Thermal Analysis of Sn, Cu and Ag Nanopowders

1. Thermal Analysisof Sn, Cu and Ag Nanopowders Pavel Brož, Jiří Sopoušek, Jan Vřešťál Masaryk University, Faculty of Science, Department of Chemistry, Kotlářská 2, 611 37, Brno, Czech Republic broz@chemi.muni.cz, sopousek@chemi.muni.cz, vrestal@chemi.muni.cz

2. Masaryk University Campus(Brno-Bohunice)

3. Outline • Introduction- nanoparticles - Netzsch STA 409 CD/3/403/5/G Apparatus (thermal analysis (TA), Knudsen cell MS) differential scanning calorimetry (heat flow DSC) • Studies - Lead free solders (DSC testing, CALPHAD calculations) - Nanopowders of pure metals: Sn, Cu, Ag (DSC,surface effects, CALPHAD calculations) • Conclusions

4. Introduction Melting point depression Equation and Diagram showing melting point depression in dependence on particle diameter J. Liu (SMIT,Göteborg)Development of Nano Lead Free Solders – Challenges and Future Research Topics, MP0602, Joint Working Group meeting, Brno,2007 Sn - 0,5wt%Cu- 4wt%Ag Nano alloy particles  Promising materials for leadfree solders

5. Introduction Laboratory of Thermal Analysis(Dept. of Chemistry, Faculty of Science, Masaryk Univ. Brno) Research project: Physical and chemical properties ofadvanced materials and structures

6. Introduction DSC/KC/QMS Apparatus (Netzsch STA 409 CD/3/403/5/G ) 1…Furnace (0.1 – 20 K min-1, 25-1450ºC) 2…QMS range 1-512 amu resolution 0,5amu IE = 25 -100 eV 3…Turbomolecular Pump 4…TASystem Controller (TASC) 5..Vacuum Controller, (cca 9·10-6mbar) 6…QMS Controller 7..Purification Column (oxygen) (Argon 99,999) Mass Flow Controller (MFC)

7. Studies Lead free solders (Ag-Cu-Sn system) • COST MP0602 Advanced Solder Materials for High-Temperature Application- their nature, design, process and control in a multiscale domain • Example for Sn-0,7wt%Cu-3,5wt%Agalloy (bulk) 4… liquid + BCT_A5 + ETA Phase diagram of the Sn - 0,7wt% Cu - Ag system liquid liquid + Ortho 4 BCT_A5 + Ortho + ETA BCT_A5 + Ortho + Cu6Sn5_P

8. Studies Lead free solders (Ag-Cu-Sn system) • Detection of two phase transitions, the appearance of the first one visible at the beginning of the peak for Sn based material • Pure Sn chosen as convenient standard Onset DSC curves for ― solder Ag-Cu-Sn and ― pure Sn

9. Studies Sn nanopowder Complications due to existence of oxide layer can be expected (massive oxidation) –melting point temperature of Sn Phase diagram of the Sn - O system 232ºC

10. Studies Sn nanopowder Sn packed  no particle coagulation,in oxide layer melting point depression heating Flat curve  oxidized sample Wide low peak indicates solidification of oxidized particles of various distribution cooling Temperature decrease due to nucleation process DSC curves for ――Sn nanopowder and ― pure Sn

11. Studies Sn nanopowder 100 nm SEM of Sn nanoparticles before heating

12. Studies Sn nanopowder N particles V particles / .10-3 nm3 Diameter of particles / nm Diameter of particles / nm Distribution of particle size before heating

13. Studies Sn nanopowder 100 nm SEM of Sn nanoparticles after heating

14. Studies Sn nanopowder N particles V particles / .10-3 nm3 Diameter of particles / nm Diameter of particles / nm Distribution of particle size after heating

15. Studies Cu nanopowder Complications due to existence of oxide layer can be expected but with more optimal stoichiometry than that for Sn (less massive) –melting point temperature of Cu Phase diagram of the Cu - O system 1083ºC

16. Studies Cu nanopowder Flat curve  oxidized sample Cu packed  no particle coagulation,in oxide layer melting point depression heating Partial coagulation thanks to instability of oxide layer Number of small peaks indicates existence of coagulated microsized particles. Higher udercooling indicates absence of nucleation centre. cooling Particles coagulate macroscopic object forms having behaviour like bulk material effect of undercooling bulk melting point - 1083 ºC DSC curves for ――Cu nanopowder

17. Studies Ag nanopowder No existence of oxide layer can be expected –melting point temperature of Ag Phase diagram of the Ag - O system 962ºC ~200ºC

18. Studies Ag nanopowder –– – … first, second and third run Deoxidation, melting and coagulation (sintering) (waiting for analyses) Oxidation DSC curves for Ag nanopowder

19. Studies Ag nanopowder Partially oxidized sample becomes deoxidized during the heating and particles coagulate Coagulated material  no melting point behaves like bulk depression heating cooling Behaviour like bulk material  effect of undercooling bulk melting point - 962 ºC DSC curves for ――Ag nanopowder

20. Conclusions • Even oxygen traces cause formation of massive and compact oxide cover layer which disables coagulation of Sn nanoparticles • Concerning Cu nanoparticles the oxidation process is less dramatic. Coagulation in liquid phase is observed. • Ag nanoparticles do not undergo oxidation at higher temperatures and coagulation (sintering) takes place. • These facts follow from nobility of the elements. • Nanopowders are promising materials for preparation of lead free solders applicable at higher temperatures but there are problems with oxygen affinity for currently used basic materials (Sn, Cu) or with coagulation (Ag). • Chemical and phase analyses on samples from the measurements are currently performed in order to support results of thermal analyses.

21. Acknowledgement: This work has been supported by the Ministry of Education of the Czech Republic under the project MSM0021622410 Any cooperation is welcome

22. Introduction Netzsch STA 409 CD/403/5/ SKIMMER http://www.netzsch-thermal-analysis.com/en/products/detail/pid,34.html

23. Introduction Knudsen effusion method coupledwith a mass spectrometer Configuration of Knudsen cell and ion source. 1. Ion source, 3. shutter, 4. radiation shields,5. particle beam, 7. sample crucible with a lid, 8. sample, 10. heating shield, 11.thermocouple Construction detail of DSC/KC/QMS instrument.The instrument is not equipped with Skimmer but with a ceramic disc with orifices of various diameters enabling or disabling enter of effusing particles from studied sample

24. Introduction STA 409 CD/3/403/5/G - details DSC sample carrier Ion source Iontový zdroj Knudsen cell