426621 advanced ceramic processing ieng.sut.ac.th/ceramic/old/course_link/43.pdf · 426621 advanced...

Adv.Cera. Pro. I:synthesisAdv.Cera. Pro. I:synthesis 11

426621 Advanced 426621 Advanced Ceramic Processing ICeramic Processing I

Synthesis, preparation methods, properties, characterization of Synthesis, preparation methods, properties, characterization of starting materials and active powdersstarting materials and active powders

Lectured by Lectured by Asst. Prof. Dr. Asst. Prof. Dr. SiriratSirirat T. T. RattanachanRattanachanSchool of ceramic engineering, Institute of Engineering School of ceramic engineering, Institute of Engineering

SuranareeSuranaree University of Technology University of Technology


Lecture and assignmentLecture and assignment

� Lecture (5 h for 80% of this part examination): Intro., Techniques of powder preparation, Sol-gel and characterization of starting powders.

� Assignment (1 h for 20% of this part): presentation and report in the topic of new/novel method of powder preparations and their characterization methods.


ReferencesReferences

� D. Ganguli and M. Chatterjee, Ceramic powder preparation: a handbook, Kluwer Academic Publishers (1997)

� Yosry A. Attia, Sol-gel processing and applications, Plenum press (1994)

� Chaitanya K. Narula, Ceramic precursor technology and its applications, Marcel Dekker, Inc. (1995)

� Other related textbooks and more information in web sites, journals and research papers


What are ceramic powders made of ?What are ceramic powders made of ?


Ceramic Materials by powder technology and Ceramic Materials by powder technology and from molecular unitsfrom molecular units

Ref.: Bill J. et al. , PrecursorRef.: Bill J. et al. , Precursor--derived ceramicsderived ceramics


The competitive forces in agglomeration The competitive forces in agglomeration during synthesis during synthesis

� Electrostatic forces� Van der Waals forces� Liquid bridges: form during drying after synthesis from an aqueous solution

� Capillary forces� Solid bridges: 1. when liq. Bridges formed from salt solutions are dried to the stage of precipitation and

2. when the synthesized particles undergo calcination at elevated temperatures.

� Polymer bridges: steric stabilization


Electrical double layer Electrical double layer

� Stern layer: layer where counterions and oriented dipoles are adsorbed on the particle surface.

� Diffuse layer: layer which the opposite charge concentration is high, though marked by a sharp gradient.

� Zeta potential: the charge concentration (potential) which decreases to 0 at the outer surface of the double layer

� Isoelectric point (IEP): pH at which the zeta potential is 0

� Point of zero charge (PZC): pH at which the particle surface is neutral.


The electrical double layer near the charged surface The electrical double layer near the charged surface of a particle in a solution of a particle in a solution


Solid bridges between solSolid bridges between sol--gel derived silica spheresgel derived silica spheres

Agglomerated in submicron Agglomerated in submicron zirconiazirconia powders powders


Characteristics of an ideal powderCharacteristics of an ideal powder

�� Fine powder less than 1 Fine powder less than 1 µµmm�� Soft or no agglomerationSoft or no agglomeration�� Narrow particle size distributionNarrow particle size distribution�� Morphology: sphereMorphology: sphere�� Chemical composition controllable Chemical composition controllable �� Microstructure controllableMicrostructure controllable�� UniformityUniformity�� Free flowingFree flowing�� Fewer defects, dense particlesFewer defects, dense particles�� Less stressLess stress�� Reactivity, Reactivity, sinterabilitysinterability�� CrystallinityCrystallinity�� ReproducibilityReproducibility�� Process controllableProcess controllable


Major operational parameters to be considered for obtaining Major operational parameters to be considered for obtaining agglomerateagglomerate--free powders starting from solutions free powders starting from solutions


Why synthetic ceramic powders?Why synthetic ceramic powders?

� Natural minerals are generally impure.

� Synthetic processes can now produce particles with controlled shape and size, and narrow size distribution

� Composition of natural powders has variation.


Powder preparation methodsPowder preparation methods

� Solid-solid reaction: mixing and calcination, microwave, mechanochemical synthesis

� Solution techniques: precipitation and co-precipitation, hydrothermal, Sol-gel process, hydrolysis of metal-organics

� Solvent vaporization: simple evaporation, spray drying, spray pyrolysis, freeze drying

� Vapor-phase techniques: vaporization-condensation, vapor-vapor reaction, vapor-solid reaction, vapor-liquid reaction

� Precursor decomposition: salt decomposition, polymer pyrolysis


Powder Synthesis TechniquesPowder Synthesis Techniques�� CarbothermalCarbothermal Reduction Reduction �� VaporVapor--PhasePhase ReactionsReactions�� Thermal Decomposition Thermal Decomposition �� CCVDVD ProcessProcess�� Dc Arc Plasma Process Dc Arc Plasma Process �� RfRf PlasmaPlasma ProcessProcess�� Plasma Rapid Solidification Technology Plasma Rapid Solidification Technology �� ReactiveReactive ElectrodeElectrode SubmergedSubmerged ArcArc�� SolSol--Gel Techniques Gel Techniques �� AlkoxideAlkoxide RouteRoute�� Internal Internal GelationGelation�� PrecipitationPrecipitation and coand co--precipitationprecipitation�� Hydrothermal Process Hydrothermal Process �� EmulsionEmulsion ProcessProcess�� Laser Synthesis Laser Synthesis �� CombustionCombustion SynthesisSynthesis//ShsShs


Techniques of powder preparationTechniques of powder preparation

� Solid-solid reactions:� Mixing and calcination:

� Breaking and reconstruction of bonds at the contact region, leading to the nucleation of a product phase.

� Transport of matter to the contact region

1.1. Reactants (AO and BOReactants (AO and BO22) ) in contact at zero timein contact at zero time

2.2. Intermediate stage of Intermediate stage of reaction indicating reaction indicating partial formation of the partial formation of the product (ABOproduct (ABO33) )

3.3. Product after completion Product after completion of reactionof reaction


Solid Solid –– SolidSolid reactionsreactions

�� NiONiO (s) + Al(s) + Al22OO33 (s) (s) �� NiAlNiAl22OO44 (s)(s)�� NiONiO (s) + Sr(s) + Sr22OO33 (s) (s) �� NiCrNiCr22OO44 (s)(s)�� MgOMgO (s) + Fe(s) + Fe22OO33 (s) (s) �� MgFeMgFe22OO44 (s)(s)�� ZnOZnO (s) + Al(s) + Al22OO33 (s) (s) �� ZnAlZnAl22OO44 (s)(s)�� 4B(s) + C (s) 4B(s) + C (s) �� BB44C (s)C (s)�� 7C (s) + 2B7C (s) + 2B22OO33 ((l,gl,g) ) �� BB44C (s) + 6CO (s) C (s) + 6CO (s)

2 different mechanisms:2 different mechanisms:�� Vaporization of one solid reactantVaporization of one solid reactant�� Solid Solid interdiffusioninterdiffusion


Modern techniquesModern techniques

�� MechanochemicalMechanochemical synthesis: feeding the charge into synthesis: feeding the charge into a cylindrical vial containing the milling media in a cylindrical vial containing the milling media in required proportions. Vibratory, planetary or ordinary required proportions. Vibratory, planetary or ordinary ball mills are used with tungsten carbide, alumina etc, ball mills are used with tungsten carbide, alumina etc, and matching grinding media. The charge (powder) and matching grinding media. The charge (powder) undergoes 3undergoes 3--dimensional, largedimensional, large--amplitude vibrations amplitude vibrations commonly at a frequency of ~ 20 Hz for 24commonly at a frequency of ~ 20 Hz for 24--30 h.30 h.

�� Microwaves: coherent and polarized electromagnetic Microwaves: coherent and polarized electromagnetic waves with the frequency range 0.3waves with the frequency range 0.3--300 GHz (~ 1 m300 GHz (~ 1 m--1mm wave length). 1mm wave length). Ex.ultrafineEx.ultrafine mullitemullite, , superconductor, superconductor, SiCSiC


MechanochemicalMechanochemical SynthesisSynthesis of Ceramicsof Ceramics

�� Avoid the high temperature sinteringAvoid the high temperature sintering

�� High energy milling of a reactant High energy milling of a reactant powder chargepowder charge

�� Inducing chemical changes directly or Inducing chemical changes directly or activating chemical reaction during activating chemical reaction during subsequent lowsubsequent low--temperature heat temperature heat treatment.treatment.


Milling systems for Milling systems for mechanochemicalmechanochemical processingprocessing

�� SpexSpex 8000 mixer/mill8000 mixer/mill

�� Planetary millPlanetary mill

�� AttritorAttritor millmill


Powder contaminationPowder contamination

�� Relative hardness of the powder charge and Relative hardness of the powder charge and grinding mediagrinding media

�� The duration of milling The duration of milling �� The chemical nature of the powder chargeThe chemical nature of the powder charge

To avoid the contaminationTo avoid the contamination

•• use the same materials for the media and use the same materials for the media and containercontainer•• minimizing the milling durationminimizing the milling duration•• ensuring the hardnessensuring the hardness of the grinding media of the grinding media and container is greater than the powder.and container is greater than the powder.


Examples of ceramic powders synthesized Examples of ceramic powders synthesized by mechanical alloyingby mechanical alloying

2020--3030

100100

2222--3939

66

1515

1515

2020

2424

6060

3535

2424

4848

PbO+MgO+NbPbO+MgO+Nb22OO55

BaCOBaCO33+6Fe+6Fe22OO33

CaCa33(PO(PO44))22+3Ca(OH)+3Ca(OH)22NiO+FeNiO+Fe22OO33

MgO+ZrOMgO+ZrO22

AlAl22OO33+ZrO+ZrO22+Y+Y22OO33

Pb(MgPb(Mg1/31/3NbNb2/32/3)O)O33

BaFeBaFe1212OO1919

CaCa1010(PO(PO44))66(OH)(OH)22NiFeNiFe22OO44

MgOMgO--ZrOZrO22

AlAl22OO33--YY22OO33--ZrOZrO22

Crystallite Crystallite

size (nm)size (nm)

Milling time Milling time

(h)(h)

ReactantReactantProductProduct


Reaction millingReaction milling

Vial temperature as a Vial temperature as a function of time during function of time during milling milling of a combustive of a combustive

reaction systemreaction system

Variation in the critical Variation in the critical ignition temperature for ignition temperature for

(a) combustion, (a) combustion, (b) gradual reaction(b) gradual reaction


Solution techniquesSolution techniques

� Precipitation and Co-precipitation: � Concentration, pH, temperature, timeThe equilibrium saturation concentration, c* is given by:

c* = s0 + s1θ + s2θ2Where θ = the solution temp.

s0, s1,… = the coefficients of the components A supersaturated solution (the conc. Exceeds the saturation limit) tries to obey the equilibrium conditions by precipitating out the dissolved solute in the form of solid of the same composition. Crystalline salts obtained in this way are often thermally decomposed to convert them to oxides of ceramic interest.


Precipitation techniquesPrecipitation techniques

A A x+x+ + y H+ y H22O O ↔↔ A(OH)A(OH)yy ((xx--yy)+)+ + + yHyH++

General: General: zMzM x+x+ + yH+ yH22O = O = MMzz(OH)(OH)yy ((xzxz--yy)) + + yHyH++

The hydrolysis can occur at even very low pH if the The hydrolysis can occur at even very low pH if the charge/diameter ratio is high and hydrolysis product charge/diameter ratio is high and hydrolysis product can grow in size with the degree of hydrolysis .. can grow in size with the degree of hydrolysis .. ��condensationcondensation

H OHH OH

MM--OH + MOH + M--OH OH �� MM--OO--MM �� MM--OO--M + HM + H22OOFor For cationscations of large size and small charge, hydrolysis of large size and small charge, hydrolysis takes place at a relatively high pH. takes place at a relatively high pH. �� hydroxides or hydroxides or hydrated oxides.hydrated oxides.


Precipitation reactionPrecipitation reaction

� Aqueous salt solutions of metal nitrates, chlorides or sulphatesare used. For a multicationic solution, intermediate compound formation and precipitation must not occur by the exchange of the ions.

� The starting salts must be system-compatible to obtain a homogeneous solution.

� The precipitants commonly selected are NH4OH, NaOH, Na2CO3

or a suitable mixture.

� The sequence of addition is an important point.

� To avoid stepwise and local precipitation, the starting mixed solution is added in a stream into an excess of NH4OH solution, � “co-precipitation”

� The final pH of the solution is also important in the precipitation reaction.


AgglomerateAgglomerate--free powderfree powder

� Vigorous stirring of solution during and after precipitation

� Spraying or atomization of solutions on to the surface of a pool of ammonia solution under stirring, keeping pH at constant.

� Addition H2O2 to the salt solution.� forms peroxo complexes with the metal ions.

� Washing of the precipitate with organic solvents of lower surface tension than that of water (methanol, ethanol, acetone, isopropanol)�soft agglomerates after calcination

� Drying of the precipitate at high humidity (~95%) and temp (~90ºC) can produce agglomerates which are easily crushable.

� Fine crystalline growth by hydrothermal treatment of the amorphous precipitate.

� Freeze-drying of the precipitate


Hydrothermal synthesisHydrothermal synthesis

� Reaction takes place in an aqueous or aquo-organic environment, but at relatively high temperatures (80-400 ºC) and pressures (to 100 MPa or more).

� Five groups� Oxidation: e.g. Zr + H2O -> ZrO2 + H2

� Precipitation e.g. KF + MnCl2 -> KMnF3� Synthesis e.g. La2O3 + Fe2O3 + SrCl2 -> (La, Sr) FeO3

� Decomposition e.g. FeTiO3 -> Fe-oxide + TiO2

� Crystallization e.g. hydrous Zr-oxide -> ZrO2 (t- or m- phase)


Hydrothermal synthesis Hydrothermal synthesis

�� AutoclaveAutoclave

�� Reaction vesselReaction vessel


SolSol--gel processgel process

Sol: stable dispersion of colloidal particles (up to 1 µm) in an aqueous, aquo-organic or organic liquid medium.

By dispersing a batch of particles in a liquid medium

By causing nucleation and growth of particles of the desired size range within the solution : hydrolysis of alkoxides

By precipitating large particles and agglomerates in the liq.

gel: Semigel: Semi--rigid mass formed when the colloidal rigid mass formed when the colloidal particles are linked together by surface forces,particles are linked together by surface forces,gel: semigel: semi--rigid mass formed when the polymer rigid mass formed when the polymer

molecules interlink or crosslink.molecules interlink or crosslink.


C. J. Brinker and G. W. Scherer, Sol-Gel Science - The Physics and Chemistry of SolThe Physics and Chemistry of SolThe Physics and Chemistry of SolThe Physics and Chemistry of Sol----Gel Processing, New York, Academic Press, 1990.Gel Processing, New York, Academic Press, 1990.Gel Processing, New York, Academic Press, 1990.Gel Processing, New York, Academic Press, 1990.


ReactionsReactions

� The hydrolyzed products polymerize and condense to form relatively large poly-nuclear species which can be termed “particles”


Routes for the transformation of Routes for the transformation of precursors into ceramic materialsprecursors into ceramic materials

Molecular precursorMolecular precursor

Solid state Solid state thermolysisthermolysis

SSTSST

Chemical vapor Chemical vapor deposition deposition

CVDCVD

Chemical liquid Chemical liquid depositiondeposition

CLDCLD

PrecursorPrecursor--derived ceramicderived ceramic


Solid state Solid state thermolysisthermolysis


What are ceramic precursors?What are ceramic precursors?

�� Ceramic precursors: monomers or polymers containing Ceramic precursors: monomers or polymers containing all the elements to be present in the final materials all the elements to be present in the final materials and can be processed to obtain the final materials.and can be processed to obtain the final materials.

�� Precursors should not expensive.Precursors should not expensive.

�� Precursors should be soluble in common solvents.Precursors should be soluble in common solvents.

�� Precursors should be stable under ambient conditions.Precursors should be stable under ambient conditions.

�� Ceramic yield from the precursors should be high.Ceramic yield from the precursors should be high.

�� The evolved decomposition products should be nonThe evolved decomposition products should be non--toxic. toxic.


Precursor SynthesisPrecursor Synthesis

�� Ammonia method Ammonia method Anhydrous metal halides + anhydrous ammonia + anhydrous alcohol Anhydrous metal halides + anhydrous ammonia + anhydrous alcohol �� alkoxidealkoxide

CC66HH66, 5, 5ººCC

MClMCl44 + 4NH+ 4NH33 + 4 ROH + 4 ROH �� M(OR)M(OR)44 + 4NH+ 4NH44ClCl

M = transition metals EX. Ti, M = transition metals EX. Ti, ZrZr, , HfHf, Ta, , Ta, NbNb

R = organic groupR = organic group

ก��ก�� NHNH44Cl Cl ��ก�ก��ก�ก� � �� metal metal alkoxidealkoxide ��ก�� ก�� ammonia chloride ammonia chloride �� Amide Amide �� nitrilenitrile ��ก��ก��


OrganosiliconOrganosilicon polymerspolymers

SiliconSilicon--containing containing polymers for the polymers for the preparation of silicon preparation of silicon nitridenitride-- and carbideand carbide--based ceramic.based ceramic.


PolysilazanesPolysilazanesTernary SiTernary Si--CC--N ceramics: N ceramics: organochlorosilanesorganochlorosilanes with ammonia with ammonia

Synthesis of boronSynthesis of boron--containing containing polysilazanespolysilazanes by the monomer and by the monomer and polymer route:polymer route:SiSi--BB--CC--N ceramics N ceramics


PolyPoly--silysily--carbocarbo--didi--imidesimidesSiSi--,C,C--, and N, and N--containing precursors can be obtained by saltcontaining precursors can be obtained by salt--free reactions of free reactions of chlorosilaneschlorosilanes with with bis(trimethylsilyl)carbodiimidebis(trimethylsilyl)carbodiimide..

BoronBoron--containing containing polysilylcarbodiimidespolysilylcarbodiimides can be synthesized by the reaction can be synthesized by the reaction of of bis(trimethylsilyl)carbodiimidebis(trimethylsilyl)carbodiimide with with hydroboratedhydroborated vinylchlorosilanesvinylchlorosilanes


CeramizationCeramization of of preceramicpreceramic polymerspolymers

Transformation of polyTransformation of poly--hydridomethylsilazaneshydridomethylsilazanes into into

amorphous silicon amorphous silicon carbonitridecarbonitride

450450--750750°°CC


Bulk gels can be used for powder preparation in different ways:Bulk gels can be used for powder preparation in different ways:

�� The gel is dried under high vacuum, followed by grinding and sieving to obtain the precursor gel of powder. Calcination of the gel powder at the desired temperature produced a crystalline oxide powder.

� The gelled mass is dried and calcined at the required temperature for crystalline. -> milling to fine powders.

� The wet gel, after drying at 100°C, is milled in alcohol, dried and re-milled to obtain a gel powder. The amorphous gel powder is calcined at the desired temperature to obtain a crystalline oxide powder.


Solvent vaporizationSolvent vaporization

� Simple evaporation: agglomerate

� Spray drying

� Spray pyrolysis

� Freeze drying


Spray dryingSpray drying

� Preparation of the feedstock

� Atomization of the feedstock: rotary, pressure nozzle, pneumatic (or two-fluid)

� Drying of the droplets into solid agglomerates

� Calcination and if necessary, sintering of the products


Hollow particlesHollow particles

� Formation of a film around the droplet, resulting in a reduced surface evaporation rate. The internal liquid vaporizes and expands, causing a ballooning effect.

� Creation of voids in droplets of salt solutions due to the relatively high rate of surface evaporation and salt crystallization.

� Movement of particles from the center to the surface of slurry droplets, causing internal hollowness.

� Presence of air bubbles in the fluid feedstock


Spray Spray pyrolysispyrolysis

� Atomization of the liquid-rich starting material

� Evaporation of the liquid component, solute condensation within the droplet, and drying of the droplets converted into spherical solid particles composed of the solute.

� Pyrolysis (or thermolysis, thermal decomposition) and sintering of the dried precursor spheres.


Freeze dryingFreeze drying� Spraying into a chamber kept below the freezing point of the solvent,

� Freezing of the solvent so as to force the solute to precipitate out,

� Sublimation of the frozen solvent under vacuum.

� Ex. Aluminium sulphate-> Al2O3, magnesium salphate -> MgO


Freeze drying Freeze drying

Freeze drying (blue arrow) brings the system around the triple point, avoiding the direct liquid-gas transition seen in ordinary drying (green arrow).

http://http://en.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_drying


Freezing processFreezing process

•• FreezeFreeze--drying in flask and rotating drying in flask and rotating the flask in a bath. (mechanical the flask in a bath. (mechanical refrigeration, dry ice and methanol or refrigeration, dry ice and methanol or liq. Nitrogen) liq. Nitrogen) •• freeze the material at a temperature freeze the material at a temperature below the eutectic point ( the lowest below the eutectic point ( the lowest temperature where the solid and liquid temperature where the solid and liquid phase can coexist.phase can coexist.•• Amorphous (glassy) materials have a Amorphous (glassy) materials have a critical temperature. At below critical temperature. At below TTcc, , material must be maintained to prevent material must be maintained to prevent meltmelt--back or collapse during drying. back or collapse during drying.

http://http://http://http://http://http://http://http://en.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_dryingen.wikipedia.org/wiki/Freeze_drying


VaporVapor--phase techniquesphase techniques

� Vaporization-condensation

� Vapor-vapor reaction:

3SiH4(g) + 4NH3 (g) -> Si3N4(s) + 12H2 (g)

2SiH4 (g) + C2H4 (g) -> 2SiC (s) + 6H2 (g)

SiH4 (s) + CH4 (g) -> SiC + 4H2 (g)


VaporVapor--liquid reactionliquid reaction

� Ex: n-C6H14, 0ºC

SiCl4 (l) + 6NH3 (g) -> Si(NH2) + 4NH4Cl

Si(NH2) -> 1200ºC -> α- Si3N4


VaporVapor--solid reactionsolid reaction� Direct synthesis, i.e., nitridation or carbide formation from metal powders: widely used for the production of Si3N4 and AlN.

3Si + 2N2 -> Si3N4

Al + N -> AlN

� Carbothermal reduction of oxide powders for the formation of nitrides or carbides:

3SiO2 + 6C + 2N2 -> Si3N4 + 6 CO

Al2O3 + 3C + N2 -> 2AlN + 3CO

SiO2 + 3C -> SiC + 2CO

Drawbacks: 1. excess carbon required, large quantities of CO and CO2 form.

2. limited control on the particle shape and impurity content.


SpraySpray--dried dried hydroxyapatitehydroxyapatite powder powder ((SivakumarSivakumar, 1995) a) as, 1995) a) as--sprayspray--dried, dried, b) sintered at 1200b) sintered at 1200ººC/2 h C/2 h


The synthesis of The synthesis of hydroxyapatitehydroxyapatite, , CaCa1010(PO(PO44))66(OH)(OH)22

� Ca(NO3)2 and (NH4)2HPO4 or (NH4)H2PO4, temp. 80-90°C so as to obtain a precipitation.

� Spray pyrolysis: Ca(NO3)2-(NH4)2HPO4 and Ca(NO3)2-H3PO4 or Ca(CH3COO)2-(NH4)2HPO4� at 600ºC

� Freeze drying: Ca(CH3COO)2.H2O and (C2H5O)3PO with an excess of P (Hattori et.al,1987). Rapid freezing in liquid nitrogen followed by calcination at 400-1000ºC for 2-6 h. showed that the process could yield HA, but variable quantities of CaO and CaCO3 generally co-existed.

� A mechanochemical method (Toriyama et.al,1996): Brusite and anhydrous CaCO3, milling time varied from 3 to 48 h.. Under limited conditions, poorly crystallized HA was obtained, which turned to well-crystallized HA and β-TCP after calcination.

426621 advanced ceramic processing ieng.sut.ac.th/ceramic/old/course_link/43.pdf · 426621 advanced...

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