Sensitivity to heat

A variation of these methods, in which the volume of gas evolved in a vacuum at a fixed temperature is measured, is also in common use. This approach is particularly useful when treating long-term, relatively mild thermal effects and the compatibility of explosives with other materials. Still other techniques for determining thermal stability are differential thermal and thermogravimetric analysis. These are coming into more common use, but are not yet standardized with respect to the explosive azides. 

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Explosives are commonly categorized as primary, secondary, or high explosives. Primary or initiator explosives are the most sensitive to heat, friction, impact, shock, and electrostatic energy. These have been studied in considerable detail because of the almost unique capabiUty, even when present in small quantities, to rapidly transform a low energy stimulus into a high intensity shock wave. 

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

Types of internal enamel for food containers include oleoresins, vinyl, acryflc, phenoHc, and epoxy—phenoHc. Historically can lacquers were based on oleoresinous products. PhenoHc resins have limited flexibiHty and high bake requirements, but are used on three-piece cans where flexibiHty is not required. Vinyl coatings are based on copolymers of vinyl chloride and vinyl acetate dissolved in ketonic solvents. These can be blended with alkyd, epoxy, and phenoHc resins to enhance performance. FlexibiHty allows them to be used for caps and closures as weU as drawn cans. Their principal disadvantage is high sensitivity to heat and retorting processes this restricts their appHcation to cans which are hot filled, and to beer and beverage products. 

These pigments are sensitive to heat and bleed ia most paint solvents. They are, however, resistant to acids and bases. Their tinctorial strength is considerably greater than that of inorganic yellows but they are weaker than the diaryUde yellows. They are used extensively ia emulsion paints, paper coating compositions, inks (qv), and, depending on particle size, can ia some cases be used outdoors because of excellent lightfastness ia full shades. 

Polyarylates are sensitive to heat. Although mechanical properties are not much affected, colors darken. Properties are given in Table 8. Hydrolytic stability and resistance to organic solvents are fair. 

Evaporators These are used extensively for the concentration of ammonium nitrate, urea, and other chemicals sensitive to heat when... 

Hydroxyl groups are stable to peracids, but oxidation of an allylic alcohol during an attempted epoxidation reaction has been reported." The di-hydroxyacetone side chain is usually protected during the peracid reaction, either by acetylation or by formation of a bismethylenedioxy derivative. To obtain high yields of epoxides it is essential to avoid high reaction temperatures and a strongly acidic medium. The products of epoxidation of enol acetates are especially sensitive to heat or acid and can easily rearrange to keto acetates. 

Hitze-einheit,/. heat unit, thermal unit, -ein-wirkung,/. action or influence of heat, hitzeempfindlich, a. sensitive to heat. Hitzeerzeugung, /. heat generation, hitzefest, a. resistant to heat. 

Copolymers of acrylonitrile are sensitive to heat, and melt spinning is not used. Solution spinning (wet or dry) is the preferred process where a polar solvent such as dimethyl form amide is used. In dry spinning the solvent is evaporated and recovered. 

Passive movement detection senses radiated heat, such as that from a human body. These units are also sensitive to heat emitted by radiator, convection heaters and direct sunlight, so careful siting is required. 

The advantage of sol-gel technology is the ability to produce a highly pure y-alumina and zirconia membrane at medium temperatures, about 700 °C, with a uniform pore size distribution in a thin film. However, the membrane is sensitive to heat treatment, resulting in cracking on the film layer. A successful crack-free product was produced, but it needed special care and time for suitable heat curing. Only y-alumina membrane have the disadvantage of poor chemical and thermal stability. 

Physicochemical Aspects. Other than toxicity toward insects, the protein of the crystals has no unique characteristics not shared by other protein molecules. It contains between 17.5 (15) and 18% (1) nitrogen, present in 17 to 19 amino acids (Table I), none of which are unusual or present in any unusual concentration. The protein is sensitive to heat and when dissolved (0.01N hydroxide) absorbs characteristically at the 280-m/ maximum displayed by aromatic amino acids. 

Westra, A. Dewey, W.C. (1971). Variation in the sensitivity to heat shock during the cell cycle of Chinese hamster cells in vitro. Inti. J. Radiat. Biol. 19,461-417. 

The shade of the blue color produced from P. aerugineum does not change with pH. The color is stable under light, but sensitive to heat. Within a pH range from 4 to 5, the blue color produced from P. aerugineum is stable at 60°C for 40 min (this is not typical of blue colors from Cyanobacteria). This property is important for food uses because many food items, particularly drinks and confections, are acidic. The blue color was added to clear Pepsi Cola (without heat application) and to Bacardi Breezer and these beverages retained their color for at least 1 month at room temperature. 

Organic peroxides have a low toxicity. The diacetyl peroxides are sensitive to heat, friction, and shock and may detonate upon the slightest mechanical disturbance. Benzoyl peroxide dust may explode easily by friction. Anyone designing... 

The filter cake at this point is 60% to 80% water, and the material is sensitive to heat and to light. The drying, therefore, is difficult and slow, and the exact procedure will depend upon the equipment available. One satisfactory method is to set the Buchner funnel containing the wet material in a large forced-draft oven for 8 hours at 50°. The material, still very wet, is then easily spread on a tray and is placed in a dark but ventilated storeroom, where it is allowed to air-dry for 48 hours or until the weight of the product is less than about 90 g. The product now contains from 10% to 20% of water and is best recrystallized without more thorough drying. 

A titanium-containing sludge from a nitric acid bath was separated, before completely dry it exploded, killing a workman. Investigation showed the dry sludge to be a powerful explosive sensitive to heat, friction and impact, composed of about 60 40 silver nitrate titanium. 

Highly explosive, sensitive to heat, impact and friction (e.g. of a spatula when removing solid from a flask). 

It is fairly stable as an ethereal solution, but the isolated acid is explosively unstable, and sensitive to heat, shock or friction [1], In a new method of preparation of the acid or its salts, pyrolysis of 4-oximato-3-substituted-isoxazol-5(4//)-ones or their metal salts must be conducted with extreme care under high vacuum to prevent explosive decomposition [2],... 

Picric acid, in common with several other polynitrophenols, is an explosive material in its own right and is usually stored as a water-wet paste. Several dust explosions of dry material have been reported [1]. It forms salts with many metals, some of which (lead, mercury, copper or zinc) are rather sensitive to heat, friction or impact. The salts with ammonia and amines, and the molecular complexes with aromatic hydrocarbons, etc. are, in general, not so sensitive [2], Contact of picric acid with concrete floors may form the friction-sensitive calcium salt [3], Contact of molten picric acid with metallic zinc or lead forms the metal picrates which can detonate the acid. Picrates of lead, iron, zinc, nickel, copper, etc. should be considered dangerously sensitive. Dry picric acid has little effect on these metals at ambient temperature. Picric acid of sufficient purity is of the same order of stability as TNT, and is not considered unduly hazardous in regard to sensitivity [4], Details of handling and disposal procedures have been collected and summarised [5],... 

Explosive, very sensitive to heat or shock. See Other DIAZONIUM PERCHLORATES... 

An oil of extreme instability when impure, and sensitive to heat or impact, exploding more powerfully than dibenzoyl peroxide. 

The dry material is readily ignited, bums very rapidly and is moderately sensitive to heat, shock, friction or contact with combustible materials. When heated above its m.p. (103-105°C), instantaneous and explosive decomposition occurs without flame, but the decomposition products are flammable. If under confinement (or in large bulk), decomposition may be violently explosive [1], An explosion which occurred when a screw-capped bottle of the peroxide was opened was attributed to friction initiating a mixture of peroxide and organic dust in the cap threads [2], Waxed paper tubs are recommended to store this and other sensitive solids [3], Crystallisation of the peroxide from hot chloroform solution involves a high risk of explosion. Precipitation from cold chloroform solution by methanol is safer [4], Water- or plasticiser-containing pastes of dibenzoyl peroxide are much safer for industrial use. 

It is very sensitive to heat, oxygen or light, and should not be dried. 

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