Mechanical and thermal properties of CNT-reinforced quartzite nano-composite for furnace lining
Nigerian local foundries employ the used-imported bricks from iron and steel industries to line the foundry cupola furnace. On the event of the closure of these industries, the alternative left was to identify the locally available refractory material that would be used for most effective lining...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2018
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/77281/1/FK%202018%20179%20ir.pdf |
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| Summary: | Nigerian local foundries employ the used-imported bricks from iron and steel
industries to line the foundry cupola furnace. On the event of the closure of these
industries, the alternative left was to identify the locally available refractory material
that would be used for most effective lining of the cupola. Thus, after several trials of
different locally available clays, natural crystalline quartzite refractory ceramic
material; crystalline silica (SiO2) was eventually resorted to. The main problem
associated with ceramic lining material is lack of good thermal shock resistance. This
is more pronounced with silica/silica-based refractory linings; for instance, lining
material used in a typical local foundry furnace in Kano State of Nigeria and vicinity
that is prepared from local quartzite/crystalline silica, which develops unduly cracks
on its surface during cooling after melting. This has been attributed to poor thermal
conductivity by the previous researchers. To substantially obviate this setback, the
present research aimed to incorporate carbon nanotubes (CNTs) within the matrix of
quartzite brick. This entails manufacturing and characterization of CNT reinforced
quartzite nano-composite. To obtain a stable suspension of CNTs that would be used
in the preparation of homogeneously dispersed nanotubes in the quartzite matrix, the
as-received pristine CNTs were functionalized with 6M H2SO4 acid by
ultrasonication using a water bath sonicator. The pristine/functionalized CNTs were
then comprehensively characterized by Fourier-transform infrared spectroscopy (FTIR),
Raman spectroscopy, Thermogravimetric analysis (TGA), Differential scanning
calorimetry (DSC), and Scanning electron microscopy coupled with Energy
dispersive X-ray spectroscopy (SEM/EDX). Also, the as-mined quartzite and clay
were purified by soaking/washing with water and subsequently dried. The as-dried
raw material were then subjected to crushing, grinding, pulverizing and grading
using Jaw and Cone crushers, ball mill, pulverizer, and size distribution particle
analyzer respectively. This is followed by structural and morphological
characterization of the powdered quartzite and clay by Energy dispersive X-ray fluorescence spectrometer (ED-XRF), X-ray diffraction (XRD), and SEM/EDX. The
durable refractory material for lining foundry cupola is developed by modified
conventional powder processing (wet mixing method); involving preparation, cold
compaction (by manual hydraulic press) and pressureless sintering (using tube
furnace) at 1450oC, for 2 hours dwelling time, under argon atmosphere. Physical,
mechanical, morphological and thermal characterizations were determined for the
sintered 0, 0.01, 1, and 4 wt. % CNT-quartzite nano-composite blends. The compareable bulk density range obtained for the blends; 1.722 - 1.760g/cm3 is an evidance
of a complete densification and good homogeneous dispersion of CNTs in teh green matrices,
thus, good thermo-mechanical properties of the nano-composites. High proportion of tridymite,
low percenttage of residual quartz (1.1%), low reversible thermal expansion, modest tensile
(2.49 MPa), and compressive
strenghts (17.39MPa), moderate Young's modulus; tensile (190MPa), high fracture strain
in tension (0.013027), high (on-duty)thermal shock cycles (7 cycles), high thermal
diffusivity (>8 x 10-7 m2/s at 117'C) and remarkable thermal conductivity >0.2 k/Wm-1
at 117'C of 1wt. % CNT-quartzite nano-composite signifies the possibility of potential
application of CNTs as suntering aid (stabilizer, mineralizer, etc.) and toughening
filler in conventional quartzite/silica refractory mixture for high durability. Finally,
the Levenberg Marquardt Back Propagation Artificial Neural Network (LMBP ANN) models were
developed to predict the physical, mechanicals and thermal properties of the CNT-quartzite
nano-composites having formulations within the range of those employed in the experimental
process through dataset training, validation and testing. Additionally, the Graphical User
Interface (GUI) was created in the study in order to have a user friendly interface for
easy characterization of the CNT-quartzite nano-composites. |
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