Popcorn effect

When oil shale is retorted, the inorganic portion of the shale expands considerably. The spent shale remaining has no direct commercial value and, ideally, it is placed back in the mine. However, because of the popcorn effect, the volume of spent shale is greater than the volume of the mine from which it was taken. 

The characteristics of a metal which contribute to a good incendiary capabUity are not yet fully understood nor have they been completely defined. Hillstrom (Ref 64) found that pyrophoricity is related to the ratio of the oxide volume to the metal volume, a ratio above one giving rise to the popcorning effect which is... 

The prepared CEB material has pores in the size order of a few hundreds pm, and this may result in the so-called popcorn-effect yielding a larger effective surface area. As plugging of the pores is probably the main cause for the inconqslete utilization of CaO-based materials, the high porosity of CEB is an indication of the potential of CEB as a desulfurization sorbent, as has been shown in TGA experiments. 

Materials which sublime can experience a popcorn effect in which the part of the source granules in contact with the substrate vaporizes first and... 

Fig. 4.4. A schematic cross-section of two evaporation boats showing the popcorn effect. In (a), the boat is open, and the evaporant material sublimes first at the hottest point of the assembly, which is the bottom of the material granules. This creates a vapor jet which can eject solid particles of evaporant from the boat. In a baffled arrangement (b), the source is constructed so as to prevent line of sight contact between the source and the substrate. Solid particles which are propelled are trapped, whereas material vapor can escape and deposit.

A fourth generation of electrically conductive adhesives based on cyanate esters and modified cyclo-olefin thermoset (MCOT) resins was introduced in the 1990s. These resins were specially formulated for low moisture absorption, high thermal stability, and low stress to be compatible with solder-reflow conditions. They were developed to prevent or reduce the so-called popcorn effect, a failure mode attributed... 

Subsequently the solder reflow process used in PCB assembly may produce a dramatic reaction, known as the popcorn effect , due to rapid expansion of the moisture within the package which then bnrsts with resulting physical damage. The problem is avoided by pmchasing components in vacuum-sealed moisture-controlled packs which have to be stored in a controlled enviromnent after being opened. The use of the components is then governed by the supplier s instructions as printed on the packaging. 

Component lead finish is another important aspect that must be considered to achieve total lead-free implementation. The matter of component and PWB finish is discussed in detail in Chap. 12. Both Ni/Pd and Ni/Pd/Au are among the major surface finish candidates for lead-free component leads. Important aspects to consider are the adhesion of a lead finish to the molding compound and process compatibility. The typical thicknesses for these finishes are listed in Table 13. Inadequate adhesion can lead to delamination, followed by moisture ingress and possible popcorn effect. 

Chloroprene monomer will autoxidise very rapidly with air, and even at 0°C it produces an unstable peroxide (a mixed 1,2- and 1,4-addition copolymer with oxygen), which effectively will catalyse exothermic polymerisation of the monomer. The kinetics of autoxidation have been studied [1], It forms popcorn polymer at a greater rate than does butadiene [2],... 

Chemical modification of simple sugars during drying, baking, or roasting operations can either have a desirable or undesirable effect upon the organoleptic quality of the final product. We have become accustomed to the characteristic roasted or baked flavors of coffee, peanuts, popcorn, and freshly-baked bread. The color and flavor and aroma of caramel make it a useful additive for the food industry. On the other hand, the burnt flavor of overheated dry beans or soy milk reduces marketability of these products. 

Studies in the grafting of mixed monomers to cellulose have also been reported by Sakurada (113). Binary mixtures studied included butadiene with styrene or with acrylonitrile, and styrene with acrylonitrile. Remarkable increases in rate in the case of mixed monomer similar to those found by RAPSON were found in many cases. For example, about 10% of butadiene increased the grafting yield about ten fold. Similar results were found with the addition of acrylonitrile to butadiene and to styrene. Ternary mixtures of monomers were also investigated by both Rapson (109) and Sakurada (113). The large increases in rate with certain mixtures were interpreted by Sakurada as due to a particular balance of gd effects akin in many ways to popcorn polymerization. The effects were found also with polyvinyl alcohol but not with polyethylene where gel effects would perhaps be less prominent. 

Figure 8-46 Relationship Between Water Activity and Crispness of Popcorn. Source. Reprinted with permission from E.E. Katz and T.P. Labuza, Effect of Water Activity on the Sensory Crispness and Mechanical Deformation of Snack Food Properties, J. Food Sci., Vol. 46, p. 403, 1981, Institute of Food Technologists.

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