Machinable ceramics

Figure 9.32. Experimental set-up (a) Machinable ceramic holders and two proton conducting pellets showing the location of catalyst, counter and reference electrodes, (b) Twenty four pellet unit, (c) High-pressure reactor, gas feed and analysis unit.43 Reprinted with permission from the American Chemical Society.

MHz) for spin decoupling and H (61 MHz) for field locking. The container for liquid samples is shown in Figure 2.5. It consists of a normal high precision 5 mm NMR tube cut to a length of 60 mm and closed with a piston and a cap made from the machinable ceramic Macor. These probes were successfully used to study solvent exchange on solvated metal ions and metal ion complexes [14, 15]. 

Design and fabrication of strong machinable ceramics is emerging as an inevitable requirement for flexible use of advanced ceramics, especially for... 

The reference electrode is an internal silver-silver chloride type. It was based on a design of A. K. Agrawal, et al. (H). For supercritical water studies, the electrode body was made from 902 precision machinable ceramic (Cotronics Corporation Brooklyn, NY). 

The cell housings were machined from MACOR (machinable ceramic) blocks and type 316 stainless steel bar stock. The housings were 3" diameter and 1" deep cylinders. Gas flow chaimels were machined into the large surface faces with dimensions of 0.3 cm by 0.3 cm. Gas flow tubes were connected to supply process and sweep gases to the cell. Once the electrode and membrane materials... 

J. C. Dubois, P. Exbrayat, M. L. Couble. Effect of New Machinable Ceramic on Behavior of Rat Bone Cells Culture Dinvitro, 7. Biomed Mater Res, 43, 215-225(1998). 

Figure 7.9 shows the structure of mica. The van der Waals bonding between the sheets is not usually shown since it is so weak. Mica comes in several forms including muscovite, biotite, and the lesser-known phlogopite variety. Micas are used to provide easy paths for crack propagation in some commercial machinable ceramics. 

Brittle fracture is used for shaping and machining ceramics after they have been fired. Ceramics can be modified to make them machinable this is controlled fracture and is the approach we adopt with machinable glass-ceramics such as Macor (Chapter 26). Of course, many ceramics already are machinable and can be shaped into intricate and beautiful forms as illustrated in the carved marble sculpture shown in Figure 18.1. 

Machining flred ceramics can be expensive and can represent a significant fraction of the total fabrication costs. Ceramic materials are difficult to machine because they are hard and brittle. The tooling costs are high because diamond tools are likely to be required or if conventional tools are used the tool life is very short. Also the time required to machine ceramics is long because if high tensile loads are applied to the ceramic part it might fracture. 

Mechanical approaches to machining ceramics include the following ... 

Ahn, Y., Chandrasekar, S., and Farris, T.N., 1993, Measurement of residual stresses in machined ceramic using the indentation technique, NIST SP 847, pp. 135-146. 

The cleaning of the cooling lubricant assumes a special importance in terms of aspects such as its function and service life. Ceramic chip particles moreover increasingly attack guides and bearings when they circulate in the machine. Therefore, enhanced demands on the cleaning process must be placed when machining ceramic materials. 

Machineable Ceramics. All ceramics can be machined in the green state, and in the fired state with diamond tooling. Machineable ceramics are those which can be shaped when fired, to engineering tolerances with ordinary high speed metal cutting tools. See machining, and... 

Photon. Trade-name. A machineable ceramic made by Photon Ceramics Ltd, Tokyo. 

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