Thermal Analysis of 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 1 Masaryk University Campus (Brno-Bohunice) 2 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) 3 Conclusions Introduction T Tmbulk Melting point depression 2 bulk 3 s 2Tm Equation Tm ( r ) bulk s L Hm sr L and Sn - 0,5wt%Cu - 4wt%Ag Nano alloy particles Diagram showing melting point depression in dependence on particle diameter Promising materials for lead free solders 4 J. Liu (SMIT,Göteborg) Development of Nano Lead Free Solders – Challenges and Future Research Topics, MP0602, Joint Working Group meeting, Brno,2007 Introduction Laboratory of Thermal Analysis (Dept. of Chemistry, Faculty of Science, Masaryk Univ. Brno) Research project: Physical and chemical properties of advanced materials and structures 5 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…TA System Controller (TASC) 5..Vacuum Controller, (cca 9·10-6 mbar) 6…QMS Controller 7..Purification Column (oxygen) (Argon 99,999) Mass Flow Controller (MFC) 6 Studies Lead free solders (Ag-Cu-Sn system) COST MP0602 Advanced Solder Materials for HighTemperature Application- their nature, design, process and control in a multiscale domain Example for Sn-0,7wt%Cu-3,5wt%Ag alloy (bulk) 4… liquid + BCT_A5 + ETA liquid liquid + Ortho 4 BCT_A5 + Ortho + ETA BCT_A5 + Ortho + Cu6Sn5_P 7 Phase diagram of the Sn - 0,7wt% Cu - Ag system 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 8 DSC curves for ― solder Ag-Cu-Sn and ― pure Sn Sn nanopowder Studies Complications due to existence of oxide layer can be expected (massive oxidation) – melting point temperature of Sn 232ºC 9 Phase diagram of the Sn - O system Sn nanopowder Studies 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 Temperature decrease due to nucleation process 10 DSC curves for ― ― Sn nanopowder and ― pure Sn cooling Sn nanopowder Studies 100 nm 11 SEM of Sn nanoparticles before heating Sn nanopowder Studies N particles V particles / .10-3 nm3 120 100000 80000 N particles V of particles / .10-3 nm3 80 60000 40000 40 20000 0 0 0 40 80 120 Diameter of particles / nm 160 Diameter of particles / nm 12 200 0 40 80 120 Diameter of particles / nm 160 Diameter of particles / nm Distribution of particle size before heating 200 Studies Sn nanopowder 100 nm 13 SEM of Sn nanoparticles after heating Sn nanopowder Studies V particles / .10-3 nm3 NN particles particles V of particles / .10-3 nm3 60000 400 300 40000 200 20000 100 0 0 0 20 40 60 80 Diameter of particles / nm 100 Diameter of particles / nm 14 120 0 20 40 60 80 100 Diameter of particles / nm Diameter of particles / nm Distribution of particle size after heating 120 Cu nanopowder Studies Complications due to existence of oxide layer can be expected but with more optimal stoichiometry than that for Sn (less massive) 1083ºC – melting point temperature of Cu Phase diagram of the Cu - O system 15 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 16 DSC curves for ― ― Cu nanopowder Ag nanopowder Studies No existence of oxide layer can be expected 962ºC ~200ºC 17 – melting point temperature of Ag Phase diagram of the Ag - O system Ag nanopowder Studies – – – … first, second and third run Deoxidation, melting and coagulation (sintering) (waiting for analyses) Oxidation 18 DSC curves for Ag nanopowder Ag nanopowder Studies Partially oxidized sample becomes deoxidized during the heating and particles coagulate Coagulated material behaves like bulk no melting point depression heating cooling Behaviour like bulk material effect of undercooling 19 bulk melting point - 962 ºC DSC curves for ― ― Ag nanopowder Conclusions 20 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. Acknowledgement: This work has been supported by the Ministry of Education of the Czech Republic under the project MSM0021622410 Any cooperation is welcome 21 Introduction 22 Netzsch STA 409 CD/403/5/ SKIMMER http://www.netzsch-thermal-analysis.com/en/products/detail/pid,34.html Introduction Knudsen effusion method coupled with a mass spectrometer 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 23 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 Introduction STA 409 CD/3/403/5/G details DSC sample carrier Ion source IontovýKnudsen zdroj cell 24