Side growth

The prismatic faces of natural rock-crystal are characterized by the development of striations parallel to the edges between m, r, and z faces (perpendicular to the c-axis). Natural rock-crystal showing no distinct striations is almost exceptional. In industrially mass-produced synthetic quartz using NaOH or KOH as mineralizers, no striations are observable on 1010 faces. As shown in Fig. 10.5(a), five-sided growth spiral hillocks are generally observed. However, if quartz crystals are synthesized in hydrothermal solution with NaCl as the mineralizer, the prismatic faces exhibit similar striations to those observed on natural crystals [5]. 

An example of polarity determination and its application is the study of the growth mechanism of ZnO nanowires. During ZnO growth, asymmetric side growth is... 

In addition to gel-type matrices and activated carbon, which typically result in spherical support systems, immobilized systems sometimes consist of a membrane surface for cell adhesion and cells are immobilized on long fibers of tubes (Fig. 3). The reactor then resembles a shell and tube heat exchanger. The membranes are made of materials such as nylon, polystyrene, cellulose acetate, or ethyl cellulose. These membranes are semipermeable membranes. Cells are immobilized on the shell side growth nutrients are pumped in and diffuse through the membrane while metabolic products diffuse back across the membrane, and are removed from the reactor system. 

Figure 19. (a) Schematic of an apatite crystal with a three-sided growth hillock on a (100) face. 

Equations 4 to 6. Initially, tip growth occurs, yielding fibers with a tubular structure and diameters comparable to those of the catalyst particles (<15 nm). Subsequent side growth adds multiple secondary growth rings and increases the diameter [7], The iron particles become encapsulated in the fiber tips after thickening. 

Unsupported carbon fibers are formed in a continuous process [47-48] where the metal catalyst particles are continuously mixed into the flow of the feed gases, and where fibers carrying a metal catalyst particle in their tips are continuously removed. A specific process [51] that is currently under commercial development uses iron pentacarbonyl as a catalyst and hydrocarbons such as methane, natural gas, or others which can be derived from coal, recyclate and discarded rubber tires. These fibers are only several pim long and have much lower diameters (0.1 to 0.2 jm). Apparently, less time is available for side growth (or thickening) in a continuous process. 

Figure 11. Tip grown single-crystal LCVD germanium fiber with secondary amorphous germanium side growth. Courtesy of Dr. P. C. Nordine, Containerless Research Incorporated, Evanston, IL...

In summary, a typical aluminate fiber is spun between 1500 and 1700°C (Table VIII). Carbon enters into the skin of the still liquid jet. A secondary carbon sheath is obtained when more carbon is present in the reactive propane environment than needed to stabilize the liquid jet, but after the fiber is solidified (<500°C). At higher temperatures it would oxidize (bum off). Thus, only some fibers have a secondary carbon sheath. If it is formed, it results from side growth, a secondary growth mode, that has already been discussed with regard to the growth of carbon whiskers in a carbon vapor environment (Chapter 2.1.1). 

Hiqh and low pressure LCVD fibers (a) Reactor pressure vs. growth rate (t>) Tip temperature vs. properties (c) Side growth versus rip growth (a) Versatility versus whisker processes Commercial hot filament CVD fibers... 

In order to clarify the role of adhesion in the filtration process, let us examine the deposition of particles on isolated cylindrical fibers placed in an aerosol stream. They way in which the dust deposit is formed on individual cylindrical fibers of a permeable filter barrier, with a flow velocity of 1 m/sec, is shown in Fig. XII. 1. The clearly visible local side growths of lead and zinc oxide dust particles (particle size approximately 1 jim) are directed at an angle of 110-120° to the flow axis. When more aerosol passes through the filter, the growths may meet, forming a continuous layer that acts as a secondary filter medium [322]. 

In some cases, step 6 can be bypassed when sideways line growth is not a problem (Fig. 31.3). In such a case, the plating speed is redueed by 20 to 30 percent, from the normal speed of 2.0 to 2.5 lira, in order to avoid copper deposition on unwanted areas (bare laminate areas). Conductors must be made narrower than the intended final width at the design stage to compensate for the side growth. 

On the other hand, Sunagawa [1964] has studied growth spirals on phlogopite crystals and found that, at least for his specimens, phlogopite is IM, but shows five-sided growth spirals. The orientation of these growth features indicated that the crystals consist of many domains, which are in twin relationships to one another. The twinning is not polysynthetic, but is the ordinary rotation type of twin. 

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