FORECASTING THE CHANGE IN ELECTROPHYSICAL PROPERTIES
OF ENGINEERING CERAMICS SUBJECTED TO LONG-TERM HEATING
M. I. Podkovyrkin
Translated from Ogneupory i Tekhnicheskaya Keramika, Nos.7–8,pp.35–39,July – August, 2002.
The changes in electrophysical properties of M-4, UF-46, and M-7 ceramic materials during thermal aging at
170 to 350°C over a testing period of up to 10 thousand hours are measured. Aging mechanisms are consid
ered and semi-empirical analytical models for predicting the resistance of engineering ceramics to long-term
heating are proposed.
Many kinds of engineering ceramics have originally
been intended for long-term service (for tens of thousand
hours) under moderately elevated temperatures. Literature
survey has revealed a nearly complete lack of data concerned
with the effect of long-term temperature exposure on physi-
cal and operational properties of ceramic materials. One of
the major reasons for this state of things is that studies in the
field are labor-intensive and costly. Therefore, forecasting
the possible change in physical properties of ceramics in-
tended for long-term service based on the results of
short-term tests remains an issue of great practical interest.
Our goal in this work was to develop a method that
would enable prediction of changes in the electrophysical
properties of widely used radio engineering ceramic materi
als of types M-4, M-7, and UF-46 subjected to thermal aging.
For that purpose, the change in properties (aging) of these
materials was studied at temperatures of up to 350°C over a
period of 10 thousand hours; based on the data obtained,
forecasting of their behavior for a longer service life (up to
100 thousand hours) was made.
Thermal aging of the M-4, M-7, and UF-46 ceramic test
specimens (available from the “Radiokeramika” Plant,
Yuzhnoural’sk, Chelyabinsk District, Russia) was carried out
using a SNBS-type heating chamber equipped with high-pre
cision VRT-2 controllers. The temperature control precision
was ± 0.5°C. The volume resistivity r
, dielectric constant e,
and loss-angle tangent tan d were measured in conformance
with State Standard GOST 5458–75, and electric strength E
— in conformance with GOST 5775–68.
CHANGES IN THE PROPERTIES OF MATERIALS
SUBJECTED TO LONG-TERM HEATING
Changes in the properties of ceramics heated over time
are clearly nonlinear in character. This poses major problems
for data processing and requires the use of an appropriate
mathematical apparatus. Conventional probabilistic models
for description of functional failures are based on the fami-
liar principle “parameter – tolerance margin” [1, 2]. An ana-
lysis of the electrophysical parameters for M-4, M-7, and
UF-46 ceramic materials measured during the thermal aging
has revealed, despite the large spread in individual test speci
mens, regularities in the change of these parameters. Rele
vant data are presented in Fig. 1a and b. One will note that
the error of measurement (shown by error bars) is rather
large. This notwithstanding, the data were used for develop
ing a method for forecasting the temperature change in ce
ramic properties based on accelerated test results.
Electrophysical properties are directly related to the
composition and structure of crystalline and glassy phases
and their ratio in the ceramics under study . These materi
als, during their thermal aging, are characterized by two time
periods in the change of volume resistivity, dielectric con
stant, and loss-angle tangent.
Within the first two to four thousand hours of heating
time, the volume resistivity r
in M-4, UF-46, and M-7 ma
terials tended to decrease. Within the subsequent period ex
tending to ten thousand hours, there was a tendency for r
increase to the initial level or even higher.
Refractories and Industrial Ceramics Vol. 43, Nos.7–8, 2002
1083-4877/02/0708-0260$27.00 © 2002 Plenum Publishing Corporation
Verkh-Isetskii Metallurgical Plant, Russia.