Fusion sealing

Glasses are very well suited for the production of mechanically reliable, vacuum-tight fusion seals with metals, ceramics, and mica. Some particularly favorable properties are the viscosity behavior of glass and the direct wettability of many crystalline materials by glasses. As a result, the production technology for such seals is characterized by uncomplicated procedures with few, easily manageable, well-controllable process steps. 

Materials used for substrates can be broadly classified into ceramics and metals. Gommonly used ceramics, ie, alumina, aluminum nitride, and beryUia, can be easily incorporated into a hermetic package, ie, a package permanently sealed by fusion or soldering to prevent the transmission of moisture, air, and other gases. 

Joining NonmetaUic Pipe Thermoplastic piping may be joined by a qiiahfied hot-gas welding procedure, a qnalined solvent-cement procedure, or by a qualified heat-fusion procedure. The general welding and heat-fiision procedures are described in ASTM D-2657 and solvent-cement procedures in ASTM D-2855. Two other techniques, for flared joints and elastomeric-sealed joints, are described in ASTM D-3140 and D-3139, respectively. 

Arsenic III oxide (arsenic trioxide, arsenious oxide) [1327-53-3] M 197.8, three forms m 200°(amorphous glass), m 275°(sealed tube, octahedral, common form, sublimes > 125° without fusion but melts under pressure), m 312°, pKj 9.27, pK 13.54, pK 13.99 (for H3ASO3). Crystd in octahedral form from H2O or from dil HCl (1 2), washed, dried and sublimed (193°/760mm). Analytical reagent grade material is suitable for use as an analytical standard after it has been dried by heating at 105° for l-2h or has been left in a desiccator for several hours over cone H2SO4. POISONOUS (particulary the vapour, handle in a ventilated fume cupboard). 

Hermetic Seal—an impervious seal made by the fusion of metals of ceramics, which prevents the passage of gas or moisture. The seal can be achieved by brazing, soldering, welding, fusing glass or ceramics. 

Hermetically sealed electrical devices must be verified by a testing laboratory to meet mechanical abuse and to withstand aging and exposure to expected chemicals. Devices potted with common silicones and similar materials by an end user or even a manufacturer, without testing, and devices merely provided with O-rings seldom meet acceptable criteria. Normally, hermetically sealed devices must be sealed through metal-to-metal or glass-to-metal fusion. Many electrical relays, switches, and sensors are available as hermetically sealed devices for common oil and gas producing facility applications. Hermetically sealed devices are often desirable to protect electrical contacts from exposure to salt air and other contaminants. 

Abschmelzdraht, m. fuse wire, fusible wire. Vbschmelzeu, v.i. melt off, melt. fuse, separate by melting seal off, seal. — v.i. melt off. Abschmelz-konstante, /. fusion coeflScient. -achweissung, /, flash welding, -sicherung, /, (Elec.) safety fuse. 

The product is analytically pure and shows a pasty fusion at 104°C (sealed tube). Yield 89%. 

Hermetically Sealed. A hermetically sealed device shall be sealed against the entrance of an external atmosphere and the seal shall be made by fusion, e.g., soldering, brazing, welding, or the fusion of glass to metal. 

Laser fusion, (a) A mixture of deuterium and tritium is sealed inside tire tiny capsule (1 mm in diameter] at the tip of the laser target. 

Continuous transition of state is possible only between isotropic states it may thus occur between amorphous glass (i.e., supercooled liquid of great viscosity) and liquid ( sealing-wax type of fusion ), or between liquid and vapour, but probably never between anisotropic forms, or between these and isotropic states. This conclusion, derived from purely thermodynamic considerations, is also supported by molecular theory. 

Heavens Field suggest that both gas cavities, sealed off during fusion of the sample, and high flow rate shearing near the impacting striker edge contribute to hot spot formation during PETN impact initiation... 

Where a chrect fusion of glass-to-metal or metal oxide is obtained (sometimes termed the wetting of metal by glass) two types of seal can result—one matched, the other mismatched, depending on how the relative coefficients of thermal expansion of the glass and the metal compare. 

Ampoules that have been sealed by fusion must be tested to ensure that a hermetic seal was obtained. The leaker test is performed by immersing the ampoules in a dye solution, such as 1% methylene blue, and applying at least 25 in. (64 cm) of vacuum for a minimum of 15 minutes. The vacuum on the tank is then released as rapidly as possible to put maximum stress on weak seals. Next, the ampoules are washed. Defective ampoules will contain blue solution. 

Stirrer, for caustic fusion, 30, 104, 105 seal for, 30, 54 Stobbe condensation, 30, 18 Styrene, 33, 72 Styrene dibromide, 30, 73 Styrene oxide, 31, 3 Succinic acid, cc-benzhydrylidene-,... 

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