1,721,081 research outputs found
Development of a pre-ceramic suspension for free form fabrication of ceramic parts by stereolithography
No full textLaser Stereolithography represents one the most widely used processes for rapid prototyping with new equipments and materials covering each year new applications. Recently the application of stereolithography to the production of ceramic objects for engineering and biomedical applications has been proposed. In this work the development of UV curable pre-ceramic suspensions for free form fabrication of alumino-silicate ceramic parts by stereolithography is presented. The ceramic green is obtained in a stereolithographic system operating with a He-Cd laser (325nm). The suspensions is characterised by at least 50% by volume of powder content and by a viscosity similar to that one of commercial resins. The building of ceramic objects is described in detail for each stage of the process. Finally, some characterisation of the macroscopic properties and microstructure of samples is also presented
Stereolithography of Ceramic Suspensions
Full text linkThe need of fast production of prototypes of complex shapes in very short time lead to the development in the last years of many additive rapid prototyping (RP) technologies for the production of single objects or of very limited series. The new fabrication concept allowed the construction of complex parts, starting from a 3D-CAD model, without using a mould. However, most of these additive processes produce polymeric objects and only recently the laser sintering of metal powders has been commercially introduced. In this work the production of ceramic objects by stereolithography is presented starting from the development of UV curable pre-ceramic suspensions for free form fabrication of alumino-silicate parts. The suspensions are characterized by 40%-50% by volume of powder content and by a reactivity and a viscosity compatible with their application in stereolithography. The ceramic green is built in a stereolithographic system operating with a He-Cd laser (325 nm). Then, the ceramic objects are obtained by pyrolisis of the organic binder and subsequent sintering of the green at 1600 degreesC. Finally, a characterisation of the mechanical properties and of the microstructure of the samples is presented
Natural or synthetic yarns with heat transmission barrier property obtained by aerogel deposition
No full textSilica moulds built by stereolithography
No full textIn this work the production of ceramic moulds for aluminium casting using a stereolithographic apparatus is presented. Suspensions of silica powders in a photoreactive resin were used in standard STL equipment in order to build green parts. UV curable pre-ceramic suspensions have been studied using photocalorimetric and rheological characterizations. Thermogravimetry was used to analyse the behaviour of the pre-ceramic green during thermal treatment. Stereolithgraphy apparatus (SLA) was modified in order to fabricate ceramic green. Silica objects were obtained by pyrolysis of the organic binder and subsequent sintering at high temperature. A characterization of mechanical properties of the green and sintered ceramic materials was performed. Finally moulds for investment casting of aluminium were built by stereolithography and used for casting as a green as well as after sintering
Piezoceramics: an introductive guide to their practical applications
No full textPiezoceramics are used to
convert mechanical energy into
electrical energy and vice versa. Due
to their ability to be tailored
towards the requirements of
particular applications, they have
replaced natural and synthetic piezo
crystals in many devices and their
application range is continuously
expanding. The aim of this work is
to provide a clear and useful
introduction to piezoceramics that
will orient the reader to the
selection of the most suitable
material for a specific application.
After a brief description of the
piezoelectric material development,
the properties of piezoceramics will
be described and correlated with the
crystalline structure. Finally, as a case
study the various developmental
phases of an ultrasonic probe
suitable for the dynamic mechanical
analysis of polymers at high
frequency will be presente
The origin of highly efficient selective emission in rare-earth oxides for thermophotovoltaic applications,
Full text linkRare-earth oxide materials emit thermal radiation in a narrow spectral region, and can be used for a variety of different high-temperature applications, such as the generation of electricity by thermophotovoltaic conversion of thermal radiation. However, because a detailed understanding of the mechanism of selective emission from rare-earth atoms has so far been missing, attempts to engineer selective emitters have relied mainly on empirical approaches. In this work, we present a new quantum thermodynamic model to describe the mechanisms of thermal pumping and radiative de-excitation in rare-earth oxide materials. By evaluating the effects of the local crystal-field symmetry around a rare-earth ion, this model clearly explains how and why only some of the room-temperature absorption peaks give rise to highly efficient emission bands at high temperature (1,000–1,500 °C). High-temperature emissivity measurements along with photoluminescence and cathodoluminescence results confirm the predictions of the theory
Metodo per la realizzazione di componenti in materiale composito a matrice ceramica, PCT patent n. .
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