Home-built Apparatus for Measuring Thermal Conductivity of Glass and Polymer Materials
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Home-built Apparatus for Measuring Thermal Conductivity of Glass and Polymer Materials William R. Heffner1 Shera Demchak2, John Scruggs3 and Ray Pearson4 1 International Materials Institute for New Functionality in Glass, Lehigh University, Bethlehem, PA 18015, USA 2 University of Massachusetts, Amherst, MA 01003, USA 3 Tuskegee University, Tuskegee, AL 36088, USA 4 Material Science & Engineering, Lehigh University, Bethlehem, PA 18015, USA ABSTRACT As a part of the IMI-NFG’s series of low-cost experiments in glass science [1,2] we have developed a simple home-built apparatus for measuring the thermal conductivity of glassy materials, from polymers to oxide glasses, in the range of 0.1 to 1.5 W/ °C. Our apparatus is inexpensive, relatively easy to construct and accurate enough for students to use for quantitative measurements of their own glass or polymer samples. Standard materials are used to demonstrate good correlation with literature values. We also measured the thermal conductivity of a silica filled epoxy and showed a linear increase with fill fraction to 20%. This simple, lowcost method can provide students and researchers with a much broader access to this important property. INTRODUCTION Thermal conductivity (K) is an important property in the materials selection for many applications. Approximate K values for common engineering materials are widely available. However, for new materials, special formulations or composites, these data will not be available. This is especially true for polymers and inorganic glasses, where the compositions can be adjusted over wide ranges and the physical properties may also dependent on processing parameters. Filled polymer composites constitute another important class of materials where the K can be tailored over a wide range based on fill composition. Standard measurement approaches for K, such as Modulated DSC [3, 4] or commercial Thermal Conductivity Meters[5], are expensive and generally not available outside of the specialized research lab. We present here a simple, home-built apparatus for the low budget exploration of thermal conductivity in polymers and glasses. EXPERIMENTAL The Low-Cost Student-Built Thermal Analysis Apparatus Our apparatus is based on a straight forward application of the definition of thermal conductivity (K) as the ratio of the heat flow (Q) through a sample relative to the temperature difference across the sample (ΔTsample), appropriately scaled by a sample geometry factor (thickness (t) divided by the area (A)), as illustrated in Figure 1. It is relatively simple to construct, consisting of a heated aluminum block placed on the top side of a flat sample, and a two-tiered pedestal base on the cold side. The pedestal allows an independent measurement of actual heat flow through the sample. Two embedded resistors (1/2 watt, 47 Ω in parallel with 5 v supply) provide
about one Watt of power to the top plate. The base pedestal provides a fixed, low thermal conduction heat path enabling us to establish a direct relationship between the heat flow (
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