1 Chemistry at the Earth’s surface at 100 kPa Chemistry in the Universe at hight pressures and temperatures deep within the planets and stars Laboratory: Pressures up to 250 GPa, high temperatures ~7000 C 1 bar = 100 kPa 1 Mbar = 100 GPa p-V work during compression to 1 Mbar equivalent to approx. 1 eV chemical bond energy In-situ observations by diffraction, spectroscopy to probe chemical reactions, structural transformations, crystallization, amorphization, phase transitions Methods of obtaining high pressures  Anvils, diamond, tetrahedral and octahedral  Shock waves (km s-1)  Explosions, projectiles  Go to another planet: Jupiter (hydrogen is metallic at 100 Gbar) Dry High-Pressure Methods 2 Earth Core 3.4 Mbar = 340 GPa, 6000 K ε-Fe hcp MgSiO3 most abundant silicate mineral within our planet ! Olivine Mg2SiO4 > pyroxene (silicate chains) > spinel Mg2SiO4 ilmenite > garnet (HT) > perovskite MgSiO3 Si CN = 6 3 PRESSURE SCALE Pressure, bar System 1 Mbar = 100 GPa 10-12 high vacuum chamber 1 atmospheric pressure 1.5 kitchen pressure cooker 2.0 car tire 50 a lady in stilleto heels 60 breakdown of human nervous system - divers 73.8 critical pressure of CO2 150 autoclave (safety burst disc) 221.2 critical pressure of H2O 103 pressure at the bottom of the ocean (11 km) 2.103 LDPE 104 Earth crust (30 km) 105 synthetic diamond production 3.4.106 pressure at the center of the Earth (6378 km) 107 Saturn, Jupiter, metallic hydrogen 108 neutron stars 4 Dry High-Pressure Methods Pressure techniques useful for synthesis of unusual structures TD metastable yet kinetically stable when pressure released = pressure and temperature quenching reconstructive transformation hindered at low temperature insufficient thermal energy for bond-breaking •high pressure phases •higher density •higher coodination number •higher symmetry •transition to from nonmetal to metal •band mixing Pressure/Coordination Number Rule: increasing pressure – higher CN Pressure/Distance Paradox: increasing pressure – longer bonds 5 Dry High-Pressure Methods Gray Sn (diamond type, stable below 13 C, semiconductor) Coordination number 4, Sn-Sn bond length 281 pm White Sn (metallic) Coordination number 6, Sn-Sn bond lengths 302 and 318 pm 6 Examples of high pressure polymorphism for some simple solids Solid Normal Typical Typical High pressure structure and transformation transformation structure and coordination conditions conditions coordination number P(kbar) T(o C) number C Graphite 3 130 3000 Diamond 4 CdS Wurtzite 4:4 30 20 Rock salt 6:6 KCl Rock salt 6:6 20 20 CsCl 8:8 SiO2 Quartz 4:2 120 1200 Rutile 6:3 Li2MoO4 Phenacite 4:4:3 10 400 Spinel 6:4:4 NaAlO2 Wurtzite 4:4:4 40 400 Rock salt 6:6:6 Dry High-Pressure Methods 7 High-Pressure Phase Transformations 8 Unusual Stoichiometries under High-Pressure + Cl2 + Na Laser heating 60 GPa, 2000 K NaCl NaCl 9 p-T Phase Diagrams 10 11 12 Water 17 phases of ice Ice-VII m.p. 100 C Ice-X fluorite, ionically conductive above 10 GPa Equalization of O-H covalent and hydrogen bonds above 60 GPa Max pressure attained for water 210 GPa Ca ccp at ambient pressure bcc (!) above 20 GPa 4s-3d mixing, Ca become a transition metal MgSiO3 most abundant silicate mineral within our planet ! pyroxene (silicate chains) ilmenite > garnet > perovskite Si CN = 6 1 GPa floats sinks 13 Condensed gases H2 metallic conductivity in dense fluid hydrogen H2 + H2 NO2 + N2O NO+ NO3 - calcite N2 semiconducting oligomers (-N-)x at 100-240 GPa cubic diamond 110 GPa, 2000 K Heating: 1-μm B plate (absorber of laser radiation rests on c-BN pieces that thermally insulate the plate from the bottom anvil. The sample squeezed between the anvils is surrounded by the c-BN/epoxy gasket followed by the metallic (Re) supporting ring. 840 cm–1 2410 cm–1 14 Phase Diagram of Hydrogen 15 Phase Diagram of CO2 I III CO2-V Quartz superhard CO2 heating at 10-20 GPa sp3 bonded CO4 cristobalite, tridymite 40 GPa quartz (noncentrosymmetric) 16 Reaction Equlibrium and Pressure The reaction volume V the volume difference between the products (A) and the reactants (C) A ⇄ C Associative type = negative V K increases with increasing pressure Dissociative type = positive V0 K decreases with increasing pressure A C K  17 Reaction Kinetics The activation volume V≠ the volume difference between the transition state complex and the reactants Associative type = the rate determining step involves the formation of a covalent bond negative V≠  reaction rate increases with increasing pressure Dissociative type = the breaking of a covalent bond positive V≠  reaction rate decreases with increasing pressure Room-temperature pressure dependence of the rate constant for different activation volume V≠ values (in cm3 mol1) 18 Diamond Anvil Cell Percy Williams Bridgman (1882 – 1961, NP in Physics 1946) 19 Diamond anvil cell p = F/A p = 40 GPa Atable / Aculet = 10 : 1 Aculet = 100-200 μm laser heating T > 2500 C Re, steel gasket Diamond transparent to radiation from IR to X-ray pressure transmitting medium: solid Ar, N2, O2, Diamond Anvil Cell 20 Diamond Anvil Cell 21 Diamond Anvil Cell 22 Calibrating a high pressure diamond anvil  Ruby - fluorescence transition  Bi, Tl, Ba pressure induced phase transition High pressure synthesis SnO2 + Pb2SnO4 2 PbSnO3 perovskite 7 GPa, 400 C At ambient pressure only SnO2 and PbO products Dry High-Pressure Methods Ruby = Cr doped corundum 23 Rb2KCrF6 24 pressure - transmitting medium pressure - transmitting medium Fe ring (electrical connection) Corundum disc (thermal insulation) Mo disc (electrical connection) sample container + lids graphite heating mantle High Pressure Two-Die Belt-Type Apparatus 25 Synthesis of Diamonds The hardest known substance, the highest thermal conductivity Difficult to transform graphite into diamond Industrial diamonds (GE) made from graphite around 3000 oC and 13 GPa 26 a – shock wave production of diamond b – high-temperature, high-pressure synthesis of diamond c – catalytic region for diamond formation d – CVD diamond e – transformation of C60 into diamond p, T Diagram of Carbon 27 The activation energy required for a sp2 3-coordinate to a sp3 4-coordinate structural transformation is very high, so requires extreme conditions Ways of getting round the difficulty  Catalyst: transition metals (graphite is dissolved in molten metal: Fe, Ni, Co, 6 GPa, 1000 C), alloys (Nb-Cu), CaCO3, hydroxides, sulfates, P (7.7 GPa, 2200 C, 10 min)  Squeezing (uniaxial not hydrostatic pressure), no heating, buckyball carbons are already intermediate between sp2-3 C60, diamond anvil, 25 GPa instantaneous transformation to bulk crystalline diamond, highly efficient process, fast kinetics  Carbon onions, electron irradiation of graphite, concentric spherical graphite layers, spacing decreases from 3.4 Å to 2.2 Å in the onion center, 100 GPa, 200 keV beam, in several hours, pressureless conversion to diamond  Using CH4/H2 microwave discharges to create reactive atomic carbon whose valencies are more-or-less free to form sp3 diamond, atomic hydrogen saturates the dangling bonds, dissolves soot faster than diamond, a route for making diamond films, 50 m Synthesis of Diamonds 28 Graphite 29 Carbon onions 30 31 Organic molecule theory of diamond cleavage The jeweler's chisel if placed correctly on a diamond, with a well oriented blow, always cause cleavage along {111} greater than 90% of the time, imagine the cost of a mistake with a large crystal The number of bonds broken per unit area (that is, surface energies) for different planes does not explain the observations of preferential {111} cleavage!!! Diamond viewed in terms of layers of polycondensed cyclohexane rings with axial bonds between layers and equatorial bonds within layers Unfavorable axial-axial C-C bond interactions at 2.51 Å versus equatorial-equatorial at 2.96 Å 32 Model compounds like cis-decalin versus trans-decaline comprised of two fused cyclohexane rings trans-decalin is 11-12 kJmol-1 more stable because cis-strain cannot be relieved by bond rotation as in cyclohexane itself, cis can only isomerize to trans by bond cleavage followed by recombination, hence origin of the high activation energy for the cis-to-trans isomerization of decalin. A breaking molecule theory: axial-axial unfavorable interactions cause the mechanical energy of the jeweler's chisel to be funneled into preferential breakage of an axial C-C bond This then induces a kind of domino effect whereby the adjacent axial C-C bonds break and C-C bonds throughout the entire {111} plane are severed H H H H 33 Topochemical 3D Polymerization of C60 under High P and T Micro-Vickers hardness (MVH) 34 Polymerization of C60 35 • Electrical conductivity of semiconductors increases with T. The change of conductivity with T is one way of measuring the band gap. • Conductivity also increases with P, because atoms are pushed closer together. • All elements eventually adopt metallic structures at high P. • The interior of Jupiter is thought to contain metallic hydrogen!