Electrolyte Thermodynamics:A Crystallization Tool for Engineering Materials

From the Nanoscale to the Microscale

Richard E. Riman and Eugene ZlotnikovDepartment of Materials Engineering

Rutgers, The State University of New Jersey607 Taylor Road

Piscataway, NJ 08854-8065

Sponsors

• Office of Naval Research• Defense Advanced Projects Research

Agency• National Science Foundation• New Jersey Commission on Science and

Technology• PPG Industries, Inc.• Ceramare Corporation

Outline

• Hydrothermal-derived ceramic materials• Rational approach to low temperature

hydrothermal synthesis• Thermochemistry-engineering the reaction

medium for ceramic materials synthesis

Current Research Areas

• Processing Science– Hydrothermal/Solvothermal Crystallization – Mixing– Assembly

• Functional Areas– Biomedical(tissue engineering)– Electronic (piezoelectric, dielectric) – Optical (amplifiers, lasers, taggants,

chameleon optics)– Structural (corrosion, ferroelastics)

Hydrothermal Synthesis• Chemical precursors are heterogeneous slurries, gel and or

homogeneous solutions, acid or base mineralizer required

• Aqueous, mixed solvent or solvothermal solution medium

• Focus is on mild reaction conditions (T<300oC, P<250 atm)

• Anhydrous oxides form in a single process step

• P-T-H2O interaction => unique phase equilibria

• Solution-mediated reaction => labile reaction kinetics relative to solid state reaction

• Controlled nucleation, growth and aging => controlled size and morphology

• Inexpensive processes

Hydrothermal Reactor

Thickness

(m)

Density

(kg/m3)

Heat

Conductivity5

Wt/(m deg)

Heat

Capacity5

(kJ /(kg deg)

Mass

(kg)

Outer

Surface

(m2)

Stainless steel 304 0.008 7900 0.502 3.27 0.04

Teflon 0.011 2120

16.0

0.26 0.350 0.44 0.02

Parr 4748 Autoclave, 125 ml, < 240°C

Batch Hydrothermal Crystallizers

Parr Instrument Company: Model 4530Hastalloy C276 alloy

Temperatures < 350˚CStirring Speed < 1700 rpm

Parr Instrument Company: Model 4530Hastalloy C276 alloy

Temperatures < 350˚CStirring Speed < 1700 rpm

Rational Approach to Low Temperature Hydrothermal Synthesis

• Compute thermodynamic equilibria as a function of the processing variables for phase of interest

• Generate equilibrium diagrams to map processing variable space for phase of interest

• Design hydrothermal experiments to test and validate computed diagrams

• Utilize processing variable space maps to explore opportunities for control of reaction and crystallization kinetics

Equilibria of Ca(OH)2-H3PO4-NH4OH-HNO3-H2O System1. H2O = H+1 + OH-1

2. HP2O7-3 = H+1 + P2O7

-4

3. H2P2O7-2 = H+1 + HP2O7

-3

4. H3P2O7-1 = H+1 + H2P2O7

-2

5. H4P2O7 (aq) = H+1 + H3P2O7-1

6. HPO4-2 = H+1 + PO4

-3

7. H2PO4-1 = H+1 + HPO4

-2

8. 2 H2PO4-1 = (H2PO4)2

-2

9. H3PO4 (aq) = H+1 + H2PO4-1

10. HNO3 (aq) = H+1 + NO3-1

11. NH3 (aq) + H2O = NH4+1 + OH-1

12. NH4NO3 (aq) = NH4+1 + NO3

-1

13. CaH2PO4+1 = Ca+2 + H2PO4

-1

14. CaNO3+1 = Ca+2 + NO3

-1

15. CaOH+1 = Ca+2 + OH-1

16. CaPO4-1 = Ca+2 + PO4

-3

17. CaHPO4 (aq) = Ca+2 + HPO4-2

18. Ca(OH)2 (aq) = Ca+2 + 2OH-1

19. Ca(NO3)2 (aq) = Ca+2 + 2NO3-1

20. Ca5(OH)(PO4)3 s = 5Ca+2 + OH-1+ 3PO4-3

21. CaHPO4 (s) = Ca+2 + HPO4-2

22. CaHPO4.2•H2O (s) = Ca+2 + HPO4-2+ 2H2O

23. Ca3(PO4)2 (s) = 3Ca+2 + 2PO4-3

24. Ca(H2PO4)2 • H2O (s) = Ca+2 + 2H2PO4-1 + H2O

25. Ca(H2PO4)2 (s) = Ca+2 + 2H2PO4-1

26. Ca4O(PO4)2 (s) + H2O = 4Ca+2 + 2OH-1 + 2PO4-3

27. Ca10O(PO4)6 (s) + H2O = 10Ca+2 + 2OH-1 + 6PO4-3

28. Ca4H(PO4)3 (s) = 4Ca+2 + HPO4-2 + 2PO4

-3

29. Ca8H2(PO4)6.5 • H2O (s) = 8Ca+2 + 2HPO4-2 + 4PO4

-3 + 5H2O

30. Ca(NO3)2.3 H2O (s) = Ca+2 + 2NO3-1 + 3H2O

31. Ca(NO3)2.4 H2O (s) = Ca+2 + 2NO3-1 + 4H2O

32. Ca(NO3)2 (s) = Ca+2 + 2NO3-1

33. Ca(OH)2 (s) = Ca+2 + 2OH-1

34. (NH4)2HPO4.2H2O (s) = 2NH4+1 + HPO4

-2+ 2H2O

35. (NH4)2HPO4 (s) = 2NH4+1 + HPO4

-2

36. (NH4)3PO4.3 • 3H2O (s) = 3NH4+1 + PO4

-3+ 3H2O

37. (NH4)H2PO4 (s) = NH4+1 + H2PO4

-1

38. (NH4)NO3 (s) = NH4+1 + NO3

-1

39. H2O (v) = H2O

40. NH3 (v) = NH3 (aq)

41. HNO3 (v) = HNO3 (aq)

Calculated Solubility of Various Calcium Phosphates

Stability Field Diagrams for HA

Ca(OH)2 has Limited Retrograde Solubility

Thermochemical Validation: Alkaline Earth Titanate Perovskites

Minimum Mineralizer Concentrations

Increasing Pb/Ti Reduces PT Processing Space

Use of EDTA to Eliminate Phase Heterogeneities

No EDTA EDTA

Control of Phase Space Using EDTA

No EDTA

EDTA

Acmite Pourbaix DiagramNaOH + 2SiO2 + Fe + H2O = NaFeSi2O6 + (3/2)H2 (g)

Na2SiO3 Concentration Effects

0.0E+00

4.0E-06

8.0E-06

1.2E-05

1.6E-05

2.0E-05

20 40 60 80 100 120

Temperature [°C]

Con

cent

ratio

n Fe

(OH

) 4- [m]

0 mol/l

1 mol/l

2 mol/l

Solu

ble

Spec

ies

X

Reaction Rate Maximization

0

1

2

3

4

5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Na2SiO 3 [m]

T2, C2

T1, C1

[X]*

[Sili

cate

] 10-5

*m2

Na2SiO3 Concentration Increases Acmite Thickness

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 0.2 0.4 0.6

Na2SiO3 [mole/kg]

R

Fe

Acmite

IIIR

)()(

110

310221 +=

Temperature 210°C, Fe(NO3)30.124 mole/kg, 11.5 h

Thermochemistry Breakthrough:Instant Hydrothermal

• Uses same precursors as conventional solid state reaction

• Reactions in open vessels

• Phase pure powder• Controlled size

distribution

30 s BaTiO3

Setting Nucleation Targets

Effect of Ethanol on pH

pH vs. EtOH added to 28.8% w solution of NH4OH

11.1

11.4

11.7

12

12.3

0 4 8 12 16

[EtOH] m

pH

Non-ideality of Ethanol-Water-Ammonia Mixtures

K1

(1) NH3 +H2O ↔ NH4+ + OH-

K2

(2) NH3 + nC2H5OH ↔ [NH3•(C2H5OH)n]

(3) [NH3]0 =[NH3] + [NH4+] + [NH3•(C2H5OH)n]

(4) {[NH3]0 – [OH-] – [OH-]2/K1} / [OH-]2/K1 = K2 (C2H5OH)n

Ethanol-Ammonia Interaction Parameters

Ln-Ln Linearization for Water-Ethyl Alcohol -NH4OH

R2 = 0.97142

2.2

2.4

2.6

0 2 4Ln ([Ethyl Alcohol])

Ln(F

([OH

], [N

H4O

H]in

itial

)

n=0.13

K2=2.14

HA coated Titanium

In-Situ HA Coating/Synthesis

Non-Isothermal Phosphate Kinetcs

0

0.2

0.4

0.6

0.8

1

0 50 100 150

Time [min]

Con

vers

ion

40

80

120

160

200

Tem

pera

ture

°C

ConversionTemperature

HA & Ca-titanate: temperature scan

HA & Ca-Titanate: phosphate slow supply

Summary• Design of materials

– Phase pure materials– Optimization of formulations

• Design of processes– Optimization of processes– Process insight– Assessment of parametric sensitivity– Process monitoring

• Design of experiments– Feasible ranges of processing variables– Phase diagrams validation– “Go-Not Go” study

Conclusion

• Thermochemical modeling is an effective design tool for engineering phase assemblage, precursor and reaction kinetics

Questions?