Magnetic Microspheres – Paramagnetic

Magnetic microspheres, more accurately called paramagnetic microspheres have unique properties that are useful for a variety of applications.

Paramagnetism is a form of magnetism that occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields and hence have a relative magnetic permeability of ≥1 (a positive magnetic susceptibility). The magnetic moment induced by the applied field is linear in the field strength and rather weak.¹

1. Wikipedia “paramagnetism“

Calculating microspheres per gram

During scientific experiment design and analysis it is common to need to know the number of spheres per gram of dry material.  We have put together the table below to help speed up the process.

If you have material of a density different from those listed in the table, divide the number of spheres per gram in the density ~1.0 g/cc column by the true particle density of your material to get an estimate of the number of spheres per gram.

Note: This table assumes the mean diameter is half way between the upper and lower size.

Monodisperse Silica Microspheres

Scientists are always pushing the limits, and looking for more precise products and equipment to enable the next technology.   In an effort to provide those scientists with the right tools Cospheric LLC has added monodisperse silica microspheres to their broad product line.

Silica particles are now available in distributions of less than 10% CV in the sizes of 0.25 micron, 0.5 micron, 0.62 micron, 1 micron, 4 micron and 8 micron.

Silica Microsphere Products now available:

SIO2MS 0.25um <10% CV

SIO2MS 0.48um <10% CV

SIO2MS 0.62um <10% CV

SIO2MS 1.15um  <10% CV

SIO2MS 3.8um <10% CV

SIO2MS 7.8um <10% CV

SIO2MS 4-6um  (2-19um range)

Microparticles for simulating fish egg dispersion and recruitment

Understanding survival and mortality of fish in the early life stages has been a fundamental issue in biology and a central problem in fisheries oceanographic study for more than a century. It has been argued that most marine fishes begin life as an egg that floats in the sea, and, during their evolutionary history, the early life of fishes has surely been shaped to ensure the “continued existence of species” by the sheer pressure of natural selection, and stated that a fish to survive must deal with and exploit its physical and biological environments. However, although we are now in the 21st Century, there still remains a lot to be made scientifically clear in the early life of fishes. In the present lecture, I will talk about fundamental issues in the isolated floating eggs of marine fish, which many pelagic species spawn in thousands, millions, or sometimes almost billions during a life of an individual female. The topics contain description and discussion on the egg size, buoyancy and rising speed. Measurements on the eggs naturally spawned in aquaculture systems are firstly introduced. Several examples of egg vertical distribution, accumulation and dispersion observed through field surveys will be shown to consider how the egg size and buoyancy are adaptive to survive in the pelagic environment.¹

Scientists who study fish require artificial micro-particles to simulate fish eggs and their dispersion behavior in water. In order to accurately simulate the dispersion of fish eggs it is important to use particles of the proper size and buoyancy/density. Particles with accurate size ranges and densities are now available from Cospheric LLC. Densities from 1.00g/cc up to 1.12 g/cc are available in size ranges from 10-27um on up to 0.85-1.0mm. Sea water particles of 1.025g/cc (UVPMS-BG-1.025), and fresh water beads of 1.00g/cc are in stock and available for quick delivery.

Most fish eggs are in the size of 0.5-5mm¹ with the typical size of 1mm being the most common.   Salt water fish eggs tend to be slightly less dense than medium saltwater at a density of about 1.020g/cc¹.

Continue reading “Microparticles for simulating fish egg dispersion and recruitment” »

Microspheres as bond line spacers in epoxies

Today’s electronics are demanding tighter and tighter tolerances, and the assembly of many items require holding precise spacing between parts during assembly.  The spherical shape and precise sizes available make microspheres the ideal candidate as a precision spacer in various liquid adhesives and epoxies.

Important considerations:

1) The actual bond line will correspond to the largest spheres, not the average size.  Narrow size ranges of a few micron ensure the proper gap is maintained.

• If a 30um gap is required use a spacer grade size range of 27-30 micron.
• If a 40um gap is required use a spacer grade size range of 37-40 micron.
• If a 53um gap is required use a spacer grade size range of 50-53 micron.

3) Functionality gained from using different materials.

• Glass offers the best mechanical and chemical stability at a wide range of temperatures.
• Plastic such as PMMA can be used where some deformation is desirable.
• Metal coated glass spheres can be used where conductivity is desirable.
• Hollow Glass spheres can be used where assembly pressures are low, and reduced thermal conductivity is desired, available as uncoated hollow glass or silver coated hollow glass spheres.

4) The importance of sphere loading (% spheres by volume in the adhesive)

• Theoretical maximum loading by volume for a monolayer is 61%
• A mixture of about 5% by volume should work for most applications.
• Narrow bond lines with high assembly forces will require higher loadings
• Low crush strength spheres will require higher loadings.
• Proper dispersion in the adhesive will help to minimize the loading needed.

5) Adhesive / Epoxy selection

• High viscosity epoxies will help maintain sphere dispersion.
• For best results choose an adhesive that adheres to the spheres and the base material.
• Long pot-life materials work best, as they allow excess adhesive to flow out of the bond line during assembly.

6) Spacer Availability – Cospheric LLC stocks a wide variety of sizes and materials, and can custom produce spacer grade microspheres for your application.

• Spacer Grade Solid Glass Spheres, narrow 3um ranges, >95% in range, 22-53 micron
• Silver Coated Solid Glass Spheres, >90% in range, 22-110 micron sizes
• Soda Lime Glass Spheres, >90% in range, 27 micron to 3.4 mm sizes
• Solid PMMA Spheres, >90% in range, 20-150um sizes

Applications for Bond Line Spacers

Spacer Grade Glass Microspheres are presently used in gas plasma displays, automotive mirrors, electronic displays, flip chip technology, filters, sporting goods equipment, calibration standards and transformer manufacturing.  Every day engineers are finding new and innovative uses for bond line spacers.  One area that has had the most publications is in die attachment in the semi-conductor industry, a particularly interesting area is in using spacers for building multi-die packages. Continue reading “Microspheres as bond line spacers in epoxies” »