Fabrication processes process

There have been numerous efforts to inspect specimens by ultrasonic reflectivity (or pulse-echo) measurements. In these inspections ultrasonic reflectivity is often used to observe changes in the acoustical impedance, and from this observation to localize defects in the specimen. However, the term defect is related to any discontinuity within the specimen and, consequently, more information is needed than only ultrasonic reflectivity to define the discontinuity as a defect. This information may be provided by three-dimensional ultrasonic reflection tomography and a priori knowledge about the specimen (e.g., the specimen fabrication process, its design, the intended purpose and the material). A more comprehensive review of defect characterization and related nondestructive evaluation (NDE) methods is provided elsewhere [1]. 

Greskovioh C 1976 Milling Ceramic Fabrication Processes, Treatise on Materials Science and Technology vo 9, ed F F Y Wang (New York Aoademio) pp 15-33... 

Brindiey G W 1960 ion exchange in ciay minerais Ceramic Fabrication Processes ed W D Kingery (New York Wiiey) pp 11-23... 

Fig. 7. Fabrication process for MLC capacitors. Steps are (a) powder (b) slurry preparation (c) tape preparation (d) electroding (e) stacking (f) lamination (g) dicing (h) burnout and firing and (i) termination and lead attachment.

M. H. Leipold, "Hot Pressing," ia F. F. Y. Wang, ed.. Treatise on Materials Science and Technology, Vol. 9 (Ceramic Fabrication Processes), Academic Press, New York, 1976. 

Fabrication and Processing. PVDF is available in a wide range of melt viscosities as powder or pellets to fulfill typical fabrication requirements latices are also commercially available. 

For high temperature fuel ceUs, there is stiU a strong need to develop lower cost materials for ceU components. In the case of SOFCs, improved fabrication processes and materials that permit acceptable performance in fuel ceUs at lower operating temperatures are also highly desirable. 

Etching. After a resist is patterned on a wafer, the exposed or unwanted substrate is removed by etching processes. Subsequentiy the resist is removed, leaving a desired pattern in a functional layer of the integrated circuit. Etching is performed to pattern a number of materials in the IC fabrication process, including blanket polysiHcon, metal layers, and oxide and nitride layers. The etch process for each material is different, and adapted to the material requirements of the substrate. 

There are several important fabrication processes for metal-matrix composites. 

Plastics Fabrication and Processing. The apphcation of microwave or r-f energy in various stages of fabrication of plastic products is widespread. Most apphcations operate at low frequency, ca 27 MHz. The estabhshed processes are weU known (180). 

The cost of a PV device is determined by several factors. These include the kind of materials used and the amount of materials requited, choice of substrates, device design, and fabrication processes. Crystalline devices ate generally mote efficient, but thin-film devices ate anticipated to cost less in flat-plate configurations. The use of concentrated light permits retention of efficiency with simultaneous reduction in cost. 

Antioxidants (qv) are used to prevent thermal and oxidative degradation of nylon in manufacturing, post-fiber and fabric processing, and final use. 

Methacrylate monomers are most effective with derivatives of bisphenol A epoxy dimethacrylates, in which the methacrylate—methacrylate cross-linking reaction proceeds at a much faster pace than with styrene monomer. This proves beneficial in some fabrication processes requiring faster cure, such as pultmsion and resin-transfer mol ding (RTM). 

Catalyst Selection. The low resin viscosity and ambient temperature cure systems developed from peroxides have faciUtated the expansion of polyester resins on a commercial scale, using relatively simple fabrication techniques in open molds at ambient temperatures. The dominant catalyst systems used for ambient fabrication processes are based on metal (redox) promoters used in combination with hydroperoxides and peroxides commonly found in commercial MEKP and related perketones (13). Promoters such as styrene-soluble cobalt octoate undergo controlled reduction—oxidation (redox) reactions with MEKP that generate peroxy free radicals to initiate a controlled cross-linking reaction. 

Some fabrication processes, such as continuous panel processes, are mn at elevated temperatures to improve productivity. Dual-catalyst systems are commonly used to initiate a controlled rapid gel and then a fast cure to complete the cross-linking reaction. Cumene hydroperoxide initiated at 50°C with benzyl trimethyl ammonium hydroxide and copper naphthenate in combination with tert-huty octoate are preferred for panel products. Other heat-initiated catalysts, such as lauroyl peroxide and tert-huty perbenzoate, are optional systems. Eor higher temperature mol ding processes such as pultmsion or matched metal die mol ding at temperatures of 150°C, dual-catalyst systems are usually employed based on /-butyl perbenzoate and 2,5-dimethyl-2,5-di-2-ethyIhexanoylperoxy-hexane (Table 6). 

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