The Challenges of Powder Characterisation

Whether as raw materials, intermediates or final products, powders are integral to a huge range of industrial processes, contributing to some 80% of all manufactured goods. However, despite their ubiquity they continue to present challenges during product development, manufacturing, and in quality assurance.  Often powders are labelled as ‘bad’, when it would be more accurate to say we simply don’t understand how they are behaving. A good understanding of powder behaviour is an essential foundation for optimising production processes and developing a high-quality product.

A series of educational guides are now available from Freeman Technology on powder characterisation for industrial applications. They provide a valuable foundation for those with little prior knowledge of powders, as well as being a useful resource for anyone looking to expand their understanding of the factors relevant to product development and processing performance.

The complexity of powders

Powders are more than just the particles alone, they are bulk assemblies containing particles. It is often the case that the terms ‘particle’ and ‘powder’ are used interchangeably, but this can be misleading. Powders also consist of gases, normally in the form of air, and liquid, usually water, on the surface of the particle or within its structure.

It is the properties of each phase of a powder, and the interactions between them, that define bulk powder behaviour. This means that behaviour is influenced by several variables and an array of potential interactions, as well as process or ‘external’ influences, which is why they are complex and why powder performance cannot be accurately predicted from measurements of physical properties alone.

Powders perform in different ways, depending on how they are formulated and manufactured, as well as the environment to which they are subjected. While this can make them difficult to predict it is ultimately what underpins their industrial value.

There is a misconception that powder behaviour can be described by just understanding its flowability and that flowability is a discrete property that can be quantified with a single number. Unfortunately, neither of these assumptions are correct, which explains why we still do not possess a fundamental understanding of powder behaviour. Consider a loosely packed powder in a glass jar and visualise its behaviour whilst the jar is tumbled. Then consider how differently it would behave if the jar was first tapped several times on a hard surface. Any differences in behaviour from a loosely packed state to a tapped state would be due to the characteristics of the powder. If the powder were dry sand, then it would behave in a similar way before and after tapping. However, if the powder were flour, for example, it would flow very differently after it had been tapped.

Understanding powder behaviour is an essential precursor to efficient processing. ‘An Introduction to Powders’, the first in the series, focuses on how the three components of powder – the particles, surrounding air and any moisture present – interact to define powder behaviour, and provides answers to the most frequently encountered powder processing problems throughout industry. The guide goes on to explore the importance of powder flowability across a range of industrial processes, explaining the significance of operational conditions in the context of powder processing.

Choosing a Powder Tester

Once the fundamentals of powder behaviour are understood it is beneficial to review the strengths and limitations of the different types of powder testing techniques available. There are numerous powder testing techniques in route use across industry and a wide variety of powder testers in the commercial marketplace. This makes choosing the most appropriate tester for a specific application quite a challenge. Powder testers vary considerably in terms of their capabilities, complexity, degrees of automation and cost. ‘Choosing a Powder Tester’ addresses important questions facing powder processors looking to invest in powder testing instrumentation. These include: what powder testing techniques are available, what should powder handlers look for in a testing method and what features make powders more or less suitable for industrial applications?

The Value of Powder Testing

It is also important to assess the potential economic benefits a powder tester can deliver. There are many circumstances in which the generation of analytical data is an absolute requirement. The levels of investment can vary considerably but so too can the potential economic return. It is important to understand the ways in which powder testing can deliver value and how the features of an instrument or technique may influence the magnitude of any gains.  ‘The Value of Powder Testing’ explores key questions associated with such an investment. These include: what makes powder test data valuable, how does powder testing deliver an economic return, and, how can I identify ways in which powder testing might deliver value for a specific process or R&D laboratory? The guide also provides example studies to demonstrate how to estimate potential gains.

Each guide is written in a straightforward easy to understand style and draws on nearly 20 years’ of experience in powder characterisation.

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