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## Direct Pressure Measurements and Insights on Current Pressure Scales

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**Baosheng Li**ESS Building SUNY Stony Brook Stony Brook, NY 11794 Direct Pressure Measurements and Insights on Current Pressure Scales This research is supported by NSF Elasticity Grand Challenge Grant**Simultaneous P-V-T Eos and Sound Velocity (Vp,Vs)**Measurements CCD/SSD Press Incident slits Sample NSLS X17B2 Ultrasonic Interferometer YAG and CCD Camera X-ray Imaging Experimental Techniques**Amp**Details of SAM 85 cell assembly Pt NaCl C-heater TC TC Boron sample Cell assembly for ultrasonics at High P and T. Frequency Ultrasonic Interferometry P and S wave travel times (tp, ts) inside the sample are measured at the same time**SEM Image of Hot-pressed MgO Polycrystalline sample**Bulk density: 3.57 g/cm3 (99.6% of theoretical density)**Results of Unit Cell Volume of MgO at High P and T**1073K 473K**Finite Strain Data Analysis**1. Finite Strain Equations rVP2 = (1-2e)5/2(L1+L2e+ ...) (1) rVS2 = (1-2e)5/2(M1+M2e+ ...) (2) with e = [(1-(r/ro)2/3]/2 L1 = KS+(4/3)G; L2 = 5(KS+4G/3) - 3KS(KS’ + 4G’/3) M1 = G; M2 = 5G-3KSG’ 2.Solve for: KS0, Ks0’, G0, G0’,dKS/dT, dG/dT, d2K/dPdT, d2G/dPdT, d2K/dP2, d2G/dP2 by minimizing S(Vmea-Vcal) 2 3. Calculation of sample pressure P = - (1-2e)5/2(C1e+0.5C2e2+ ….) with C1 = 3L1–4M1; C2 = 3L2–4M2+7C1**Comparison of Elastic Properties from Selected Studies**1: This study, 2: Jackson & Niesler (1982); 3: Yoneda (1990); 4: Zha et al. (2000); 5: Sinogeikin and Bass (2000); 6: Chopelas (1992); 7: Karki et al. (1999); 8: Matsui (1999) ; 9: Anderson and Andreatch(1966); 10: Fei (1999); 11: Utsumi et al. (1998); 12: Speziale et al. (2001) ; 13 : Dewaele et al. (2000).**Exp. Points Using NaCl/Ruby P scale**Comparison of V/V0 for MgO Collected Using Different P scales 20 GPa 10**Difference Between Calculated Pressures on MgO**and Those from NaCl (obs)**RUS**Brillouin Scattering P >50 GPa Expanding P T Range for P-V-VP-VS-T- e Measurement**Conclusions**• Unit cell volume, P and S wave velocities of MgO have been measured up to ~11GPa and 1073K. • Combined analyses of the volume and velocity data yield direct determination of K, G, K/P, G/P, K/T, G/ T without relying on previous pressure scales (cross-derivatives and second order derivatives can be derived as well). The sample pressure can be directly calculated from the derived • The discrepancies between previous EoS results likely results from pressure range and pressure scales. • Comparison of the 300K isotherm of MgO suggests that MgO EoS from different studies are consistent within <1%. • Direct pressures and those from NaCl/Ruby differ by an average of ~6% at the current experimental pressure range at room T. The difference becomes smaller at temperatures above ~1100k, within the claimed uncertainties of NaCl pressure scales (e.g., Brown, 1993).