Screens, coating

Another name for a beam of electrons is a cathode ray. Cathode ray tubes, or CRT for short, are used extensively in video monitors and televisions. The electrons are ejected from the electron gun and directed at a screen coated with substances that glow different colors when struck with the electrons. The electron beam must strike different regions of the screen at different times and frequencies to create a clear... 

Filter. A filter is used in some cases when coagulation and sedimentation do not completely separate the solids from the liquid waste in areas where sand and sandstone formations are susceptible to plugging. Filters with a series of metal screens coated with diatomaceous earth or cartridge filters are typically used.27 Where limestone formations with high solution porosity are used for injection, filtration is usually not required. 

Polythiophene derivatives are being used in FETs. Polypyrrole is being used as microwaveabsorbing stealth screen coatings and in sensing devices. PPV derivatives are being used in the production of electroluminescent displays. 

Provision for the heating of metal parts to at least 800°C. Very short lengths and screen coatings need not be so heated. 

Fig. 4. Arrangement for calibrating fluorescence spectrometer.17 L, xenon arc lamp Mi, excitation monochromator B, silica plate beam splitter. F, 0.5 mm. silica optical cell containing fluorescent screen solution Pi, monitoring multiplier phototube S, screen coated with MgO Mj, fluorescence monochromator Pa, fluorescence multiplier phototube.

Fig. 25. Current-potential curves for hydrogen evolution in 5MKOH at 70°C. (1) 80 mesh Ni screen coated with thermally prepared Ni+Mo coating (2) 80 mesh Ni screen. After ref. 505, by permission of IAHE.

A great variety of techniques is available but as a basis for vinyl wallcoverings two only have become popular—reverse-roll coating and screen coating—both of which have the virtues of accuracy and high speed. 

Screen coating is described later in this chapter. The system used most widely is reverse-roll coating, which is capable of applying uniform coating of weights ranging from 80 to several hundred g m-2, within limits better than 5% and at speeds up to 150 m min-1. The usual form of the equipment is three-rolls, nip-fed, as illustrated in Figure 108. 

Figure 114 Screen coating increased delivery of paste when the blade of the squeegee is above the centre of the counter roller...

Also in the early 1900s Ernest Rutherford performed his famous Gold Foil Experiment. Rutherford set up an experiment in which a radioactive substance released alpha particles. These particles were aimed at a thin sheet of gold foil. A screen coated with zinc sulfide was set up around the gold foil to detect the alpha particles when they hit the screen. Rutherford s experiment... 

Screen coating, typically used for wallcoverings, relies on plastisol being pumped into a cylindrical metal screen with fine perforations. The paste is forced through the perforations via a rubber blade onto the substrate the amount deposited being controlled by the screen mesh size and rubber blade pressure and angle. 

The production of flat-panel cathode ray tubes (CRTs) is essentially a fabrication issue. The basic principle of operation is the same as a standard CRT. Electrons are emitted from a hot cathode. These are guided by a magnetic field to the glass screen coated in a layer of phosphorescent material. Upon impact the energy of the electron is transferred to the phosphor and light is emitted. A regular pattern of red, green and blue phosphors creates a dense pattern of... 

A cathode-ray tube. The fast-moving electrons excite the gas in the tube, causing a glow between the electrodes. The green color in the photo is due to the response of the screen (coated with zinc sulfide) to the electron beam. 

Rutherford and his students used a screen coated with zinc sulfide to detect the arrival of alpha particles by the pinpoint scintillations of light they produce. That simple device has been developed into the modern scintillation counter. Instead of a ZnS screen, the modern scintillation counter uses a crystal of sodium iodide, in which a small fraction of the Na ions have been replaced by thallium (TH) ions. The crystal emits a pulse of light when it absorbs a beta particle or a gamma ray, and a photomultiplier tube detects and counts the light pulses. 

The experimenters set up a lead-shielded box containing radioactive polonium, which emitted a beam of positively charged subatomic particles through a small hole. Today, we know that the particles of the beam consisted of clusters containing two protons and two neutrons and are called alpha particles. The sheet of gold foil was surrounded by a screen coated with zinc sulfide, which glows when struck by the positively charged particles of the beam. 

Brethour J.M. 2000. Coating with Deformable and Permeable Surfaces Focus on Rotary Screen Coating. [LES]... 

Coating consistency is crucial when producing screens for photorealistic printing. If the emulsion thickness is not controlled, it could lead to uneven ink deposits and visual distortions such as moire. For this reason, automatic coating devices are recommended. But if the cost of such devices is prohibitive, then maintain consistency by introducing as few variables as possible to the manual screen-coating process, including the number of personnel involved. 

Rotary-screen coating is also used to apply either continuous or discontinuous coatings to nonwovens. The screen is a sleeve, perforated according to a mesh size which corresponds to the size and number of hole per unit area of surface. A... 

The nature of the experiment is indicated by the drawing in Figure 3-11. A piece of radium emits alpha particles in all directions. A narrow hole in a lead block defines a beam of the alpha particles. This beam of alpha particles then passes through the metal foil, and the directions in which the alpha particles continue to move are observed. The direction in which an alpha particle moves can be detected by use of a screen coated with zinc sulfide. When an alpha particle strikes the screen a flash of light is sent out. 

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