Transparent materials

Conventional materials that are optically transparent mainly include glasses, polymers, and alkali hydrides, which have various applications in industries and daily life. However, these materials have relatively poor mechanical strength and sometimes insuflicient chemical and physical stabilities. More importantly, conventional transparent materials have strong absorption in the IR range, making them not suitable for applications in this spectral range. Also, they usually possess 

Besides the internal factors, there are also external factors that affect transparency of a ceramic sample, including thickness and surface finish. A rough surface means a significant diffuse scattering, so the sample should be as smooth as possible. Generally, transparency decreases with increasing thickness. Thickness-independent transparency is only possible when the material reaches its theoretical maximum of in-line transmission. 

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Figure Bl.18.6. Schematic representation of Zemike s phase contrast method. The object is assumed to be a relief grating in a transparent material of constant index of refraction. Phase and amplitude are varied by the Zemike diaphragm, such that an amplitude image is obtained whose contrast is, m principle, adjustable.

The chaimel-flow electrode has often been employed for analytical or detection purposes as it can easily be inserted in a flow cell, but it has also found use in the investigation of the kinetics of complex electrode reactions. In addition, chaimel-flow cells are immediately compatible with spectroelectrochemical methods, such as UV/VIS and ESR spectroscopy, pennitting detection of intennediates and products of electrolytic reactions. UV-VIS and infrared measurements have, for example, been made possible by constructing the cell from optically transparent materials. 

J. B. Olson, "Design, Development and Testing of a Lightweight Bird-Proof Cockpit Enclosure for the E-111," presented at The Conference on Aerospace Transparent Materials and Enclosures, Long Beach, Calif., Apr. 24—28,1977. 

Chemical Durability. The resistance of nontransparent vitreous sihca to chemical attack is slightly less than the resistance of transparent vitreous sihca. This difference results primarily from the higher surface area of the former caused by the presence of a large number of bubbles. Most data in the hterature are on the transparent material. 

C. B. Greenberg, in S. A. Marolo, ed.. Proceedings of the 15th Conference on Aerospace Transparent Materials and Enclosures, II, WRDC-TR-89-4044, Wright-Patterson AFB, Dayton, Ohio, 1989, p. 1124. 

Both subtractive and additive color reproduction are utilized in instant color films. Subtractive systems include all of the instant print and large format transparency materials except Polachrome 35-mm sHde films, which are additive. 

Shock Luminescence. Some transparent materials give off copious amounts of light when shocked to a high pressure, and thus they can serve as shock arrival-time indicators. A technique used by McQueen and Fritz (1982) to measure arrival times of release waves is based on the reduction of shock-induced luminescence as the shock pressure is relieved. Bromoform, fused quartz, and a high-density glass have been used for their shock luminescence properties. 

In principle, there is no upper bound in measurements of particle velocity (or stress) using laser velocity interferometry. In practice, very high-pressure shock fronts can cause copious jetting of microparticles from the free surface (Asay et al., 1976), obscuring the surface from the laser beam. To alleviate this, optically transparent materials can be bonded to the specimen, and particle velocity measurements are then made at the specimen/window interface. This has the added advantage of simulating in situ particle velocity... 

McQueen, R.G. and J.N. Fritz (1982), Some Techniques and Results from High-Pressure Shock-Wave Experiments Utilizing the Radiation from Shocked Transparent Materials, in Shock Waves in Condensed Matter—1981 (edited by W.J. Nellis, L. Seaman, and R.A. Graham), American Institute of Physics, New York, 193-207. 

All three techniques probe 500 A to 1 pm or so in depth for opaque materials, depending on the penetration depth of the incident light. For transparent materials, essentially bulk properties are measured by PL and Modulation Spectroscopy. All three techniques can be performed in ambient atmosphere, since visible light is used both as incident probe and signal. 

Commercial poly(methyl methacrylate) is a transparent material, and microscopic and X-ray analyses generally indicate that the material is amorphous. For this reason the polymer was for many years considered to be what is now known as atactic in structure. It is now, however, known that the commercial material is more syndiotactic than atactic. (On one scale of assessment it might be considered about 54% syndiotactic, 37% atactic and 9% isotactic. Reduction in the temperature of free-radical polymerisation down to -78°C increases the amount of syndiotacticity to about 78%). 

As indicated in the previous section poly(methyl methacrylate) is a hard, rigid, transparent material. Commercial grades have extremely good weathering resistance compared with other thermoplastics. 

Optics Electrochromic displays, optical filters (windows with adjustable transparency), materials with non-linear optical properties... 

Due to the above requirements, typical optically-transparent materials, such as oxides (glass, quartz, alumina, zirconium oxide etc.) and halides (sodium chloride, lithium fluoride, calcium fluoride, potassium bromide, cesium bromide etc.) are usually unsuitable for use with fluoride melts. Therefore, no standard procedure exists at present for the spectral investigation of fluoride melts, and an original apparatus must be created especially for each particular case. 

Two crossed polarizers are frequently used to inspect transparent materials placed between them for optical activity, either for birefringence or for optical rotary effects. Birefringence effects are produced by materials with a regular ordered structure that allows light to pass through at one orientation at a higher velocity than at another orientation. As a result of this, the two wave trains generated by the different velocities... 

Plastics are suitable for most optical applications that utilize transparent materials, including color carriers. Color filters have all types of standard transmission characteristics that can be made and, because of the uniqueness of the plastic structure, a large number of dichroic and trichroic materials are possible that have different colors when viewed from different angles. One application for this is in polarizing filters. 

Transparent Materials and Adhesives for Ballistic and Impact Shields , Report No AFML-TR-70-167, Contract F33615-67-C-1315, Monsanto Research Corp, Dayton (1970) 4) H.F. 

S.A. Marolo, Conference on Aerospace Transparent Materials and Enclosures , AFML-TR-76-54 (1976)... 

Amorphous polyarylates are light-amber transparent materials which exhibit mechanical properties comparable to that of unfilled PET in terms of tensile or flexural strength and modulus (Table 2.13) but are notably superior in terms of heat resistance (HDT = 174°C vs. 85°C for PET) and impact strength. 

Noell et al. reported the preparation of silica-poly(ether ether ketone) hybrid materials with improved physical properties.155 An amine-end-capped poly(ether ether ketone) was used to react with isocyanatopropyltriethoxysilane in tetrahydrofuran (THF). The triethylsilane-end-capped poly (ether ether ketone) was mixed with tetraethoxysilane (TEOS) in THF. Quantitative amounts of water were introduced into die system, and the mixture was reduxed at 80°C. The entire reaction mixture was allowed to further react in Tedon molds. Tough transparent materials were obtained by diis approach. 

The compact structure of diamond accounts for its outstanding properties. It is the hardest of all materials with the highest thermal conductivity. It is the most perfectly transparent material and has one of the highest electrical resistivities and, when suitably doped, is an outstanding semiconductor material. The properties of CVD and single-crystal diamonds are summarized in Table 7 2.[1][18]-[20]... 

Internal thermal noise of mirrors. Mirror substrates are transparent material cylinders. They are affected by thermal noise and each one of their modes of vibration can be represented by an harmonic oscillator. The study of thermal noise in solids is a complex task, made difficult because no... 

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