Shrinking the dimensions
Trend: particle size is becoming a significant quality factor

Discussions about fine dust, new products with nanocoating and even creamier vanilla ice cream are everyday examples which demonstrate the fact that the size of even the tiniest particles can make a crucial difference. However, size is not the only criterion, and particle analysis often needs to provide other information as well.

Particle analysis is undoubtedly one of the most interesting measurement applications, but it is also one of the most challenging. Today’s systems have to offer more than just size analysis. The design of the analysis equipment must take into account the type and range of particles as well as the medium (fluid or dry). Additional information, for example whether organisms in the sample are living or dead, may also be required. However, even simple size analysis on its own can present a real challenge. The number of factors which can induce errors increases as the size of the particles decreases. Effects such as sedimentation and diffusion have to be considered in the design of optical counters. When there is little difference between the fractions, the sensitivity of the devices is often not sufficient to distinguish the particles by size. Border zone errors and particle deposition must also be taken into account.

Even the slightest inaccuracy negatives the validity of the measurement results. It is therefore hardly surprising that nanotechnology presents a significant challenge to makers of particle counters. Gerhard Raatz, Direct Sales Manager at Retsch Technology, explained that “currently everyone who is involved in the production and use of nano particles is very interested in particle characterization.” Patricia Kessler from the marketing team at Palas commented that “the latest engineering advances and increased demands in disciplines such as environmental engineering have created a need for new particle measurement solutions. This is particularly true if ‘hot topics’ are involved such as diesel soot, fine dust, atmospheric analysis and nanotechnology.”
Laboratory analysis is unquestionably the most accurate method, but it is also the slowest. It has the further disadvantage that when unforeseen events occur, the results are not available until it is too late to make any adjustments to the process. The online method can provide timely information about the number of particles, but the bypass control also introduces measurement errors.
Feedback to the process
Engineers at Haver & Boecker see timely analysis during ongoing production as a particular challenge. “What you really want to do is use the result to control the process,” explained Marquardt von Hodenberg, Manager of the Particle Analysis Department at Haver & Boecker. Investment in this technology by the process manufacturing and chemical industry continues to grow, and the acceptance level is increasing rapidly. Haver & Boecker in Germany and the American company W. S. Tyler have been major contributors to the development of international test sieve and the sieve analysis standards. One of the newest products is an upgraded real time particle analysis system with a camera which has a equivalent matrix resolution of 24 megapixels. All particles are measured using the real time function with no statistical errors. The high-resolution digital image analyzer with a suitable camera system guarantees that all of the particles are measured. Every single particle between 25 µm and 200 mm is captured at more than 40 million pixels per second. Length, width and circumference are calculated from pixel to pixel rather than in gradient increments. Around 50 percent of the installed devices are used for online process analysis in the mineral processing, chemical and food industries, etc. Hodenberg is convinced that “in the future, customers will definitely be looking for process control functionality and automation combined with ease of operation.”
Additional information
Kessler cited the following example to illustrate the problems that the industry is currently struggling with: “In some applications such as air pollution assessment, traditional measurement techniques are still being used which do not provide all of the relevant data. There are other applications where particle distribution over time and particle size distribution is not just helpful, it is actually essential. It would also be an advantage to have measurement systems that work with different sample volumes for different particle concentrations. For example, flexible particle measurement based on a modular design would enable users to select only the equipment that they need and then add cost-effective upgrades when necessary. Users would also welcome improved ease of operation and maintainability. Kessler believes that the analysis system may be combined with other measurement techniques in the future. Retsch is convinced that the challenge now is to provide more than just size data. “Users will increasingly want to see particle morphology information in the millimeter and micrometer range. The company manufactures and supplies the Camsizer particle measurement system. This system uses dynamic digital image analysis to characterize dry powder and granulate. The company also offers Horiba laser diffraction particle analyzers. “In particle characterization using dynamic digital image analysis, the focus is currently on improving particle morphology analysis. The hardware and software must be designed to hide the underlying complexity from the user,” added Raatz. It is crucial that the systems provide fast results. “We see a general trend to increase the level of rationalization in the labs. There is demand for fast, user-friendly systems which provide reliable, reproducible results and reduce the need for manual intervention.” The Retsch LA-950, which measures particles between 10 nm and
3 mm, is a good example of this approach. 87 high sensitivity detectors capture scatter and diffraction patterns at a sampling rate of 5,000 measurements per second, guaranteeing extremely high resolution and sensitivity over the entire measurement range. It takes less than a minute to feed in the sample, measure particle size, clean the dispersing system and get ready for the next measurement. This is only a quarter of the time that this process normally takes. Every step in the ongoing analysis process is clearly indicated to the operator, so that even inexperienced users are able to use the system effectively.
The Welas aerosol spectrometer from Palas features a modular design which makes the system suitable for a wide range of analysis applications. Three models have been introduced so far which cover the range down to –90°C and up to +120°C. “The new welas 3000, for example, uses two sensors to take nearly simultaneous measurements at two different points,” explained Kessler. “All of the systems can be combined with each other. Our latest innovation is a CNC module, which can be simply plugged on to the sensor to count ultra-fine particles in high concentrations. This upgrade significantly expands the analysis range and the range of applications.” This analysis system still offers a lot of potential for future development. Various projects are at the planning stage, for example a combination of the welas system and a Sigma 2 sampling head for external air analysis. This combination has already been tested successfully.
Detection of particle sources
More and more production facilities are spending an increasing amount of time and money on protecting their products from particulate contamination. Pharmaceutical and chip production are two examples. In many cases, particle sources are not identified until the quality of the product has already been degraded. Rap.ID helps detect particle sources and visualize problem areas. Rap.ID’s patented Liquid Particle Explorer can be used to perform fast chemical characterization of particles in super-pure liquids (medicines, process media). The source of process contamination can be identified and eliminated within hours. The system, which is based on Raman spectroscopy, automatically performs a chemical analysis of the particles. It identifies all organic and inorganic particles which are 2 µm or larger. Automatic detection of the Raman spectra takes places with the aid of a pharmaceutical and customer specific database.j