Many industrial processes generate large amounts of waste. Typical examples include the fertiliser industry (phosphogypsum), ferro-alloy and steel producers (slag), as well as the power generating industry (fly ash). Although some waste products are currently used to a limited extend (e.g. fly ash and cement in cement), there is a constant need to find more uses and newapplications for these. This investigation describes work done to develop a novel ceramic body, which can potentially be used as a ceramic filter for purification of waste water and potable water.

No description available.

Thesis (MS)-Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Stephen W. Sofie Includes bibliographical references (leaves 77-78).

No description available.

No description available.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1939. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed April 26, 2010) Includes bibliographical references (p. 25).

Ceramic colloidal processing routes such as slip casting, gelcasting and direct ink writing provide valuable insight into the role of interaction forces between particles, solvents, and polymeric additives in the rheology, particle packing, and strength of a ceramic green body. For difficult-to-densify ceramics such as the UHTCs, which find their place in extreme environment applications, precise control of each step of the manufacturing process is key. In this work, a fundamental study on the interaction between particles in non-aqueous slip casting is performed comparing the rheological behavior and consolidation with current models for interaction potential within a suspension. The advantages and drawbacks of such a model are discussed in relation to formulating a colloidal process for advanced ceramics such as ZrB2, and a case for a cyclohexane slip casting system resulting in low viscosity, shear-thinning behavior and green density of 64%, is made. The focus on non-aqueous colloidal processing is extended to gelcasting, involving three different sets of chemically curable polymer systems: HEMA+MBAM, TMPTA, and PEGDA. Merits of the gelcasting process including homogeneity, green strength, and processing time reduction are discussed, with the HEMA+MBAM system resulting in nearly an order of magnitude increase in green density from slip casting. Gelcast samples were also sintered to a density of 88% and capable of being processed in a variety of complex shapes with fine feature size on the mm scale. The properties examined in slip casting and gelcasting, as well as others pertaining to the setup of an extrusion-based additive manufacturing system, are carefully considered to design an ink that has been used to print ZrB2. The role of each additive as well as the solvent in creating an ink that is not only within the correct viscosity range for extrusion and shape retention, but also produces a strong and densely packed green body, is discussed. Finally, adjustment of printing parameters, and the method of using a low-cost rheology match to tune the settings of a pneumatic screw-extrusion printing setup, are explained. Each of these processes points to new and practical methods of complex shaping ZrB2 that can provide insight into processing of these challenging materials and create new avenues for their use in extreme environment applications, such as thermal protection systems in atmospheric re-entry vehicles. / Doctor of Philosophy / This work examines the use of ultra-high temperature ceramics (UHTCs), which are materials with some of the highest melting points in existence. These are an intriguing option for extreme environment applications. One such application is the protection of rockets, scramjets, and other hypersonic (speed > Mach 5) vehicles from the high temperatures experienced during flight and re-entry. In this work, the UHTC Zirconium diboride (ZrB2) is used as a reference material. For many of the same reasons UHTCs such as ZrB2 have extreme melting points, they can be difficult to manufacture, particularly in complex shapes. Like many ceramics, UHTCs are not melted and cast as metals are, but rather are processed in powder form to a compact known as a green body. The green body is placed in a high-temperature furnace at 2/3 - 3/4 of the melting point, where the powder undergoes sintering, or consolidation into a dense part. The manufacture of a green body that is versatile in its capacity to be molded into any shape, and allows for close packing of the particles in the powder compact to avoid failure-inducing flaws in the final component under intense loads, remains a challenge for UHTCs. Most UHTCs are hot pressed, where the powder alone is consolidated under intense heat and pressure, but this process offers very little complex shaping capacity or control of the uniformity of the part. In this work, three methods for green body manufacture using colloid-based routes, which all have unique capabilities and challenges, are described. The first process is slip casting, which is a centuries-old process that has been used for the manufacture of pottery, whitewares, and art ceramics. When used effectively, slip casting ensures that the forces between ceramic particles in a suspension, or "slip", are well-controlled such that the ceramic particles will not form clumps, or agglomerates, which create non-uniformities that weaken the final component. With information about the powder, solvent, and additives in a slip, the extent to which this will be effective can be predicted with mathematical models. This work compares the results of these models with slip casting suspensions in different solvent environments to gain knowledge about slip casting as an option for complex shaping of ZrB2. The second colloidal process discussed is gelcasting, in which the suspension of ceramic powder can undergo chemical gelation, or a reaction that transitions the suspension from a liquid to a solid, not unlike that of a natural gel such as gelatin, agarose, or albumin (egg white). The gel, which is loaded with ceramic powder, allows for more versatile shaping than slip casting, and shorter processing time; a gelcast ceramic is generally solidified in less than an hour, while a slip cast typically dries overnight. The presence the gel also provides strength to the green body, which is advantageous in handling as well as any machining to adjust the shape that may be necessary prior to sintering. The final process detailed in this work is direct ink writing, a type of additive manufacturing (or 3D printing). Knowledge gained from slip casting and gelcasting was used to carefully design a ceramic colloid that could be deposited in a layer-by-layer fashion to create a complex shape with high uniformity and control, as well as minimal surface cracking. The printed green bodies were compared in strength and sintering behavior to the gelcasts from previous chapters, and the expansion of shaping capacity for each route as it relates to aerospace applications, is described.

Porous ceramics have successfully been used in a wide variety of highly advanced applications. Current routes to porous ceramics are limited in the types of porosity they can create and no one process is flexible enough to create any desired structure. This study introduces the use of ice particles as pore forming agents to fabricate porous materials. This novel method possesses several advantages over current industrial techniques including environmental friendliness, low cost, and flexibility in size and shape of resulting pores. Porous ceramic structures were created by adding preformed ice particles to an alumina slurry which was quickly frozen, air dried, and then sintered. Porosity was characterized using Scanning Electron Microscopy (SEM), Archimedes measurements, and gas sorption techniques. Small spherical pores were successfully created in the 20-200?m range and larger spherical pores were also created in the 2-3 mm range. Amount of porosity was controlled through specifying the amount of ice added to the ceramic slurry. Samples were prepared with porosity levels ranging from 30-75%. As a completely new process, these initial results are quite promising and further development will allow for even greater morphology control. / Master of Science

The term Nanoceramics is well known in the ceramic field for at least two decades. In this project a detailed study was performed on the synthesis of α-alumina nanopowders. High solids content nanoalumina suspensions were prepared and used to form green bodies using both wet and dry forming routes. The green bodies were then sintered using both conventional single and two-step sintering approaches. Synthesis: Two different synthesis methods, viz. precipitation and hydrothermal treatment, were used to synthesize fine α-alumina powders from aluminium chloride, ammonia solution and TEAH (Tetraethyl ammonium hydroxide). XRD, TEM and FEG-SEM were used to characterise the powders produced. The presence of commercial α-alumina powder as seed particles did not affect the transformation to α-alumina phase during the hydrothermal treatment at 220˚C in either basic or acidic environments. The results obtained from the precipitation route showed that the combined effect of adding α-alumina seeds and surfactants to the precursor solution could lower the transformation temperature of α-alumina from about 1200˚C for unseeded samples to 800˚C, as well as reducing the level of agglomeration in the alumina powders. The difference in transformation temperature mainly resulted from the nucleation process by the α-alumina seeds, which enhanced the θ → α transformation kinetics. The lower level of agglomeration present in the final powders could be due to the surface modifying role of the surfactants preventing the particles from growing together during the synthesis process. By introducing a further high-temperature step for a very short duration (1 minute) to the low-temperature heat treatment route (800˚C/12 h), the unseeded sample with added surfactant transformed into pure α-alumina phase. The newly-added step was shown to be an in-situ seeding step, followed by a conventional nucleation and growth process. The best final powder was compared with a commercial α-alumina nanopowder. Processing of alumina ceramics: The effect of low-molecular weight ammonium dispersants including Dispex-A40, Darvan-C and Dolapix-CE64, on high solids content nanoalumina suspensions was investigated. The nanosuspension prepared using the most suitable dispersant, Dolapix-CE64, was slip cast into ~53% dense, very homogeneous green bodies. This nanosuspension was also spray freeze dried into crushable granules using Freon as a foaming agent. Green compacts with density of ~53.5% were then formed by dry pressing the 2 vol% Freon-added spray freeze dried granules at 40 MPa. Both slip cast and die pressed green bodies were sintered using conventional single-step and two-step routes followed by characterising the density and grain size measurement of final dense compacts. The results have been compared with that of a submicron alumina ceramic prepared using a commercial α-alumina suspension. Highly dense alumina with an average grain size of ~0.6 μm was fabricated by means of spark plasma sintering at 1200˚C. The application of 500 MPa allowed achieving almost fully dense alumina at temperature as low as 1200˚C for 30 minutes with no significant grain growth.

The term nanoceramics is well known in the ceramic field for at least two decades. Even though there are many reports that nanoceramics are superior in terms of mechanical and other properties, no comprehensive and conclusive study on the grain size dependent variation in mechanical properties. So this study was an attempt to study the property variation with grain size and yttria content for a well known ceramic, yttria stabilised zirconia. High solids content but low viscosity YSZ nanosuspensions have been slip cast into -52% dense, very homogeneous green bodies in sizes up to 60 mm in diameter. Sintering cycles have been optimised using both hybrid and conventional two-step heating to yield densities >99.5% of theoretical whilst retaining a mean grain size of <100 nm. The sintered samples have been characterised for hardness, toughness, strength, wear resistance and hydrothermal ageing resistance. The results have been compared with that of a submicron zirconia ceramic prepared using a commercial powder. The strength of the nanoceramics has been found to be very similar to that of conventional submicron ceramics, viz. -10Pa, although the fracture mechanism was different. Two toughness measurement approaches have been used, indentation and surface crack in flexure. The results indicate that the nano 1.5YSZ ceramics may be best viewed as crack, or damage, initiation resistant rather than crack propagation resistant; indentation toughness measurements as high as 14.5 MPa m 112 were observed. Micro-Raman mapping was demonstrated to be a very effective technique to map the phase transformations in zirconia. The wear mechanism of nanozirconia has been observed to be different compared to that in conventional, submicron YSZ and the wear rates to be lower, particularly under wet conditions. In addition, and potentially most usefully, the nan03YSZ ceramics appear to be completely immune to hydrothermal ageing for up to 2 weeks at 245°C & 7 bar; conditions that see a conventional, commercial submicron ceramic disintegrate completely within 1 hour.