The Effect of Structure on the Mechanical Properties of Phosphate Glass Fibers

Adam J. Lang, Richard K. Brow

Ceramic Engineering DepartmentUniversity of Missouri-Rolla, Rolla, Missouri 65409

GOMD Fall 2002 Student Poster

Introduction

Phosphate glasses are used in a growing number of applications and as such it becomes increasingly important to understand their physical behavior. This work is focused on finding the relationships between the strength of phosphate glasses and their composition/structure. The glasses used in this study vary from Fe-phosphates developed for nuclear waste encapsulation to commercial laser glasses. A two-point bend technique is used to measure the strain at failure. Stress is calculated using an acoustically determined elastic modulus. Phosphate glasses are weaker than silicate glasses and exhibit an anomalous dynamic fatigue behavior.

Glass Compositions

• “Pristine fibers” (80 – 200 micron diameters) drawn for strength measurements.• Fibers ~ 1 to 2 mm diameter (10 - 15 cm long) are used for elastic modulus measurements.

* J.H. Campbell et al., J. Non-Cryst. Solids 263&264 (2000) 318.

569----8.5----19.57------E-glass

------6515--------20----ZAP-A15

------5010--------40----ZAP-Z40

------6010--30----------BAP

100----------------------Silica

60------------20------2060-20-20

------63--37------------F-40

------50----------50----ZP-Z50

------6010--------30----ZAP

------6010------30------MAP

------6010----30--------CAP

------6010----------30--KAP

------6010------------30NAP

----0 - 255 - 608-12--10-15------13 - 17--LHG-8*

----0 - 258 - 626-10------5-10--20 - 25--LG-770*

SiO2B2O3Nd2O3P2O5Al2O3Fe2O3BaOCaOMgOZnOK2ONa2O

Composition in Mole %Glass

Measuring Strain and Elastic Modulus

• Fiber is continuously up-drawn from a small box furnace onto a wheel with open sides. The fiber are supported by threaded rods held in place by radial spokes at either end of the wheel. This setup produces pristine sections of fiber roughly 3.5” long.

•A computer controlled two-point bend* apparatus is used to fracture the fibers. The equation used to relate gap at fracture to strain is:

???

???

??

dDd

f 198.1?

• An acoustic wave setup was used to determine the elastic modulus of the glasses. Transverse wave velocity (VT), longitudinal wave velocity (VL) and density (?) are measured for the calculation of elastic modulus (E):

v = (1-2(VT/VL)2) / (2-2(VT/VL)2)

E = VL2 × ? × ((1+v)(1-2v))/(1-v)

v = Poisson’s ratio.

? = Density.

*M.J. Matthewson, C.R. Kurkjian, S.T. Gulati, J. Am. Ceram. Soc., 69, 815 (1986).

Fiber Strength Depends on Composition

• Unusual strength distributions in liquid nitrogen fractures.

• Fiber strength depends on composition (higher strength for greater field strength modifiers).

Liquid Nitrogen Breaks -- 4000 ?m/s

Failure Stress (GPa)

1.4 2.4 3.4 4.4 5.4

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3

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40

60

8090

99

Failure Stress (ksi)

300 500 700

F-40m = 12? Avg = 4.60 GPa

LG-770m = 7? Avg = 2.42 GPa

LHG-8m = 20? Avg???2.40 GPa

NAPm = 4.7? Avg = 2.13 GPa

KAPm = 10? Avg = 1.65 GPa

BAPm = 10? Avg = 3.41 GPa

MAPm = 12? Avg = 3.97 GPa

CAPm = 17? Avg = 4.06 GPa

ZAPm = 33? Avg = 4.90 GPa

Room Temperature Breaks -- 4000 ?m/s

Failure Stress (GPa)

1 1.5 2 2.5 3

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Failure Stress (ksi)

200 300 400

LG-770RH ~ 49%m = 30?Avg = 1.38 GPa

LHG-8RH ~ 30%m = 60? Avg???1.55 GPa

F-40RH ~ 46%m =75? Avg = 2.82 GPa

NAPRH ~ 52%m = 72? Avg = 1.59 GPa

KAPRH ~ 48%m = 17? Avg = 1.11 GPa

BAPRH ~ 44%m = 42? Avg = 1.59 GPa

MAPRH ~ 44%m = 105?Avg = 1.94 GPa

ZAPRH ~ 30%m =19?Avg = 1.86 GPa

CAPRH ~ 30%m = 16? Avg = 1.95 GPa

Modifier Field Strength

•Failure strength and Elastic modulus increase with modifier field strength.

•Fe field strength is weighted average of 18% Fe2+ and 82% Fe3+

Modifier Feild Strength Vs Glass Strength30 RO - 10 Al2O3 - 60 P2O5 (R = K2, Na2, Ba, Ca, Mg, Zn)

Field Strength (Z/r2)

0 1 2 3 4 5

GP

a

0

2

4

6

30

40

50

60

70

80

K Na Ba Ca MgFe

Zn

Liquid Nitrogen ? 50

Room Temperature (4000 ?m/s) ? 50

Elastic Modulus (E)

LHG-8 -- E = 43.5 GPa

Failure Stress (GPa)1.4 1.9 2.4

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Failure Stress (ksi)

300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300

RH ~ 30%4000 ? m/sm = 60? Avg?? ?1.55 GPa

RH ~ 30%1000 ? m/sm = 51? Avg?? ?1.51 GPa

LN 1000 ? m/sm = 20? Avg?? ?2.40 GPa

RH ~ 30%500 ? m/sm = 59? Avg?? ?1.51 GPa

RH ~ 30%100 ? m/sm = 74? Avg?? ?1.48 GPa

LG-770 -- E = 39.5 GPa

Failure Stress (GPa)

0.9 1.4 1.9 2.4 2.9

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Failure Stress (ksi)

200 300 400

RH ~ 50%4000 ? m/secm = 30? Avg = 1.38 GPa

RH ~ 50%1000 ? m/secm = 46? Avg = 1.37 GPa LN

m = 7? Avg = 2.42 GPa

RH ~ 50%500 ? m/secm = 14? Avg = 1.28 GPa

RH ~ 50%100 ? m/secm = 40? Avg = 1.35 GPa

Phosphate Laser Glasses

• Similar strengths at room temperature and in liquid nitrogen

• Weaker than silicate glasses

• Fractures in air show limited fatigue effects

LHG-8 -- Liquid Ni t rogen, 30%, and 70% RH Fractures

Fai lure Stress (GPa)

0.9 1.4 1.9 2.4

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Failure Stress (ksi)

200 300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300300

RH ~ 30%4000 ? m/sm = 60? Avg?? ?1.55 GPa

RH ~ 30%1000 ? m/sm = 51? Avg?? ?1.51 GPa

LN 4000 ? m/sm = 20? Avg?? ?2.40 GPa

RH ~ 30%500 ? m/sm = 5 9? Avg?? ?1.51 GPa

RH ~ 30%100 ? m/sm = 74? Avg?? ?1.48 GPa

RH ~ 70%4000 ? m/sm = 31? Avg?? ?1.48 GPa

RH ~ 70%1000 ? m/sm = 21? Avg?? ?1.40 GPa

RH ~ 70%500 ? m/sm = 14? Avg?? ?1.37 GPa

RH ~ 70%100 ? m/sm = 10? Avg?? ?1.35 GPa

Fatigue Effects

• Weaker in higher humidity air

•Little dependence on “face plate velocity” (~ strain rate)

Dynamic Fatigue Dependence

*W. J. Duncan et al., in “Strength of Inorganic Glass,” ed. C.R. Kurkjian, Plenum Press, NY, (1986).

• The fracture strength dependence on face plate velocity provides the fatigue parameter, n from n = (dlog ? 50/dlog(?/s))-1.*

• Phosphate glasses exhibit little strength dependence on strain rate.

Strain Rate Dependence of Phosphates

LOG(face velocity(? m/s))

0 1 2 3 4 5 6 7 8 9 10

LOG

(Fai

lure

Stre

ngth

)

0.0

0.1

0.2

0.3

0.4

0.5F-40 (46% RH) n=194

CAP (30% RH) n=49MAP (44% RH) n=38

LHG-8 (27% RH) n=84

BAP (44% RH) n=35

NAP (52% RH) n=31

LG-770 (49% RH) n=116

KAP (48% RH) n=-170

ZAP (30% RH) n=141

60-20-20 (50% RH) n=19

Some Phosphate Glasses Are Relatively Strong

•Zn-aluminophosphate fibers have the highest strength of any phosphate glasses to date.

•Fe-phosphate glasses have aqueous durability's greater than common window glass.

LN -- ZAPm = 33? Avg?= 4.9 GPa

LN -- ZAP-A15m = 17? Avg = 6.7 GPa

LN -- F-40m = 12? Avg = 4.6 GPa

LN -- E-glassm = 176? Avg = 10.0 GPa

LN -- Silicam = 103? Avg = 12.9 GPa

Failure Stress (GPa)3 4 5 6 7 8 9 10 11 12 13 14

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Failure Stress (ksi)

500 700 900 1100 1300 1900

LN -- 60-20-20m = 24? Avg = 6.24 GPa

Zinc Aluminophosphate Comparison

• Adding Alumina to Zinc Phosphates increases ? .

Failure Stress (GPa)0.8 1.8 2.8 3.8 4.8 5.8 6.8 7.8

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Failure Stress (ksi)200 400 600 800 1000

ZAP-Z304000 m? /sm = 19? Avg = 1.86 GPa

ZAP-Z40LNm = 13? Avg = 4.08 GPa

ZAP-Z30LNm = 33? Avg = 4.91 GPa

ZAP-Z404000 ? m/sm = 34? Avg = 1.64 GPa

ZAP-A15LNm = 17? Avg = 6.70 GPa

ZAP-A154000 m? /sm = 8? Avg = 3.09 GPa

ZP-Z504000 m? /sm = 13? Avg = 1.16 GPa

ZP-Z50LNm = 9? Avg = 3.89 GPa

Alumina Increases Zinc-Metaphosphate Strength

Mol % Al2O3 Vs Glass Strength(50-2X) ZnO - (X) Al2O3 - (50+X) P2O5 where X= 0, 10, 15

Mol % Al2O3

-5 0 5 10 15 20

GP

a

0

2

4

6

8

10

30

40

50

60

70 Liquid Nitrogen ? Avg

Room Temperature (4000 ? m/s) ? Avg

Elastic Modulus (E)

• Strength of phosphate gasses increases with the field strength of modifying ions.

• Phosphate glasses show limited strength dependence (high dynamicfatigue parameters) on strain rate.

• Phosphate glasses exhibit a decrease in strength with increasinghumidity. How is this effect related to the limited dynamic fatigue response.

• Why is there always more scatter in liquid nitrogen strengths than room temperature strengths for phosphate glasses?

Acknowledgements• DOE/OIT and Mo-Sci, Inc. (Rolla, MO) for supporting this project.• Thanks to Chuck Kurkjian for his assistance and expertise.• Special thanks to Nate, Lucas, and Trent Lower for the design and

construction of the fiber puller and 2-point bender.

Conclusions and Questions