40 1
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 401-403
using catalyst Cu200. The value of 112 kJ/mol obtained is the same as that for the hydrogenolysis step within experimental error. The rate of the decarbonylation step is described by the following equation: rA2
= 2.2 x
io9 exp(-13471/T)pMF
(9)
The reaction rate constants have units of (mol min-’ m-2cubar4.22)and (mol min-’ m-2cubar-’) for the hydrogenolysis and decarbonylation reactions, respectively. The rate expressions given by (8) and (9) are useful in determining reactor performance for the hydrogenolysis reaction in the two-step route to methanol. They show the importance of producing a highly selective catalyst that minimizes byproduct CO formation. Conclusions The reaction kinetics of the hydrogenolysis of methyl formate have been found to depend on both methyl formate and CO partial pressures whereas hydrogen and methanol partial pressures have no influence on the reaction rate. CO formed by the decarbonylation of methyl formate inhibits the hydrogenolysis reaction and leads to a reversible deactivation of the catalysts at higher concentrations. The hydrogenolysis and decarbonylation of methyl formate have similar activation energies, suggesting that the reaction sequence may involve a common intermediate for both reactions. Copper on silica catalysts prepared by an ion-exchange method have been shown to have high selectivity and activity for the hydrogenolysis of methyl formate. As a result of the low levels of CO produced over these catalysts there is no evidence of the deactivation observed in earlier
studies of this reaction using other copper catalysts. This suggests that these catalysts may have an important use in a two-stage route to methanol comprising carbonylation and hydrogenolysis steps. Acknowledgment Funding of this project under the Australian Research Grants Scheme is gratefully acknowledged. Support was provided under the National Energy Research Development and Demonstration Programme administered by the Department of National Development. Registry No. HC(O)OMe, 107-31-3; M e O H , 67-56-1; CO, 630-08-0; CU, 7440-50-8.
Literature Cited Christiansen, J. A. U.S. Patent 1302011, 1919. Evans, J. W.; Cant, N. W.; Trimm, D. L.; WainwriQht, - M. S. A.m. / . Catal. I983a, 6, 335. Evans, J. w.; Casey, P. S.; Wainwright, M. S.; Trimm, D, L,; Cant, N, w, Appl. Catal. I963b, 7 , 31. Evans, J. W.; Tonner, S. P.; Wainwright, M. S.; Trhnm, D. L.; Cant, N. W., presented at the Eleventh Australian Conference on Chemical Engineering, Brisbane, 1 9 8 3 ~p 509. Evans, J. W.; Wainwright, M. S.; Bridgewater, A. J.; Young, P. J. Appl. Catal.
-~.
1Q83d. .~ 7 . 7 5 .
.
Evans, J. W.; Wainwright, M. S.; Cant, N. W.; Trimm, D. L. J . Catal 1984, 88. 203. Kiier, K. Adv. Catal. 1982, 31, 243. Kobayashi, H.; Takezawa, N.; Minochi, C.; Takahashi, K. Chem. Left. 1980, 1197. Kung, H. H. Cafal. Rev. Sci. Eng. lQ80,22(2), 235. Petrole Informations, 1982, May 13, 34. Sorurn, P. A.; Onsager, 0. T. Roc. I n t . Congr. Catal. 8th 1984, 11-233. Tonner, S. P.; Trimm, D.L.; Wainwright, M. S.; Cant, N. W. Ind. Eng. Chem. prod. Res. D ~ V .1 ~ 8 4 ~ 2 3 , 3 8 4 .
Receiued f o r review November 1, 1984 Accepted April 3, 1985
GENERAL ARTICLES
Evaluation of Manganese Phosphate Coatings Rlchard A. Farrara U S . Army Armament Research and Developent Center, Benet Weapons Laboratory, Watervllet, New York 12189
The corrosion and wear resistance of the basic or normal manganese phosphate coating is compared with that of manganese phosphate that has been modified or converted by a chemical solution named “Endurion”. Supplementary coatings of either oil or solid-film lubrlcant are applied over both types of phosphate.
Introduction The coating commonly used to protect steel from corrosion is the basic, heavy, manganese phosphate and either oil per VV-L-800, [Federal Specification-lubricating oil, general purpose, preservative (water-displacing, low temperature)] or heat-cured solid-film lubricant (SFL) per Mil-L-46010, [Military Specification-lubricant, solid-fib heabcured, corrosion-inhibiting]. This correlates with type M, class 1, of the phosphate specification DOD-P-16232, [Military Specification-phosphate coatings; heavy, manganese, or zinc base (for ferrous metals)]. Oil applied to
basic manganese phosphate is a relatively low cost coating that results in respectable corrosion and wear resistance whereas solid-film lubricant applied to manganese phosphate is a relatively expensive coating that results in good corrosion resistance and excellent wear resistance. The Endurion-modified manganese phosphate (patented process of the LEA Manufacturing Co.), which correlates with type M, class 4,of DOD-P-16232, was selected for comparison with the present manganese phosphate because it has the potential for significant improvement in performance (corrosion and wear resistance) with an associ-
This article not subject to U S . Copyright. PIublished 1985 by the American Chemical Society
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ated low or small increase in cost. Immersing steel into a hot solution of manganese phosphate results in a crystalline product that drastically reduces the electrical conductivity of the surface. Since corrosion depends upon the flow of electrons between the anodes and cathodes (hills and valleys) that exist on a surface, decreasing the electrical conductivity of the surface will retard the corrosion process. Although the phosphate crystals help to prevent the flow of electrons, there is a space or valley that exists between the crystals of the basic manganese phosphate coating. The bottom of the space between the crystals has a very thin layer, if it exists, of nonconductive material; hence, moisture that eventually goes through the supplementary coating (oil or SFL) reaches this area that is marginally protected. The result is the appearance of rust or corrosion spots after a short period of time. The Endurion process deposits particles of tin that fill or seal the space between the phosphate crystals, thereby preventing moisture from reaching the bottom of the space and, thus, preventing fast corrosion or rusting problems. The phosphate crystals are also desirable for allowing a supplementary coating to adhere to the surface. The crevices between the phosphate crystals provide space for entrapping the supplementary coating. If the supplementary coating has lubricating properties, the load-carrying capacity and wear resistance of the surface will be enhanced. Since the supplementary coating is the primary provider of lubrication for wear-resistance tests, the basic manganese phosphate crystal should be comparable to the Endurion coating. However, the tin particles provided by the Endurion process have lubricating properties; hence, improvement in the wear resistance of the final coating system could be expected.
Experimental Section The approach used for determining if the Endurion coating is more desirable (performance and cost) than the basic manganese phosphate was to conduct standard tests for evaluating and comparing corrosion resistance and wear resistance of protective coatings. Corrosion and wear test specimens were coated with either basic or Endurion manganese phosphate, and a supplementary coating of oil or SFL was added over all the phosphated specimens. Three different oils were selected for testing in order to determine if the oil presently specified (VV-L-800)should be replaced by either oil per MIL-L-3150 [Military Specification-lubricating oil, preservative, medium (P7)] or oil per MIL-L-63460 [Military Specification-lubricant, cleaner and preservative for weapons and weapon systems (break-free)]. a. Corrosion Test. The accelerated corrosion test is conducted in an environment of 5% salt spray that is controlled in accordance with ASTM B 117. The protective coating is applied to plain carbon (AISI 1020) steel panels (3 in. X 6 in. X 0.030 in. thick) purchased to type I of ASTM D 609 (cold rolled, matte finish). The coated panels are placed in the salt-spray chamber and supported in a wooden holder at a 15' angle from the vertical. The criterion for failure that was selected is taken from the heat-cured solid-film lubricant specification (MIL-L-46010) which states that failure is reached when more than three rust spots form per panel that are at least 1mm in length, width, or diameter. Two panels with each coating were tested until failure, and the average of the two times required to generate failure is the reported corrosion resistance. b. Wear-ResistanceTest. The wear-resistance test is performed on a Falex Lubricant Tester produced by
Table I. Falex Wear-Life Test Procedure (0-3000 in.-lb gauge)" time to reach or cumulative hold load total increase load from 0 to 300 lb 25 s 25 s 3 min 3 min 25 s hold a t 300 lb 20 s 3 min 45 s increase load from 300 to 500 lb 1 min 4 min 45 s hold at 500 lb increase load from 500 to 750 lb 25 s 5 min 10 s 1 min 6 min 10 s hold at 750 lb increase load from 750 to 1000 lb 25 s 6 min 35 s hold a t 1000 lb until failure "Failure is indicated by a torque rise of 5 in.-lb above the steady-state torque value or breakage of the shear pin. Both pin and v-blocks are coated with SFL.
Table 11. Specification Requirements for Corrosion Resistance (5% Salt Spray) of Manganese Phosphate with and without Supplementary Coatings requiretype of coating specification ment basic manganese DOD-P-16232, type M, class 3 11/2h phosphate without , suppl coating basic manganese DOD-P-16232, type M, class 2 24 h phosphate with oil per MIL-L-3150 basic manganese MIL-L-46010 100 h phosphate with solid-film lube per MIL-L-46010 Endurion without DOD-P-16232, type M, class 4 24 h suppl coating Endurion with suppl DOD-P-16232, type M, class 4 72 h coating (suppl coating is not specified) Table 111. Corrosion Resistance (5% Salt Spray) of Basic Manganese and Endurion Phosphate with and without Supplementary Coatings supplementary basic manganese phosphate Endurion __ coating (type M, class lf (type M, class 4) oil Der VV-L-800 91 h 600+ h oil per 122 h 600+ h MIL-L-3150 oil per 133 h 600+ h MIL-L-63460 solid-film lube 206 h 744+ h Per MIL-L-46010 no supplementary 1 'f2-3 h 24-30 h coating
Faville LeValley Corp., Chicago. The testing is conducted in accordance with ASTM D 2625, procedure A (endurance life of solid-film lubricants). The protective coating is applied to a cylindrical (1/4 in. d. X 11/4in. long) alloy steel pin (AISI 3135) with a hardness of RB 80183 and to two steel v-blocks (AISI-1137) with a hardness of R, 20/24. The two v-blocks are stationary and are loaded radially against the pin, which is rotated at 290 f 10 rpm. The load is applied in increments and held for a period of time (see Table I) until 1000 lb is reached. The torque required to rotate the pin is monitored at all times. If the load of lo00 lb is reached before failure occurs, the load is maintained at 1000 lb and the time required to create failure is monitored. Failure is indicated by a torque rise of 5 in.-lb above the steady-state value. If failure occurs before reaching the 1000-lb load, the load (not time) reached prior to failure is reported. Four tests (four pins and eight vblocks) with each coating are done to provide an average
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985 403 Table IV. Falex Test of Oils a n d Solid-Film Lubricant (Heat-Cured) Applied to Manganese Phosphate (Type M, Class 1, a n d Type M, Class 4) basic manganese phosphate Endurion supplementary coating (type M, class 1) (type M, class 4) (failure load or time for failure a t lo00 lb load) (failure load or time for failure a t 1000 lb load) 500 lb, 2 tests 500 lb, 4 testa oil per VV-L-800 750 lb, 2 tests 750 lb, 1 test 750 lb, 2 tests oil per MIL-L-63460 1000 lb/20 s, av of 3 tests 1000 lb/15 s, av of 2 tests 1000 lb/74 min 10 s, av of 4 tests solid-film lube per MIL-L-46010 1000 lb/138 l/z min, av of 4 tests
value that is the reported wear-life of the coating.
Results a. Corrosion Resistance. The data reported in Table I1 are the specification requirements for the corrosion resistance of basic and Endurion manganese phosphate with and without supplementary coatings. These data are summarized to provide a feel or basis for comparing the phosphate and supplementary coatings. These data reveal that the Endurion process is expected to provide better corrosion resistance than the basic manganese phosphate and that a supplementary coating, especially solid-film lubricant, will improve corrosion resistance significantly. The data reported in Table I11 are actual test data, which are the average number of hours required for twa steel test panels with each coating to result in failure (three rust spots per panel). The data clearly indicate that the supplementary coatings (oil or SFL) provide the primary resistance to corrosion. The basic manganese phosphate fails after approximately 1' / z h, and the Endurion manganese phosphate fails after approximately 24 h if the panels are not protected with a supplementary coating. The primary result from the test is that converting manganese phosphate via the Endurion process drastically improves the corrosion resistance. Applying oil to the basic manganese phospate resulted in failure, depending upon the type of oil, after approximately 100 h (from 91 h for W-L-800 to 133 h for MIL-L-63460), whereas the panels coated with Endurion manganese phosphate and oil did not show any signs of rust after 600 h of testing. Applying heat-cured solid-film lubricant over the basic manganese phosphate improved the corrosion resistance (206 h), but this is significantly less than that of the Endurion phosphate plus oil (600+ h). b. Wear Resistance. The data reported in Table IV are the maximum loads reached for coatings that failed prior to the load reaching 1000 lb or the time required to create failure at the maximum load of 1000 lb. The data clearly reveal that the load-carrying capacity of oils is signficiantly less than that of solid-film lubricant; hence the wear resistance of solid-film lubricant is far beyond
that of oil. Also, conversion of phosphate via the Endurion process did not improve wear resistance (slight improvement with oils; severe degradation with solid-film lubricant). This is explained by the reasoning that the role of the phosphate is to provide numerous cavities that trap the supplementary coating of oil or SFL. The Endurion coating has tin deposited in the cavities that reduces the space for the supplementary coating. The supplementary coating is the primary vehicle for resisting wear, and if there is some space remaining in the cavities after the Endurion process, the supplementary coating will remain for resisting wear. While the tin supposedly acts as a lubricant, once the supplementary coating is removed or breaks down, the tin does not prevent failure. Conclusions A coating of manganese phosphate converted by Endurion and coated with oil or SFL provides excellent corrosion resistance for steel as measured by the 5% salt-fog test. The oil per MIL-L-63460provided the highest corrosion resistance of the oils when applied to the basic manganese phosphate. However, all three oils tested provided over 600 h of resistance when applied t o the Endurion phosphate. Solid-film lubricant can withstand high loads (1000 lb) and will break down only after a considerable length of time (minutes) as measured by the Falex test. Oil cannot withstand high loads as measured by the Falex test. Converting manganese phosphate by the Endurion process does not significantly improve wear resistance. Solid-film lubricant applied over regular manganese phosphate provides better corrosion resistance than oil applied over regular phosphate but has significantly less corrosion resistance than oil applied over converted manganese phosphate. Registry No. AIS1 1020,12725-36-9; manganese phosphate, 10124-54-6.
Received for review December 3, 1984 Accepted March 21, 1985
