Powders, test methods density

One of the advantages of the FTIR spectrometer is the facility of sample preparation procedure. It is possible to press powder into pellet. In this method, different diluents (matrixes) can be selected for several applications. For mid-IR frequency range, KBr, KC1, or diamond dust can be used. For far-infrared testing, high-density polyethylene (HDPE) or diamond dust is suitable. For near-infrared analysis, Csl or KBr can be selected or mulls may be used as alternatives to pellets. The sample... 

Other Methods of Flow Characterization A variety of other test methods to characterize flowability of powders have been proposed, which include density ratios, flow from funnels and orifices, angles of repose and sliding, simplified indicizer flow testing, and... 

Sometimes the density of powder compacted over and above what can be achieved by tapping may be needed. There are no standard procedures for this other than the rather specialized soil compaction tests and density determinations (2.5 and 4.5 kg rammer methods) quoted in a British Standard for soils16. 

On the other hand, the powder tensiometry method can be applied with any Wilhelmy type tensiometer. A special thin glass tube, which has a porous plug at the bottom, is filled with the powder which will be tested and the powder column is then brought into contact with the testing liquid. The mass of liquid absorbed into the porous solid is measured as a function of time by means of an electrobalance. The amount absorbed is a function of the viscosity, density and surface tension of the liquid, the material constant of the solid, and the contact angle of the interaction, as given in the following relationship ... 

For other powder properties, such as bulk density, particle attrition, or dustiness, some standardized methods [160] exist that may serve as a guide to establishing a test method but may not be applicable in every case. For example, the dustiness of a material is a matter of definition, depending on the initial particle size of the tested product. If the determination of dustiness is combined with testing the attrition stability of the particles, the stress mechanism also has to be considered. Consequently, the methods for determining dustiness and particle attrition are mostly very specific to the product and the stress mechanism that is to be simulated [161]. In many other cases (e.g., solubility, moisture, and temperature sensitivity), no general standardized tests are available, and different approaches are nsed to describe the powder properties (see examples in Refs 110 and 162). 

Highlights The characterization of UO2 powders and pellets to examine compliance with specifications involves the use of several physical and analytical test methods. The chemical analyses include determination of the uranium content and isotopic composition, the 0 U ratio, and the measurement of the content of several elemental impurities. Of special importance are elements that may affect the neutron absorption properties of the fuel pellets. Each of these elements is determined and the total neutron absorption of all these impurities is summed up as EEC. Modern nuclear fuel may include burnable neutron poisons that are used to increase the operational lifespan of the fuel. The intentional addition of these poisons, like gadolinia, must be carefully controlled to avoid fluctuations of the neutron density in the reactor. Basically, after dissolution of the nranium oxide samples the analytical methods that... 

The tap density, p, p, expressed in kg.m corresponds to the apparent density of a powder obtained from filling a container with the sample material and vibrating or tapping it under specified conditions (e.g., ASTM standard test methods B527, D1464, and D4781) to obtain near-optimum packing. 

Apparent density is a measure of the fluffiness of a material. Bulk density is defined as the weight per unit volume of a material, including voids inherent in the material as tested. Bulk density is commonly used for materials such as molding powders. The test method to determine bulk density has been discussed in detail in Chapter 7. 

In the United States, a number of physical tests are performed on siUcon carbide using standard AGA-approved methods, including particle size (sieve) analysis, bulk density, capillarity (wettabiUty), friabiUty, and sedimentation. Specifications for particle size depend on the use for example, coated abrasive requirements (134) are different from the requirements for general industrial abrasives. In Europe and Japan, requirements are again set by ISO and JSA, respectively. Standards for industrial grain are approximately the same as in the United States, but sizing standards are different for both coated abrasives and powders. 

The most common method for measuring bulk density is to pour the powder into a tared graduated cylinder and measure the bulk volume (Vb) and mass of the material. Other methods, however, have been employed to ensure reproducibility, and a standard procedure has been reported [62,64]. For this testing, a sample of 50 g is passed through a U.S. Standard No. 20 sieve and is poured into a 100-ml graduated cylinder. The cylinder is then dropped from a height of 1 inch onto a hard surface three times at 2-second intervals. The volume of the powder is then read and used to calculate the bulk density. This three-tap method was found to give consistent results between laboratories. 

The flotation method is especially suitable for powdered polymers. A liquid of higher density is added to a liquid of lower density until the test particles neither sink nor rise to the surface. The densities of the solid and liquid mixture are then equal and it remains only to determine the density of the latter. The experiment is conducted as follows The powdered polymer is placed in a small beaker with a certain amount of less dense liquid. The heavier liquid is then run in from a burette with gentle stirring until the state of suspension is attained. 

The quality of eucalypt woods for producing chemical pulps was evaluated using NIR spectra and chemometric methods [124]. NIR spectroscopy was used to predict pulp yield and cellulose content from spectra of powdered wood samples [137]. In another application, in addition to estimating lignin content, NIR spectra were used to quantify hardwood-softwood ratios in paperboard [138]. NIR spectra taken from solid European larch samples subjected to axial bending and compression tests revealed an excellent ability to model the variability of mechanical properties [139]. The study demonstrated that the model is based not only on the measurement of density, but also on surface geometry, composition, and, possibly, lignin content. The authors concluded that NIR spectroscopy shows considerable potential to become a tool for nondestructive evaluation of small clear wood specimens, e.g., increment cores. 

After fabrication, the samples are tested for the superconductive transition temperature and critical current density by conventional methods. X-ray diffraction is the technique most consistently used to roughly determine the quality of the powders prepared. In general, the XRD analysis must be free of second phases (in particular, unreacted BaCO ) to work well. A program to examine these materials by electron microscopy is being pursued. Initial results show considerable unreacted material... 

In addition small-scale exposures at 870"C were used to study further the role of water vapour with 20 vol.-% and 30 vol.-% water vapour in air in an alumina tube furnace. Phase morphology was studied with scanning electron microscope (SEM). To distinguish between the glassy and crystalline phases some samples were etched in 2-% HF-solution. Phase composition was determined by a quantitative X-ray diffraction (XRD) analysis based on the internal standard, Cap2, method. The chemical composition of the amorphous phase in the binder was determined locally with EDS analysis in SEM. A bulk chemical analysis of the amorphous phases in binder was performed by Induction Coupled Plasma Mass-Spectrometry (ICP-MS). The samples were crushed powders of as-received and 500 h at water vapour bulk exposed (w) materials. The glassy phase was dissolved in HF-HNO3 solution. Open porosity, apparent and bulk densities of each specimen were determined by Archimedes method before and after the tests. 

---