SELF PROPAGATING HIGH TEMPERATURE SYNTHESIS SHS OF ADVANCED HIGH TEMPERATURE CERAMICS

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SELF PROPAGATING HIGH TEMPERATURE SYNTHESIS (SHS)
OF ADVANCED HIGH TEMPERATURE CERAMICS
S. K. Mishra
National Metallurgical Laboratory, Jamshedpur
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SALIANT FEATURES OF SHS PROCESS
SHS uses the exothermic heat of chemical reaction
for the completion of reaction and the final
product in single step
Once the SHS reaction is initiated at a
temperature the Combustion wave propagated with a
velocity and complete the reaction
ADVANTAGES OF SHS
IMPORTANT SHS PARAMETERS Ignition
Temperature Combustion velocity Adiabatic
Temperature Combustion Temperature
HIGH PURITY OF PRODUCT ENERGY EFFECIENCY
METASTABLE STATE FORMATION NEAR NET SHAPE
FABRICATION FABRICATION OF FGM
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The condition for a reaction to be
self-propagating
For a chemical reaction A B AB ?H
Adiabatic temperature (Tad) can be calculated
from
Tig Ignition temperature
?H Change of Enthalpy at 298 k Cp Heat
capacity Tad Adiabatic temperature (Melting,
Phase transformation, Ignition is ignored)

• It is empirically found out that adiabatic
  temperature gt1800 K is necessary for SHS
• ZrO2B2O35Mg ZrB25MgO (Tad 2930K)

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SHS PREPARATION OF ZrB2 POWDER
In this process, the mixture is ignited using an
electrical arcing, MgO was leached out, dried and
characterized by XRD, SEM TEM. Powder was
compacted and sintered with and without sintering
aids
TEM IMAGE
SEM IMAGE
S. K. Mishra et. Al. US, european, Japan Indian
patent
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J. Mat.Res. 2000, S. K. Mishra et.al
J. Am Ceram. Soc. 2002 S. K. Mishra et.al.
ZrB2 (01-11)
Microstructure of sintered ZrB2 sample sintered
at 1800C (95 density)
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PREPARATION OF NANO-CRYSTALLINE DIBORIDE POWDER
BY A MODIFIED SHS ROUTE
In this process, powder mixture (with NaCl) was
ignited using an electrical arcing/furnace
heating,
J. . Mat. Sci. lett 2003
Variation of adiabatic temperature with NaCl
content
TG/DTA Plot
Particle size Distribution
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MICROGRAPHS OF DIBORIDE POWDER
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SEM IMAGES of SHS LUMPS
10
0
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TEM images of TiB2 powder
400nm
100 nm
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Zirconium Diboride prepared by non SHS
carbothermic process
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MSE A 2003, S. K. Mishra et. al.
ZrB2 Powder prepared by SHS process
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Comparative sintering behaviour
Density curve
Pathak et. al. J. Am ceram Soc. 2005
A
B
SEM of TiB2 pellets sintered at 2123 K (A- SHS,
B- Commercial)
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Mater. Trans. A Sept. 2003, S. K. Mishra et. al.
Time-Temperature graph during SHS reaction of the
synthesis of sample S1
3ZrO2 3B2O3 10Al 3 ZrB2 5 Al2O3
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Phil. Mag. Lett. 2003, S. K. Mishra e. tal.
X-Al o-ZrB2 -Al2O3
o

x
Dynamic Xray Analysis
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ZrB2-Al2O3 COMPOSITES BY SHS
Insitu composite grain growth inhibition, higher
density (97) SHS powder then sintered sintering
temp. lower by 300oC, (95 density) but larger
grain growth
Dendritic Growth of ZrB2 during formation of
Composite
Mishra et. al. Met. Trans A 2003
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1800C
1800C
Sintered Microstructure of ZrB2-Al2O3 composite
1900 C
1800C
Al
Zr
S. K. Mishra et. al. Mater. Sci. eng. A 2006
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DIBORIDE BASED COMPOSITES BY SHS DYNAMIC
COMPACTION TECHNIQUE

• In SHS dynamic compaction technique, the
  exothermic heat of reaction is exploited for the
  densification of the high temperature composites
• A SHS dynamic compaction system is fabricated on
  the basis of our design
• Several high-temperature materials such as
  TiB2-Al2O3, TiB2-ZrB2-Al2O3 and Ni-TiB2-Al2O3
  in-situ composites are prepared
• Densification gt 98 of the theoretical density
  and hardness gt 5000 HVN is achieved in TiB2-Al2O3
  composites

SHS dynamic compaction system designed
indigenously
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Timer
Power Panel
Hydraulic Press
Green samples
Power source
Base plate
Schematic of SHS dynamic compaction
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97
SHS dynamic compaction
1850C
1850C
95
Mishra et.al, US, indian Patent
SHS powder sintered at 1850o C
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A significant enhancement in modulus and hardness
due to fine and nano dispersion of diborides and
fine grain size of composite of alumina (20 Gpa,
350Gpa) matrix.
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Indigenous SHS reaction chamber and online
monitoring
Indigenous SHS dynamic compaction
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FABRICATION OF Al2O3-SiC COMPOSITES
J. am. Cerm soc. 2002
Pellets of AlSiO2C were heated at the rate of
400oC/min to above 1200oC
XRD pattern showed complete phase formation after
30 min.
SCHEMATIC OF THE RAPID HEATING FURNACE
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SEM IMAGE OF Al2O3-SiC COMPOSITES
a
c
b
d
Pellets heated at different heating rates a) 10
K/min, b) 100 K/min, c) heated at 2000 K and d)
showed shape retention
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FACILITIES AT NML

• SHS APPARATUS
• SHS DYNAMIC COMPACTION SYSTEM
• RF SPUTTERING UNIT
• ARC EVAPORATION UNIT
• PACVD SYSTEM
• HOT ISOSTATIC PRESS
• HIGH TEMPERATURE FURNACES
• THERMAL SPRAY SYSTEM (oxy-acetelene)
• PLASMA SPRAY
• HVOF
• AFM, SEM/EDX, TEM, EBSD, TG/DTA/DSC
• THERMAL CONDUCTIVITY

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Dr. L. C. Pathak,NML Acad. A. G. Merzhanov,
ISMAN Dr. V. Shcherbakov,ISMAN Late Dr. S.
Mamyan, ISMAN DST-ILTP collaboration
THANK YOU