Green Shape

The blue line represents a chain of RNA nucleotides, and a sequence of three bases, known as the anticodon, is represented by the green shapes at the bottom of the structure. Each transfer RNA has a specific amino acid attached to the 3 terminal end. The anticodon determines which amino acid the t-RNA will pick up. 

At this voliime fraction, the viscosity diverges because the shear stress is now given by the particle-particle contact in the tightly packed structure. As a result, we obtain a fluid with visco-elastic properties similar to polymeric solids. In ceramic processing, we extrude and press these pastes into green shapes. As a result, the rheology of ceramic pastes is of importance. The rheology of very concentrated suspensions is not particularly well developed, with the exception of model systems of monodisperse spheres. This section first discusses visco-elastic fluids and second the visco-elastic properties of ceramic pastes of monodisperse spheres. The material on visco-elastic fluids draws heavily from the book Colloidal Dispersions by Russel, Saville, and Schowalter [31]. 

Url-22 http //www.vaude.com/de-NL/Verantwortung/Green-Shape/ (date received 29.08.14.). Url-23 http //www.marque-nf.eom// (date received 29.08.14.). 

In some cases the compacts are soft machined or green shaped into a proper shape prior to sintering. 

Development of forming techniques to produce green shapes, aiming at the possibility to produce complex-shaped components as required by industrial applications. 

Reaction-bonded titanium nitride (RBTN) ceramics are like RBSN made from a porous green shape of titanium powder that is reacted with nitrogen to titanium nitride (TiN) at temperatures up to 1000°C. Here the titanium hardly increases in molar volume when nitrided and the initial porosity remains the same but the gas permeability of a pressed titanium tablet is increased after it has been converted to titanium nitride. If the titanium powder particles are too large, the reaction stops after passivation of the metal surfaces the TiN formed at the surface is a diffusion barrier that stops the reaction. A fractal powder morphology of the starting metal (such as can be obtained from gas-phase preparation) is a very suitable reactant for complete reaction at modest temperatures. 

Fig. 15 Comparison between the experimentally measured [11] and numerically predicted [17] profiles of the Z-shaped section as shown in Fig 14. The outer thick frame shows the initial (green) shape of the section.

Fig. 14.13. The red shape illustrates the eroded right lung, while the green shape represents the dilated left lung...

Many techniques are used to consolidate a ceramic powder to the desired shape (green shape). The most commonly used can be summarized as follows. 

Extrusion. Extrusion is a major technique which is favored for the production of parts having a constant cross-section, such as electrodes. The mix is cooled to just above the softening point (approximately 125°C), then extruded through steel dies, cut to length and rapidly cooled to solidify the pitch before distortion occurs. The resulting shape is known in the industry as a green shape . 

Conventionally, each block is measured in the air and in water and the density determined (Archimedes method). This value is a good technological parameter for control of the green shape. Usually, each block is stamped (Fig. 2.26), and the number is used for the records. 

Large grains of graphite and anthracite (imperfect sewing) and big pieces of baked shapes and green shapes, considered to be defects, are implemented in the process as raw materials. 

For a long time, the standard problem for the specialist in the technology of refractory materials was to obtain the minimum possible porosity of the green shape, which opened the possibility to obtain the minimum possible porosity in fired refractory material. 

The porosity size distribution of the green shape is formed by the shape of grains between the big grains are the pores of large sizes. Between the small grains are the pores of small sizes. Hence, to obtain a pore size structure with a more or less narrow and small size distribution, it necessary for the grains of small sizes to form a continuous matrix. 

Amount of fraction <0.075 mm, % Specific surface area, sm /g CCS, MPa Apparent density, of green shapes, g/sm Apparent density of fired materials, g/sm Electrical resistivity, mkf2m Thermal conductivity, W/m-K Shrinkage at firing, % Total porosity, %... 

The weight of Si3N4 is bigger than the weight of Si in the green shape ... 

The theoretical weight increase of the green shape in the process of sintering of nitride-bonded SiC is easily calculated, taking into account the amount of silicon in the green mixture. 

Usually, N-SiC producers finish the process of thermal treatment above the melting point of silicon, which is 1,410 °C. In the green shape, the sihcon is in the form of fine grains, and the surface of the reaction is rather high. If the green shape is fired at an increased velocity, sihcon might melt, and the surface of the reaction will diminish several times as a consequence, the full nitridization whl not take place. 

Table 2.13 Porosity and composition of N-SiC near the surface and in the middle (the porosity of the green shape is 17-19 %, and the width of the green shape is 70 mm) [143]...

Anode baking furnace a complex construction for the temperature treatment (firing, sintering, baking) of carbon anode and cathode shapes. The green shapes are placed in (and after heat treatment taken out) the chambers while the fire is moving in the flue walls along the chambers. 

---