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Processing ZnS based electroluminescent precursor powder mixtures with TNT

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The research has been financed by companies in a very competitive and fast growing field ... Traps are formed, causing long time phosphorescence ... – PowerPoint PPT presentation

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Title: Processing ZnS based electroluminescent precursor powder mixtures with TNT


1
Processing ZnS based electroluminescent
precursor powder mixtures with TNT
5/9/2008
Greg Kennedy and S. Itoh
2
Outline
  • Introduction
  • Electroluminescence
  • Summary of patent application
  • US patent application pub (20070080327)
  • European Union Patent (WO2007043676)
  • Investigation of the process
  • ZnS explosive processing literature
  • Preliminary experiments
  • Conclusions and Future Work

3
Display Technology
EL-11 inch 3mm 2500
LCD
Plasma
4
Electroluminescence
Examples of different wavelengths obtained by
doping
5
Electroluminescent material search
  • The research has been financed by companies in a
    very competitive and fast growing field
  • Most publicly available information is found in
    patents and patent applications
  • Look at one recent patent and some older
    published works

6
Patent Application InformationUS patent
application pub (20070080327)
  • Starting Materials
  • Primarily ZnS, (Zinc Sulfide)
  • Mn and Ir (activators, emission centers)
  • Ba and Mg
  • Explosive Chamber discussion
  • Final heat treatment
  • Gallium Arsenide compound semiconductor
  • Standard manufacturing of EL element

7
Explosive Chamber (patent info)
  • 0.01mmHg vacuum (1Pa)
  • 32g TNT selected for 50MPa in one liter chamber
  • TNT is exploded by heater (4) upon heating to
    450C
  • 109g Sample mixture(8) is placed under TNT
  • Produced calcined cake

8
Concerns due to limited information in the Patent
  • Is the explosive separated from the sample?
  • Does the TNT detonate by heating?
  • Does the TNT melt, boil before detonation?
  • How does the vacuum change the detonation
    process?
  • What is heating rate?
  • Controls temperature of the powder
  • And detonation of TNT
  • Maybe electric detonator is ok, but heating of
    powder might be necessary for desired final
    performance

9
Final Material Processing
(patent info)
Sample B
Sample C
  • Explosive loading
  • Calcined cake is allowed to cool
  • Washed with deionized water, Dried
  • Pulverizer/Separator powder (5-20µm)
  • 8 hours Calcining in nitrogen atmosphere at 700C
    in a silica tube
  • Washed with glacial acetic acid
  • Remove excessive compounds, flux and impurities
  • Rinsed with deionized water
  • Explosive Loading
  • Calcined cake is allowed to cool
  • Washed with deionized water, Dried
  • Pulverizer/Separator powder (5-20µm)
  • 0.005g GaAs mixed with 15g of powder in
    mechanical stirrer
  • 8 hours Calcining in nitrogen atmosphere at 700C
    in a silica tube
  • Washed with glacial acetic acid
  • Remove excessive compounds, flux and impurities
  • Rinsed with deionized water

10
Increased Luminosity
Patent application US2007/0080327A1
  • Increased from 400 to 4000 cd/m2
  • The reason for the excellent properties is due
    to instantaneous high temperature, light emission
    and/or shock wave produced by the explosion.
    However, particulars of the mechanism for the
    development of such favorable properties are
    still unknown.

11
Zinc Sulfide
Phase Change ---gt 1019C
  • Sphalerite
  • Cubic
  • Band Gap
  • 3.54eV
  • Wurtzite
  • Hexagonal
  • Band Gap
  • 3.67eV

High pressure phase change to a different Rock
Salt type structure 15GPa Mashimo (1999)
12
Photoluminescence of Zinc Sulfide after Dynamic
Compression
  • Pure ZnS does not exhibit photoluminescence, but
    after dynamic compaction bright photoluminescence
    occurs due to microdefects created by shock
    loading
  • Phase change from sphalerite to wurtzite
  • Fluorescence microscopic observation showed blue
    particles and green particles
  • Blue particle concentration can be increased by
    adding sulphur
  • The increase in Zn vacancies from the increase
    in sulphur causes an increase in
    photoluminescence intensity
  • Photoluminscence is reduced after roasting shock
    loaded sample
  • Batsonov, Fizika Goreniya I Vzryva, Vol. 3, No.
    3, pp441-448 1967

13
Shock Assisted Doping
  • Efficient process
  • Vacancies and interstitials
  • Heterogeneous distribution of defects
  • Heterovalent doping is possible
  • Eu2 in NaCl type systems (example)
  • Create charge defects

Lapshin and Kurnikova, ZPS, Vol 28. No1, 95-100,
Jan. 1978
14
Explosive Doping
Lapshin, et. al, ZPS, vol 14, no 6, 1020-1026,
June 1971
  • Emission bands are shifted to longer wavelengths
    compared to thermally processed materials
  • Same occurs in thermally produced material after
    shock loading
  • The chemical form of the can change the
    wavelength
  • MnS emission band at 589µm
  • Mn(NO3)2 demission at 570µm
  • Inhomogeneous phase transformation of cubic and
    hexagonal phase generates large number of defects
  • Emission bands are wider than thermally produced
    ZnSCu
  • Traps are formed, causing long time
    phosphorescence

15
Explosive Doping Literature
  • Pre-shock starting material before firing
  • 8GPa Detonating pressure from tetryl
  • Fired for 2hrs at 1250oC
  • The pre-shocked sample had 40 increased
    intensity with slight shift to shorter
    wavelengths under excitation by 254µm source

Horiguchi - Pre-shock Treatment for Preparation
of Zn2SiO4(Mn) Phosphor having High Luminescence
Intensity, Naturwissenschaften (1966)
16
Hypothesis of patent mechanism
  • The TNT is heated to 450oC
  • Melting point 80.9oC
  • Boiling Point 295oC
  • Location for Temperature not described
  • TNT
  • Melts, then boils
  • The boiling tnt mixes with EL powder
  • Vapor evolves and is ignited by the hot nichrome
    heater wire
  • Localized heating causes deflagration in the TNT

17
Experimental Procedure
  • Heat the TNT to 450 and test for deflagration or
    detonation
  • Examine mixing of liquid TNT and precursor powder
  • Test the powder for exothermic reaction upon
    heating to 450 (thermal analyzer)
  • Duplicate the patent experiment
  • Initiation of deflagration by heated wire
  • Heating from the base by heater external to the
    powder container

18
Heating the TNT
19
Video of TNT burning
20
Frame 1
21
Frame 2
22
Mixing of TNT and ZnS
  • Examine the possibility of mixing of the TNT and
    precursor powders
  • Nichrome wire heater in plaster
  • 10grams of ZnS
  • 20grams TNT
  • Glass container
  • video

23
Conclusions
  • TNT deflagrates upon heating
  • There is no explosion as described in the patent
  • Heating the TNT and the powder can lead to
    extensive mixing
  • This would allow good heat transfer to the
    precursor powder and promote localized doping

24
Future Work
  • Using the observations from this work
  • Proceed to examine the powder mixture described
    in the Chatani Patent

25
Starting Materials (patent info)
  • Sample A -conventional method
  • Sample B
  • ZnS 100g
  • MnSO4 0.27g
  • ZnO 0.5g
  • BaF2 3g
  • MgCl2 3g
  • IrCl3 0.012g
  • NaCl 2g
  • Sample C
  • 15g of Sample B after explosive processing and
    pulverizing
  • 0.005g Gallium Arsenide (1-3µm) compound
    Semiconductor
  • Mechanical stirrer in plastic bottle (20 minutes)

26
Comparative Sample A
  • 7g ZnSO4 0.5g CuCl 0.5g CuSO4
  • 800oC for 40 minutes
  • From JP-A No. 2005-126465

27
Luminance
Example 1 and 2 ,Measurement is at 280V at 8
KHz Example 3 voltage was increased to maintain
constant luminance , 315 V after 24hrs, and 330
after 100 hours, stable 120 hours to 1000 hours
28
EL Element
  • Silk screen of sample A, B, C onto BaTiO3
  • Greater than 80 of particles 12 to 18µm
  • Barium titanate is deposited on the emitting
    layer
  • Electrode is deposited on the BaTiO3
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