RESEARCH IN THE AREA OF PREPARING MATERIALS
BASED ON FUZED QUARTZ HCBS.
PART 4. STUDY OF ISOTHERMAL AND NONISOTHERMAL
Yu. E. Pivinskii
and P. V. Dyakin
Translated from Novye Ogneupory, No. 4, pp. 20 – 28, April, 2015.
Original article submitted November 13, 2014.
Isothermal and nonisothermal sintering are studied for castings based both on fuzed quartz suspensions with
different fineness, and cast systems with a granular filler based on them. An effect is detected of considerable
sintering of the test materials in the specimen heating stage (nonisothermal sintering) up to a final firing tem
perature of 1250°C. Depending on original specimen solid phase dispersion and particle grain size composi
tion for the majority of materials their optimum properties are achieved after isothermal exposure for
0.5 – 1.0 h at 1250°C. Although exceeding it is accompanied by a certain reduction in porosity, it is connected
with material weakening in view of the initial stage of christobalitization.
Keywords: fuzed quartz HCBS, isothermal and nonisothermal sintering, cristobalite, nanoparticles, integral
and differential particle distribution, highly-dispersed fuzed quartz, polydispersion coefficient K
, slip casting,
porosity, shrinkage during sintering.
By sintering ceramic or refractory materials it is normal
to understand a thermal activation process occurring within a
porous semifinished product (compact, casting, etc.) under
action of surface tension forces, leading to strengthening of a
system and facilitating its transition into a thermodynami
cally more equilibrium condition [1 – 3]. From a physical
viewpoint sintering is an arbitrary process of reducing a dis
persion-porous body free energy on heating. The “moving
force” of the process is the free energy of particles [1, 4].
From a production point of view sintering is a process of pre
paring a strong lightly porous stone-like body from semifin
ished product with action of high temperature. In ceramic
and refractory technology the sintering mechanism is imple
mented by means of firing, i.e., heat treatment, including
heating material, exposure at a maximum temperature, and
cooling to room temperature. In ceramic and refractory tech
nology firing is normally classified as the most energy-con-
Compared with sintering other ceramic and refractory
materials, sintering those based on HCBS of transparent and
opaque quartz glass differs in a number of features. To a sig
nificant extent features are caused by an exceptionally high
degree of fine particle packing directly in the stage of a
molded semifinished product [1, 5 – 8]. As a result of this
high or even similar to maximum achievable values of me
chanical strength of quartz ceramic are achieved with insig
nificant (1.0 – 1.5%) shrinkage indices or proportion of
sintering pores [1 – 4]. On the other hand, for the over
whelming majority of forms of quartz ceramic or refractories
as a result of the features noted a requirement for achieving a
densely sintered condition is superfluous. In addition, along
side the advantages noted above on sintering materials of the
class in question under certain conditions unfavorable forma
tion of cristobalite within them is possible [1, 5, 9, 10].
In contrast to all other ceramic and refractory materials
quartz ceramic has an amorphous (glassy) condition. Pres
ence within it of a marked amount of crystalline phase leads
to a reduction in thermal shock resistance and mechanical
strength. In this connection quartz ceramic from the point of
Refractories and Industrial Ceramics Vol. 56, No. 2, July, 2015
1083-4877/15/05602-0172 © 2015 Springer Science+Business Media New York
Part 1 of the article was published in Novye Ogneupory No. 7
(2014), and Parts 2 and 3 in Nos. 1 and 3 (2015).
OOO NVF Kerambet-Ogneupor, St. Petersburg, Russia.
FGBOU VPO St. Petersburg State Technological University
(Technical University), St. Petersburg, Russia.