Results of an extensive investigation of the optical properties of CaWO₄:Sm³⁺are reported. Absorption, fluorescence, and excitation spectra and pulsed fluorescence measurements were obtained at temperatures from below 8 K to room temperature on an undoped single crystal and crystals containing samarium concentrations ranging between 0.01% and 1.0%. An empirical energy-level diagram is determined for trivalent samarium in this host and the existance of several different nonequivalent crystal-field states is established. It is found that host-sensitized energy transfer to the samarium occurs in varying degrees from all four of the lowest excited states of calcium tungstate and the efficiency of transfer is different for different crystal-field sites. The ratios of the integrated fluorescence intensities and decay times were measured and from these the temperature and doping concentration dependences of the energy transfer rate were found for excitation in the different host excited states. A model is proposed to explain the results which is based on energy transfer from self-trapped excitons at low temperatures and thermally activated exciton hopping migration to activator-induced host traps at high temperatures. This model predicts the correct dependences for all of the observed data. Quantitative estimates indicate that exchange is somewhat stronger than dipole-dipole interaction for both migration and transfer and the exciton diffusion coefficient is found to be on the order of 10^-7cm²sec^-1.

 

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Comparing with the results of normally vacuum sintered, the strengthening phenomena of hot isostatic tungsten carbide inserts by direct observation obtain following results,

Firstly, when closely examining the hot isostatic tungsten carbide inset, there is a slight change of WC in terms of grain size, the composition as well as distribution of the binder phase and etc., although these changes were considered to have no relation to the strength increasing. Secondly, the strengthening mechanism of hot isostatic tungsten carbide insert is directly related to a small number of large pores disappearance while the large pores usually exit in normally vacuum sintered ones. It should be noticed that since there are some large WC grains are contained in the structure, a sharp increase in strength is not always visualized as a result of hot isostatic pressing.

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Cryogenic processing is referred to a range of below zero heat treatment, which are currently employed by the dozens of materials and components treatment process. Generally, it contains steps to cool the tungsten carbide inserts to the temperatures below -130℃ in order to permanently or semi-permanently alter their microstructures. As in such ways, it could offer tool’s improvement regarded to machining performance, wear resistance and ultimately increased service life.

Cryogenic processing of tungsten carbide inserts commonly involves a use of liquid nitrogen into a thermally insulate tank containing the parts to be treated. The three ways of application of cryogenic fluid include, to perform as a cryo-quench by direct immersion of parts, to cool air within the tank as a working fluid, and to create a dry atmosphere by acting as a gas which circulated by fans.


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Due to its high density, excellent absorption behaviour against radiation and environmental friendly characteristics, tungsten alloy can be widely used to produce tungsten Sr-90 radiation detector.Sr-90 undergoing beta decay is exposed to the aluminum sheets. On the other side of the sheet there is a tungsten Sr-90 radiation detector called Geiger counter which detects how much radiation has penetrated the sheet.

Sr-90 undergoes beta decay. Of the three types of radiation, beta radiation is the most appropriate due to its penetration powers as a thickness gauge for aluminum. This is due to the fact that alpha particles such a low penetrating power that it cannot pass through a sheet of paper, certainly not sheet metal, and gamma rays have such a high penetrating power that all gamma particles would easily pass through the aluminum. Beta particles have a moderate penetrating power that can be blocked by a thick sheet of aluminum, but it can pass through a thinner piece. This property makes it suitable for use as a thickness gauge of aluminum sheets.

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