1. Shock-induced reactions in ball-milled Ti-Si powder mixtures J. J. Liu 1, N. F. Cui 2, P. W. Chen 2 1 Faculty of Science, Beijing University of Chemical Technology, Beijing 100029, China 2 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, 100081, China 2012.5.4 Strausbourg France XI EPNM

2. Outline Introduction Experimental Results and discussion Conclusions

3. Introduction Ti-Si system CompositionComposition: TiSi, TiSi 2, Ti 5 Si 3, Ti 5 Si 4 Synthesis: Application: Combustion synthesis Self-propagating reaction Mechanical alloying Shock induced reaction Heat resistant material High hardness Microelectronics Photocatalyst

4. Ti-Si photocatalyst As new functional materials, the light-absorption characteristics in UV-visible region (ca.360  800nm) of TiSi 2 are ideal for solar applications and have a good photocatalytic activity of splitting water into hydrogen. Ritterskamp P., et al, Angew.Chem. Int. Ed, 46:7770, 2007

5. Ti-Si photocatalyst Liu J J., et al, AIP Conf.Proc., 1426: 1403, 2012 The coupled photocatalyst of Ti 5 Si 3 and Ti 8 O 15 were shock-sythesized by adding oxidant and exhibits superior photocatalytic activity.

6. Experimental A planetary ball mill (Fritsch, P-7) was used for grinding the Ti-Si samples. 300 steel balls of 3mm diameter (  32g)and 8g of mixed powder in 80 ml bowl At 300  900rpm for 3h

7. Experimental. (1) detonator; (2) upper cover; (3) booster charge; (4) nitromethane; (5) bottom cover; (6) flyer; (7) steel protection tube; (8) copper sample container; (9) sample; (10) copper screw lid; (11) PVC plastic tube; (12) steel momentum block Scheme of shock-loading apparatus

8. Experimental conditions

9. Photocatalytic test Set-up scheme of photocatalytic evaluation 1. Hg lamp, 2.rubber plug, 3. quartz reactor, 4.water and photocatalyst, 5.magnetic stirrer, 6.dark box.

10. Results and discussion Figure 1 XRD patterns of ball-milled Ti-Si2 mixtures at different rotary speeds (a)300rpm; (b)500rpm; (c)700rpm; (d)900rpm. Figure 2 XRD patterns of shocked Ti-Si2 mixtures(2.25km/s) at different rotary speeds (a)300rpm; (b)500rpm; (c)700rpm; (d)900rpm. Q7: The milled Ti-Si2 reacted to form little Ti 5 Si 3 at 900rpm. 414:The next shock does not initiate further reaction.

11. Results and discussion Figure 3 XRD patterns of ball-milled Ti5-Si3 mixtures at different rotary speeds (a)300rpm; (b)500rpm; (c)700rpm; (d)900rpm. Figure 4 XRD patterns of shocked Ti5-Si3 mixtures(2.25km/s) at different rotary speeds (a)300rpm; (b)500rpm; (c)700rpm; (d)900rpm. Q8: The milled Ti5-Si3 has not any reaction at 900rpm. 415:The next shock initiated reaction to form little Ti 5 Si 3.

12. Results and discussion Figure 5. XRD patterns of samples derived from Ti-Si2 at different conditions: a  direct shock loading at 3.37km/s without ball-mlling; b  ball-milling after 3h at 900rpm; and c  shock loading of sample b at 2.25km/s. Why?

13. Results and discussion Figure 6 XRD patterns of samples derived from Ti5-Si3 at different conditions: a  direct shock loading at 2.25km/s without ball-mlling; b  ball-milling after 3h at 900rpm; and c  shock loading of sample b at 2.25km/s

14. Results and discussion Figure.7 SEM images of samples. (a) Q7, (b)Q8,(c)414, (d)415. b c d a Partly react Obviously react no reaction Partly react

15. Results and discussion Mill-activated(a>b)(Mill+Shock)-activated(b>a) Figure.8 DSC analysis of Ti-Si samples

16. Photocatalytic test for producing hydrogen Same activity sequence: shocked+milled(a)> shocked(c) >milled (b) Figure.9 Curves of photocatalytic activity for Ti-Si samples

17. Conclusions Milling treatment to some extent could decrease the threshold of shock reaction of Ti-Si and the reaction product is different from the designed one. The direct shock synthesis may give a designed Ti-Si product under heavier loading conditions. Both of milling and shock loading can activate and initiate reaction of the Ti-Si samples which exhibit better photocatalytic activity than that of only milling or shock loading.

19. Phase diagram of Ti-Si system Back

20. Results and discussion Thermodynamic stability of Ti x Si y compounds: TiSi 2 <TiSi<Ti 5 Ti 4 <Ti 5 Si 3 Ti 5 Si 3 is easier to form than TiSi 2 or if TiSi 2 is formed, has a tendency to transform to Ti 5 Si 3. However, the direct shock loading could get the metastable TiSi 2 because of high quenching and strain rate. Ref: Guan Q.L., et al, J.Mater.Sci., 44:1902, 2009 back