High temperature class compositions

Nevertheless some allowance must be made for ignition technique and for storage. It is necessary to ignite them correctly by using the techniques described in Part 3. The compositions have to be sealed also to protect them from moisture. In practice however simpler dampf-proof-ing methods can be used for firework pieces which are used up in a short time. 

At low temperatures in winter or in small quantities it may be possible to consolidate the compositions into stars with water and soluble glutinous rice starch except few compositions when we use a magnesium powder which is coated with linseed oil. It is an important rule however to use a binder solution in an organic solvent for this consolidation in place of the water and glutinous rice starch, this is to avoid the danger of generating heat and hydrogen gas. Nitrocellulose solution in amyl acetate or in acetone is very convenient to use for this(s.14.2 (D).  

This composition is somewhat hygroscopic because it contains strontium nitrate. When moistureproof stars are manufactured with this composition using nitrocellulose paste, they can be used in practice. The burning rate is adjusted by changing the ratio of magnesium to oxidizers. Potassium perchlorate decreases the ash. 

For yellow flame there is no problem, because it is always obtained easily. The polyvinyl chloride has no relation to the flame spectrum, but it has a role in making the flame transparent and for obtaining a clear yellow. 

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Potassium perchlorate c) High temperature class compositions which contain... 

A high temperature class composition, consolidated by pressing. 

Too much organic fuel in a composition produces a continuous spectrum in the flame which is caused by the emission of carbon particles at high temperature. In the case of the low temperature class compositions this... 

The purpose of these compositions is to produce a flower in coloured lights or flames. There are two kinds generally used one is the low temperature class(a flame temperature 1700-2200 C) and the other is the high temperature class(a flame temperature 2500-3000 C), where the compositions contain magnesium. 

Firework flames of such a high temperature are obtained by burning compositions which contain an oxidizer and a fuel. An organic fuel, such as shellac or rosin, gives a temperature of about 2200°C to the flame, which is called the "low temperature class flame". Magnesium as the fuel gives 2500 3000 °C to the flame, and is called the "high temperature class flame". 

The band CuCl appears in a flame which is rich in chlorine or hydrogen chloride gas, and gives the flame a pretty violet blue colour. For example, a composition of 75% ammonium perchlorate, 15% shellac and 10% Paris green produces such a coloured flame. The band CuCl seems to decompose at high temperatures, and it is difficult to produce blue with this band in the high temperature class flames, unless the magnesium content is decreased to about 10%. 

Carbon Composites. In this class of materials, carbon or graphite fibers are embedded in a carbon or graphite matrix. The matrix can be formed by two methods chemical vapor deposition (CVD) and coking. In the case of chemical vapor deposition (see Film deposition techniques) a hydrocarbon gas is introduced into a reaction chamber in which carbon formed from the decomposition of the gas condenses on the surface of carbon fibers. An alternative method is to mold a carbon fiber—resin mixture into shape and coke the resin precursor at high temperatures and then foUow with CVD. In both methods the process has to be repeated until a desired density is obtained. 

Ceramic-matrix composites are a class of materials designed for stmctural applications at elevated temperature. The response of the composites to the environment is an extremely important issue. The desired temperature range of use for many of these composites is 0.6 to 0.8 of their processing temperature. Exposure at these temperatures will be for many thousands of hours. Therefore, the composite microstmcture must be stable to both temperature and environment. Relatively few studies have been conducted on the high temperature mechanical properties and thermal and chemical stability of ceramic composite materials. 

Because of their unique blend of properties, composites reinforced with high performance carbon fibers find use in many structural applications. However, it is possible to produce carbon fibers with very different properties, depending on the precursor used and processing conditions employed. Commercially, continuous high performance carbon fibers currently are formed from two precursor fibers, polyacrylonitrile (PAN) and mesophase pitch. The PAN-based carbon fiber dominates the ultra-high strength, high temperature fiber market (and represents about 90% of the total carbon fiber production), while the mesophase pitch fibers can achieve stiffnesses and thermal conductivities unsurpassed by any other continuous fiber. This chapter compares the processes, structures, and properties of these two classes of fibers. 

The ester class also comprises natural oils, such as vegetable oil [75] spent sunflower oil [940,941,992,993] and natural fats, for example, sulfonated flsh fat [161]. In water-based mud systems no harmful foams are formed from partially hydrolyzed glycerides of predominantly unsaturated Ci6 to C24 fatty acids. The partial glycerides can be used at low temperatures and are biodegradable and nontoxic [1280]. A composition for high-temperature applications is available [1818]. It is a mixture of long chain polyesters and polyamides. 

Foam cement is a special class of lightweight cement. The gas content of foamed cement can be up to 75% by volume. The stability of the foam is achieved by the addition of surfactants, as shown in Table 10-9. A typical foamed cement composition is made from a hydraulic cement, an aqueous rubber latex in an amount up to 45% by weight of the hydraulic cement, a latex stabilizer, a defoaming agent, a gas, a foaming agent, and a foam stabilizer [359,362]. Foamed high-temperature applications are based on calcium phosphate cement [257]. 

Once a particular class of unit has been decided upon, the choice of a specific unit depends on initial and operating costs, the space available, the type and size of the product, the characteristics of the feed liquor, the need for corrosion resistance and so on. Particular attention must be paid to liquor mixing zones since the circulation loop includes many regions where flow streams of different temperature and composition mix. These are all points at which temporary high supersaturations may occur causing heavy nucleation and hence encrustation, poor performance and operating instabilities. As Toussaint and Donders(72) stresses, it is essential that the compositions and enthalpies of mixer streams are always such that, at equilibrium, only one phase exists under the local conditions of temperature and pressure. 

The O isotopes show signihcant heterogeneity between the different meteorite classes (Fig. 8a Clayton et al. 1976, 1977). Differences are small, but, each chondrite group has a distinct bulk O isotopic composition. O isotopes also indicate the close ties between the Earth and the Moon. O therefore can be used to identify members of a family that formed from a common reservoir, which is the definition of a tracer. Such differences are also formd between chondrules within the same meteorites related to their size (Gooding et al. 1983). This is a survival of the initial isotopic heterogeneity in already high temperature processed materials like chondrules. 

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