OBJECTIVES: To investigate the effect of different alumina fabrication techniques and sintering temperatures on the biaxial flexural strength. Also, to assess the resulting color of multiple metal salt solutions at different concentrations in monolithic alumina and its effect on the optical properties of the restoration. MATERIAL & METHOD: Forty disk-shape alumina specimens were divided into 4 groups (n=10) based on the fabrication process (slip cast or die press) and sintering temperature (1530°C or 1600°C). Biaxial flexural strength was calculated using universal testing machine at a crosshead speed rate of 0.5 mm/min until failure occurred. For the coloring part of the study, nine elements (Ba, Ce, Cr, Fe, Mn, Nd, Pr, Sm, Zn) were used to form metal-salt coloring solutions at a concentration of 0.1%, 1% and 5% wt. The solutions were then used to infuse 162 pre-sintered porous alumina disks that are either slip-casted (A1000) or die-pressed (CT3000). Color coordinates were recorded in CIE L*a*b* system using spectrophotometer. Color differences relative to the control (ΔE), translucency parameter (TP), contrast ratio (CR) and total transmission were calculated and analyzed using two-way analysis of variance (ANOVA) with Tukey post hoc test at α = 0.05. RESULTS: Slip cast group sintered at 1530°C had the highest flexural strength (479.14 MPa), but there was no significant difference between the four groups neither by fabrication process (p = 0.127) nor by sintering temperature (p = 0.276). Die press specimens colored with Ba at 0.1% and 1% showed significantly higher TP (2.65 and 2.49) and lowest CR (96.15 and 96.30) among the groups. There was a statistically significant effect on TP and CR when changing alumina powder on specimens colored by Ba, Ce, and Zn (p < 0.05). Changing the concentration of the coloring solution caused a significant effect on the optical properties of specimens colored by Ba, Nd, Cr, Mn. ΔE was significantly changed when changing alumina powder and coloring concentration for all elements except Ce, Pr, and Sm. CONCLUSION: Changing fabrication method and sintering temperature did not affect the biaxial flexural strength. However, the fabrication method and metal-salt colorant concentration affected the optical properties of the specimens. / https://hdl.handle.net/2144/35681

A study has been made of the enhancement of the mechanical strength of bricks fabricated from five Sri Lankan Quaternary and post-Quaternary brick clays with the objective of identifying and optimising those factors which control the quality and performance characteristics of fired clay products of this type. Mineralogical investigations have shown that the clays are predominantly kaolinitic. Of the accessory minerals, feldspars and gibbsite are the chief constituents. The experimental programme involved the development of feasible processing techniques for clay bodies, the establishment of optimum heat treatments for their firing, and the testing and evaluation of material properties of the fired products. The microstructures of fired materials have been characterized using optical and electron microscopical techniques, as well as X-ray diffraction, electron probe microanalysis and chemical analysis. A limited study was also made of the durability of laboratory fired specimens. Methods of strength enhancement included use of the reactions of phosphates with natural clays, use of mineralizers to induce mullitization and surface coating by an efflorescence process. A kinetic analysis based on the first order kinetics is proposed for the estimation of optimum firing conditions for kaolinitic clays. The study has shown that surface coating of bricks increases the load at the elastic limit by up to 30% and the ultimate failing load by 19% in the clays examined. The measured increases in modulus of rupture and modulus of elasticity are over 33% and 40% respectively. A fabrication technique which requires the incorporation of phosphates has been developed. This provides the possibility of lowering the peak temperature of firing to 500°C. Flexural strength increase of up to 60% over the normally fired unbonded specimens can be achieved using this technique. Relevant compatibility relations in the ternary system Si02- P205-AI203 at 500'C are proposed. The presence of an optimum amount of mineralizer in a clay body may alter its sintering characteristics resulting in an increase in modulus of rupture up to 55%. However, uncontrolled additions exceeding 4 wt% cause deleterious effects. Microstructural analysis provides evidence that liquid phase sintering, development of mullite, development of pores and bloating are the dominant strength determining features in these clays. An empirical equation correlating the functional relation between modulus of rupture, mullite content and porosity is proposed. Mechanisms of strength development are discussed in the light of these findings.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / As we adopt and implement the doctrines of reengineering, we at NASA/Jet Propulsion Laboratory (JPL) are asked to make a giant leap in how we think of and design SpaceCraft. We call what we are doing a revolution, since we are not “evolving” to the next step in our activity, but literally leaping beyond it. This is fully in concert with the concepts of reengineering, in that areas that need to be changed are indeed literally invented anew. To be successful, JPL and its industry partners, must perfect processes, techniques and methods that allow them to work together at all levels of the SpaceCraft development cycle. If all other parts of the discipline have moved on and changed, but a key portion remains locked in a time warp of yesterday, we will not be able to reach our desired goal. At the present time change is occurring all over JPL, and it is our intent to describe how it applies to areas where prototype, or one of a kind hardware are fabricated, and how these areas might look when new approaches to doing business are applied. Since all activities in an organization must attain similar levels of expertise or be in danger of hampering the entire process, the issues of Packaging Engineering, Manufactureability, and fabrication become key items.

Les progrès technologiques considérables menés depuis ces dernières décennies nous permettent aujourd’hui de disséminer dans notre environnement une nuée de noeuds de capteurs communicants combinant la taille micrométrique et la consommation dérisoire caractéristiques des MEMS avec la puissance des protocoles de communications Internet. L’Internet des Objets, formé par ce réseau de capteurs, possède le potentiel d‘optimiser un grand panel d’applications industrielles et domotiques. Le nouveau défi, que la communauté du Energy Harvesting tente de relever depuis une décennie maintenant, est de rendre ces noeuds de capteurs autonomes en les alimentant grâce à l’énergie perdue dans leur environnement. Dans ces travaux de recherche, nous explorons le potentiel d’un principe thermo-fluidique auto-oscillant pour la génération d’énergie utile à partir d’une source thermique de faible qualité. L’implémentation de cette technologie en tant que machine thermique est étudiée et mène à la caractérisation d’un nouveau cycle thermodynamique caractéristique du SOFHE (Self Oscillating Fluidic Heat Engine). Nous montrons, par une approche phénoménologique, que notre machine thermique se comporte comme un oscillateur mécanique, excité par les évaporations et condensations successives du fluide de travail. Ces changements de phase alternatifs mettent en mouvement une colonne d’eau, jouant le rôle de masse, couplée à une zone de vapeur, jouant le rôle d’un ressort. Une étude de l’influence du couplage du SOFHE avec un transducteur électromécanique, représenté par un oscillateur, mène à la conception et la fabrication d’une spirale piézoélectrique. L’intégration de cette spirale à notre machine thermique forme un générateur thermo-électrique dont les capacités de conversion sont démontrées par la charge d’une capacité. Finalement, la miniaturisation du principe thermo-fluidique SOFHE est rendue possible par la réalisation d’un procédé de fabrication utilisant les techniques MEMS. Des dispositifs miniatures parviennent à exhiber un comportement oscillatoire montrant le potentiel d’intégration de cette technologie. / Abstract : The tremendous technological progresses realized in the last decades allow us to swarm our environment with Wireless Sensors Networks. These WSNs combine the MEMS’ miniature size and low energy consumption, and the powerful Internet communication protocols. This Internet of Things shows great potential in many applications such as industry or housing. For a decade now, the Energy Harvesting community wants to build autonomous WSNs by enabling them to feed off energy wastes. In this work, we study the electricity generation capabilities of a Self-Oscillating Fluidic Heat Engine (SOFHE) and present its characteristic thermodynamic cycle. Our model shows that the SOFHE acts as a mechanical resonator excited by the successive evaporation and condensation processes underwent by the working fluid. These phase changes put a liquid mass in motion, coupled with a vapor spring. The coupling of our heat engine with an electromechanical transducer is studied and leads to a piezoelectric spiral conception and fabrication. Their association forms a thermo-electrical generator able to power and charge an electrical capacitor. Eventually, we demonstrate the miniaturization prospects and integration potential of this SOFHE technology. A micro-fabrication process enables a SOFHE MEMS implementation. Our process includes a deep glass wet etching step as well as a Au-Si eutectic wafer bonding.