Measuring Insulating Properties

Heatshield thickness and weight requirements are determined using a thermal prediction model based on measured thermophysical properties. The models typically include transient heat conduction, surface ablation, and charring in a heatshield having multiple sublayers such as bond, insulation, and substmcture. These models can then be employed for any specific heating environment to determine material thickness requirements and to identify the lightest heatshield materials. 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

The measurement of properties such as the resistivity or dielectric constant of PS requires some kind of contact with the PS layer. Evaporation of a metal onto the PS film-covered silicon sample produces a metal/PS/Si sandwich, which behaves like an MIS structure with an imperfect insulator. Such sandwich structures usually exhibit a rectifying behavior, which has to be taken into account when determining the resistivity [Si3, Bel4]. This can be circumvented by four-terminal measurements of free-standing PS films, but for such contacts the applied electric field has to be limited to rather small values to avoid undesirable heating effects. An electrolytic contact can also be used to probe PS films, but the interpretation of the results is more complicated, because it is difficult to distinguish between ionic and electronic contributions to the measured conductivity. The electrolyte in the porous matrix may short-circuit the silicon filaments, and wetting of PS in-... 

The insulating properties of the PhO-OTS layers were tested in capacitor devices. Figure 6.14 shows the breakdown characteristics of the PhO-OTS SAM gate dielectric, determined on twenty Si-SAM-Au capacitors measured on structures with a... 

Since the electroconductivity of pure water is by several orders of m itude hi er than those of polymers, even smaU amounts of moisture markedly reduce electrical insulation properties of foams. For this reason, measuren nt of dielectric properties is a precise, rapid and non-destructive method of monitoring the kinetics and level of moisture absorption. Thus, the establishment of correlations between dielectric properties and the hygroscopicity of plastic foams makes it possible to solve two practical problems how moisture affects dielectric properties and how to determine non-electrical properties by electrical measurements ... 

For the purpose of estimating the solubility of a solute it is necessary to have some measure of the polarity of a solute or a solvent. Based on Eqs. (1) and (2), a useful polarity index should be a measure of a material s intermolecular forces, Cn and C22-Table 1 contains a list of solvents that are typically used in liquid pharmaceutical formulations and three measures of solvent polarity. Each measure of solvent polarity, or polarity index, is based upon a different measure of a material s property. For example, dielectric constant is a measure of the electrical insulating properties of a solvent, solubility parameter is determined from the molar energy of vaporization, and... 

ASTM C 165-91 Standard Test Method for Measuring Compressive Properties of Thermal Insulation, 5 (DOD Adopted) (Area MISQ (84) (Comm C-16)... 

The third problem associated with water based varnishes is poor electrical insulation properties of the laminate after moisture conditioning. This problem is probably the most critical problem because insulation failures of the laminate can lead to electrical failure of the finished printed circuit board. This property is measured by conditioning the finished laminate in a high moisture environment and then testing the dielectric breakdown strength. ED24574 has excellent insulation resistance. This was achieved by a proprietary resin composition. 

R-Value - A measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value). The larger the R-Value of a material, the greater its insulating properties. 

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