Density, Porosity, and Related Characteristics

Even if the refractory product is not subjected to critical applicatitMis, a quality record in the form of Shewhart charts will give the customer a sense of ctMifidence, but it may tell the producer about the tendency for quality to diminish (probably due to some minor changes in raw materials or the occasional lack of temperature control, etc.). 

Without a doubt, cathode carbon blocks in the reduction ceU have a critical application. One crack in the cathode carbon block may shut down the reductimi cell within 10 days of startup. Of course, it is impossible to measure a crack (at least if one isn t using nondestructive quality control, which we will briefly discuss in Sect. 2.3, devoted to carbon cathode blocks). However, it is possible to keep a continuous record on strength, and excessive strength may push you to start thinking about possible tensions (and a consequent crack) due to an unexpected increase in the strength (in comparison with regular values see Fig. 1.2b). 

Another example is the strength of vermiculite slabs (Fig. 1.2a). Certainly, the probability of a shutdown of the reduction ceU due to low strength of vermicuUte heat insulation slabs in the bottom part of the reduction cell is very low (and probably close to zero). However, this graph may give the producer of these slabs initial information in order to understand of the following issues  

With critical applications of refractories, statistical quality control might become the link for long-term relationships between the customer and the producer of refractory materials. 

In the ferrous industry, the characteristic specific consumption of refractory per ton of the metal is now being replaced by the characteristic refractory consumption in money equivalent. However, in A1 production, neither the first nor the second characteristic attracts big attention. Aluminium producers usually calculate the cost of production for the high-temperature device itself, not differentiating to construction or refractories. It is probably a question to be addressed in the future. 

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Density, Porosity and Related Characteristics The Types of Porosity... 

Characteristics of a catalyst particle include its chemical composition, which primarily determines its catalytic activity, and its physical properties, such as size, shape, density, and porosity or voidage, which determine its diffusion characteristics. We do not consider in this book the design of catalyst particles as such, but we need to know these characteristics to establish rate of reaction at the surface and particle levels (corresponding to levels (1) and (2) in Section 1.3). This is treated in Section 8.5 for catalyst particles. Equations 8.5-1 to -3 relate particle density pp and intraparticle voidage or porosity p. 

Specific gravity is the most critical of the characteristics in Table 3. It is governed by ash content of the material, is the primary deterrninant of bulk density, along with particle size and shape, and is related to specific heat and other thermal properties. Specific gravity governs the porosity or fractional void volume of the waste material, ie. 

The shape of particles is normally that of more or less regular spheres, dense or hollow, with smooth surfaces and sometimes cracks. This is related to the composition and the rate of solvent evaporation, with possible existence of internal pressure inside the drops when a rigid surface layer is being formed (Walton and Mumford 1999). All these characteristics will have some effect on handling properties of powders such as bulk and tapped densities, particle density, (mixing with other powders, storage) wettability and solubility, porosity, specific area (rehydration, instantisation) flowability (size, surface asperities), friability and creation/existence of dust, stability in specific atmosphere and medium (oxidation, humidification, active component release) (Huntington 2004). 

It is useful to calibrate the EXJCM, i.e., to determine Cf, e.g., by electrodeposition and electrodissolution of silver. The rigidity layer behavior can be tested by depositing films of different thicknesses. Usually relatively thin films (10 nm - some hundreds nm) show rigid layer behavior. The deviation from the linearity regarding the Am vs. Q function is related to the appearance of the viscoelastic effect. By the help of impedance measurements the viscoelastic characteristics of the surface film can also be tested [4, 5, 6, 7, 10]. In the absence of any deposition the change of the density and viscosity in the double layer or in the diffusion layer may cause 0.1-10 Hz frequency change. It may interfere with the effect caused by the deposition of monolayers or submonolayers. In some cases other effects, e.g., stress, porosity, pressure, and temperature, should also be considered. 

The fabric substrate used for the filter media will need to provide certain characteristics, dependent on the application. The typical properties required include abrasion resistance, stretch resistance, dimensional stability, and resistance to flex fatigue. All these performance criteria can be assessed by using suitable test methods. The fabric will also be tested for correct warp and weft sett, air permeability, thickness, density, and fabric tensile properties. All the factors will affect the performance of the filter as they are directly related. If woven fabrics are considered, the porosity will be directly related to the sett and therefore air permeability. The combinations of the fibre types, fabric constructions, and coating substrate will provide the filter manufacturer with a range of properties for use in a range of appUcations. 

The combustion rate of a pyrolant is determined by ambient pressure, p (kPa), and parameters inherent to a specific pyrolant such as stoichiometry, (wt%), porosity, d (vol%), and specific surface area of its ingredients, E (m g ). The latter factors, in turn, determine density, p (g cm ) and thermal diffusivity, k (m s ), of a pyrolant, which are also functionally related to the combustion characteristics. 

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