Specks

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

The soft weathered granodiorite and pegmatites can vary in color from white to pink, depending on iron content and type of feldspar present. The mica content of these deposits ranges from 6—15% and varies in particle size from tiny (<44 specks to thumbnail size. Large books of mica that weigh several hundred kilograms have been found in these deposits. 

Fig. 3. Cross-section photomicrograph of a color-negative product showing the film base, the emulsion layer (the black specks are microcrystalline silver hahde grains), and a protective overcoat. The emulsion layer and overcoat are - 3.5 x 10 m thick.

Fig. 13. A speck of developing sdvei on the surface of a sdvei hahde crystal. The silver acts as an electrode for the electrochemical reduction of silver ions.

The developer molecule, D, delivers an electron to the developing speck, and ia turn the electron is neutralized by an approaching silver ion which, ia the... 

Ink particle redeposition on cellulose fibers can reduce deinked paper brightness. Should larger ink particles redeposit on fibers, visible ink specks may result. Sodium siUcate is often added to the pulper to act as a dispersant and reduce this redeposition (6,14). Up to 5% based on dry paper weight may... 

Specifications vary with use. The paper and detergent industries are concerned with whiteness and specify various methods to describe color and black or dark specks. It is also important in the detergent industry that sodium sulfate has a particle size and density compatible with other components in the blend to eliminate segregation when it is handled. A typical specification for detergent-grade sodium sulfate is given in Table 5. 

Distressing Stains. Interest and charm can be added to furniture by the dehberate infliction of imperfections. These imperfections may be caused by physical distress such as hammers, files, nails, chains, or rocks or caused by finish distress such as "dy specking" or staining to simulate past abuse, such as waterstains caused by the careless placement of a drinking glass. 

Sediment. Sediment is most commonly used as an operational check of filter efficiency and leakage, although some customers, especially those who iatend to melt the sugar iato clear solutions, write sediment restrictions. The measurement is normally done by passiag the 50% solution used for the color determination through a half black—half white filter pad and visually counting the white and black specks. 

If a small amount (less than 5% of the blend) of a strong pigment is used as a component in a blend, it will be difficult to obtain sufficiently uniform mixing to avoid specking. It is preferable to use larger concentrations of a less intense pigment. 

Enamel Defects. Characterization of defects in porcelain enamel surfaces frequently requites detailed examination via microscopy to determine the sources of the defects. Defects ate divided into processing and material defects. The greatest number of defects result from processing bhsters, pinholes, black specks, dimples, tool marks, and chipping. Defects often occur from unobserved sources at almost every stage of the enameling process, but they ate not recognizable until the ware is fired. Conscientious process control helps to minimize the incidents of unacceptable finishes. 

Fleck, m. spot speck, stain, blot, flaw, patch ... 

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