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.

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.

Textile preforms for tungsten fibre-reinforced composites

Demanding high heat flux applications, as for example plasma-facing components of future nuclear fusion devices, ask for the development of advanced materials. For such components, copper alloys are currently regarded as heat sink materials while monolithic tungsten is foreseen as directly plasma-facing material. However, the combination of these materials in one component is problematic since they exhibit different thermomechanical characteristics and their optimum operating temperatures do not overlap. In this context, an improvement can be achieved by applying composite materials that make use of drawn tungsten fibres as reinforcement. For the manufacturing processes of these composites, suitable tungsten fibre preform production methods are needed. In the following, we will show that tungsten fibres can be processed to suitable preforms by means of well-established textile techniques as studies regarding the production of planar weavings (wire distances of 90–271 µm), circular braidings (multilayered braidings with braiding angle of 60° and 12°) as well as multifilamentary yarns (15 tungsten filaments with 16 µm diameter) are presented. With such different textile preforms tungsten fibre-reinforced tungsten (W f/W) with a density of over 99% and pore-free tungsten fibre-reinforced copper W f/Cu composites were produced which proves their applicability with respect to a composite material production processes.

EBSD Analysis of Tungsten-Filament Carburization During the Hot-Wire CVD of Multi-Walled Carbon Nanotubes

Filament condition during hot-wire chemical vapor deposition conditions of multi-walled carbon nanotubes is a major concern for a stable deposition process. We report on the novel application of electron backscatter diffraction to characterize the carburization of tungsten filaments. During the synthesis, the W-filaments transform to W2C and WC. W-carbide growth followed a parabolic behavior corresponding to the diffusion of C as the rate-determining step. The grain size of W, W2C, and WC increases with longer exposure time and increasing filament temperature. The grain size of the recrystallizing W-core and W2C phase grows from the perimeter inwardly and this phenomenon is enhanced at filament temperatures in excess of 1,400°C. Cracks appear at filament temperatures >1,600°C, accompanied by a reduction in the filament operational lifetime. The increase of the W2C and recrystallized W-core grain size from the perimeter inwardly is ascribed to a thermal gradient within the filament, which in turn influences the hardness measurements and crack formation.

Effect of Au Doped WO3 Gas Sensors for NO2 Detection

Gas sensor based on point contact tungsten trioxide (WO3) was prepared by in-situ induction-heating thermal oxidation of tungsten filaments. X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM) were employed to analyze the phase and the morphology of the fabricated thin films. The results showed that the WO3films exhibited a monoclinic phase and were composed of hierarchical micro and nano crystals. The NO2(1-8 ppm) sensing properties of the point contact sensors based on Pure and Au-sputtering doped (2.5 at%) WO3films were investigated. The results showed that the gas sensing properties of the Au (2.5 at%) doped WO3sensors were superior to those of the undoped. The obtained point contact WO3sensor exhibited the maximum NO2gas response at 100°C.