Optimal design and freeform extrusion fabrication of functionally gradient smart parts

An extrusion-based additive manufacturing process, called the Ceramic On-Demand Extrusion (CODE) process, for producing three-dimensional ceramic components with near theoretical density was developed. In this process, an aqueous paste of ceramic particles with a very low binder content (\u3c1 vol%) is extruded through a moving nozzle at room temperature. After a layer is deposited, it is surrounded by oil (to a level just below the top surface of most recent layer) to preclude non-uniform evaporation from the sides. Infrared radiation is then used to partially, and uniformly, dry the just-deposited layer so that the yield stress of the paste increases and the part maintains its shape. The same procedure is repeated for every layer until part fabrication is completed. Sample parts made of alumina and fully stabilized zirconia were produced using this process and their mechanical properties including density, strength, Young\u27s modulus, Weibull modulus, toughness, and hardness were examined. Microstructural evaluation was also performed to measure the grain size, and critical flaw sizes were obtained. The results indicate that the proposed method enables fabrication of geometrically complex parts with superior mechanical properties. Furthermore, several methods were developed to increase the productivity of the CODE process and enable manufacturing of functionally graded materials with an optimum distribution of material composition. As an application of the CODE process, advanced ceramic components with embedded sapphire optical fiber sensors were fabricated and properties of parts and sensors were evaluated using standard test methods --Abstract, page iv

Additive manufacturing of non plastic porcelain material by direct writing and freeze casting.

Two direct consolidation methods usually used for advanced ceramics have been combined in this project in order to develop a novel fabrication route for traditional ceramics. Specifically the method used is based on the Additive Manufacturing extrusion process using direct writing of high solid loading ceramic pastes and then freeze-casting to solidify the deposited material. This novel fabrication method, for which a patent has been granted, has been christened “Direct Writing Freeze-Casting” (DWFC). Although the DWFC process is the subject of investigation by other researchers for a range of different applications, including the production of medical implants with alumina, the research presented in this thesis focuses on its use in the manufacture of white wares, giftware, and applied arts and crafts in general. This new system will provide designers, potters, artists, craft makers and manufacturers with a flexible and automated way of manufacturing porcelain objects. One of the major challenges to be overcome to exploit the DWFC process is the development of suitable slurry material formulations. Initial trials demonstrated that it is not possible to use conventional clay based porcelain materials with a platelet shaped microstructure which inhibits freeze casting. In this thesis the development and characterisation of non plastic porcelain slurry, based on substitution of kaolin (clay) with a calcined clay material (molochite), which can be processed using this new method is presented. The new non plastic porcelain formulation, which has a high solid load of 75.47% wt., has been subjected to detailed analysis to assess its suitability at each stage of the process; extrusion, freeze-casting (solidification) and firing.National Consul of Sciences and Technology Mexico, CONACY

Additive Manufactured Zirconia-Based Bio-Ceramics for Biomedical Applications

Zirconia was established as one of the chief vital ceramic materials for its superior mechanical permanency and biocompatibility, which make it a popular material for dental and orthopedic applications. This has inspired biomedical engineers to exploit zirconia-based bioceramics for dental restorations and repair of load-bearing bone defects caused by cancer, arthritis, and trauma. Additive manufacturing (AM) is being promoted as a possible technique for mimicking the complex architecture of human tissues, and advancements reported in the recent past make it a suitable choice for clinical applications. AM is a bottom-up approach that can offer a high resolution to 3D printed zirconia-based bioceramics for implants, prostheses, and scaffold manufacturing. Substantial research has been initiated worldwide on a large scale for reformatting and optimizing zirconia bioceramics for biomedical applications to maximize the clinical potential of AM. This book chapter provides a comprehensive summary of zirconia-based bioceramics using AM techniques for biomedical applications and highlights the challenges related to AM of zirconia

Effect of Fabrication Methods on the Porosity, Microstructure, Strength and In-Vitro Bioactivity of Porous Hydroxyapatite Scaffolds

Porous Hydroxyapatite (HA) scaffold has been prepared from stoichiometric HA powder. The HA powder has been prepared in the laboratory by the wet chemical method. The as-prepared powder was amorphous. On calcination at 850oC, stoichiometric HA powder crystallized. The HA phase was stable till 1250oC and Tricalcium phosphate (TCP) formed at 1300oC. The HA scaffolds were prepared by three different routes. In the Solid State Fugitive route, porous HA scaffolds were prepared by mixing HA powder and Naphthalene (NA) granules. Five different volume percent (30, 40, 50, 60 and 70) NA was used. At a lower NA content, mostly isolated open pore were observed. Large and interconnected pores were seen at 50 and 60 vol% NA addition. The strength - porosity variation showed an inverse relation and the strength was low at 60 vol% NA. At 70vol%, NA strength could not be measured due to the fragile nature of the sample. The microstructures of Simulated body Fluid (SBF) aged porous HA scaffold show that apatite formation starts from the surface of large grains. The scaffolds prepared by Gel Casting Route had only 22% porosity. When NA was additionally added, the porosity and interconnectivity increased. At 45vol% NA addition, the pores were mostly open pores. The interconnectivity increases with the increase in NA content. At 45 vol% NA, the compressive strength was 0.96 MPa. In-vitro bioactivity showed that the apatite growth was more in higher porosity samples. With the increase in aging time, the morphology of the deposited apatite changed from granular to flower like. After 21 days aging, petal-like apatite crystals were observed. Porous scaffolds were also prepared by Protein Coagulation Casting method using Egg white as the foaming and binding agent. The foaming behavior was modified by varying the Egg White: Water (EWH) ratio (1:1, 1:2, 1:3, and 1:4). The foaming was less at higher water contents. The foaming was also less in pure Egg white sample. It was also noted that at a higher Egg White: Water ratio, foaming was more. At any EWH ratio, the minimum solid loading that could be cast without cracking was nearly ten times the foam height. The cracking of the samples at a lower solid loading was related to the fast foam drainage rate. Use of Poly-vinyl alcohol (PVA) and Nitric acid (HNO3) reduced the drainage rate and reduced the cracking tendency. The in-vitro bioactivity tests showed that the apatite crystals were globular shaped. The porosity development was non-uniform in the Protein Coagulation Casting method. In the summary, it can be said that the three different methods of scaffold preparation produced different microstructures and pore sizes. The different microstructures resulted in varying compressive strength and bioactivity

Transparent polycrystalline ceramics at visible and infrared wavelenghts

Tato práce se zabývá přípravou průhledných keramických plátů vyrobených ze sub-µm prášku oxidu hlinitého. Zhutnělá keramická tělesa jsou připraveny ultrafialovým (UV) vytvrzováním UV vytvrzovací pryskyřice obsahující keramický prášek s následným vypálením organické složky za zvýšené teploty. Vysoká relativní hustota takto vypálených těles je nezbytná ke snížení smršťování během následujícího slinovacího procesu. Proto jsou použity vysoce plněné disperse obsahující > 57 obj.% keramických částic. K dosažení transparentního chování, porozita uvnitř plátů musí být úplně odstraněna. Proto jako závěrečné operace je použito isostatického stlačování za zvýšené teploty. Nakonec jsou prezentovány měření světelné propustnosti a tvrdosti. Možnosti výroby mikrostruktur s vysokým rozlišením za použití bezmaskové litografie a návrhy na použití UV vytvrzovací metody pro produkci tvarově náročných 3D struktur jsou krátce zmíněny.his thesis deals with preparation of transparent ceramic sheets made out of sub-µm alumina powder. Green bodies are prepared by ultraviolet (UV) curing of UV curable resin containing ceramic powder followed by debinding of organic parts at elevated temperature. High relative density of green bodies is essential for reduction of shrinkage during subsequent sintering process. Therefore high solids loading dispersions containing > 57 vol% ceramic particles are used. To reach transparent behaviour, porosity within the sheets must be reduced completely. Therefore hot isostatic pressing (HIP) is used as a final operation. Finally, light transmission and hardness measurements are presented. Possibilities of making high resolution microstructures using maskless lithography and some suggestions for use of the UV curing technique for production of complex-shaped 3D structures are briefly mentioned.

Sintering Applications

Sintering is one of the final stages of ceramics fabrication and is used to increase the strength of the compacted material. In the Sintering of Ceramics section, the fabrication of electronic ceramics and glass-ceramics were presented. Especially dielectric properties were focused on. In other chapters, sintering behaviour of ceramic tiles and nano-alumina were investigated. Apart from oxides, the sintering of non-oxide ceramics was examined. Sintering the metals in a controlled atmosphere furnace aims to bond the particles together metallurgically. In the Sintering of Metals section, two sections dealt with copper containing structures. The sintering of titanium alloys is another topic focused in this section. The chapter on lead and zinc covers the sintering in the field of extractive metallurgy. Finally two more chapter focus on the basics of sintering,i.e viscous flow and spark plasma sintering

Bioceramic Composites

Biomaterials—the materials used for the manufacturing of medical devices— are part of everyday life. Each one of us has likely had the experience of visting a dentist’s office, where a number of biomaterials are used temporarily or permanently in the mouth. Devices that are more complex are used for to support, heal, or replace living tissues or organs in the body that are suffering or compromised by different conditions. The materials used in their construction are metals and metallic alloys, polymers—ranging from elastomers to adhesives—and ceramics.Within these three cases, there are materials that are inert in the living environment, that perform an active function, or that are dissolved and resorbed by the metabolic pathways. Biomaterials are the outcome of a dynamic field of research that is driven by a growing demand and by the competition among the manufacturers of medical devices, with innovations improving the performance of existing devices and that contribute to the development of new ones. The collection of papers forming this volume have one particular class of of biomaterial in common, ceramic (bioceramic) composites, which as so far been used in applications such as orthopaedic joint replacement as well as in dental implants and restorations and that is being intensively investigated for bone regeneration applications. Today’s bioceramic composites (alumina–zirconia) are the golden standard in joint replacements. Several manufracturers have proposed different zirconia–alumina composites for use in hip, knee, and shoulder joint replacements, with several other innovative devices also being under study. In addition, bioceramic composites with innovative compositions are under development and will be on the market in years to come. Something that is especially interesting is the application of bioceramic composites in the regeneration of bone tissues. Research has devoted special attention to the doping of well-known materials (i.e., calcium phosphates and silicates) with bioactive ions, aiming to enhance the osteogenic ability and bioresorbability of man-made grafts. Moreover, high expectations rely on hybrid biopolymer/ceramic materials that mimic the complex composition and multiscale structure of bone tissue

Novel indirect additive manufacturing for processing biomaterials

PhD ThesisThe aim of this work was to identify methods for the production of patient-specific biomedical devices via indirect additive manufacturing (AM) methods. Additive manufacturing has been shown to provide a good solution for the manufacture of patient specific implants, but in a limited range of materials, and at a relatively high cost. This research project considered what are known as “indirect” AM approaches, which typically consider AM in combination with one or more subsequent processes in order to produce a part, with a maxillofacial plate and mandible resection used as a demonstrator application. Three different approaches were considered: (i) using AM to produce moulds for powder pressing of bioceramic green parts for subsequent sintering; (ii) using AM to produce moulds for biopolymer sintering; and (iii) 3D printing of bioceramic powders into green parts for subsequent sintering. Apatite wollastonite glass ceramic (AW) and poly-Lactide-co-glycolide (PLGA) were selected as the bioceramic and biopolymer materials to process. These were characterised before and after processing in order to ensure that the processing route did not affect the material properties. Geometric dimensions, the morphological structure and mechanical properties were studied to establish the accuracy, shrinkage and strength of the fabricated biomaterial implants. The use of AM processes to produce moulds for PLGA sintering, and the 3D printing of bioceramic powders formed the best overall results in terms of the definition and properties of the manufactured parts. Parts produced were accurate to within 5% of the as designed dimensions for both the PLGA sintering and the bioceramic powders 3D printing. The indirect AM methods are considered to be promising processing routes for medical devices.University Malaysia Perlis and the Malaysian Higher Education Ministr