TY - THES

T1 - Mechanical Characterization of Zinc Oxide produced by an optimized Cold Sintering Process

AU - Ribul, Elija

N1 - embargoed until 10-10-2026

PY - 2023

Y1 - 2023

N2 - 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).

AB - 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).

KW - Cold Sintering Process

KW - ZnO

KW - Festigkeit

KW - Bruchzähigkeit

KW - B3B-KIc

KW - Cold Sintering Process

KW - ZnO

KW - Strength

KW - Fracture Toughness

KW - B3B-KIc

M3 - Master's Thesis

ER -