Spray drying, test atmospheres

Annex A2 describes a cyclic salt spray test that uses a 5% NaCl solution acidified to pH 3 with acetic acid in a spray chamber at a temperature of 49 °C (120 °F). The modified ASTM acetic acid salt/intermittent spray (MASTMAASIS) test is applicable for exfoliation testing of 2xxx (dry-bottom operation) and Ixxx (wet-bottom operation that is, with approximately 25 mm, or 1 in., of water present in the bottom of the test chamber) aluminum alloys with a test duration of 1 to 2 weeks. Results with 7075 and 7178 alloys in various metallurgical conditions have been shown to correlate well with results obtained in a seacoast atmosphere (4 year exposure at Point Judith, RI) (Ref 8). There is no record of the MASTMAASIS test being overly aggressive that is, causing exfoliation of a material that did not exfoliate at the seacoast (Ref 7). 

The test solution should not contain more than 5 per cent (v/v) concentrated hydrochloric acid and must have a pH < 2. It is spotted on a paper strip and allowed to evaporate for 10-15 minutes. Diffusion of the solvent takes place in an atmosphere saturated with respect to the vapour of a saturated solution of methyl acetate in water, and the temperature is maintained constant at 22°. The solvent moves sufficiently far in 20-30 minutes to effect a complete separation. After evaporation of the solvent, the strip is made alkaline by exposure to ammonia vapour and then sprayed with a 1 per cent solution of diphenyl-carbazide in alcohol. Mercury is indicated by a narrow blue band in the dry solvent front. 

The handling (drying, transportation) of explosive powders is often performed under an inert atmosphere. Because of economic considerations, air is not completely excluded but is diluted by Ng or CO2 to an O2 concentration insufficient for dust explosion. The maximum permissible oxygen concentration to prevent ignition in a dust cloud is measured in a Hartmann tube or in a Godbert-Greenwald furnace by spraying the powder with the test gas mixture instead of air. 

This point was considerably amplified by Carter (1972), who refers to comments by Sample in a paper on the use and misuse of salt spray testing in which he also pointed out that a plentiful supply of well conducting electrolyte could lead to erroneous results by comparison with atmospheric exposure where there is alternate wetting and drying by a poorly conducting electrolyte. In such a case there is an acceleration of the yield of the voluminous white corrosion products that appear on zinc and can cause zinc to have a poor rating from some organizations. 

Fig. 167. Rapid testing of the influence of heavy metals on steroids on adsorbent layers. I silica gel G layer, prepared with a 0.6% solution of Pb(N03)2 6 variously substituted oestrenols applied nitrogen atmosphere in the chromatography chamber plate kept 12 weeks at room temperature in this chamber, under exclusion of light then chromatographed with heptane-acetone (80 -f- 40) dried, sprayed with sulphuric acid (Rgt. No. 241B) and inspected in 366 nm UV-light. II as / but using layers prepared with 10% HgCh solution...

The majority of freeze-drying and spray-freeze-diying methods are batch oriented. In terms of cost-effectiveness continuous processes are generally preferred [4]. It was intended to create a closed, continuous process for the production of monodisperse, spherical lyophilisates for nasal and pulmonary application of biological APIs. Different approaches were tested. Droplets generated by a DSG or 2N were to be frozen in a cold gas atmosphere and sublimation-dried in a counter-current gas flow, in an evacuated lyophiUzation tunnel [5], or by a percolating gas flow on a sieve [6]. 

---