Sourcing microspheres that are the best fit for a specific application or project is not a trivial task and requires significant consideration and understanding of the microsphere market. It is important to keep in mind that the quality and prices of different types and grades of microspheres vary widely and are a function of a variety of factors, including order volume (quantity), purity and cost of raw materials, precision level of true particle density, crush strength, particle size and distribution, functionality, shape uniformity (sphericity and roundness), and complexity of the manufacturing process, just to name some of the variables to consider.
Sourcing Microspheres: Quality
When sourcing microspheres is it is important to ask the question of whether quality of the product is important to you. Microsphere market is huge, serving a wide variety of applications and uses as diverse as a filler for a composite in a construction industry (quality is not that critical) to precision pharmaceutical that carries a radioactive compound to attack targeted cancer cells (quality is extremely critical). Most of applications will fall somewhere on that continuum.
Are the particles spherical and uniform?
It is critical to actually obtain a sample of microspheres and put them under a microscope to convince yourself of the sphericity and uniformity of the particles. At a glance, you will be able to quickly judge whether you are looking at high quality uniform product or not.
For example, cenospheres are often marketed as high quality microspheres and many manufacturer’s website show images that are highly Photoshoped and are not realistic representation of the product. Sales people and technical literature will often insist that the particles indeed have a spherical shape.
Closer inspection under the microscope reveals particles in a large range of sizes, with inconsistent color, many broken/crushed particles, and associated dust and debris.
Cenospheres is an example of material with low sphericity and uniformity. It is an extremely low cost hollow ceramic product that is somewhat spherical and is frequently used an additive to mix into cement for production of low-density concrete. It is a by-product of burning coal in thermal power plants, also called fly ash. Some manufacturers list this material for sale at $500 per ton.
Cenospheres are a great material and a bargain for the construction industry, but would the quality of the microspheres still be acceptable for use in medical devices, diagnostic tools, or biotechnology applications?
For comparison, we can look at the other end of the quality spectrum by evaluating monodisperse silica spheres. Even though cenospheres and monodisperse silica spheres will look identical to the naked eye (just a fine free flowing powder), quick inspection under the microscope reveals a completely different story.
Under the microscope with sufficient level of magnification to be able to observe individual spheres, one will notice that monodisperse silica spheres are highly uniform in size, shape, and color. There is no presence of dirt, dust, debris, flakes, or crushed particles. Because of the complexity of processing the spheres to ensure such tight tolerances, these microspheres have a dramatically higher price tag at $500 per gram or more (compared to $500 per ton for cenospheres).
While cenospheres are a by-product collected in large quantities, monodisperse silica spheres are a specialty engineered material, produced in a controlled laboratory process to desired specifications.
When sourcing microspheres, the buyer is always looking for the best quality but the conversation about quality cannot take place without the conversation about price, especially in a microsphere market were the differences in quality and price can be quite dramatic.
When scientists reach out to us at Cospheric for a product recommendation, we usually ask about technical specifications of the product as well as the budget that is available. It is the only way we can direct inquiries to the right product. On some occasions, the tight product specifications and the low price requirements do not match. It might not be possible to source microspheres as specified for the application and still be able to reach the desired cost target. In that situation either the quality requirements need to loosen or the budget for the spheres needs to be increased.
Sourcing Microspheres: Price
Slight difference in quality correlate to dramatic differences in price. When sourcing microspheres, purchasing personnel needs to work very closely with the technical team to evaluate product options.
For example, particle size distribution is a measure of degree of monodispersity or polydispersity of the spheres. You will notice that spheres with a specification of greater than 85% of particles in specified size range are relatively cheap compared to greater than 90% of particles in size range. The price goes up dramatically if the requirement of 95% particles in size range is chosen and much higher for super monodisperse spheres where 99% of particles are guaranteed to fall in a very narrow size range.
The increase in price for each % tighter size range is exponential and is representative of the dramatically increased cost of additional processing and characterization of particles to achieve these super tight specifications.
Another important component of the price equation is the raw material that the microsphere is made out of. Are microspheres manufactured from recycled glass or are they made out of custom biodegradable polymer with a gold-coating?
Costs also depend on specialized surface treatments and coatings that add functionality beyond that of the raw materials and construction of microspheres and allow manufacturers to tailor their products for specific applications.
Surface treatments can be added to make microspheres magnetic, fluorescent, and/or conductive, or to simply improve the bond between microspheres and the matrix.
Sourcing Microspheres: Quantity
How much microspheres do you actually need?
When comparing the cost of microspheres to resins and competing mineral fillers, it is critical to think in terms of cost per unit of volume rather than cost per pound because microspheres can displace a large volume of higher-density material at a very low weight. For example, hollow microspheres can have half or quarter the weight and proportionally more volume compared to solid fillers.
Bondline spacers are extremely precise particles and may seem expensive but we need to consider that only a minimum amount of spheres is needed to be mixed into the epoxy to hold the spacing of the bond. Typically ~5% of spheres by volume (~10% by weight) in epoxy bondlines is sufficient. Taking into account the high potential cost of defects if the bondline is not held and the cost of rework, bondline spacers become a worthwhile investment.
Flow visualization seed particles in large systems of 100 liters or larger can be used in quantities as low as 0.5g of spheres per liter of liquid.
For calibration or reference spheres, only one single sphere may be all that is needed to calibrate a device. However, the precision of that single sphere is critical to the integrity of the large quantity of measurements.
Sourcing Microspheres: Technical Specifications
Quality specifications, which typically refer to tolerances for particle size and distribution, are important to define in order to chose the right grade of the product. However, when sourcing microspheres, it is also critical to understand the requirements for the technical specifications of the material.
Technical specifications typically listed for microspheres often include chemical composition and physical properties of the material. Beyond that, different applications might have widely different requirements. Optical clarity, index of refraction, surface roughness, crush strength, maximum processing temperatures, melt temperature, solvent resistance, shelf life, storage and handling, safety, dielectric constant, porosity, color, density, fluorescent response (excitation and emission wavelength), phosphorescence, hydrophobic vs. hydrophilic properties, magnetism, conductivity, flash point, inertness – are just some of the properties that may be important for the microsphere product to work correctly in a given application and need to be carefully considered.
Sourcing Microspheres: Suppliers
Even though there are only a handful of true microsphere manufacturers in the world, sourcing just the right microsphere for the project, with the right specifications, and at the right price can be a challenge.
Sourcing microspheres for industrial applications:
The companies below specialize in large volumes and industrial applications with associated long leadtimes (material often comes in large drums). Online checkout is not available on the website and purchasing will probably need to go through a distributor. Obtaining technical support may be challenging.
- 3M Ceramic Microspheres – solid ceramic spheres
- 3M Glass Bubbles – hollow glass spheres
- PQ Corporation – solid and hollow glass spheres, some with metal coatings
- Expancel – hollow polymer microspheres
Sourcing microspheres for science and technology applications:
Fluorescent Spheres for Particle Dispersion Experiments
Companies specializing in high quality small quantity microspheres for scientific and research-oriented applications. The benefits of working with a smaller more specialized company is the convenience of online check-out, fast turn-around, and accessible technical support. In addition, when you only need a few spheres for a research project, a few grams, or even a few hundred grams, you would probably want a vial of material to show up at your desk in a few days. You would not want to wait over a month to just get a quote for a truckload.
Specialized companies know their product really well. The products are usually highly characterized and precise, targeted to specific needs of scientists and specialty applications.
- Cospheric – specializing in colored, fluorescent, precision size and density microspheres, prompt worldwide shipping (most products offered as dry powder)
- Spherotech – monodispersed micro and nanoparticles for biomedical applications, diagnostics, and drug discovery (most products offered in solution)
- Polysciences – monodisperse particles for diagnostics, bioprocessing and instrument standardization (most products offered in solution)
- Mo-Sci Corporation – specialized and bio-active glass products
Additional microsphere suppliers and distributors are listed on ThomasNet. Please note that a lot of companies on this list are distributors even though they often position and present themselves as a manufacturer.
A wide variety of bulk microsphere products is listed for sale by Asian manufacturers. Quality of the products offered varies widely and minimum order quantities are large. It is extremely important to properly qualify the product prior to purchasing large quantities. Pictures on the websites and in marketing literature can be deceiving. When sourcing microspheres, it is essential to obtain a test quantity of the product and perform your own quality analysis for the critical specifications prior to making an investment.
Sourcing Microspheres: Technical Support
How critical is availability and quality of technical support when sourcing microspheres?
Unfortunately, when purchasing particles from a distributor who are carrying tens of thousands of items or from a giant corporation, competent technical support of the specific products is often lacking. Even if the customer succeeds in reaching a sales representative, they are often not able to provide any additional information beyond the product code and name of the material. They might point to the technical information available on the website. For some applications, where specifications are loose and the functionality of the spheres is not critical for the success of the application, this scenario might be acceptable.
In other situations, researchers value the ability to contact a knowledgeable technical specialist who is competent and experienced in working with the specific product being considered. Even though every application is unique and every customer needs to verify product performance to ensure desired functionality in their specific process, technical support proves invaluable in directing the scientist towards the right product option and/or relevant research articles and publications.
When sourcing microspheres for a specialty application, It is valuable to have a technical support resource who can walk over to the lab and look at the material under the microscope, as opposed to someone who is getting all their information from a computer screen and has never physically worked with or even seen the actual material.
Summary
In summary, sourcing microspheres is not a trivial task and requires careful consideration of many factors, such as finding a compromise between quality specifications and price of the desired particles, availability of technical support, and a reliable supplier that meets the needs for volume with acceptable leadtime. The concept of “quality” has a different meaning when we are talking about a microsphere filler for cement or bioactive microsphere for drug delivery. When sourcing microspheres for a large project, any “quality” claims need to be evaluated and verified in-house or by an independent laboratory.
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