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The fundamental properties of carbon black determine application performance. These include:Particle SizeStructurePorositySurface Chemistry or Surface ActivityPhysical FormPARTICLE SIZEMeasured by electron microscopy, this is the fundamental property that has a significant effect on rubber properties, as well as color properties for specialty carbon blacks.For specialty carbon blacks, smaller particle diameter gives rise to higher surface area and tinting strength. High surface area is usually associated with greater jetness, higher conductivity, improved weatherability, and higher viscosity, but requires increased dispersion energy.For rubber, finer particles lead to increased reinforcement, increased abrasion resistance, and improved tensile strength. To disperse finer particles size, however, requires increased mixing time and energy. Typical particle sizes range from around 8 nanometers to 100 nanometers for furnace blacks. Surface area is utilized in the industry as an indicator of the fineness level of the carbon black and, therefore, of the particle size.STRUCTUREThis is a measure of the three-dimensional fusion of carbon black particles to form aggregates, which may contain a large number of particles. The shape and degree of branching of the aggregates is referred to as structure.Highly structured carbon blacks provide higher viscosity, greater electrical conductivity and easier dispersion for specialty carbon blacks. Measures of aggregate structure may be obtained from shape distributions from EM analysis, oil absorption (OAN) or void volume analysis.The structure level of a carbon black ultimately determines its effects on several important in-rubber properties. Increasing carbon black structure increases modulus, hardness, electrical conductivity, and improves dispersibility of carbon black, but increases compound viscosity.POROSITYThis is a fundamental property of carbon black that can be controlled during the production process. It can affect the measurement of surface area providing a total surface area (NSA) larger than the external value (STSA).Conductive specialty carbon blacks tend to have a high degree of porosity, while an increase in porosity also allows a rubber compounder to increase carbon black loading while maintaining compound specific gravity. This leads to an increase in compound modulus and electrical conductivity for a fixed loading.SURFACE CHEMISTRY OR SURFACE ACTIVITYThis is a function of the manufacturing process and the heat history of a carbon black and generally refers to the oxygen-containing groups present on a carbon black’s surface.For specialty carbon blacks, oxidized surfaces improve pigment wetting, dispersion, rheology, and overall performance in selected systems. In other cases, oxidation increases electrical resistivity and makes carbon blacks more hydrophilic. The extent of surface oxidation is measured by determining the quantity of the “volatile” component on the carbon black. High volatile levels are associated with low pH.While difficult to measure directly for rubber, surface chemistry manifests itself through its effects on such in-rubber properties as abrasion resistance, tensile strength, hysteresis, and modulus. The effect of surface activity on cure characteristics will depend strongly on the cure system in use.PHYSICAL FORMThis is important in matching a carbon black to the equipment by which it is to be dispersed. The physical form (beads or powder) can affect the handling and mixing characteristics.The ultimate degree of dispersion is also a function of the mixing procedures and equipment used. Powdered carbon blacks are recommended in low-shear dispersers and on three-roll mills. Beaded carbon blacks are recommended for shot mills, ball mills, and other high energy equipment. Beading provides lower dusting, bulk handling capabilities, and higher bulk densities, while powdered carbon blacks offer improved dispersibility.

Separating mixtures techniques will depend on what kind of mixture you are separating. The standard methods widely used and known are as follows:1. Distillation:This technique of separation is driven by boiling point differences of the two in the mixtures. As a normal operating procedure mixture is heated gradually and the substances that vaporize the easiest will separate first. Distillation is widely used in industries and in our daily life also. The best example is in the decaffeination of coffee.2. FloatationThis technique of separation is driven by separation of solids by density differences. When you put into water, some substances will sink while others will float.3. ChromatographyThis technique of separation is driven by separation by inner molecular attractions. Some mixtures have components that "stick" to materials in different ways. These attractions take place at the molecular level. The different techniques of HPLC,GC are based on this. The retention time is usually identified here for its application for analysis.4. MagnetismThis technique of separation is driven by some substances are attracted to a magnet field.5. FiltrationThis technique of separation is driven by separation by particle size. The particle size of substances can be very different. Passing a mixture through a screen or filter will allow the small particles to pass and be separated from the larger particles that get trapped. Various membranes are available for it.6. ExtractionThis technique of separation is driven by separation of liquids by density and solubility. As you keep the mixtures for a long time the mixtures of liquids of different densities and solubility will form layers. The top layer can be skimmed off or siphoned, and the bottom layers can be removed via a siphon or mechanical means.7. CrystallizationThis technique of separation is driven by separation by solubility. Substances have different solubilities at temperatures. A solution can be cooled to the point where the solute will begin to form crystals and separate from the mixture.8. Mechanical SeparationThis technique of separation is driven by separation by particle size. If the mixture is made up of large enough particles, or pieces, you can separate them by hand or tool. Simple screening also falls under this category.To add though I consider evaporation as the process of concentration it can be also treated as separation technique for example the best known example of this is a salt and water mixture where the water can be evaporated in order to leave the salt behind.

They are different processes and each has its good points and its drawbacks. In recrystallization, first of all you have to have a material that you can get actual crystals from. There are many compounds that do not form crystals when solidified or co-crystallize with other materials and cannot be fully purified that way. It is also a very wasteful process because a large amount of your product is often left in the supernate liquid. If you manage to recover 90% of your product with each crystallization and have to do it 3 times to obtain the requisite purity then you end up with only about 72% recovery. That is very wasteful in an industrial sense unless you can set up a continuous process.With column chromatography you are often limited in volume and the fact that you have to determine the best combination of substrate and solvent combination. You have to determine what combination gets the desired product to adsorb to the substrate and allow the undesired impurities to be removed before you then remove it (or vice versa - you can adsorb the undesired materials and wash off the desired product). This is a very simplified concept of what actually happens.If you hook up the outflow to an analyzer then you can determine the separation between the different solutes as they are washed off the column. If you use a GC-MS or FTIR analyzer for example you can obtain real-time analysis of the identity and purity of the product.Recrystallization can be scaled up to industrial continuous-flow processes so the material dissolved in the supernate is not lost - sugar manufacture is an age-old example of this.Column chromatography is used commercially but due to the expense is used more in the realm of pharmaceuticals manufacture. Usually HPLC (High Performance Liquid Chromatography) is used instead of open column chromatography where high pressure is used to force the liquid through extremely small particle size silica gel, alumina, specially coated silica gel or coated alumina packing. It is possible to separate very small amounts of desired products using gas chromatography but that is usually used for qualitative analysis rather than physical separation.