Transparent insulation materials

Kaushika, N.D. and Sumathy, K. (2003) Solar transparent insulation materials a review. Renew. Sustain. Energy Rev., 7, 317-351. 

Transparent or translucent insulating materials (TIMs) can provide light or solar gains without view. TIMs typically have thermal properties similar to conventional opaque insulation and are thicker than conventional insulating glass units, providing significant resistance to heat transfer. 

Chapter 4, presents details of the absorption and reflectivity spectra of pure crystals. The first part of this chapter coimects the optical magnimdes that can be measured by spectrophotometers with the dielectric constant. We then consider how the valence electrons of the solid units (atoms or ions) respond to the electromagnetic field of the optical radiation. This establishes a frequency dependence of the dielectric constant, so that the absorption and reflectivity spectrum (the transparency) of a solid can be predicted. The last part of this chapter focuses on the main features of the spectra associated with metals, insulators, and semiconductors. The absorption edge and excitonic structure of band gap (semiconductors or insulator) materials are also treated. 

Silicon is a Group 14 (IV) element of the Periodic Table. This column includes C, Si, Ge, Sn, and Pb and displays a remarkable transition from insulating to metallic behavior with increasing atomic weight. Carbon, in the form of diamond, is a transparent insulator, whereas tin and lead are metals in fact, they are superconductors. Silicon and germanium are semiconductors, ie, they look metallic, so that a polished silicon wafer is a reasonable gray-toned mirror, but they conduct poody. Traditionally, semiconductors have been defined as materials whose resistance rises with decreasing temperature, unlike metals whose resistance falls. 

Due to the inability to deposit eleetrochemically stable gate-insulating materials for GaAs, another approach was developed based on amorphous silicon (a-Si), prepared as a thin layer for LAPS devices on transparent glass substrates [40]. The diffusion length in this material was reported to be as small as 120 nm [41] and a resolution down to 1 gm has been demonstrated, which was mainly limited by the optical set-up. The electrochemical properties of the a-Si-based structures were investigated later with a LAPS device thus, the above results for SPIM were transferred back and proved for the LAPS, too [42,43]. 

A substrate 10 of HgCdTe is provided with an upper surface region 11 formed by an annealing procedure, or as an epitaxial layer or evaporated film. A layer of insulating material 12 is formed in which windows are provided. The windows are partially filled with a thin layer of metal 13 which is deposited therein to form a metal-semiconductor diode with the upper surface region. The metal layer is deposited to a thickness on the order of 10-50 nm thick and is sufficiently thin to be semi-transparent to infrared radiation. A thick layer of metal 14 is deposited to form an expanded contact and an anti-reflection coating 15 is provided. External conductors in the form of jumper wires 16 are ball bonded to the contact 14. 

As mentioned above, hrst consider the diamagnetic, transparent, insulator already mentioned. When such a sample is exposed to an electric held, it responds. The electrons around each atom move in such a way as to reduce the potenhal energy (or minimize the Gibbs free energy if the system is at a constant temperature and pressure) of the system. Electrons have a low mass compared to the nucleus which they surround and can move in response to the electric held. If the held is oscillating, the electrons will oscillate as well with the same frequency. The electric held, E, induces in the material a polarizahon ... 

Ceramics used for thermal insulation of microwave caskets include alumina, aluminosilicates, mullite, and fused silica, each of which is relatively transparent to microwave radiation and thus have low dielectric loss at room temperature. The insulating materials included in the casket are typically in the form of ceramic fibers, fiberboard, or a granular bed of ceramic... 

PMMA is a transparent, glassy material, which is known from X-ray studies to be amorphous at the molecular level. It is clearly polar, as is shown by its poor insulating properties relative to poly(ethylene) and its solubility in solvents such as ethyl propano-ate and trichloroethane. 

Polyimides have been used up to 100 h at 600°F (315.6°C). They have been used as a transparent head cover for fire fighters and as excellent flame- and high-temperature-resistant foams, which can be used as structurally stable insulation materials at high temperatures. Polyimide/glass fiber composites have many uses in the electronics and aerospace industries and in other high-performance applications. 

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