Thermal conductivity sapphire

The gray values in Fig. 10 and in Fig. 11 are 2D projections into the. rv-plane. Because of the phase contrast technique, they are approximately linear functions of the integral over the refractive index along the z-direction. The temperature and concentration distribution and, hence, also the refractive index are fully 3D objects. The high thermal conductivity of the sapphire windows enforces a constant temperature boundary condition at the top and bottom windows. 

The high thermal conductivity of the sapphire windows ensures a fixed temperature T = To at the boundaries z = Ls/2 and x = LX/2. The boundary condition for the diffusion equation is a vanishing flux at the walls (normal vector en) ... 

The hybrid circuit 10 comprises a buffer structure 16 which is comprised of a material which accommodates the difference in thermal expansion coefficients of the HgCdTe detector array 12 and the silicon read-out chip 14. The buffer layer is made of sapphire which also has good thermal conductivity properties. The buffer structure has laser drilled vias 18 which are formed in registration with unit cells of the detector array and the read-out circuit. Each of the vias is provided with indium bumps 20 at opposing ends thereof. The buffer structure is interposed between the detector array and the read-out chip. Cold weld indium bump technology is employed to couple the bumps 20 to the buffer structure. The buffer structure is further... 

The theoretical estimate of Slack has predicted k = 1.7 W/(cm K) for room temperature thermal conductivity of GaN [12], The thermal conductivity of GaN layers grown on sapphire substrates by the HVPE method [23] was measured by Sichel and Pankove using the heat flow method [24], The room temperature thermal conductivity was k = 1.3 W/(cm K). Sichel and Pankove attributed the smaller value to high impurity content, at least 1018 cm 3, and the presence of small angle grain boundaries. 

As a result, cuvettes for Raman spectroscopy should be carefully selected. They may, due to their impurities, add a background to the spectrum of the sample. In addition, all cuvette materials produce their own Raman spectra, which have to be considered, when the Raman spectra of the sample are evaluated. Fig. 3.5-17 a shows a Raman spectrum of a typical optical glass BK7, Fig. 3.5-17 b that of quartz glass suprasil, and Fig. 3.5-17 c of sapphire. Suprasil is a synthetic quartz which does not normally contain impurities. Therefore, Suprasil of ESR quality is highly recommended as Raman cuvette material. Also, sapphire is a good cuvette material, as it is very hard, inert, has a good thermal conductance, and shows only weak but sharp Raman lines (Porto and Krishnan, 1967). It is used for the production of the universal Raman cell (Schrader, 1987). The sharp Raman lines of sapphire observed in the spectra of the sample may be subtracted from the spectrum or used as internal standard for quantitative analyses (Mattioli et al, 1991). 

Sapphire fibers are hard, strong and scratch resistant to most materials and provide excellent wear surfaces. They can withstand higher pressures than polycrystalline alumina since they lack the grain boundary interface breakdown of the latter. Sapphire fibers transmit ultraviolet, visible, infrared and microwaves and serve as excellent wave guides between 10.6 and 17 microns, and offer durable and reliable IR transmission. By virtue of their high thermal conductivity they can be rapidly heated and cooled. 

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