Full text of DOI:10.1007/BF03214842

Design of New Gold Alloy
A New Electrical
Contact Alloy With
High Reliability
Based on Gold
Electric contact materials are essential electronic
components in electronic products. Reliability is the most
important performance characteristic for light duty electric
contact materials used in mini relays. In addition to high
electrical and thermal conductivity, gold has high chemical
stability and does not form surface films of oxide, sulfide and
‘brown powder’ in oxygen-, sulfur- and organic vapor-
containing atmospheres, so maintains low and stable contact
resistance. Gold is suitable for applications in light duty
precision contacts, and is rarely replaced by other metals or
alloys under the condition of the power distribution with very
weak electric current of 1-10μA and low voltage of 1-50mv.
On the other hand, however, gold contacts are liable to arc
and form sharp splinters and even to weld, due to its low yield
strength, elasticity and melting point as well as its volt-
ampere characteristic. Therefore the alloying of gold is
necessary to enhance the above properties.
Yuantao Ning, Ying Peng, Hong Dai
Kunming Institute of Precious Metals,
Kunming 650221, Yunnan, China
E-mail: ytning2002@yahoo.com.cn
Received 13 April 2002
A new gold alloy (NSCGA) was designed and prepared
for light duty precision contacts. The microstructure,
mechanical, electrical and applied properties of the
NSCGA alloy were studied. The NSCGA alloy contains
copper, palladium, platinum, nickel and rhodium as
well as gold. The unique structure comprised of two
phases, a gold-rich solid solution as the matrix and a
platinum-rich solid solution as a strengthening phase.
The matrix presents short-range ordering in the
temperature range 200-900°C, which leads to the
specific resistance of the alloy decreasing, and a
modulated structure at low temperatures, which is
responsible for age strengthening. The NSCGA alloy
has low specific resistance, high tensile strength and
high Vickers hardness. Various TO-5 type relays (TO-5
relay is a sealed mini relay with magnetic preservation)
with NSCGA alloy as contacts were prepared and tested
in a special relay factory under industrial conditions.
NSCGA alloy contacts showed stable and low contact
resistance, long loading life and high reliability,
superior to that of an available conventional six-
component palladium alloy. The NSCGA alloy and the
composites with NSCGA alloy as a covering layer and
copper alloys as a base have been evaluated in various
TO-5 type mini relays and other electric products.
Multi-component alloying has been a main trend for the
development of electric contact alloys since the 1970s. In the
1980s, the price of gold was ca. 3-4 times higher than that
of palladium. As a results of this a series of multi-component
palladium alloys were studied and used as contact materials
in weak electric current and light load field. Among them, a
palladium alloy, composition Pd-30 Ag-14 Cu-10 Pt-10 Au-1 Zn
(wt.%) [1-3], had more extensive applications and was also
used in mini relays. Electrical contact materials made of
palladium alloys, however, are often unable to satisfy the
demand for low electric current level and high reliability due
to the formation of insulating polymers from organic vapors.
On the other hand, the price of palladium fluctuates rapidly
and has been much higher than that of gold in recent years.
To satisfy the demand for an electrical contact material with
higher reliability and lower price, a new electrical contact
alloy with high reliability based on gold was studied in the
present work.
The design of the compositions of the new gold alloy
reflected two principles. At first, it should be a multi-
component alloy based on gold in order to ensure high
reliability and good comprehensive properties. Secondly, it
must have high hardness and strength by means of second
phase strengthening in order to have high wear resistance
and long duration of service. More specifically, the alloy is six-
component, composed of gold, copper, palladium, platinum,
nickel and rhodium. The content of gold of a typical alloy is
equal to 61 wt.%, and that of copper, palladium and
platinum is 14, 10, and 10 percent in weight, respectively, in
addition to small amounts (5 wt.%) of nickel and rhodium.
Because the solubility of rhodium in gold is negligible [4],
rhodium must be alloyed to platinum to form a second
phase. The alloy is a new six-component gold alloy
Gold Bulletin 2002 • 35/3
75

recrystallisation after annealing at 500°C and 700°C for
0.5 h, the second phase still presented as a fibre texture
because it has higher melting and recrystallisation
temperatures than the matrix phase.
TEM photos (Figure 2) showed the microstructure of
NSCGA alloy annealed at high temperature and aged at low
temperature. At high temperature of 1050°C, which is close
to the melting temperature (1090°C) of the matrix, the alloy
is still two-phase and the matrix phase presented a layered
structure. The results indicated that the layered matrix
structure and second phase were not precipitates but
formed through crystallisation. The matrix phase of the alloy
annealed at 850°C maintained the structure characteristic at
high temperatures. Cold deformation made the grains of the
second phase distribute along lines. Figure 2b shows the
distribution of the second phase in the alloy annealed at
800°C after cold deformation. The alloy aged at low
temperatures was still a two-phase structure made of layer a
matrix and granulated second phase (Figure 2c, 2d).
Figure 1
Low magnification metallographs of NSCGA alloy: (a) as cast, (b, c) alloy
cold deformed and followed by annealing at 500°C (b) and 700°C
(c) for 0.5 h
The spacing (L) between layers of the matrix for the alloy
quenched from 800°C is about 0.373 nm. The smooth-
granulated second phase, less than 100 nm in length was
distributed in the layered structure and after aging also on
twins, grain boundaries and dislocation lines (Figure 2c, 2d).
The X-ray diffraction patterns of NSCGA alloy annealed at
high temperatures and aged at low temperatures presented
a two-phase structure as shown in Figure 4. For the alloy
annealed at 850°C, the matrix phase is a face-centered cubic
(fcc) solid solution with lattice parameter a1 = 0.3905 nm,
and the second phase is also a fcc solid solution with lattice
parameter a2 = 0.3775 nm. Figure 3 showed the changes of
the lattice parameters a1 and a2 of the matrix phase and
second phase as well as spacing (L) between layer structure
of the matrix phase in the aging process. In the aging
process, the changes of a1 and a2 values are very small,
Figure 2
TEM photos of NSCGA alloy at different states: (a) annealed at 1050°C
(b) annealed at 800°C after cold deformation; (c) aged at 350°C and
(d) aged at 200°C
corresponding to the Pd-30Ag-14Cu-10Pt-10Au-1Zn six-
component palladium alloy and was designated NSCGA. In
order to compare the physical properties, especially the
applied performance in electrical contacts, an available six-
component palladium alloy with compositions of Pd-30Ag-
14Cu-10Pt-10Au-1Zn [5], which was named SCPA, was used as
a reference alloy. SCPA is a well-known contact alloy in sliding
contacts and also in contacts and spring leaves in TO-5 type
mini-relays.
0.395
0.390
0.385
0.380
0.375
0.370
70
60
50
40
30
20
a1
L
Microstructure of NSCGA Alloy
a2
The low magnification metallographs shown in Figure 1
showed two phases in casting and the cold deformed NSCGA
alloy. The second phase in the casting alloy appeared as an
irregular petal dendrite form. During cold deformation, the
second phase was extended along the rolling, (drawing),
direction and formed a fibre texture. Although the cold
deformed matrix phase showed obvious recovery and
0
100
200
300
400
Aging temperature °C
Figure 3
Changes of lattice constants of the matrix phase (a1) and the second
phase (a2) as well as layer spacing (L) of the layer structure of matrix
phase with aging temperatures
76
Gold Bulletin 2002 • 35/3

composition modulation wavelength ꢁ ≈ 9 nm existed in the
alloy aged at low temperature, which should be related to
the spinodal decomposition that occurred in Au-Ni [6] and
Au-Pt [7] alloys aged at low temperatures.
(Au)
(Pt)
Physical Properties of NSCGA Alloy
The Vickers-hardness (Hv) and tensile strength (ꢀb) of the
annealed NSCGA alloy were Hv = 222 and ꢀb = 746 Mpa,
respectively. The alloy has high strain hardness. The hardness
increased nearly linearly with (ε) compressive strain and
reached Hv = 310 and ꢀb = 1350 MPa when ε = 60%. The alloy
is able to be age hardened to a certain extent. During the
aging process, the hardness and tensile strength increased
about 12% and 10%, respectively. It can be seen from
Figure 6 that the aging peak temperature decreases with an
increase in compression strain. This is due to the increase of
the stored energy of deformation. An example is given, from
350°C for alloy annealed at 800°C (curve 1 in Figure 6) to
300°C for alloys with ε = 60% (curve 2 in Figure 6) and 200°C
for alloy with ꢂ = 90%(curve 3 in Figure 6), here ꢂ is the
shrinkage of a section of NSCGA alloy wire. A modulated
structure with composition modulation occurring at low
temperatures in the NSCGA alloy could be responsible for the
age hardening effect.
5.00 20.00
40.00
60.00
2ꢄ
80.00
100.00
Figure 4
X-ray diffraction pattern of NSCGA alloy annealed at 850°C.
(Au) = Au(Cu,Pd,Ni) solid solution
(Pt) = Pt(Au,Rh,Cu,Ni) solid solution
Figure 5
The specific resitivity (ꢃ) of the annealed NSCGA alloy was
31.7 μΩ -cm at room temperature. The electrical resistance
measured for wire with diameter of 0.01 mm and length of
about 1 m increased with rising temperature but deviated
negatively from a straight line from 200°C to 900°C (Figure
7). This could be due to the short-range order effect existing
in the alloy over the same temperature range, which led to
the decrease of electric resistance.
Electron diffraction photos of NSCGA alloy aged at 250°C(a) and
annealed at 850°C(b)
demonstrating no precipitated phase separating out, but the
spacing between layers of matrix tended to increase slightly.
The analytic results of an electron probe indicated that the
matrix is an Au (Cu, Pd, and Ni) solid solution based on gold
without rhodium, and the second phase is a Pt (Rh, Au, Cu,
Ni) solid solution based on platinum. The matrix phase did
not contain rhodium, all rhodium in the alloy was present in
the solid solution based on platinum. The lattice constants of
the matrix and second phases were less that of gold
(aAu = 0.4078 nm) and platinum (aPt = 0.3923 nm),
respectively, because the dissolved elements in them have
smaller atomic radii than gold and platinum.
The basic physical properties of NSCGA alloy are listed in
400
300
200
1500
1400
1300
1200
1100
ꢀb
3
2
HV
A diffused diffraction peak at low angles was observed in
the samples annealed at high temperature and aged at low
temperature. X-ray diffraction analysis showed that short-
range order existed in the alloy with the grade of order
ꢀ = 0.1102 in the annealed state at 850°C and ꢀ = 0.1170
for the aged state at 200°C. The structure of the short-range
order is Au3(Cu,Pd). Satellite spots on the (200) plane in
electron diffraction pattern were observed in the alloy aged
at low temperature but disappeared in the alloy annealed at
850°C, as shown in Figure 5. It was confirmed by X-ray
diffraction analysis that a modulated structure with
1
HV
0
100
200
300
400
Temperature °C
Figure 6
Changes of tensile strength ꢀb and Vickers Hardness Hv of NSCGA alloy
with aging temperature: 1. Alloy annealed at 800°C; 2. Cold
deformation ε = 60%; 3. Cold deformation ψ = 98%
Gold Bulletin 2002 • 35/3
77

follows:
55
50
45
40
35
30
Contact Resistance at Low Electrical Level
The static and dynamic contact resistances were measured
for five similar TO-5 type relays at low electric level of 50μA
and 30mv and at temperature of 85°C before and after
running 106 times. Here, the dynamic and static contact
resistances are those measured under conditions with or
without electric pressure applied on the coil with contacts.
The contact resistance data measured is listed in Table 2.
Relays made of NSCGA alloy as contacts and spring leaves,
showed the static and dynamic contact resistances keeping
stable with small values. No fault whatsoever occurred during
106 operations. For relays made of SCPA alloy as contact and
spring leaves, the static and dynamic contact resistances of 5
products before testing were higher than that of relays made
of NSCGA alloy. After testing, the static contact resistance of
one relay was as high as 940mΩ, much larger than a
specification of contact resistance (500mΩ). Moreover, the
static contact resistance of one relay and the dynamic
contact resistance of another two relays with SCPA alloy
contacts are infinite due to formation of PdO film on surfaces
of the contacts, which lead to the electric current being
turned off. The data of contact resistance measured by
present work at low electric level shows that the electric
contact reliability of NSCGA gold alloy is superior to that of
SCPA palladium alloy.
0
100 200 300 400 500 600 700 800 900 1000
Temperature °C
Figure 7
Changes of electric resistance of NSCGA alloy wire in the process of
rising temperature
Table 1, together with the same properties of the available
six-component palladium alloy (SCPA). The basic properties
of both alloys are quite close.
Applied Properties and Applications of
NSCGA
Using NSCGA and SCPA alloys as contacts and spring leaves,
the various TO-5 type relays were prepared and tested under
industrial conditions in a special relay factory. Internationally,
TO-5 relay is a general term for a sealed mini relay with
magnetic preservation. The experimental results were as
Loading Life and Climbing Limit
The various TO-5 types sealed mini relays with NSCGA and
SCPA alloys as contacts and spring leaves were used for
experiments on specified loading life and climbing limits
under industrial conditions. The experimental results are listed
in Table 3. In all tests, the NSCGA gold alloy showed longer life
and higher reliability than the SCPA palladium alloy. In the test
of loading life at ambient temperature and at the electric level
of 0.5A and 28VDC , the loading life of TO-5 relays with NSCGA
alloy as contacts reached above 106 times. This was one order
of magnitude higher than originally specified life of 105 times
set for TO-5 relays with SCPA alloy contacts. During the
operations before 105 times, one relay with SCPA alloy
contacts was faulty 9 times. In the tests of loading life at
temperatures of 85°C and 125°C, the loading life and
reliability of relays with NSCGA alloy contacts were significantly
higher than that of relays with SCPA alloy contacts for all test
conditions listed in Tables 2 and 3. For mechanical life at room
temperature, the TO-5 relays made of NSCGA alloy as contacts
reached 108 times and remained stable through various
parameters and qualities, but the TO-5 relays made of SCPA
alloy lost efficiency after running 106 times. At the
environment temperatures from -65°C to 125°C, the quality
level of reliability of TO-5 type mini relays with NSCGA alloy
Table 1 Basic physical properties of NSCGA alloy
Properties
NSCGA
1090*
15
SCPA [5]
1085
11.9
Melting point, °C
Density, g/cm3
Specific resistance ꢃ20°C,μΩ-cm
31.7
32
Temperature coefficient of
4.2
113
3.0
110
resistance ꢅ0-100°C , x10-4/°C
Modulus of elasticity E, Gpa
Tensile strength, ꢀb , MPa
Annealed alloy
Worked alloy(ε = 60%)
Aged alloy
746
1350
1480
680
1200
1480
Vickers Hardness, Hv
Annealed alloy
220
310
350
180
280
360
Worked alloy (ε = 60%)
Aged alloy
* Solidus melting temperature of matrix phase of NSCGA alloy,
the second phase has a higher melting point
78
Gold Bulletin 2002 • 35/3

Table 2 The Contact Resistances (mΩ) of NSCGA and SCPA Alloys in low Electric Level. (Test condition: electric level, 50μA,
30mv; temperature, 85°C; times for running, 106)
After test for running 106 times
Before test (set limit value 100mΩ)
Alloys of contact and
spring leaf
(set limit value 500mΩ)
Static
Dynamic
62, 64
Static
Dynamic
49, 52
1
2
60, 58
54, 53
55, 57
62, 58
57, 58
56, 56
61, 60
72, 66
77, 68
65, 68
65, 66
67, 65
59, 59
60, 63
62, 65
62, 65
65, 77
65, 89
65, 77
65, 69
69, 74
48, 47
49, 51
48, 50
48, 50
60, 52
62, 56
55, 50
∞, ∞
3
4
50, 51
56, 62
56, 61
59, 59
940, 58
55, 54
58, ∞
NSCGA gold alloy
5
6
7
SCPA palladium alloy
8
9
10
67, 66
59, 56
contacts was assessed as grade W. (The quality level of
reliability for relays is divided generally five grades, the fifth
grade, namely grade W, is the highest quality level.)
metals and to guarantee high reliability and long life. For
SCPA alloy contacts, the gold-plated films on the surfaces of
contacts and spring leaves mostly disappeared. The upper
contact contained 100% Pd and was covered by PdO film.
The other components were not present at all on the surface
of the upper contact. The surface films made of silver-rich
Ag-Pd-Cu alloy and palladium-rich Pd-Cu-Ag alloy were
formed on the lower contact and intermediate spring leaves,
respectively. The components of gold and platinum in
contacts and spring leaves made of original SCPA palladium
alloy was not measured. The formation of a PdO film lead to
higher contact resistance. The surface composition is the
direct reasons for serious loss and transfer of metals and
adhesion due to welding. Frequent faults of contacts and
spring leaves of the SCPA alloy are also observed.
Surface Composition of Contacts of used TO-5 Type
Mini Relays
All the contacts and spring leaves of TO-5 mini relays for tests
and applications in present work were gold-plated (NSCGA
and SCPA alloys) with pure gold film of 2μm thickness in order
to guarantee high reliability of the relays. The surface
compositions of NSCGA and SCPA alloy contacts were
determined by the electron probe micro-area analysis,
examining the damage of the gold-plating film as well as the
transfer and loss of metals on the surfaces of the contacts.
Table 4 lists the compositions on the surfaces of NSCGA and
SCPA alloy contacts and spring leaves after loading life tests
under conditions of the electric level of 0.5 A and 28VDC and
temperature of 125°C. For NSCGA alloy contacts, from the
data in Table 4, the gold contents of the upper and lower
contacts and intermediate spring leaves are in the range of
91-93 wt.% Au, much higher than the 61 wt.% Au of the
original NSCGA alloy. This indicates that the gold-plated films
at the surfaces of NSCGA alloy contacts are basically perfect
and losses and transfer of gold are small and uniform. The
quantity of copper, palladium, nickel and platinum is very
small but that of rhodium is quite high on the surface layers
of NSCGA alloy contacts and spring leaves. This means that
there is a tendency for rhodium to concentrate at the
surfaces of grains of the second phase under operating
conditions because rhodium is distributed mainly in the
platinum-rich second phase with high melting point. It is
advantageous to reduce adhesion due to welding and loss of
Application of NSCGA Alloy as Contacts
NSCGA gold alloy has been used in a series of TO-5 type
sealed mini relays and other products as contacts and spring
leaves with high reliability and has substituted for the
traditional six-component palladium alloy (SCPA). Moreover,
the NSCGA alloy/copper alloy composites were also used in
TO-5 type mini relays and other relays as contacts for saving
the gold alloy and reducing cost.
Conclusions
A new alloy based on gold with multi-component alloying
and second phase strengthening was designed and
prepared. The gold alloy is composed of two phases from
high temperature close to the melting point of the matrix
Gold Bulletin 2002 • 35/3
79

Table 3 Experiments of loading life and climbing limits of TO-5 type mini relays made of NSCGA and SCPA alloys as contacts and spring leaves.
Contact materials of TO-5 mini relays*
Test items
Test conditions
NSCGA alloy
SCPA alloy
Loading life reached above 106 times,
no fault occurred, the quality of relays occurred faults of 9 times
qualified
Loading life was 105 times, one relay
0.5A, 28VDC (specified life
106 times)
Loading life at
ambient
temperature of
20°C
1.0A, 28VDC
Quality of relays qualified at running
105 times
0.5A, 28VDC (specified life
106 times)
No fault was observed during running Welding and serious metal loss
above 106 times, the contacts and
spring leaves were in good condition
with small metal transfer and clear
gaps between them
occurred at running 9 x 105 times
between contacts and spring leaves,
none reaching specified life of 106
times
Loading life at
high temperature
of 125°C
1.0A, 28VDC
Contacts and spring leaves were in
good condition with small metal
transfer after running 105 times
Welding and serious metal transfer
and loss were occurred between
contacts and spring leaves
100mA, 28VDC
No fault was observed at running
5 x 104 times in the test at temp. of
125°C
All tested relays lost efficiency even in
the test at temp. of 85°C
Test was qualified by 10μs supervising Test was qualified by 10μs supervising
under the conditions of 10-2000Hz
frequency, 196m/s2 acceleration and
20g loading
under the conditions of 10-2000Hz
frequency, 147m/s2 acceleration and
15g loading
Vibration test
Mechanical life
Vibrating acceleration
Mechanical life reached 108 times,
various parameters and qualities
indexes kept stable
Contact resistance was as high as
1300 mΩ at running 106 times, relays
lost efficiency
At ambient temperature.
Running 3000 times at
No fault was observed for
During operating process at high
temp. (85°C) and low temp. (-55°C),
20-30% relays were not qualified.
125°C for 1h. Followed by 18 relays
running 3000 times at
-55°C for 1h.
Operating at high
and low temp.
Quality level of
reliability
Environment temperature: Grade W
-65-125°C
* The fabrication and applications of all TO-5 type sealed mini relay were finished in a special relay factory
phase to the ambient temperature. The matrix phase is a
solid solution Au (Cu, Pd, Ni) based on gold with the lattice
parameter a1 = 0.3905 nm and layer structure. The lattice
parameter keeps essentially constant but the spacing
between layers increases lightly in the aging process at low
temperature. The second phase is a platinum-rich solid
solution Pt(Au, Rh, Cu, Ni) with lattice parameter
a2 = 0.3775nm. The particles of second phase are distributed
in the layer structure, twins, on grain boundaries and
dislocation lines of the matrix. This is responsible for the high
strength and high wear resistance of the alloy. A short-range
order with ordered structure Au3(Cu, Pd) and low grade
ordering occurs in the range of 200-900°C, leading to a
decrease in the specific resistance and an increase of
strength of the alloy. A modulated structure with
composition modulation wavelength ꢁ = 9nm occurred in
the aged state at low temperature and disappeared in the
annealed state at 850°C, contributing to age strengthening
at the lower temperature.
The new six-component gold alloy (NSCGA) has low
electric resitivity and temperature coefficient of resistance,
high strength and hardness. The various TO-5 type sealed
mini relays were prepared by a special relay factory and used
for industrial application tests. The static and dynamic
contact resistance remained stable and small, and no fault
occurred during 106 operations at low electric level of 50μA
80
Gold Bulletin 2002 • 35/3

Table 4 The Surface Compositions on the Contacts and Spring Leaves
made of gold-plating NSCGA and SCPA alloy after loading life tests at
temperature of 125°C and 0.5A and 28VDC.
About the Author
Professor Yuantao Ning is a Research Fellow at the Kunming
Precious Metals Institute in China, working on a variety of
research projects related to alloying principles and new
materials based on precious metals. He has gained considerable
scientific achievements and published about two hundred
papers in international and domestic academic periodicals. He
has been awarded national prizes for his achievements in
scientific research. His work has also been concerned with
research into applications for gold and its alloys.
Contents of components on the
surfaces of contact materials wt.%
Locations of
contacts and
spring leaf
NSCGA alloy
SCPA alloy
Au:93.35,Cu:0.95,
Pd:1.67,Pt:0.00,
Ni: 0.60, Rh:3.42
Pd:100, (gold-plating
film disappeared)
Upper contact
Pd:54.00,Ag:16.43,
Cu:29.56 (gold-
plating film
Au:91.23,Cu:1.41,
Pd:1.57,Pt:1.61,
Ni: 0.77, Rh:3.40
Mrs Ying Peng is a senior engineer in QY radio factory. She
has been engaged in design, fabrication and testing of radio
components and relays. She has been awarded national
prizes for her research achievements
Intermediate
spring leaf
disappeared)
Pd:39.86,Ag:41.57,
Cu:18.57 (gold-
plating film
Mrs Hong Dai is a senior engineer in Kunming Institute of
Precious Metals for research of new materials based on
precious metals. She has published several papers and has
been awarded national prizes.
Au:91.38,Cu:0.94,
Pd:2.02,Pt:1.65,
Ni: 0.6, Rh:3.40
Below contact
disappeared)
and 30mV. The various loading life at different electric levels
and temperatures from 20°C to 125°C reached above 106
times, an order of magnitude higher than the originally
specified life set for TO-5 type mini relays with SCPA
palladium alloy contacts. The quality level of reliability of the
TO-5 type sealed mini relays with NSCGA alloy contacts and
spring leaves was assessed as grade W, which is the highest
quality level, at the environment temperatures from -65°C to
125°C. The NSCGA gold alloy has been used in TO-5 type and
other mini relays. This has been used as a contact with high
reliability and has been substituted for the conventional six-
component palladium alloy with composition of Pd-30Ag-
14Cu-10Pt-10Au-1Zn.
References
1
2
3
4
E.M. Wise, ‘Gold Recovery, Properties and Applications’, D. Van
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T. Sakamoto, Z. Henmi and Y. Matsui, J. Japan Institute of Metals, 1965,
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S. Zhang and Y. Yu, Precious Metals, 1983, 4(3), 15
F. Hofer and P.Z. Warbichler, Z. Metallkd., 1985, 76(1), 11
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Gold Bulletin 2002 • 35/3
81