Opaque materials

The attenuated total reflectance (ATR) technique is used commonly in the near-infrared for obtaining absorption spectra of thin Aims and opaque materials. The sample, of refractive index i, is placed in direct contact with a material which is transparent in the region of interest, such as thallium bromide/thallium iodide (known as KRS-5), silver chloride or germanium, of relatively high refractive index so that Then, as Figure 3.f8... 

Whereas ATR spectroscopy is most commonly applied in obtaining infrared absorption spectra of opaque materials, reflection-absorption infrared spectroscopy (RAIRS) is usually used to obtain the absorption spectrum of a thin layer of material adsorbed on an opaque metal surface. An example would be carbon monoxide adsorbed on copper. The metal surface may be either in the form of a film or, of greaf imporfance in fhe sfudy of cafalysfs, one of fhe parficular crysfal faces of fhe mefal. 

ASTM D1729, Practice for Visual Evaluation of Color Differences of Opaque Materials, Vol. 6.01, ASTM, Philadelphia, Pa., 1989. 

Another test method appHcable to textiles is ASTM E313, Indexes of Whiteness and Yellowness of Near-White, Opaque Materials. The method is based on obtaining G, ie, green reflectance, and B, ie, blue reflectance, from X, Y, and Z tristimulus values. Whiteness and yellowness index are then calculated from the G and B values. This method has particular appHcability to measurement of whiteness of bleached textiles. AATCC test method 110 also addresses measurement of the whiteness of textiles. 

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... 

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. 

Many inorganic solids lend themselves to study by PL, to probe their intrinsic properties and to look at impurities and defects. Such materials include alkali-halides, semiconductors, crystalline ceramics, and glasses. In opaque materials PL is particularly surface sensitive, being restricted by the optical penetration depth and carrier diffusion length to a region of 0.05 to several pm beneath the surface. 

It has been also shown that when a thin polymer film is directly coated onto a substrate with a low modulus ( < 10 MPa), if the contact radius to layer thickness ratio is large (afh> 20), the surface layer will make a negligible contribution to the stiffness of the system and the layered solid system acts as a homogeneous half-space of substrate material while the surface and interfacial properties are governed by those of the layer [32,33]. The extension of the JKR theory to such layered bodies has two important implications. Firstly, hard and opaque materials can be coated on soft and clear substrates which deform more readily by small surface forces. Secondly, viscoelastic materials can be coated on soft elastic substrates, thereby reducing their time-dependent effects. 

Nitroprusside infusion bottles are wrapped in aluminum foil or other opaque material to protect the drug from light. The administration tubing does not require a covering. If the solution is protected from light, it remains stable for up to 24 hours. The newly prepared solution normally has a very light brownish tint. The nurse should discard the solution if the mixture becomes blue, green, or dark red. 

In 1896, the French scientist Fienri Becquerel happened to store a sample of uranium oxide in a drawer that contained some photographic plates (Fig. 17.2). He was astonished to find that the uranium compound darkened the plates even though they were covered with an opaque material. Becquerel realized that the uranium compound must give off some kind of radiation. Marie Sklodowska Curie (Fig. 17.3), a young Polish doctoral student, showed that the radiation, which she called radioactivity, was emitted by uranium regardless of the compound in which it was found. She concluded that the source must be the uranium atoms themselves. Together with her husband, Pierre, she went on to show that thorium, radium, and polonium are also radioactive. 

Scanning acoustic microscopy (SAM) is a relatively new technique which broke through in the mid-seventies and was commercialized recently. The SAM uses sound to create visual images of variations in the mechanical properties of samples. The ability of acoustic waves to penetrate optically opaque materials makes it possible to provide surface or subsurface stmctural images nondestmctively, which might... 

The left side of the animal will be covered with opaque material (aluminum foil). 

ASTM E313-73, (reapproved 1993), Standard Test Method for Indexes of Whiteness and Yellowness of Near-White, Opaque Materials. 

Sometimes molded plastics have opaque material called bloom on the surface. Explain. 

The same is true for the STI process, because after the CMP and the nitride strip, polysilicon is deposited. Polysilicon is also an opaque material, and if the nonplanarity is not present or reduced, the stepper cannot locate the alignment mark to align the polysilicon pattern to the STI pattern. 

The coalescence of atoms into clusters may also be restricted by generating the atoms inside confined volumes of microorganized systems [87] or in porous materials [88]. The ionic precursors are included prior to irradiation. The penetration in depth of ionizing radiation permits the ion reduction in situ, even for opaque materials. The surface of solid supports, adsorbing metal ions, is a strong limit to the diffusion of the nascent atoms formed by irradiation at room temperature, so that quite small clusters can survive. 

With its high peak power, pulsed light penetrates opaque materials more effectively than does continuous light. 

Topical medications useful in protecting against sunlight contain either chemical compounds that absorb ultraviolet light, called sunscreens, or opaque materials such as titanium dioxide that reflect light, called sunshades. The three classes of chemical compounds most commonly used in sunscreens are p-aminobenzoic acid (PABA) and its esters, the benzophenones, and the dibenzoylmethanes. 

Ultraviolet sources are chiefly mercury-discharge lamps in various forms. These lamps are fragile and quite inefficient. The design of reactors using these lamps is hampered by these considerations, and by the limited ultraviolet transmission, of common glasses and solvents. The transmission is further decreased by coatings of opaque materials which form... 

Some substances, such as alkaline-earth sulphides, emit visible light when irradiated by X-rays for these substances it is essential to have a sheet of optically opaque material (such as black paper) between the specimen and the film. 

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