belong to
the type I morphology indicating that the
deposition time does not have a
remarkable effect on the film
morphology.
Influence of the deposition time for the
Taylor-cone mode spraying using the ESD
set-up. Film morphology after 45 min (a)
and 300 min (b). Layer with ESD looks
dense with many particles on the surface,
type II morphology. Increasing the
deposition time to 300 minutes shifts the
morphology to type IV (porous with
agglomerates of small particles).
This is due to effect of droplet spreading. Most of the droplets arriving at the substrate are
nearly dry and spread slowly hence discrete particles are formed on the surface, this gives
more rough surface. This enhances preferential landing and agglomeration [24 ,17].
ESD ESD
PSD PSD
DEPOSITION TIME
18

19. SEM image of cross-section of an YSZ film
deposited on Si wafer in two hours at 280°C
by PSD technique. Precursor solution: 0.085
mol/l Zr(C5H702)4 + 0.015 mol/l YCl3-xH20
ethanol (50 vol%) + butyl carbitol (50 vol%)
solution. Nozzle to substrate distance: 44 cm.
Air pressure: 0.75 bar. Solution flow rate: 30
ml/h.
Deposition time versus thickness for YSZ film
deposited at 280°C by the PSD technique.
Precursor solution: 0.085 mol/l Zr(C5H702)4 +
0.015 mol/l YCl3 xH20 ethanol (50 vol%) +
butyl carbitol (50 vol%) solution. Nozzle to
substrate distance: 44 cm. Air pressure: 0.75
bar. Solution flow rate: 30 ml/h.
DEPOSITION RATE
PSD
PSD
19

20. Influence of the air pressure on the droplet
size distribution. Precursor solution flow rate:
30 ml/h.
Mean droplet diameter and droplet
number fraction of the pressurized spray
with respect to the radial distance. Flow
rate: 30 ml/h, distance to substrate: 210
mm.
PSD PSD
SPRAY DISTRIBUTION
20

21. •Acetate, nitrate, and oxalate precursors for YBCO have been
spray pyrolyzed under different conditions.
•Shelled and nonhollow microparticles were obtained from
acetate and nitrate precursors, and
•nonhollow agglomerates were obtained from the oxalate
•suspension.
YBCO Powder Production
A,Atomizer, AC,Air
Compressor, AF,Air
Filters, FN,Furnace,
FH,Filter Heater,
H,Preheater,
I,Insulation,
PF,Powder Filters,
PP,Peristaltic Pump,
The model shows the absorbed
radiation heat by the particles
from the furnace walls is
significant in heating the gas.
The gas and the particle
temperatures are fairly close due
to the effective heat transfer to
the particles. [32]
At furnace temperatures of 700
°C, the maximum predicted
particle temperature is about
500C.
This explains the incomplete
reactions obtained under these
conditions. Above 900°C the
reactions are predicted to be
complete within the first half of
the furnace, leaving sufficient
residence time for partial
conversion into YBCO.
Q,Quartz Tube Reactor,
R,Rotameters, RG,Regulator, S,
Solution, T,Thermocouples,
V,Valves
21

22. CERAMIC COATING
Advance ceramic coating to replace an existing ceramic pipe subjected to the severe
chemical conditions, i.e. operated in hi-temperature and corrosive environment.
A rectangular piece is coated with special attachment over an iron base structure, using
yttrium aluminum garnet (YAG), which is having high strength, low creep rates at high
temperature, anti-corrosive, hi-stability against alkali-vapor.
Technical Specifications
• Ceramic coating was formed using
PT800 plasma technique with
spraying conditions of Ar gas flow
rate; 501 l/min, H2 gas flow rate; 14
l/min, current; 600 A, powder feed
rate; 16 g/min. Ni-20%Cr and Al2O3
feed stock.
• YAG coating was made from Ni-
20%Cr and 35%Y2O3 + 65% Al2O3
mixed powder.
• Speed of Gun scanning 250 mm/s
[33]
22

23. ULTRASONIC SPRAY PYROLYSIS
Ultrasonic spray pyrolysis of precursor drops. Precursor concentration plays a predominant
role in determination of product particle size.
The YSZ particle diameters were much smaller than those predicted by the one-particle-
per-drop mechanism.
Uniform dense spherical nano-particles of 73-nm diameter were produced by spray
pyrolysis through the use of uniform precursor drops (5– 8-m diameter) and a low
precursor concentration (0.01 wt%).
Technical Specification
Precursor zirconium hydroxyl
acetate, concentration 0.01
wt%, spray pyrolysis at 750°C
using precursor drops 5–8 µm
in diameter, by an ultrasonic
nebulizer at 2.66 MHz,
Yield uniform densed spherical
YSZ particles 73 nm in diameter
measured by SEM. [34]
650° C 700° C
23

24. STRONTIUM TITANATE FILMS
1-valve, 2-flowmeter, 3-aerosol generator, 4-
solution, 5-aerosol, 6-substrate, 7-heatingplate,
8-valve and 9-valve.
Deposition parameters, such as solution concentration, time and temperature of deposition,
and flow rate of carrier gas were optimized to obtain dense films without cracks. Prepared thin
films were homogeneous, well crystallized, with uniform grain size. 35.5 nm and 44.1 nm and
thickness 129 nm and 212 nm for 60 and 120 min deposition time resp.
Advantage: one-step, simple, cheap equipment, universal precursors (inorganic, organic or
metal-organic compounds), easy and precise composition control, (d) various film morphologies
possible, and (e) accurate control of the deposition kinetics. [35]
60 min
120 min
24

25. TECHNICAL SPECIFICATIONS
25

26. TECHNICAL SPECIFICATIONS
26

27. REFERENCES
1 J.M. Mochel, US Patent 2,564,707, "Electrically Conducting Coating on Glass and other Ceramic
Bodies", 1951.
2 J.E. Hill and R.R. Chamberlin, US Patent 3,148,084, "Process for Making Conductive Film", 1964.
3 W.J. DeSisto and R.L. Henry, "Deposition of (100) oriented MgO thin films on sapphire by a spray
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28. REFERENCES
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30