Everything about Microspheres
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  • Silane and Fluorochemical Coated Glass Spheres

    Solid glass imparts visual and material benefits that cannot be replicated when spheres are made of other materials such as ceramics or polymerics, aluminum oxides, or silicas and mineral fillers. Solid glass refracts [bends] and reflects light. Most ceramics [with exceptions] do not transmit light or exhibit specular [mirror-like] reflection due to their internal crystalline structures and surface irregularities. Instead of being reflected back, the light is “trapped” in the structure and emitted as diffuse or scattered reflectance, which is not as strong or direct as light transmitted through glass, which produces mirror-like reflectance.  Prizmalite glass spheres distributed by Cospheric offer off the shelf pre-coated spheres for enhancing these effects.

    Silane coated solid glass spheres with increased hydrophobicity are offered to improve the dispersion of spheres throughout paints and coatings.  Silane coated spheres are not recommended for pure water solutions as the spheres will be too hydrophobic to wet.

    Fluorochemical Coating is available for paint and coating applications where it is desired to bring the spheres to the top of the surface of the coating.  This is best used in applications where retro reflectance is desired.

    The following products are offered in both Silane and Fluorochemical Coating.
    P2011SL  3-6um mean diameter solid soda lime glass
    P2015SL  8-12um mean diameter solid soda lime glass
    P2050SL  35-45um mean diameter solid soda lime glass
    P2075SL 65-75um mean diameter solid soda lime glass
    P2453BTA 40-60um mean diameter solid barium titanate glass with aluminum shell.

    Solid Glass Spheres:

    • Act as mini-magnifying glasses to deliver visually truer color
    • Clarify and magnify the visual impact of pigments and metallic flakes
    • Create a richer, wetter, deeper look
    • Visually extend expensive color-shift pigments to create cost-effective new looks
    • Prop up other pigments, mica and aluminum flakes
    • Increase exposed surface area and visual impact
    • Facilitate even dispersion of colorants and reflectors
    • Are anti-mottling agents that enhance visual consistency
    • Act as mini-ball bearings to improve material flow and reduce flow lines
    • Provide color consistency from all viewing angles
  • 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.

    Product Size Polyethylene
    Density ~1.0 (g/cc)
    Soda Lime Glass
    Density ~2.5 (g/cc)
    Lower (um) Upper (um) Spheres per Gram Spheres Per Gram
    20 27 147,162,715 58,630,564
    27 32 74,393,558 29,638,868
    32 45 33,467,185 13,333,540
    45 53 16,233,536 6,467,544
    53 63 9,788,528 3,899,812
    63 75 5,813,720 2,316,223
    75 90 3,401,258 1,355,083
    90 106 2,029,192 808,443
    106 125 1,239,525 493,835
    125 150 734,672 292,698
    150 180 425,157 169,385
    180 212 253,649 101,055
    212 250 154,941 61,729
    250 300 91,834 36,587
    300 355 54,371 21,662
    355 425 32,196 12,827
    425 500 19,305 7,691
    500 600 11,479 4,573
    600 710 6,796 2,708
    710 850 4,025 1,603
    850 1000 2,413 961
    1180 1400 890 354
    1400 1700 513 204
    1700 2000 302 120
    2000 2360 184 73
    2360 2800 111 44
    2800 3350 66 26

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

  • 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.

    Applications for Bond Line Spacers

    Image courtesy of Nikkei Business PublicationsSpacer 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” »

  • High Density Glass Microspheres

    Barium Titanate Glass microspheres are high density solid glass spheres.  At a Density of 4.5g/cc these solid glass spheres can be used for many scientific applications where high density and optical clarity is needed.  In addition to high density they also offer an index of refraction of more than 1.9.

    Bulk quantities are available in 30-100um and 0.3-1.0mm size ranges.

    For experiments requiring the highest precision the beads can be purchased in classified grades offering >90% of the spheres within a specific size range.  Standard Sizes include the narrow ranges below.

    38-45um, 45-53um, 53-63um, 63-75um, 75-90um, 90-106um, 0.25mm-0.3mm, 0.3mm-0.35mm, 0.36mm-0.42mm, 0.43mm-0.5mm, 0.5mm-0.6mm, 0.6mm-0.7mm, 0.71mm to 0.85mm, and 0.85mm to 1.0mm.

    Product pricing and availability can be found under Cospheric’s BTGMS (barium titanate glass microspheres)

  • BioCompatability of Metal Coated Spheres

    For those scientists who are looking to use silver coated materials such as silver coated microspheres in biomedical applications, it is important to understand whether they are bio-compatable.  A selection of abstracts and article references related to the biocompatability of silver follow:

    The Biocompatibility of Silver2

    The experiments reported have referred to some of the characteristics of the biocompatibility of Ag. Silver has been shown to display interactions with albumin, as an example of a plasma protein, quite different from those of most metals. Such studies shed further light on the complex issue of protein adsorption on biomaterials. It has also been demonstrated that Ag at concentrations < 1 ppm exerts a considerable influence on the activity of lactate dehydrogenase, this effect being reversed in the presence of albumin. A significant but transient increase in blood levels of Ag following intramuscular implantation of the metal has been observed. This is not reflected in any raised urine level. It is proposed that the richly vascular tissue immediately surrounding the implant in the acute phase of the response gives rise to the transient increase, but a subsequent decrease in vascularity reduces this possibility. It appears that Ag released from implants following this initial period substantially remains in the local area.2

    Lack of toxicologocial side-effects in silver-coated megaprostheses in humans1

    Deep infection of megaprostheses remains a serious complication in orthopedic tumor surgery. Furthermore, reinfection gets a raising problem in revision surgery of patients suffering from infections associated with primary endoprosthetic replacement of the knee and hip joint. These patients will need many revision surgeries and in some cases even an amputation is inevitable. Silver-coated medical devices proved their effectiveness on reducing infections, but toxic side-effects concerning some silver applications have been described as well. Our study reports about a silver-coated megaprosthesis for the first time and can exclude side-effects of silver-coated orthopedic implants in humans. The silver-levels in the blood did not exceed 56.4 parts per billion (ppb) and can be considered as non-toxic. Additionally we could exclude significant changes in liver and kidney functions measured by laboratory values. Histopathologic examination of the periprosthetic environment in two patients showed no signs of foreign body granulomas or chronic inflammation, despite distant effective silver concentrations up to 1626 ppb directly related to the prosthetic surface. In conclusion the silver-coated megaprosthesis allowed a release of silver without showing any local or systemic side-effects.1

    Specific Article References for the biocompatability of silver are below: See the References