RAM materials

The most common mode of aircraft detection is radar. Essentially, radar is the detection of radio waves that have been thrown out and which bounce off objects returning to the site of origin. Today s radar, if properly used, can help identify the location, speed, and identity of the aircraft. The radar cross-section (RCS) of an aircraft is how much echo the plane sends from radar. Birds have an RCS of about 0.01 m. The Stealth Bomber has an RCS of 0.75 m. The Stealth Bomber and many stealth aircraft gain their stealth character from both the shape of the aircraft and the presence of radar absorbing material (RAM), which is made to absorb and eliminate radio waves rather than reflect them. Most of the RAM materials are polymeric. 

The dual-phase nature of these RAM materials allows the direct injection of the biological sample matrix onto the column without pretreatment. Some disadvantages with the use of RAM columns are that retention times can be long (> 10 minutes) the column must be washed between injections and the mobile phases are not always compatible with some ionization techniques used in LC-MS/MS. Dual-column RAM techniques are also used. These methods use an analytical separation column placed in series downstream from the RAM column. A general overview of the use of RAMs in LC has been published in two parts [117,118]. 

The two constraints specific to RAM materials are surfacic mass and volume of material. Depending on the final application, one or both will be emphasised. We shall see. further, that the classes of materials which are employed have a strong influence on mass or thickness. 

The following section describes the bibliographic synthesis of work done in the field of microwave properties of conducting polymers more as an aid to understanding rather than from the RAM material applications point of view. 

Compo. A siliceous, highly grogged fireclay composition, with crushed coke or graphite sometimes added, for use as a general ramming material in the casting-pit of a steelworks or in a foundry. A typical composition is (per cent) crushed firebrick, 65-70 chamotte, 15-20 siliceous fireclay, 14 foundry blacking, 1. The batch is made up with... 

Ramming Material. Graded refractory aggregate, or a mixture of aggregates, with or without the addition of a plasticizer ramming materials are usually supplied at a consistency that requires a mechanical method of application chemical bond(s) may be incorporated. The rammed mass becomes strong and monolithic by vitrification or sintering in situ. 

Run or Run-down. A fault in vitreous enamelling resulting from an excessive amount of cover-coat becoming concentrated in one area of the ware. Runner. (1) The channel in which molten iron or slag flows from a blast furnace when it is tapped. The runner is usually lined with fireclay refractories which are then covered with a layer of refractory ramming material, e.g. a mixture of fireclay, grog and carbon. Refractory concrete has also been used to line runners. 

When considering the final properties the ramming material receives during preheating of the cell and startup, it is necessary to remember that the temperature of carburization goes from the surface of the rammed material to the lower end of the shaft or seam, and the process takes a rather long time. 

Fig. 2.55 Pore size distribution in baked (without infiltration of electrolyte) ramming material from the shaft between the carbon blocks. Porosity is 18 %...

Many bonds are mixed. For instance, in the case of phosphate-boned ramming materials, a combination of chemical and ceramic bonds are used. Also, in the case of materials that are repaired with a hydraulic bond, the bond is made up of calcium aluminate cements and considerable amounts of clays. This means that the total bond is a mixture of hydraulic and ceramic bonds. When it is a mixed bond, the bond is named after the material that plays the major part during hardening. 

The equilibrium thickness increases as the thermal conductivity of the insulation increases. This is why conductive ramming materials are used behind high thermal conductivity basic refractories to ensure the best possible cooling effect of the shell. 

Provisional supplementary classification of refractory ramming materials and mouldables 1973 1978... 

Of course, a lot of bonds are mixed bonds This is, for example, the case with phosphate-bonded ramming materials (= chemical—ceramic) or materials for repairs with a hydraulic bond which contain besides calcium aluminate cements... 

Similar to the plastic refractory materials, ramming materials can have a ceramic or chemical (chemical ceramic) bond. Table 15 shows the properties of several ramming mixes, which, if installed properly, can be an excellent refractory lining. This is especially the case if liquid phases, slags, melts, etc., and thermal shock resistance are the main stress factors for the wear layer. The physical properties of these materials are comparable to those of dry-pressed refractory bricks. The production of ramming mixes is on the decline for two main reasons ... 

There are very few well-skilled operators who can install a ramming material properly without layers or free of lamination. 

The first-mentioned material A is a pure zirconia ramming mix, which provides good service results at extremely high service temperatures like in carbon black reactors. In addition to its high price, specific mention is made of the high B.D., which corresponds to a material requirement of approximately 4.5 t/m. The second example B is a SiC-C-ramming material, which is occasionally used in blast furnace troughs but also in foundries. 

Figure 3 Ramming material, which failed a CO test.

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