Note: Descriptions are shown in the official language in which they were submitted.
~0~3~
This inyention relates -to a voltage-dependent resistor
(varistorl having npn-ohmic properties (voltage-dependent pro~
perties) due to the bulk thereof and method of making the same,
more particularly to a yoltage-dependent resistor, which is
suitable for a surge absorber and a D,C. stabilizer used in low
voltage circuits.
Various voltage~dependent resistors have bee~ wiclely
used for stabillzation of voltage of electrical cirFults or
suppression of abnormally high surge induced in electrical
circuits. ~he electrical charactèristics of such voltage-
. . .
dependent resistors are expressed by the relation-
I = (V/C)n (1)
where,V is the voltage across the resistor, I is the current
flowing through the resistor, C is a constant corresponding to
the voltage at a given current and exponent n is a numerical
::
value greater than l.~ The value of~n lS calculated by the
following equation~
n~= ¦loglO~(I2J~ [loglo(v2/vl);] (2)
where Vl and~V2 are the voltages at glVen currents Il and I2,
~respectlvely. The~desired value~of C'depends upon the kind of
ap,plication to which the resistor is to be put. It is ordinarily
deslrable that the value of n;be as large~ as possible since this
exponent determines the extent to which~the resistors depart
from ohmic~characte.ristics. Conveniently, the n-value defined
by Il, I2,'Vl and V2;as shown in equation (2) is expressed by
In2 to dlstlngulsh lt from~the n-value calculated by other cur~
rents~or voltages.
There have been known voltage-dependent resistors o~
the bulk type comprising a sintered~body~of zinc oxide with
:
30~ additives, as seen in U.S. Patents 3,663,458, May 16, 1972,
3,632,529, January 4, 1972, 3,~634,~3~37, January 11, 1972,
3,598,763, August 10, I971, 3,&82J841, August 8, 1972, 3,642,664,
:
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~37~L
Februar~ 15~ 1972, 3~658~725( ~pril 25~ 1972, 3~687~871~ Au~ust
29, lq72, 3~723,175! March 27~ 1~73! 3,778,743, December 11, 1973,
3,806,765, April 23, 1974, 3,811,103, May 14, 1974, 3,936,396,
February 3, 1976, 3,863,193, January 28, 1975, 3~872,582, March
25, 1975 and 3,953,373, April 27, 1976, all of which are assigned
to Matsushita Electric Industrial Co., Ltd. These zinc oxide
voltage-dependent resistors of the bulk type contain, as addi-
tives, one or more combinations of oxides or fluorides of bismuth,
cobalt, manganese, barium, boron, berylium, magnesium, calcium,
strontium, titanium, antimony, germanium, chromium,;nic]cel,
niobium, tantalum, tungsten, uranium, iron, cadmium, aluminum,
gallium, indiumj silicon,-tin, lead, lanthanum, praseodymiu~,
neodymium and samarium. The C-value thereof may be controlled,
primarily by changing the compositions of said sintered body ~ -
and the distance between electrodes.~ They have excellent
vo1tage-dependent properties for the N-values in a region of
current below lOA/cm2. For a current higher than~lOA/cm2,
however; the n-value~falls to below 10.
~ Thls defect of these zinc oxide voltage-dependent
resistors of bulk type is presumably due mainly to their low
n-value for the lower C-value, espécially less than 80 volts.
~In~general, these zinc oxide vo~ltage-dependent resistors of the
bulk type, mentioned above, have very low ~-value, i.e. less
than 20, when the C-value is lcwer~than 80 volts. The power
dissipation for surge energy, however,~ has a relatively low
~; value as compared with that of the conventional silicon carbide
vo1tage-depende~t res1stor~ so that the~ohange rate of C-value
exceeds e.g. 20 percent ~fter two standard surges of 8x?0 ~sec
wave form in a peak~ourrent of 500A/cm2, applied to the zinc
oxide voltage-dependent resistors~of the bulk type.
~ 3 _
3~701
~ nothex defect Qf these zinc Qxide volta~e-dependent
resistors o~ the bulk type is a poor stabillty to D.C~ load,
particularly their remarkable decrease of C~value measured even
in a current region such as lOmA, a~ter applying a high D. C .
power to the voltage~dependent resistors especially when they
have a C-value of less than 80 voltsO This deterioration in the
C-value, especially less than 80 volts, is unfavorable e.g. for
a voltage stabilizer which requires high accuracy and low loss
for low voltage circuits. ~ ~
These defects of these zinc oxide voltage-dependent
resistors of bulk type are presumably due mainly to~their low
n-value for the lower C~values, especially of less th~an~80~vo1ts.
Th evelopment of the voltage-dependent resistors having a C-
value e.g. less than 80 volts has~been strongly d~esired for the
appllcatlon~;of~ the low voltage clrOU~Lts~; such~as in~the automoblle
industry~and home appliances,;~but~the n-value~of conventional
voltage-dependent resistors having lowe~C-values~is too~small
to satls~fy~uses~such~as~voltage~s~ab~ zers~and surge~absorbers. ~-
~ For~thes~e~reasons~ voltage~dependent reslstors of this type,
20 ~ ~having~a~C-value less than 80 volts,~have~ hardly been used in
low~voltagè app1lcatlon.
In order to satisfy these desires, many~improvements
were~tried and~, at~he~pr~sent,~s ~b~de~sl~es~are~satisfie~;by
the~improvements~shown in U.~S.~Patents~3,962,144, June~8, 1976
and 4,028,277, June 7, 1977,~hoth.of;~which are assigned~to ; ;~
Matsushita Electric~Industria~ Co.~ Ltd, and~which inclùde ~he
new,technology ln~compos~itions~and~`fabrlcatlon process o~
res~istor~bodles.~ However, the~;~des~ire~for~voltage-dependent
resistors becomes stronger~ espec~ially~in~the~application
30~ of low voltage circuits such as~in~aut.omotive~use~. For this;
purpose, the voltage-dependent ~resistor must~satlsfy the newly~
desired electrical~properties.~ As;~the~ircuit voltage is D.C.
~ ~
~ 4 ~ `
:
3~
. ~
12 tR 16 yolts in ~utomotiye use and the protection level ~or
semiconductor elements is fairly low~ the C-value of voltage-
dependent resistor should be smal].er than thak already satisfied
by the previous techniques. ~ most important problem is to
develop a new voltage~dependent resistor having low C-value
below 40 volts, high n-value in the high current region, i.e.
above lOA~cm2 and additionally having a large surge energy
withstanding capa~ility of 50 to 150 joules and a high operating
temperature up to 150C, that is more speFifically a low
: ~ . .,
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~93~
. ,`
leakage current at a high temperature up to 150C. The latter
two requirements are not yet satisfied by the improvements in
the previous pa-tentsO
In order to suppress the surge observed in a battery
circuit oE an automobile, the so called giant surge, a surge
absorber is required to have a surge energy withstanding
capability above 50~joules. The voltage-dependent resistor
according to the previous patents has a surge energy withstanding
capability of about 1 to 25 joules for the low C-values, which
cannot satisfy the desired value mentioned above. The ambient
temperature of voltage-dependent resistors set in the engine com-
partment of an automobile is supposed to be 150C at the maxi ~ .
The voltage-dependent resistors according to the previous patents
have a maximum operating temperature of 70C and such temperature
lS too low to satisfy the new desire mentioned above. ~Conven-
tionally, titanium oxide ~TlO2) or~beryllium oxide (BeO) is
used as an additive for obtaining~a voltage-dependent resistor
having a low C-value. However, by~the sole technique of
using such an additive, the surge energy withstanding capability
of the resistor is-poor. ;~
An object of this lnvention is to provide a voltage~
dependent resistor having a low C-value less than 40 volts, a
high n-value éven in~a region of current above IOA/Cm2 and a
high surge energy withstanding capability of above 50 joules.
Another object of thls~lnvention is to provide a
voltage-dependent resistor which has a high operating tem-
perature up to 150C~in addition to the above desired properties.
These and other objects of this invention will become
apparent upon consideration of the follo~ing detailed des-
cription taken together with the accomp~nying drawing in which
the single FIGURE is a cross-sectional vlew of a voltage dep-
endent resistor in accordance ~ith this invention.
-- 5 --
~ ~?93'7C~
.,
Before proceeding with a detailed description of the
manufacturing process of the voltage-dependent resistor contem-
plated by this invention, its construction will be described
~, with reference to the single FIGURE wherein reference numeral
7 designates, as a whole, a voltage-dependent rësistor com-
prising, as its active element, a sintered body having a pair
of electrodes 2 and~3 in ohmic contact applied to opposite surfaces
thereof The sintered body ]. is prepared in a manner hereinafter
set forth and is in any form such as circular, square or rec-
tangular plate form. Wire lead5 5 and 6 are attached conductively
to the electrodes 2 and 3, respectively, by a connection means
4 such as solder or the like.
It has been discovered aacording to this .invention
that a low C-value and a high surge energy withstanding capa-
bil~ty, without deterioration of a high n-value due to an ad-
ditive component for giving the~sintered body a voltage-
dependent property, can be obtained by a voltage-dependent
resistor comprlsing~a slnterad body of bulk type, whlch body
comprises a zinc oxlde component as a main component and 0.1
20 ~ to 25 mole percent, in total, of an additive component for
giving the sintered body a voltage-dependent property, charac~
terized in that the zinc oxide component comprises 10 to 100
wélght~percent of~zinc~oxide grains havlng a grain slae in
the range rom 50 to 500 microns ~such zinc oxide gralns
heing deined herein as zinc oxide~core grains) uniformly
dispersed in the sintered body. It has been also dissovered
;according to thls lnventlon that~zuch a ~oltagé-dependent
~resistor can be made~by a method~comprising: homogeneously
mixing zinc oxide grains havlng~:a graln size~o~ 20~to 200
; 30 microns (such z~inc oxide gralna being deflned herein as zinc
oxide seed grains, SG) with a zinc oxide powder and an ad-
di~ive componsn for giving the sintered ~ody a voltage-
:
- 6 -
93~
dependent property in an amount that the thus made mixture
comprises 0.1 to 25 mole percent of the additive componen*, and
that the zinc oxide component composed of the zinc oxide seed
grains and the zinc oxide powder comprises 0.1 to 60 weight
percent of the zinc oxide seed grains; compressing the thus made
mixture into a compressed body; and sintering the thus made
compressed body at a temperature of 1100 to 1400C, whereby
the zinc oxide seed grains grow to an increased grain size
in the range from 50 to 500 microns by taking the zinc oxide
powder thereinto.
The thus made grains having an increased grain size
are what are defined above as zinc oxide core grains~ The~
growth of the zinc oxide seed grains is caused by the phenomenon
that the zinc oxide powder particles having a particle size
usually in the range of 0.1 to 2 microns are adsorbed in neigh-
boring z1nc oxide seed grains to form zinc oxlde grains having
an increased grain size. The zinc oxide powder particles can
have a larger particle size than 2 microns, but should be smaller
than 20 microns. In order for the seed grain~ to grow~ the
zinc oxide seed grains should have a grain size larger than the
particle size of the zinc oxide powder particle. As the dlf~
ference between the grain size~of the seed grains and the par-
ticle size of the zinc oxide becomes larger, the seed grains
can grow more. Further, for the resultant sintered body to
have a lowerporosity or a higher density, the zinc oxide powder
should preferably have a smaller partlcle size. For this-
` reason~ a preferred particle slze of the zinc oxiae powder isbetween 0.1 and 2 microns, more preferably between 0.1 and 1
micron. The grain size of the~seed~grains is measured by using
a sieve or mesh. The grain size of the core grains is measured
by: cutting the resultant sintered~body by a plane perpen-
dicular to both the electrodes to be applied on opposite major
~ 7 -
.. . :
33 71~
`~
surfaces of the sintered body; and drawing, on the cut sur-
face of the sintered body, two tangential lines which are par-
allel to the opposite major surfaces of the sintered ~ody and
i which respectively pass the points of each cut grain on the
cut surface o the sintered body which points are nearest to
the opposite major surfaces, respectively, of the sintered
body. The grain size of each core grain is the distance
between the thus drawn two tangential lines for the core grain.
It is known that a leakage current in a voltage-~
dependent resistor, which should be as small as possible, in
creases as the temperature o~ the resistor increases. The
operating temperature range of a voltage-dependent resistor~is~
the temperature range in which the leakàge current i 5 not too
large to keep the resLstor operable. The maximum operating
temperature of a voltage-dependent resistor depends on the
composition of sintered body. Generally, the sintered body
containing antimony oxide (Sb203) has a smaller leakage current
at a high temperature. However, conventionally, the addition of
antimony oxide to the sintered body causes a disadvantage in
~ that the C-value is greatly increased thereby. The sintered
body of the resistor of this~invention, however, can conta~
antimony oxide to have a high operating temperature without
a~great increase of the C-value. ~It is~the;~disoovery according
to a further development of this invention that when the a~dition
of the antimony component is carried Otlt in the form of a
. .. :
compound of spinel type polycrystalline~Zn7/3Sb2/304, the
leakage current at a high temperature c~an be more ef~fectively
suppressed without an undesired increase of the C-value and
without undesirably deterloratlng~the ~surge~energy~withs~anding
capability.
The sintered body l oan be prepared by per se well
known ceramic techniques. The starting materials oE ZnO,
~- .
.
`~ ~09371:)~
additives and ZnO seed grains with or without the spinel type
polycrystalline Zn7/3Sb2/3O4 are mixed in a wet mill so as to
produce homogeneous mixtures. The mixtures are dried and pressed
in a mold into desired shapes at a pressure from 50 kg/cm2 to
500 kg/cm2. The pressed bodies arè sintered in air at 1100C
to 1400C for 0.5 to 20 hours, and then furnace-cooled to room
temperature (about 15C to about 30C). The mixture to be
pressed can be admixed with a suitable binder such as water,
polyvinyl alcohol, etc. It is advantageous that the sinte~ed
body be lapped at the opposite surfaces by abrasive powder such
as silicon carbide in a particle size of about 10 to 50 ~ in
mean diameter. The sintered bodies are;provided, at the op~
posite surfaces thereof, with electrod s in any available and
suitable method such as silver painting, vacuum ~vaporation or
.
flame spraying of metal such as Al, Zn~ Sn, etc.
The voltage-dependent propertles are not practically
affected by the kind of electrodes l~sed, but are affected by
the thickness of the sintered;~bodles. Particularly, the C-
value varies in~proportion to the~thickness of the slntered
bodies, while the n-value is~almost independent of the thicknes5.
This surely means that the voltage-dependent property is-dile~
to the bulk itself, not to the electrodes.
Lead wires can be attach~d to the electrodes in a
per se conventional manner by using conventional solder. It
:
is convenient to employ a conductive adhesive comprising silver
powder and resin in an organic~ solvent in order to connect the
lead wires to the electrodes.~ Voltage-dependent resistors
according ~to this invention have~a high stability for the surge
~test~. The n-value does not change~remark~bly after the~
heating cycles, the load life~test,~humidity-test and surge
life test. It is advantageous for achievement of high stability
with respect to humidity that~the resultant voltage-dependent
_ g ~
:,
'
3~0937~
resistors be embedded in a humidity proof resin such as epoxy
resin and phenol resin in a per se well known manner.
Conventionally, a fine zinc oxide powder in the particle
size usually between 0.1 and 2 microns is mixed with proper addi-
tives for giving the resultant sintered body a voltage-dependent
property, and the thus made mixture is compressed and sintered
to make a voltage-dependent resistor. The feature of this inven-
tion is that when zinc oxide grains (as seed grains), each of
which is composed of or comprises a zinc oxide single crystal
or a zinc oxide polycrystal in the grain size between 20 and
200 microns, are substituted for a portion of the fine zinc
oxlde powder, the zinc oxide seed grains remarkably~grow to~
have an increased grain size (as zinc oxide~core gralns) by
absorbing the fine zinc oxide powder. In the case that the thus
made sintered body comprises æinc oxide core grains having a
- grain size in the range between 50 and 500 microns in an amount
between lO and 100 weight percent on the basis ~f the zinc oxide
component composed of the zinc oxide core~grains~and~ the fine
zinc oxlde powder, the~sintered body can~have~a desirably low
C-value and a desirably~;high~surge~energy withstanding capability.
The zinc oxide seed grains are designated herein by SG, and`~
the other component of the starting mixture composed of the
fine zlnc oxide powder and the~additives~(which~may contain
a~spinel type polycrystalline powder, SP, ma1nly of Zn7/3Sb2/3O~
as will be described later) is designated herein by base powder,
BP.
According to this invention, the preferred amount and
grain size of the zinc oxide seed grains are from O.l~to 60
weight percent on the basis of~the~ total æinc oxlde component
~in the sintered body~and from 20 to~200 microns, respectively.
The preferred amount of the additives to be added to the
~: -
sintered body and to give the~sintered body a voltage-dependent
- 10 -: ~
3'~
property is from 0.1 to 25 mole percent on the basis of the
sintered body. Thereby, a sintered body comprising zinc oxide
core ~rains having a grain size of 50 to 500 microns in an
amount of 10 to 100 weight percent on the basis oF the total
zinc oxide component can be obtained.
An example of the method of making a voltage-dependent
resistor according to this in~ention will be described herein-
below. In the first place, it is necessary to homogeneously
mix a starting material containing zinc oxide seed grains.~ For
this mixing step, a mixing method which does not pulverize
the seed grains is necessarily used. For example, a wet ball
mill method using resin balls (each having an iron core in~
which have a low pulverization power, can be used therefor. By
.
compressing the thus made homogeneous mixture into a compressed
body, and by sintering the compressed~body, and applying elec-
trodes to the opposlte ma]or surfaces of the~thus made sintered
body, a voltage-dependent resistor can be made. The grain growth
rate o~ the~zinc oxide~seed grains ~lS determined malnly by the
sintering temperature and the sintering time. When a higher
sintering temperature is used,~ the sintering time can be
shorter, or vice versa. A preferred sintering temperatu~re~
rom 1100 to 1400C,~and a preferred slntering time is from
0~5~to`20 hours.~ When the sintering temperature is too low,
the seed grains cannot yrow to the desired core grains even
: :
if the sintering time is very long.~ On the other hand, if the ~ ;
slntering tempeIature is too high,~the grain growth rate does
~not lncrease, and rather the additlve ~omponent may undesirably
evaporate and the sintering furnace~may be~damagedO If the
slntering time is too short, the grain growth rate of the seed
grains is too low, and`the sintered~body may not be~sufficiently
unlform. On the other hand, i~ the sintering time is too long,
:
~ the grain growth rate of the seed grains does not increase with
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an increase in sintering time because the grain growth
becomes saturated after a sufficient sintering time.
The grain size of the zlnc oxide seed gralns is pre-
ferably between 20 and 200 microns. In a sintered body, the
æinc oxide grains grown from zinc oxide particles usually
havin~ a particle size of from 0.1 to 2 microns or of at least
smaller than 20 mic~rons have a grain size usually between 10 an~
~0 microns. So, the effect of the addition of the zinc oxide
seed grains appears with the grain size OI the seed grains of
at least 20 microns. On the other~hand, if the grain size of the -
seed grains is larger than 200 microns, the~distribution of the
zinc oxide grains in the resultant sintered body loses its~
desired uniformity and density, although the C-value can be
lowered by using seed grains having a larger grain size. By
using seed grains having grain sizes d~istributed within~the
,
range of 20 to 200 microns, the C-value can be remarkably
lowered without deteriorating other properties.~ The reason
why the~preferred grain size of the zinc oxide core grains is
between 50 and 500 microns is~slmilar to the reason why the
preferred grain size of the zinc oxide seed grains is between
20 and 200 microns.
A preferred amount of the zinc oxide seed grains is
~rom 0.1 to 60 weight ~ercent on the~basis~of the total zlnc
oxide component. If the amount of the seed grains is too small,
-
the distribution of the zinc oxide grains in the sintered body
becomes undesirably~non~uniform, and the residual voltage ratio
~ ~ -
VloA/VlmA, which will be described~later~,~becomes undeslrably
high, and the surge~energy wlthstandlng capabillty of the
sintered body becomes too low.~ On the cther hand, if the amount
30~ o the seed grains is too l~argel the porosity of the resultant
sintered body becomes ~oo high, which~léads to a decrease of the
contact areas between adjaaent zinc oxide grains in the sintered
~ - 12 -
:
- ` ~033 7~31
body, resulting in an increase of the C-value and of the
residual voltage ratio VlOA/Vl A and in the deterioration of
the surge energy withstanding capability and of the stability
to the ambient humidity. By using such zinc oxide seed grains,
the seed grains grow to core grains in an amount of lO to lO0
weight percent on the basis of the total zinc oxide component
in the sintered body. If the amount of the zinc oxide core grains
is too small, similar disadvantages to those appearing in the
case of seed grains having a too small grain size appear, such
as too low surge energy withstanding capability.
The zinc oxide seed grains to be used in the method
of making a voItage-dependent resistor according to thi~s in-
vention can be made by pulverizing zinc oxlde single crystals
having a very large crystal size. ~owever~ more preferably,
the zinc oxide seed grains are made by the following method.
A zinc oxide powder having a particle size usually in the range
~of 0.1 to 2 microns~is prepared in~the flrst place. To the
thus~prepared zinc oxide~powder as~a starting zinc oxlde powderl
a grain growth promoting agent selected ~rom amongst barium oxide,
~;2~0 strontium oxide, calcium oxide, sodium oxide, potassium oxide,
rubidium oxide, praseodymium oxide, samarium oxide, niob1um~
oxide, tantalum oxide, tungsten oxide, uranium oxide and bismuth
~oxide, is added in~an~amount that the s~tarting zinc oxide powder
is 95 to 99.9 mole percent (which may contain cobaIt oxide,
manganese oxlde or nickel oxide as wil1 be described later~
and the grain growth~promot~ng dgent is 0.1 to S mole percent.
If the amount of the~grain growth~promoting agent is too
small,~the startiny zinc oxide powder particles do not suf-
ficiently grow to seed grains, whereas the particle growth
rate of the starting zlnc oxide powder to seed grains levels
of at a certain amount of the grain growth promoting agent,
- and thus an amount thereof exceeding the certaln amount
::
- 13 ~
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~3~;.' ` ~ 3LO913 ~
(5 mole percent) is unnecessary or rather decreases the pro-
duction yield rate of the seed grains.
The mixture of the starting zinc oxide powder and the
grain growth promoting agent is heated or fired at a temperature
preferably between 1100C and 1600C for a time period preferably
between 0.5 and 50 hours. If the firing temperature is too low
or the firing time ~is too short, the starting zinc oxide powder
does not grow to grains having a sufficiently large grain size
as seed grains. Qn the other hand, the particle growth leveIs
off at a certain temperature (1600C) or at a certain firing time
(50 hours), and thus a firing temperature higher than 1600C
and a firing time longer than 50 hours are unnecessary. ~
The desired zinc oxide seed grains can be made by
pulverizing the thus made fired mixture and selecting grains in
an appropriate grain size range with the ald of a sleve.~ In
this case, the zinc oxide seed grains contain the slight a unt
of the grain grow~h promoting agent remaining therein. However,
more preferrably, a water soluble oxide i5 used, selected from
amongst barlum oxide, strontlum oxlde, calcium oxide, sodium
., :
oxide, potassium oxide and rubidium~oxlde in the above described
amount, or more preferably in an amount of 0.3 to 0.8 mole~
percent on~the basis of the ~sum~of the starting zinc oxide
powder and the grain growth~promotlng agent. ~The most preferred
one is barium oxide in view of the~grain growth of the starting
zinc oxide powder and its water solubility. When the mixture
of the starting zinc~oxide powder and;the water soluble grain
growth promotoing agent is oompressed and flredj the graln growth
promoting~agent gathers at the ~rain boundaries of the zinc
oxlde seed grains in the fired~mixture. So, by immersing the
flred mixture in water or further bolling the water, the grain
growth promoting agent can be dissolved into the water. That
is, the grain growth promoting agent is removed by washing.
~-- I4
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; ~093'7~
Thereby, the fired mixture is broken at the grain boundaries
into separate seed grains.
Since the thus obtained seed grains have a grain size
mostly in the range between 20 and 200 microns, the seed grains
can be made by such method with a yield rate of nearly 100%.
In this case, if the amount of the water soluble promoting agent
is too small, the s~tarting zinc oxide powder does not sufficiently
grow, whereas if the amount is too large, it is difficult to
completely remove the wa~er soluble grain growth promoting~
agent by washing. The seed grains produced by using and removing
the water soluble grain growth promoting agent are better than
the seed grains produced by using grain growth promoting agent~
and pulverizing the fired mixture, because the former seed
grains are mainly composed of primary seed grains, whereas the
latter seed grains often con~ain an agglomerates of plural seed
grains and/or broken seed grains, so that the former seed grains
cause:a more uniform and homogeneous sintered body having zinc
ox~ide core grains of a higher grain sixe in the resultant voltage-
dependent resistor.
: .
By using zinc oxide seed grains in the grain size
range between 20 and 200 microns, voltage-dependent resist~ors~
having low C-values can be obtained. The C-value can be varied
b~ selecting the grain size dlstribution~of the seed grain in
accordance with the deslred use o the voltage-dependent resistors.
When the resistors are used for absorbing so-called giant surges
which may appear in automobiles, the C-values are preferably
in the range between 10 and 15 volts, and the residual voltaye
ratio VlOA/Vlm~ lS preferably low~ For this usel the desired
~grain size~ of the zinc oxide s;eed~grains is in the range hetween
- 30 44 and 150 microns, and the amount of the seed grains in this
case on the basis of the tota~l zinc oxide component ln the
93~7~L
.
resultant sintered body is more preferably from 2 to 15 weight
percent.
~ According to the above method, the starting zinc oxide
powder need not necessarily be pure. Generally, in voltage-
dependent resistors using ~inc oxide sintered bodies, when
cobalt oxide, manganese oxide and/or nickel oxide is used as
an additive for giv~ing the sintered body a voltage dependent
property, such additive is partially dissolved in zinc oxide
grains. Such additive can be preliminarily dissolved in the
zinc oxide seed grains to form a solid solution by Lncorporating
such additive into the starting zlnc oxide p~owder before
firing the mixture of the starting zinc oxide powder and~the~
grain growth promoting agent. In this case, the preferred
amounts of cobalt oxide, manganese oxide and nickel oxide are
0.1 to 15 mole percent, 0.1 to 5.0 mole percent and 0.1 to 30
mole percent, respectively.
. ~ ~
Preferred;additives~;to be~added to the sintered body
~in conjunction with the~zinc oxide seed grains and the flne
zinc oxide powder are known oxides (or known fluorides of some
20~ of~) magnesium, beryllium, calcium, strontium, barium, tltanium,
niobium, tantalum,~ chromium, tungsten, uranlum, manganese;,;~ron,~
cobalt, nickel, cadmium, boron, aluminum, gallium, indium,
si:icon, germanium, tin, lead, antimony, bismuth, lan~hanum,
praseodymium, neodymlum and samarlum.~ However r when the
additives among them other than strontium oxide, barium oxide,
manganese oxide, ~obalt oxide~and bismu~h o~ide are used, they
are desired to be used in con~junction with at least one of
~:
these five oxides, in order to obtàin practically suf~icient
~voltage-dependent properties o~ the resultant resistors.`
According~to a ~urther development of this invention,
a voltage-~ependent resistor having a low leakage current even
at a high temperature can be obtained. That~is, when the
- 16 - ~
09~ 70~
. . .
voltage-dependent resistor is used for absorbing giant surges
in an automobile, it is required to have not only a low C-value
or a low varistor voltage and a low residual voltage ratio
V10A/VlmA, but also a high operating temperature such as 150C,
i.e. a low leakage current even at a high temperature such as
150C. It is the discovery according to the further development
of this invention t~at such low leakage current can b~ attained
by adding antimony oxide without undesirably increasing the
C-value or the varistor voltage. It is known that the leak.age
current at a high temperature can be reduced by the~addition
of antimony oxide. (~hen antimony oxide is used, bismuth oxide
is usually used at the same time.) However, in a conventio~al~
voltage-dependent resistor, the addition of antimony oxide causes
the conventional resistor to increase in its C-value. However,
in the voltage-dependent resistor~of this invention which~has
~inc oxide core grains in the grain size from 50 to 500 microns
made from~zinc oxide seed grains in the grain si~e from ~0 to
; 200 microns, the addition~o~-antlmony oxide does not ~cause
undesired increase of the C-value. This is presumably because
the seed grains can yrow to the;~ore grains even in the
presence of antimony oxide.
When antimony oxide is used and hence ~ismuth oxide
s~used~at the same time, a preferred;~amount of each of antimony
~oxide and bismuth oxide is betw~en 0.1 to 10 mole percent on
.
the basis of the resultant sintered body. If the àmount of each
of these two oxides is too small, su~ficient effects of the -
addltlons thereof do not appear. On the o her hand, if~the
amount of antimony oxide is too large, the resultant C-value
~ becomes undesirably hlgh~ the~amount of bismuth~oxide is
30~ to~o large, when plural compressed bodles to be sintered are
stacked on each other and sintered in a sintering furnace,
the adjacent sintered bodies ar ~likely to be bonded to each other.
:
~ ~ 17 -
'
,
,
3'7~
.. .
It is a further finding according to the further
development of this in~ention that when antimony oxide is pre-
liminarily mixed with a portion of the fine zinc oxide powder
to be mixed with the zinc oxide seed grains and an additive or
additives for giving the resultant sintered body volt~ge
dependen-t properties, and is heated or fired to form a spinel
type polycrystalline Zn7/3Sb2/3O4, and when the thus made spinel
compound is pulverized to granules, and the thus made granules
are added to the remaining fine zinc oxide powder and the zinc
oxide seed grains and the additive or additives, then the more
or less undesixed effect of the antimony oxide addition to
increase the C-value of the ~resultant voltage-dependent~resi;~or
- can more efectively be suppressed. Thereby, a lower C-value
and a low leakage current at a high temperature can be attained.
The preferred heating temperature and time for making
the spinel compound are between 13Q0C and 1~00Cj and between
,
~ ~0. 5~and 10 hours, respectively.; If the heatlng temperature
; ~ and tim are too low an~d too short, respectively, the~desired
~splnel phase ls not su~iciently made, whereas~an excessively
hlgher temperature and longer time than 140DC and 10 hours,
respec~ively, are simply unnecessary. The~preferred granule~
size of the pulverized spinel compound is between 0.1 and 60
microns. If the granule slze~ls~ too~large,~the~residual voltage
ratlo V10A/VlmA becomes undesirably~high and the surge energy
withstanding capability becomes undesirably low. On the other
handj if the granule size is ~oo small, the effect of the use of
the spinel compound ~to suppress the lncrease of the C-value does
not appear.
~ ~ In the case where 0~.l to 10 mole percent of antimony
oxide~and 0.1 to 10 mole percent of bismuth oxide are used,
when at least one member of cobalt oxlde, manganese oxide,
;chromium oxide and nickel oxide is also used in an amount that
- 18 ~~
.,
:,
'`` ~lO~37~L
,
the amount of antimony oxide is between 99.2 and 7~7 mole
percent on the basis of the sum of the antimony oxide and the
above-mentioned at least one member, then the resultant voltage-
dependent resistor can have better properties as a low C-value
resistor for absorbing current surges. In this case, when the
antimony oxide and the above-mentioned at least one member are
mixed with a portion of the fine zinc oxide powder (to be mixed
with the zinc oxide seed grains and an additive or additives
for giving the resistor a voltage-dependent property) and heated
or sintered to form a sintered po~der mainly of a spinel type
polycrystalline compound, then the addition of such sintered
powder to the remaining fine zinc oxide powder and the zinc~oxlde~
seed grains and the additive or~additives causes the resultant
resistor to have a-lower C-value, a higher surge energy with-
standing capability and a higher n-value than in the~case when
the spinel type compound lS on1y of Zn7/35b2/3O4. In this case,
the heating temperature and time for obtaining the sintered
powder mainly of ~he spinel type polycrystalline material are
:: :
pr~ferably between 1100 and 1400C and between 0.5 and 20 hours,
respectively. If the heating temperature is too low, the sin-
tered powder mainly of the splnel type polycrystalline material
cannot be ma~e stably. On the other hand, an excessive ~empera-
~-~ ture i.e. higher~than 1400C, is simply unnecessary. The granule
size or the particle Si2~ of the slntered powder Ithis can be ob-
tained by pulverizing the s1ntered mixture~ is preferably between
0.1 and 60 microns for similar reasons to those why the granule
;~size of the slngle use of the spinel~type polycrystalline
2n7/35b2/3O4 is preferably between 0.1 and 60 microns as set
forth above. HereIn, the sintered~powder mainly of the spinel
~ type material or the single phase powder of spinel type
Zn7/3Sb2/3O4 is designated by spinel powder, SP~
~ 1 9 ~ `
.
,.. . .. .
1~3~
This invention will more readily be understood
with reference to the ~ollowing Examples 1 to 12, but these
Examples are intended only to illustrate this invention, and
are not to be construed to limit the scope of this invention.
(In the Examples, the C-value is designated by a voltage across
each sintered body at 1 mA/cm2 of applied current per 1 mm
thickness of the si~tered body.)
Example 1
Zinc oxide with additives as shown in Table 1 were
mixed in an agate mortar for 3 hours. Each of the thus made
mixtures was pressed into a mold disc of 40 mm in diameter
and 5 mm in thickness under a pressure of 250 kg/cm2 to a co
pressed body. Each of the thus compressed bodies was~ sintered
in air at 1400C for 10 hours, and then furnace-cooled to room
temperature. The sintered body was~crushed into powder by an
agate pestle, and then the thus made powders of 44 to 150
microns in diameter from each~body were selected by sieves.
The thus selected powders are designated as SG (seed grains).
On the other hand~ a zinc oxide powder having an
2~0 average particle size of 0.8 micron was mixed with additives
as shown in Table 2 in an agate mortar for 3 hours. Each of~the
thus made mixtures is designated as BP (basic powder). 10
weight parts of SG was mixed with 90 weight~parts of BP, and
the mixture was mixed in~a we~: mlll with resin balls for 24
hours. The mixture was dried and~pressed into a mold~disc of
17~ mm in ~iiameter and 1 to 3 mm in thickness under a pressure
of 250 1~g/cm2 into a compressed body. Each of the thus com-
press,ed bodies was sintered in air at 1350C for 5 hours,
and ~hen furnace-cooled to room temperature, and was then lapped
to a suitable thickness. The opposite~major sur~aces of each
of the thus sintered and lapped bodies were provided w1th a
spray metallized film of alumlnum, as electrodes, by a per se
- 20 -
:
:
)937al~
well known technique~
On the other hand, sintered bodies with electrodes
similar to those prepared above were prepared, except that in
~s this case no SG was used for comparison.
The measured electrical characteristics of each of
the thus made various sintered bodies are shown in Tables
3 and 4. It is apparent fro~ Tables 3 and 4 that the C-value
decreases with the addition of SG without appreciably de-
grading n-value and the residual voltage ratio, whlch are proper
characteristics of BP, and that the energy withstanding
capability increases with the addition of SG. ~erein, the
residual voltage ratio V10A/V1 A means the ratio of the
voltage across the sintered body supplied with the current of
10 A/cm2 to the voltage across the sintered body supplied with
the current of 1 mA/cm2. Therefore, it is better Eor a surge
absorber to have a smaller residual voltage. ~The surge energy
withstanding capability~E mean~ the destruct~on energy of the
:
sinte.red bodies with electrodes of 1 cm in diameter when the
surge is applied to the sintered hody the varistor voltage
~20 (which means the voltage~across the sintered body when the
current of l mA/cm2 is applied;) of which is~adjusted~to 20
volts. It will be readily recognized that the addition of
SG~improYes~the C-value~and the energy wlthstanding aapabllity
~without degrading the inherent n-value and residual voltage
r atio for each material composition.
Example 2 ~
Zinc oxide~and additives as shown by samples Nos. A
to F ln Table l were~fabricate;d into~the~SG by the same method
as that o~ Example 1, except that in this Example 2, SG was
made by washing and boiling in~pure~water for 10~hours the
sintered bodies produced by using~water s~oluble grain ~rowth
promoting agents. Various mixtures of zinc oxide with SG
- 21 -
'
.
. , , . - , : :
37~
and additives as shown in Table 2 were fabricated into the
sintered bodies with electrodes by the same method as that of
Example 1, except that in this Example 2, the SG was made by
washing and boiling the sintered bodies in pure water as des-
cribed above.
The electrical characteristics of the thus made
` various sintered bo~ies are shown in Table 5. It is apparént
from Table 5 that the C-values can be lowered from those in
Example 1 by using the SG made by washing and boiling the
1~ sintered bodies in pure water employing water soluble grain
growth promoting agents. The n-value and residual voltage
ratio change only slightly. The energy withstanding capabllity
increases in comparison to the result of Example 1. It can
be easil~ understood that the addition of SG made by washing
and boiling in pure water the slntered bodles employing water
soluble grain growth promoting agents impro~es the C-value and
the energy-withstanding capabllity.
: ` .
Example 3
`
.
Zinc oxide and additives as shown by sample Nos. A
and B in Table 1 were fabricated into the SG by the same
:
method as that of Example 2. Zinc oxide with SG and additi~es
as shown ln Table 2, sample No. 2, were fabricated into thè
sintered bodies~with electrodes~ by the~ same method as that
of Example 1, except that the a~ount of SG in this Example
3 was varied from zero to 80 weight percent.
The electrical characteristics of the thus made
various sintered bodies are shown in Table 6. It lS apparent
rom Table 6 that C-value, residual voltage ratio and the
energy withstanding capability~changes with the~amount of the
added SG. It can be understood that the addition of SG of
less than 0~1 weight percent and more than 60 weight percent-
causes an undesired decrease of the energy withstanding
;:
- 22 -
capability and increase of the residual voltage ratio.
Example 4
zinc oxide and additives as shown in Table 1, sample
No. A, were fabricated into the SG by the same method as that
of Example 2, except that the grain size of SG in this Example
4 was varied from less than 20 microns to more than 200 microns.
Then, zinc oxide and additives as shown in Table 2, sample
No. 2, were fabricated into the sintered bodies with electrodes
by the same method as that oE Example 1, except that the grain
size of the added SG in this Example 4 was ~aried rom less
than 20 microns to more than 200 microns.
The electrlcal characteristics of the thus made~
various sintered bodies are shown in Table 7. It is apparent
from Table 7 that C-value, the energy withstanding capabiIity
and residual voltage ratio change wlth the graln size of the
added SG. It can be understood~that the;addition of SG of
less than 20 microns and more than 200 ml~crons~are not~pre-
. . ,
~ ~ferred for obtaining~excellent C-value, energy withstanding
.
capability and residual voltage ratio~
Example 5
Zinc oxide and additives in Table 1, sample No.~A
were fabricat~d into the SG by the same methcd~as that of ~ ample
2, except that the amount of the additive in this Example 5
was~varied from zero to 10 mole percent. ~
.
The production yield rate of SG from 20 microns to
20~0 microns~are shown in Table~8.~ It is apparent from Table
:: . ~ :
8~that the addition ~f additive of~less than O.l moIe % and
the addition of the~additive~oE~more than 5 mole~% cause poor
yield rate in production o~ the SG having a grain size useful
~for improving the electxical characteristics~ of ~the resUltant
sintered bodies with electrodes~ ~
: .
- 23 - ~
937~.
... .
Example 6
zinc oxide and additiYes in Table 1, sample No. A,
were abricated into SG by the sameimethod as that of Example
2, except that the sintering temperature and the sintering time
in this Example 6 were varied from 1000C to 1600C and from
0.5 hour to 50 hours, respectively.
The produ~tion yield rate of SG having a grain size
in the range from 20 microns to 200 microns ar~ shown in Table
9. It is apparent from Table 9 that the sintering a-t a tem,
perature lower than 1100C and for a time period of shorter
than 0.5 hour causes a poor production yield rate of SG because
of poor growth of the ZnO grains~ The sintering at a temperature~
::
higher than 1600C causes saturation of the grain growth, so
that temperatures higher than~1600C~cause little improvement
of SG production yield rate in comparison with 1600C. The
sintering for a time~perlod shorter than 0.5~hour causes little
~grain growth, resulting in poor~production~yleld rate. On the
,
other hand~, the slnt;ering for~ atime~period longer than 50 hours
causes the saturation of the grain growtll, so that the sintering
20~ time longer~than 50 hours causes llttle improvement in the SG
productlon yield rate in comparison with 50 hours.
Example 7
Zlnc oxidè and additlves in Table 1,~ sampLe No. A,
~; were~fabricated lnto SG by the~same~ method as~that of Example 2.
-~ Zince oxide with SG and additlves as shown in Table
10~ were fabricated into the sintered~bodies with electrodes
~by the same method as~that of~Example l~
The electrical characterlstic~s of the~thus made various
slntered bodies are shown in Table~ which shows the leakage
~;~current characterlstlcs~in addition~to the C-valuej n-value,
~residual voltage ratio and surge~energy withstanding capa-
bility. Hereln, the leakage~current is a current flowing
- 2 4 -
.. ~
~l~937~J~
.~ .
through the sin-tered body when 80 percent of its varistor
voltage (VlmA~ is applied to the sintered body at 150C.
` For attaining high temperature operation, the leakage current
is required to be smaller. It is deslred that the leakage
current defined herein be smaller than 100 ~A. By comparing
the leakage current characteristics of the materials made from
BP using Sb2O3 with~those not using Sb2O3, it can be readily
understood that the addition of Sb2O3 improves the leakage
current characteristics.
Example 8
,
Zinc oxide and additives in Table 1, sample No. A,
were fabricated into SG by the same method as that of Example
2.
Meanwhile, antimony ox.ide as shown in Table 10,
sample Nos. 27 to 31, was mixed with a portion of fine zinc
oxide. The ratio of antimony oxide to zinc oxide was 7 to 1
. in molar ratio. The mixed:powders wexe sintered in air at
13:50C for 2 hours, and then f;urnace-cooled to room temperature.
: The sintered powders were crushed by an agate pestle, and then
. .
2~ the powders of smaller than 60 microns and larger than 0.1
microns in diameter ~ere selected by sieves. The powders were
~ composed of splnel type polycrystalline ~SP) Z~,7/3Sb2/3O4.
: : ~ The rest of the fine zinc oxide powder and additives - : ` : : ' '
as shown in Table 10, sample Nos. 27 to 3], were mixed with
the above prepared SG and SP .(employing the same amount of
: ~ .
Sb2O3). Ths thue made mixtures were fabricated into the .
:sint~ered hodies with electrodes by the same method as that
o~ Example 1.
`
The measured electrical characteristics of the thus
~: :
- 30 made various sintered bGdies a~re~shown in Table ]2, which
~shows better C-values and energy withsta:nding capabilitiQs
than in the case when Sb2O3 is used without any preliminary
- 25 - :
.. , . . ' . - - .
~093'7~
preparation of thP splnel type polycrystalline Zn7~3Sb2/304.
It can be understood that by adding the Sb2O3 in the form of
Zn7/3Sb2/304, the C-value and energy withstanding capability
are improved without deteriorating other electrical properties.
Example 9
Zinc oxide and additives in Table 1, sample No. A,
were fabricated into SG by the same method as that of Example
~ .
Meanwhile, antimony oxide (and a portion of zinc ~xide
powder for BP) as shown in Table 10, sample No. 28, was fabri~
cated into SP by the same method as that of Example 8, except
that the granule slze of the~added SP ln the Example 9 was~
varied from 0.1 to 60 microns.
The rest of the zinc oxide powder and the additives
as shown in Table lO, sample No. 28, were mixed with SG and SP,
and the thus made mixtures were fabricated into the sin~tered
bodies with electrodes by the same method as that o~ E~ample 8.
The elec~rical characteristics of the thus made
sintéred bodies are shown in Table~13. It is apparent from
:: :: : :
~o Table 13 that the residual voltage ratio becomes undeslrably
high by adding the SP ha~ing a granule size larger than 60~
~microns.~ It can be understood~that by adding the SP having a
granuIe slze in the~range~from~O.~ to 60 mlcrons,~ the residual
voltage ratio is improved without degrading the leakage current
characteristics.
Exam~le 10
Zinc oxide and addltives ln Table 1, sample~No~ A,
were fabricated into SG by;the same~method as that of Example 2.
Meanwhile, antimony axide~(and~a portion of~zinc oxide
powder for BP) as shown in Table 10~, sample N0. 28, wére fabri-
cated into SP by the same method as that of Example 8, except
that the sintering temperature and time in this Example 10
~ 26 -
,
. ~ , .
37~
~,
were from 1200C to 1400c and for from 0.5 hour to 10 hours,
respectively.
The rest of the zinc oxide powder and the additives
in Table 10, sample No. 28, were mixed wi.th SG and SP, and the
thus made mixtures were fabricated into the sintered bodies with
electrodes by the same method as ~hat of Example 8.
The electrical characteristics of the thus made sinter-
ed bodies are shown in Table 14. It is apparent from Table 14
that the SP obtained by being sintered at a temperature lowbr
than 1300C or for a time shorter than 0.5 hour causes undesir-
ably high C-value and low energy withstanding capability, and
that the SP obtained by being sintered at a temperature~higher~ :
than 1400C or for a time period longer than 10 hours does not
cause much improvement~of C-value and the energy withstanding
capability than by a temperature of 14Q0C or a time period
of 10 hours.
Example 11 : :
Zinc oxide additi~es~ln Table 15, sample Nos. A
an~d N to Qj were fabricated into SG:by the same method as that
.
~20 of Example 2, except that the additives in this Example 11
were those as shown in Table~15.
Zinc oxide and the additives as shown in Table 2,
sample No. 2, and SG~were fabrlaated lnto the~sintered bodies ~;
with electrodes by the same method~as that oE E~mple.l,~except
that the additives for SG in~this Example 11 were as
~shown in Table 15.
~: The electrical char~acteristics of the thus made
:`sintered bodies are ~shown~in:Table 16, which:shows improvement
of n-values in comparison with those of the sintered bodies
:made by SG without further~additivés (except barium~oxlde)
as shown in Table 15. It can:be understood that the addition
of cobalt oxide, manganese oxide or nickel o~ide to SG causes
.
- 27 ~
937~
improvement of the n-value without degrading other electrical
properties.
Example 12
zinc oxide and additives in Table l, sample No. A,
were fabricated into SG by the same method as that of Example
2.
Meanwhile; antimony oxide and a portion of zinc oxide
for BP and additives as shown in Table 17 were mixed. The thus
made mixtures were fabricated into SP by the same method as that
of Example ~, except that the additives for SP in~this Example
12 were those as shown in Table 17.
The rest of the zin~ oxide powder and additlves~a~s
shown in Table lO, sample No. 28, were mixed with SG and SP
~composed of the same amount of Sb2O3~and fabricated into the
sintered body with electrodes by the~same method as that of
Example lj except that the SP~in this~Example 12, was composed
of~zinc~oxide, antimony~oxlde and one of cobalt oxide, manganese
oxide, nicke1 oxide and chromium oxi~de.
The electrical characteristics of the thus made
:
~20 ~sintered bodies are~shown in Table 18, which shows better n- ~
- :
values in comparison with those of the sintered bodies~with~
SP~without a further additive~ of cobalt oxide, manganese oxide
nlckel~oxide or chromium ox~de~.~ It~can be understood that the
~further addition o~;cobalt oxide, manganese oxide, chromium
oxide or nickel oxide for SP improves the n-value;without de-
grading other electrical properties.
While part~icular embodiments~of this lnvention have
been shown and described, it wi~lI be~obvIous to those sXilled
~ in thè art that changes and m~difications may be made without
~departing from this invention in its broader~aspects and, there
fore, the aim in the appended claims is;to cover all such changes
and modifications as fall with-in the true spirit and scope of thi5
invention.
~ 2~ -
.:
~ ~ 10~3'70~
~ .... ~ .
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1~3'7~
.
Table 3
_ .... ~
Sample Electrical Characteristics
No of C-value (V) n-value / E (Joule)
____ . : -- --__,, , . _
i 1 ~.23 44 1.6 12
2 118 45 1.5 12
3 133 47 1.5 12
4 35 ` 28 2.0 25
1~ 2.0 22
6 125 25 1.6 12
7 90 35 : 1.6 18
8 151 45 ~ 1.6 6
9 120 45 ~1.6 12
~ 105 ~ 4o ~ .6 12
;~11 - 120 ~ 43 ~~1.6 12
12 ;123 43 ~ 1.7 ~ ~ ~12
13 118 ~ 45~ ~: 1.7 ~12
~14` 123 40~ ~~ 1.6 ~; ~12
;:15 ~ 115 ~ ~38~ ~: 1.7~ ~ ~ 12
16 ~ ~116 ~ ~39 ~ 1.7: : 12
~: ~17 121 40 1.6 ~ ; 12
18 126 ~33 ; 1.6 12
19 118~ 30 : 1.5 12
20~ ~ ~120 ~ ~ 31 ~ .5~ ~12
21 124 33~: 1.5 ; 12
;22 115`~ ~ 40~ ~ .7 ~12
: ~23: 119 ~ ~ 31 ~ ~ 1.7 ~ 12
2~4 ~ ~:~ 121 ~ ~ 35~ ~ :~1.6 ~ 12
~25~ 121 ;~ :~ 37~ : ~1.6~ : : 12
: ~~ :' ~ ~ ~ : ~ : . - ~
.
2 - : : : :
:
: ~:
, - . , ~" : :
t7C~9L
. ~ -
.~ ,.`
Table 4
.
Sample Sample - Electrical Characteristics
SG No of C-Value (V) n-Value V1oA/V1mA E (Joule)
, . . .... . . _ I
1 32 42 1.6 65
2 33 45 1.6 67
3 38 47 1 ~ 6 51
4 ` 21 27 ' 2.0 80
24 19 2.0 75
6 36 2~ 1.6 53
7 30 33 1.7 56
8 39 45 - 1.6 50
9 33 ~41 1.~ 58
38 1.6 63
11 33 43 1~ 6 59
12 32 ~40 ~ 1.7 58
13 29 40 1.7 67
14 29 38 1.7 67
1.7 69
16 27 39 1.8 66
17 33 40 1.6 58
18 33 30 1.7 58
19 3 ~ 30 1.6 63
31 ~ 28 ` 1.5 55
21 32 30 ~ .5 52
22 ~ 27 35 1.7 70
23 27 ~ 31 1.7 63
24 30 ~ ~ 35 1.6 - 61
~ ~35 1.6 61
~ . ~: ~ .-
'~ : '
33 -
L0~93 7C~
~ . ~
Table 4 ~Continued)
: - ' . .._
Sample Sample - E~ectrical Characteristics
No. of No. of ____
SG BP C-yalue:(V). n-value VloA/~lmA E (Joule)
~'' ... _ .. . . _ .
` 1 36 44 1.6 53
B 2 36 46 1.6 53
18 2.0 70
6 38 24 1.7 54
__ . _ _ _ _ .
. 1 38 40 1.8 54
C 2 37 45. 1.7 53
26 15 2.2 65'
6 40 - ~ 20 1.8 51 ~ :
. : : . .~... ~ ..
1 38 30 1.8 - 55 ~ ~:
: D 2 37 : 35~ 1.7 53 :
27 ~ 16 ;2.1 : 63 :
~ 6 39 - ~ -~20 ~ 1~.8~ ~.~ . :
-: :: : 1 39 ~35 ~ 1.8 : 51
E:: ~2 : 37 ~: 35 ~ 1.8 ~ 53
~ 20 1.9 63
6 38 . -22 : : 1.8 : 51
. . . ,. .:__. _ . ~
:~ ~ 1 37 :~ 30 I.9 51
: ~ : F 2 ; 33 : 1.~8 ~ 53
5~ ~ 25~ ~ ;21`~ ~ ~2.;2~ ~ 62
: : ~ 6-: 38 ~: 23 1.8 : 54
.
: '. : 1 : ~ 43~ 1.6 55
G 2 36 ~ ~ 4~5; : 1.5 54
24~ ; : ~18 ; - 2.0: 72
: ~ 6 : 37: ~: :21 1.6:~ : 53
:: : ~ ~: - : - : ~ ~ ~
~: ~ ~ ~ 1 39 ~ ~ 40:~:~ ~ 1.7 53
: ~ ~ ~ 40 ~~46~ -: 1.8 51
: : ~ ~ 5 26~ :~ 16 200 ~ 61
~ _ 6 40 21 _ 1.8 51
-
3 7 01
Table 4 (Continued)
- -
Sample Sample - Electrical Characteristics.
No. o No. of .
; SG BP C-~alue tV) n-value VloA/vlmA E (Joule)
. . _ ,
1 36 43f 1.7 53
I 2 35 45 1.6 55
23 19 2.1 71
6 39 23 1.7 53
. _ _ . _
1 36 4~ 1.7 53
J 2 35 43 1.7 53
: : 5 23 19 2.0 67
6 39 : : 21 1.7 52
. _
. 1 35 40 1.6 : 55
~ K 2 34 ~ 45 1.6 55
: 5 23 16 2.0 60 ~
: 6 40 ~ 23 ~ 1.6. 52 -
_ _ _
1 ~38 : 35 :1.7 51
L 2 ; 3~3 35 1.7 53
: 5 26 ~:~ 16 ~ 2.0 ~3
: 6 38 30 1.7 52
_.. , .
1 33 :46 1.6 57
M 2 40 ~ ~ 46 1.5: 51 ~ ~
:: 23 ~ 2~.0 62 :
6 39 ~ 26 ~ 1.:6 53
. _ _ _
: ' :
- : :~ ; .
~ ~ 35 ~ :
.
:'
:
. ~
37 C3~L
~` Table 5
.. __ ._ . ~ . . _ . .... _ . .. ,.. _
Sample Sample Electrical Characteristics
No. of No. of _. . . ._ _ _
SB BP C-value (~) n-value VlOA/V1mA E (Joule)
i 1 13 41 1.6 101
,.~ 2 15 46 1.5 96
3 16 46. 1.7 108
~ 9 25 2.0 12~
18 ` 2.0 120
6 12 25 1.7 108
7 10 34 1.7 120
8 13 46 1.7 103
9 12 46 1.7 ~ 104 ~ ;~
12 3~ l o 7 105
11 12 40 1.6 105
: : A 12 13 40 : 1.6 :lQ5 :
13 12 : ~ 1.7~ ~ :107
14 12 4~1 ~1:.6 101
~ : 15 12 41~ ~1.7 ~ 103
: : 16 12 4o 1 . 7 101
: ~ 17 13~ ~;;35 1.7 10~
; 18 13 35 1.7 100
:~ ~ ~ 19~ 13 ~ 28 ~ 1.7 105 :
:~ 2~0~ 13~ ~ :~29~ 1.6~; : ~121
. 21 ~ 13 31 1.6 115
. 22 12 ~ 3s 1:. 7 113
:; - ~ ~ 23 12 ~ 29 1.7 107
~:: 24 13 : ~34 ~ 1.6 ~ 106
;~ ~ 25 :13 ~36 1.6 ~l05 :
~ : , ~ ~ ~ ~ :
= ' . ~ . :. . : ~, , ,:
: : : :~
: - 36 -
7~
~ Table 5 (Continued)
_ . . ~
Sample Sample Electrica1 Characteristics
No. of No. of _ _
SB BP C-value (y~ n-value VloA/VlmA E (Joule)
_ ~ .;, -.-~ _. __ . ...
1 15 44 1.6 90
2 17 45 1.6 90
3 18 , 40 1.5 83
~ `~ 11 30 2.1 114
12 19 1~9 123
6 13 26 1.7 114
7 12 ~35 1.7 ~ 120
8 13 40 1.6 110
9 ~ 15 ~-41 1.6 ~85
~33 ~1.6 ~ 88
~` 11 15 37 ~ 1.6 ~ 93
B 12 15 37 1.7 90
~13 ~ 14; ~ ~ ~40 ~1.6 ~ ~90
14 ~14~ ; ~ 41 ; 1.7 ~ ~ 91
14~ ~ ~ 30 ~1.7~ 92
16 ~ 14 ~ ~0 1.7~ 93
17 15 ` 31 ~ 1.6~ 90
18 14 ` 35 1.6~ 91
~; ~ ~~ 19 14 ~ ~30 ~ 1~.5~ ~9'1~
, ~ ~20~ ~ ~ ; ~ ~31~` ~ 6~ ~ ~ 93
21 15 :~30 loS 97
22 ~ 15 ~ ~ 39~ ~ ~1.7 ~9
r i ~ 23 ~14 ~ ~31 ;~ 1.7 ~ ~ ~ 95
~~ ~ 24 ~ 15 ~~33 ~ 1-7 95
; 25 ~ ~ 15 ~ ~ 36~ 1.7 90
~ : ~ ~ . ~
~ ~ ~ : : ~ ~ ~ : : ~
- : ~ ~ ~ ~; _, ..... :::_., .
:
~ 37 ~
.
, . ~ -
' ' ' -~: . : . . . .
Table 5 (Continued)
,, ~
Sample Sample - Electrical Characteristics
No. of No. of
SB BP C-value (y) n-value VlOA/VlmA E (Joule)
.__ _ . . .___ _
1 18 43 1.7 80
2 16 45 1.7 95
3 20 45 1.5 83
4 ~ 13 30 2.1 108
C 5 13 15 2.0 120
6 15 30 1.8 12
7 14 35 1.8 108
. 8 15 40 1.6 ~ 88 .
9 ~ 15 40 1.7 :92
~ 41 1.7 91
. . .. . _ .
~, 1 17 ~ 39 :1.7 85
D 2 17 45~ :1.6 87
17 : ~:~ 18 ~ ~2~.0 ~ 89
6 : ~15 ~ 26~ ;~1.7:~` : ~90 :
; :1 . ~;17~ ; ~ 41~ ~1.6 ~92 : :~
2 18 43 ; :1.6 ~90
. ~12 ~ ~ 19 ~ 2.~0 ~ 110
6 14 26 1.7 103 ;
: ~ : .: _ ,~ . : ~
1 -~ 15 ~ ~:;~39~ : 1.7 ~ ~93 -~
F ~ ~ ~ 2 :~ 16 ~ ~ ~ 46~ ~ 1~.6 91 :~
~15 ~ 17 l.Y~ ;~ g5
;;( ~~ ~ ~ ; ~ ~C 1.`7 ; ~ ~1 :
:
: : ~ :
~ - '. : ~ ~ ~ : :
~ - .... ~_ ~ ~ .. _ -:
-:38 - ~
.
.
3~10 gl
Table 6
: Sample Sample Amount of : - Electrical Characteristics
No. of No. of additiye C-Value n _ E
BP SG to SG ~(V) ~ value ~lOA/VlmA (Joule)
. (mol-e %) . . -. . . . . . . .,, . _ . _ _ ~
0.05 63 45 1.9 24
0.1 28 44 1.7 72
1 16 45 1.6 75
2 15 45 1.5 94
A 5 15 46 1.5 95
46 1.5 96.
4S 1.5 95
. 20 16 46 ~ 1.5 78
. 40 17 45 1.5 73
:~ ~0 ~18 45 1.6 63
: .~ ~2 _ 80~_ 25 43 . 2.5 _ ~ 35
0.0569 45 l.g 25
: ~ ~ : 0~.135 ~ :44 1.7~ ~ 65
. 1 19 ~44 1.6 84 . .
~: ~ ~ 2 ;~ ~17~ ~ 45 1.5 86
17 ~ 45 1.5 89
. : I0 17 46 1.6 ~: 90
. : B 15 ~ 17 45 1.6 90
: : : ~: 20 ~ ~~ 18 45 1.6 77 :
~0 19 44 1.6 65
60~20~: 43 1.7 51
~0 31 : 43 . _ 30
,
-
:
3 9 _ r
~ : :
" ~937a~
.
.
Table 7
. .
Sample Sample Grain size Electric-al Characteristics
No. of No. of (microns) . C-Value n~ V /V E
: _ BP SG . . ........ : (V1 va1ue l~A 1mA (Joule)
,. less than
~5 45 1,5 36
20 to 44 25 46 1.5 78
2 A 44 to 10515 47 1.5 96
105 to 150 11 ~7 1.5 118
150 to 200 9 46 ~ 85
more than
20~ _ _ 7: _ 45 2.~3 _ 42 _
,
Table 8~
:
Sample Amount ofYield rate ~ : -
:: No. of additive ~o~ SG : ~ :
to SG : (weight percent)
: (mole:~) . ~ : :
_ ~ _ : ~ .
0.05 ~ ~45
: : 0~1 ~3
~: ~` 0. : ~8~
. 5.0 ~ ~ ~:1
: ~ 10.0 ~ 36 ~ :
' : ~ :
~: :
:
- 40 - .
:
..
.~
~ 1937~0gL
Table 9
...... ... ~. .
.. _ . . _ _ . _ _ ,
Sample Sintering Sintering Yield rate
No. of temperature time of SG
SB (C) ~ lhours) ~weight percent3
,. , .. .. __ . ... ......
~: 1000C 0.5 23
. lO 39
S0 ~8
A . _ ..... .. .. __ . _
1100C 0~5 75
83
... _ . ~ ~: , _._ -
1200C ~ 0.5 ~ 80 ~
; lO ~ 88 ` ;
: 50~ 96
A .. _. ... . . .
- ' 1 1400C I 0.5 ~ ~ 97
_ ~ ~ . .
1600C 0:.5 : : : 97
; : : ~ ~ :~ : 10 ~ ~ ~: 98
~: . :~ 50 : 99
. . . . ~. _ .. . .. _ ~ .
~ .
:~:
` ::: ; :
:
:
: .
: - 41~-
~: :: ' ~:
- . ' ' :
1~93701
.
.
Table 10
Sample - = Additives (mole percent) _ _ _
No of 3nO Bl2O3 Co2O3 MnO2 Sb203 NiO Cr2O3 SnO2 TiO2 3eO
, 26 96.9 1.0 0.5 0.51.0 0.1
27 96.8 1.0 0.5 0.50.1 1.0 0.1
28 95.9 1.0 0.~ 0.51.0 1.0 0.1
29 93.9 1.0 ` 0.5 0.5 3.0 1.0 0.1
91.9 1.0 0.5 0.55.0; 1.0 0.1
31 86.9 1.0 0.5 0.5 10.0 1.0 Ool
32 99.0 0.5 0.5
33 98.5 0.5 0.5 0.5
34 98.0 0.5 0.5 0.5 0.5
97.0 0.5 0.5 0.5 1.0 0.5
36 97.0 0.5 0.5 0.5 1.0 0.5
37 96.9 0.5 0.5 0.5 0.1 1.0 0.5
38 97.5 0.5 0.5 0.5~ 0.5 0.5
39 97.4 0.5 0.5 0.5 0.1 3.5~ 0.5
98.0 0.5 0.5 0.5 ~ 0.5
41 97.9 0.5 0.5 0.5 0.1 0.5
97.8 0.1 ~ 0.5 0.5 1.0 0.1
43 97~.3 0.1 0.5 0.5 0.5 1.0 0.1
44 ~7.9 10.0 0.5 0.5 1.0 0.1
87.4 10.0 0.5 0.5 0~.5 1.0 0.1
46 99.0 0.5 0.5 ~
~7 98,5 0.5 0 5 0.5 _ _
,,
- 42
~:)937~
,p .
Table 11
. . ... .. ..
_ . . . .. . _ . .
Sample Sample -- Electr;i-cal-Chaxacteristics
No of SG C-value n-value ~loA/vlmA (Joule) Current
. . . . . . (uA)
. _
26 15 45 1.5 96 385
27 15 45 1.5 96 78
28 I6 46 1.5 96 31
29 23 4~ 1.7 78 32
28 45 1.7 60 30
31 35 45 1.8 51 31
32 12 28 1.8 ~ 108 565
33 : 15 30 ~ 10 8 96 97
34 10 ~34 ~~,7 120 435
l2 34 ~ 1.7 108 ~~75
36 A 9 25~ ~ 2.0 ~ 120 634
37 10 25; ~ ~ 2.0 120 98
38~ 8 23 ~ ; ;2.0 138~ 535
9 9 24~ ~ 2~.0 138 89
~ ~7 22~ ~ 2.1 ~ 150 516
d l : 8 24; ~ 2.1 138 93
42 13 39 1.7 108 321
~43 13 ; 43 ~ ~1.7 102 83
44 ~ ~11 ~ ~46~ ~ 1.7 114 313
12 45 1~7 114 78
46 13~~28 ~; ~ 1.9 ~102 ~513
47 ~ 14 ~2~8 ~ ~ 1 9 102 89
_ ,
, ~~
- 43 - ~
~: : i
:~ :
.
.,, ~ ~ . . _
93~7(~L
,~ ~
X
~ ~ .
~ i s~
. ... . __. l ~ ~ ~ ~
. . . C~ In ~ ~.
. a~
. . ~ o CJ O
~ . ~ ~ N ~ :
u~ ~_ ~ m .:
U ~1 ' ~U ~ o ~ ~
S-i _ - ---------- ~, '~ ~:) ~ ~ :
' ~ ~' ~? ~ ,
'. h ~1/lLt) u) ~D ~ : ~ ~ :
~` 1~ ~ . ~ .. fd' ~
~, o ~ . ~; ~ tn :~ o ; ~ '
~: ~ : r-l ~: ~: . ~ ~ ~
, rd: ~. : ~ ~ ~ ~ ~ : ~ .'
-: h ~` ~- ~ ~ U ~ ~ : :
`` ` :~ : ~ . : ~ ~ :: ~ h : ::
U ~ ~ ~ : ~ ~ R ~ ~: ~ :~ :
Ln Ln :: ~ ~ ~ I '~ U) L~l Ln
~ ~ ' ~ : ~ ~ , ~
~ ~ :~ ~ :
: ~ : : _ :
::: - . ~. .: ' '
: ~ ~- ~ ~ ' ~ U;
~: ~ ~; ~ r~ 9: _ _ : ~ ~. ,,
:~ C) ~ ~ ~ ~0~ ~ ~: `0 ~
. I _ _ _ = _ . .. ~ .,~ ~ ~ ~ ~: . ` ' I' - ~ :: ~ ~ ~ : ~ ~ ~ o ~D ~ O ~ ~
a) ~ : ~ : : : :: ~ o ~ ~:
-`. : ~1 0 : : ~ : , ~ _ _ ---- :
~ : : ~ :~: ;:; ~ 4~ : :~ ,
:~z~A : ; ~ ` ~n~z~ ` : ~ ;.
~: ~ Q~ O ~ '~ o ~ ~ , ~ ~ .
~` ~ I~ CO ~ o ,~ ~ p,,
~: ~ P~ ~ ~ ~ : ~ O m: ~ co ::
U~ Zi : : : ~ U~ Z : :
........ : : ~_. : ' ~
:~
: ` :~: :
:
:
,
~.
~317~L
.
.
`,, ~ -
_ ~
~- ~
Id ~ ~ ~ ~1 ~ ~ ~ .`
. h
_ , .
~ ~ ;
O ~ O ~D O O O O
. u~ ~ a~ ~
h ~ ~I r-l ~1 ,1
~ ` ~J ~:1 - ~
C) ~' ______ `: '
, '..
' ~ i
: U o .
; 5 1 . , _, .. _ . : , .
. ~, 'a)~ ~:1 :, . ~ ~
~1 ~ - u) u~ '
G~l ~ ' ~ ~ r
: ~ ' 1:: : ~
; ~_ - - --: ~' :
. ~ ~ ~ U~ s~
:` ~ ~: ~
Q - t~D ~ :
: : : ~ ~ :
a) ~
:, ~ ~ ~ LO u~ In
: U~ o o; o o o o
: _ ~
~ ~ ; :: ~ : ~ ~ :
~ ~ ~ :
i-J ~d ~ o o o
O O a O
,~ ~J ~ ~ ~ ,:
~1 0 ~ .: ~
~ ~ ;; ~
: _ : ~ :
;~ ~ ,_~:0 ~ ) ' : ; ~
~ O ~ :
:U~Z
~ _ - ~ .
:- :
'
-- dy5 _
.
'- ... _
~ 3'7Q~
.~ .
` Table 15
- :- : : . : :
. .
Sample Addi:ti:ves (mole percent)
No of ZnO. BaO. Co.2O3 MnO2. .Nio
__ ,
A 99.5 0.5
N 98.5 0.5Q~5 Q~51.0
O 9~3. 0~50.1 5.00.1
P 84.3 Q~515.0 0.10.1
Q 69.3 0.50.1 0.130.0
.
Table 16
Sample Sample _ Électrical Characteristics
: No. of No. of C-value n-value VloA/VlmA E Leakage ¦
SG BP (V) : (~oule) Curre~t
.~ A . 16 ~46 ~ 1.5 ~ 96 33
: N 16 ;51 ~ 1.5 102 31
2 16 50~ 1~5 102 32
~ ~: P 16 ~ 52 1.5 101 33
: . ~ Q 16 50 : l.S 100 33
.
:; ' '
~:
: ~:: ` :
~ '
-
~ 46
::
_ .. . - - :
~L~)937C~L
` Table 17
., Sample Additl~es (mole percent)
No. o . . . . .
SP ZnO sb23 C23 ~nO2 Nio . Cr23
__~ . __ __ .. _. ... .
1 87.5 12.5
2 35 5 14.~14.428.2 3.0
3 87.412.2 0.10.1 0.1 0.1
4 35 5 60 .
6 35 5 60
7 35 5 60 .
8 74.351~.8 3.29~3.296.58 1.69
. g . 55.258.6 8.598.5917.18 1.79
~ _. : .
;~ Table 18
.
. ~.. . . . . .. : .. _
: Sample Sample Sample Electrical Characteristics
: No. of No. of No. of- . ~ .
: BP. SG SP C-value n-value V10A/VlmA E Leakag~
~(:V) ~ ; ~ (Joule Current
. ~ ~ - _ ~
: 1 ~16 46;~ ~1.5 : 96 31
2 15 51 1.5 113:: 30 ~ :
: 3 ~ 17~ 50 :1,5. 100 32
. 4 ~16 51 105 105 28
: ` 28 A : 5 16 50: 1.5 : 10~ 28 :
6 16 50 ~ ~ 1.5 ~ 104 31
~ :: 7 16 50~ 1.5 105 30
8 ~:~15~53 1.5 113 28
9 _~15~ 53 1.5 115 23
,
- 47 ~
:: : :
. .
