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Патент USA US3093606

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United States Patent
' r:ICC
_
3,093,598
Patented June 11, 1963
1
2 _
electronic volume conductivity when prepared in the form
3,093,598
of thin blown ?lms of less than about one-thousandth of
ELECTRICALLY CONDUCTIVE GLASSES
an inch in thickness; develop electronically-conductive
-
‘Peter William McMillan and Brian. Purdam Hodgson,
surface layers on prepared surfaces when subjected to
Sta?ord, England, assignors to The English Electric
Company Limited, London, England, a British com
speci?ed heat treatment; and can be used to prepare
volume~conductive articles of appreciable thickness by
pany
applying sintering techniques to the ground glass. They
No Drawing. Filed Jan. 3, 1961,'Se'r. No. 80,039
Claims priority, application Great Britain Sept.'13, 1957
18 Claims. (Cl. 252-521)
may also be applied to ceramic articles to form electroni
a
10
This application is a continuation-impart of our appli
cation Serial 757,444 ?led on 27th August 1958 (now
abandoned).
-
a
cally-conductive glazes thereon.
;A number of glass compositions that have been in
vestigated experimentally are set out, as percentage mo
lecular compositions, in Table I.
This invention relates to electrically-conductive glasses
and to processes for their manufacture.
>
'
1
Table I
15
Glasses are normally ionic conductors having resistivi
ties which vary widely in dependence upon the glass com
position. It is generally accepted that it is the alkali ions
which make the major contribution to the ionic conduc
Glass ____ “I 'A i B i G
tivity of normal types of glass since these ions are more
D . E 1 F i G
40
40
40
40
45
' 50
55
5
55
10
50
15
45
20
40
10
45
10
40
10
35
readily transported through the glass structure than the
alkaline-earth ions. Under unidirectional applied voltage
?elds, however, the movement of alkali ions through the
The raw materials which may be used in the prepara
glass structure is not continuous over a long period of
t-ion of the glasses are manganous carbonate MnCO3, cal
time since these ions migrate to the negative electrode 25 cined alumina, and ground quartz. The glasses are
producing a cathode layer rich in alkali ions. Thus, un
melted in recrystallized alumina crucibles, or in refrac
less the glass at the anode is supplied with an external
tory ceramic crucibles containing a high proportion of
source of alkali ions, the conduction current will slowly
zircon, at temperatures in the region of 1400° C.- Main
decrease with time, i.e. polarization will occur. This
tenance of a controlled furnace atmosphere is not essen
phenomenon may be a disadvantage in applications where 30 tial, air being suitable.
it is desired to utilize the conductive properties of the
The characteristic physical propertiesof these glasses
glass: an example of such an application occurring in the
are as follows: they melt easily at a temperature of about
“targets” of conductive glass employed in photo-respon
1350° C. being quite ?uid at this temperature; the soften
sive electronic discharge devices such as those known as
“image orthicons.”
ing temperatures, measured as the dilatometric turnover
35 temperature, range from 660° C.—720° C; their co
The present invention has ‘for a primary object the pro
e?icients of linear thermal expansion, over the tempera
ture interval 20° C.—500° 0, range from 40x10-7 to
become, an electronic conductor, and in which the phe
66X 10*’7 per degree centigrade, and their chemical dura
nomenon ofpolar-ization under unidirectional applied volt
bilities are good—-for example, they are not affected to
‘ages therefore does not occur. Such glasses may advan 40 any appreciable extent by exposure to the action of steam
tageously be used in the photo-responsive discharge de
for a period of 200 hours.
vices mentioned above, and other applications will be
With regard to‘ spectral transmission properties, the
mentioned later in this speci?cation.
glasses are found to transmit more readily in the infra-red
‘According to the invention, the said object is achieved
region of the spectrum than in the visible region. For
by the provision of certain mangano-silicate glasses and 45 example, a sample 0.2 cm. in thickness of glass F trans
oxidizing treatment thereof.
7
mits only slightly at the red end of the visible spectrum
vision of a glass which is, or which can be caused to
A glass article homogeneous in physical composition
and cuts‘ off the blue end completely, and a 0.4 cm. sample
cuts off all visible radiation completely; in the infra-red
region, however, the 0.2 cm. sample transmits radiation
up to a wavelength of-5 microns, whereas bore-silicate
glasses, for example, will not transmit beyond wave
lengths of 3 to 3.5 microns.
The. melted and re?ned glasses can be moulded by cast
may contain manganese ions in diiferent states of valency
and in such proportions and so distributed as to cause
‘the glass to exhibit electronic conduction within a limited
portion only, for example within only a surface layer.
‘Manganese ions can exist in glass in the divalent and
trivalent states and possibly also in the quadrivalent state;
it is thought that electron transfer between divalent and
ing and other normal techniques. The shaped articles
trivalent ions in the ‘interstices of the glass network is at 55 are placed in an electric mu?ie furnace immediately after
least primarily responsible for the conduction mecha
the forming process, and annealed; a typical annealing
schedule consists in maintaining the article at 650° C.
for one hour and then allowing it to cool slowly to room
msm.
According to one aspect of the invention, a manganese
silicate glass has the following molecular percentage com
position:
60
Percent
Manganese, expressed as MnO ______________ __ 36-55
Aluminum, expressed asAl2O3 ______________ __ 50~20
Silicon, expressed as Si02 ___________ __' ______ __ 35—56
the manganese being predominantly in its Mn+2 valence
state, and normal impurities being neglected.
In alternative compositions, not more than 5 molecular
percent of the manganese is replaced by an alkaline-earth
temperature.
There is some evidence for believing that the surface
of the article at this stage would exhibit electronic con
ductivity, but the nature of the surfaces precludes ac
curate measurement, and in any event the article would
have limited practical application if it could not be ground
65 and polished to an accurate form.
The surfaces of the shaped articles are now ground to
their required form, and polished.
‘
'
The surface electrical resistivities of ground and
oxide, preferably magnesium oxide (MgO), calcium ox 70 polished surfaces of sample glasses having the composi
ide (CaO) or barium oxide (BaO).
Glasses having compositions within these ranges exhibit
tions given in Table I have been measured and the results
are set out in Table II.
3,093,598
3
4
Table II
this effect in a marked degree, and Table V records ex
Surface resistivity in
ohms at ‘1000 volts p.d.
Glass:
perimental results obtained for blown ?lms of this glass
of various thicknesses.
A ________________________________ __ 4O><1O12
Table V
B ________________________________ __ 3 l ><1012
C --_
Volume resistivity at
45x1012
D _.__
__
Glass F ?lm thicknesses, inches:
6X10l2
100 volts p.d., ohm-cm.
E ________________________________ __ 4()><1012
2l><l0—5
25><10~5
F ________________________________ .._ 45 X1012
30><10-5
_________________________ __ 74x1010
G _
36><10-5
38x10‘5
39x10‘5
42x10‘5
_________________________ __ 25x1010
_________________________ __ 10><1010
_________________________ __
5><l01°
_________________________ __ 28x1010
_________________________ __ 39>< 101°
____
__
17><l012
These resistivities are too high for the glasses in this
form to be of practical use as conductive glasses, and
indeed for practical purposes the ground and polished
_________________________ __ 51><101o
_________________________ __ 49><101°
It is not
43><1O—5
known whether the very slight conductivity exhibited is
44><l0"5
_________________________ __ l5><l01°
electronic or ionic.
45><1()—5
_________________________ __
surfaces can be considered to be insulating.
9><l0l°
57x10~5 _________________________ __ l5><l01°
The ground and polished article is therefore now heat
6l><10—5 _________________________ __ 14><101°
treated to produce a conductive surface layer. The tem
64><10-5 _________________________ __
4><101°
perature employed for the heat treatment is preferably
between 550° C. and 700° C.; heating at these tempera 20
These are the results of a particular series of resistivity
tures for a period between 30 minutes and 4 hours is
measurements, but they appear to show that there is some
found to be satisfactory, preferably about 4 hours.
degree of correlation between resistivity and ?lm thick
The presence of oxygen is essential for the formation
ness at least for the particular glass composition investi
of the conductive layer, but the amount of oxygen in the
gated. The volume resistivity of the ?lms rises if they
furnace atmosphere is not critical. Air is quite suitable, 25 are heat treated in air .at temperatures of about 600° C.
and the use of an atmosphere containing a higher per
Another method of utilizing a glass having a composi
centage of oxygen than .air conveys no corresponding
tion within the range herein generally speci?ed consists in
advantage. Commercial grade nitrogen contains about
treating it in powder form in an oxidizing atmosphere at
2% of oxygen, and this (as in one of the examples given
a temperature within the range 550° C. to 1000° C. for a
below) is sufficient to cause the development of the con 30 period between 30 minutes and 4 hours.
ductive layer when the article is heated in this atmosphere.
Before forming the desired article, the powdered glass
Table III shows the results of surface resistivity deter
may be heat treated in an oxidizing atmosphere, in the
minations carried out on surfaces of discs of the glasses
manner already described, at a temperature within the
whose compositions are given in Table I, the surfaces were
range 550° C. to 700° C., below the softening tempera
ground and polished, and the discs heated in air for 4 35 ture of the glass, for a period between 30 minutes and 4
hours at 600° C.
hours, preferably 4 hours. Thereafter it is sintered in
Table III
an inert atmosphere to form the article.
Surface resistivity in
Alternatively, the powder need not be heat treated, the
ohms, after heat treat
conductive effect ‘being developed by sintering in an oxi
Glass:
ment, at 100 volts p.d.
This sintering can be
A _______________________________ __
1.2><1O9 40 dizing atmosphere such as air.
B _______________________________ __
3.5><10‘~‘
C __
2.9)(109
D _
_____
_____
E
17.2><109
__
--_
1.7 x 109
F _______________________________ __
0.6><109
G _______________________________ __
1.0 x 109
carried out at a temperature within the range 950° C. to
1100° C. during a period between one hour and three
hours, preferably three hours at 1000° C.
Articles produced by either of these sintering processes
45 are mechanically strong, and have practically equal vol
ume resistivities: a typical article produced by sintering
a powder of glass P at 1000° C. for three hours had a
It will be seen that glass F shows the development of
the conductive layer to ‘the most marked degree. By way
volume resisitvity of 48x106 ohm-cm.
It is suggested that the conduction process in these
of demonstrating the effects of varying conditions of heat 50 glasses involves electron transfer between ions of the
treatment on the development of the conductive layer,
same element which are present in different states of
Table IV gives the relative surface resistivities of samples
valency in the interstices of the glass network. It is
of this glass heated for 4 hours in various atmospheres
thought that the increase in surface conduction which
and at various temperatures.
takes place when these glasses are heated in atmospheres
55 containing oxygen is due to the absorption of oxygen
Table IV
with a change in the state of oxidation of some of the
Tempera-
Atmosphere
ture, °C.
Relative
surface re
sistivity at
100 volts
p.d.
_
75% oxygen plus 25% n1trogen____
50% oxygen plus 50% nitrogenm.
25% oxygen plus 75% nitrogen_.__
550
600
650
700
15.5
5. 5
1.3
1. 7
600
5. 6
600
600
__.-
600
manganese ions from the initially predominating divalent
ions to the trivalent ion. Heat treatment of the glasses
in neutral or reducing atmospheres does not result in the
60 conversion of divalent manganese ions to the trivalent
form and does not therefore result in the development of
5.0 65
2. 7
10.0
Nitrogen (commercial quality) ______________ __
600
12.3
90% pure nitrogen plus 10% hydrogen _______ _.
600
>105
the conducting effect.
Observations of the development of surface conduc
tivity during heat treatment have been carried out on
ground and polished surfaces of the glasses. Any surface
effects developed during the moulding of the glasses and
their subsequent annealing were removed by the grinding
process. This did not however apply to the thin ?lms
of the glasses on which determinations of volume resist
An alternative method of utilizing the glass is to pre 70 ivity were carried out and in this case the surfaces of the
pare it in the form of thin ?lms, say between 10"‘1 inch
glasses formed during the blowing operation were re
.and 5 X l0~4 inch thick, by means of a blowing technique,
tained. It is thought that a certain proportion of the
using a silica or stainless steel tube. Resistivity measure
manganese ions in the surface layers of these ?lms were
ments show that ‘the ?lms are volume-conductive, the
converted from the divalent to the trivalent forms result
mode of conduction being electronic. Glass F exhibits 75 ing in the development of volume conducting ?lms of the
3,093,598
6
shaped article from said melt, annealing said article, cool
glasses. Subsequent heat treatment of the ?lms in oxygen
containing atmospheres then resulted in the conversion of
too large a proportion of the divalent ions to the trivalent
form resulting in the development of glass film with in
creased volume resistivity.
It has already been mentioned that an important ap
ing said article to room temperature, grinding and polish
‘ing' the surface of said annealed article, and thereafter
maintaining said article at a temperature within the range
550° C. to 700° C. for a period of approximately four
hours in an oxidizing atmosphere.
8. A process for producing a glass article which is
electronically surface conductive which comprises form
ing a glass melt having the molecular percentage com
plicaton of conductive glasses prepared in accordance with
the present invention is in the manufacture of targets for
“image orthicon” discharge tubes or similar tubes where
thin electronically conducting ?lms or targets are re
quired. Other applications are as electrically conducting
glazes for application to ceramic insulators or other ar
10
ticles, the glaze being fixed on to the ceramic in air or
position, neglecting impurities: silicon, expressed as SiO2,
35-56%; aluminum, expressed as A1203, ‘0-20%; man
ganese, expressed as MnO, 36-55%, the manganese being
predominantly in its Mn+2 valence state; forming a solid
shaped article from ‘said melt, annealing said article, cool
other oxidizing atmosphere to ensure the development of
electronic conductivity in the glaze; or ‘for the construc 15 ing said article to room temperature, grinding and polish
ing the surface of said annealed article, and thereafter
tion of insulators which could be heat treated to develop
maintaining said article at a temperature within the range
electrically conducting surface layers. The last mentioned
550° C. to 700° C. ‘for a period of between thirty min
application would be of use in the graduation of high
utes and approximately four hours in an oxidizing at
voltages between two conductors.
What we claim as our invention and desire to secure 20
mosphere.
9. A process according to claim 8 wherein the glass
melt has the molecular percentage composition: silicon,
tronically conductive which comprises maintaining glass
expressed as SiOZ, 40%; aluminum, expressed as A1203,
10%; manganese, expressed as MnO, 50%, the manganese
having the molecular percentage composition, neglecting
impurities: silicon, expressed as SiO2, 35-56%; aluminum, 25 being predominantly in its Mn+2 ‘valence state.
10. A process according to claim 8 wherein not more
expressed as A1203, 0-20%; manganese, expressed as
than 5 molecular percent of the manganese in the glass
MnO, 36-55%, the manganese being predominantly in
melt is replaced by an alkaline-earth oxide.
its Mn+2 valence state, and said glass also having a soften
by Letters Patent is:
1. A process for producing a glass article which is elec
11. A process for producing an electronically conduc
ing point, measured as the dilatometric turnover tempera
ture, in the range 660-720° C., at a temperature within 30 tive glass article which comprises forming a glass melt
by heating batch materials in an oxidizing atmosphere,
the range 550° ‘C. to 1,000° C. for a period of between
said glass melt having the molecular percentage composi
thirty minutes and approximately four hours in an oxidiz
tion: silicon, expressed as SiOZ, ‘35-56%; aluminum, ex
ing atmosphere.
pressed as Al2O3, 0-20%; manganese, expressed as MnO,
'2. A process as claimed in claim 1 wherein said glass
is in powder form.
35 36-55%, the manganese being predominantly in its Mn+2
valence state; said glass having a softening point, meas
3. A process according to claim 2 wherein the powdered
glass has the molecular percentage composition: silicon,
expressed as SiOg, 40%; aluminum, expressed as A1203,
ured as the dilatometric turnover point in the range of
about 660° C.-720° C., and blowing said melt in an oxi
tion, neglecting impurities: silicon, expressed as SiOz,
13. A process according to claim 11 wherein not more
dizing atmosphere to form an electronically conductive
10% ; manganese, expressed as MnO, 50%, the manganese
being predominantly in its Mn+2 valence state.
40 glass ?lm having a thickness in the range 1X10‘4 to
5 X 10-4 inches.
4. A process according to claim 2 wherein not more
12. A process according to claim 11 wherein the glass
than 5 molecular percent of the manganese in the pow
melt has the molecular percentage composition: silicon,
dered glass is replaced ‘by an alkaline-earth oxide.
expressed as SiOg, 40%; aluminum, expressed as A1203,
5. A process for producing a glass article which is elec
10%; manganese, expressed as MnO, 50%, the man
tronically conductive which comprises sintering glass in
ganese being predominantly in its Mn+2 valence state.
powder form and having a molecular percentage composi
than 5 molecular percent of the manganese in the glass
35-56%; aluminum, expressed as A1203, 0-20%; man
melt is replaced by an alkaline-earth oxide.
ganese, expressed as MnO, (56-55%, the manganese being
14. A process according to claim 13 wherein said al
predominantly in its Mn+2 valence state and said glass 50
kaline-earth oxide is selected ‘from the .group consisting of
also having a softening point measured as the dilatometric
magnesium oxide, calcium oxide and barium oxide.
turnover temperature in the range 660° C. to 720° C.,
15. A manganese silicate glass which is electronically
at a temperature within the range 950° C. to 11-00° C.
volume conductive, having the molecular percentage com
for a period between one hour and three hours in an
oxidizing atmosphere to form said article.
55 position, neglecting impurities: silicon, expressed as SiO2,
6. A process for producing a glass article which is elec
35-56%; aluminum, expressed as A1203, 0-20%; and
manganese, expressed as MnO, 36-55%, the manganese
tronically conductive which comprises maintaining glass
being predominantly in its rMn+2 valence state, said glass
in powder form and [having the molecular percentage
composition, neglecting impurities: silicon, expressed as
SiOg, 35-56%; aluminum, expressed as A1203, 0-20%;
having a softening temperature, measured as the dilato
60 metric turnover temperature, in the range 660-720" C.
manganese, expressed as MnO, 36-55%, the manganese
being predominantly in its Mn+2 valence state and said
glass also having a softening point measured as the dilato
and said glass having been heated in an oxidizing atmos
phere to convert part of said manganese to the Mn+3
valence state, and thereby to produce said electronic con
metric turnover temperature in the range 660° -C. to 720°
C., at a temperature within the range 550° C. to 700° C. 65
ductivity.
neglecting impurities: silicon, expressed as SiO2, 35-56%;
over temperature, in the range 660° C.-720° C. and said
16. A manganese silicate glass as claimed in claim 15
for a period between thirty minutes and four hours in
having the molecular percentage composition: silicon, ex
an oxidizing atmosphere and thereafter sintering the
pressed as SiO2, 40%; aluminum, expressed as A1203,
treated powdered glass in an inert atmosphere to form
10%; manganese, expressed as MnO, 50%, the man
the article.
ganese being predominantly in its Mn+2 valence state;
7. A process for producing a glass article which is elec 70 normal impurities being neglected; said glass having a
tronically surface conductive which comprises forming a
softening temperature, measured as the dilatometric turn
glass melt having the molecular percentage composition,
glass having been heated in an oxidizing atmosphere to
aluminum, expressed as A1203, 0-20%; manganese, ex
convert
part of said manganese to the Mn+3 valence state,
pressed as MnO, 36-55%, the manganese being pre 75
and thereby to produce said electronic conductivity.
dominantly in its Mn+2 valence state; forming a solid
3,093,598
7
17. A glass according to claim 15 wherein not more
than 5 molecular percent of the manganese is replaced by
‘an alkaline-earth oxide.
18. A glass ‘according to claim 17 wherein said alkalineearth oxide is selected from the group consisting of mag- 5
nesiurn oxide, calcium oxide and barium oxide.
References Cited in the ?le of this patent
_
2,290,107
2,720,573
2,785,142
UNITED STAThS PATENTS
Luks ________________ __ July 14, 1942
Lundquist ____________ __ Oct. 11, 1955
MacIntyre ___________ __ Mar. 12, 1957
a‘mnW
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