Particle size blending powder samples

The first sample is a reactive poly(tetrafluoroethylene)/polyamide 6 (PTFE/ PA) blend [43]. When mixing PTFE micro-powder and PA in an extruder at about 280°C, relatively large PTFE particles occur in the final product because of immiscibility. By irradiation with electrons in air reactive groups in the PTFE powder are formed. These functionalised particles react with the molten PA in the extruder, and graft copolymers are formed, improving the compatibility of the components. At the same time a decrease in PTFE particle size proportional to the irradiation dose can be observed, and a PTFE/PA compound with better properties is produced. 

To characterize a ceramic powder, a representative sample must be taken. Methods of sampling and their errors therefore are discussed. Powder characteristics, including shape, size, size distribution, pore size distribution, density, and specific surface area, are discussed. Emphasis is placed on particle size distribution, using log-normal distributions, because of its importance in ceramic powder processing. A quantitative method for the comparison of two particle size distributions is presented, in addition to equations describing the blending of several powders to reach a particular size distribution. 

The nature of individual particles and their size in comparison with the size of the sample must be considered. The size of a sample should correspond to the use of the mixture. The reason for unit-dose samples in powder blend testing is to ensure that individual doses contain the intended amoimt of each constituent. 

Workers in Russia [27] have carried out sintering experiments using rubber powder that had been prepared by high-temperature shear deformation of EPDM vulcanisates with different crosslink densities. They prepared and tested samples that had been sintered under different conditions. They also blended the EPDM powder with virgin EPDM and tested the blends. The performance of the EPDM powder was found to be dependent on particle size, surface area and composition. 

Another difference is that in blending liquids a well-mixed product usually means a truly homogeneous liquid phase, from which random samples, even of very small size, all have the same composition. In mixing pastes and powders the. product often consists of two or more easily identifiable phases, each of which may contain individual particles of considerable size. From a well-mixed product of tliis kind small random samples will differ markedly in composition in fact, samples from any given such mixture must be larger than a certain critical size several times the size of the largest individual particle in the mix) if the results arc to be significant. 

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