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1. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Phosphating for Adhesion of
Hydroxyapatite on Metallic
Substrates
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2. Materials Science & Engineering Dept.
Research Experience for Undergraduates
OutlineOutline
 Background Information
 Why coat metals with hydroxyapatite?
 Why phosphating?
 Specific Project Goals
 Procedures
 Results
 Conclusions
 What was learned?
 Where to go in the future?

3. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Background:Background:
 What is hydroxyapatite?
 Hydroxyapatite (Ca10(PO4)6(OH)2) is a ceramic with
composition similar to bone and teeth
 Develops strong bond with surrounding bone when
implanted
 Used in dental implants
 Great implant material except for poor mechanical
properties

4. Materials Science & Engineering Dept.
Research Experience for Undergraduates
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• www.indiandentalacademy.com
• Leader continuing dental education
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5. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Background:Background:
 Why coat hydroxyapatite on metal?
 Take advantage of the superior mechanical properties
of metals compared with ceramics (impact resistance)
 Create strong bond between bone and metallic implant
 Hip replacements could benefit
 Current procedure uses a cement to bond metal
shaft to bone
 Problem: Cement degrades over time and metal
shaft loosens
 Result: More surgery needed to replace cement

6. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Background:Background:
 Hip replacement

7. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Background:Background:
 Coating hydroxyapatite
 Plasma spraying
 Most widely used technique
 Differences in thermal expansion cause cracking
during cooling
 Bond is not strong
 Why phosphating?
 Create intermediate layer that:
 Creates stronger bond between hydroxyapatite
and metal
 Helps match thermal expansion coefficients

8. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Background:Background:
 Phosphating
 Traditional uses:

Base for paint

Corrosion protection

Only used on low alloy plain carbon steels
 How it works:

“Conversion coating”

Super-saturated phosphate solution

Simultaneously dissolves surface of metal and
deposits a metallic phosphate on surface

9. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Project Goals:Project Goals:
1. Synthesize hydroxyapatite without second
phases or impurities
2. Phosphate metallic substrates
3. Coat hydroxyapatite on phosphated substrates

10. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Procedure:Procedure:
 Hydroxyapatite Synthesis
 Chemical Precipitation Method

Calcium nitrate + ammonium hypophosphate +
ammonium hydroxide in excess water

Stir for 7 hours (minimum)

Centrifuge, filter & rinse with water

White gelatinous mass
 Test for second phases (Calcium phosphate) by XRD

11. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Hydroxyapatite Synthesis
XRD: Hydroxyapatite Powder Scan
(No Second Phases)
0
100
200
300
400
500
600
700
800
900
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
2θ
Counts/sec
No Second Phases

12. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Procedure:Procedure:
 Phosphating
 Choose metallic substrates

Plain carbon steel

Type 308 stainless steel

CCM (Cobalt Chromium Moly. medical alloy)
 Make-up phosphating solutions
Table I. Phosphating Solutions
Solution 1. (Zn) Solution 2. (Zn) Solution 3. (Mn)
Component Amount Used Component Amount Used Component Amount Used
Zinc Oxide 18.006g Zinc Oxide 8.20g Mn3(SO4)2 31.4g
Phosphoric Acid (85%) 30mL Phosphoric Acid (85%) 11mL Phosphoric Acid (85%) 43.8mL
Calcium Chloride 10.180g Calcium Chloride 12.022g NaNO3 .75g
Ferric Chloride .796g Ferric Chloride 1.05g CuO .159g
Ammonium Fluoride .780g Ammonium Fluoride 1.03g Distilled H2O To make 250mL
Distilled H2O To make 1L Distilled H2O To make 1L

13. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Procedure:Procedure:
 Phosphating Experiments
1. Prepare metallic substrates
2. Create ‘paper clip’ hanging system for suspending
metal samples in phosphating solution
3. Clean samples with acid wash and water rinses
4. Test effectiveness of each solution on plain carbon
steel
5. Try other alloys with most promising coatings
6. Try different times and temperatures to get most
effective phosphate coating on high alloy metals

14. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Phosphating
 Preliminary Trials

Solution 1 was ineffective

CCM alloy would not phosphate

Plain carbon steel used only in first trials
 Best Results

Zn (Solution 2)

Macro-etch surface

Phosphated at 75°C for 1hr

Mn (Solution 3)

Phosphated at 85°C for 20 min

15. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Zinc Phosphate: SEM photomicrographs

16. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Zinc Phosphate: XRD

17. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Manganese phosphate

18. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Procedure:Procedure:
 Hydroxyapatite coating
 Coated and uncoated samples used
 Thin layer of the gelatinous hydroxyapatite was
brushed on surface
 Dried in oven at 75°C to 85°C for 12 hours
(minimum)
 Sintered in hydrogen (reducing) atmosphere to
prevent oxidation
 Put in furnace at room temperature, allowed to heat
to 900°C, held for 1 hour, and furnace cooled

19. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Hydroxyapatite coating
 Uncoated metal showed virtually no adhesion
 Mn phosphate
 Small improvement in adhesion
 Sporadic amounts of adhesion
 Very small hydroxyapatite particles
 Zinc phosphate
 Improvement in adhesion
 Sporadic regions of adhesion
 Much greater particle size
 Best adhesion results

20. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Hydroxyapatite
Coatings
Manganese
Phosphate
Zinc
Phosphate

21. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Cross section of hydroxyapatite on Zn
phosphated stainless steel
Metal Substrate
Chrome Paint
(surface hardening
agent)
Hydroxyapatite
Zinc Phosphate

22. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Results:Results:
 Mn vs. Zn
 Adherence of hydroxyapatite

Zn was much better
 Adherence to substrate

Zn was good

Mn tended to flake off during handling
 Reproducibility

Mn formed more consistently than Zn
 Factors effecting reproducibility
 Temperature and time controlled
 Loss of phosphate ions
 ‘Paper clip’ hanging system

23. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Conclusion:Conclusion:
 What was learned?
 It is possible to phosphate high alloy steels by
evidence of the Zn and Mn phosphate coatings on
stainless steel
 An increase in adhesion between a metallic substrate
and hydroxyapatite was achieved by phosphating
 A large crystal zinc phosphate layer produced
sporadic but good regions of adherence

24. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Conclusion:Conclusion:
 Future Work?
 Quantitative data on adhesion is needed
 Thicker consistent layer of hydroxyapatite is needed
 Change process from drying on substrate to either

HIP (Hot Isostatic Pressing)
or

Plasma spraying
 Future phosphating work should include:

Easily reproducible coatings

Better understanding of coatings on high alloy
metals

25. Materials Science & Engineering Dept.
Research Experience for Undergraduates
Questions?Questions?