All posts by atascientific

Laser Diffraction System Breaks New Ground in Dry Powder Particle Sizing

Particle Science - Guide

Equipped with the Aero S dry dispersion unit, the new Mastersizer 3000 from Malvern Instruments is extending the boundaries of dry powder particle sizing. Recent studies have revealed this new laser diffraction system will deal equally efficiently with a variety of materials ranging from pigments to milk powder and coffee, and delivers effective dispersion without particle damage, even for fragile materials. The modular design of the Aero S dry dispersion unit provides options for controlling dispersion that include an adjustable hopper, different feed tray designs and a choice of two different venturis — one that uses shear forces to disperse the sample and another that uses impaction. The flexibility of the system allows the user to develop a robust method for every type of sample and, compared with other laser diffraction systems, the Mastersizer 3000 significantly broadens the range of materials and applications to which this measurement technique can be applied.

Source: http://www.engineerlive.com/Process-Engineer/Materials_Handling/Dry_powder_particle_sizing/24426/

Benefits of Online Particle Size Measurement in Mineral Processing

Particle Science - Guide

Automated online particle size measurement is being embraced more and more by the mineral processing industry because of the distinct advantages it offers over manual offline measurement and the cost efficiencies it is able to deliver.

Measuring particle size after milling, prior to further processing, is essential for reducing operating costs and extracting the maximum value from the ore being processed.

This measurement task has traditionally been carried out manually offline in a laboratory, occupying an operator’s full attention around the clock.

Not only is this costly from a manpower perspective, but because the testing is done periodically (only once every half hour or so), by the time a problem is detected or it is realised that a change is required (such as unblocking a separator, or adjusting material feed rate), valuable time and ore has been wasted.

By contrast, automated online particle size measurement provides a continuous stream of data, which allows for smaller changes to be made more often, thereby reducing wastage during reaction time, allowing problems to be rectified before they can escalate further and optimising operational flow. Where the ore being extracted is of particularly high value (such as gold), these cost efficiencies can be significant.

One of the earliest types of automated online particle measurement employed in the mineral processing industry involved the use of ultrasonics, but there were a number of clear limitations to this technology, and today, laser diffraction is the leading technology delivering the best results.

Laser diffraction particle size analysers are analytical instruments that determine particle size by the patterns produced when light interacts with them. Covering a particle size range from 0.1 to 2500 microns, they are ideal for the measurement of ore particles and can be used on both wet and dry flows.

The sample preparation rquired for laser diffraction analysis will vary depending on the process.  For wet minerals processing sample dilution is typically required and in some cases demagnetising or applying ultrasound to break up any agglomerates (clusters or accumulations of particles).

The samples are then analysed. Larger particles scatter the laser light narrowly at high intensity, while smaller particles produce a much weaker signal at wider angles.

Scientific instruments such as the laser diffraction particle size analyser are proving valuable tools, not just for the mineral processing industry, but across all kinds of manufacturing industries where automation of analysis is desired. Such instruments can deliver:

  • A marked saving through reduced manpower costs
  • Much greater control of particle size
  • The ability to immediately detect and resolve potential problems
  • Much faster optimisation of plant operation
  • A lot less energy consumption
  • A reduction in waste

By adopting these measurement techniques, those involved in the mineral processing industry are able to achieve a more favourable balance between the cost of liberation and the value of the mineral being processed. This translates into a higher return on their investment, with payback time from installation typically being six months to a year.

Superhydrophobic Tracks: Guided Transport of Droplets

Guides & Resources

Recent work by research groups including Mertaniemi et al.has shown that superhydrophobic tracks can be used for fast and simple transport of water droplets in microfluidic devices.

The wetting properties of the superhydrophobic surfaces were characterised by measuring dynamic contact angles using an optical tensiometer. These are scientific instruments are used to measure surface tension, interface tension and contact angles.

This article describes how the dynamic contact angle was measured by changing
the droplet volume on superhydrophobic surfaces.

A surface is defined as ‘superhydrophobic’ if the contact angle of water is larger than 150° and water droplets readily slide off the surface if tilted slightly.

Two factors are required to create a superhydrophobic surface. Firstly, the surface must have suitable roughness at micro and nanoscales. Secondly, the surface must have a hydrophobic surface chemistry

Only when the contact angle hysteresis (difference between the advancing and receding contact angle) is negligible can the wetting properties of a surface be characterised by a static contact angle, which is measured by placing a droplet on the surface and optically determining the contact angle.

For rough surfaces, dynamic (advancing and receding) contact angles need to be measured, since a static contact angle can take any value between the advancing and receding ones.

In the study, the superhydrophobic tracks were prepared in metal plates by milling or laser cutting and in silicon by ion etching. The metal surfaces were coated using a combination of silver microstructure and a fluorinated thiol surfactant, and the silicon wafers were coated with a fluoropolymer in CF3 plasma.

Wetting properties of a superhydrophobic copper surface were characterised using a Theta optical tensiometer from Attension (part of the Biolin Scientific Group, a global provider of analytical instruments).

First, a 1-μl droplet was applied on the surface, and the needle was lowered into the drop so that the tip was about at the midway of the droplet height.

The volume of the droplet was slowly increased to 2 μl, at a drop rate of 0.05 μl/s. In order to minimise hysteretic effects, the addition of water was stopped for 30 seconds before starting the contact angle measurement.

To measure the advancing contact angle, the volume of the droplet was increased from 2μl to 10 μl at 0.05 μl/s, recording images at 0.6 frames per second.

Next, the droplet volume was increased to 15 μl and decreased back to 11 μl. After this, the droplet volume was decreased slowly to 10 μl.

In order to minimise hysteretic effects, the removal of water was stopped for 30 seconds before starting the receding contact angle measurement.

The receding contact angle was measured by decreasing the volume at a rate of 0.05 μl/s, starting at a drop volume of 10 μl. Images were recorded at 0.6 frames per second until the drop lost contact with the surface.

A similarity of contact angle values of the zinc and copper surfaces was expected, since both surfaces were coated using the same method. However, the larger variance of receding contact angles observed for the zinc surface suggests that the coating had some defects.

The very small contact angle hysteresis of the silicon surface makes it the optimal choice for applications where extremely high mobility of water droplets on a surface is desired.

Pulsating Drop Module Used to Study Surfactant Behaviour in Flotation

Guides & Resources

The choice of surfactant influences the recovery yield of minerals during flotation separation processes. Scientific instruments such as the Theta force tensiometer with Pulsating Drop Module are now being used to measure the rheological properties of bubble surfaces.

The principle of flotation is simple. In the flotation tank, fine bubbles are dispersed in the pulp containing finely ground ore particles which, depending on their hydrophobicity, attach to the air bubbles. Thus, valuable ore is lifted to the top of the tank, where it is skimmed off, while gangue minerals stay in the pulp.

The dispersed air bubbles play a key role in the process. Their properties are strongly influenced by the composition of the fluid medium, which consists of water and flotation reagents, such as frothers, collectors and depressants.

Frothers are surface-active substances that have an effect on the formation and behavior of the air bubbles. The frother molecules adsorb on the bubble surface creating an adsorption layer. During the adsorption, the surface tension decreases until it reaches an equilibrium value.

Under dynamic conditions, the kinetics of adsorption and desorption of surfactants to and from a solution have a major effect on the behavior of bubbles. Understanding the rheological properties of the adsorbed layers is important for the characterisation of commercial surfactants.

The capillary wave and oscillating bubble techniques were the first two methods developed to measure surface dilatational elasticity. The bubble oscillation method, developed by Lunkenheimer and Kretzschmar, uses harmonic interfacial disturbance to measure the surface dilatational elasticity.

A small bubble is formed at the end of a capillary tip and a membrane is used to create harmonic oscillation. This technique allows measurement of the surface dilatational elasticity at relatively high frequencies.

The modified pendant drop technique works on the same principle as the oscillation bubble method. The high resolution and excellent accuracy provides a useful tool to study the dynamics of adsorption layers. The method can be applied to liquid-gas as well as liquid-liquid interfaces.

The Pulsating Drop Module was provided by Attension (part of the Biolin Scientific Group, a global provider of analytical instruments). It is a compact, optional module to the Theta optical tensiometer for measuring surface dilatational elasticity based on the modified pendant drop technique.

In this study, the Attension Pulsation Drop Module was used to investigate the effect of two well-known commercial frothers; Nasfroth 240 (NF240) and Dowfroth 250 (DF250), on dilatational elasticity and viscosity of the bubbles surface.

The aim was to investigate how the surface properties changed when the concentration of the frothers was increased from below the CCC point (critical coalescence concentration) to above the CCC point.

The increasing concentration of surfactant caused a different effect on the surface elasticity in the presence of the two different types of frothers. In the NF240 solution the increasing concentration caused higher elasticity due to the decrease of surface tension. However, in the presence of DF250 with increasing frother concentration, the elasticity of the interface decreased.

This phenomenon could be explained by the faster molecule exchange. The higher the concentration, the faster the exchange and the lower the elasticity.

This study shows that the pulsation drop technique is an accurate way to investigate the rheological properties of interfaces with relatively high frequencies and is a valuable tool for characterising commercial surfactants used in the flotation process.

Introducing the Mastersizer 3000

Particle Science - Guide

The Mastersizer 3000 is a new particle size analyser that is capable of providing accurate and fast distributions in both wet and dry dispersions. In this article, we’ll take a closer look at the Mastersizer 3000, discussing how it works and some of its key features.

What is particle size analysis?

Firstly, for those who may be unfamiliar with the role of a particle size analyser such as the Mastersizer 3000, allow us to explain very briefly

In order to properly understand many products, it is critical to understand the particle size distribution of those products. Without this knowledge, the physical and chemical properties of the product cannot be fully grasped.

There are many products where this is the case. Particle size can, for example, affect the load-bearing capabilities of soils. It can affect the reactivity of solids in a chemical reaction. It can affect the taste of coffee, the efficacy of drugs, the consistency of cement and much, much more.

As a result, the measurement of particle size — more commonly known as particle size analysis — becomes a critical function in the manufacturing process across a wide range of industries.

What is the Mastersizer 3000?

The Mastersizer 3000 is a state-of-the-art particle size analyser that produces robust and reproducible data in for particle size analysis. Some of its most important features include:

  • Measurement range: It’s a particularly broad one, ranging from 10mm to 3.5mm. It has particularly outstanding resolution at the “sub-micron” level.
  • Minimal footprint: The optical bench spans no more than 690mm.
  • High performance in both wet and dry dispersions: The Aero S dry powder dispersion accessory aids in dry dispersion, while the Hydro range accessories handle wet dispersion extremely effectively.
  • Intuitive software: Every measurement is delivered quickly and easily, yet the software is still extremely powerful.
  • Rapid Analysis: The Mastersizer 3000 captures light scattering at a rate of 10,000 snapshots per sec, with typical measurement times of 10sec for even polydisperse samples.

How does the Mastersizer 3000 work?

The Mastersizer 3000 operates with the principle of laser diffraction, which states that particles will scatter light in different ways depending on their size. Analysis of the scattered light’s angular intensity leads to accurate conclusions relating to particle size distribution.

Operating the Mastersizer 3000 is a three-step process:

1. Preparing the sample

There are two dispersion modes that can be utilised — wet dispersion, for aqueous or organic dispersants, and dry dispersion, for powder samples. This ensures that everything from coarse granulates to incredibly finely dispersed emulsions is covered.

2. Measurement

The accuracy of the laser diffraction technique is dependent on two factors: the stability and wavelength of the light source, and the sensitivity of the detector array. The Mastersizer 3000 features a top-of-the-line detector array, with red and blue light sources is capable of resolving materials as small as 10 nanometres and as large as 3.5mm in size. As a result, even high-polydisperse samples are able to be measured accurately.

3. Reporting

Utilising the Mie theory of light scattering, the Mastersizer 3000 measures angular intensity of light scattering in order to determine a particle size distribution. From there, results will be presented volumetrically, and measurement parameters can be tracked in real time. This allows for immediate analysis and data comparison alongside defined standards.

4 Benefits of On-Line Particle Analysis for Mineral Processing

Particle Science - Guide, , , ,

In order to extract valuable minerals from naturally occurring ores, the process of comminution and milling must take place to produce materials of an appropriate particle size. This process is critical in order to ensure operating costs stay low and to ensure the minerals extracted are of high value. Traditionally, particle size analysis has been performed through manual measurement, but increasingly the industry is turning towards on-line particle size measurement methods such as laser diffraction. In this article, we’ll look at four reasons that laser diffraction is the optimum method for particle sizing in the mineral processing industries.

1. Quicker and higher ROI

Most studies have confirmed that return of investment for on-line laser diffraction occurs anywhere between six months and a year following installation. The biggest reason for this is that there is much less reliance on manpower; manual analysis methods generally necessitate highly-skilled individuals to be working around the clock, while on-line systems only require occasional intervention from a semi-skilled worker, lowering costs in terms of both time and expertise. These lowered man hours have the added benefit of minimising the risk of hazard material exposure.

2. Greater levels of process control

With off-line measurement, the frequency of analysis is quite low, occurring an average of once or twice an hour. This has the flow-on effect that operational changes are bound to be much less frequent; the operator will receive the data and make a change (perhaps a very large change), and won’t see the outcome of that change until the next analysis. With online particle size analysis, however, there is a constant flow of information, meaning that smaller changes can be made on a more consistent basis.  Additionally, the on-line method of measurement allows for a steadier stream of automated control. Both of these factors lead to more efficient process control.

3. Faster process optimisation

Since finding the optimal particle size is crucial to extracting the most valuable from the ore, the optimal processes must be put in place. Much like discussed above, off-line particle size analysis requires the analyst to wait until several samples have been taken and analysed before they can see the outcomes of their changes. With an on-line particle size analyser, however, this process is much quicker. Assessing new operating scenarios requires nothing more than a new steady state to be established, meaning the changes can be evaluated in minutes.

4. Immediate upset detection

The impact of an upset can be disastrous for the batch, leading to significant loss of profit. To avoid this kind of situation, it’s important to detect problems as soon as possible. With off-line particle size measurement, problems can go undetected for hours, but with on-line methods such as laser diffraction, there is constant monitoring of the process and upsets can be detected as they occur. Rio Tinto, for example, has enjoyed a two year period without unplanned stoppages, and it’s all thanks to their installation of an on-line particle size analyser. Problems are detected and the appropriate action is taken to remedy the situation before it escalates.

What is Particle Size Analysis?

Particle Science - Guide, , , ,

Particle size analysis: it sounds tricky, but mark our words, it’s something that everyone would be well-served learning more about. Whether you realise it or not, particle size analysis plays an extremely important role in many of the products we use, consume and interact with in our everyday lives. In this article, we’re going to offer you a brief introduction to particle size analysis, listing some of its most common applications as well as its most established methods. We’ll also take a look at zeta potential, a measurement that is often used along side particle size analysis.

What is particle size analysis?

There are a huge number of industries which rely on methods of particle size analysis to ensure products are of the highest quality. From powders to creams, gels, lotions, and other mixtures, the size and characteristics of the particles contained within can have dramatic effects on properties such as stability, appearance, flow and chemical reactivity. As a result, a highly important industry has developed centred on particle size analysis, with constant innovation in methods that provide more and more accurate ways of analysing particle size.

What are the applications of particle size analysis?

As we’ve already mentioned, the applications of particle size analysis are numerous; too numerous to mention here. However, some of the industries that rely heavily on the understanding of particle size distribution include:

  • The cosmetics industry
  • The pharmaceutical industry
  • The cement industry
  • The food and beverage industry
  • The plastics industry
  • The pigments and inks industry
  • The ceramics industry
  • The metal powders industry

What are some common particle size analysis methods?

Probably the most popular method of particle size analysis is laser diffraction , which involves particles being illuminated by a laser beam, causing the light to be scattered in various directions. The scattering patterns are then measured with specially-designed detectors and particle size distribution can be calculated from this data. For example, larger particles bring about a higher intensity of scattering at lower angles to the beam, while smaller particles offer a low intensity of scattering at higher angles.

Laser diffraction has the advantage of offering real-time particle analysis that allows for several benefits, including:

  • Increased return of investment
  • Lower energy consumption
  • Better troubleshooting
  • Increased efficiency
  • Reduced operator risk

What is Zeta Potential?

When measuring particle size distribution, it’s also important to consider the particle’s zeta potential or ‘charge’ measurement. Most particles will gain a charge on their surface when dispersed in an aqueous system. These charges change the distribution of the surrounding ions, leaving a layer around the particle that does not have the same properties as the rest of the solution. Zeta potential determines how particles interact within solution and measurement of zetapotential can give valuable insight into stability and reactivity of a material.

The Best Ways to Measure and Analyse Particles

Particle Science - Guide,

For many people, the thought of measuring and sizing particles (that are often too small to be visible) can seem completely baffling. Just the thought of how this could possibly be done can seem daunting.

These days there are several types of particle size analyser instruments available that operate using different measurement techniques. laser diffraction is one such technique that can give us great insight into the properties of different materials.

Of course, there is no single measurement technique that can be used to measure all materials and all particle sizes. As such, some industries use a range of different techniques to measure different materials.  The problem with this is that different techniques measure different dimensions of particles, so when they often yield different results.

In order to understand more about the different results that are obtained through particle measurement and analysis, it is useful to be aware of some commonly used methods. These include:

Sieves:

This is one of the oldest and most traditional of all the methods of measuring particle size and is so often used because it is cheap and reasonably effective when measuring larger particles. The measurement of large particles occurs in a number of industries, including the mining industry.

However, the use of a sieve makes it impossible to measure particles within sprays or emulsions.  Even dry powders become very difficult to measure when particle are very fine. A further disadvantage is that the ability to reproduce results is difficult, particularly when the technique of wet sieving is applied.

In order for particle size results from sieves to be useful and informative, the operating methods and measurement times need to be standardised.

Sedimentation:

This is another technique which has been around for a long time and has historically been used in certain industries.  Soil scientist have long used sedimentation to measure course grained soils (ie.sand) and it has also been widely used in the ceramics industry. While some industries have a long history with sedimentation, it has also provided these industries with some problems.

For a start, the calculation of size from sedimentation rate is only valid for spherical particles.  If the particles are not spherical then the results reported can be very different from reality.  It is also necessary to know the density of a material.  If density is not known, or if a sample contains a mixture of materials, it is difficult to obtain accurate results. It is impossible to determine the size of emulsions particles, where the material does not settle. Similarly, it is difficult to get accuratete measure of large and very dense materials where the material quickly settles.

Electrozone Sensing:

This technique is particularly useful for measuring the size of blood cells but it poses some problems as a technique for measuring industrial materials. Samples must be suspended in a salt solution so it is not possible to measure emulsions and many dry powders.  Measuring the particle size within sprays simply cannot be done.

Laser Diffraction:

A popular and preferred measurement technique, laser diffraction also has the advantage of being one of the most accurate ways of measuring particle size. Other advantages of laser diffraction include:

  • It provides a great degree of flexibility for different materials
  • Results and answers can be provided quickly (in less than one minute)
  • It is an absolute method of particle analysis
  • There is no need to calibrate instruments against a standard
  • It is possible to measure dry powders, suspensions, emulsions, sprays and many other materials
  • The technique provides a wide and dynamic range of measurement
  • The measurement of an entire sample is possible
  • The technique can be repeated easily.

While there are a range of ways to measure and analyse particle size, the most appropriate way of measuring any given material will and should depend on the type of material that is being measured.

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Facts About Laser Diffraction

Particle Science - Guide,

As a technique of particle size analysis, laser diffraction is widely used and has many advantages. It offers a high level of precision, a fast speed of response, high potential for the repetition of results and a wide measurable particle diameter range. Particle size analysers offer a sophisticated way of measuring particle size and enable incredible insight and understanding of the particles that make up materials used in a range of industries.

Laser diffraction is an important technique for measuring particle size. Here we offer a range of facts about this technique:

  • It is also known as Low Angle Laser Light Scattering (LALLS).
  • Considered a standard method in many industries because of its ability to characterise particles and for reasons of quality control.
  • Huge advances have been made in instrumentation over at least the last two decades.
  • The method is founded on the fact that the angle of diffraction is inversely proportional to particle size.
  • The instrument consists of a laser (as a source of coherent intense light that has a fixed wavelength), a detector (typically an array of photo sensitive silicon diodes) and a means of passing the sample through a laser beam.

Laser diffraction is so popularly and extensively used because it offers a number of advantages. These advantages include:

An absolute method grounded in fundamental scientific principles – In this method it is not necessary for an instrument to be calibrated against a standard. However, validation of equipment is possible to prove that it is performing to a standard that can be traced.

Wide and dynamic range – In measuring particle size, good equipment will allow the user to measure particles sized between approximately 0.1 and 2000 microns.

Flexibility – Laser diffraction offers new possibilities for measuring materials. It is even possible to measure the paint that is sprayed from a nozzle in a paint booth. The pharmaceutical and agricultural industries are two of the many industries that have benefited greatly from such advances.

Dry powders – Even dry powders can be measured through the technique of laser diffraction. Although this may result in a poorer level of dispersion than if a liquid dispersing medium was used, it is an advance that dry powders can be directly measured. In combination with a suspension analysis, it can support the assessment of the amount of agglomerated material in a dry state.

Liquid suspensions and emulsions – It is possible to use a recirculating cell to measure liquid suspensions and emulsions. This technique promotes a high level of reproducibility and facilitates the use of dispersing agents and surfactants to determine the primary particle size. If it is possible to do so, it is preferable to take measurements in a liquid suspension.

Sample measured – This technique allows for the whole of the sample to be measured. As the sample passes through the laser beam, diffraction is measured for all particles.

Rapid – This technique is so rapid that results can be derived in one minute or less. Feedback can therefore quickly be provided to plants and repeat analyses can also be made quickly.

Repeatable – This technique is highly repeatable and knowing that the results can be relied upon provides peace of mind.

A sophisticated method for determining particle size, laser diffraction is widely used and offers distinct advantages that are beneficial for many industries.

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Particle Size Analysis Basics

Particle Science - Guide,

In many industries, the ability to determine the size of particles is not only useful but can be very important. A Laser diffraction particle size analyser is commonly used to provide this sort of information but the processes used to obtain particle size can be quite complex. Sampling, dispersion processes and the shape of materials all contribute to the complexity of particle size analysis.

Here we provide key information for understanding particle size analysis.

What does it mean to describe a particle?

When dealing with a three dimensional shape, one unique number cannot accurately be given to describe its size. While this remains true in so many situations and circumstances, it is particularly relevant when seeking to describe complex shapes such as a grain of sand or even a particle within a can of paint.

While many of us may question why this information is so important, it is imperative and influential for people such as Quality Assurance Managers within particular industries and organisations. For example, a Quality Assurance Manager may need to know whether the average size of particles has increased or decreased since the last production run.

The equivalent sphere

So often we seek to describe a shape by only one number. As has been mentioned, this is problematic as there is only one shape – a sphere – that can be accurately described by one number.

In order to arrive at a particular number to explain the size of a shape, equivalent sphere theory is frequently used. Using the equivalent sphere theory, some property of the particle is measured and it is then assumed that this refers to the diameter of a sphere to describe the particle. Essentially, this means that three or more numbers do not have to be used to describe a three dimensional particle. Although it is more accurate to describe three dimensional particles with three or more numbers, it is also inconvenient and can become unmanageable.

Using different techniques

When a particle is examined under a microscope, a two dimensional image is seen and the information that is deduced relates to the two dimensional shape. Consequently, there are a number of different diameters that can be reported. If the maximum length of the particle is used, then the result relates to a sphere with diameter of the maximum dimension. Conversely, if the minimum length is used for the calculation, then the result pertains to a sphere with diameter of the minimum dimension.

It is therefore important to note that each technique used to measure a particle will provide a unique result because it measures a different property of a particle.

In light of this, there is no absolute right or wrong answer. All answers are correct for the techniques that are used and the dimension of the particle that they are measuring.

What does this all mean?

For those to whom particle size analysis is important, different techniques for measuring particle size mean that there can be no standard size for particles such as grains of sand. If meaningful comparisons are to be made between different techniques, it must be done with standards containing spherical particles. Further to this, characterisation of particle size standards is only possible when the same technique has been used and this allows comparison between instruments that use the same technique.

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