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Effect of heat treatment on the microstructure and fracture toughness
of glass-ceramics obtained from igneous rocks
Titton, A.P.¹, Ramos, G.R.¹, Perottoni, C.A.¹, Segadães, A.M.², Mantas, P.Q.², Cruz, R.C.D.¹[email protected], [email protected], [email protected], [email protected], [email protected], [email protected]
¹Instituto de Materiais Cerâmicos, Universidade de Caxias do Sul, 95765-000, Bom Princípio – RS
²Universidade de Aveiro, Departamento de Engenharia de Materiais e Cerâmica, 3810-193, Aveiro, Portugal
EXPERIMENTAL
RESULTS AND DISCUSSION
CONCLUSION
SUPPORT
REFERENCES
XV Brazil MRS Meeting – September 25th to 29th, 2016
ACKNOWLEDGMENTS
INTRODUCTIONGlasses are defined as amorphous solids, obtained from abruptly cooled liquid. When subjected
to controlled heat treatments, these glasses undergo partial to complete crystallization and
develop a characteristic microstructure. Partially devitrified materials (glass-ceramics) exhibit
interesting mechanical properties. Igneous rocks, such as basalts and granites, have been used
for centuries as pavement structural element in buildings, support for tubs and sinks in kitchens
and bathrooms and as ornamental rocks. More recently, due to the depletion of traditional
sources of raw materials and environmental issues associated with waste generation in its
processing, this class of rocks, in particular, basalt, was the subject of considerable attention
from European researchers. As raw material for the manufacture of engineering products,
literature shows various studies for the production of the base glass of volcanic rocks. In Asian
and European countries, fibers, fabrics, rods and wires made from cast basalt became products
with increasing demand in the chemical, petrochemical and construction industries (Figure 1)
[1, 2]. In this study it is analyzed the effect of microstructural features on the mechanical
properties of glass-ceramics obtained from basalts of Serra Geral. Different heat treatments
were used to change the type and amount of crystalline phases in the glass-ceramics.
RESULTS AND DISCUSSION
Glass-ceramics were prepared from a basic igneous rock from the Serra Geral Formation, RS,
Brazil (basalt).
Table 2 shows the heat treatments parameters for the samples studied in this work.
Figure 1 – Products for industrial use based on molten basalt
SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O TiO2 MnO P2O5 LoI
50.57 13.83 13.39 10.13 6.11 0.70 2.45 1.33 0.20 0.15 1.13
MELTING – 1550 °C
THERMAL ANALYSIS XRDHEAT TREATMENTS
XRDMICROSCOPY MECHANICAL TESTS
YOUNG'S MODULUS HARDNESS CRACK LENGTH
FRACTURE TOUGHNESS
SampleAnnealing T = 654 °C Crystallization T = 1070 °C
TIME
A+C 0.7 h 0.7 h
A+C(6h) 0.7 h 6 h
A+C(36h) 0.7 h 36 h
The evolution of samples’microstructure was followed by optical microscopy, Figure 4.
5 mm
Figure 4 – Optical microscopy images of samples A+C, A+C(6h) and A+C(36h). All images were taken at a
magnification of 1500x.
Table 2 – Temperatures and times of annealing and crystallization.
The crystallinity index of each sample, plotted in Figure 5, was evaluated as the ratio of the area of the
Bragg peaks to the global area in the corresponding x-ray diffraction pattern (Figure 3).
With the hardness, elastic modulus, and crack length measurements, it was possible to calculate the
fracture toughness of the samples [3,4]. Figure 5 shows the evolution of the fracture toughness together
with the crystallinity index with the increasing of the crystallization time at 1170 ºC. When compared
to vitrified sample, the sample crystallized during 0.7 h showed an increase of ~30% (1.91 MPa.m1/2 )
and the samples crystallized during longer times (6 (1.26 MPa.m1/2) and 36 (1.24 MPa.m1/2) hours)
showed a decrease of ~15% in fracture toughness. In another measurement, for which the vitrified
sample was submitted only to the annealing process (in this case, for 5 hours), the fracture toughness
decreased by 5 times (0.38 MPa.m1/2), (Figure 5). This demonstrates that the glass relaxation is an
aggravating factor. Although a more reliable phase identification would require an auxiliary technique,
such as electron probe microanalysis, the x-ray diffraction patterns of samples submitted to
crystallization show Bragg peaks which are consistent with the presence of plagioclase, pyroxenes,
magnetite (Fe3O4), and hematite (Fe2O3).
Figure 3 – X-ray diffraction patterns of quenched and heat treated samples described in Table 2. The
diffraction patterns were displaced vertically for sake of clarity.
An increase of the crystallinity index and of the size of the crystals is accompanied by a decrease of
the fracture toughness of glass-ceramics obtained from igneous basaltic rocks from Serra Geral
Formation. The maximum fracture toughness was observed for the sample kept for 0.7 h at the
crystallization temperature, which exhibited only small crystals, thus suggesting that probably it is the
nucleation steps that promote the mechanical strength in these glass-ceramics.
The authors acknowledge the financial support from the Secretaria de Desenvolvimento Econômico,
Ciência e Tecnologia do Estado do Rio Grande do Sul (SDECT/RS), Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento
Científico e Tecnológico (CNPq). Thanks are due to Janete Zorzi for her help on the mechanical tests.
[1] Pelino et al – Characterization of basaltic tuffs and their applications for the production of ceramic and glass-
ceramic materials – Ceramics International 35, 2789-2795 (2009)
[2] Karamanov et al – Ceramic material from basaltic tuff - Industrial Ceramics 27 (2), 89-94 (2007).
[3] Rangel, E. R. Fracture Toughness Determinations by Means of Indentation Fracture. Nanocomposites with Unique
Properties and Applications in Medicine and Industry, Dr. John Cuppoletti (Ed.), 2011.
[4] Kruzic, J. J.; Ritchie, R. O. Determining the Toughness of Ceramics from Vickers Indentations Using the Crack-
Opening Displacements: An Experimental Study. Journal of the American Ceramic Society, 86 [8] 1433–36 (2003).
Figure 2 – DSC measurement of vitrified basalt.
Table 1 – Basalt chemical composition obtained by XRF. The values are in wt. %. LoI means loss on ignition.
QUENCHING
Table 1 shows the chemical composition of the as-received rock determined by XRF. The
amount of SiO2, ca. 50%, is typical for basalts, a basic rock. Two crystallization peaks were
identified by DSC of the vitrified basalt obtained by quenching (Figure 2). Using this
information, the heat treatments were performed at temperatures up to 1070 °C.
Figure 5 – Fracture toughness and crystallinity index as a function of square root of time, t, at the
crystallization temperature.
0 1 2 3 4 5 6
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
KIC
Crystallinity index
t1/2
(h1/2
)
KIC
(M
Pa.
m1/2)
Only annealing for 5 hours
0
10
20
30
40
50
60
70
80
90
100
Cry
stal
linit
y i
ndex
(%
)
