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To evaluate the effectiveness of four selected cleaners based on previous testing results.
Four cleaning solutions were selected for testing based on their performance from the previous trials. Two sets of the cleaning solutions were made into two percent solutions using DI water in 600 mL beakers. One set was evaluated at room temperature and the other set was heated to 130 F on a hot plate.
Thirty coupons were wiped with Isopropyl Alcohol and air dried. The coupons were weighed to establish a baseline level of cleanliness. Ten coupons were photographed using Polaroid Microcam SLR attached to a microscope at a 10x magnification. All 30 coupons were observed for particulate matter using an UVP Inc. Black light, Model UVL-56 longwave UV-366nm. The contaminant was sprayed onto the coupons for five seconds. The ten coupons were photographed and all 30 coupons were observed for fluorescence under the black light. Three coupons were cleaned in each solution for five minutes using stir-bar agitation. Parts were rinsed for two minutes in DI water also with stir-bar agitation. The group cleaned at room temperature were rinsed in DI water at room temperature and the heated cleaning was rinsed with heated DI water at the same temperature.
The parts were dried in a convection oven at 212 F for 15 minutes. After allowing parts to cool to room temperature, final weights were recorded. All coupons were observed again under black light for particulate matter. The same ten coupons were photographed again. Visual observations were made on all the coupons for any visible signs of contamination.
SUBSTRATE MATERIAL: Ceramic-Alumina coupons
CONTAMINANTS: DuPont Evanol (Vinyl Alcohol Polymers & Copolymers CAS#s: 9002-89-5, 25213-24-5, 54626-91-4; Methanol Bulk/Packaged CAS #: 67-56-1; Sodium Acetate CAS#: 127-09-3)
The initial viewing of the black light test showed no signs of particulate matter on the precleaned coupons. After application of the contaminant showed multiple spots of particulate matter on all of the coupons. The cleaning removed almost all of the particulate matter except on a few coupons. Visual inspection of the coupons also yield similar results, with most coupons being free of contamination. Table 2 lists the coupons and the observations made.
Table 2. Black Light and Visual Observations
|Cleaning Temp RT||Coupon #||# of BL Spots||Visual|
|Micro 90||20||Clear spot|
|DI Water||25||Clear spot|
Gravimetric analysis further gave quantitative proof that all the cleaning solutions were efficient in removing the contaminant from the ceramic coupons. Table 3 lists the calculated efficiencies for both cleaning temperatures.
Table 3. Gravimetric Analysis Results
Micro-photography did not yield anything conclusive. Figure 1 shows the precleaned, dirty and cleaned coupon at about 10x magnification.
Figure 1. Stages of Cleaning
Success Rating:A follow up test, usually based on company input.
All of the chemistries tested, including DI water, were effective in removing the Evanol from the ceramic coupons. Gravimetric analysis provided quantitative data which was also backed up by two forms of qualitative assessment, visual inspection and black light fluorescence. The micro-photography did not prove to be a reliable evaluation method. This may have been due to the age of the film.