Mechanical Characterization of Zinc Oxide produced by an optimized Cold Sintering Process
Research output: Thesis › Master's Thesis
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Abstract
Conventional sintering of
ceramics requires relatively high temperatures (> 1000 °C), which are
necessary for solid-state diffusion. Due to the energy crisis and
climate change, energy-saving processes have gained more and more
industrial interest in recent years. A novel alternative sintering
method for the densification of ceramics is the "cold sintering process"
(CSP), which aims to significantly reduce the sintering temperature and
time. In the CSP process, a chemically active liquid phase is added to
the ceramic powder and pressure is applied at relatively low
temperatures (< 300 °C). Recent scientific research has led to
successful densification of numerous ceramic systems using CSP up to a
relative density of 99%. Nevertheless, the mechanical properties of the
samples produced by CSP have been sparsely explored, so their potential
application as structural materials is still unclear. In this work, the
CSP of zinc oxide is investigated and optimized. The aim of this Thesis
was to understand the effects of various processing parameters on the
densification and strength of cold sintered ceramic parts. After
identifying the optimal process parameters, cold sintered samples were
mechanically characterized regarding their strength distribution and
fracture toughness under biaxial bending (B3B-test) and an adapted
B3B-SCF method. The results were compared and discussed with
conventionally sintered counterparts. A process pressure of 200 MPa, a
process temperature of 140 °C, a liquid phase fraction of 2M Formic Acid
of 150 µl/g, a heating rate of 5 °C/min and a 60-minute holding time
were identified as ideal process parameters, resulting in samples with
~97% relative density. Cold sintered ZnO exhibited a characteristic
strength of σ0 = 116 [114 – 118] MPa and a Weibull modulus of m= 11 [9 –
12]. Compared with the conventionally sintered ZnO, CSP was able to
achieve ~50% of the characteristic strength (i.e. σ0 ≈ 220 MPa). The
lower strength of cold sintered samples is attributed to their lower
fracture resistance as confirmed by the fracture toughness measurement
showing a value of KIc = 0.57± 0.05 MPa*m1/2, which is ~50% of the
toughness of conventionally sintered ZnO (i.e. KIc = 1.15 ± 0.07
MPa*m1/2).
Details
Translated title of the contribution | Mechanische Charakterisierung von kaltgesintertem Zinkoxid |
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Original language | English |
Qualification | Dipl.-Ing. |
Awarding Institution | |
Supervisors/Advisors |
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Award date | 20 Oct 2023 |
Publication status | Published - 2023 |