Production(?) of chalcogenide glass optics : motivation, current status and future development
Xiang-Hua ZHANG, Laurent CALVEZ Hongli MA and Jacques LUCAS
Laboratory of glasses and ceramics, UMR CNRS “Sciences chimiques de Rennes”, Université de Rennes I, 35042 Rennes cedex, France Outline
Background and motivations
Current technique for chalcogenide glass fabrication
Challenges and future trends for chalcogenide glass and lens fabrication
Summary Thermal imaging was developed for defense application
with more and more commercial applications Why infrared is interesting for driving assistance
Visible camera Infrared camera Thermal Imaging – A growing market
350
Driver's vision enhancement 300 Maintenance
250 Process control
Fire fighting 200 Surveillance
150 Other commercial applications
Weapon guidance
MillionsMillions US US dollars dollars 100 Civil and military ground applications
50 Other civil and military applications
0 2005 2006 2007 2008 2009 2010 2011 Year
Great progress achieved in uncooled infrared detectors Constant need for cheaper, more efficient materials Thermal Imaging : how it works
Based on the detection of the radiations emitted by hot bodies
Visible range 3-5µm 8-12µm Atmospheric transmission ) -1 14 .m 10 -1 13
.sr 10 -2 6000K 10 12 11 (W.m 10 3000K 10 10 9 10 1000K 10 8 500K 10 7 10 6 300K 5 200K 10 10 4 100K 10 3 10 2 10 1 10 0 Monochromatic luminescence energyenergy luminescence luminescence Monochromatic Monochromatic 0,1 1 10 100 Wavelength (µm) • 2nd atmospheric window (MWIR) : 3-5 µm • 3rd atmospheric window (LWIR) : 8-12 µm Need for materials transparent in these windows Cost of Infrared detectors euros)
Defense
consumer Cost of detector + cooler ( ( coolercooler++ detectordetector of of CostCost Typical IR Optics Materials for thermal imaging optics
Single Crystalline Germanium
• Expensive • Single point diamond turning
Polycrystalline Zinc Selenide (ZnSe)
• Synthesized by CVD • Single point diamond turning Chalcogenide glasses - Definition
S
Se
Te
Ga Ge As Sb Chalcogenide glasses - Properties
Silica Fluorides
Sulfides Large Selenides transparency Tellurides in the Infrared
Wavelength (µm)
moldable
Low dn/dT Bulk / Fibers Lenses Chalcogenide glass samples Chalcogenide glass synthesis
Vacuum pump Sealing
Liquid Nitrogen Starting raw elements
quenching Industrial fabrication of chalcogenide glass Ge-As-Se
Dr. A. Ray Hilton, Sr. Amorphous Materials, Inc. Garland, Texas Industrial fabrication of chalcogenide glass Ge-As-Se
Dr. A. Ray Hilton, Sr. Amorphous Materials, Inc. Garland, Texas Casting of chalcogenide glass
Dr. A. Ray Hilton, Sr. Amorphous Materials, Inc. Casting of chalcogenide glass Different steps of Chalcogenide glass production
Maximum size : 200 mm
Raw materials, sealed under vacuum
Reaction et distillation
Homogenisation, cooling and annealing Homogeneity control
CCD Camera
Glass to be controlled Homogeneity control Fabrication of optical lenses
Grinding/polishing : spherical surfaces Single point diamond turning Molding
Molding of chalcogenid glass lenses Examples of molded chalcogenide glass optics Challenges for chalcogenide glass molding
Sumitomo patent
In inert gas or in vacuum to avoid upper mold oxidation
vapor pressure non negligible at Ts glass Necessity to prepare preform before molding
lower mold Toshiba patented molding machine Amorphous Materials Inc molding machine Challenges and future trends for chalcogenide glass and lens fabrication Synthesis of chalcogenide glasses
100000
S As Se 10000
Important difference in Te Sb vapor pressures for the 1000 Ga different elements 100 Ge 10 Vapor Pressure Vapor (Pa) Pressure Closed systems 1 200 400 600 800 1000 1200 1400 1600 1800 2000 Temperature (°C)
Highly sensitive to contamination by oxygen
Controlled atmosphere Set-up for chalcogenide glass synthesis in argon Vapor pressure of As and Se Vapor pressure (Pa) (Pa) pressure pressure Vapor Vapor
Temperature ( °C) Photos of good sample
Example of glass obtained with sealed λ=3-5 µm silica tube Index reproducibility
3 glasses tested
Index precision :2.10 -3
Index at 1.55 µm glasses Lower Upper difference Techniquesample cansample not be used for synthesizingA 2.8204 Germanium 2.8198 containing6. 10 -4 glass B 2.8112 2.8120 - 8. 10 -4 C 2.8099 2.8104 - 5. 10 -4
Difference B-C 3. 10 -4 1.6. 10 -3 Continuous production line
Umicore patent For IR optics New approach for chalcogenide glass production Mechanosynthesis using mechanical energy instead of thermal energy to induce chemical reaction
Starting elements Mechanosynthesis Glass powder
Milling jar Consolidation Milling balls
• Melting in reusable silica chamber • Hot Uniaxial Pressing Bulk material • Spark Plasma Sintering Mechanosynthesis 80GeSe 2-20Ga 2Se 3
Evolution of powder coloration with milling duration
0h3h 5h 8h 10h 20h 40h 80h Progressive reaction between the elements and lowering of particle size
Particle size distribution XRD Spectra 6 3000 10h 80h 5 3h 2500 40h
4 2000 20h 40h 10h 3 1500 8h 80h 2 1000 5h Frequency (%/µm)
1 units) counts(arb. 500 3h
0 Ge 0,1 1 10 100 1000 10 20 30 40 50 60 70 Particle size (µm) Angle (°2 θθθ) Mechanosynthesis
• Synthesis of micrometric glass powder
• Thermal properties close to that of glasses prepared in sealed silica ampoule
To produce bulk glasses or optics
Melting and casting Sintering Melting of the powders/casting
experimental set-up
Agitation system In closed silica chamber under Argon Argon argon atmosphere exit entrance
The powders already possess the desired composition Rotating Helix
Reduced risks of Furnace evaporation of selenium Glass Bulk glass/lenses fabrication by hot pressing
Principle: sintering of the powder at a temperature above the glass transition temperature (Tg) but below the melting temperature (Tm)
Hot Uniaxial Pressing (HUP) Spark Plasma Sintering (SPS)
Pressure control Pressure control P P
furnace Vacuum die chamber
powder Power pistons powder supply protective plate
P P Faster temperature ramps reached with SPS Conventional hot pressing needs stable glasses
80GeSe 2-20Ga 2Se 3 composition: T<100 °C
Materials obtained: • Inhomogeneous sintering (thermal profile of the press)
• Uncontrolled crystallization
• No optical transmission
1µm
Crystallization due to prolonged stages at T>Tg Need to reduce sintering process duration => SPS Fast sintering of 80GeSe 2-20Ga 2Se 3 powder with SPS
Experimental conditions Dr Synter 505 Syntex SPS machine • Under vacuum • Thermal treatment
2 min, 390°C 400 350 300 Densification > 99% 250 200 150
Temperature (°C) (°C) Temperature Temperature 100 50 0 0 2 4 6 8 10 Time (min)
Sample surface area x 16 Total duration: 10 min (more than 2h for HUP) glass bulks sintered at different dwell temperatures (50 MPa, 2-min )
250 °C 350 °C
390 °C
G. Delaizir et al
J. Am. Ceram. Soc., 95 [7] 2211–2217 (2012) Fast sintered 80GeSe 2-20Ga 2Se 3 glass discs
Powder sintered 2 minutes at 390 °C (Tg+40 °C), 50MPa
Thermal camera visible 8-12µm
Densification > 99%
Transparent bulk samples Ø = 8 mm, 20 mm et 36 mm
Maximum diameter obtained using silica tubes = 9 mm Fast sintered 80GeSe 2-20Ga 2Se 3 Glass-Ceramics
Sintering at 390 °C for longer durations
2 min 15 min 30 min 60 min
70 • Progressive controllable Glass prepared 0.3 60 in silica tube crystallization (crystals < 100 nm) 2 min and ground 50 0.2 15 min • Glass-ceramics transparent in the 40 0.1 infrared range 30 30 min Ge-O critical load (N).
Transmission (%) Transmission 20 0• Important pollution by oxygen 0 20 40 60 80 100 120 140 10 60 min (transmission cut-off at 12 µm) Ceramisation time (hours) 0 0 2 4 6 8 10 12 14 16 18 20 Cooperation with LARMAUR Wavelength (µm) Summary
Chalcogenide glasses are fabricated batch by batch in sealed silica tube Discontinued process Expensive single use silica ampoules Only for highly stable glasses
Fabrication in controlled atmosphere Highly homogenous glasses Only for Ge-free glasses
Mechano-synthesis + Spark plasma Sintering Possibility of continuous process Wide choice of glass composition Large size glass ceramic optics
We need process revolution