Preformulation: Bulk Powder Properties

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What best describes loosely packed powders?

They exhibit minimum airspace and maximum density.

They lead to the highest porosity rates in packaging.

They contain a maximum of airspace between particles. (correct)

They have maximum interparticulate contact.

Which packing arrangement is associated with the lowest porosity?

Loosely packed powders

Cubic packing

Rhombohedral packing (correct)

Tightly packed powders

What factor primarily influences the porosity of powders?

Liquid content in the mixture

Temperature of the environment

Weight of the powder

Shape and size of the particles (correct)

What is the densest packing arrangement achieved by a mixture of particles?

75% coarse and 25% fine particles Signup and view all the answers

How is porosity measured during the determination of powder packing?

By placing powder in a measuring cylinder without any disturbance. Signup and view all the answers

What is the relationship between bulk volume and particle volume in terms of void volume?

Void volume is the difference between bulk volume and particle volume. Signup and view all the answers

How is porosity represented mathematically?

ε = (Vb - Vp) / Vb Signup and view all the answers

What does the packing fraction (k) represent in relation to density?

The ratio of bulk density to true density. Signup and view all the answers

What best describes the term 'apparent porosity'?

It is measured without considering internal pores. Signup and view all the answers

In a tapped density measurement, what happens to the particles during tapping?

Interparticulate forces are reduced, allowing rearrangement. Signup and view all the answers

What is the main purpose of a tap volumeter in powder characterization?

To evaluate bulk and tapped volumes. Signup and view all the answers

Which statement is true regarding the lowest and highest bulk densities?

The lowest bulk density corresponds to the highest volume. Signup and view all the answers

Which condition affects the measurement of true density in powders?

Presence of internal pores or capillaries. Signup and view all the answers

What does a Carr's compressibility index of 12 indicate about powder flow?

Good flow Signup and view all the answers

Which Hausner ratio value indicates that added glidant may improve flow?

1.25 - 1.5 Signup and view all the answers

In the context of powder properties, what is the significance of a larger difference between poured and tapped densities?

Reflects stronger interparticulate forces Signup and view all the answers

What happens to a powder with a Hausner ratio greater than 1.5?

Flow is poor and glidant will not improve it Signup and view all the answers

A Carr’s compressibility index of 42 would classify the powder's flow as what?

Extremely poor Signup and view all the answers

What does a volume drop suggest about the most cohesive powders?

They have low aspect ratio Signup and view all the answers

Which factor primarily influences the difference between poured and tapped densities?

Interparticulate forces Signup and view all the answers

If corn starch shows a 35% drop in volume on tapping, what does this suggest?

It is a cohesive powder Signup and view all the answers

Study Notes

Preformulation - Bulk Powder Properties

Powders exhibit various packing states, ranging from loosely packed (maximum airspace, minimum contact points) to tightly packed (minimum air entrapped, maximum interparticulate contact).
Porosity is the relative amount of air entrapped between particles, affected by particle shape and size. Smaller particles fill voids between larger ones.
A packing arrangement consisting of 75% coarse and 25% fine particles yields the densest arrangement.
Porosity of isotropic shapes like cubes can vary. Cubical packing has approximately 48% porosity and rhombohedral packing has approximately 26% porosity.
Cubic shapes with 55% porosity and 0% porosity are also considered.
Coarse and fine particles influence packing density. Increasing the proportion of fine particles increases packing density.
Determining porosity involves placing a powder in a measuring cylinder without disturbance (loose packing). This volume is the 'poured bulk volume'. Reciprocal of this is minimum bulk density. The void volume (difference between total volume and particle volume) is used to calculate porosity (ɛ). Porosity can also be expressed as a packing fraction (k).
Tapped density is determined using a tapping volumeter. A rotating cam in the device creates a series of taps on the powder, leading to a minimal bulk volume, termed tapped volume (Vt). Reciprocal of this is 'maximum bulk density' or 'tapped density'. This method monitors dynamic powder packing with time.
Packing and flow properties are closely associated. A larger difference between poured and tapped densities suggests that more tapping is needed to reach the tightest packing.
Carr's compressibility index is used to assess flow properties. It is calculated as: ((Tapped density-bulk density)/Tapped density) x 100.
Carr's Index ranges from 5-15 (Excellent flow), 12-16 (Good flow), 18-21 (Fair to passable flow), 23-35 (Poor flow), 33-38 (Very poor flow), >40 (Extremely poor flow).
A glidant improves flow characteristics particularly in poor flow classifications.
Hausner ratio is determined by tapping the powder and calculating (Tapping density/Poured density). Values less than 1.25 indicate good flow. Between 1.25 and 1.5, a glidant normally improves flow. Values greater than 1.5 indicate poor flow. Glidants do not necessarily improve flows well beyond ratio of 1.5.
Table 1 provides characteristics of bulk powder. It includes measurements of median particle size, aspect ratio, volume, and Carr’s Index. Based on this data, lactose displays good flow properties while others like corn starch or MCC 50M have poor flow properties.
Lactose's low volume drop and relatively larger particle size contribute to its good flow.
Microcrystalline cellulose (MCC) exhibits a considerable drop in volume and low bulk density, limiting its suitability for certain applications (e.g., capsule filling).
Angle of repose is the maximum angle between the surface of a pile of powder and a horizontal plane, indicating flow characteristics. Lower values suggest better flow.
Hopper design impacts the flow from the hopper. Funnel flow involves some stationary powder, potentially causing rat-holing and segregation problems. Mass flow involves all powder in motion, promoting uniformity, and requiring specific manufacturing.
Arch formation and rat-holing relate to hopper design; strong interparticle forces create arches in funnel flow.
Inadequate emptying in funnel flow silos might result due to insufficient cone angles for bulk substance drainage.
Mass flow enables the uniform movement of powder along the hopper walls.
Critical orifice diameter is a powder characteristic related to arching/rat holing; it depends on particle size, flow, and the ratio between orifice and particle diameters (Do/Dp).
Flow is improved with various measures including particle properties (size, shape, charge, moisture), equipment like hoppers, aeration, and force feeders and formulations like glidants.

Additional Notes

Aeration and vacuum techniques enhance powder flow in hoppers and feeding devices.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the fascinating world of bulk powder properties in the study of preformulation. This quiz covers essential concepts such as packing states, porosity, and the influence of particle size and shape on powder density. Test your knowledge on the arrangements of coarse and fine particles and their effects on packing density.