Ceramic powder characterization density

This chapter has described the various techniques of ceramic powder characterization. These characteristics include particle shape, surface area, pore size distribution, powder density and size distribution. Statistical methods to evaluate sampling and analysis error were presented as well as statistical methods to compare particle size distributions. Chemical analytical characterization although veiy important was not discussed. Surface chemical characterization is discussed separately in a later chapter. With these powder characterization techniques discussed, we can now move to methods of powder preparation, each of which 3uelds different powder characteristics. 

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. 

Among the six interfacial variables discussed in this section, the surface charge density oo, the surface potential (fo, and the potential at the OHP fd (usually called the diffuse layer potential), are most important in characterizing interfacial properties. The three remaining variables (i.e., ap, /p, and Od) can be estimated using Eqs. (5), (7), and (8) if oo, and /rf are known exactly. ao can be determined experimentally by the potentiometric titration method, and detailed explanation of the potentiometric titration is given, for example, by Yates [10]. The estimate of fo for the ceramic powder/aqueous solution interface is discussed in the next section, yd is perhaps the most important interfacial electrochemical parameter since it is closely correlated with the kinetic stability of a given colloidal suspension and it can be conveniently determined (approximately) experimentally. 

The density of the compact as a function of the applied pressure is usually used to characterize the compaction behavior of a ceramic powder, which can be used for process optimization and quality control of the green bodies. If the density is plotted... 

A supercritical fluid is defined as a material above its critical temperature and critical pressure (see Table 2.1). These fluids are characterized by gas-like transport properties and liquid-like densities. They also offer a greatly enhanced solvating capability in comparison with gases. Recently, the use of supercritical fluids has been applied to the generation of ceramic powders. The rapid expansion of a supercritical fluid solution results in the formation of a powder. As the pressure is reduced, the solubility of the solute decreases and supersaturation occurs. Stable... 

Ceramic powders of BaCeo.9Yo.1O2.95 (BCYIO) have been prepared by the sol-gel method [115]. Barium and yttriimi acetate and cerium nitrate were used as ceramic precursors in a water solution. The reaction process studied by DTA-TG and XRD showed that calcination of the precursor powder at r>1000°C produces a single perovskite phase. The densification behavior of green compacts studied by constant heating rate dilatometry revealed that the shrinkage rate was maximal at 1430 °C. Sintered densities higher than 95% of the theoretical one were thus obtained below 1500 °C. The bulk and additional blocking effects were characterized by impedance spectroscopy in an wet atmosphere between 150 and 600 °C. Proton conduction behavior was clearly identified. 

Characterization. Ceramic bodies are characterized by density, mass, and physical dimensions. Other common techniques employed in characterizing include x-ray diffraction (XRD) and electron or petrographic microscopy to determine crystal species, stmcture, and size (100). Microscopy (qv) can be used to determine chemical constitution, crystal morphology, and pore size and morphology as well. Mercury porosknetry and gas adsorption are used to characterize pore size, pore size distribution, and surface area (100). A variety of techniques can be employed to characterize bulk chemical composition and the physical characteristics of a powder (100,101). 

Ceramic characterization 30-32 range from a process as simple as determining the bulk density of a green powder compact from its mass and dimensions, to a process as complicated as identifying the composition and structure of a submicron size crystal in a dense ceramic matrix using analytical electron microscopy (AEM). Some of the important characteristics evaluated during ceramic consolidation are outlined in Figure 5.2. 

In many areas of powder technology, scientists need to characterize the properties of powder beds. Thus, in powder metallurgy and ceramics, the powder is poured into a container and then consolidated, either by heat or the application of pressure. The rate of consolidation, and the achievable consolidation are often governed by the structure of the spaces, known as pores, between the powder grains in the initial powder bed. When a powder is poured into a container, the volume of the freshly poured powder bed, divided into the weight of the powder is the apparent density of the powder bed or the aerated powder density. 

---