Hematite (α-Fe2O3) powder compacts have been subjected to controlled, quantitative high pressure shock loading at peak pressures from 8-27 GPa and preserved for post shook analysis. The broadened x-ray diffraction peak profiles have been analyzed to determine the residual lattice strain and the coherent crystallite sizes. Maximum modification effects are observed near 17 GPa with strain values near 3 x 10-3 and size values near 200 Å suggesting annealing at higher shock pressure, resulting from the higher shock temperature.

Sir:Yellow or brown diamagnetic planar and blue-violet paramagnetic octahedral are both well-established forms for nickel(I1). With certain polyamine complexes, both conformations exist in solution in detectable concentrations. Thus, blue aqueous solutions containing Ni(trien)(HzO)z2+, Ni(en)n(HzO)z2+, or Ni(pn)z-(Hz0)22+ turn brownish yellow on heating. The absorption band at -440 mp characteristic of tetragonal nickel(I1) is developed, and the original color returns on cooling the so1ution.ls2 Aqueous solutions of the nickel complex of the quadridentate ligand NH2(CH&-NH(CH2)3NH(CH2)2NH2 (abbreviated 2,3,2-tet) are already brown3 and thus contain substantial amounts of the planar form at room t e m p e r a t~r e .~ Information on the rate at which such equilibria as (L = trien, or 2,3,2-t et) octahedral-Ni(L)(HzO)?2f e planar-Ni(L)z-+ 2 H i 0 are established is lacking, but the system is amenable to the relaxation method of rate measurement.j Sizable absorbance changes at 440 mp with a small temperature rise, 2.5-6.5 O, particularly with the 2,3,2-tet complex, allowed work at low amplification and thus at the shortest time ranges of the temperature-jump apparatus.j It was found, however, that with the 1 : l nickel(I1)-trien and nickel(II)-2,3,2-tet systems, the establishment of the yellow-blue equilibria was complete at 5" within 10 psec which was the shortest time we could reach with our equipment. The first-order rate constant for the conformation change must be >lo5 sec-l. Only a slight "electronic ripple" was observed when solutions of Ni(tren)(H.O)?*f or K N 0 3 were used in the temperature-jump cell. The amine tren, N(CH2CH2NH2)3, can only coordinate to leave two cis positions in the octahedron.We believe that with 2,3,2-tet the fast transition observed is between the Trans-octahedral and the planar complex. Of relevance are the reactions of the complex with EDTA and oxalate which indicate that there are at least two blue isomers of Ni(2,3,2-tet)(H20)22+ present in solution. Upon mixing EDTA and Ni-2,3,2-tet (1 : l ) complex there is an absorbance jump at 380 mp corresponding to about 40% of the total complex present. the remainder, both blue and yellow forms, reacting by a slow first-order process (k = 9.3 X sec-l at pH 8.34).6 The fast transition with the trien complex may be due to a trans-octahedral-planar equilibrium although Ni(trien)(H20)2?+ is believed to have predominantly the cis-octahedral structure in aqueous(1) C. I<. Jprgensen, Acta Chem. aqueous solution (25", p = 0.5 M ) the yellow form of Ni (2,3,2-tet)Z+ cannot be more than 25 % of the total Ni(2,3,2-tet)?' as opposed to 50% suggested in a n earlier report.3 This estimate is based on spectral measurements, using a n approximate value for the molar absorptivity of the yellow form at 440 m p of 67 (obtained in high electrolyte concentration, 7.4 M NaCIO1). The planar yellow form is at most 2 ' % of the total Ni(trien)'+ under the conditions p = 0.5 M , 25 ^. ( 5 ) M . Eigen and L. work in progress.solution. The high rate constant resembles...

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Zirconia (Zr02) powder compacts have been subjected to controlled, quantitative high pressure shock loading at peak pressures from 5-27 GPa and preserved for post-shock analysis. The overlapping broadened X-ray diffraction peak profiles have been separated by least-squares fitting procedures. The separate lines have been analysed in the usual manner to determine the residual lattice strain and the coherent crystallite sizes. Maximum modification effects are observed near 20 GPa with strain values near 3 x 10-3 and size values near 200 A.