T
he
hy
drogenation of t
he CaH
2+MgB
2 composite an
d t
he
de
hy
drogenation of t
he resulting pro
ducts areinvestigate
d in
detail by in situ time-resolve
d sync
hrotron ra
diation pow
der X-ray
diffraction,
hig
h-pressure
differential scanning calorimetry, infrare
d, an
d t
hermovolumetric measurements. It is
demonstrate
d t
hat aCa(BH
4)
2+MgH
2 composite is forme
d by
hy
drogenating a CaH
2+MgB
2 composite, at 350
![](/images/entities/<font color=)
deg.gif">C an
d 140 bar of
hy
drogen. Two p
hases of Ca(BH
4)
2 were c
haracterize
d:
![](/images/gifc<font color=)
hars/alp
ha.gif" BORDER=0>- an
d ![](/images/gifc<font color=)
hars/beta2.gif" BORDER=0 ALIGN="mi
ddle">-Ca(BH
4)
2.
![](/images/gifc<font color=)
hars/alp
ha.gif" BORDER=0>-Ca(BH
4)
2 transforms to
![](/images/gifc<font color=)
hars/beta2.gif" BORDER=0 ALIGN="mi
ddle">-Ca(BH
4)
2 at about 130
![](/images/entities/<font color=)
deg.gif">C. Un
der t
he con
ditions use
d in t
he present stu
dy,
![](/images/gifc<font color=)
hars/beta2.gif" BORDER=0 ALIGN="mi
ddle">-Ca(BH
4)
2 decomposes first toCaH
2, Ca
3Mg
4H
14, Mg, B (or MgB
2 depen
ding on experimental con
ditions), an
d hy
drogen at 360
![](/images/entities/<font color=)
deg.gif">C, beforecomplete
decomposition to CaH
2, Mg, B (or MgB
2), an
d hy
drogen at 400
![](/images/entities/<font color=)
deg.gif">C. During
hy
drogenation un
der140 bar of
hy
drogen,
![](/images/gifc<font color=)
hars/beta2.gif" BORDER=0 ALIGN="mi
ddle">-Ca(BH
4)
2 is forme
d at 250
![](/images/entities/<font color=)
deg.gif">C, an
d ![](/images/gifc<font color=)
hars/alp
ha.gif" BORDER=0>-Ca(BH
4)
2 is forme
d w
hen t
he sample is coole
dto less t
han 130
![](/images/entities/<font color=)
deg.gif">C. Ti isopropoxi
de improves t
he kinetics of t
he reactions,
during bot
h hy
drogenation an
dde
hy
drogenation. T
he
de
hy
drogenation temperature
decreases to 250
![](/images/entities/<font color=)
deg.gif">C, wit
h 1 wt % of t
his a
dditive, an
dhy
drogenation starts alrea
dy at 200
![](/images/entities/<font color=)
deg.gif">C. We propose t
hat t
he improve
d kinetics of t
he above reactions wit
hMgB
2 (compare
d to pure boron) can be explaine
d by t
he
different boron bon
ding wit
hin t
he crystal structureof MgB
2 an
d pure boron.