Tungsten Filament Research Articles

Heat Control simulation for variothermal injection moulding moulds using infrared radiation

Mould temperature control has a significant influence on component quality and costs in the plastic injection moulding process. In the case of standard applications isothermal temperature control, in which the mould temperature is maintained at one level, is sufficient. For special applications (e.g. plastic optics; long, thin components; moulding of microstructures) variothermal temperature control using cyclically changing temperatures is beneficial. Therefore, the use of infrared radiators offers advantages in terms of achievable temperatures and investment costs but at low heating rates and efficiency. This paper therefore investigates the possibility of increasing the efficiency of energy input by infrared radiation into metals in particular into aluminium. For this purpose, a simulation model is developed. The numeric models used are validated by means of experiments. A short-wave infrared radiator is investigated, consisting of a tungsten filament in a quartz glass tube. The emitter power is varied from 1200 to 400 W. An aluminium sample with a thickness of 10 mm and a square base with an edge length of 60 mm is investigated. The temperature is measured on the non-irradiated side in the centre of the sample surface and at a distance of 20 mm from it while being irradiated. For the numerical model, a ray tracing simulation is carried out in a first step, the result of which is used as a Neumann boundary condition for a thermal simulation in second step. The model created can serve as a basis for the thermal design of more complex geometries.

Functionalized carbon nanotubes for thermionic emission and cooling applications

Barium strontium oxide-coated carbon nanotubes (CNTs) were implemented as a work function lowering and field enhancing functional coating on a coiled tungsten filament to create a new thermionic cathode. This cathode resembles conventional oxide cathodes in structure. It has the same coiled tungsten filament as a conventional oxide cathode but uses barium strontium oxide-coated CNTs instead of the traditional barium strontium calcium oxide powder mixture as an emissive coating. The cathode produces a strong thermionic emission. At 1395 K and 2.5 V/μm, the thermionic emission current of 0.87 A or current density of 2.9 A/cm2 was obtained from this oxide-coated CNT cathode. This level of emission is about three times as large as a conventional oxide cathode operating at similar temperature and field strength. Strong thermionic emissions from the cathode also lead to a large thermionic cooling effect. Temperature reduction as large as 90° was observed from the cathode surface when it was emitting electrons. Strong thermionic emission and a large cooling effect obtained are the result of the combination of the low work function of barium strontium oxide (1.6 eV) and the large field effect induced by the CNTs. Plasma enhanced chemical vapor deposition was used to grow CNTs, and magnetron sputtering deposition was used to deposit the barium strontium oxide functional coating; details of the cathode fabrication are presented to illustrate both the versatility of the processing techniques and the adaptability of barium strontium oxide-coated CNTs as a functional coating. Measurements on thermionic emission and thermionic cooling of the cathode are also presented.

Structure-dependent adsorption and desorption of hydrogen on FCC and HCP cobalt surfaces

The interaction of hydrogen with cobalt surfaces is of fundamental interest for Fischer-Tropsch synthesis. In the present work, the adsorption and desorption of hydrogen was studied on various cobalt single crystal surfaces that together represent the surface structures exposed by FCC and HCP cobalt nanoparticles used in applied catalysis. Dissociative hydrogen adsorption is activated on flat Co(0001), especially for hydrogen coverages beyond 0.5 ML. A tungsten filament creates hydrogen atoms and hot hydrogen molecules that increase the dissociative sticking probability and make it possible to obtain hydrogen coverages above 0.5 ML. Hydrogen in excess of 0.5 ML binds more weakly and desorbs in a separate low temperature desorption peak, in line with theoretical predictions. A third desorption peak appears above 1 ML and is attributed to subsurface hydrogen, the formation of which is attributed to hydrogen atoms produced by the tungsten filament. Adsorbed hydrogen atoms form (islands) of an ordered (2 × 2)-2H honeycomb structure for coverages between 0.3 and 0.8 ML which points to a specific stability of this structure. Step and kink sites on vicinal close-packed surfaces provide a low energy path for both hydrogen adsorption and desorption which results in a much higher dissociative sticking probability and a lower desorption temperature. The hydrogen adsorption strength on various FCC and HCP cobalt surfaces varies between 30 and 45 kJ/mol Had and is strongest on threefold hollow sites on the close-packed terraces while it is significantly lower on fourfold hollow sites on FCC-(100) and on threefold hollow sites on various open HCP surfaces. Under reaction conditions, the structure-dependent adsorption energy translates to a two to three orders of magnitude variation of the equilibrium constant for hydrogen.

A simple replacement of tungsten filament hot cathodes by DC heated LaB6 rod and its noise characteristics with laser-induced fluorescence.

Hot cathode discharges are common plasma sources for fundamental plasma physics studies and other applications due to their quiescent and relatively simple properties, and tungsten filaments are commonly used for the ease of heating them. Recently, tungsten filaments are increasingly being replaced by less luminous alternatives, such as barium oxide or lanthanum hexaboride. These materials can emit electrons at temperatures close to 1000K lower than tungsten, greatly reducing their blackbody radiations. This results in significant improvement in signal recovery for active spectral diagnostic, such as laser-induced fluorescence. However, these less luminous cathodes often come in vastly more complicated designs than those of tungsten hot cathodes and are much more expensive to procure and difficult to operate. In this paper, we present a simple, low cost direct current heated designof a LaB6 cathode that is manufactured at suitable dimensions and make a comparison of the laser-induced fluorescence (LIF) signal-to-noise ratio of this LaB6 hot cathode discharge with that of a typical tungsten filament discharge, revealing that LaB6 has, indeed, an improved LIF signal-to-noise ratio compared with the tungsten filament.

Degradation processes in tungsten filaments at high temperatures

Degradation processes in tungsten filaments of lighting lamps under normal operating conditions are experimentally studied. The duration of each measurement in continuous mode is about 18 hours. To increase the measurement accuracy, subtraction (compensation) of the constant component of the voltage is used. To compensate for the constant component of the voltage, a low noise reference DC voltage source is used. Using this scheme allowed decreasing the influence of the inherent noise of power supplies without suppressing degradation processes. It is shown that the relative change in resistance during the measurement does not exceed 2.8·10−3. It is also shown that the joint influence of voltage fluctuations of power supplies and low noise reference voltage source on the measurement results corresponds to a relative change in a resistance equal to 2.8·10−4. The study of degradation processes can be used to assess the reliability (and durability) of products in electrical engineering and radio electronics.

Filament X-ray Tube Current Control Method Using Indirect Filament Temperature Estimation

The recent increase in ailments has increased the demand for diagnosis and surgery based on X-rays. An X-ray system using a filament-type tube heats the filament for operation, and the electrons emitted by the thermal energy during this process produce X-rays. Conventionally, current control-based methods are used to regulate heating. However, these methods do not control the temperature of the filament, resulting in lower or higher output than the desired dose rate. Therefore, we propose a filament temperature control method that enables constant temperature control, which cannot be achieved using the existing heating method for X-ray systems with filament tubes. Additionally, we developed an indirect temperature estimation algorithm for the tungsten filament to incorporate the proposed method. To validate the tube current control through temperature control, we performed experiments to compare the existing current-controlled heating and temperature control methods in terms of the filament temperature. As the tube current is proportional to the dose rate, it was measured through a comparative analysis of the change in the output of dose rate over time. The obtained results validate that the proposed method can maintain both the filament temperature and tube current at the desired level.

Modeling of tungsten filament in gas discharge in H- ion source.

Sources of negative ions such as H- are essential elements of proton accelerators and tokamaks. They have limited lifetime. The replacement of an ion source is a costly process causing delays in the operation of the entire machine. The hot tungsten filament is the key element that limits the lifetime of the H- ion source at the Los Alamos Neutron Science Center (LANSCE) facility. An accurate model, which describes the filament physics and provides a reliable estimate on its lifetime, may significantly improve the operation of the facility. Here, we describe such a model, including a comprehensive list of relevant physical processes from first principles. The model can be used to describe different regimes of operation using diagnostics data as input parameters. It has been benchmarked against the data collected during the production cycle at LANSCE and shows good agreement with experimental data.

Fluorescent lamp tungsten filament thermionic emission gun as a novel humidity optical sensor

Detecting humidity have been remained a continuing concern within some important areas such as structural health, food processing, industrial as well as agricultural products. In this study, a novel humidity optical sensor is introduced based on the thermionic emission of tungsten filament using the fluorescent lamp set-up. Estimated blue compliant using a charged coupling device camera in optical image of the tungsten filament was confirmed as an appropriate detection system for relative humidity (RH) sensing. The fabricated optical sensor has wide linear range (2.0–98% RH), improved detection limit (< 5.0% RH), acceptable saturated limit (> 99.0% RH), improved percentage of relative standard deviation (4.18%, n = 2), adequate hysteresis (< 4.0% RH) and a shorter rise time (< 5.0 s), respectively. The mechanism behind this detection system is based on the interaction between H2O and tungsten filament during formation of W{mathrm{O}}_{3}.x {mathrm{H}}_{2}O (x = 1–2) in terms of some spectroscopic obtained evidences as well as Fourier transform infrared and X-ray diffraction spectrometries.

Laser induced visible and infrared emission of a tungsten filament.

The measurements of laser induced emission (LIE) of a tungsten filament upon irradiation with the focused beam of a CW IR laser diode are reported. It was found that the emission occurred in visible and infrared range. The influence of the applied DC electric field significantly affected the intensity of LIE of the tungsten filament. The origin of LIE is discussed in terms of multiphoton ionization of tungsten W+ atoms assisted by light emission due to the intervalence charge transfer in the tungsten hybrid domain (W, W+).

ION GENERATION BY TUNGSTEN FILAMENT FOR PYROELECTRIC PULSED ACCELERATOR

The article is devoted to investigation of ion generation by tungsten filament in vacuum. Electron and ion currents from tungsten filament at different residual air gas pressures are measured and compared. Dependencies of ion and electron currents from tungsten filament on its supply voltage are measured. Production of ions in the vicinity of the filament is discussed. Prospects of tungsten filament’s application in pyroelectric and piezoelectric pulsed accelerators are discussed.

Bridge Method for Studying the Spectra of Current Fluctuations in Tungsten Filaments in the Frequency Range 1.5·10–5–5·10–1 Hz

Bridge Method for Studying the Spectra of Current Fluctuations in Tungsten Filaments in the Frequency Range 1.5·10–5–5·10–1 Hz

Injection of positrons into a dense electron cloud in a magnetic dipole trap

The creation of an electron space charge in a dipole magnetic trap and the subsequent injection of positrons have been experimentally demonstrated. Positrons (5 eV) were magnetically guided from their source and injected into the trapping field generated by a permanent magnet (0.6 T at the poles) using a cross field E × B drift, requiring tailored electrostatic and magnetic fields. The electron cloud is created by thermionic emission from a tungsten filament. The maximum space charge potential of the electron cloud reaches −42 V, which is consistent with an average electron density of (4±2)×1012 m−3 and a Debye length of (2±1) cm. We demonstrate that the presence of this space potential does not hamper efficient positron injection. Understanding the effects of the negative space charge on the injection and confinement of positrons represents an important intermediate step toward the production of a confined electron–positron pair plasma.

Correlation between Raman spectra and color of tungsten trioxide (WO3) thermally evaporated from a tungsten filament

The color exhibited by tungsten trioxide (WO3) can be associated with both its stoichiometry and crystallinity. Correlation between the color exhibited by WO3 powders and their purity and crystalline properties is reported in this paper. The WO3 powders were deposited by evaporation of tungsten trioxide from the surface of a tungsten filament. The WO3 powders exhibited three different shades of blue: navy, royal, and sky. The color of the WO3 powders changed to white after thermal treatment at 500 °C for 30 min in an ambient atmosphere. Raman analyses showed that transition from amorphous to crystalline WO3 started when the powders exhibited navy-blue color and ended when WO3 powders exhibited a white color. Scanning electron microscopy analysis showed particle agglomeration characteristics in all WO3 powders, even after they were thermally treated. The mechanism of deposition of WO3 from the tungsten filament was suggested to be governed by thermal evaporation of tungsten trioxide from the surface of the oxidized tungsten filament.

Low-Cost Radiant Heater for Rapid Response, High-Temperature Heating

High-temperature processing has an irreplaceable role in many research and industrial applications. Despite remarkable development spanning over a century, the pursuit of even higher thermal flux density and more rapid thermal transients has not slowed down. As part of the ongoing energy evolution, many industrial applications are transitioning from direct combustion of fossil fuels as primary energy sources to increasing electrification, capable of adapting to renewable power grids. Thus, there is an emerging need for electrical heaters that can replace burners and supply the heat demand, especially at the highest temperatures. In this study, we report on a radiant heater design that can achieve cyclic heating/cooling rates of up to 400 K min–1 and a temperature range in excess of 1,800 K, comparable to those of commercial infrared gold image furnaces, at high surface and volumetric power densities. The heater consists of a modular unit of incandescent tungsten filament and is enclosed in an evacuated ceramic envelope, chemically inert, tolerant of thermal shock, and impervious to gasses. The material and manufacture cost of such heaters, which is estimated at ∼$0.05/W, is less than 0.03% of that for infrared gold image furnaces, which is at &amp;gt;$2/W. Tests of more than 10,000 demanding cycles (high temperature and high heating/cooling rate) over 350 h of total operational time and in different temperature ranges confirm the robust performance of radiant heater prototypes. The design is widely applicable to high-temperature reactor and furnace designs. In thermochemistry research and practice, these radiant heaters could offer multiple benefits compared to solar simulators, lasers, infrared gold furnaces, ceramic heaters, or direct concentration of solar input.

Super-Resolution Photoacoustic Microscopy Using Structured-Illumination.

A novel super-resolution volumetric photoacoustic microscopy, based on the theory of structured-illumination, is proposed in this paper. The structured-illumination will be introduced in order to surpass the diffraction limit in a photoacoustic microscopy (PAM) structure. Through optical excitation of the targeted object with a sinusoidal spatial fringe pattern, the object's frequency spectrum is forced to shift in the spatial frequency domain. The shifting in the desired direction leads to the passage of the high-frequency contents of the object through the passband of the acoustic diffraction frequency response. Finally, combining the low-frequency image with the high-frequency parts in four regular orientations in the spatial frequency domain is equivalent to imaging the targeted object with an imaging system of two-fold bandwidth and thus half lateral resolution. In order to obtain the image of out-of-focus regions and improve the lateral resolution outside the focal region of a PAM imaging system, Fourier-domain reconstruction algorithm based on the synthetic aperture focusing technique (SAFT) using the virtual detector concept is utilized for reduction in the required computational load and time. The performance of the proposed imaging system is validated with in vivo and ex vivo targets. The experimental results obtained from several tungsten filaments in the depth range of 1.2 mm, show an improvement of -6 dB lateral resolution from 55- [Formula: see text] to 25- [Formula: see text] and also an improvement of signal-to-noise ratio (SNR) from 16-22 dB to 27-33 dB in the proposed system.

The Research of Tool Wear Mechanism for High-Speed Milling ADC12 Aluminum Alloy Considering the Cutting Force Effect.

Tool wear is a major cause of accelerated tool failure during the milling of aluminum alloy. The periodically cutting force directly affect the cutting heat and tool wear due to the intermittent cutting characteristics of the milling process. The focus of this paper is to analyze the influence of the variation of cutting force on tool wear behavior. The change law of cutting force by cutting parameters was analyzed firstly. Secondly, the variation of the wear land width (VB) of tool flank face by the milling length was analyzed. Thirdly, the wear morphology and the energy dispersive spectrometer (EDS) results of tool rake face and flank face in different cutting parameters were observed by tungsten filament scanning electron microscope. Finally, considering the cutting force effect, the tool wear mechanism during high-speed milling of Aluminum-Alloy Die Castings 12 (ADC12, 12 means aluminum number 12) was analyzed. The cutting force in tangential direction is predominant during high-speed milling aluminum alloy, which decreases gradually with the increase of cutting speed but increases gradually with the feed rising. The adhesion-oxidation wear was main wear mechanism of tool rake face during high-speed milling. While adhesive wear was the main wear mechanism of the tool flank face during high-speed milling. It is found that the formation of adhesive wear is the process from particle adhesion to melting until the formation of adhesive layer, which related to the change of cutting force.

Generation and Demolishment Mechanisms of Vapor Bubble Around Hot Tungsten Filament in Superfluid Helium-4

The electric transport I–V characteristics of a tungsten filament immersed in superfluid helium are experimentally studied. The forward sweep I–V characteristics show an abrupt jump from the linear ohmic regime (C state) to the high-resistance non-ohmic regime (H state). In the H state, the filament is covered with a He gas bubble. In the C state, there is no gas bubble, that is, liquid He directly touches the filament surface. The transitions between these two states exhibit a well-developed hysteresis and bistability. The transition from the H state to the C state occurs at the equilibrium gas–liquid phase transition point, as reported by Date et al. (J Phys Soc Jpn 35(4):1190, 1973), whereas the C-to-H-state transition occurs in the superheat region.

Bridge method for studying the spectra of current fluctuations in tungsten filaments at the frequency range 1.5∙10–5–5∙10–1 Hz

The problem of the absence of methods for measuring low-frequency fluctuation processes at high temperatures is considered. An original bridge method is proposed for measuring the spectra of low-frequency current fluctuations in tungsten filaments of electric lamps in a controlled temperature range of 300–2700 K. Application of the bridge measurement scheme allows us to reduce the influence of degradation processes in the filament and the power source's own noise on the measurement results by several orders of magnitude. Spectral analysis of low frequency current fluctuations is performed at the frequency range 1.5∙10–5–5∙10–1 Hz using an automated setup based on a personal computer under the control of specially developed software.

Study on the Validity of Wien’s Displacement Law on Tungsten Bulb

This work was mainly based on three interdependent parameters, which are temperature, emissivity and peak emission wavelength. Temperature is the primary parameter that determines how much light the filament gives off, and at what wavelengths. The work was focused on temperature determination of tungsten filament with different values of emissivity. The different values of emissivity taken for the work were 0.433, 0.431, 0.427, 0.421 and 0.415. Peak emission wavelength was calculated at different tungsten temperatures for different wattage bulbs which was in the order of 10-6m. 6, 60, and 500 watt bulb were taken for the work. The peak of the spectrum lay in the infrared region. Wien’s displacement law was used to calculate the value of peak emission wavelength. The work was based on theoretical model. Blackbody spectrum curve was used to analyze the emitted radiations from the bulb. In each spectrum curve, radiations having higher wavelengths were emitted in greater amount than the radiations having lower wavelength. Spectral radiance was found to be dependent upon both emissivity and power of the bulb. The area under the blackbody spectrum curve indicated the total number of emitted radiations and hence the total energy radiated across all wavelengths. The total energy emitted from tungsten filament was found to be increased rapidly with temperature. Brightness of the bulb increased with the increase in temperature of the tungsten. The peak in the blackbody spectrum curve shifts towards left, when temperature increased. There is a direct consequence of the brightness of bulb with the peak emission wavelength.

A prototype Multi-X-ray-source array (MXA) for digital breast tomosynthesis

The design and testing of a prototype Multi-X-ray-source Array (MXA) for digital breast tomosynthesis is reported. The MXA is comprised of an array of tungsten filament cathodes with focus cup grid-controlled modulation and a common rotating anode housed in a single vacuum envelope. Prototypes consisting of arrays of three-source elements and eleven-source-elements were fabricated and evaluated. The prototype sources demonstrated focal spot sizes of 0.3 mm at 45 kV with 50 mA. Measured x-ray spectra were consistent with the molybdenum anode employed, and the tube output (air kerma) was between 0.6 mGy/100 mAs at 20 kV and 17 mGy/100 mAs at 45 kV with a distance of 100 cm. HVL measurements ranged from 0.5 mm Al at 30 kV to 0.8 mm Al at 45 kV, and x-ray pulse widths were varied from 20 ms to 110 ms at operating frequencies ultimately to be limited by source turn-on/off times of ∼1 ms. Initial results of reconstructed tomographic data are presented.