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3-1 SECTION 3 EXPERIMENTAL PLAN This section describes the rationale, based on laboratory testing, for down-selecting the components of alternative deicing and anti-icing aircraft and airfield formulations selected from literature reviews and computational modeling, as described in Section 2. Tables 3-1 through 3-3 summarize the tiered testing that was conducted to evaluate the components of the alternative deicing and anti-icing formulations. Pure candidates and simple mixtures with water were tested in Tier 1. Candidates that survived Tier 1 testing were subjected to Tier 2 tests involving more-complex mixtures. TABLE 3-1. Number of components and deicer formulations tested in Tiers 1 and 2. Tier No. Deicer Component Deicer Formulations FPD Surfactant/ Antifoam Corrosion Inhibitor Thickener 1 26 19 14 6 â 2 2 1a 3 2 3 Type IV AAF Runway PDM aEvaluated with two anti-caking materials. TABLE 3-2. Tier 1 deicing/anti-icing formulation tests. Key Area Test/Evaluation Deicing Performance Freezing point depression, viscosity, contact angle Environmental Impact BOD, aquatic toxicity Safety Properties Flash point Cost Supplier cost estimates TABLE 3-3. Tier 2 tests for Type IV and runway PDMs. Key Area Test/Evaluation Type IV AAFs Deicing Performance Surface tension (contact angle), viscosity, foaming Environmental Impact BOD, aquatic toxicity Materials Compatibility Total immersion and sandwich corrosion testing (aluminum clad and anodized aluminum)
ALTERNATIVE AIRCRAFT ANTI-ICING FORMULATIONS 3-2 TABLE 3-3. Tier 2 tests for Type IV and runway PDMs. Key Area Test/Evaluation Runway Deicer Deicing Performance Water absorption, anti-caking Upon review of the Tier 1 results, there did not appear to be substantial potential to improve BOD and aquatic toxicity in Type I fluids, nor did there appear to be potential to improve on BOD in PDMs when compared to the current products with the most favorable environmental characteristics. For this reason, the Project Panel directed the research team to focus the Tier 2 tests on Type IV aircraft anti-icing formulations and anti-caking additives for sodium formate runway deicers. The results of the Tier 2 tests yielded a final selection of components for complete Type IV formulation development. Further tests to certify the down-selected formulations, including deicing/anti-icing performance and materials compatibility, are very extensive and were not undertaken as part of this research. Tier 1 Testing The objective of Tier 1 testing was to efficiently screen candidate components for applicability. The following tests were conducted for each of the candidate formulation components: ⢠Freezing Point Depression: 1:1 (by weight) mixtures of FPDs with water were prepared. Mixtures were placed in baths maintained at -20°C (requirement for aircraft, AMS 1424) and -14.5°C (requirement for airfields, 1435). FPD mixtures frozen at -20°C were rejected; mixtures not frozen at -20°C but frozen at -14.5°C continued to be evaluated for aircraft deicing applications; and mixtures not frozen at -14.5°C continued to be evaluated for both aircraft and runway deicing applications. ⢠Flash Point: Mixtures were tested for flash point. FPD mixtures having flash points lower than 100°C were rejected. ⢠Aquatic Toxicity and Oxygen Demand for FPDs: Mixtures meeting the requirements for freezing point and flash point were tested for aquatic toxicity, chemical oxygen demand (COD) and five day biochemical oxygen demand (BOD5). Methods for these tests are presented in the Tier 2 section Environmental Characteristics. FPDs that showed low levels of BOD5 and/or COD relative to propylene glycol were evaluated further for 28- day BOD. Candidates were ranked first for aquatic toxicity and then for COD (due to uncertainties in BOD testing). Two FPDs were selected for further evaluation as Type IV anti-icers in Tier 2 and one FPD (sodium formate) was selected as a runway deicer in Tier 2. ⢠Aquatic Toxicity and Contact Angle for Surfactants: Neat surfactant solutions were tested and ranked for aquatic toxicity. Each of the eight top ranked surfactants was mixed with water (1:99 by weight), and the contact angle of the mixture was measured in a drop shape analyzer at room temperature (20°C). The contact angle is directly related to the
EXPERIMENTAL PLAN 3-3 surface tension of the fluid. Three surfactants were down-selected for further testing in Tier 2. ⢠Aquatic Toxicity and Viscosity for Thickeners: Neat solutions of six thickeners were tested for aquatic toxicity. The viscosity of the six thickener:water mixtures, 1:99 and 2:98 (by weight) were determined at two temperatures (0°C and 25°C) and multiple shear rates. At a given concentration and temperature, the viscosity, η, is a function of the shear rate, γ (in sec-1), η = K γn, where K and n are constants for a specific thickening agent and FPD. The constant K is fairly linear with the thickener concentration, so only two thickener concentrations needed to be tested. The viscosities were compared at room temperature (20°C) and 5°C to examine the effect of temperature. The viscosities of the thickener/water mixtures were also compared to a commercial Type IV anti-icing formulation to evaluate the direction in the changes of the thickener concentrations in the thickener:water mixtures necessary to match the viscosity of the commercial formulation. Three thickeners were down-selected for further evaluation in Tier 2, based on aquatic toxicity and the changes in the direction of the thickener concentrations. ⢠Aquatic Toxicity for Corrosion Inhibitors: Neat solutions were tested and ranked for aquatic toxicity. Two corrosion inhibitors with the lowest toxicity were down-selected for further testing in Tier 2. At the conclusion of Type I testing, the number of candidate components for the deicer formulations were reduced to the levels indicated in Table 3-1. Tier 2 Testing Type IV Aircraft Anti-Icing Formulations In Tier 2, more complex mixtures of components were tested. The two FPDs selected for Type IV anti-icing formulations were each mixed with an equal amount of water by weight. The two FPD:water mixtures were combined with progressively complex mixtures of additives and evaluated for a range of physical, chemical, and environmental characteristics, as described in the following steps: ⢠FPDs and Surfactants: The FPD:water mixtures were blended separately with the three down-selected surfactants at various concentrations. The control was a commercially available Type IV anti-icing formulation. For each mixture of FPD:water and a surfactant, a surfactant concentration was determined to match the contact angle (surface tension) of the control. The aquatic toxicities of the resulting mixtures were measured and compared to the estimated values based on the neat solution results of Tier 1. The FPD:water:surfactant mixture that had the lowest aquatic toxicity was selected for further Tier 2 testing. The down-selected surfactant also had the lowest cost. ⢠FFPDs and Thickeners: The FPD:water mixtures were blended separately with the three down-selected thickeners at various concentrations. The control was the same commercially available Type IV anti-icing formulation used in the previous tests with the surfactants. For each mixture of FPD:water and a thickener, a thickener concentration was determined to match the viscosity/shear rate of the control at room temperature. The aquatic toxicities of the resulting mixtures were measured and compared to the estimated values based on the neat solution results of Tier 1. The
ALTERNATIVE AIRCRAFT ANTI-ICING FORMULATIONS 3-4 aquatic toxicity of the FPD/water/thickener formulations was determined primarily by the FPD and not by the thickener itself. The thickener was down-selected based on the cost of the thickener. ⢠FPDs, Surfactants and Thickeners: Each FPD:water mixture was combined with the down- selected thickeners and surfactants at concentrations that were determined to match the characteristics of the commercial Type IV anti-icing formulation. The contact angles and viscosities were measured and compared to the values measured in the previous two tests to determine if there was an interaction between the surfactants and thickeners. Foaming tests were conducted with and without the addition of an anti-foaming additive and compared to the control. The aquatic toxicities of the mixtures were measured and compared to the estimated values based on the neat solution results of Tier 2. One of the two FPD:water:thickener:surfactant mixtures were down-selected. ⢠FPDs, Surfactant, Thickener, and Corrosion Inhibitors: Two corrosion inhibitors were added to the down-selected FPD:water:thickener: surfactant formulation and total immersion and sandwich corrosion tests were carried out with aluminum clad and anodized aluminum coupons. The FPD and corrosion inhibitor mixtures were ranked according to the degree of corrosion on the metal surfaces and compared to the controls to determine if the mixtures would meet the SAE AMS 1428 material compatibility requirements. One corrosion inhibitor was down-selected based on performance and estimated aquatic toxicity of the formulation. BOD, COD, and full aquatic toxicity determinations were conducted on the down-selected formulation. Runway Deicers A testing procedure was developed to determine the extent of sodium formate caking under controlled humidity with and without the addition of two anti-caking agents (potassium carbonate and tripotassium citrate). The materials were placed in a humidity chamber set at 50 percent humidity and 30°C, and the amount of water absorbed by each of the materials individually and in combination with each other was measured by weighing the samples over a period of 2 days. A sieve analysis was conducted of the materials before and after they were placed in the humidity chamber to assess the degree of caking.
