Abstract
Transparent alumina doped with rare‐earth or transition metal oxides represents a group of materials suitable for optical applications. Because of the birefringence of alumina, their ...preparation is demanding on the quality of starting materials, their advanced shaping, and pressure‐assisted sintering. Spark plasma sintering and hot isostatic pressing have proven at achieving pore‐free fine microstructures exhibiting high in‐line transmission and a sufficient intensity of emitted light. The present review aims to summarize the results published on this topic, to compare them and on this base to propose other possible and/or appropriate approaches to future.
In this study, a reproducible method of fabricating hierarchically 3D porous scaffolds with high porosity and pore interconnectivity is reported. The method is based on in-situ foaming of a ...dispersion of diisocyanate, polyol, water and hydroxyapatite (HA) to form a hard foamed HA/polyurethane composite which after heat treatment provided a bi-phase calcium phosphate scaffold. This technique, combining the advantages of polymer sponge and direct foaming methods, provides a better control over the macrostructure of the scaffold. A modification of the multi-scaled porous macrostructure of scaffolds produced by changing the ratio of input reactants and by sintering temperature was studied. The pore morphology, size, and distribution were characterized using a scanning electron microscope and mercury porosimetry. The pores were open and interconnected with multi-scale (from several nanometres to millimetres) sizes convenient for using in tissue engineering applications. The bioactivity was confirmed by growing an apatite layer on the surfaces after immersion in simulated body fluid. The material was biocompatible, as shown by using normal human adipose tissue-derived stem cells (ASC). When seeded onto the scaffolds, the ASC adhered and remained healthy while maintaining their typical morphology.
The contribution deals with modelling and prediction of failure of mechanically loaded open cell ceramic foam structures by using 3D volume FE models constructed from CT scans of real foam specimens. ...The condition for crack initiation in particular struts comes from the coupled stress-energy criterion which combines two fracture-mechanics parameters of the investigated material – tensile strength and its fracture toughness. By combining of both stress and energy condition one obtains information about the crack initiation length which is later used (together with the tensile strength) for determination of the strut failure in the complex 3D FE model of the ceramic foam structure. The crack onset is considered in the critical location at the moment when the (tensile) principal stress under the strut surface (in a depth corresponding to the crack initiation length) exceeded the tensile strength of the strut. Such approach enables us to define failure also on relatively coarse meshes of the FE models where potential stress concentrations are not described precisely and therefore it is not possible to decide about the failure just based upon the value of tensile stress on the strut surface.
The proposed material design of BaTiO3/Al2O3/ZrO2 laminate structure predetermined for energy harvesters taking advantage of residual stresses developed during processing was prepared by ...electrophoretic deposition. The main aim of developed residual stresses is to enhance overall mechanical reliability of piezoceramic functional layers and/or to enhance piezoelectric effects acting in the laminate. The concept of co-sintered BaTiO3 piezo ceramic functional layers with protective ZrO2 and Al2O3 layers is based on strongly bonded layers. In this contribution will be described particular behaviour of the specific material configuration BaTiO3/Al2O3 laminate where an interface interlayer among other effects was formed. The influence of sintering conditions on the microstructure development of the laminate as well as the formation of the interlayer was investigated. The relationship between observed microstructural changes and resulting mechanical properties as hardness and indentation elastic modulus was analyzed by means of nanoindentation technique. The cracks propagation through the individual layers and specific formed interfaces were observed and analyzed. The crack deflection due to the presence of developed residual stresses during the cooling stage of sintering as well as the consequence of microstructural changes on mechanical properties was confirmed.
The present study deals with ballistic performance of corundum and silicon carbide ceramics against 7.62 mm calibre projectile. In particular, ceramic samples of dimension 100 x 100 mm with various ...thickness in the range of 6.94 – 6.96 mm and 7.77 - 7.79 mm were glued to Al plate with thickness of 8 mm and tested against 7.62 mm calibre projectiles, namely 30.06 M2 AP, 7.62 mm x 51 AP (WC) and 7.62 mm x 54 R B32. The conducted tests have provided the V50 value for tested materials composed of 8 mm Al plate and ceramic.Furthermore, applying linear approximation the value V50 for normalized ceramic areal density of 26 kg/m2 was calculated. From the given V50 values, the energy of projectile absorbed in ceramic and in Al plate was also calculated. Finally, the results showed that corundum ceramic exhibited significantly lower ballistic efficiency probably due to lower thickness (26 kg/m2 corresponds to thickness of 6.61 mm) in comparison with SSiC ceramic (26 kg/m2 corresponds to thickness of 8.33 mm). The highest efficiency showed 7.62 mm x 51 AP (WC) with a hard core against both ceramics. An unexplained point remains similar V50 value for 30.06 M2 AP and 7.62 mm x 54 R B32 projectile for corundum ceramic and significantly different for SSiC ceramic.Graphical abstract
The work was focused on the preparation of layered ceramic materials and their characterizations. The direct measurment of weight deposite for enhanced description of one component system was studied ...within this work. The kinetics of electrophoretic deposition obtained from theoretical calculation and from experimental values were confronted. It was prepared a lot of depositions for described kinetic of electrophoretic deposition with applied constant currents. The relative density and porosity were determined on the annealled and sintered bodies. The hardness measurments were performed on sintered bodies and then resulted values were confronted with the used currents. A ceramic composite based on Al2O3 and ZrO2 was prepared by using of precision describtion of electrophoretic deposition kinetic.
The doctoral thesis is orientated to preparation of advanced ceramic materials by electrophoretic deposition (EPD). The vertical mode of EPD in constant current regime was used in this study. The ...morphology of prepared materials (image structural analysis), physical properties (EPD yields, relative density, roughness of deposit surface) and mechanical properties (hardness, fracture toughness, elastic module) were characterized on the prepared deposits from alumina (Al2O3), zirconia (ZrO2) or their composites. It was found that the surface charge of alumina or zirconia particles was opposite (inversion charge) in stabilized isopropanolic dispersions than in case of water dispersions. The model of alumina or zirconia particles “inverse” stabilization was proposed. This type of EPD was further studied in presence of different acidic stabilizers. The obtained results from the experimental work (-potential and electric conductivity of dispersions, EPD yields, relative density of deposits, roughness of deposit surface etc.) showed the monochloracetic acid as the optimal type of acidic stabilizer. The kinetic of EPD process from dispersions containing isopropanol, monochloracetic acid and Al2O3 or ZrO2 particles and its influence on the final properties of prepared deposits was studied. The new method of kinetic measurement was developed. Due to good knowledge of EPD kinetic the ceramic laminates (Al2O3/ZrO2) with optimized layer thickness were prepared. The internal stresses and their influence on crack trajectory in ceramic laminates contained 100-150 strongly bonded layers were studied. It was found that the dominant role of crack deflection played the internal compressive stresses, i.e. with increasing of amount of internal compressive stresses the crack deflection was also increased. This work brought a new knowledge in the area of non-aqueous ceramic dispersion stabilization and preparation of heterostructured ceramic materials.
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