Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 420-425
420
bricants, and Elastomers Branch.
+-CF2
COF
1 CF3 0 C F p - - l r y G
t
I
I
CH30H
C f 5 0 C F p 0 CF3 t
Cf5OCF20CF2CFpOCF3 t
C f 5 0 CF2 0 CF2 CF2 0 CF2 0 CF3 t
CF3 0 CF2CF2 C 0 2 C H 3 i
C F 3 0 CF2CF2OCF2CF2 OCF2C02CH3
Figure 5. Products obtained on degradation of an unbranched perfluoroalkyl ether in the presence of Ti(4A1,4Mn) at 288 " C in 0%.
surface protection as compared to the absence of additives. The few products identified confirmed the structural arrangement of Fomblin Z type fluids and proved further the chain scission mechanism. Acknowledgment We acknowledge the assistance of C. E. Snyder of the Air Force Wright Aeronautical Laboratories, Fluids, Lu-
Registry No. I, 60950-97-2; 11,65288-70-2; M50 (tool steel), 12725-39-2;Al, 7429-90-5; Ti, 7440-32-6; Ti(4Al, 4Mn), 12633-21-5; Cr. 7440-47-3; V, 7440-62-2; fomblin Z, 64772-82-3.
Literature Cited Gumprecht, W. H. "The Preparation and Thermal Behavior of Hexafluoropropylene Epoxide Polymers", presented at the Fourth International Symposium on Fluorine Chemistry, Estes Park, CO, July 1967. Jones, W. R., Jr.; Paciorek, K. J. L.; Ito. T. I.;Kratzer, R . H. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 166. Kratzer, R. H.; Paciorek, K. J. L.; Kaufman, J.; Ito, T. I.J . Fluorine Chem. 1977, 10, 231. Paciorek, K. L.; Kratzer, R. H.; Kaufman, J.; Nakahara, J. H. "Determination of Fluorocarbon Ether Autoxidative Degradatlon Mechanism", Wright-Patterson Air Force Base, OH, AFML-TR-77-150, 1977. Paciorek, K. J. L.; Kratzer, R. H.; Kaufman, J.; Nakahara, J, H. J . Appl. folym. Sci. 1979, 24, 1397. Scherer. K. V., Jr.; Yamanouchi, K.; Ono, T. "Structure Elucidation of Perfluorochemicals by Negative Chemical Ionization Mass Spectrometry: Application to F-Alkanes, Ethers and Amines, and Comparison with E1 and PCI Mass Spectra", presented at the Sixth Winter Fluorine Conference, Daytona Beach, FL, Feb 1983. Sianesi, D.; Pasetti, A,; Fontanelli, R.; Bernardi, G. C.; Caporiccio, G. C h h . Ind. (Milan) 1973, 55, 208. Snyder, C. E., Jr.: Tamborski, C.; Gopal, H.; Svisco, C. A. Lubr. Eng. 1979, 35, 451. Snyder, C. E.,Jr.; Gschwender, L. J.; Tamborski, C. Lubr. Eng. 1981, 3 7 , 344. Snyder, C. E.. Jr.; Gschwender, L. J.; Campbell, W. B. Lubr. Eng. 1982, 3 8 , 41.
Received for review September 24, 1984 Accepted April 1, 1985
Reactions of Molten Urea with Formaldehyde? Thomas P. Murray Department of Chemistry, University of North Alabama, Florence, Alabama 35630
Ernest R. Austln," Robert G. Howard, and Timothy J. Bradford International Fertilizer Development Center, Muscle Shoals, Alabama 35662
When small amounts of formaldehyde are added to molten urea during manufacture, the physical properties of the urea are improved. Several compounds resulting from the urea-formaldehyde reaction become impurities in the urea matrix. In this study, high performance liquid chromatography (HPLC) has been used to analyze the products formed as a result of this conditioning process. A new compound, biuretmethyleneurea,has been isolated from formaldehyde-conditioned urea. The reaction of molten urea with paraformaldehyde has been studied and the reaction products have been analyzed for methylenediurea, dimethylenetriurea, biuret, triuret, and biuret-
methyleneurea.
Introduction Formaldehyde has long been known to react with urea, and various commercial urea-formaldehyde condensation products have been in the marketplace for years as materials ranging from insulating foams to fertilizers. In the fertilizer industry, formaldehyde has been used to condition urea and also to prepare nitrogen fertilizers having Presented to the Fertilizer and Soil Chemistry Division a t the 188th National Meeting, of the American Chemical Society, Philadelphia, PA, Aug 1984. 0196-4321/85/1224-0420$01.50/0
controlled-release properties. The use of formaldehyde to condition fertilizer-grade urea is a common practice among urea manufacturers. The amount of formaldehyde added as a conditioning agent is usually 0.3-0.4%. The aldehyde can be added as either formalin solution, paraformaldehyde, or UF Concentrate-85, which is 60% formaldehyde and 25% urea with 15% water. In general, conditioning is used to improve the physical properties of the product. It improves the resistance to caking and also the physical strength of granules while a t the same time reducing dust problems (IFDC, 1979). 0 1985
American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985 421
Table I. Sensitivity Factors for HPLC Standards sensitivity, compd urea MDU
BIU DMTU
BMU TRI
retention time," min 2.03 2.47 2.66 3.33 4.16 5.44
aFlow rate of 1.5 mL/min. multiple injections.
(mg/mL)/ pV-S
9.60 x 1.05 x 2.38 X 4.36 X 1.16 X 3.74 x
% RSDb
10-5 10-5
1.08 0.19
lo4
0.29 1.40
lo4 lo+ lo-'
0.10 1.10
bRelative standard deviation for
When larger amounts of formaldehyde are added to urea, ureaform fertilizers result. The development of commercial ureaform fertilizers can be traced to the process development work of Clark et al. (1948,1951). The process technology for production of ureaforms has been reviewed (Fowler, 1976))and the agronomic experience gained with the use of commercial products has been well documented in a paper presented before the Fertiliser Society of London (Schneider and Veegens, 1979). The potential of ureaforms as slow-release fertilizers has been contrasted to other slow-release nitrogen fertilizers in an IFDC technical bulletin (Murray and Horn, 1979). In this study, high-performance liquid chromatography (HPLC) techniques previously developed (Murray et al., 1982) have been expanded to study the reaction of formaldehyde with urea. Biuretmethyleneurea (BMU), a new compound having the structure below, has been isolated 0
0
0
I1 II I1 H2N C NHC NHCH2NH CNH 2 biuretmethyleneurea
and characterized. Data are presented on a new method for the preparation of ureaforms by the reaction of molten urea with paraformaldehyde. Experimental Section General Methods and Materials. NMR spectra were taken on JEOL FX-90 and Varian EM-360 spectrometers. IR spectra were recorded on a Perkin-Elmer Model 238 infrared spectrophotometer, and UV spectra were recorded on a Beckman Model UV 5260 spectrophotometer. A Perkin-Elmer Series-2 HPLC single-pump system with a Rheodyne 7125 injector, equipped with a 10-pL loop, was used for HPLC analysis. The column was a Waters Associates RCM-100 radial compression module equipped with a C-18 5-pm Radial-PAK cartridge. The detector was a Perkin-Elmer LC-55 variable wavelength single-beam ultraviolet spectrometer set at 200 nm. Chromatograms were recorded on a Leeds and Northrup Speedomax XL recorder, and peak area integrations were obtained with a Columbia Scientific Supergrator-2 programmable computing integrator. A Perkin-Elmer DSC-2 differential scanning calorimeter was used to determine melting points. The mobile phase for analytical chromatography was a 1% phosphate buffer at pH 6 containing 5% (v/v) methanol. Analytical chromatography standards were prepared as previously reported (Murray et al., 1982; Davidson, 1983). Retention times and sensitivity factors for HPLC analytical standards and the percent relative standard deviation for multiple injections of each standard are shown in Table I. The paraformaldehyde used was Fisher purified and the 37 % formalin solution was Fisher-certified ACS with methanol stabilizer. The fertilizer-grade urea that was formaldehydeconditioned came from Nederlandse Stikstof Maatschappij (NSM), and the nonformaldehyde-condi-
tioned urea came from Mississippi Chemical. The reagent-grade urea was Fisher-certified ACS. Flash chromatography was accomplished by use of EM Reagents silica gel 60 silanized adsorbent in a 120 cm X 30-mm column and Baker octadecyl (C18)absorbent in an 18 cm X 1%" column. A Buchler Fractomette Alpha 400 automatic fraction collector was used to gather fractions. The general technique of flash chromatography has been previously described (Still et al., 1978). Preparation of Ureaforms from Molten Urea. The urea starting material (Mississippi Chemical) was melted in either a 200-mL round-bottom flask equipped with a heating mantle, magnetic stirrer, and thermometer or in an open beaker heated on a hot plate and equipped with a thermometer and either a mechanical stirrer or a magnetic stirrer. The results from both experimental setups were the same. Two different procedures were used to react paraformaldehyde with urea. In the first procedure, urea was melted, and while the temperature was held between 130 and 140 "C, paraformaldehyde was rapidly mixed into the urea. In a second procedure the paraformaldehyde was premixed with the urea and the solid mixture heated to 130 OC and stirred. In both methods the molten reaction mixture was poured into a rectangular (25 X 15 X 1 cm) Teflon mold and allowed to cool and solidify before being ground and analyzed. The total charge for each reaction was 100 g. The percentage paraformaldehyde used for each reaction, the conditions, and an HPLC analysis appear in Table 11. In samples 14 through 18 the total for the analysis is low because the samples were not completely water soluble. Isolation of Biuretmethyleneurea. Method A. From Formaldehyde-ConditionedUrea. A 100-g sample of fertilizer-grade urea known to have been conditioned with formaldehyde was blended with an equal weight of methanol in a Waring blender at high speed. The sample was then rapidly filtered and the methanol was evaporated from the filtrate to afford a urea sample in which the concentration of biuretmethyleneurea (BMU) was doubled. After the initial extraction was complete, a 20-g sample was chromatographedon a large column (120 cm X 30 mm) packed with EM Reagents silica gel 60 reversed-phase adsorbent. The column was gravity fed, and water was the elutant. Several 100-mL fractions were collected, and each fraction was assayed by HPLC. By using this large column it was possible to remove much of the urea present in the original sample. Fractions containing BMU were combined, and the excess water was removed by freeze-drying. The frepze-dried sample was then rechromatographed by using .lash chromatography with a column having characteristics similar to the reversed-phase column used in the analytical HPLC. The flash chromatography column (18 cm X 18 mm) was prepared with octadecyl (C18) absorbent and then conditioned by passing 150 mL of methanol through the column at a head pressure of 5-10 psi. The methanol was followed by 50 mL each of 7570, 50%, and 25% methanol-water mixture. Finally, 150 mL of water was passed through the column to make the column ready for use. The sample was introduced onto the column and eluted with water under a pressure of 5 psi. Since elution was rapid, a fraction collector was used. Individual fractions were assayed by HPLC and then combined to afford a sample of high purity. The combined fractions were analyzed a final time as a purity check and then freeze-dried to afford 10 mg of pure BMU. As can be seen from this description, the purification process was difficult, and very
422
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985
Table 11. Urea-Paraformaldehyde Reactions: Conditions a n d Product Analysis compn, 70 HPLC anal. of react prod., 70 sample urea' PFAb reaction time, min urea BIU TRI MDU DMTU 1 97 3 60 81.4 6.5 0.20 10.8 0.78 2 95 5 60 66.3 8.0 0.14 17.8 1.8 1 3 92.5 7.5 74.1 1.3 0.09 24.6 4.4 1.1 4 7.5 71.0 92.5 25.4 5 0.05 4.3 5 7.5 71.2 1.5 15 92.5 27.1 0.05 4.6 7.5 70.9 6 2.1 92.5 28.1 4.7 0.06 30 n 7.5 66.9 0.08 , 60 4.7 92.5 4.6 23.0 1 64.7 0.10 1.5 8 10 90 24.9 6.1 64.4 9 0.08 0.8 10 90 31.1 5 6.5 65.2 0.06 1.2 90 32.2 10 10 15 6.9 62.9 1.4 11 30 0.05 7.5 90 33.1 10 59.3 1.8 90 10 60 12 0.05 7.0 31.6 52.8 1.9 88.5 60 34.7 13 11.5 0.07 9.9 47.5 2.2 11.4 87 60 13 14 0.12 35.8 41.5 2.4 12.0 85 60 28.0 15 0.07 15 25.1 2.1 12.9 80 60 25.3 16 20 0.10 18.5 1.2 15 10.8 75 20.0 17 25 0.07 1.0 10 2.1 0.04 4.3 18 50 50 7.8 7.0 97.1 d 0.3 0.3 98.9 e 0.03 Manufactured by Mississippi Chemical-Fertilizer Grade. *Paraformaldehyde. sample/mL of HzO). dBlank; heated, no PFA. eBlank; no heat, no PFA. Table 111. Chromatographic Isolation of Biuretmethyleneurea run no.
1,2 3 4 5 6 T
8 9
combined wt BMU, mg 78.4 NA 43.0 45.8 34.9 32.9 32.7 30.0
fractions collected 22-35 22-35 20-32 22-35 22-33 22-33 24-35 24-33
little sample was available at the completion of the procedure. Method B. From Urea-Paraformaldehyde Melt Reactions. The isolation procedure for BMU began with a cold water extraction of 10 g of urea-paraformaldehyde sample number 14 (Table 11) using 20 mL of water. The extraction time was 5 min a t 0 "C. After extraction, the filter cake and the filtrate were freeze-dried, and both Table IV.
BMU 1.0 2.5 0.8 1.1
1.3 1.4 2.1 0.95 1.1 1.3 1.7 1.8 2.3 2.8 2.0 2.2 1.3 0.5
Analysis of water-soluble components (0.025 g of
samples were analyzed by HPLC. The filtrate, which contained approximately 50% of the original sample, was richer in BMU and was, therefore, chosen as the starting material for chromatography. A 1-g sample of the freeze-dried material or 4 mL of the filtrate (concentration E 0.25 g/mL) was placed on the head of the 18 cm X 18 mm flash chromatography column as described above, and the sample eluted with water. A head pressure of 5 psi gave a flow rate of 4.5 mL/min. The fraction collector was set up with 50 tubes, and the first fraction collected was allowed to flow for 1min. After the first fraction, 50 additional fractions were collected at 0.5-min intervals. An additional 100-200 mL of water was eluted between runs to make sure all components were off the column. After elution the fractions were analyzed, and those containing the pure unknown were combined and freeze-dried. The results in Table I11 are for nine successive runs using the same column and packing material. The results were consistent, and the column worked well. It should be noted, however, that it was necessary to an-
* H NMR Correlation of BMU with Model Compounds compound name urea
functional group resonance frequenciesa structure
NH 2 5.59s
0
/I
NH
CH,
HzNCNHz
biuret
triuret
BMU
0
0
0
0
It I/ HzNCNHCNHz 0
DMTU
a
0
0
I1 /I II HzNCNHCNHCH~NHCNH~ (a) ( c ) (dl
MDU
0
I1 /I II HzNCNHCNHCNHz
6.83s
8.58s
6.90s
9.51s
6.84s ( a ) 5.69s ( b )
8.65s (c) 7.94t ( d ) 6.68t ( e )
4.36t
5.65s
6.50t
4.18t
5.60s 6.46t
6.62t
4.20t
(el (bl
0
0
0
0
11 I/ HzNCNHCHzNHCNH2 0
I1 I1 /I HZNCNHCHZNHCNHCH~NHCNH~
totale 99.7 94.0 105.3 102.9 105.9 107.3 99.3 98.0 104 106.9 106.7 99.8 99.4 97.0 84.0 65.5 51.9 15.7
All frequencies given as chemical shift in ppm 6 . s = singlet; t = triplet. TMS internal standard.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985 423 Scheme I. Possible Mechanisms for BMU Formation 0
II HzNCNHCHpOH
0
3
MDU
8 NHZ-C-NH-CHZ-NH-C-NH2
4
BIU
NH~-~-NH-~-NH~
5
DMTU
fi
EMU
0
,
FI
r o u t/e L A
MDU
o
0
I1 HzNCNHp
0 0
-
heal
Figure 1. Chromatogram of a typical formaldehyde-conditioned urea.
Table V. 13C NMR Correlation of BMU with Model Compounds functional group resonance frequenciesa
MDU
BMU
0
0
0
I1 ll H2NCNHCHzNHCNH2 0
0
CH 2
155.7
0
II II H2NCNHCNH2
0
I/ I1 I1 HzNCNHCNHC H2 NHCN H p (a) (b)
a
c=o
structure
158.8
45.7
155.0 ( a )
44.9
154.5 ( b ) 158.3 (c)
(C)
All chemical shifts given in ppm 6 . TMS internal
standard. alyze the individual fractions by HPLC to determine which fractions would be saved from each run. BMU was recrystallized from methanol and had a DSC melting point of 196 "C.The purified material had the following spectral characteristics: IR (KBr) 3320,3440,1540,1610,1680,and 1715 cm-'; UV (ethanol) A,, 195 nM; NMR 'H and 13C in Tables IV and V, respectively. Anal. Calcd for C4H9N503:C, 27.43; H, 5.18; N, 39.99. Found: C, 27.79; H, 5.40; N, 39.64. Results and Discussion The chromatogram of a typical sample of fertilizer-grade urea is shown in Figure 1. In a previous paper (Murray et al., 1982) it was noted that peaks number 5 and 6 were unknown. Since that publication, peak number 5 has been identified as dimethylenetriurea (Davidson, 1983),and this work has now identified peak number 6 as BMU. Determination of the BMU structure is based primarily on spectroscopic evidence. Fundamental to the interpretation of the BMU spectral data were spectra of a series of model compounds. Table IV shows correlation of lH NMR spectra of BMU to the spectra of several model compounds, including urea, biuret (BIU), triuret (TRI), methylenediurea (MDU), and dimethylenetriurea (DMTU). The NH2 resonance frequencies for urea, MDU, and DMTU are all approximately 5.6 ppm, while the NH2 frequencies for biuret and triuret show up at approximately 6.9 ppm. BMU has two types of NH2 groups-one on the biuret end of the molecule and the other on the urea end. Interestingly, as can be seen in the table, both groups correlate well to the model compoundswith NH2resonance lines at 6.84 and 5.69 ppm, respectively. A similar situation
BMU
isocyanic acid
0
0
/I II HpNCNHCNHp biuret
C H20
-
0
II II II H2NCNHCNHCH2NHCNt+
NH3 t HN=C=O
HNCO
name biuret
0
I1 II H2NCNHCH2NHCNHp
m e t hylolurea
0
0 NHZ-&NH-CH2-NH-C-NH-cHz-N~-e-~~z 0 0 0 NH~-~-NH-~-NH-cH~-NH-~-NH~
compound
-
urea
0
0
0
II /I H2NCNHCNHCHzOH methylolbiuret
exists for the NH protons. In the case of biuret and triuret, the NH protons absorb between 8.5 and 9.5 ppm, whereas the NH protons in MDU and DMTU absorb in the 6.5to 6.6-ppm region. BMU has three different types of NH protons. The NH absorption labeled (c) in Table IV is in the biuret portion of the molecule and has an appropriate chemical shift of 8.65 ppm. The NH proton labeled (e) is similar to the NH of MDU and DMTU, and the chemical shift is appropriate; the NH proton (d) is unique to the BMU structure. The final lH NMR evidence involves the absorption position of the methylene protons in BMU, and this correlates closely with the same functional groups in MDU and DMTU as shown in the table. Nuclear magnetic double resonance experiments were also helpful in the structural assignments since the N-H and CH2 triplets were easily decoupled adding further confirmation to the assigned structure. To further aid in confirmation of structure, 13Cspectra were obtained on BMU and appropriate model compounds. The data are summarized in Table V. As is evident from these data, the 13Cresonance lines correlate well. The three different types of carbonyls present in BMU are all evident in the spectrum as is the methylene carbon. Furthermore, the proton off-resonance spectrum shows the methylene carbon split into a triplet by the attached hydrogens. At least two possible mechanisms appear feasible for the formation of BMU in the urea melt either during the conditioning process on an industrial scale or during a laboratory-scale reaction of molten urea with paraformaldehyde. These mechanisms are outlined in Scheme I. In route A, methylolurea from the condensation of urea with formaldehyde could react with additional urea to afford MDU, which is present in most samples of urea. The MDU could then react with isocyanic acid to form BMU. Route B is similar in that the isocyanic acid first reacts with urea to form biuret which then condenses with formaldehyde to give methylolbiuret. Condensation of methylolbiuret with urea would then afford BMU. Although no attempt has been made to elucidate the mechanism, route A appears more likely on statistical grounds because the concentration of MDU is always much higher than the concentration of BMU or biuret in any reaction mixture. Furthermore, when excess (10%) biuret was added to urea-paraformaldehyde reaction mixtures, there was no significant reduction in the biuret level during the course of the reaction. This would also support route A as the more likely mechanism: Figure 2 shows the concentrations of BMU and other components as a func-
424
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985 40
I
10 1
0
d
I
/
I
I
1
I
5
10
15
20
I
% PIRLFORMILDEWVDI
F i g u r e 2. Concentrations of biuret, MDU, DMTU, and BMU in the reaction product as a function of paraformaldehyde starting con130 "C. centration. Reaction time = 60 min; reaction temperature
=
tion of the paraformaldehyde concentration for several reactions up to 20% paraformaldehyde. During initial attempts to duplicate in the laboratory the process by which urea is conditioned on an industrial scale, a series or reactions of molten urea with formaldehyde were tried. The goal was to use higher concentrations of formaldehydethan that used in the conditioning process in order to produce larger amounts of BMU. This led to a systematic study of the reaction of urea melt with formaldehyde. In some preliminary experiments it was found that reaction of urea melt with 37 % formalin solution gave materials with complex chromatograms having a large number of partially separated, unidentified components. The chromatograms were similar to those from the HPLC analysis of UF Concentrate-85, and the samples appeared to contain substantial concentrations of methylolureas. When paraformaldehyde was used as the formaldehyde source, the product chromatograms were clean, and it did not appear that methylolureas were present. A review of the literature shows that, although many processes for the production of ureaforms for fertilizer use have been patented, most are solution processes that rely on a series of pH changes to produce methylolureas under base-catalyzed conditions and methyleneureas under acid-catalyzed conditions. The reaction of paraformaldehyde with molten urea has generally been neglected as a potential process for ureaform fertilizer production. It appears that the reactions described herein for laboratory-scale preparation of ureaforms could easily be adapted to an industrial situation where molten urea is available. Process patents for ureaform preparation from UF Concentrate-85 are held by 0. M. Scott and Sons, Inc. (Renner, 1966; Czurak and Thompson, 1976), Allied Chemical Corp. (Butler, 1964, Smith and Formaini, 1964), and many others. Companies including Hercules Powder Co. (O'Donnell, 1965,1966)and Fertilizers and Chemicals Ltd. (Greidinger et al., 1978, 1979) hold patents for the preparation of ureaforms by the reaction of formalin solution with urea using a series of pH changes. A few patents have been issued for the preparation of ureaforms from paraformaldehyde. A three-stage concentrated solution process starting with paraformaldehyde and producing ureaform with activity indices (Horowitz, 1980) as high as 75% is covered in a process patent (Nobell, 1973). A similar process (Schafer and Kohlhaas, 1969) utilizes paraformaldehyde in a dilute, acid-catalyzed solution reaction. The Borden Co. (Murphy et al., 1969) holds a
unique patent for a process in which urea, paraformaldehyde, diammonium phosphate, potash, and a filler are blended together, heated and extruded through a die to afford a low bulk density fertilizer. The process reported here for the reaction of urea with paraformaldehyde worked well on a laboratory scale. As indicated by the data in Table 11, the amount of free urea in the final product is substantially reduced by the addition of Paraformaldehydeto the melt. In fertilizer applications where it is necessary to reduce the burn potential of a fertilizer by a reduction of the free urea present, it should be possible to condition the urea melt with 5 1 0 % paraformaldehyde to give a "super conditioned" urea with a low burn potential. Biuret is, of course, a potential problem for any ureabased fertilizer material. In this series of experiments it increased rapidly at the low paraformaldehyde levels in samples 1,2, and 7 as shown in Table 11. The biuret level was at a maximum with 5% paraformaldehyde and a 1-h reaction time, and the concentration was almost the same as the heated blank. When the concentration of paraformaldehyde was increased above 5%, the biuret concentration dropped off as shown in Figure 2. An explanation for the decrease in biuret with increasing paraformaldehyde lies in the fact that the MDU formed competes with urea for the available isocyanic acid producing BMU and thus holds biuret formation to a minimum. It does not appear that biuret formation would be a major problem for a commercial process built around the concept of "super conditioning" with high (5-10%) levels of paraformaldehyde. Summary A new compound, biuretmethyleneurea, has been isolated from commercial urea that has been conditioned with formaldehyde. The material is present, albeit in low concentration, in all samples of formaldehyde-conditioned urea that have been analyzed. The reaction of molten urea with paraformaldehyde has been examined and used to afford larger amounts of BMU for characterization. The melt reaction seems to hold promise as a new technique for ureaform preparation in general. Agro-economic studies on ureaforms made by this melt technique are currently underway at IFDC. Acknowledgment The authors thank Professor Thomas M. Harris of Vanderbilt University and Dr. Robert Radel of TVA for help in obtaining NMR spectra. R e g i s t r y No. BMU, 95935-98-1; MDU, 13547-17-6; DMTU, 15499-91-9; urea, 57-13-6; biuret, 108-19-0; triuret, 556-99-0; formaldehyde, 50-00-0.
Literature Cited Butler, A. E. U.S. Patent 3 129091, 1964. Clark, K. G.; Lee, J. Y.; Love, K. S. Znd. Eng . Chem. 1948, 4 0 , 1178. Clark, K. G.; Lee, J. Y.: Love, K. S.;Boyd, T. A. Znd. Eng. Chem. 1951, 4 3 , 871. Czurak, R. H.; Thompson, R. M. U.S. Patent 3989470, 1976. Davidson, A. 0. J. Assoc. Off. Anal. Chem. 1983, 66, 769. Fowler, C. W. "Chemical Technology Review No. 59, Urea and Urea Phosphate Fertilizers"; Noyes Data Corp.: Park Ridge, NJ, 1976. Greidinger, D. S.;Cohen, L.; Blaiik, K. U.S. Patent 4089899, 1978. Grealnger, D. S.; Girshowitsh, L. C.; Epstein, S. U S . Patent 4 173 582, 1979. Horowitz, W., Ed. "Official Methods of Analysis of the Association of Official Analytical Chemists"; 1960; 2.078-2.081. International Fertilizer Development Center (IFDC). "Fertilizer Manual" (also available from the United Nations Industrial Development Organization, Vienna, Austrla), IFDC: Muscle Shoals, AL, 1979. Murphy, A. M.; Retzke, F. A,; Johnson, J. R. U.S. Patent 3479 175, 1969. Murray, T. P.; Austin, E. R.; Howard, R. G.; Horn, R. C. Anal. Chem. 1982, 5 4 , 1504. Murray, T. P.; Horn, R. C. "Organic Nitrogen Compounds for Use as Fertilizers"; IFDC: Muscle Shoals, AL, 1979. Nobell, A. U.S. Patent 3 759 687, 1973. O'Donnell, J. M. U.S. Patent 3 198761, 1965.
425
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 425-431 O’Donneli, J. M. U.S. Patent 3 227 543, 1966. Renner, V. A. U.S. Patent 3231 363, 1966. Schafer, H. K.; Kohlhaas, R. US. Patent 3441 539, 1969. SchneMer, H.; Veegens, L. “Practical Experience With Ureaform Slow Release Nitrogen Fertilizer During the Past 20 Years and Outlook for the Future”; Proceedings No. 180, The Fertiliser Society of London, 1979.
Smith, J. A,; Formaini, R. E. US. Patent 3 150956, 1964. Still, W. C.; Kahn, M.; Mira, A. J . Org. Chem. 1078, 4 3 , 2923.
Received for review October 18, 1984 Accepted February 19, 1985
Surface Effects of Corrosive Media on Hardness, Friction, and Wear of Materials Kazuhlsa Mlyoshl,” Donald H. Buckley, George W. P. Rengstorff,t and Hlroyukl Ishlgakit National Aeronautics and Space Administration, Le wls Research Center, Cleveland, Ohio 44 135
An investigation was conducted to examine the hardness, friction, and wear behavior of MgO, Fe, and Ni exposed to corrosive medii. The results indicate that MgCl, films are formed on cleaved MgO surfaces from their interactions with HCI-containing solutions. The MgCI, films soften the MgO surfaces and cause high friction and considerable deformation. Neither the pH value of nor the immersion time in NaOH-containing, NaCI-containing, and HN0,containing solutions influences the hardness of MgO. NaOH forms a protective and low-frictionfilm on Fe surfaces at concentrations of NaOH greater than 0.01 N. NaOH at concentrations of 0.001-20 N forms a protective film on Ni that provides low friction and reduces damage due to wear. I n ordinary water the nickel surface sustains considerable wear damage.
Introduction
The presence of surface-active agents on metals and nonmetals can alter the surface activity of these materials as well as their mechanical properties (Miyoshi and Buckley, 1978; Westwood and Goldheim, 1968). Tribological properties such as adhesion, friction, deformation, wear, and lubrication of solid surfaces in contact are extremely dependent on the adsorbed surface-active ions or molecules (i.e., environmental constituents). It was anticipated that the hardness of solids would be influenced by environment because hardness is one of the measurements used to indicate the extent of surficial plastic deformation. Many investigators have studied the effects of environment on the hardness of a variety of nonmetals such as CaF2, A1,03, and LiF (Westwood and Goldheim, 1968; Westwood, 1962; Gilman, 1961; Westbrook and Jorgensen, 1965). These effects include strengthening by dissolution of the solid surface, the Joffe effect (Joffe, 1928); surface hardening, the Roscoe effect (Roscoe, 1936; Harper and Cottrell, 1950); surface softening, the Rehbinder effect (Rehbinder and Shchukm, 1972); correlation between hardness and the {-potential (Macmillan et al., 1973; Macmillan and Westwood, 1974); and the effect of adsorbed water on indentation creep (Westbrook and Jorgensen, 1965, 1968). Since environmental effects on the hardness of nonmetals are so surface dependent, we took a different analytical approach to determining environmental effects on hardness. A surface analytical tool (i.e., X-ray photoelectron spectroscopy (XPS)) was used to study the surficial or outermost atomic layers of solids. The first objective of the present paper is to examine the surface chemistry, hardness, friction, and wear of a ceramic (single-crystal magnesium oxide) exposed to varSummer Faculty Fellow. Research Associate.
8 NRC-NASA
ious corrosive media including two acids, a base, and a salt. Although corrosion is recognized as an important variable in the friction and wear of metals (Eyre, 1976),its role is not well understood. In the sliding, rolling, or rubbing contact of materials the surfaces become strained as a result of the mechanical activity that takes place. A wear surface is different electrochemically from its surroundings. It contains metal that is highly strained and that reaches locally high temperatures at shearing points or asperities (Bowden and Tabor, 1964; Rabinowicz, 1965). Electrochemical potentials may be established locally to either impede or enhance corrosion; cyclic stresses may promote stress corrosion and corrosive fatigue (Staehle, 1976). Resistance to corrosion is often the result of the formation of some type of film on the metal. Sliding action can destroy such films, or it can develop better corrosion-resistant films by producing new surfaces. The coefficient of friction is, like corrosion resistance, highly sensitive to surface films. The second objective of this paper is to examine the surface chemistry, hardness, friction, and wear of elemental iron and nickel exposed to various concentrations of NaOH and to water, as well as to analyze their surface chemistry by XPS. Materials
The arc-melted, single-crystal magnesium oxide used was 99.99% pure as determined from the manufacturer’s data. Magnesium oxide was selected as the material to examine for a number of reasons: its slip and fracture behavior are well understood, the Rehbinder effect has been observed with it, fresh, atomically clean surfaces can be prepared by cleavage, and it can be used as a bearing material (Dufrane and Glaeser, 1967). The iron used was more than 99.99% pure and had been fully annealed. Its hardness was Rockwell B40. The nickel used was electrolytic and had been annealed to a hardness of Rockwell B30.
This article not subject t o U S . Copyright. Published 1985 by the American Chemical Society
