Pressed pellets

Meanwhile, prepare a pellet of the substance, using a pellet press of the type shown in Fig. 78 (p. 431), but having the cylinder C of about 3 mm. internal bore to enable a pellet of 20-50 mg. to be compressed and then ejected. (Do not compress the pellet more than is necessary for manipulation, otherwise it may dissolve too slowly in the boiling solvent.) Transfer the pellet to a watch-glass, which preferably should be kept in a small desiccator before and after weighing. 

The direct transmission experiment is the most elegant and yields the most quantifiable results. The beam makes a single pass through the sample before reaching the detector. The bands of interest in the absorbance spectrum should have peak absorbances in the range of 0.1—2.0 for routine work, although much weaker or stronger bands can be studied. Various holders, pellet presses, and liquid cells have been... 

The chemical composition of the samples was determined using an inductively Coupled plasma atomic emission spectrometer (ICP-AES) JY 38 from Jobin Yvon. Specific surface area values were determined by BET method using a Micromeritics Instrument Corp. FlowSorb 2300. The basicity of the materials was studied by temperature programmed desorption (TPD) of C02 used as a probe molecule. The equipment was described in a previous work [7]. FTIR spectra of pellets pressed at 2.5xl08 Pa were recorded with a Vector 22 spectrometer from Brucker. The samples were diluted with KBr (lOOmg KBr - 1.5mg of the sample). 

Lead Salt. Pb[00CC6H(N02)30H]2. Schmitt determined the ignitability of pellets of this salt (Ref 2). On exposure to flame, pellets pressed at 500 kg/cm2 detonated, while pellets... 

Variations in density reflect variations in dimensions with those of the bulk density and flow characteristics of the expl, and those of the measured volume. With frequent pellet density determinations and occasional adjustment of the pelleting press, expls with good flow properties can be pressed into pellets reproducible in density to 1% in an automatic pelleting press... 

The pellet (pressed-disk) technique depends on the fact that dry, powdered potassium bromide (or other alkali metal halides) can be compacted under pressure in vacuo to form transparent disks. The sample (0.5-1.0 mg) is intimately mixed with approximately 100 mg of dry, powdered KBr. Mixing can be effected by thorough grinding in a smooth agate mortar or, more efficiently, with a small vibrating ball mill, or by lyophili-... 

To form a f-in.-diam. pellet of Bi4Ti30i2, a sample is first made by mixing 0.47 g. (1 mmole) of bismuth oxide and 0.12 g. (1.5 mmole) of titanium(IV) oxide. The mixture is pressed into pellets with a calorimeter pellet press. The pellets are placed in Alundum or zircon boats and heated at 700°C. for 4 hours. Then the pellets are ground, pressed again, and reheated at a temperature of 920°C. for one hour. 

When the beets to be analysed are already in slices, these are pulped by a mincing or other machine or by the Pellet press. 

Finely-divided TNT, as obtained by fume condensation, is more sensitive to impact than the crystalline material (Ref 1) TNT which has been exposed to light is also more sensitive. TNT pellets pressed from flake TNT undergo substantial reductions in rate of detonation and sensitivity to initiation after storage for one week at 65° (Ref 2). These changes are accompanied by exudation of oily impurities, and recrystn and sementation of the TNT... 

The pellet (pressed-disk) technique depends on the fact that dry, powdered potassium bromide (or other alkali metal halides) can be compacted under pressure to form transparent disks. The sample (0.5-1.0 mg) is intimately mixed with approximately 100 mg of dry, powdered KBr. Mixing can be effected by thorough grinding in a smooth agate mortar or, more efficiently, with a small vibrating ball mill, or by lyophilization. The mixture is pressed with special dies under a pressure of 10,000-15,000 psi into a transparent disk. The quality of the spectrum depends on the intimacy of mixing and the reduction of the suspended particles to 2 gm or less. Microdisks, 0.5-1.5 mm in diameter, can be used with a beam condenser. The microdisk technique permits examination of samples as small as 1 fxg. Bands near 3448 and 1639 cm-1, resulting from moisture, frequently appear in spectra obtained by the pressed-disk technique. 

In this shaping process a powder is pressed between two punches in a pelleting press. The three different steps in the process are presented in Fig. 8.11. In step I the free-flowing powder is poured into the cylindrical hole. In step II the lower punch and the upper punch are moving towards each other and the powder is pressed at a pressure of about 102 - 5 x 103 atm and a pellet is formed. In step m the upper punch moves upwards and the lower punch pushes the pellet out of the hole. In the next step the pellet is moved away, the lower punch moves downwards and the hole is filled again. 

Bomb-assembly stand cylinder of oxygen with appropriate fittings large pail for leak-testing the bomb benzoic acid (5 g) naphthalene (5 g) or other solid to be studied pellet press spatula 0.004-in.-diameter iron wire (50 cm) device for checking electrical continuity (optional). 

Dry reagent-grade cyclohexane (50 mL) glass wool naphthalene or other solid pellet press acetone for rinsing ice (3 lb) ice grinder or shaver coarse rock salt (2 lb). 

Figure 12. Electrode 7 mm i.d., set 1.5 mm above the pellet. Pellet pressed Rh SO, 1-mm bore. Potential -V240 Volts. Flow, ml/min. Hg 33, Ng 50, Air 215 (Ref. 75).

The granulated mixtures are compacted in double-acting, cam-operated automatic pellet presses. The ends of the green pellets are dished by means of punches with slightly convex faces. The dished configuration provides space for thermal expansion of the pellet... 

Pellet pressing Binder removal 138-207 MPa, 53% theoretical density green density... 

The ultrafme powder obtained from the treated samples resisted pellet formation by extrusion. Thus a pellet-pressing method was used. Sample surface properties and their catalytic activities are listed in Table 1. It is evident from the data that a significant improvement in catalytic performance (for example, the selectivity increases by 23%) as compared with spent catalyst (Dl) can be achieved as a result of mechanochemistry, but it is not possible to regain the initial efficiency of the samples (F). 

Compaction conditions affect the total pore volume and shape of pores for some materials. In general, pore volume is smaller for a catalyst granulated by a tabletting machine than that by a pellet press. Partial pore closure is possible for tablets having a very high crush strength. 

Figure 333. Diagrams showing two different designs of flat die pellet presses. (a) Bottom drive, (b) top drive for very wet pastes or sticky materials...

The frictional and deformation characteristics of the feed play a decisive role in the ability of a pellet press to pull the material into the nip region between the roller(s) and die, compress it, and extrude agglomerates of good quality. A measure for acceptable feed consistency is the slip between the roller(s) and die. Therefore, a recent patent proposes to measure the slip or its rate of change and correct the feed composition based on this information. 

Pellet or pill formation is illustrated in Fig. 6.25. The process is essentially powder compression in a pelleting press. Powder is poured into a... 

The membrane is a conducting solid. Both single crystal and peUet-pressed crystalhne substance mixtures can be used in membrane construction. Table 2, accumulated from data available from several electrode manufactmers data sheets, shows information relative to crystal membrane electrodes and then-application capabilities. As can be seen, crystal membrane electrodes, with the exception of that selective to F, involve Ag2S or crystal mixtures where one component is Ag2S and the other the sulphide of the selective ion of interest. The membranes are generally produced by pressing the polycrystalline substance in a pellet press. 

VA Bell, VR Citro, GD Hodge. Effect of pellet pressing on the infrared spectrum of kaolinite. Clays and Clay Minerals 39 290-292, 1991. 

---