衝撃圧縮に伴う温度変化の重 要性と衝突現象 -...
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衝撃圧縮に伴う温度変化の重要性と衝突現象
広島大学大学院理学研究科
地球惑星システム学専攻 関根 利守
[日本における超高速衝突 実験の現状と展望] 2011.12.13 惑星科学研究センター HIROSHIMA UNIVERSITY
Objectives of this study Impact phenomena; Planetary formation and evolution,
origin of meteorites, and origin of life
• How we reveal the shock strength in impacts from shocked meteorites and impactites
• Currently we have no full knowledge for that • We need to understand impact phenomena
comprehensively, but not individual changes in them • It is important to understand totally physical changes
during impact to improve the basic knowledge including temperature
Regolith
Fractured bedrock
High-velocity Impacts
breccias
Difference between volcanic craters and impact craters
• Mechanism - Energy; external (shock waves=SW) or Internal
(explosive eruptions=EE) - Strain rate; 104-106/s (SW) or 10-3-10-6/s(EE) - Stress level; ~5 GPa-100 GPa (SW) or < 2 GPa(EE) - Deformation; uniaxis or not • Geophysical - Negative anomaly and - Positive anomaly • Geological, Geochemical ー Breccias and regolith on
the surface, Pt group elements, and isotope ratios • Petrological, Mineralogical ー Shutter cones, Planar and
planar deformation feature(PDF), HP minerals, and HP glasses
• No Morphological difference
S1�
S2�
S3�
S4�
S5�
S6�
Shock Melting�
Shock Vaporization �
Shock stage
75-90
45-60
20-30
10-15
5-10
4-5 Planar fractures
Undulatory extinction �(Cpx lamera)
Ir-cracks
Mosaicism R-cracks
Rep. minerals Whole rock Shock Pressure (GPa)
Melt pockets
Dark shock veins
Whole rock melting
Maskelynite
Recrystallization HP phase
Melt HP phase
Melt HP phase
Ol Opx Pl
HP phase β
Current status for shock metamorphism
?15~25 GPa based on the phase equilibrium
Feldspar Hugoniots
Compiled by Sekine and Ahrens (1991)
NaCaK Hollandite LPP
HPP
maskelynite
Release paths from Hugoniot states
Oligoclase Ab75An19Or5 Ahrens et al.1969
Orthoclase Ab25Or75 Grady & Murri (1976)
HEL HEL
HP feldspar (hollandite) is unquenchable! Why does Hol exist in some meteorites?
The system KAlSi3O8-NaAlSi3O8 at HPHT Static pressure data by Liu (2006)
Cf. DAC Exp. Liu (1978) and Tutti (2007)
Limit
No Ab-rich Hollandite
Pl-Msk-Hol
1
2 3r
3c
4 5 6
7 4
6 5
7 7 7
W W
W
W 8
飛翔体
金属板
ネジ試料
容器
回収実験�
その場観察実験�
圧縮法の相違点
1. 衝撃圧縮 2. 静的圧縮 (準静的圧縮) 3. 等エントロピー圧縮
衝撃波の立たない動的圧縮
ー圧力発生原理と熱力学的相違ー
Volume
Pre
ssur
e
V0 V
PH
PS
P
Shock temperature calculation
Hugoniot
Isentrope
V0 V1
PH PS
€
TS = Ti exp ( γV)dV
Va
Vb
∫
TS : temperature along the isentropeTi : initial temperatureTH : shock temperature
Vγ(PH − PS ) = CV
TS
TH
∫ dT
PH2(V0 −V1) = − PdV +
V1γV0
V1
∫ (PH − PS ) + ETR
P = d0UpUs = d0Up(C0+SUp)
Impedance match diagram
Pres
sure
Particle velocity
Sample
ContainerFlyer
Reflection
P1
P0
Vimp
P2
Us Us
Ur
P0
P1 P2
Shock pressure, internal energy, and residual temperature
Multiple shock process
Single shock process
(Porous samples)
P, T
PH
TH
Ris
ing
Rel
ease
TR
(a) Ideal solid
Thermal conduction
P, T
PH
TH
Ris
ing
Rel
ease
TR
(b) Porous body
Thermal conduction
Surface of grain
Center of grain Average
PT profiles during impact process
Shear Band A region where plastic deformation in a material is highly concentrated
• Ductile materials ( metals, alloys, plastic, polymers, granular materials, and soils) • Quasi-brittle materials (concrete, rock, ice, and some ceramics) • not observed in brittle materials such as glass at room temperature
Fracture surface of a metallic glass along shear band (Chou & Spaepen, 1975)
Shear bands
Shear band formation mechanism
τ
γ<γc
τ
γ>γc
γ
τ
γc
γ γc
initial
Temperature increase by shear bands Stress τ, strain γ, work W
Density ρ, heat capacity Cv Efficiency of conversion of work β
Wright & Walter
γ (or time)
τ Temp
dγ/dt Perturbed
γ at
seve
re lo
catio
n
dγ/dt
101 102 103 104 105 /s
s t a b l
e
€
dW = τdγ
dT =βρCv
dW =βρCv
τdγ
T =βρCv
τdγ0
γ
∫
Local heating at a shear band, calculated by heat diffusion equation
ns
Heat content Heat content
N2 reduction to NH3 by impacts
Fe
N2
Ocean
N2 + H2 Hot
NH3
Fe + H2O = FeO + H2
2 mm
30 mm
Sample Fe, Ni, H2O, N2 (NH3) , 13C(Solid)
30 mm
Pb gasket
Propellant gun
Shock P; 6 GPa, duraBon; 0.7 μs、T; 5,000~3,000 K
projecBle Container
Sample
Experimental method
Containers to recover aqueous solutions
0.68 km/s 0.80 km/s 0.82 km/s
0.90 km/s 1.01 km/s 1.04 km/s
Shock process in Ol + H2O
SUS304 Olivine Aqueous sol Air
Summary • HV impacts generate shock wave and rarefaction
wave in materials at high strain rates • They affect the state with a time lag, and interact
each other to change local conditions of P and T • The initial physical state of target is important, but
in most case remains unknown • Crystal sliding systems and pore distribution in the
initial state generate higher T locally • Adiabatic shear bands may play a key role to form
shock veins where the T is locally higher than that of the host rock