Powder volume

Dental stone is generally used at a water—powder volume ratio of about 30 parts water to 100 parts of stone. The mix is not easily poured, but can flow readily under mechanical vibration. The physical property requirements include a setting time of 10 3 min fineness of powder, where 98% should pass a number 100 sieve (ca 0.15 mm) and 90% pass a number 200 sieve (ca 0.07 mm) linear setting expansion at 2 h of <0.20% compressive strength at 1 h of 20.6 MPa (2987 psi) and consistency such that the slump test disk is 30 2 mm diameter. 

Continuous Model "C0NGAS". This model predicts performance of an ideal continuous wellstirred polyreactor. The model system consists of a continuous backmix reactor in which the total powder volume is held constant. There are four inlet streams 1) Makeup of pure propylene, 2) Catalyst feed, 3) Hydrogen feed, and 4) Recycle. The single effluent powder stream is directed through a perfect separator that removes all solids and polymer and then the gases are recycled to the reactor. The makeup propylene is assumed to disperse perfectly in the well-mixed powder. 

P = ambient pressure Vc — cell volume Vp = powder volume... 

The values of IF/M calculated from equation (16.8) must be corrected for the weight of adsorbate contained in the column void volume, which can be obtained by subtracting the powder volume from the volume of the empty column. 

In many areas of powder technology the need to measure the powder volume or density often arises. For example, powder-bed porosities in permeametry, volume specific surface area, sample cell void volumes as well as numerous other calculated values all require accurately measured powder densities or specific volumes. It is appropriate, therefore, to introduce some discussion of powder density measurements. 

Consequently, the pressure drops to a lower value Pj in the cell while increasing from ambient to Pj in the added volume. Using Pj and P2, the powder volume V is calculated from... 

When measuring powder volume in the manner described above it is necessary to avoid using any gas which can be even slightly adsorbed. If so much as a thousandth of a monolayer were adsorbed the equivalent volume of gas would be in the order of 0.001 cm for each 2.84 m of area, if nitrogen were used. Since the sample cell used in the apparatus described in Fig. 21.1 can hold 130 cm, the total surface area of the sample can be hundreds or even thousands of square meters. Thus errors of O.l-l.O cm can be incurred due to very small amounts of adsorption. This is another reason helium is recommended in any gas pycnometer. 

Apparent powder density Mass of powder divided by its apparent powder volume, which is defined as the total volume of solid matter, including open pores and closed pores and interstices (BSI) ... 

Linear profiles are the simplest profiles to use for powder compressions. Typically, a sawtooth or v-shaped profile is used where the punch is extended at a constant velocity and retracts at a constant velocity. In theory, during a sawtooth profile, the punch reverses its motion instantaneously between the compression and a decompression strokes. At low speeds (e.g.. <1 mm/sec), the hydraulic response system can easily accommodate this discontinuity. However, at high speeds (>100mm/.sec), the control system may show a small lag in the position-time waveform (<10 milliseconds) as it attempts to rapidly reverse the direction of punch. The sawtooth waveform is commonly used for more fundamental compression studies (e.g.. Heckel analysis), where the desired powder volume reduction is proportional to time. It is also u.seful when evaluating instrument performance during factory acceptance testing. 

In this density, volume is defined as the sum of the volume of the solid material and any closed pores within the solid. These pores cannot be penetrated by any fluid and become part of the powder volume. A mass of catalyst is placed in a flask of known volume, and the amount of helium needed to fill the flask measured, giving the powder volume by difference. Care should be taken to dehydrate all pores thoroughly. Because helium is used as the displacing fluid, this density is sometimes called the helium density. See Table 7.1 for an example of typical values. 

Size reduction operations can be related with particle or powder bulk volume reduction. The objective of particle size reduction is to produce smaller particles from larger ones. Furthermore, bulk powder volume reduction through compression or compaction can also be considered a size-reduction operation. 

Fig. 2 Reciprocal torque as a function of the binder SiC powder volume ratio. Extroplation to zero reciprocal torque (i.e. infinite torque) permits an estimate of the maximum powder loading for the feedstock to be made [Cle 05]...

Markhoff CJ, Mutsuddy BC, Lennon JW (unknown) A method for determining critical ceramic powder volume concentration in the plastic forming of ceramic mixes. In Chemical Bibliography 878, Columbus Laboratories, Columbus, OH, 43201... 

The emitted radiation in this case is the sum of all the individual elements dV of the penetrated powder volume. The solution for determining the total emitted radiation is found using... 

In order to reduce the unavoidable variations in sample filling factors the following standard procedure was established for te transfer of test material to the sample tubes used for the spectrometric work. The sample was first vibrated in the test tube at a frequency of 1000 p/s which reduced the powder volume by some 20%. The vibrated sample was then subjected to a pressure of 30 kg over the sample tube area, giving rise to an additional 20% reduction in volume. The volume densities so obtained were determined by weighing to arrive at the filling factor correlation. All sample handling and transfer of material was carried out in a glove box kept at the spectrometer temperature and conditioned to the relative humidity of the individual sample. 

Powder densities Absolute powder density Absolute powder volume Absolute volume... 

Apparent powder density Apparent powder volume Bulk powder density Effective solid density Green density Pressed density Immersed density... 

Scott volumeter Since the definition of bulk density is related to the apparent powder volume under defined conditions, the methodology outlined in ISO 3923-2 (1981) andEN 23923 (1992) may be used to determine the bulk density of metals and other powders using the Scott volumeter to give an as poured bulk density. 

Figure 28. Effect of powder volume fraction on feedstock strength [13],...

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