Can Ultra-fast High Temperature Sintering (UHS) Boost Transparency of Alumina?

Established routes for consolidation of transparent alumina ceramics by pressure-less sintering requires several hours of dwelling in a reducing atmosphere at a temperature exceeding 1600 ℃. Here, for the first time, we report on low temperature and ultrafast consolidation of translucent alumina ceramics. Transparency was promoted by the synergistic of high initial green density (62.7 %) and rapid sintering using Ultra-fast High Temperature Sintering (UHS) technique. The proposed approach, using a heating rate of 430 ℃/min and dwelling time of 15 minutes, resulted in ultra-fine-grained translucent alumina ceramics at 1359 ± 57 ℃ with a grain size of 0.39 µm, and an in-line transmittance of 28.7 % at a wavelength of 700 nm. For comparison, conventionally fired counterparts were opaque due to their incomplete densification, pore coalescence.

Growth of less than 20 nm SnO Nanowire Using AAO Template for Gas Sensing

Large-scale stannous oxide (SnO) nanowires were synthesized via a template and catalyst-free thermal oxidation process. After annealing Sn nanowires embedded AAO template in atmosphere, we observed a large scale of SnO nanowires. SnO nanowires were first prepared via the electrochemical deposition and an oxidization method based on an AAO template. The preparation of SnO nanowires use aluminum sheet (purity 99.999%) and then two-step anodization procedure to obtain raw alumina mold. Finally, transparent alumina mold (AAO template) were obtained by the reaming, soaking with phosphoric acid for 20 minutes and a stripping process. We get a pore size of < 20 nm transparent alumina mold. In order to electroplating needs, we produce platinum film on the bottom surface of AAO template by using sputtering method as the electrode of electroplating deposition. The structure was characterized by X-ray diffraction (XRD). High resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) with x-ray energy dispersive spectrometer (EDS) was used to observe the morphology. The EDS spectrum showed that components of the materials are Sn and O. FE-SEM results show the synthesized SnO nanowires to have an approximate length of ~ 10 - 20 μm with a highly aspect ratio > 500. SnO nanowires with an Sn/O atomic ratio of ~ 1 : 1 were observed from EDS. The crystal structure of SnO nanowires showed that all the peaks within the spectra can be indexed to SnO with a tetragonal structure. This studies may lead to the use of the 1D structure nanowires into electronic nanodevices and/or sensors, thus leading to nanobased functional structures.

Growth of Less than 20 nm SnO Nanowires Using an Anodic Aluminum Oxide Template for Gas Sensing

Stannous oxide (SnO) nanowires were synthesized by a template and catalyst-free thermal oxidation process. After annealing a Sn nanowires-embedded anodic aluminum oxide (AAO) template in air, we obtained a large amount of SnO nanowires. SnO nanowires were first prepared by electrochemical deposition and an oxidization method based on an AAO template. The preparation of SnO nanowires used aluminum sheet (purity 99.999%) and then a two-step anodization procedure to obtain a raw alumina mold. Finally, transparent alumina molds (AAO template) were obtained by reaming, soaking with phosphoric acid for 20 min, and a stripping process. We got a pore size of < 20 nm on the transparent alumina mold. In order to meet electroplating needs, we produced a platinum film on the bottom surface of the AAO template by using a sputtering method as the electrode of electroplating deposition. The structure was characterized by X-ray diffraction (XRD). High resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) with X-ray energy dispersive spectrometer (EDS) were used to observe the morphology. The EDS spectrum showed that components of the materials were Sn and O. FE-SEM results showed the synthesized SnO nanowires have an approximate length of ~10–20 μm with a highly aspect ratio of > 500. SnO nanowires with a Sn/O atomic ratio of ~1:1 were observed from EDS. The crystal structure of SnO nanowires showed that all the peaks within the spectrum lead to SnO with a tetragonal structure. This study may lead to the use of the 1D structure nanowires into electronic nanodevices and/or sensors, thus leading to nano-based functional structures.

Fabrication of α-alumina by a combination of a hydrothermal process and a seeding technique

This paper describes a method for producing [Formula: see text]-Al2O3 at low temperatures by a combination of a hydrothermal process and a seeding technique. White aluminum hydroxide precipitate was prepared by a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution. Peptization of the precipitate by acetic acid at room temperature transformed it into a transparent alumina sol. The alumina sol was treated with a hydrothermal process. [Formula: see text]-Al2O3 particles serving as seeds were added to the hydrothermally treated alumina sol. The sol containing the [Formula: see text]-Al2O3 particles was transformed into an [Formula: see text]-Al2O3-seeded alumina gel by drying at room temperature. The non-seeded alumina gel was amorphous or showed fine crystallites and began to crystallize into [Formula: see text]-Al2O3 at 900[Formula: see text]C. The [Formula: see text]-Al2O3-seeding promoted the crystallization of the alumina gel to [Formula: see text]-Al2O3. A remarkable [Formula: see text]-Al2O3 crystallinity was achieved with an increase in [Formula: see text]-Al2O3 particle content by weight in the final seeded alumina gel. For an [Formula: see text]-Al2O3 particle content of 5%, the seeded alumina gel was partially crystallized to [Formula: see text]-Al2O3 by annealing at temperatures as low as 600[Formula: see text]C.