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  • Inorganic Materials Chemistry

    and Functional Materials

    Helmer Fjellvg and Anja Olafsen Sjstad

    Lectures at CUTN spring 2016

    Material Synthesis

  • 2

    Materials

    Natural materials (wood, bone, leather, cellulose, minerals, etc..)

    Metals

    Semiconductors

    Non-metallic inorganic materials (oxides, ceramics, glass)

    Organic Polymers

    Composite materials (polymer-, ceramic-, metal matrix)

  • Inorganic Materials Synthesis

    Bulk powders

    Nanoparticles

    Thin films - coatings

    Metals-alloys

    Surfaces

    Single crystals

  • Inorganic Materials Synthesis

    Solid State Reactions Nanoparticle synthesis

    Solids from the gas phase

  • Inorganic Materials Synthesis

    Solid State Reactions

  • Our text book has extended the definition

    to any reaction involving a solid:

    Solid/solid

    Solid/gas (Reaction, decomposition)

    Intercalation

    (Solid/liquid)

    Solid state reaction: a reaction between two or more solids.

    Solid State Reactions

  • 7

    - Direct reaction between two or more solids to form the final product. In

    principle no decomposition is involved.

    Ceramic Method Shake and Bake

    - Solids do not react with solids at room temperature even if

    thermodynamics is favorable; i.e. high temperatures needed.

    - Solid-solid reactions are simple to perform, starting materials

    are often readily available at low cost and reactions are clean;

    i.e. do not involve other elements (beneficial for the industry.)

    - Disadvantages include the need for high temperatures, the

    possibility of inhomogeneity, contamination from containers etc.

  • 8

    Ceramic Method Synthesis of YBCO

    ABO3

    YBCO = YBa2Cu3O7x

  • 9

    YBCO = YBa2Cu3O7x

    Oxidation step

    Ceramic Method Synthesis of YBCO

    - Direct reaction between Y2O3, BaO2, CuO

    (Reaction between three solid components)

    - Grind to obtain large surface area (see next slide)

    - Press into pellets (contact)

    - Heat in alumina boat, temperature profile:

  • 10

    Surface area:

    Surface area is increased by crushing/milling

    1 cm cube: surface area 6 cm2

    1 mm cubes: surface area 60 cm2

    10 m cubes: surface area 6000 cm2

    10 nm cubes: surface area 6000000 cm2 (600m2)

    Solid State Reactions General Aspects

  • 11

    - Other precursors may be used; e.g. BaCO3, which may be decomposed to

    fine grained BaO during the reaction.

    (oxalates, nitrates, cyanides etc. also work fine). Why such precursors?

    Ceramic Method Synthesis of YBCO

    Keywords:

    - Create more surface area of component by chemical grinding

    - Decomposition of the precursor must be performed in a controlled manner in

    order to avoid violent decomposition (i.e. choosing an appropriate

    temperature). Why?

    Keywords:

    - Splashing in furnace alternate composition, contamination of furnace

    - Other reasons why e.g. BaCO3 or Ba-oxalate is a better precursor than BaO

    in synthesis of YBCO by the ceramic method?

    Keywords:

    - BaO very basic oxide, i.e. react with CO2 and H2O air alter composition

  • 12

    - Will chloride salts be suited precursors? E.g. BaCl2?

    Ceramic Method Synthesis of YBCO

    Note:

    Many other ways of synthesizing YBCO:

    Precursor methods

    Sol/gel

    Flux

    Many melt-texturing methods

    including partially melting/fluxing

    - Regrinding Why?

    Keywords:

    - Chlorides not form volatile products i.e. reminds in the powder

    Keywords:

    - Reduce diffusion distances see next slide

  • 13

    Nucleation at the interface (depends on the

    degree of structural rearrangement involved)

    Formation of product layer, two reaction

    interfaces

    Diffusion/counter diffusion through the

    product layer - growth

    Longer diffusion paths, slower reaction rate.

    Simple case: lattice diffusion through a planar

    layer (rate law 1/x):

    Solid State Reactions General Aspects

    Ctktxxkdt

    dx )ln()(1

    A(s) + B(s) C(s)

    x = thickness of layer

    t = time

  • 14

    Solid State Reactions General Aspects

    How to increase rate of reaction, dx/dt?

    1. Increase area of contact between reactants

    2. Increase rate of nucleation

    3. Increase rate of diffusion ions through various phases

  • 15

    Solid State Reactions General Aspects

    How to increase rate of reaction, dx/dt?

    1. Increase area of contact between reactants

    (cross-reference to earlier slide)

    - Small particles by grinding, ball milling, freeze drying etc.

  • 16

    Solid State Reactions General Aspects

    How to increase rate of reaction, dx/dt?

    2. Increase rate of nucleation

    Nucleation may be facilitated by structural similarity between the reacting

    solids, or products.

    For compounds produced by solid state reaction, often a structural

    orientational relationship between the reactant, nuclei and product is seen.

    (In the reaction between MgO and Al2O3 to form MgAl2O4 (spinel), MgO

    and spinel have similar oxide ion arrangements. Spinel nuclei may then

    easily form at the MgO surfaces (see below)).

  • 17

    Epitactic: structural similarity restricted to the surface / interface

    between two crystals (common arrangement of ions at the interface)

    Topotactic: Structural similarity through the crystal. Reaction is

    controlled by the crystal structure of a reactant.

    Structural similarity through - Epitactic and Topotactic

    Reactions

    Solid State Reactions General Aspects

  • MgO and MgAl2O4 have O atoms in cubic close packing

    Al2O3 crystallizes in a completely different structure (Rhombohedral)

    Spinel nuclei form on the MgO surface - structural orientational relationship

    as well as similar interatomic distances (topotactic reaction)

    18

    Solid State Reactions General Aspects

    MgO

    Example: Production of the MgAl2O4 spinel from MgO and Al2O3

    Al2O3 MgAl2O4

  • 19

    Topotactic Reduction

    Solid State Reactions General Aspects

    O2

    LaNiO3.00

    LaNiO2.75

    LaNiO2.50 LaNiO2.00

    LaNiO3-x LaNiO3-x + O2(g)

    Zr + O2(g) ZrO2

    Sample

    Oxygen getter

    Zr, NbO,..

  • 20

    - High temperatures, as a rule of thumb, at 2/3 of the melting

    temperature (of one component) the diffusion is sufficient to achieve solid

    state reactions.

    Solid State Reactions General Aspects

    How to increase rate of reaction, dx/dt?

    - Reduction of diffusion distances by incorporating the cations in the

    same solid precursor or perform a co-precipitation reaction calls for

    more advanced methods

    3. Increase rate of diffusion ions through various phases

    - Diffusion is a thermally activated process, following an Arrhenius

    behavior

  • 21

    Nucleation limited reactions may be described by the Avrami-Erofeyev

    equation:

    x(t) = 1-exp(-ktn) {or x(t) = 1-exp(-(kt)n)}

    n is a real number, usually between 1 and 3 (n>4 is often interpreted as autocatalytic

    nucleation)

    For n > 1 the curve is sigmoidal

    Note: This is more empirical for most solid state reactions. It is difficult to talk about

    reaction order and activation energy for these reactions.

    Solid State Reactions General Aspects

    x = thickness of layer

    t = time

    Will not be discussed at lecture

  • 22

    BaTiO3 - electroceramic (thermistors, capacitors, optoelectronic devices, DRAMs)

    Formation of BaTiO3 by reacting BaCO3 and TiO2 is an example of a seemingly simple reaction is

    more complex than expected.

    BaO react with the surface of TiO2, forming nuclei and a surface layer of BaTiO3.

    Reaction between BaO and BaTiO3 to form Ba2TiO4. NB! This is a necessary phase for

    increasing migration of Ba2+ ions.

    Ba2+ ions from the Ba-rich phase migrate into the TiO2 phase and form BaTiO3.

    Solid State Reactions General Aspects

    Recipie Shake and bake

    BaCO3 is decomposed to reactive BaO: (Rock salt type structure, ccp of the oxide anions, Ba2+ in

    octahedral sites),

    TiO2 (Rutile type structure, hcp of oxide ions, Ti4+ in half of the octahedral sites)

    Synthesis of BaTiO3 nucleation of an intermediate phase

    At least three stages are involved in formation of BaTiO3 from BaO and TiO2.

    Will not be discussed at lecture

  • 23

    Reactions between two solids:

    Reaction rates depends on:

    Area of contact between the reacting solids, i.e. surface area and density

    The rate of nucleation

    Rates of diffusion of ions (and other species)

    Disadvantages, e.g.:

    Nucleation and diffusion related problems (high temperature)

    Formation of undesired phases (reaction paths) (e.g. Ba2TiO4)

    Homogeneous distribution, especially for dopants, is difficult

    Difficult to monitor the reaction directly, in-situ??

    Separation of phases after synthesis is difficult

    Reaction with containers/crucibles

    Volatility of one

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