A - 05 Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts, chemical passivation, stainless Format, Pages, Price. PDF. Designation: A – 05e1. Standard Specification for. Chemical Passivation Treatments for Stainless Steel Parts1. This standard is issued. Designation: A 05e1. Standard Specification for. Chemical Passivation Treatments for Stainless Steel Parts1 This standard is issued under the fixed.
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Designation: A – 05 Standard Speci?cation for Chemical Passivation Treatments for Stainless Steel Parts1 This standard is issued under. Passivation is a chemical treatment applied to stainless steel parts to provide resistance to oxidation, rusting and mild chemical attack. The Passivation process. ATSM A HTERHATIONAL. Standard Specification for. Chemical Passivation Treatments for Stainless Steel Parts. This standard is issued under the fixed.
This chelation process significantly contributes to the improved results of citric versus nitric. In addition, ASTM A lists several acceptance tests for determining if the passivation process created an adequate passive layer. Table 1 lists these tests with characteristics of each.
Common among the tests is the qualitative interpretation of results through visual inspection.
Also noteworthy is the varying severity and sensitivity of the tests. The lack of clarity for proper test selection and unlikely correlation of results and interpretations among the tests due to different severity and sensitivity levels allow manufactures to choose a test based upon convenience or likelihood of a passing result irrespective of whether an adequate passive layer is restored.
Table 1: Acceptance Tests The health and product risks corrosion presents for medical devices along with an increase in process scrutiny from the FDA, drives the desire for device manufacturers to improve the passivation process to achieve the best possible result, i. Even so, ASTM A provides little guidance to device manufactures for selecting the formulation that will yield the best result.
Passivation process development prior to device validation is now commonplace. Developing the best process is particularly challenging for laser-marked devices since maintaining mark integrity must be balanced with creating an improved passive layer. Characteristics and Challenges of a Laser-Marked Surface The laser marking process applies heat to etch the mark into the surface, similar to welding. The two modes of laser marking are the ablative mode, which uses high power with short contact time and oxidation mode, which uses lower power with longer contact time.
The surface characteristics within the marked area will vary based on the laser mode used. The ablative mode evaporates and oxidizes material from the surface but otherwise does not significantly change the base material, although the layer is thinner, higher in iron oxide and susceptible to localized corrosion such as pitting. The oxidative mode, on the other hand, melts the surface material completely, forming a thick iron oxide layer and loss of passive characteristics.
However, there are very different objectives in the two applications. Alloy components oxidize and turn black during either welding or laser marking, similar to a charred forest after a fire. The black color is an oxide layer and results from exposing the elements to oxygen when they melt from the heat, forming iron oxide, chromium oxide, carbon and other oxidized compounds.
A laser mark visually contrasts with the natural color of the alloy to make the mark visible — the purpose of the mark. For welding, the discoloration is not desired and the passivation pickling process is designed to remove it by chemically etching the surface.
The opposite is true for laser marks. It is important not to significantly remove or dull the oxide layer during passivation so the mark remains visible.
Thus, restoring the passive layer without degrading the mark beyond the intended purpose is the challenge for developing a passivation process for laser marked devices. This requires precise process controls and quantitative, not qualitative, analysis to chemically profile the surface, otherwise the passive layer may not be restored or the laser mark will be dulled beyond the intended purpose.
Since degradation of the laser mark is immediately noticeable, the tendency is to under passivate so the mark is not dulled, but this does not adequately restore the passive layer. Without a quantitative test, this quality flaw only comes to light after corrosion develops well after the part has been released to the market and, even more concerning, perhaps in use. For the medical device manufacturer interested in achieving the best possible result to minimize corrosion risk, a more quantitative test is preferred to determine the extent to which the passive layer has been established.
This test is completed to initially prove effectiveness when the process is being developed. Once the process is in control, the quantitative test can be correlated to one of the qualitative tests listed in ASTM A for production process and quality control purposes.
Since the objective of the passivation process is to create a passive layer by raising the chrome content relative to the iron content, an indication of the quality of the passive layer, a quantifiable determination of the chrome-to-iron ratio seems most applicable.
Refer to Figures 2 and 3. The vertical axis plots the percent composition of the elements present and the horizontal axis plots the depth in angstroms for laser markings on and stainless, respectively.
The marks were made using the oxidation mode as evident by the thick iron oxide layer shown by the high concentration of oxygen the top green line and iron the blue line. This layer makes up approximately 90 percent of the surface composition. Chromium is indicated by the red line and is significantly lower in content than iron blue line throughout the depth of the surface. Chromium rises to 20 percent at angstroms in the sample, equal to the iron content but at a very deep depth, and remains constantly low relative to iron in the sample.
The high iron with low chromium and nickel content indicates corrosion susceptibility at the surface, as the iron is in the ferrous oxide state and, with moisture and oxygen, will oxidize to ferric red oxide.
Formation of ferric red iron oxide will result in growth and release of the iron from the surface as particulate. Figure 2: Unpassivated Mark Figure 3: Unpassivated Mark Passivation of these surfaces results in significantly higher chromium-to-iron ratio and formation of a protective layer.
Both samples and failed the medical device copper sulfate CuSO4 inspection test prior to passivation.
After passivation, both passed the CuSO4 test percent of the time. A pump Beckman Coulter Inc. The mobile phase consisted of mM sodium phosphate, mM sodium chloride, and 0. Protein was detected using a Beckman Gold UV detector at nm. Adsorption of mAb to Microparticles The amount of mAb adsorbed to microparticles was determined by depletion of protein from solution after mixing with particles and performing a mass balance.
A stock suspension of microparticles in buffer was prepared for stainless steel the particles were directly weighed into 1.
Samples were prepared by mixing buffer, the microparticle suspension, and a stock mAb solution to yield samples with a constant final protein concentration of between 0.
Triplicate tubes were prepared and analyzed for each sample conditions. Adsorption experiments with silica showed that between 5 min and 1 hour of mixing gave essentially the same results, suggesting that adsorption was essentially complete within 5 minutes. In experiments with stainless steel microparticles we observed formation of soluble mAb aggregates. Reversibility of mAb Adsorption Reversibility of adsorption was assessed by dilution of samples of microparticles in buffer.
The final sample supernatant was analyzed for desorbed protein using SEC. Mass balances were used to evaluate reversibility of mAb adsorption to glass vials , cellulose and stainless steel microparticles.
To determine whether adsorbed mAb might be released from microparticles in vivo, we examined desorption following resuspension of centrifuged particles containing adsorbed protein in phosphate buffered saline mM NaCl, 10 mM phosphate and 2.
Reversibility of adsorption was tested by collecting the initial pellet as above and resuspending it in the initial volume 0. Again, mass balances were used to evaluate reversibility of mAb adsorption to glass, cellulose, and stainless steel microparticles. The pH was measured after addition of microparticles, but because addition of microparticles resulted in at most a 0.
Two methods were used for incubation studies. In the first method method A we overfilled vials to remove the headspace and therefore eliminate the air-water interface. The method of overfilling vials to remove headspace was used to incubate mAb with glass, cellulose, stainless steel and Fe2O3 microparticles.
This is the main method we recommend for performing accelerated stability studies of protein with respect to effects of microparticles alone. In the second method method B; used for silica, alumina and titania we investigated the potential for synergistic effects of microparticles and the air-water interface by performing incubations in vials with headspace.
To allow for the initial adsorption of protein to microparticles, using method A incubation in overfilled vials without headspace , 1 mL samples of mAb-microparticle dispersions were first prepared and incubated for 30—60 min in 1. Then 0. Triplicate 0.
Some of the 0. The sample assay results were compared those for control samples prepared and incubated without microparticles. Studies using method B incubation in vials with headspace were performed over five days in 1. This method of incubation was used for silica, alumina and titania microparticles. Protein absorption spectra were calculated by subtraction of appropriate buffer blank spectra from the sample spectra.
The previously published procedures for water vapor noise subtraction was applied if necessary. Spectral quality was assessed according to previously published specifications. Because the cell had a path length of 6.
Therefore, all infra-red spectra measurements were made on the fine fraction of particles obtained after settling under gravity. We found that the larger size of the steel microparticles were unsuitable for dispersion between the IR cell surfaces. We suspended microparticles in buffer and allowed the larger particles to settle to obtain a dispersion of the smaller fraction of microparticles. Sufficient particles were added to adsorb all of the protein as verified by UV absorption of the supernatant.
The samples were then centrifuged to form a pellet of particles, which was then re-suspended in fresh buffer. Tertiary structure of the mAb was assessed by performing acrylamide quenching of tryptophan Trp fluorescence.
Surface-exposed Trp are collisionally quenched by acrylamide to a greater extent than buried Trp and therefore can be used to infer relative tertiary structure of the protein.
The intensity of the fluorescence signal was strongly dependent upon the exact angle of the cuvette, so the overlay of the long wavelength edge of the excitation scattering was used as a quality check that the cuvette angle had not changed during measurements. Quenching of mAb adsorbed to ground glass vials, ground glass syringes, cellulose microparticles, and silica microparticles was performed. A pipette was used to manually mix the glass and silica dispersions before readings.
For cellulose, settling was a problem for manual mixing therefore a small motor was used to drive an impeller in the cuvette to give well-mixed dispersion that did not have a decrease in intensity due to settling. Acrylamide was used to quench the intrinsic tryptophan fluorescence of the mAb, both when free in solution, and when fully bound to microparticles.
The protein concentration used was 0.
Excess microparticles were added so that the mAb surface coverage was only about a quarter of the total available surface or half for cellulose if it forms a double layer. Protein adsorbed to silica in 10 mM sodium acetate buffer pH 5. A wavelength of nm with a bandwidth of 4 nm was used to excite the tryptophan fluorescence, which was monitored at nm for native and adsorbed protein, nm for protein unfolded in 9 M urea, and nm for NATA.
The emission was scanned at 0. Acrylamide was freshly prepared as a 7. The measured fluorescence intensities were corrected for dilution from addition of stock acrylamide aliquots before further analysis.
We compared quenching results for the native mAb in solution, the unfolded mAb in solution, and the mAb adsorbed to the different particles surfaces. A p-value of less than 0.
In this work we used these multiple particle characterization techniques because for real-world particles like ground glass the size and shapes are far from uniform and the agglomeration state can vary depending upon whether dry or suspended in solution.