DRY HIGH PRESURE METHODS OF SOLID STATE SYNTHESIS

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DRY HIGH PRESURE METHODS OF SOLID STATE SYNTHESIS

• Pressures up to Gbars accessible, at high T with
  insitu observations by diffraction and
  spectroscopy - can probe chemical reactions,
  structural transformations, crystallization,
  amorphization, phase transitions - kinetics and
  mechanism of solid state transformation - think
  about this? Nucleation and growth of one phase
  within another!!!
• Methods of obtaining high pressures anvils,
  diamond tetrahedral and octahedral pressure
  transmission, shock waves, explosions
• Go to another planet, recall hydrogen is metallic
  at 100 Gbars (explain why this is so?)

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DRY HIGH PRESURE METHODS OF SOLID STATE SYNTHESIS

• Pressure techniques useful for synthesis of
  unusual structures, metastable, yet stable when
  pressure released (why?)
• Often high pressure phases have a higher density,
  higher coordination number
• In fact ruby is used for calibrating a high
  pressure diamond anvil, so explain how this
  method works?

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HIGH PRESSURE DIAMOND ANVIL SOLID STATE SYNTHESIS
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HIGH PRESSURE POLYMORPHISM FOR SOME SIMPLE SOLIDS

• Solid Normal structure Typical transformation
  High P structure
• and coord. no. conditions P kbar, T C and
  coord. no.
• C Graphite 3 130 3000 Diamond 4
• CdS Wurtzite 44 30 20 Rock salt 66
• KCl Rock salt 66 20 20 CsCl 88
• SiO2 Quartz 42 120 1200 Rutile 63
• Li2MoO4 Phenacite 443 10 400 Spinel 644
• NaAlO2 Wurtzite 444 40 400 Rock salt
  666

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DIAMONDS ARE FOREVER
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P-T PHASE DIAGRAM OF CARBON
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RELATIVE STABILITY OF GRAPHITE AND DIAMOND
Graphite sp2
Diamond sp3
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SO WHY IS IT SO DIFFICULT TO TRANSFORM GRAPHITE
INTO DIAMOND?

• Industrial diamonds made from graphite around
  3000oC and 130 kbar
• Problem is activation energy required for a sp2
  3-coordinate to a sp3 4-coordinate structural
  transformation is very high, requires extreme
  conditions
• Ways of getting round the difficulty
• Squeezing and heating buckyball whose carbons are
  already intermediate between sp2-3. In the case
  of C60, diamond anvil, 20 GPa instantaneous
  transformation to bulk crystalline diamond,
  highly efficient process, fast kinetics
• Using 1 CH4/H2 microwave discharges to create
  reactive atomic carbon whose valencys are
  more-or-less free to form sp3 diamond, in this
  case with atomic hydrogen this is the route for
  making diamond films

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CHIMIE DOUCE WITH DIAMOND SYNTHESIS
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APPLICATIONS OF SUPERHARD DIAMOND MATERIALS
-CRYSTAL, POWDER, FILM
? Superabrasives (200 t/year) ? Gemstones ? Heat
sinks for microelectronics ? Radiation windows ?
Speaker tweeters ? Mechanical bearings ? Surgical
knives ? Coatings - frying pans ? Semiconductors
- wide band gap
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HYDROTHERMAL SYNTHESIS AND CRYSTALLIZATION OF
ZEOLITES

• Typical zeolite synthesis
• NaAl(OH)4(aq) Na2SiO3(aq) NaOH(aq), 25oC,
  condensation-polymerization, Na(H2O)n template
  ?
• Naa(AlO2)b(SiO2)c.NaOH.H2O(gel) ? 25-175oC,
  hydrothermal crystallization of amorphous gel
• Nax(AlO2)x(SiO2)y.zH2O(crystals)

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HYDROTHERMAL SYNTHESIS AND CRYSTALLIZATION OF
ZEOLITES

• Nax(AlO2)x(SiO2)y.zH2O(crystals)
• Extraframework charge-balancing cations,
  templates, ion-exchangeable
• Framework Al(III)O4 and Si(IV)O4 tetrahedral
  primary building-blocks
• (AlO2)- and SiO2 stoichiometry for building
  blocks as bridging O
• Occluded water, removed by 25-500oC vacuum
  thermal dehydration
• Organic cationic templates, quaternary
  alkylammonium, structure-directing,
  space-filling, charge-balancing, discovery of new
  structures

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BUILDING-BLOCK APPROACH TO ZEOLITE SYNTHESIS,
STRUCTURES AND PROPERTIES

• Primary tetrahedral units, AlO2-, SiO2, PO2 and
  so forth, combined to give open-framework and
  framework charge, balanced by extraframework
  cations
• Existence of primary and secondary units in a
  synthesis mixture including
• 4R, 6R, 8R, D4R, D6R, 5-1, cubooctahedron

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ZEOLITE POST MODIFICATION FOR CONTROLLING
PROPERTIES OF ZEOLITES

• Tailoring channel, cage, window dimensions,
  adsorbents, gas separation, purification
• Tuning Br?nsted acidity, hydrocarbon cracking
• Ion exchange capacity, Lewis acid-base character,
  water softening, detergents
• Size-shape selective catalysis, separations,
  sensing -reactant, product, transition state
  selectivity

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ZEOLITE POST MODIFICATION FOR CONTROLLING
PROPERTIES OF ZEOLITES

• Host-guest inclusion, atoms, ions, molecules,
  radicals, organometallics, coordination
  compounds, clusters, polymers (conducting,
  insulating), nanoreaction chambers
• Advanced zeolite devices, electronic, optical,
  magnetic applications
• Entry to nanoscale materials, size tunable
  properties, QSEs

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SHAPE SELECTIVE CATALYSIS - REACTANT, PRODUCT,
TRANSITION STATE SELECTIVITY
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ALKYLATION OF TOLUENE BY METHANOL - SHAPE
SELECTIVE CATALYTIC PRODUCTION OF p-XYLENE
Used for manufacture of terephthalic acid for
production of polyester fibers
Snug fit can diffuse through channels
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Shape slective dehydration of normal and
iso-butanols to butenes over calcium ion
exchanged zeolite A and zeolite Y
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DIAMOND LATTICE OF 1.3 nm SPHERICAL SUPERCAGES IN
ZEOLITE Y
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SIMPLIFIED NOTATION FOR ZEOLITE ION EXCHANGE,
BR?NSTED ACID SITE FORMATION AND DEALUMINATION TO
HIGH SILICA ZEOLITES
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The changing face of zeolite science and
technology - pore and channel dimensions way
beyond 1 nm - periodic table of compositions
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LAYER-BY-LAYER GROWTH OF ZEOLITE THIN FILMS FOR
PERMSELECTIVE MEMBRANES
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ORGANICS ORGANIZING INORGANICS ABIOGENIC
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ARCHITECTURAL CONTROL - TEMPLATE DIRECTED
TRANSFORMATION OF BUILDING BLOCKS TO OPEN
FRAMEWORK SOLIDS
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LEARNING FROM NATURE - TEMPLATING INORGANICS WITH
SINGLE MOLECULES AND SUPRAMOLECULAR ASSEMBLIES