Cooling composition

Microstructurc. Crystal size, porosity, and impurity phases play a major role in fixing the fracture characteristics and toughness of an abrasive grain. As an example, rapidly cooled fused aluminum oxide has a microcrystalline stmcture promoting toughness for heavy-duty grinding appHcations, whereas the same composition cooled slowly has a macrocrystalline stmcture more suitable for medium-duty grinding. 

An example of a binary eutectic system AB is shown in Figure 15.3a where the eutectic is the mixture of components that has the lowest crystallisation temperature in the system. When a melt at X is cooled along XZ, crystals, theoretically of pure B, will start to be deposited at point Y. On further cooling, more crystals of pure component B will be deposited until, at the eutectic point E, the system solidifies completely. At Z, the crystals C are of pure B and the liquid L is a mixture of A and B where the mass proportion of solid phase (crystal) to liquid phase (residual melt) is given by ratio of the lengths LZ to CZ a relationship known as the lever arm rule. Mixtures represented by points above AE perform in a similar way, although here the crystals are of pure A. A liquid of the eutectic composition, cooled to the eutectic temperature, crystallises with unchanged composition and continues to deposit crystals until the whole system solidifies. Whilst a eutectic has a fixed composition, it is not a chemical compound, but is simply a physical mixture of the individual components, as may often be visible under a low-power microscope. 

The formation of a glass takes place when a liquid of any composition, cooled to room temperature, solidifies and retains a random liquid structure. Freezing-in of the random structure is facilitated by a rapid downshift of temperature when the liquid contains a high proportion of species known as glass formers. The common oxides of the high ionic charge elements, such as silicon, aluminum, and phosphorus, are well-known glass formers. 

Many minerals show exsolution textures. For these minerals, there is complete solid solution at sufficiently high temperatures, but a miscibility gap at lower temperatures. The alkali feldspar, (Na, K)AlSi30s, is an example. Suppose a roughly homogenous mineral of intermediate composition cools down and into... 

The formation of metal glasses by rapid cooling was first reported by Paul Duwez and co-workers in the 1960s. They achieved cooling rates of thousands of degrees per second by shooting a fine stream of liquid metal onto a water-cooled copper drum. With the early compositions, cooling rates of about 105 K/s were necessary to prevent crystallization. This limited alloys to thin ribbons or wires. 

Data on the effective metastable limit at the conditions you are interested in (composition, cooling rate, and stirring) are important because you normally wish to operate a crystallizer away from the edge of the effective metastable zone. As we will see in later chapters, formation of small crystals, which are known as fines, is a common problem. Fines cause filtration problems and... 

The idealised microstructure of a solid formed when other hquid compositions cool is derived in a similar way. Suppose that the liquid with composition Cl, richer in lead than the eutectic composition (Figure 8.5a), is slowly cooled. At temperature T, below the fiquidus, some solid a phase will have nucleated (Figure 8.5b). The composition of the solid phase, given by the tie line, is r. Similarly, the composition of the liquid phase is l. As slow cooling continues, the composition of the solid a crystallites will move along the solidus, as described in Section 8.2.1 for the nickel-copper alloys. At the same time, the composition of the liquid phase in contact with the crystallites will move along the fiquidus. For example, at temperature T2 the solid has a composition of S2 and the liquid a composition of I2 (Figure 8.5a). Ultimately, the horizontal solidus fine will be reached at the eutectic temperature. At this point, any further drop... 

Impregnation with PP is done on a double belt press that consolidates the fibers with PP under the influence of pressure and temperature. After the composites cool, the GMT semifinished product can be cut for specific applications. 

The post-fire elastic modulus, E, can be estimated from Eq. (8.2). The recovered elastic modulus for the DuraSpan material used was 88% of Eg, which was obtained from two-mn DMA, see Section 8.2.3. It should be noted that such a modulus recovery is a general behavior for FRP composites cooled down from glass transition, but before decomposition. For comparison, another pultraded GFRP material (from FiberHne, Denmark) is shown in Figure 8.16 [14], which exhibited a recovery to 96% of the initial value. 

The hot, plastic MES product extruded from the TTD plodder must be cooled to solidify the composition. Cooling the molten MES product can be accomplished continuously with a double-chilled belt cooler or chilled drum flaker (see Figure 11.8) that forms a 2- or 0.5-mm-thick flakes, respectively. 

Diluents/solvents affect the crystallization of polymers in several ways. One is that they lower the concentration of the polymer, limiting the rate of nucleation and growth. The other is that they lower the equilibrium dissolution temperature. Diluents/solvents can, therefore, be used to get controlled conditions for PSC with very regular crystal structures. Just as with composites cooled from a melt, CNTs can be used to nucleate PSCs in dilute and semi-dilute solutions as well. The precise control offered by dilution allows CNTs to crystallize polymer at temperatures above the homogeneous nucleation temperature. In some cases, this results in the transcrystallinity discussed in the last section, and in other... 

A.7 Effect of Carbon Fiber on the Cooling Time of a Composite. A 0.4064 cm thick laminate (layers of polymer sheet reinforced with long continuous fibers) consisting of 60 volume % carbon fiber and 40 volume % PEEK is cooled from 350 °C to 100 °C in a mold with the wall temperatures set at 75 °C. Neglecting crystallization and assuming constant thermal properties, determine how much faster the composite cools down to the final temperature relative to the pure matrix of the same thickness. The properties of the fiber and matrix are given in Table 5.11. 

The incorporation of the HDPE resin and the slip additive into the film base resin, at the appropriate let-down ratios, can be done by dryblending in a tumbler mixer, or other suitable vessels. An antioxidant may also be incorporated in the film base resin at a ratio from 0.03 to 0.2 parts by weight per 100 parts of the film base resin. The relatively well-blended mixture can then be extruded and converted into films or bags. After dryblending, as the composition cools down, the HDPE resin will give rise to the formation of larger crystals, which will be uni-... 

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