Development of water-based core technology for light alloys

This thesis describes, in a manufacturing context, the development of new waterbased core technology for light alloys. Cores used for steel casting are made from fused silica and are removed using hot sodium hydroxide under refluxing (pressurising hot acids). However, aluminium and other light alloys are attacked by sodium hydroxide. Currently there is no good core system for aluminium and other light alloys. It is therefore desirable to find an alternative material/leaching agent combination for casting aluminium and other light alloys. The recent research review has shown that ceramic cores are mostly made by fused silica with different additives. The previous research has suggested using fused silica (different mesh size) as filling material and using magnesium oxide to control the slurry working life of core mixes. Calcium silicate assists core leaching in dilute acid. The plaster (calcium sulphate) in the form of proprietary plasters (Crystcal R, Fine Casting Plaster) is used to create bond and gives strength to the core. Lithium carbonate acts has an accelerator, improving the strengthening effect of the plaster in the cores. The binder (Ludox® AM) and water act (as added materials) to bind the composition Core compositions were made with different core trials to produce a core, which records suitable strength and quick leaching properties for light alloys. Core trials were individually mixed and poured into a wooden core box. Cores were pre-dried for twenty-four hours. Cores were fired to different temperatures for two hours, followed by two hours cooling. The cores were subjected to computerised three-point bend test to record the Modulus of rupture (MOR). The plain strain fracture toughness and Weibull parameters were calculated. The Weibull parameter was plotted using Minitab analysis software. Using the cores, gravity die casting process were carried out. The subsequent castings was dipped in diluted nitric, citric and acetic acid to leach out the core. Using different core compositions, core trials were mixed, poured, dried, tested and leached. The high amount of plaster in core trials records high MOR when cores were fired between 200°- 400° C and the opposite result when fired between 600°- 800° C. The different grade of plasters(CRP,FCP) do not influence the strength. One percent of magnesium oxide gives a very short working life. High amount of binder(Ludox® AM) in core produce strong cores. Workable MOR results can be obtained depending on composition allowing manual handling or a waxing process. The fracture toughness is typical of a brittle material, with matching Weibull parameters. The casting process suggests that the new materials are sufficiently refractory. The cores are leached out using diluted nitric, acetic and citric acid at rates compatible with commercial manufacture. This methodology has successfully produced a core using fused silica with plaster and magnesium oxide for aluminium and possibly for light alloys. Different core trials can be used depending on the specific industrial application relating to strength and removal with acid attacking the metal. Further work is needed to fine tune optimum leaching conditions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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

Tableware for everyday food and feast: the ceramics of Fay Morris.

Master of Arts in Fine Art. University of KwaZulu-Natal, Pietermaritzburg, 2018.This practice-based MAFA-R consists of integrated theoretical and practical components. The theoretical component is divided into two volumes, with Volume I looking at the potential of commensality (eating together) to create a sense of community, whether tableware can enhance communal eating and a discussion of original tableware created by Fay Morris. Volume II, the Ceramics studio manual, documents technical knowledge gained through the research and studio practice of Fay Morris. This includes information such as ceramic raw materials, studio safety and other practical guidelines that would assist practitioners setting up a ceramics studio. An exhibition of selected tableware created by the researcher-practitioner forms the practical component. Several theories and philosophies underpin this research. Academic findings on commensality and its potential to create a sense of community are explored. The value of handmade utilitarian wares in our culture of mass production and convenience is discussed as well as the Japanese philosophy that ceramic wares have spiritual content. Furthermore, the Japanese method of kintsukuroi is found to be a personal metaphor for healing. The practical component involves the creation of original tableware for everyday use and festive occasions. Unique ceramic wares, some with glass components, are created using the methods of throwing, slip-casting and glass slumping. Details referencing rockpool life are incorporated into many festive wares, inviting close inspection. Both functional and aesthetic considerations for tableware are taken into account. Adopting a practice-based approach, studio practice is built on tacit knowledge and existing skills. New knowledge and additional skills are acquired through practice and discoveries direct further research. Thumbnail images in text illustrate these discoveries

Infusing Communication Skills into Financial Accounting Curriculum: A perspective from the Digital Era

This study investigates financial accounting students’ attitudes about several aspects related to modern pedagogies focusing on communication skills development. The paper focuses on areas of students’ need to develop communication skills irrespective of cultural diversity and gender inequality, quiz-based learning, requirements, and assessment. The study employed an online survey of students at one of the largest business colleges in the Sultanate of Oman. The study surveyed 96 currently registered students to cover the research objectives and questions. The findings showed that the students enjoyed a high level of awareness of the importance and relevance of communication skills in relation to future employability. Students believed developing communication importance was not limited to careers in financial accounting as it was also extended to other careers requiring a post-secondary degree. Quiz-based learning strategies were found to be relevant in improving communication skills. The results also highlighted adaptability as a main assessment criterion of communication skills. The study provided bases for higher education institutions in the Sultanate of Oman or other countries to empower the generalizability of the findings. Another possible research could replicate the investigation in other fields of study. This paper brings several implications for instructional practice and pedagogies, as well as for policies of instructional training and development. The study is original in its particular context and specific time during the COVID-19 pandemic as attitudes toward online technologies have been shifting paradigms

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

Fabrication and characterisation of complex shaped Si-Al-O-N ceramic components via additively manufactured moulds

This research programme was aimed at manufacturing complex-shaped components, such as gears and turbocharger rotors from SiAlON for use in engineering applications. SiAlONs are alloys of Si3N4 ceramics and offer the combination of good mechanical strength and chemical inertness together with the ability to perform at temperatures up to ~1400$^o$C. Although a lot of progress has been made for the fabrication of dense Si3N4 (and its alloys) components, research is still being conducted to find fabrication processes that are economical in terms of money and time and that yield high quality components. The manufacturing route evaluated in the current study was based on the use of complex-shaped additively manufactured polymeric moulds that could then be used during the green forming of the ceramic components, followed by their densification by sintering. The goal was to reduce (ideally eliminate) the need for any machining, leading to faster and lower cost production of complex-shaped ceramic components. The heart of the project was thus the additive manufacturing machine (Solidscape, UK & Ireland). Although intended for use in jewellery making, its ability to 3D-print fine details using high-grade synthetic polymer was exploited. Once each batch of moulds was designed and produced, the process involved mixing the precursor SiAlON powder with additives, pressing the powder into the moulds and subsequent mould removal, debinding and then sintering at 1750$^o$C. Dense (up to 99% of theoretical density) SiAlON ceramics were obtained. Components were characterised at every step of the process via visual inspection and physical and chemical analysis, including powder flowability, scanning electron microscopy, X-ray micro-computer tomography, X-ray diffraction, etc, for qualitative and quantitative analysis. Parameters affecting the resultant green and sintered body in terms of mechanical stability and surface finish were investigated. The study also included oxidation behaviour of the ceramic at temperatures from 1250 to 1450$^o$C. An organic binder was chosen from a select few based on its adhesion property and flowability when mixed with the ceramic powders. The moulds’ examination revealed irregular surfaces leading to non uniform surface profiles on the sintered parts. An interfacial surface on the moulds was introduced to improve the surface finish of the green body. Phase analysis coupled with microscopic examination of the sintered ceramic revealed the presence of two phases namely α – SiAlON and β - SiAlON. The Vickers hardness was measured to be HV10 = 2545 and the flexural strength was measured to be 87 MPa. Oxidation study revealed the onset of degradation of the ceramic from 1100$^o$C. With an increase in the oxidising time and temperature, an increase in the prominence of cristobalite, grain growth and phase separation was observed. Limitations of indirect additive manufacturing in the current study are identified. These include the part size limitation, the inefficiency of the printing unit to print uniform moulds without the presence of any debris, the strength of the moulds under stresses, failure in assessing the residual stresses in the sintered compacts and disadvantages of the powder compaction are discussed. The study concludes by suggesting future work to improve the fabrication process including the use of stronger mould material, pressureless green forming technique of consolidation such as gelcasting, development of simulations to predict the behaviour of the ceramic and its residual stresses

Fabrication of ceramic and ceramic composite microcomponents using soft lithography

This PhD project is set out to develop a high precision ceramic fabrication approach suitable for mass production, and to meet the needs of microengine application. A group of new processes have been developed and the results are characterized for fabrication of high precision ceramic oxides and composite microcomponents using soft lithography and colloidal powder processing. The materials chosen in the research are alumina, yttria stabilised zirconia and their composite for their excellent properties at high temperature