Types of twins

This type of twin evolves and covers part of the (100) face for a 2. It disappears for a 2. 

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The following table compares the single screw extruder with the main types of twin screw extruders. 

Twin geometry may refer to just one set of atoms in the crystal rather than all. This type of twinning is met, for example, in cases where a fraction of octahedral or tetrahedral cation sites in a close-packed array of anions are occupied in an ordered fashion. The close-packed anion array remains unchanged by the twin plane, which applies to the cation array alone (Fig. 3.24). These boundaries are of low energy and are often curved rather than planar. In oxides such as spinel, MgAl204, in which cations are distributed in an ordered fashion over some of the octahedral and tetrahedral sites, boundaries may separate regions that are twinned with respect to the tetrahedral cations only, the octahedral cations only or both. 

Type of twin pair Number of pairs Intraclass R... 

There are some qualities—some incorporate things, That have a double life, which thus is made A type of twin entity which springs From matter and light, evinced in solid and shade. 

Twinning. Two or more crystals of the same species are sometimes found joined together at a definite mutual orientation, this orientation of the individual crystals being constant in different examples of any one species. Such crystals are said to be twinned. Certain species show this phenomenon frequently, and some species invariably. The most frequent type of twinning is that of calcium sulphate dihydrate (gypsum), which is often found in the form shown in Fig. 41 a. The two crystals appear to be joined at the 100 plane. At the junction there is presumably a sheet of atoms common to the two individuals when the crystal nucleus was formed, two lattices were probably built by deposition on opposite sides of this common sheet of atoms. 

In many cases, the martensite phase is internally twinned and is composed of two types of thin twin-related lamellae, as illustrated in Fig. 24.10. In such cases, the lattice-invariant shear is accomplished by twinning rather than by slip as has been assumed until now (see Fig. 24.106). The critical amount of shear required to produce the invariant habit plane is then obtained by adjusting the relative thicknesses of the two types of twin-related lamellae shown in Fig. 24.106. 

The two types of twin-related lamellae present are labeled 1 and 2. 

Twinning in crystals results front the intergrowth of two or more individuals in such a way as to y ield parallelism in the ease of certain parts of the different individuals und. at the same time, other parts of the different individuals are in reverse positions in respect to each other. For example, an octahedral crystal of magnetite is twinned when one-half of the crystal is rotated ISO parallel to an octahedral facial plane. This type of twinning is known as spinel rn inirini . owing to its common occurrence in the spinel group of minerals. 

Types of Twin Screw and Twin Rotor-based Machines, 525... 

TYPES OF TWIN SCREW AND TWIN ROTOR-BASED 525... 

Figure 6. Schematic diagrams of sections through two types of twin calorimeters. A Twin heat conduction (micro)calorimeter (vessels not shown). B Semiadiabatic twin calorimeter, a, vessel holder b, thermopile c, heat sink d, vessel (stirrer, thermometer, heater not shown) e, air or vacuum.

Figure 1.2 Japan law contact twin quartz crystal. This type of twinning was discovered in 1829 by C. S. Weiss in quartz crystal from the La Gardette mine in France. However, because of the abundance of these specimens in Japan, they are now known as Japanese twins.

The temporal evolution of twins has been investigated with an aid of computer simulation by Wild et al, [84]. Figure 6.1 shows a result of a twin evolution on a (111) face of a cubo-octahedral crystal, assuming that a =1.75. Note that time t is in arbitrary units, and the crystal size is normalized. It is seen that a small twin on a (111) face at t = 0 laterally increases the area, reaches the adjacent (100) faces, and induces a secondary nucleation on the (100) faces. According to the computer simulation, there are three types of twin evolutions, as shown in Figure 6.2. The types and characteristics of the twins shown in Figure 6.2 are summarized below. Note that the definition Tjijk here is different from that of Section 5.5. 

In total, seven types of twin screw extruders are on the market ... 

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