John Bulmer
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As a scientist at the University of Cambridge, I’m closely involved in a fascinating project on Carbon Nanotubes. In cooperation with Bronkhorst, we are working on a reactor to control the fabrication of this exceptionally strong and conductive material. Let me explain more about this subject and why I consider Carbon Nanotubes to be a material of the future.

History and future of Carbon Nanotubes (CNT)

In the beginning, carbon came in three molecular forms: • diamond • graphite • amorphous carbon Suddenly, in the mid-1980’s, a new molecular form of carbon surfaced in research and ignited the multidisciplinary field of nanotechnology. This all carbon molecule, Buckminsterfullerene, is a nanometre-sized cage of carbon atoms with a molecular structure that resembles a football.

A few years later, another molecular carbon cousin came to light: carbon nanotubes (CNT). Similar to Buckminsterfullerene, the football structure is vastly elongated into a nanometre-wide tube with length millions of times greater than its diameter. Captivating scientific attention; CNT’s strong carbon bonds with its ordered molecular structure make it the strongest material ever made. Electrons glide down CNT’s effortlessly, as stable one-dimensional conductors, which makes CNT’s electrical conductivity four times greater than copper and with a maximum current carrying capacity 1,000 times greater than copper.

3d-model-of-buckminsterfullerence 3D model of Buckminsterfullerene

By the early 2000's, researchers created processes to fabricate textiles composed of CNT’s with densely packed and aligned microstructure. Initially, the bulk properties of CNT textiles lagged well behind the exciting properties of their individual molecules. After steady incremental improvement, the state-of-the-art CNT fibre is as strong as conventional carbon fibre and about four times more conductive. With continued development we expect CNT fibres that are substantially stronger than conventional carbon fibre with an electrical and thermal conductivity greater than traditional metals like Copper and Aluminium.

Application of Carbon Nano Tube fibres is in strain-resistant textiles (protective clothing, bullet-proof vests), composites, construction compounds (ceramics, lighter car bodies) and cables because of their strength. Using carbon nanotubes could have enormous impact on day-to-day life, similar to the way plastics changed the world in the mid-20th century.

Carbon Nanotubes (CNT) at the University of Cambridge

Our laboratory invented a production process that not only creates Carbon Nanotubes in industrially competitive volumes, but does so with unparalleled graphitic perfection into a macroscopic textile with aligned microstructure, all in one production step. This production process is intrinsically simpler than other fibre production processes such as conventional carbon fibre and Kevlar.

The floating catalyst chemical vapour deposition reactor (F-CVD) that is used for this process just requires a carbon source (toluene), a catalyst source (ferrocene) and a Sulphur based promotor (thiophene), which are mixed together and fed into a 1300°C tube reactor by a carrier gas (hydrogen). A floating CNT cloud is formed. Mechanically extracting the CNT cloud out of the tube reactor condenses the cloud into a bulk fibre with aligned microstructure. This is called “CNT spinning”. Specially protected personnel, also known as “the spinner”, mechanically extracts the CNT cloud into a fibre.

Consistent reactor control however, is challenging. The CNT material properties vary substantially between runs and the relationship between controlled and uncontrolled reactor input parameters are not fully understood yet.

Control of the Carbon Nanotubes Reactor

Our program seeks to implement a robust feedback loop to control the reactor’s CNT material properties. Every reactor input variables and output variables, which are specifically selected CNT material properties, are automatically measured and recorded into a database; from the outside weather, to the operating personnel, to the age of the tube, to the precursor concentrations, gas flows, etc.. The database is continually data mined for correlations, parameter interaction, and multidimensional linear regression models that statistically predict reactor behaviour using the data exploratory software JMP™.

For example, figure 1 shows a statistical model for the material’s G:D ratio, this is the ratio between graphite (G) and graphitic defects (D) from Raman spectroscopy, which indicates the degree of graphitic perfection. The model is a function of various reactor input parameters that were found the most statistically significant to the G:D ratio. On the horizontal axis in the plot below, there are the predicted G:D values of the model and, on the vertical, the actual measured vales. In a perfect model with perfect control, we would expect a straight 45 degree line. Clearly, the data points are widely spread along the red line, which indicates a low level of reactor control.

Statistical model for the material’s G:D ratio

Figure 1

The setup here involved simply mixing the precursors together (toluene, ferrocene, and thiophene) and injecting the solution into a hydrogen carrier gas via a simple gear pump. It became evident a more sophisticated system was required for greater reactor control.

Bronkhorst solution for control of the Carbon Nanotubes Reactor

Figure 2 shows our improved system. Separate liquid precursors are now independently controlled with Bronkhorst Coriolis instruments (mini CORI-FLOW series)(link product page). The Coriolis mass flow meters give precise mass flow rates without the need of recalibration between different precursors, which greatly facilitates trying out different CNT recipes. Bronkhorst is the only one who succeeded in applying the well-known high-precision Coriolis principle to an extremely small scale by applying MEMS technology.

Carbon Nanotubes Reactor Scheme

Figure 2. Carbon Nanotubes Reactor Scheme

The flow rates are in the range up to 200 g/h for toluene and even below 100 mg/h for thiophene. Hydrogen carrier gases are controlled by robust, plug-and-play Bronkhorst mass flow controllers. Finally, the precisely metered precursors are vaporized and combined with the controlled hydrogen carrier gases with vaporizer technology.

Chemical vapour deposition reactor is much more effective

Figure 3

With this new and more sophisticated instrumentation, statistical modelling of the floating catalyst chemical vapour deposition reactor is much more effective. Here, the actual versus predicted values for the graphitic perfection are much more agreeable, as is shown in figure 3. This model has substantially less noise, which means the reactor’s response is predictable and repeatable. So far, with this controllable and well modelled reactor system, we have more than doubled typical CNT production rates and tripled the degree of graphitic crystallinity.

Stay tuned! With Bronkhorst and other important commercial, academic, and government partners we hope to surpass conventional carbon fibre soon!

Bronkhorst information

If you are active in reactor technology, do not hesitate to contact us for solutions for your processes. Please contact us for more information.

• Read more about MEMS technology that is used for the research in Carbon Nanotubes in the previous blog of Wouter Sparreboom.

Chris King
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Anhydrous Ammonia Control for Nitrogen Oxides Reduction

As a technique to reduce the level of Nitrogen Oxides (NOx) in boiler or furnace exhaust gases, Selective Catalytic Reduction (SCR) has been around for years. SCR is a technology which converts Nitrogen Oxides (NOx) with the aid of a catalyst into diatomic Nitrogen (N2) and Water (H2O). A reductant agent is injected into the exhaust stream through a special catalyst. A typical reductant used here is Anhydrous Ammonia (NH3).

A customer of Bronkhorst, who has been selling and servicing boilers and pumps for commercial and industrial applications for over 50 years, had been using a mass flow controller (MFC) which was not reliable and robust enough for the application and thus their customers were suffering from poor ammonia measurement and control.

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Why use mass flow measurement in Ammonia Control?

Some NOx reduction systems are liquid ammonia based, and others are gas based ammonia. Whatever the state of the ammonia in the NOx reduction system Bronkhorst can offer accurate ammonia measurement and control. Systems in the field today are using the MASS-STREAM (gas), IN-FLOW (gas) and Mini CORI-FLOW (liquid) to accurately control the ammonia being injected into the exhaust gas stream so that proper reaction takes place without ammonia slip. Ammonia slip is when too much ammonia is added to the process and it is exhausted, un-reacted, from the system; effectively sending money out the exhaust stack.

There are very strict federal and state air quality regulations that specify the allowable level of NOx which can be released into the atmosphere and there can be very heavy fines if those levels are exceeded. The company needs to provide their customers with a reliable and robust solution. The application demands a robust and repeatable mass flow controller that is at home in industrial environments.

What kind of Mass Flow Meter or Controller can be used here?

In the NOx reduction system serviced by our customer the mass flow controllers are used to control the flow of anhydrous ammonia (ammonia in gas state) into the exhaust gas of a boiler or furnace where it is adsorbed onto a catalyst. The exhaust gas reacts with the catalyst and ammonia which converts the Nitrogen Oxides into Nitrogen and Water.

Bronkhorst recommended a mass flow controller – from the MASS-STREAM series - using the CTA (Constant Temperature Anemometer) technology which is ideal to avoid clogging in potentially polluted industrial gas applications.

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Let me explain a bit about the working principle of this kind of mass flow controller and why it is suitable for an application like this.

The CTA (Constant Temperature Anemometer) principle is essentially a straight tube with only two stainless steel probes (a heater and a temperature sensor) in the gas flow path. A constant temperature difference between the two probes is maintained with the power required to do so being proportional to the mass flow of the gas. This means the MASS-STREAM is less sensitive to dirt, humidity, or other contaminants in the gas, as compared to a by-pass type flow meter that relies on a perfect flow split between two paths. The thru-flow nature of the CTA technology is ideal to avoid clogging in potentially polluted industrial gas applications. The straight flow path and highly repeatable measurement and control capability, combined with the robust IP65 housing, allows the MASS-STREAM to thrive in tough applications.

Watch our video animation, explaining the functions and features of the Bronkhorst Mass Flow Meters and Controllers for gases using the CTA principle.

Check out the top 5 reasons why to use mass flow controllers with CTA measurement.

Walter Flamma
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In our previous blog we’ve already discussed many applications at a campsite where Bronkhorst solutions are used. However, we did not mention a very important aspect of camping life; food and beverage. Delicacies like ice cream, soda and candy are also inextricably linked to the summer and to Bronkhorst. Let me explain why…

Ice cream aeration with mass flow controllers

Have you ever celebrated summer holidays without eating ice cream? I didn’t. To create ice cream, aeration in the production process is crucial. This because air makes up anywhere from 30% to 50% of the total volume of ice cream. Higher aeration will produce a tastier and smoother ice cream. A side effect of adding air to ice cream is that it tends to melt more quickly. Thus, for attaining an optimal structure of the ice cream, it is important to have a stable inlet air flow in the production process with a constant cream/air ratio. This can be achieved by using a mass flow controller. If you got a big appetite to read more about the production process of ice cream, please read the blog about the aeration process.

Ice cream

Carbonation process of soda

During the warm days it is important that you stay hydrated. So, a tasty soft drink is by no means a frivolous luxury. The "fssst" you hear when opening a bottle of sparkling soda, is millions of carbon dioxide (CO2) molecules bursting out of their watery prisons, where they have been held against their will. In the soda industry an effective solution is needed to add CO2 gas to liquids, quick and consistent. Soft drink manufacturers add this tingling sensation by forcing carbon dioxide and water into your soda at high pressures, with the help of a thermal mass flow controller for gas. It’s important that the carbonation process is accurate. Inadequate CO2 injection will end in ‘flat’ beverage, while excessive carbonation can possibly break the bottle, which leads to safety issues and loss of product.

Carbonation soda

Surface treatment for packaging

Not only beverage itself originates with Bronkhorst products. The packaging used for foods must meet many requirements, whereby flow meters are needed. To extend the shelf life, the packaging must be sterile and oxygen must be eliminated during filling. Also here, an accurate and reproducible flow is very important. Coriolis mass flow meters, CEM (Controlled evaporation mixer) and gas mass flow controllers are the key instruments in these processes. To read more about this process, please read the blog of James Walton, where he explains the sterilization of packaging to extend shelf life.

Additive dosing in candy manufacturing

Certainly the parents among us will know the strong preference of children for candy, due of its sweetness but also because of their attractive colours. During the manufacturing of candy, additives such as colourings, flavourings and acids are added. By using ultrasonic volume flow meters, the accuracy of measurement has been improved, and so is the quality control of the manufacturing process. Many colourings and flavourings are costly agents, and a controlled and efficient use of these substances will gain a better quality product, and will save on raw materials as well.

Additive dosing candy manufacturing

Dosing colourants is not only applicable with foods. When we have finished our diner, there’s one thing everyone runs away from, certainly during vacation…

Dosing colourants in detergent with Coriolis mass flow controllers

Dishwashing; it’s one of the most tedious tasks of camp life, especially when you are used to a dishwasher at home. However, with a little help from Bronkhorst, dishwashing becomes a bit more colourful. Coriolis mass flow controllers are used for dosing colourants (or dye). This applies, among other things, to the production of dishwashing detergent. As well as in flavouring, accuracy and repeatability with dye dosing are of extreme importance for a detergent manufacturer. Every flacon has to be the same colour, you should not see any colour difference between the flacons on the shelves. For this, combining a pump with Coriolis mass flow controllers makes the pump dose mass flow instead of the usual volume flow. Since real mass flow is independent of the fluid properties of the colourant, the accuracy will be inimitable.

Dosing colourants detergent

As you can read Bronkhorst is present in many products at a campsite without you knowing it. Want to learn more about how Bronkhorst is involved in camping life? Read our blog ‘Camping applications that are made possible with mass flow control’.

Gerhard Bauhuis
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The temperatures are sky high! All winter you've thought about going camping, travelling with your caravan and planning precious family trips. Finally now it’s the time to leave everything behind, and for a moment forget the busy daily live and struggling at home. However, everywhere you go Bronkhorst is travelling with you. Bronkhorst plays a role in many more applications than you think, even when you go camping. Let me guide you through some mainstream products you often see at a camping site, and the involvement of mass flow controllers.

Surface treatment

If you are travelling to your vacation destination by car, you will constantly look at some Bronkhorst solutions. Let’s start with the dashboard of your car. Many cars have a leather dashboard; at least, it looks like leather. A major company manufactures ‘skin’ that covers a car's dashboard, to give it this ‘leather look’. The skin is produced by spraying liquid, colored polyurethane into a nickel mold. A Coriolis mass flow controller combined with a valve forms the basis of this solution to accurately supply external release agent to the nickel mold surface.

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But also the foam within the dashboard is manufactured by using Bronkhorst products. To create foam, a gas is added to a mixture containing acrylonitrile-butadiene-styrene (ABS) or polyvinyl chloride (PVC), to give it the right volume. Too much gas will make the foam unstable, too little and you’ll get a heavy solid block. Therefore, it is utterly important that the correct amount of gas is added with an accurate gas flow controller.

Glass coating

If you look beyond your dashboard, you’ll look through the front window of your car. To control the light transmittance of glass, but also to make glass water repellent, protect it from mechanical and chemical stress, increase the scratch resistance and shatter protection, thermal mass flow controllers are used for the coating process. By controlling individually process gas flows, film thickness uniformity improvements are achieved.

Coating on headlights

When polycarbonate was introduced as a replacement for headlights glass in the early 1980s, new problems arose. Headlights are subject to a harsh environment. Due to the position in the front of a car, critical parameters for lifetime and performance are weather ability, scratches, and abrasion. To protect headlights from these factors, scratch and abrasion coatings have been developed that are sprayed on the headlights with the help of robots in which Coriolis mass flow controllers control the flow to the spraying nozzles.

Hydrophobic coating

However, surface treatment is not only applicable for glass and dashboards. If you have experience with camping, you will be familiar with how fierce the summer weather sometimes can be. The awning of your caravan needs to be water repellent - this also applies to your raincoat - to sustain the heavy rainfall now and then. To make fabrics and textiles hydrophobic, Empa - a research institute of the ETH Domain, applies plasma polymerisation to deposit thin, nanoscale layers on top of fabrics and fibers. For this, they are using a Controlled Evaporation and Mixing system, in short a CEM system. In one of our previous blogs ‘Hydrophobic coating, the answer to exercising in the rain’ you can read about this application.

Image description Mass flow controllers are used to make awnings hydrophobic


Bronkhorst is also involved with many smaller attributes you will encounter on a campingsite. Most people still enjoy the comfort of gas for heating or cooking on the stove. But also with gas we are able to fire up the barbecue in no time at all, in comparison with the old-fashioned briquettes that are sometimes hard to ignite. When gas escapes from a pressurized cylinder, you’ll recognize this from its penetrating scent. However, like Sandra Wassink stated in her blog “How mass flow controllers make our gas smell”, natural gas is odorless. By controlled supply of odorants like Tetrahydrothiophene (THT) or Mecaptan with a mass flow controller, the scent is added to the natural gas on purpose.

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Let’s stay with the topic scent for a moment. For when we want to decrease the amount of mosquitos in our surroundings, we often light a citronella candle when we are getting tired of using the flyswatter. With the CORI-FILL dosing technology, Bronkhorst offers an easy-to-use setup to dose fragrances, like citronella, in candles. The addition of fragrance to a candle should be carefully monitored to ensure the candle burns cleanly and safely.

LED lighting

However a candle can bring much light to your surroundings, you won’t take a candle with you when you dash to the camping toilets at night. Instead you will use a flashlight of course. The working principle of the LED (Light Emitting Diode) inside this flashlight is a technology where Bronkhorst plays its part. LED works via the phenomenon called electroluminescence, which is the emission of light from a semiconductor (diode) under the influence of an electric field. By applying a semiconducting material like Gallium arsenide phosphide for instance, the manufacturing of red, orange and yellow light emitting diodes is possible.

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I already told you so much, but frankly, it is just a tiny bit of all the camping applications we are involved in. Hopefully you got some more insights on the importance of Bronkhorst in many industries, even when you go camping.

• If you want more information concerning the discussed applications, please contact us.

Laure Pillier
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As a researcher at the PC2A laboratory, I deal with low flows on a daily base. The PC2A laboratory (PhysicoChimie des Processus de Combustion et de l’Atmosphère) is a multidisciplinary public research unit (CNRS/University of Lille), whose activities concern the characterization of the atmosphere and combustion physico-chemistry. Physico-chemistry in general is chemistry that deals with the physicochemical properties of substances. Bronkhorst instruments play an essential role in our researches, for measuring and controlling these substances in various researches. In this blog I will provide an explanation of our research and why we need mass flow control.

Research activities of the PC2A laboratory

Research activities of the PC2A laboratory are related to energy and environment and are conducted by approximately sixty people divided into three research teams with their own disciplines:

1. Physical Chemistry of Combustion

Our first research team is working on the physico-chemistry of combustion. The initial goal of this research is to understand combustion chemistry, for instance how are formed pollutants such as Nitrogen Oxides ( NOx) and soot in flames. We develop detailed kinetic mechanisms of the oxidation and auto-ignition of substances, such as: biofuels, hydrogen, synthetic fuels, biomass or coal. All thanks to our large experimental platform containing flames, rapid compression machine and laser diagnostics techniques.

2. Physical Chemistry of Atmosphere

In the research team ‘Physical chemistry of the atmosphere’, we study chemical kinetics of reactions of atmospheric interest. The two main topics for us within this discipline are:

  1. Homogeneous and heterogeneous reactivity in the atmosphere to understand the transformation of pollutant gases and particles (pollens, soot) in the atmosphere;
  2. Air quality with experimental characterization and numerical simulation of indoor and outdoor environments, pollution sources and impacts on health and climate.

For these experiments we develop laboratory instruments to characterize the reactivity of important species that are involved in the atmospheric chemistry processes, especially reactive species (radicals). To perform our experiments it is essential to know precisely the amount of gas that is offered to our laboratory reactors and then the concentration of the reactants in the chemical system. For this application we use Bronkhorst mass flow controllers. El-Flow Select (link product page). These instruments allow us to easily perform parametric studies because of their fast response and high repeatability. Moreover, consistency in flow is crucial for accurate measurement.

3. Nuclear Safety: Chemical kinetics, Combustion, Reactivity

Our third team is a collaborative team between the PC2A and the Pôle de Sûreté Nucléaire (PSN) of IRSN (Institut de Radioprotection et de Sûreté Nucléaire), working on issues in relation to thermodynamic and chemical reactivity of fission products. The main objective of this research is to validate the estimations of radio-contaminant products emissions in case of nuclear accident by modeling development and experimental studies.

Mass flow controllers for physico-chemistry

The PC2A laboratory uses multiple mass flow controllers of Bronkhorst. And this is not only for their specifications like a fast response and high repeatability. Also because of the easy operation of these mass flow controllers with the Labview software these instruments are ready to hand. The possibility to export data and moreover the flexibility with switching between different flow controllers, make Bronkhorst a perfect match for us. The flow instruments we use in the lab are the thermal mass flow controllers ( EL-FLOW Select series) and the flow controllers with a low pressure drop ( LOW DeltaP-FLOW instruments).

Image description LOW DeltaP-FLOW instrument

Watch the video of the working principle of EL-FLOW select.

To learn more about the LOW DeltaP-FLOW, please consult the product page.

Johan van 't Leven
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The Tour de France has started this weekend, and all cyclists have prepared for this particular event for months. But, did you ever thought about how flow measurement could be of influence on the cyclists’ performance? Here’s how…

A while ago I had the chance to visit Relitech in Nijkerk. A company that is specialized in the development and design of reliable healthcare solutions. I talked to both Directors Ivar Donker and Henk van Middendorp about the activities of Relitech in the medical industry and their Metabolic Simulator. With all their enthusiasm and dedication in their line of work, I came to new insights regarding their matter and the importance of a company like Relitech.

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In sports it’s all about optimal performance. Athletes are forced to push boundaries and the devil is in the details, more than ever. A few hundreds of a second can make a huge difference in - for example - a gold medal race. So testing the athletes’ condition and endurance is an important part in the bigger picture of their performances. This can help them to train more efficiently and it provides information that can be used for maybe a change in, for example, the athlete’s diet. For metabolic measuring, a lung function device could be used and these systems often easily interfaced with ECG’s, bikes and other external devices for complete, integrated cardiopulmonary exercise testing.

The big question is how to get the best performance by meeting legal regulations? Validation is the magic word. And for that, Relitech developed a metabolic simulator. Let’s take a look at some of the technical details of a device like that.

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Metabolic simulator: quality control for respiratory products

In order to keep a high performance of respiratory products like lung function devices, they need to be validated, to meet the demands of legal regulations as well. The current situation in quality control regarding devices like these, is that it’s limited due to the fact that each sensor (O2, CO2 and flow) is calibrated separately, disregarding the critical dynamic interaction between each sensor. Relitech therefore came up with an in-field solution for their customers by developing this metabolic simulator.

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Thermal mass flow controller

As we’re getting closer to the answer on the question I asked at the very beginning of this blog, we need to dig a little deeper into the Relitech simulator. First of all it’s fully mobile, which means it’s easy to transport and secondly it is ideal for on-site testing (in for example a lung function device used for athletes). The simulator mixes pure nitrogen and carbon dioxide by using two Bronkhorst thermal mass flow controllers. By mixing those two gases you can generate breathing gas exchange patterns, real-time and extremely close to authentic human breathing patterns. The results are so-called capnographs that resemble the ones of, for example, athletes. On the readout display of the Metabolic Simulator the capnograph values are visible. V’CO2 represents the exhaled amount of carbon dioxide and V’O2 is the amount of oxygen inhaled. BF is simply an abbreviation for breathing frequency.

“Using mass flow controllers is not new to me…” Van Middendorp explains, “…as I was already involved in designing lung function systems long before I joined Relitech in 2002.”

“As we started developing the metabolic simulator here at Relitech, we were looking for compact and highly accurate mass flow controllers and that’s where Bronkhorst and I crossed paths. So partly by using these compact thermal flow controllers we were able to develop an even more compact simulator design.”

Relitech, reliable technology

With dedication and passion Relitech develops reliable technology by focusing on electronics, software and embedded software. In combination with consultancy regarding measurement technology, their core competence lies within the medical sector, such as lung function measurement, anaesthesia and hyperthermia applications. For this, the company is ISO13485 certified. By working closely with various universities and academical institutes, multinationals and small businesses they have built an impressive and very diverse customer portfolio.

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Ready for the Tour de France

So, for all the athletes out there, it’s time to put on the finishing touches and get ready for 2018. Who do you will win the Tour?

Check out the application story of quality control for respiratory products.