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 , China 2 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, , China Strausbourg France XI EPNM

Outline Introduction Experimental Results and discussion Conclusions

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

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

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.

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

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

Experimental conditions

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.

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.

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.

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?

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

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

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

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

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.

Phase diagram of Ti-Si system Back

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