Study on the Corrosion of Negative Straps in VRLA Batteries

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Study on the Corrosion of Negative Straps in VRLA
Batteries
C. Z. Qiu a, A. J. Li a, L. P. Tang a,C. L.
Dou a, W. Zhang b, D. J. Zhang b , S.Chen
b , G. M. Xiao b, S.G.Pengb,W.W.Weib,H.Wan
gb.H. Y. Chen a a.School of Chemistry and
Environment, South China Normal University,
Guangzhou,Guangdong 510006,Chinab.Zhuzhou
Smelter Group Co,Ltd,Zhuzhou,Hunan 412004,China)
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Contents
Introduction
1
2
Experimental
3
Results and discussion
4
Conclusion
3
1. Introduction

• There are many reports about improving the
  properties of the alloys as the positive grids in
  lead-acid batteries. However, studies on the
  negative straps in lead-acid batteries are
  scarce. In VRLA batteries, because the straps are
  not submerged in sulfuric acid, they cannot be
  cathodically protected. Without the cathodic
  protection, PbSO4 formed in the oxygen
  recombination cycle was not converted back to
  lead, and sulfation corrosion proceeds to
  ultimately cause the strap fracture.

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1. Introduction

• Two main types of negative strap alloys
  were used in lead-acid batteries one is the
  lead-antimony alloys, the other was the leadtin
  alloys. But antimony is poisonous, it is not
  suggested that lead-antimony be used as negative
  strap alloy. Therefore, the leadtin alloy is
  relatively better. There are literature data for
  the application of Se as an alloying additive to
  Pb-Sn alloys. But most studies were on the
  alloyselecelectrochemical behavior ,but little
  was about the alloys metallographic
  structure.The microstructures of the alloys and
  the structure of the corrosion layers play an
  important role in their properties. So our aim is
  to further compare the metallographic structure
  of Pb-Sn and Pb-Sn-Se alloys and simulate the
  corrosion atmosphere of the negative straps to
  compare their corrosion properties.

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2. Experimental

• The metallographic samples in forms of rod
  alloys were mechanically polished by 1000 and
  2000 SiC emery papers. Then the polished section
  was chemically polished using a 11 (by volume)
  acetic acid/hydrogen peroxide solution, and
  etched with a solution containing 9 g of
  ammoniummolybdate, and 15 g of citric acid in 90
  g of distilled water. The structure of the alloys
  was observed using a Nikon LV-UEPT polarizing
  microscope.
• The metal phases were identified by X-ray
  diffraction, XRD analysis over a scan range of
  1090at a rate of 0.01per 0.4 s.

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2. Experimental

• Corrosion testA scheme of the
  experimental setup is presented in Fig. 1.
  Investigated samples (the positive electrodes
  were pure lead, the negative electrodes were
  investigated samples) were 7.0 cm long, 1 cm
  wide, and 0.15 cm thick. Absorbing glass mats
  (AGM) were placed in the glasses and soaked in
  4.5 M H2SO4 solution.1 cm of the length of the
  samples were inserted into the AGM and 2-6cm were
  out of the solution. The top of the glasses were
  covered with films. All of the glasses were
  placed in the same constant temperature water
  bath which was heated at 60 C, and the samples
  were in series electrified with constant current
  0.06 A for a month.

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Fig. 1. A scheme of the
experimental setup.
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3. Results and discussion

• 3.1 Microstructure of the Pb-0.8wtSn and Pb-0.8
  wt Sn-Se alloys

• 3.2 XRD patterns of Pb-0.8wt.Sn and
• Pb-0.8Sn-Se alloys

• 3.3 Corrosion test for Pb-0.8Sn and
• Pb-0.8Sn-Se alloys

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3.1 Microstructure of Pb-0.8 wt Sn-Se alloys
Pb-0.8wtSn-Se alloys alloys (with
Segt0.02wt.) show fine grain size and regular
grain boundaries by comparing with that of
Pb-0.8wtSn. As a result ,the introduction
of Se may protect lead alloy from
recrystallization and improve its structure
stability.
Fig. 2. Micrographs of Pb-0.8Sn and Pb-0.8Sn-Se
alloys with different Se contents. (a)
Pb-0.8wt.Sn(b)Pb-0.8wt.Sn0.01wt.Se(c)Pb-0.8w
t.Sn0.02wt.Se(d)Pb-0.8wt.Sn- 0.03wt.Se
(e)Pb-0.8wt.Sn0.05wt.Se (f)
Pb-0.8wt.Sn0.10wt.Se
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3.2 XRD patterns of Pb-0.8wt.Sn and Pb-0.8Sn-Se
alloys
Fig3. XRD patterns of Pb-0.8Sn and Pb-0.8Sn-Se
alloys
The results from fig.3 feature a characteristic
peak of lead and there is no indication of the
presence of other crystal phases.
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3.2 XRD patterns of Pb-0.8wt.Sn and Pb-0.8Sn-Se
alloys

• The following relation exists among the
  interplanar spacingd, the indices of the
  crystallographic planes H, K, L and the lattice
  parameter.

1/d21/v2H2b2c2sin2aK2a2c2sin2ßL2a2b2sin2?
2HKabc2(cosacosß-cos?)2KLa2bc(cosßcos?-cosa)HL
ab2c(cosacos?-cosß) (1)
Where vabc(12cosacosßcos?-cos2a-c
os2ß-cos2?)1/2 For a cubic
system, Eq. (1) should read
1/d2(H2 K2L2)/a2
(2)
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3.2 XRD patterns of Pb-0.8wt.Sn and Pb-0.8Sn-Se
alloys
The cell parameters of six samples were
calculated on the basis of Eq. (2) and the
parameters were listed in Table 1. The results
are as follows a14.974nm, a24.924 nm,
a34.936nm, a4 4.913 nm, a54.902, a64.919657.
The cell parameters of the Pb-0.8Sn-Se alloys
are less than those of lead, which indicates that
finer grains are obtained.

• Table1.Parameters of main diffraction peaks
  of XRD patterns of Pb-0.8Sn and Pb-0.8Sn-Se
  alloys

d1 d2 d3
a 2.876(111) 1.497(311) 2.488(200)
b 2.840(111) 2.462(200) 1.743(220)
c 2.849(111) 1.746(220) 1.488(311)
d 2.831(111) 2.455(200) 1.486(311)
e 2.840(111) 1.488(311) 2.462(200)
f 2.840(111) 1.743(220) 2.455(200)
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3.3 Corrosion test for Pb-0.8Sn and Pb-0.8Sn-Se
alloys
Fig.4. SEM micrographs of the structure of the
corrosion layers formed at different heights on
Pb-0.8Sn and Pb-0.8Sn-Se electrodes inserted in
AGM soaked in 4.5 M H2SO4 solutions.
((A)Pb-0.8wt.Sn(B)Pb-0.8wt.Sn0.01wt.Se(C)Pb-
0.8wt.Sn0.03wt.Se(D)Pb-0.8wt.Sn-0.05wt.Se)
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3.3 Corrosion test for Pb-0.8Sn and Pb-0.8Sn-Se
alloys
Fig.4. SEM micrographs of the structure of the
corrosion layers formed at different heights on
Pb-0.8Sn and Pb-0.8Sn-Se electrodes inserted in
AGM soaked in 4.5 M H2SO4 solutions.
((A)Pb-0.8wt.Sn(B)Pb-0.8wt.Sn0.01wt.Se(C)Pb-
0.8wt.Sn0.03wt.Se(D)Pb-0.8wt.Sn-0.05wt.Se)
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3.3 Corrosion test for Pb-0.8Sn and Pb-0.8Sn-Se
alloys

• The SEM micrographs reveal the
  differences in the morphology of the corrosion
  layers between the Pb-0.8Sn and Pb-0.8Sn-Se
  alloys. A loose and porous corrosion layer is
  formed on Pb-0.8Sn, but a compact corrosion
  layer with fine corroded products can be observed
  on the Pb-0.8Sn alloys. The corrosion layer
  becomes more compact and the corroded products
  become finer with the addition of Se. The compact
  corrosion layer of Pb-0.8Sn alloys can reduce
  the further corrosion of inner lead alloys.

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4. Conclusions

• (2) According to the calculation of d value from
  the XRD patterns of Pb-0.8Sn and Pb-0.8Sn-Se
  alloys, it is possible to conclude that finer
  grains are obtained with the addition of Se.

(3) The corrosion test indicated that the
corrosion products of Pb-Sn-Se alloys are fine
and compact, and the adding of Se may reduce the
further penetrable corrosion of inner lead alloys
(1) The fine grain size and regular grain
boundaries obtained in Pb-0.8Sn-Se alloys (with
Se0.02wt.) may protect the lead alloy from
recrystallization.
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Thank You !