Glass-coated beads

The most stable and most useful type of thermistor is the glass-coated bead. In this design, a sintered oxide bead (0.075 to 1 mm in diameter) is sealed in glass, resulting in a probe bead with a diameter ranging from 0.125 to 1.5 mm. Important advantages of this small thermistor size are low probe heat capacity and rapid temperature response (0.1 to... 

FIGURE 16.10 Thermistors (a) glass-coated bead type, (ft) rod type, (c) disk type. 

SEM electron backscatter image of lunar soil particles, showing minute beads of metallic iron (white) in silicate glass coatings. The iron beads modify the spectra, accounting for the phenomenon of space weathering. 

Disk thermistors can be produced to dose limits of interchangeability, eg, 0.1 and 0.05° C. Disks cannot be made as small as the smallest beads 2 mm diameter seems an approximate practicable limit. Disks historically have been considered to be less stable than good beads. They are commonly protected with a coating of epoxy resin, which provides less compressive support than the glass coating of bead thermistors. More recent developments have resulted in interchangeable glass-encapsulated disk thermistors which have the stability characteristics of the best beads. 

Thermistor bead element. A thermal conductivity detection device in which a small glass-coated semiconductor sphere is used as the variable resistive element in the cell chamber. 

Enzyme kinetics were evaluated in a PDMS-glass chip using a continuous-flow system. A biotinylated enzyme (HRP or (5-galactosidase) was coupled to streptavidin-coated beads via the amide coupling of an aminocaproyl spacer. These beads (15.5 pm) were retained by a weir in the chip. The channel wall was passivated by 1 mg/mL BSA. The apparent enzyme kinetic parameters were evaluated using the Lilly-Homby model, as developed for the packed-bed enzymatic reactor systems. It was found that the apparent Michaelis constant (Km) approached the tme Km value of the free enzyme at zero-flow rate of a homogeneous reaction [845]. 

The most common design is the bead type, which is usually glass-coated. However, thermistors can also be made into washes, disks, or rods. They can also be encapsulated in plastic, cemented, soldered in bolts, encased in glass... 

Glass-coated and plastic beads are available from Cellon (Bioglas beads), ICN (Rapid Cell G and Rapid Cell P) and Nunc (Biosilon) and do not swell in aqueous solutions. They are sterilised by autoclaving at 121° for 15 min in water. 

Because they do not swell 1 g of glass coated or plastic beads will contain only about 230,000 microcarriers of surface area 30 cm2. Bead loadings of 40 g/1 are recommended. 

Platelet retention in the polymer-coated bead columns was quantified by noting the percentage of platelets removed from aliquots 2 through 5 of 5 successive 1 ml effluent fractions. (Aliquot 1 was diluted with saline and was not counted.) Retention values obtained for the 14 polymers tested are shown in Table 1. These data are plotted in Fig, 2 as a function of both the alkyl side chain length and the glass transition temperatures (Tg s) of the polymers. 

Figure 9.6 Transparent glass roll finished and mounted with 0.5 fim run-out. Visual access to plan views of flow in a coating bead is through the hollow shaft or under the cantilevered end...

Verreck, G., Vandecruys, R., De Conde, V, Baert, L., Peeters, J., Brewster, M.E. The use of three different solid dispersion formulations—Melt extrusion, film-coated beads, and a glass thermoplastic system—To improve the bioavailability of a novel microsomal triglyceride transfer protein inhibitor. J. Pharm. Sci. 2004, 93(5), 1217-1228. 

Jackson, N.B., Wang, C.M., Luo, Z., Schwitzgebel, J., Ekerdt, J.G., Brock, J.R., and Heller, A. Attachment of Ti02 powders to hohow glass microbeads-activity of the T1O2 coated beads in the photoassisted oxidation of ethanol to acetaldehyde. J. Electrochem. Soc. 1991,138, 3660. 

Figure 13.4 View through the glass roll of the coating bead as the flow rate is reduced. The roll speed was fixed capillary number (Ca) = 0.12 and no vacuum was applied to the upstream free surface. The cylinder was moving from bottom to top in each photograph. As the film thickness falls, the upstream free surface moves towards the feed slot and becomes three-dimensional. As the flow rate is decreased even further, the V pattern grows until the coating bead breaks. Reproduced from ref. 9 with the permission of Elsevier, 2014.

Roofiag panels have been made from polyisocyanurate foams, both foam- and felt-reiaforced with glass fiber. PhenoHc resias are used especially for decorative laminates for paneling. The substrate may be fiberboard or a core of expanded polystyrene beads. In one case the beads are coated with phenoHc resia, then expanded ia a mold to form a stmctural foam panel. 

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