Dry heat

In comparison to high-pressure steam sterilization, dry heat is relatively inefficient and is usually reserved for sterilizing (or drying previously autoclaved) glassware. In the absence of superheated water, organic materials take longer to be inactivated even at much higher operational tempera- 

Drying ovens should never be used to re-melt solidified agar media because too much water will evaporate from the medium. Re-autoclaving media for a complete sterilization cycle will also degrade heat-sensitive nutrients in the medium. Rather, solidified media can be melted by placement in a boiling water bath or a microwave, the later performed with hand mixing every few minutes. 

---

Burns caused by dry heat (e.g., by flames, hot objects, etc.). For slight bums in which the skin is not broken, apply tannic acid jelly ( Tannafax ), acriflavine jelly ( Bumol ) or butesin picrate ointment (butesin is re-butyl J aminobenzoate). 

Fig. 5. The effect of dry heat exposure on acetate and triacetate fibers. Tested at 65% rh, 21°C after exposure. A, acetate, 100°C B, triacetate, 130°C and C,...

PVA fiber is better in dimensional stabifity under dry heat than other synthetic fibers. 

Ophthalmic ointments usually contain petrolatum as the base. The petrolatum is sterilized by dry heat and combined with the sterile dmg powder under aseptic conditions. Ophthalmic suspensions contain very fine (- 10 ji) particle sized soHds suspended in an aqueous vehicle. The vehicle is adjusted to isotonicity and viscosity-increasing excipients, chelating agents, and surfactants also may be needed. The aqueous vehicle in these cases is generally autoclaved and mixed with sterile dmg powder asceptically (30). 

Heat-reactive resins are more compatible than oil-soluble resins with other polar-coating resins, such as amino, epoxy, and poly(vinyl butyral). They are used in interior-can and dmm linings, metal primers, and pipe coatings. The coatings have excellent resistance to solvents, acids, and salts. They can be used over a wide range of temperatures, up to 370°C for short periods of dry heat, and continuously at 150°C. Strong alkaUes should be avoided. 

Dry-heat sterilization is generally conducted at 160—170°C for >2 h. Specific exposures are dictated by the bioburden concentration and the temperature tolerance of the products under sterilization. At considerably higher temperatures, the required exposure times are much shorter. The effectiveness of any cycle type must be tested. For dry-heat sterilization, forced-air-type ovens are usually specified for better temperature distribution. Temperature-recording devices are recommended. 

Chemical indicators for dry-heat steriliza tion are available either in the form of pellets enclosed in glass ampuls, or in the form of paper strips containing a heat-sensitive ink. The former displays its end point by melting, the latter by a color change (see Chromogenic materials). 

Superheated steam results when steam is heated to a temperature higher than that which would produce saturated steam. The equiUbrium between hquid and vapor is destroyed, and the steam behaves as a gas. It loses its abiUty to condense into moisture when in contact with the cooler surface of the article to be sterilized. This process resembles dry-heat sterilization more than steam sterilization and, under ordinary time—temperature conditions for steam sterilization, does not produce stetihty. 

Dyestuffs. The use of thiophene-based dyestuffs has been largely the result of the access of 2-amino-3-substituted thiophenes via new cycHzation chemistry techniques (61). Intermediates of type (8) are available from development of this work. Such intermediates act as the azo-component and, when coupled with pyrazolones, aminopyrazoles, phenols, 2,6-dihydropyridines, etc, have produced numerous monoazo disperse dyes. These dyes impart yeUow—green, red—green, or violet—green colorations to synthetic fibers, with exceUent fastness to light as weU as to wet- and dry-heat treatments (62-64). 

Application Techniques, Structural Variations, and Fastness Properties. When appHed to polyester fiber, many of the disperse dyes originally developed for ceUulose acetate were found to be deficient in Hghtfastness, build-up properties, and especially fastness to the high temperatures employed in the newer dyeing and finishing, printing, and Thermosol (dry heat) processes. 

AHP = anhydrous heat pasteurized DH = dry heat MA = moist atmosphere SD = solvent detergent SHP = solvent heat pasteurized. 

Eor printing on polyester, the fixation conditions are more rigorous than on other disperse dyeable fibers, owing to the slower diffusion of disperse dyes in polyester. Eor continuous fixation the prints are exposed at atmospheric pressure to superheated steam of 170—180°C for 6—8 min. A carrier may be added to the print paste for accelerated and fliU fixation. Dry-heat fixation conditions of 170—215°C for 1—8 min are less popular for printed fabrics, but are sometimes employed because of lack of other equipment. 

Disperse—Vat Combinations. These require a two-step fixation. The disperse dye is fixed first, usually by dry heat, followed by impregnating of the textile with an alkaU and reducing agent solution and short steam fixation for the vat dye. The selected disperse dyes fixed in the polyester fiber are not destroyed by the reducing agent, but disperse dye remaining on the cellulose is destroyed. 

Golorfastness to Heat Treatment. To test for fastness to dry heat, ISO 105-P01 the specimen is sandwiched between adjacent fabrics and placed under slight pressure between heated surfaces where the temperature of the surface is 150, 180, or 210°C for 30 s. The effect on the shade of the pattern and adjacents is then assessed. 

Miscellaneous Fastness Tests. The fastness to hot pressiag, ISO 10S-X1 /, test is similar to the fastness to dry heat test except that the time of pressing is 15 s (again at 150, 180, and 210°C), and the test can either be carried out dry when a damp cotton fabric containing its own weight of water is placed on top of the dry test fabric, or wet when the test fabric also contains its own weight of water. 

Technology Descriptions The use of thermoplastic solidification systems in radioactive waste disposal has led to the development of waste containment systems that can be adapted to industrial waste. In processing radioactive waste with bitumen or other thermoplastic material (such as paraffin or polyethylene), the waste is dried, heated and dispersed through a heated, plastic matrix. The mixture is then cooled to solidify the mass. 

Wet in % of dry Ultraviolet Light Resistance Resistance to Fungus, Rot, and Mildew Resistance to Dry Heat Continuous OF... 

To simplify the effects of radiation and convection on dry heat transfer, the concept of operative temperature is often used. By definition operative temperature is the temperature of a uniform environment (= MRT) that has the same total dry heat loss (convection + radiation) as the actual environment where MRT. 

---