Impact of doping agent and processing parameters on spray drying the alumina nanocomposite colloidal suspensions.

This thesis was mainly concentrated on achieving the optimized formulation of doped and un-doped alumina suspensions in order to obtain spray-dried granules with the highest solid content, solid spherical morphology and narrow size distribution. The impact of the primary particle size (0.3, 0.6 and 1 μm) and the added amount of doping agent (0.065 and 0.195 vol.%) on the optimized formulation of the suspensions were investigated. The results indicated that the solid content had to be decreased as the primary particle size was reduced. The highest solid content for the suspension of 1 μm powder was 70% (with 0.3 wt% dispersant) whereas, it reached to 50 wt% (with 0.2 wt% dispersant) for the suspension of 0.3 μm powder. Moreover, it was found that any solid content more than the optimized amount resulted into huge irregular, rod shaped and elongated structures whereas any dispersant amount more than the optimized amount ended into donut-shaped or spherical granules with the blow holes on their external surface. The effect of doping agent, graphene oxide (GO), was clearly seen on increasing viscosity of the suspensions which resulted from the electrostatic interaction of neg- atively charged GO sheets and positively charged alumina particles. However, effect of GO on increasing the viscosity of the suspension for micron sized (1 μm) powder was not as strong as it was for the submicron sized powders. This effect was more pronounced when submicron sized primary particles (0.3, 0.6 μm) were used for the alumina suspensions. As a result of the increase in viscosity, 0.3 wt% dispersant was used for the doped suspensions of the submicron sized powder. Furthermore, 10 wt% reduction of solid content of the suspensions was required when the added amount of GO was increased from 0.065 vol.% to 0.195 vol.%

Breathable, Flexible, Transparent, Hydrophobic, and Biotic Sustainable Electrodes for Heating and Biopotential Signal Measurement Applications

Pressure to reduce the global amount of e-waste has increased in recent years. The optimal use of natural resources is a demanding area especially due to the overabundance of the use of resources and challenges with after-life disposal. Herein, an easy method is developed to fabricate an improved version of leaf skeleton-based biodegradable, transparent, flexible, and hydrophobic electrodes. A fractal-like rubber leaf skeleton is used as the substrate, physical vapor deposited Au interlayer to promote adhesion, and uniform deposition of overlayer silver nanowires. The fabricated surfaces present a high level of electrical stability, optical transparency, hydrophobicity, and robust mechanical properties. The prepared electrodes demonstrate a comparable level of optical transmittance to the virgin leaf skeleton. The mechanical sturdiness of the electrodes is verified by 1k bending cycles. To demonstrate the functionality of these hybrid biotic conductive network (HBCN) electrodes, their performance is evaluated as flexible transparent heating elements and as biosignal measurement electrodes. The heater can reach a temperature of 140 °C with only 2.5 V in ≈5 s and Ag nanowire loading of ≈160 μg cm−2. Likewise, electrocardiogram (ECG) and electromyogram (EMG) signals are successfully obtained from the electrodes without using any electrode gel or other electrolytes.publishedVersionPeer reviewe

Vat photopolymerization of biomimetic bone scaffolds based on Mg, Sr, Zn-substituted hydroxyapatite : Effect of sintering temperature

In response to the urgent demand for innovative bone regeneration solutions, the focus of this study is to develop and characterize Mg, Sr, Zn-substituted calcium phosphate scaffolds that replicate the trabecular architecture of cancellous bone. Ion substitution represents a promising approach to improve the biological effectiveness of calcium phosphates and composite materials used in bone tissue engineering applications. Porous scaffolds mimicking the natural bone structure were additively manufactured from the photosensitive ceramic suspensions for vat photopolymerization using digital light processing. The impact of the selected trace elements (0, 1 and 5 mol.% substitution) and the sintering temperature (900, 1000, 1100, 1200, and 1300 °C) was investigated in relation to the obtained crystalline phase content, microstructure, elemental distribution, thermal stability, and mechanical properties. After sintering, in addition to hydroxyapatite, β-tricalcium phosphate was detected as a result of the added trace elements in the calcium-deficient hydroxyapatite used as a starting powder. The obtained scaffolds exhibited uniform distribution of the trace elements, and they feature 3D-designed porosity predominantly ranged from 10 to 900 μm in diameter, with an average pore size of 546.25 ± 10.95 μm. The total porosity of scaffolds was 76.24 ± 1.32 vol% and an average wall thickness of 217.03 ± 8.98 μm, closely resembling the morphology of cancellous bone tissue. The mechanical properties of the scaffolds sintered at 1100 °C, 1200 °C, and 1300 °C were in line with those typically observed in trabecular bone. The study demonstrates the feasibility of using custom made bioactive hydroxyapatite powders together with vat photopolymerization to design the porosity and properties of the bone scaffolds on demand, based on the requirements of individual bone defects.Peer reviewe

Impact of doping agent and processing parameters on spray drying the alumina nanocomposite colloidal suspensions.

This thesis was mainly concentrated on achieving the optimized formulation of doped and un-doped alumina suspensions in order to obtain spray-dried granules with the highest solid content, solid spherical morphology and narrow size distribution. The impact of the primary particle size (0.3, 0.6 and 1 μm) and the added amount of doping agent (0.065 and 0.195 vol.%) on the optimized formulation of the suspensions were investigated. The results indicated that the solid content had to be decreased as the primary particle size was reduced. The highest solid content for the suspension of 1 μm powder was 70% (with 0.3 wt% dispersant) whereas, it reached to 50 wt% (with 0.2 wt% dispersant) for the suspension of 0.3 μm powder. Moreover, it was found that any solid content more than the optimized amount resulted into huge irregular, rod shaped and elongated structures whereas any dispersant amount more than the optimized amount ended into donut-shaped or spherical granules with the blow holes on their external surface. The effect of doping agent, graphene oxide (GO), was clearly seen on increasing viscosity of the suspensions which resulted from the electrostatic interaction of neg- atively charged GO sheets and positively charged alumina particles. However, effect of GO on increasing the viscosity of the suspension for micron sized (1 μm) powder was not as strong as it was for the submicron sized powders. This effect was more pronounced when submicron sized primary particles (0.3, 0.6 μm) were used for the alumina suspensions. As a result of the increase in viscosity, 0.3 wt% dispersant was used for the doped suspensions of the submicron sized powder. Furthermore, 10 wt% reduction of solid content of the suspensions was required when the added amount of GO was increased from 0.065 vol.% to 0.195 vol.%

A comprehensive review of the photopolymerization of ceramic resins used in stereolithography

In recent years, there have been rapid advances in our understanding of ceramic stereolithography (CSL) as a precise and high-resolution additive manufacturing (AM) technique to fabricate complex ceramic parts. This review highlights the theoretical background and engineering capabilities of CSL with an emphasis on photopolymerization of ceramic resins. We present certain constraints and characteristics designed to achieve optimal printability and photo-curability goals in ceramic resins and discuss in details about the parameters that can affect these properties. We then describe the current market status of CSL as well as its remaining challenges and promising future directions.publishedVersionPeer reviewe

Fabrication of self-supporting structures made of washcoat materials (γ-Al2O3-CeO2) by ceramic stereolithography : Towards digital manufacturing of enhanced catalytic converters

Despite increasing interest in the use of alternative fuel, conventional diesel or gasoline powered vehicles still dominate road transportation; removal of their emitted pollutants is a challenge to sustainable transportation. The automotive industry has employed catalytic converters (CCs) to effectively modify or eliminate toxic pollutants emitted by combustion engines. The efficiency of a CC greatly depends on its geometry and is hindered by limitations in fabrication techniques. To go beyond these limits and further enhance the performance of CCs, one can use state-of-the-art ceramic stereolithography (CSL) technology, which enables fabrication of complex-shaped structures. In this work, a novel photocurable ceramic resin made of γ-Al2O3 and CeO2 (the commonly used washcoat materials in CCs) is shaped into the honeycomb and twisted honeycomb structures using CSL. Measurements reveal that upon the addition of CeO2 to the plain γ-Al2O3 resin, the penetration depth of light is significantly decreased from 408.06 μm to 75.19 μm. This research also focuses on the balance between having a high surface area and achieving good physical stability in the printed structures. Accordingly, the appropriately debinded structures are sintered at two different temperatures: 900 °C and 1100 °C. It is found that the structure sintered at 900 °C has a higher surface area, and thus, it is a better candidate for catalytic applications. Furthermore, investigation of the stabilizing effect of CeO2 on printed γ-Al2O3 finds that CeO2 is effective in stabilizing the printed γ-Al2O3 at1100 °C but not 900 °C. Targeting the realization of green and sustainable transportation, the applied CSL technique in this study enables flexible control in the design and fabrication of self-supporting structures that are expected to open promising ways for the optimization of CCs.publishedVersionPeer reviewe