Transparent Aluminum Research Articles

Pressureless glass crystallization of transparent yttrium aluminum garnet-based nanoceramics

Transparent crystalline yttrium aluminum garnet (YAG; Y3Al5O12) is a dominant host material used in phosphors, scintillators, and solid state lasers. However, YAG single crystals and transparent ceramics face several technological limitations including complex, time-consuming, and costly synthetic approaches. Here we report facile elaboration of transparent YAG-based ceramics by pressureless nano-crystallization of Y2O3–Al2O3 bulk glasses. The resulting ceramics present a nanostructuration composed of YAG nanocrystals (77 wt%) separated by small Al2O3 crystalline domains (23 wt%). The hardness of these YAG-Al2O3 nanoceramics is 10% higher than that of YAG single crystals. When doped by Ce3+, the YAG-Al2O3 ceramics show a 87.5% quantum efficiency. The combination of these mechanical and optical properties, coupled with their simple, economical, and innovative preparation method, could drive the development of technologically relevant materials with potential applications in wide optical fields such as scintillators, lenses, gem stones, and phosphor converters in high-power white-light LED and laser diode.

Highly transparent Tb3Al5O12 magneto-optical ceramics sintered from co-precipitated powders with sintering aids

Highly transparent terbium aluminum garnet (Tb3Al5O12, TAG) magneto-optical ceramics were fabricated from co-precipitated nanopowders with tetraethoxysilane (TEOS) as sintering aid by vacuum sintering combined with hot isostatic pressing (HIP) post-treatment. The ball milled TAG powder shows better dispersity than the as-synthesized powder, and its average particle size is about 80 nm. For the ceramic sample pre-sintered at 1720 °C for 20 h with HIP post-treated at 1700 °C for 3 h, the in-line transmittance exceeds 76% in the region of 400–1580nm (except the absorption band), reaching a maximum value of 81.8% at the wavelength of 1390 nm. The microstructure of the TAG ceramic is homogeneous and its average grain size is approximately 19.7 μm. The Verdet constant of the sample is calculated to be −182.7 rad·T−1·m−1 at room temperature.

Single step route to highly transparent, conductive and hazy aluminium doped zinc oxide films.

Light scattering yet transparent electrodes are important for photovoltaics as they increase device efficiency by prolonging light path lengths. Here, we present a novel single step route to highly textured Al doped ZnO thin films on glass substrates that show a minimum resistivity of ∼3 × 10−3 Ω cm and high visible light transmittance of 83% while still maintaining high haze factor of 63%. Roughness was imparted into the ZnO films during the synthetic process using acetylacetone and deionized water as additives. The highly hazy yet visible and near infrared transparent nature of the conductive ZnO:Al films allow it to be potentially used as an electrode material in amorphous and microcrystalline silicon solar cells.

Optical thermometry based on up-conversion emission behavior of Ba2LaF7 nano-crystals embedded in glass matrix

Ba2LaF7:Yb3+, Er3+ nano-crystals embedded in a transparent aluminium silicate glass matrix was successfully fabricated by a traditional high temperature melt-quenching technique and the subsequently heat treatment process. The formation of Ba2LaF7 nano-crystals was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The enhancement of the up-conversion (UC) emission intensity of Er3+ in the glass ceramic (GC) was attributed to the crystallization of Ba2LaF7 nano-crystals with a low phonon energy compared to the precursor glass counterpart. The temperature-depended fluorescence intensity ratio (FIR) of thermally coupled emitting states (4S3/2, 2H11/2) behavior of Er3+ was studied under the excitation of 980nm. The maximum thermal sensitivity was approximately 0.43% K−1 at 298K. Besides, the temperature of Ba2LaF7 GC rose from 336 to 407K, when the laser pump power density increased from 1.01 to 9.59W/cm2. Moreover, the excellent thermal stability of the sample for temperature detection in the range of 398-573K was proved. The results indicate that the Yb3+/Er3+ co-doped Ba2LaF7 GCs could be potential candidates for integrating heaters and thermometers.

Supramolecular Wearable Sensors

In this issue of Chem , Jang et al. report a wearable sensor device for the rapid and sensitive detection of amphetamine-type stimulants in point-of-use conditions. The device characteristics benefit from superb supramolecular analytical chemistry and make it one of the most notable examples of sensor development.

Fabrication of highly transparent AlON ceramics by hot isostatic pressing post-treatment

Highly transparent aluminum oxynitride (AlON) ceramics were fabricated by pressureless sintering with hot isostatic pressing (HIP) post-treatment. The experimental results showed that the optical transparency of AlON ceramics was improved markedly over the visible and near-infrared range by HIP at 1825°C for 3h in 200MPa argon gas, which derived from the elimination of residual pores in the prepared ceramics. For AlON ceramics pre-sintered at 1800°C, the transmittances of the sample increased from 63.6% to 84.8% at 600nm and from 75.4% to 86.1% at 2000nm, respectively. The average grain size of the HIPed sample was about 47.9μm.

CuPc/C60 heterojunction photodetector with near-infrared spectral response

Photodetector based on copper phthalocyanine/fullerene (CuPc/C60) heterojunction with transparent indium tin oxide (ITO) and aluminum (Al) electrodes was prepared by thermal evaporation method at room temperature. The spectral response of ITO/CuPc/C60/Al photodetector was broadened from ultraviolet–visible band to near-infrared band (800–1100nm) at zero bias. The near-infrared detectivity under 800nm illumination with light intensity of 0.016mW/cm2 was 4.5×1011cm·Hz1/2/W. And the near-infrared detectivities under 900 to 1100nm illumination were also exhibited bigger than 1010cm·Hz1/2/W. Thus CuPc/C60 heterojunction was one of the most promising materials for photodetectors with high detectivity and wide spectral rang. Those photodetectors can be used in a variety of possible sensor applications.

A Novel Investigation about the Thermal Behaviour of Gases under the Influence of IR-Radiation: A Further Argument against the Greenhouse Thesis

Besides a critical discussion of the greenhouse thesis referring to its basic assumptions, a condensed report of [1] is given here. In contrast to the usual spectroscopic methods, the temperature of a gas embedded in a tube was measured, and not the intensity loss of the radiation. The starting point was to compare air with carbon-dioxide. Moreover, not medium-wave heat radiation was used but, initially, incident solar radiation and, subsequently, artificial radiation from an IR-bulb. In order to minimize the interference by the tube, light-weight building materials were used, such as Styrofoam, transparent plastic foils and aluminium foils. Surprisingly, and in contrast to the expectations, a considerable temperature enhancement could be detected being similar in both cases. The measuring apparatus was improved, and further gases were studied, in particular noble gases. In each case, a temperature increase was detected up-to a limiting value. While the warming-up rate was independent of the gas type, the limiting temperature turned out to be gas-specific, being almost equal for air, pure carbon-dioxide and argon whereas the light gases neon, and in particular helium, exhibited significant lower limiting temperatures. Applying the kinetic gas theory, and assuming a direct correlation between limiting temperature and radiative emission power, a stringent dependency of the product on mean kinetic energy and collision frequency could be deduced. Moreover, the adsorption degree could be calculated, turning out to be very low. The absorption was assumed as a result of vibration of the atomic electron shell, induced by the electromagnetic waves. Comparing the results in sunlight to those obtained in artificial light, the effective wavelength could be assessed delivering the value of 1.9µm. Since the results could be approved by numerous experiments, there is no doubt that a new effect has been discovered which allows questioning the greenhouse theory all the more.

Influence of deposition pressure on properties of ZnO: Al films fabricated by RF magnetron sputtering

Transparent conductive aluminum doped zinc oxide (ZnO:Al, AZO) films were prepared on glass substrates by rf (radio frequency) magnetron sputtering from ZnO: 3wt% Al2O3 ceramic target. The effect of argon gas pressure (PAr) was investigated with small variations to understand the influence on the electrical, optical and structural properties of the films. Structural examinations using X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that the ZnO:Al thin films were (002) oriented. The resistivity values were measured by four-point probe with the lowest resistivity of 5.76×10-4 Ω·cm (sheet resistance=9.6 Ω/sq. for a thickness=600 nm) obtained at the PAr of 0.3 Pa. The transmittance was achieved from ultraviolet-visible (UV-VIS) spectrophotometer, 84% higher than that in the visible region for all AZO thin films. The properties of deposited thin films showed a significant dependence on the PAr.

Infrared measurement of the temperature at the tool–chip interface while machining Ti–6Al–4V

The challenges associated with machining titanium alloys (e.g., Ti–6Al–4V) are directly related to high cutting tool temperatures due to the low thermal conductivity of these alloys and the heat generated in the primary shear zone and at the tool–chip interface. Transparent yittrium aluminum garnet (YAG) tools are used in the current study to orthogonally machine a Ti–6Al–4V disk. Although YAG tools are not industrially relevant, they permit the temperature on the tool–chip interface to be measured. These measurements are relevant because they can be used to validate cutting models, which are in-turn used by industry to improve cutting processes. An infrared camera, using a high frame rate (700Hz) and a large field of view (20mm2), observes the tool–chip interface through these tools and measures the temperature distribution and records the chip curl and breakage while cutting with a feed rate of 50μm/rev and cutting speeds between 20m/min and 100m/min. In addition to the temperature measurements, cutting forces are recorded and the chip formation is documented using a high-speed (3kHz) visible-light camera. Results show that radiant temperature increases with speed while the cutting and thrust forces show no significant trend. Analysis of the temperature distribution from one edge of the chip to the other reveals differences from 6 % to 21 %, indicating that caution must be used when performing thermographic measurements of chip temperatures from the side of the cutting zone. Finally, post process measurements are performed using a scanning white-light interferometer to investigate any correlation between the tool condition and cutting temperature. Although the qualitative analysis of some cases appears to reveal a correlation between the condition of the YAG tool and the measured temperature distribution, further work work is required to understand this relationship.

Microwave Heated Continuous Flow Palladium(II)-Catalyzed Desulfitative Synthesis of Aryl Ketones

A protocol for Pd(II)-catalyzed desulfitative synthesis of aryl ketones from sodium aryl sulfinates and nitriles in continuous flow has been developed. The reactions proceed with microwave heating using microwave transparent tube reactors, affording the desired aryl ketones in fair to good yields. Microwave transparent aluminum oxide reactors were identified as a safe and thermostable alternative to borosilicate glass reactors.

Polishing Characteristics of Transparent Polycrystalline Yttrium Aluminum Garnet Ceramics Using Magnetic Field-Assisted Finishing

Transparent polycrystalline yttrium aluminum garnet (YAG) ceramics have garnered an increased level of interest for high-power laser applications due to their ability to be manufactured in large sizes and to be doped in relatively substantial concentrations. However, surface characteristics have a direct effect on the lasing ability of these materials, and a lack of a fundamental understanding of the polishing mechanisms of these ceramics remains a challenge to their utilization. The aim of this paper is to study the polishing characteristics of YAG ceramics using magnetic field-assisted finishing (MAF). MAF is a useful process for studying the polishing characteristics of a material due to the extensive variability of, and fine control over, the polishing parameters. An experimental setup was developed for YAG ceramic workpieces, and using this equipment with diamond abrasives, the surfaces were polished to subnanometer scales. When polishing these subnanometer surfaces with 0–0.1 μm mean diameter diamond abrasive, the severity of the initial surface defects governed whether improvements to the surface would occur at these locations. Polishing subnanometer surfaces with colloidal silica abrasive caused a worsening of defects, resulting in increasing roughness. Colloidal silica causes uneven material removal between grains and an increase in material removal at grain boundaries causing the grain structure of the YAG ceramic workpiece to become pronounced. This effect also occurred with either abrasive when polishing with iron particles, used in MAF to press abrasives against a workpiece surface, that are smaller than the grain size of the YAG ceramic.

Substrates with high hardness and high transparency

Touchscreens are human–machine interfaces widely used in information and telecommunication products. This study used a transparent aluminum nitride (AlN) film with hardness exceeding 20 GPa in the development of antireflective SiOx–AlN multilayer films in order to obtain high hardness as well as high transparency. To one side of the glass substrate, a four-layer AlN–SiOx antireflective structure is applied to enhance transparency. On the other side of glass substrate, a thick AlN film is applied to serve as an antiscratch hard layer with an additional AlN/SiOx nano-double-layer to enhance overall transparency. Indentation measurements to a depth of 200 nm revealed hardness values of 21.18 GPa, and the average transmittance was measured at 92.89% in the visible light range (400–700 nm). The transparency of the specimens in this study is superior to that of common glass and provides hardness values 3.5 times higher.

English

In contrast to the usual spectroscopic methods, the temperature of a gas embedded in a tube was measured here and not the intensity loss of the radiation. In order to minimize the interference by the tube, light-weight building materials were used, preferably Styrofoam, transparent plastic foils and aluminium foils. Sunlight as well as infrared (IR)-bulbs was employed as radiation sources, whereby near-IR is predominant and not medium-IR as it is usually assumed. Different gases were tested, not only air and carbon-dioxide but also the noble gases argon, helium and neon. In each case, a temperature increase was detected up to a limiting value. While the warming-up rate was independent of the gas type, the limiting temperature turned out to be gas-specific. Surprisingly and contrary to the expectation of the greenhouse theory, the limiting temperatures of air, pure carbon-dioxide and argon were nearly equal while the light gases neon, and particularly helium, exhibited significant lower limiting temperatures. Applying the kinetic gas theory, and assuming a direct correlation between limiting temperature and radiative emission power, a stringent dependency of the product on mean kinetic energy and collision frequency could be deduced. Moreover, the adsorption degree could be calculated, turning out to be very low. The absorption was assumed as a result of vibration of the atomic electron shell, induced by the electromagnetic waves. Comparing the results in sunlight to those obtained in artificial light, the effective wavelength could be assessed delivering the value of 1.9 μm. Therefore, the greenhouse theory has to be questioned. Key words: Solar-tube, gas-temperature, radiation-absorption, radiation-emission, kinetic-gas-theory, near-infrared, carbon-dioxide.

Reaction Sintering of Transparent Aluminum Oxynitride (AlON) Ceramics Using MgO and Y<sub>2</sub>O<sub>3</sub> as Co-Additives

Transparent aluminum oxynitride (AlON) ceramics have been prepared through a method based on direct reaction sintering of alumina and aluminum nitride powders using MgO and Y2O3 as co-additives. The sintering additives could cause the formation of liquid phase during sintering, which would greatly promote the densification and eliminate pores. The grain size of AlON is about 50-100μm. The influence of different component of Al2O3 and AlN as well as sintering temperature on microstructure and optical properties of AlON have been studied. High transparent AlON ceramics with the in-line transmittance of 80.3% at 2000 nm wavelength have been prepared when the concentration of sintering additives was 0.16wt% Y2O3 and 0.02wt% MgO.

Effects of Anode Wettability and Slots on Anodic Bubble Behavior Using Transparent Aluminium Electrolytic Cells

Transparent aluminum electrolytic cells were used to study the effects of anode wettability and slots on bubble behavior in a similar environment to that used in industrial cells. Observations were conducted using two types of transparent cells, one with side-observation and the other with a bottom-observation cell design. Anodic bubbles rising process in the side channel is strongly affected by the wettability of the anode. After rising a short distance, the bubbles detach from the anode vertical surface at good-wetting anode cases, while the bubbles still attach to the vertical surface at poor-wetting anode cases. Anode slots of width of 4 mm are able to prevent smaller bubbles from coalescing into larger bubbles and thus decrease the bubble size and gas coverage on the anode. Anode slots also make a contribution in slightly reducing bubble thickness. With the presence of slots, the bubble-induced cell voltage oscillation decreases as well.

Aqueous Slip Casting of Transparent Aluminum Oxynitride

Highly transparent Aluminum oxynitride (AlON) body has been produced using aqueous slip casting technique. High‐purity alumina and AlN were used as raw materials for the synthesis of single‐phase AlON powder. As‐synthesized AlON powder was surface modified to enable the AlON powders resistant to hydrolysis in water during aqueous slip casting. High solid loaded aqueous AlON slip was prepared for casting followed by drying and sintering to produce transparent AlON. Phase formation and stability was characterized by XRD, pH, and viscosity measurements. AlON powders before and after surface treatments were characterized. Sintered transparent AlON samples were characterized for their mechanical, microstructural, and optical properties. Sintered and polished AlON produced in this study has shown inline transparency up to 80% between 0.22 and 6 μm wavelength region.

Enhanced light extraction of GaN-based light-emitting diodes with periodic textured SiO2 on Al-doped ZnO transparent conductive layer**Project supported by the National Natural Science Foundation of China (Grant Nos. 61204049 and 51402366), Guangdong Natural Science Foundation, China (Grant No. S2012040007363), and Foundation for Distinguished Young Talents in Higher Education of Guangdong, China (Grant Nos. 2012LYM0058 and 2013LYM0022).

We report an effective enhancement in light extraction of GaN-based light-emitting diodes (LEDs) with an Al-doped ZnO (AZO) transparent conductive layer by incorporating a top regular textured SiO2 layer. The 2 inch transparent through-pore anodic aluminum oxide (AAO) membrane was fabricated and used as the etching mask. The periodic pore with a pitch of about 410 nm was successfully transferred to the surface of the SiO2 layer without any etching damages to the AZO layer and the electrodes. The light output power was enhanced by 19% at 20 mA and 56% at 100 mA compared to that of the planar LEDs without a patterned surface. This approach offers a technique to fabricate a low-cost and large-area regular pattern on the LED chip for achieving enhanced light extraction without an obvious increase of the forward voltage.

Thermoluminescent properties of some phosphor glasses based on aluminum oxide.

The transparent thermoluminescent aluminum oxide-based glass of 15Al2 O3 -35P2 O5 -25CaO-25Na2 CO3 , abbreviated as APCN (all in mol%) doped with different concentrations of SiO2 from 0.0-500 ppm was prepared using a conventional melt-quenching technique. The TL sensitivities of the prepared glasses were investigated at 3 Gy γ-dose using a 60 Co source and measured at a heating rate 10 C/sec. The highest TL intensity of the material doped with SiO2 was found at a concentration of 500 ppm (APCNSi5 ). Deconvolution of the glow curve from APCNSi5 resulted in four peaks at about 161, 194, 237 and 293 C with a Figure Of Merit (FOM) of 1.28%. The APCNSi5 specimen had the best dosimetric properties when compared with the other samples. Reproducibility, repeatability, dose-response curve and fading effect were checked for peak 3, which appeared at about 237 C. The results displayed that the APCNSi5 glass system was a low-Z material (Zeff ≈ 10), and had good reproducibility and good repeatability. Peak 3 showed good linearity over a dose range up to 20 Gy (R2 = 0.999) and sublinearity behaviour was found. The signal from APCNSi5 faded by about 11% after 2 days post irradiation, therefore it showed almost no significant loss. Such properties make the newly prepared glasses suitable for and highly recommended for use in γ-dosimeters. Copyright © 2016 John Wiley & Sons, Ltd.

Anodic Bubble Behavior and Voltage Drop in a Laboratory Transparent Aluminum Electrolytic Cell

The anodic bubbles generated in aluminum electrolytic cells play a complex role to bath flow, alumina mixing, cell voltage, heat transfer, etc., and eventually affect cell performance. In this paper, the bubble dynamics beneath the anode were observed for the first time from bottom view directly in a similar industrial electrolytic environment, using a laboratory-scale transparent aluminum electrolytic cell. The corresponding cell voltage was measured simultaneously for quantitatively investigating its relevance to bubble dynamics. It was found that the bubbles generated in many spots that increased in number with the increase of current density; the bubbles grew through gas diffusion and various types of coalescences; when bubbles grew to a certain size with their surface reaching to the anode edge, they escaped from the anode bottom suddenly; with the increase of current density, the release frequency increases, and the size of these bubbles decreases. The cell voltage was very consistent with bubble coverage, with a high bubble coverage corresponding to a higher cell voltage. At low current density, the curves of voltage and coverage fluctuated in a regularly periodical pattern, while the curves became more irregular at high current density. The magnitude of voltage fluctuation increased with current density first and reached a maximum value at current density of 0.9 A/cm2, and decreased when the current density was further increased. The extra resistance induced by bubbles was found to increase with the bubble coverage, showing a similar trend with published equations.