V O L U M E 21, NO. 12, D E C E M B E R 1 9 4 9
1513
1 and 2 deviate considerably from the designated curve. T h a t this deviation of individual samples from the curve is a characteristic of the sample and not due to counting error was established by recounting, which always gave the same results. LITERATURE CITED I
1)
Ai n i b t i
wig, K-. I).,
and Schubert, Jack, ANAL.CHEY.,20, 270
(1948). (2) Dauben, 11'. G., Reid, J. C., and Yankwicli, P. E., Ibid., 19, 828 (1 947).
(3) Libby, W.F., I b i d . , 19, 2 (1947). (4) Reid, A. F., Weil, A . S., and Dunning, J. R., I b i d . , 19, 824 (1947). (5) Yankwich, P. E., Piorris, T. H., and Huston, John, Ibid., 19, 439 (1947). (6) Tankwich, P. E., Rollefson, G. K., and Norris, T. H., J . C'hern. Phys., 14, 131 (1946). (7) Yankivich, P. E., and Weigl, J. W., Science, 107, 651 (1948). RECEIVED April 25, 1940. Investigation supported by a research grant from the Division of Research Grants and Fellowships, National Institutes of Hralth, IT. S. Puhlir Health Servire.
Determination of Aluminum Nitride Nitrogen in Steel H. F. BEEGHLY Jones untl Laughlin Steel Corporation, Pittsburgh, Pa.
4 method for determining aluminum nitride nitrogen in steel utilizes solutions of the halogens in an anhJdrous aliphatic ester to dissol\e the iron matrix without decomposing the aluminum nitride in the steel. The residue containing the aluminum nitride is recovered from the ester-halogen solution and reaction products by filtration. The nitrogen content of the recovered aluminum nitride is obtained by the method for determining nitrogen in steel described by the author in an earlier paper. The ester-halogen method requires inexpensit e
N
ITROGEX and its compounds exercise a significant influence on the properties of steel and on its response to thermal rreatinent. Development of analytical methods which enable the total amount of nitrogen or the amount of a given nitrogen compound to be determined ~ i t ah minimum of time and labor is a prerequisite to most efficient resrarch upon the iiifluence of nitlogen in steel. Much intrrest in austenitic grain size of steel n a s aioused n hen .\Ic&uaitl and Ekin ( 2 7 ) published an account of their woik on the relation of grain size and heat treatment in 1922. Since then, the use of aluminurn in steel making for modifying such characteristics as grain size, strain sensitivitl-, and aging has become an accepted conimeicial practice. The role of aluminum in controlling these charscteristics has been investigated extensively ( 2 , 4-17. 19-2.5, SO, 31) and it has been postulated that they are governed by the presence of flee aluminum, aluminum oxide, :ind aluminum nitride. Considerable indirect evidence has heen ,recumulated regarding rach of these hypotheses, but direct experimental data arc meager (18). Recent investigations support the premise that aluminum nitride is perhaps the most impoitant tnctor in controlling the properties of aluminum-killed steel. Despite the well recognized need for a method of determining this compound quantitatively, a satisfactory procedure has heen lacking. The fractional vacuum fusion method, investigated for this purpose, involves the assumptions that only aluminum nitride nitrogen nil1 be liberated in the high temperature fractions and that the steel ill lose none of its aluminum nitride nitrogen a t Ion er temperatures. Results so obtained may be misleading. The writer has described a simple, economical method for determining combined nitrogen in steel ( 3 ) . The present paper describes convenient methods and reagents for determining its aluminum nitride nitrogen content quantitatively. The aluminum nitride is separated from the steel matrix and its nitrogen rontrnt is determined by the usual procedure involving steam
apparatus, is simple to use, and > ields highly reproducible results. It is not subject to interference from compounds of the elements commonly used in steel. The procedure is economical enough for routine use and sufficiently accurate and precise for research investigations. I t has been used successfully for a large number of analj ses in establishing the changes in the aluminum nitride content of steel caused by different thermal treatments and fabricating operations and in inrestigating deoxidation and steelmaking processes.
distillation in micro-Kjeldahl apparatus and the Sessler coloi reaction. The reagents used for separating aluminumnitride from steel are solutions of halogens in anhydrous aliphatic esters of organic acids; bromine dissolved in methyl acetate has been used most extensively. The ester-halogen method is useful for separating certain of the nonmetallic compounds such as aluminum nitride from steel in a form that enables them to be analyzed b y microchemical or spectroscopic methods and identified by x-ray diffraction techniques. The reagents and procedure are suitable both for research on the behavior of nonmetallic compounds in steel and for quantitative routine control analyses. Considerable research in chemical metallurgy and steelmaking \vas necessary in securing material to establish the validity of the ester-halogen method for the determination of aluminum nitride in carbon steel. -1detailed description of the work is not n-ithin the scope of this paper. Limited amounts of the data so obtained have been published (32) and those secured in other phases of the investigation will be presentrd in paprrs now in process of pub1ic:ttion. REAGENTS
The reagents required for the extraction of aluminum nitride from steel are bromine and methyl acetate of analytical grade. Those necessary for determining the nitrogen content of the alumirium nitride are given in an earlier paper ( 3 ) . APPARATUS
Aluminum nitride is most conveniently separated from stwl with reflux extraction units such as are illustrated in Figu,e 1. They consist of 200-ml. beakers connected to indented IVcsttype condensers by means of 55/35 standard-taper joints. -4 drying tube may be attached t o the t80p of the condenser by
ANALYTICAL CHEMISTRY
1514 means of a 24/40 joint when required. Loss of the volatile reagents from the apparatus is negligible when a 300-mm. barrel condenser is used. An electric hot plate adjustable through a range of temperatures is convenient as a source of heat. The usual arrangement for filtering with a Gooch crucible may be used. .\ sketch of the necessary apparatus for determining the nitrogen content of the residue is shown in Figure 2.
rk
S 24/40 OUTER JOIN?
INDENTED WEST TYPE CONDENSER W I T H DRIP T I P -300 MM BARREL
,-J.55/35 INNER JOINT
S 65/35 OUTER J O I N T
PROCEDURE
A Tyeighed sample is BEAKER - T A L L FORM 200 ML.- CAPACITY placed in the beaker, bromine is added, and the apparat,us is assembled as shown in Figure 3. I n general, a 1-gram sample Figure 1. Ester-Halogen will be convenient for alumiExtraction Apparatus num-killed Bessemer steels and a 3-gram s a m d e for scrap praitice open-hearth grades. The quantity of sam le should be varied, depending on the amount of aluminum nitrile present; 3 ml. (8.94 grams) of bromine for each gram of steel generally will be satisfactory. The flow of water is start,ed through the condenser and 2 ml. of methyl acetate (for a 1-gram sample) are added to the distilling flask in the assembled apparatus. The reaction initiated by the methyl acetate is exothermic and vigorous; when larger samples than 1 gram are used! proportionately less methyl acetate should be added initially and the first 6 to 10 ml. added in three or four incrementF. When the initial reaction subsides, 13 ml. of methyl acetate (or proportionally more if a sample larger than 1 gram is used) are added through t,he condenser t.o the sample, heat is applied to the flask, and the solvent is refluxed until the sample is completely dissolved. The resulting solut,ion is filtered through asbestos in a Gooch crucible, the residue is washed free from reaction products with methyl acetate, dried a t 105" C., and transferred to the digest,ion flask of t8hemicro-Kjeldahl unit, and its nitrogen cont,ent is determined by the same method used for steel ( 3 ) . The time necesxiiy for solution of the iron matrix in the esterhalogen reagent, varies with the composition and particle size of the specimens, but usually compares favorablj- to that of steel in the usual inorganic acids. The method of separating the residu? containing aluminum nitride from the ester-halogen solution may he varied to suit the purpose for which the residue is to be used. For example, the total amount of residue may be determined by using a weighed Gooch crucible; the carbon content of the residue may be determined by inserting the crucible and contents into the combustion train and determining carbon in the usual way. If the residue is to be examined spectroscopically or by x-ray diffraction methods, it may be collected on a filter paper or by means of a centrifuge.
of ester added is not critical and the reaction will proceed smoothly over a wide range in the amount of ester present. The amount of bromine used is not critical, provided a definite excess is present. The reaction products are readily soluble in the ester, and the residue can therefore be washed free from solvent quickly and easily. Water must, be avoided during solution of the iron matrix and during the washing operation following filtration, or low results will be obtained. The residues may be stored in a desiccator or in an o w n a t 105' C. Heating the residue in air to temperatures much in excess of 430" C. will cause loss of nitrogen. A blank is determined on the reagents in exactly the same manner as for the steel, except for omission of the sample. Inasmuch as standard steels with cooperatively established values for aluminum nitride content are not available, the practice of simultaneouslj- checking the extraction procedure and the nitrogen determination may be followed. Two samples of known uniformity, one of which is virtuall!. free from aluminum and therefore free from aluminum nitride and another which is aluminum-killed and known t o contain an appreciable amount of aluminum nitride nitrogen. may be used. Spectroscopically pure iron (containing less than 0.05cc total impurities) is readily available and is a good aluminum-free sample to use. Values in excess of 0.00057, nitrogen in the ester-halogen residue of this or any other aluminumfree sample, regardless of the original nitrogen content, are evidence of contamination of the residue. Failure to recover the usual amount of nitrogen in the ester-halogen residue from the aluminum-killed steel known to contain aluminum nitride is generally indicative of water in the ester or of exposure of the residue to moisture at some stage in processing. With the usual grade of reagents the blank correction is negligible and recovery of the nitrogen in the est,er-halogen residue is very consistent. The determination of a reagent blank should be made a daily practice, nevertheless. Consistent results cannot be obtained unless all apparatus is free from traces of ammonia. The amount of nitrogen in the residue from the ester-halogen extraction of commercial aluminum-killed carbon steels can be changed by subjecting the steel to suitable thermal treatments. Specimens tvith thermal histories identical with those of the physical test specimens must be selected therefore lyhen it is desired to correlate the amount of nitrogen in the ester-halogen residue with physical properties.
PRECAUTIONS
Bromine in the absence of the ester does not react with the steel so far as is evident from visual observation, even on prolonged contact with the steel a t the boiling temperature of bromine. A few drops of the ester will initiate the reaction, ham-ever, even a t room temperatui e and because the reaction is exothermic the temperature will rise to the boiling point of the solvents. Initial dilution of the bromine with ester is not a feasible means for controlling the rate of the reaction. But the rate can be controlled conveniently and effectively by adding the ester in small increments and thus restricting the amount in contact with the bromine in the initial stages of the reaction. Later the amount
STEAM
Figure 2.
Micro-Kjeldahl Apparatus for Determining Nitrogen in Ester-Halogen Residue
V O L U M E 2.1, NO. 1 2 , D E C E M B E R 1 9 4 9
__ Table I.
Recovery of Nitrogen with Different Steel Solvents Nitrocen in Residue. %" Al"min!lmkilled steel
Solvent Hydrochloric acid (1 : I ) Sulfuric acid (1:3)
Phosphoric acid (1:3) Hydriodic soid (1: 1)
0.0004 0.0006
0.0002 0.0002 0.0051 0.0049
0.0002 0.0003 0.0002 0.0003
0.0002
HydGobromio acid (1:1) Bromine-methyl acetate
Rimmedsteel
0.0005 0.0006 0.0007 0.0007 0.0002 0.0002
o.nnn5
0.0006 0.0004 0.0008
0.0003
Calculated om basis of weight of oridnal steel 88mple.
EXPERIMENTAL
Aluminum nitride in contact with water is known to hydrolyze and liberate ammonia. Primarily, the problem in isolating this compound from steel was one of finding reagents t h a t would dissolve the iron matrix without at. the same time decomposing any aluminum nitride present. A secondary problem was to find out what other elements or compounds would be isolitted along with tho aluminum nitride. Finally, i t was necessary to establish the aeouracy of the method and to determine the behavior pattern of aluminum nitride in steel in order to set up sampling techniques t h a t would enable the analytical results to be correlated with fabrieat,ing processes and physical test data in a significant manner. Reagents for Solution of Iron Matrix. Early in the work while st,udying synthetic aluminum nitride (AIR), prepared by the reaotion of high-purity aluminurn with nitrogen, it became apparent that, from a practical standpoint, aqueous solvents would not he feasible for use as reagents in isolating this component from steel. A search was made for reagents t h a t would react with &eel in the abmnce of lx.ater, and for solvents of these reagents and of their reaction products with steel. Of the reagents investigated, the hdogens and certain of their compounds appeared most promising; the elements bromine and chlorine and their anhydrous acids were known to react directly with steel in an anhydrous atmosphere a t elevated temperatures (66) but to be without significant effect a t room temperatures. From the stnndpoint of experimental teohnique, reactions a t high temperature are not attractive and results so obtained would not be necessarily indicative of the aluminum nitride content of the unheated steel. Two or more representatives each of the families of alcohols, ethers, ketones, esters, and organic acids m r e investigated as solvents for the halogens, for certain of their compounds, and for other inorganic compounds known to rea.ct with steel; carbon disulfide and carbon tetrachloride also were tried. Reagents investigated for dissolving the steel included the halogens, their acids, acid auhydrides, cornpounds such as mercuric chloride which dissolve iron by displacement, and various electrolytes. These substances were evaluated on bhe basis of: (1) rate ol attack on steel, (2) mutual solubility, (3) solubility of the reaction products in the organic solvent, (4) compatibility of the reagent and solvent st room and a t elevated temperatures, and ( 5 ) ahsence of undesired side reactions. The aliphat,ic organic esters wore superior to d l others as solvents when the experimental data were evaluated on the basis of the above criteria. The halogens were most promising as reagents for dissolving steel, for they met all the a.bove requirements in R satisfactory way. Bromine and iodine were selected for further study. Fortunately, these elements in the presence of esters reacted readily with steel a t temperatures which were eonvenient touse, and the reactionproductswereresdilysolubleinthe ester. A consideration. of the chemical and physical properties of these materials suggested t h a t methyl acetate or ethyl formate
1515 would be a good solvent for bromine, whereas butyl acetate appeared well suited as a solvent for iodine. The vapor pressure ourves of bromine and methyl acetate almost coincide, and this fact was of practical value in using these reagents. Semiquantitative trials on rimmed steel (aluminum-free) and aluminum-killed steels indicated t h a t the nitrogen contents of the residues from the aluminum-killed steels were significantly higher t,hsn those €ram the rimmed steels. D a t a are shown in Table I for later t,rials under controlled conditions with different reagents. These are d l on samples from single sets of millings from zn aluminum-killed and a rimmed steel. The results when bromine was used with methyl acetate were strikingly different from those obtained when l~queoussolutions m'ere used. This difforence between aluminum-killed and rimmed steels could not be distinguished by ordinary methods of analysis and strongly indicated that ester-halogen reagents would be suitable for isolating a nitrogen-containing constituent helieved to be aluminum nitride. Subsequent trials showed t h a t other esters could be used in place of methyl acetate if desired. Iodine may be uged in place of bromine but do= not react as rapidly.
Figure 3. Ester-Halogen Ap aratos Assembled Extracting Aluminnrn &ride from Steel
Cor
Identity of Nitrogen Compound in Ester-Halogen Residues. The spootrograph provided a simple means for determining what metals present in the original steel were retained in the esterhalogen residue. Residues separated from steels irith t,he ester-halogen solution were collected on a 4.25-cm. filter D ~ D Win a Biichner funnel by
.,
I
.
spectroscopic analysis: Care XGeiercijed to minimize the w a n -
photographed with a large quartz prism, Littrow-t.ypr s6ectrooranh
nect,ed in 6he residue."The r e d d s obtained KW; considered to be indicnt.ive of the amounts of a given metal in the residue, a s thc residues u w e all from the mmc initial quantity of st.eeel.
1516 Table 11.
ANALYTICAL CHEMISTRY X-Ray Diffraction Data for Aluminum Nitride
A. c = 4.QQ5 A. Observed Lines
a = b = 3.127
____ d(kX)
I/Io
2.70 2.38 2.50 1.56 1.417 1.322 1.83 1,303 1.350 1.188 1.247 1.133
1.00 0.89 0.71 0.65 0.57 0.48 0.43 0.20 0.12 0.09 0.04 0.02
Aluminum was present in the residues from all steels that contained nitrogen in the ester-halogen residue. The aluminum contents were very loir in the residues from the aluminum-killed steels which did not contain nitrogen in the ester-halogen residue. The amounts appeared to be about the same as those present in the residues from steels to which no aluminum had been added. The amount of aluminum present in the residue had no relation to the total amount of “acid-soluble” aluminum or nitrogen in the steel but showed a consistent correlation with the amount of nitrogen in the residue. Aluminum was the major metallic element in all the ester-halogen residues that contained nitrogen. The iron and manganese contmts of all the residues were very low, Silicon mas present in the residues from all steels containing silicon. Residues containing ester-halogen insoluble nitrogen were made into x-ray diffraction specimens and their diffraction patterns obtained using iron K-radiation and the usual Debye-Schemer method. Thepatternsof thesyntheticnitridegave data (Table 11) in agreement with those of Ott (29), but the initial trials with residues from the ester-halogen treatment gave dark filmh with little evidence that a crystalline material was present. Carbon in the residue, which appeared to be retained quantitatively from the original steel sample, was believed t o be responsible for thp unsatisfactory results. IVhen this carbon was eliminated. yatisfactory patterns were obtained yielding data in good agreement with those on the synthetic aluminum nitride. This later n as verified on residues from lowcarbon steels. I n these cases, the aluminum nitride pattern could be obtained without eliminating carbon. Thus the chemical, spectroscopic, and x-ray diffraction data all indicated that a definite compound, aluminum nitride, is a constituent of some aluminum-killed steels. Factors Influencing Recovery of Nitrogen in Ester-Halogen Residues. The preliminary work was carried out on steels known to contain only carbon, manganese, phosphorus, sulfur, aluminum (in some cases), the gases oxygen and nitrogen, and traces (0.01% or less) of other elements. It was necessary to determine whether variation in the proportions or purity of the reagents could be tolerated, and whether amounts of the various alloying elements and deoxidizers commonly used in commercial steels would interfere with recovery of the aluminum nitride in the ester-halogen residue. Initial efforts were devoted t o working out details of the method, so that reproducible results could be obtained. I t was assumed that a halogen in the presence of an ester nould react with the iron and other elements in steel in accordance with Equations I and 2 .
but would not react ~ i t compounds h having chemical properties like those of aluminum nitride. Early in the work it was discovered that the thermal history of the sample had a pronounced influence on the aniount of aluminum nitride in the ester-halogen t esidue. This additional variable was investigatecl.
P U R I T Y OF I ~ E A G E ? The ~ Teffect ~ . of changing the proportiom of the various reagents on the recovery of nitrogen in the esterhalogen residue was investigated by treating a 1-gram sample of \tee1 with different amounts of reagents and determining the nitrogen contents of the residue recovered. I t wa5 found that doublt the required amount of bromine may be used without significantl) changing the amounts of nitrogen recovered in the residue. The effect of varying the amount of methyl acetate used may be seen in Table 111; a very large excess of the ester may be used without appreciable effect on the recovery of nitrogen. Quantitips of less than 15 ml. per gram of steel are inconvenient to worl3 with, however, and mechanical loss of the sample may occur. Different quantities of water were added to methyl acetate to determine how seriously the presence of this compound in the reagents would affect the results. The effect of water was to decrease the amount of nitrogen recovered. The time of contact of the water, as well as the amount of mater present, has a bearing on the amount of aluminum nitride decomposed. Table IV shows the serious effect of water on the recovery of nitrogen in the ester-halogen residue. The same steel used in the earlier esperiments was used in securing these values and the extraction procedure was as described previously exrept that the residue was washed with hot water or sodium bicarbonate as indicated in Table IV instead of with methyl acetate. The residue was ~ a s h e d by filling the Gooch crucible 13 ith wash solution while the vacuum line Ivas open, allowing it to drain empty, and then refilling. The wash with water decomposed more than half of the original nitrogen in the residue and the loss was even greater with sodium bicarbonate. Methyl alcohol in the methyl acetate lowers the amount of aluminum nitride nitrogen recovered. The loss of nitrogen may become greater as the time of contact is prolonged; there is visual evidence of side reactions (the condensate becomes water-tvhite) which use up a portion of the halogen and an insoluble black deposit contaminates the residue trom the steel
Tahle I l l .
Keco\er> of Nitrogen with Different 2Zethql 4cetate Concentrations
ReAgents Used, hI1. Methyl acetate
Sltrogen Hecoverrd. L;“
CirT-
0.0042 0,0049 0,0053 n , 005s 0.0052 0.0058
IO 15 30 60 90
” Calculated on basis of weight ~~
of original steel sample.
~~~
Table IV.
Recovery of Nitrogen after Wash with Fater or Sodium Bicarbonate
K a s h Solution
S o . of Wawhes
Hot water S a H C O i , 15%
!li) O
Methyl acetate Q
Total Tolumr of Wash, .\I1
Nitrogen Recovered, % a
580
U.UUII
320
0.00%
10
15 10
Calculated on basis of weight of the original steel sample.
Variation in the amount 01 proportion of either the bromine or the ester or in the time of contact is without significant effect on recovery of nitrogen in the residue. CowosITIox OF S A m m c . The u3e of complex deoxidizers (ferroalloys containing selected proportions of two or more elements) is relatively common in steelmaking practice. I t was necessary to determine whether the elements in the more commonly used of these alloys would react v i t h the nitrogen in steel to form compounds that nould appear in the residue from the est er-halogen treatment.
V O L U M E 2 1 , NO. 1 2 , D E C E M B E R 1 9 4 9 Table V.
1517
Effect of Alloying and Deoxidizing Elements on Acid-Soluble Nitrogen Content of Ester-Halogen Residues Acid-Soluble
- Xitronen, % P
S
1.03 0.37 1.87 0.32 0.13 0.39 1.78 0.88 0.97 0.47 0.48 0.42 0.36 0.32
0.008 0.004 0.006 0.003 0.023 0.088 0.102 0.017 0.020 0.097 0.021 0.019
0.030 0.030 0.031 0.040 0.036 0.004 0.004 0.025 0.032 0.022 0.041 0,394 0.400 0.009 0.019 0.080 0.020 0.018
0.00001
0.001-
0.003
0.43
0.34 0.31 1.06
0.012 0.020 0.017 0.028 0.027
0.OOi
Pi 0.01 0.01 0.01 0.08 0.05 0.47 0.64 0.06 0.03 0.15 0.23 0.03 0.05 0.34 0.25 0.01 0.01 0.01 0.001-
C'ii
A1
R
1181
Si
Ti
%r
0.21 0.63 1.45 0.26 0.17
. . .... .... . . .
1.06
....
0.05 0.14 0.009
. .
.... 0.0008
0: 8 9 ' 0.611
..
....
....
... . . . . . . . . . . . . . . . . . 8:99' 0.13 0.003
18183' ' 1.29 0.004
. . . . . . . .
Several reries of heats were made in the induction furnace using wrap from a single heat selected for its low content of residual alloying elements. Some of these heats were of approximately t h r same composition as commercial grades of carbon steels, but nitrogrn in the form of ammonia and a different alloying or "deoxidizing" element \vas added to each. These elements were atltlcd in a relatively pure form, rat,her than as commercial ferro:rlloys which generally contain appreciable amount,s of one or mort' deoxidizing elements in addition to the principal one. These hcsats were rolled into bars in the laboratory mill, millings from the cross section of these bars in the as-rolled condition were est,ractcd b y the ester-halogen method, and the acid-soluble nitrogen in t,he c > $t c,r-h:tlogen resitiur \vas dc t clrnii ned. Some typical results for thcse steels in the as-rolled condition :Ire shown in Table i-, which also gives the amount of acid-soluble iiitrogen and of :illoying element in the steel, and the amouiit of :icid soluble nit1,ogeri in the ester-halogen residue. Similar information is shown i n this table for Sational Bureau of Stanchrds s:iniples 106 (rl'itralloy Gj, lOla (18-8 stainless), 8f (Bessemer), a n d high-purit y (spectroscopically inspected) iron. The acid-soluble nitrogen in the steels treated iyith such eleincints as titanium and vanadium is low. Elements, of which these are examples, mag form "acid-insoluble" nitrogen conipounds \vliich are not decomposed during the ester-halogen extraction and may appear in the ester-halogen residue along with tho aluminum nitride. The acid-soluble nitrogen of ester-halogen residues from such steels can be determined in the usual way, while the acid-insoluble nitrogen may be determined on a second sample following a digestion treatment to decompose the compouiids in Lvhich it is held; or the acid-insoluble nitrogen may lie iel):rrnted from the acid-soluble (which will include nluminuni riitritie) by use of dilute aqueous solutions of inorganic acids. .-I tlige3tion treatment for decomposiiig these acid-insoluble nitrogen compounds has been described (I). [Since preparation of this ni:tnuscript an additional method for decomposing acid-insoluble nitrogen compounds in steel has been described (16'iI).] Of all the elements added-aluminum, boron, vanadium, titanium, zirconium, copper, molybdenum, chromium, aut1 nickel-only the steels treated with aluniinum and zirconium contitined acid-soluble nitrogen compounds that appeared in the residue from the ester-halogen treatment. If both these elements are present in the same sample, it would be necessary to determine the acid-soluble nitrogen and either the acid-soluble zirconium or aluminum in the ester-halogen residue; from the information SO obtained the amount of nitrogen combined with each could lie determined. The relation between various thermal treatments and the eltsments that are recovered in the ester-halogen residue from a given grade of steel can best he determined for each grade of steel; a deseript'ion of such investigations is not within the scope of this paper. The rster-halogen reagents appear applicable for many types of
0.00006
....
. ,. . . . .
....
0.030 0.008 0.003
......... 0.0015
...
0.73 (1. e0
. .
..
. . .
...
1.03 0.01 0.16 0.001
0.00005
1, OG
. ....
0 : 039 0.024
0.0001
...
, .
, .
o:iz
0.19
.....
0.023 0.023
0.00005
.... ....
..
0.0001
..
Steel
Residue
0.027 0.008 0,015 0,010 0.017 0.001 0.001 0.001 0.002 0.025 0.019 0.015 0,015 0.044 0,009 0.015 0,009
0.010
0.027 0.0075 0.014 0.0092 0.016 0.0012 0.0011 0.0007 0.0017 0.023 0.015 0.0005 0.0005 0.0009 0.0087 0.0005 0.0062 0.0070
0,004
0.0002
Table \ I.
\itrogen Contents of Ester-Halogen Residues after Heating in i i r at Various Temperatures
Temueratiire of IIcatirig, C 340 430 540 650 YO0 a b
Time a t Ti>inyPratuir \Iin 10 10 10
10 10
Sitroprn beforr Ileating, r c 0.0047 0,004T 0,004i 0,0047 0 . 0047
YltI O Y E l l aftei Heating, r G r i 0.0014 b 0.0041 0.0038 0.0036 0.0018
Calculated o n ha\i. of n.i.iglit of original s r w l saliilJle. Carbon not all eliiiiinnted.
alloy steels arid have i~iterestingpossibilities for use as etchants; their application to a specific problem should be preceded by some exploratory work to establish the most favorable conditions for their utilization. The ester-halogen method is not subject to interference from the elements commonly present in carbon steels, although tn.0 samples of identic:tl composition may give widely differing values for acid-soluble nitrogen and for aluminum nitride as a result of :idifference i n thermal treatment or processing rendition. This fact must be taken into consideration in evaluating the reproducibility and ac'curacy of the method and in correlating results obtained with it with physical properties. THERMAL HIsToRY O F SA\IPLE.hluminuni nitride has beeri reported to have a decomposition temperature of 1400" C. or greater (25) n.hereas free carbon osidizes.at a substantially lower temperature. I t appeared that carbon could be removed from the ester-halogen residue by direct oxidation without decomposing the aluminum nitride. Several samples of a steel having a knoxn amount of ester-halogen insoluble nitrogen were extracted, their residues were heated in air by means of an ordinary muffle furnace for 10 minutes a t various temperatures, and their nitrogen contents were determined. They are shown in Table VI along with the temperature of the muffle. An appreciable loss of nitrogen from the residues occurred in air a t the higher temperatures but only a slight loss resulted in 10 minutes a t a muffle temperature of -130"C. These conditions were used to eliminate carbon from the residues when preparing samples for x-ray diffraction work. In all cases where this was required, duplicate samples were extracted and heated under identical conditions. One was retained for x-ray work, while the nitrogen content of the other was determined in order to make certain that a large loss of nitrogen was riot caused by the heating operation. Data such as are given in Table V I suggested that the thermal history of the steel sample nould have an important bearing on the amount of nitrogen that tvas recovered in the ester-halogen residue. This assumption was consistent with other experimental data indicating that some aluminum-killed steels contained aluminum nitride in substantial quantity, whereas others con-
1518
ANALYTICAL CHEMISTRY
Table VII. Relation between Temperature, Time, and Ester-Halogen Residue Nitrogen Contents of Killed Steel Time a t Temperature, Hour
Temperature, C. Hot rolled
0
Residue Sitrogen, '36"
..
100 260 490 620 730 820 960 1150 1290
REPRODUCIBILITY AND ACCURACY OF METHOD
0.0019 0,0023 0.0019 0.0027 0.0052 0.0122 0.0117 0.0119 0.0068 0.0013
1 1 1 1 I 1 1 1 1
Ten I-gram samples from a single set of millings were treated with t8heester-halogen solution under routine conditions and the nitrogen contents of the residues were determined; 3 ml. of bromine and 15 ml. of methyl acetate were used in every case, but no two extractions were made on the same day. The maximuni value obtained was 0.0057% and the minimum was 0.00507c nitrogen. The average for the series of ten runs was 0.0054%,. .4 series of samples from commercial steels and from experimental heat's made from commercial scrap selected for its low con tent of residual alloys was extracted in the same manner.
Calculated on basis of weight of original steel sample,
010
-
-20
I _
120
260
400
540 680 820 TEMPERATURE OC.
this compound in steel to the physical properties of the metal The simplicity of the method recommends it as an economical research tool.
960
It00
1240
1380
Figure 4. Aluminum Kitride Nitrogen Content of EsterHalogen Residues from Steel Heated for 1 Hour at Different Temperatures
taining identical amounts of aluminum and nitrogen contained virtually no aluminum nitride in the ester-halogen residue. The validity of this assumption was supported by experimental evidence, of which that in Table VI1 for a commercial aluminumkilled steel is typical. The analyses for aluminum nitride nitrogen shown in this table are on different portions of the same piece of steel after they had been heated for 1 hour a t different teniperatures and then cooled quickly in water. Figure 4 was constructed from these values. h very pronounced increase in aluminum nitride content of the residue occurred on the specimens heated in the range of about 620' to 1150"C. Table VI11 shows aluminum nitride nitrogen values on heats of commercial steel sampled a t different stages in processing. It is evident from a study of this table that a marked difference in the amount of nitrogen in the ester-halogen residue existed a t different stages in processing. It is apparent from the foregoing that the amount of nitrogen in the ester-halogen residue can be made t o vary by suitable thermal treatment and that it changes during commercial fabricating operations. These facts must be taken into consideration by the chemist when selecting samples for aluminum nitride analyses, as well as by the metallurgist who wishes to correlate physical properties with analytical results and by operating personnel who wish to produce a uniform product. A change in the aluminum nitride content in the ester-halogen residue of carbon steel is not necessarily accompanied by any change in either the total or the "acid-soluble" nitrogen or aluminum contents of the steel as determined by conventional methods. The ester-halogen method provides a feasible and economical procedure not available heretofore for investigating the effect of different thermal treatments and processing operations on the behavior of the compound aluminum nitride in steel, and for relating the amount of
The acid-soluble aluminum, total nitrogen, and nitrogen in tiit ester-halogen residue of these samples in the as-rolled contiitioi. are shon-n in Table IX. The reproducibility of the results on thest tests TWJ excellent, but there is no consistent correlation betweel, either the acid-soluble aluniinum coiiteilt of the steel and residuc nitrogen content, or the total nitrogen content of the original step; and that of the ester-halogen residue. This lack of correlation ivery evident in comparing values on samples -116 and 8107. Tht steels for which data are show1 in Table I X were selected to preclude the possibility that results might be influenced by t h e presence of alloying elements in different amounts or of a deoxidizer other than aluminum. Spectroscopic examination of additional residues extracted from these steels showed a close correlation between the aluminum content of the residues and their nitrogen contents. Samples A26 and A107, for example, had about the same amount of aluminum in their residues; this amount was appreciably greater than t'hat in the residues from samples such as A28 and A4. Residual alloying elements commonly present in carbon steels n-ere virtually absent from tlic spectra of these residues. The typical values in Table I X show that the reproducibilitj of t,he ester-halogen method under routine conditions is superior t o that of many of the commonly used methods of analyzing metal? for other constituents. I n no case was t'here a high recovery of' the nitrogen in the ester-halogen residue from steels that were virtually free from aluminum. hlthough the reproducibility oi the results was good, not all the steels containing aluminum coiit,ained all or even a major portion of their original nitrogrJn i n tht ester-halogen residue.
Table VIII. Ester-Halogen Residue Nitrogen Contents of Killed Steel at Different Stages in Processing Hot Rolled, '36 Annealed Sample * Slab Sheet Sheet, R 0.0046 0.0036 0.0032 0.0044 0.0028 0.0027 0
0.0008 0,0005 0.0004 0.0007 0,0006 0,OOOR
0,0057 0.0028 0.0034 0.0053 0.0031 0,0036
Calculated on basis of weight of original steel sample.
The quantitative recovery of alumlnunl nitride from steels COII taining known amounts of the compound could not be checked 111 the conventional manner, because standard samples or other methods of analyzing for this compound were not available to use as a basis for comparison with the ester-halogen method. Substantially all the nitrogen in a nuinber of steels \vas recovered ir the ester-halogen residue, however (note samples 12 to 16, in c h i v e , and B.S.106 in Table V). The excellent reproducibilitj of the method on duplicate analyses from the same set of millings and the recovery of all the nitrogen in some steels as aluminuni nitride indicate the method is quantitative, as does the fart that when investigating thermal treatments, rz given treatment n-hid
1519
V O L U M E 2 1 , NO. 1 2 , D E C E M B E R 1 9 4 9 ACKNOWLEDGMENT
fable 1X. Reproducibility of Nitrogen Recovery in Residue from Ester-Halogen Treatment of Carbon Steels Composition, % Sample Identity Weight,
Steel
x
Nitrogen in residue“
4 10
1.0000 3,0000 3.0000
0,013
0.011
0.0011 0.0007 0.0009
4 11
1 0000 3.0000 3.0000
0.014
0.023
0.0012 0.0012 0.0014
4 12
1.0000 3.0000 3.0000
0 . no3
0.003
0.0006 0.0003 0.0003
4 13
1.0000 3,0000 3.0000
n . 004
0.019
0,0005 0.0004 0.0002
1. ooon
n . 006
0.004
0,0005 0.0002 0.0003
4 15
1.0000 3 . ooon 3.0000
0.006
0,023
4 16
1.0000 1.0000 3.0000
I). 023
0.019
0.0019 0.0023 0.0014
4 27
1.0000 1.0000
0,012
0,015
0.0005 0.0003
4 28
1.0000 1. ow0 1IO000
0.075
0.018
0.0023 0.0022 0.0026
4 3
3.0000 3,0000 3.0000 3,0000 3,0000 3.0000
0.031
0.002
0.0008 0.0012 0.0007
0,044
0,008
0 . oooa 0.0009 0.0009
1.0000 1.0000 1 0000 1,0000
(1.11
0.019
0.012 0.013 0.013 0.012
1.0000 1.0000
0.025
0.020
0.012 0.012
4 14
g
3.0000 3.0000
44
4 26
AI
~
4 107
’ Calculated
’
0.0011 0,0008 0,0008
on basis of weight, of original steel sample
HEM., 4N.41.. ED., 14, 137-40 (1942). (4) Bolsover, G. R., J . Iron Steel Inst. (London). 119, 473-500 (1929). (5) Case, S. L., Metal Progress, 32, 669-74 (1937). (6) Davenport, E. S., and Bain, E. C., Trans. Am. Soc. Metals, 23, 1047-106 (1935). (7) Ehn, E. W., J . Iron Steel Inst. (London), 105, 157-200 (1922). (8) Eilender, W., Cornelius, H., and Knuppel, H., Arch. E i s m hiittenw., 8, 507 (1935). (9) Eilender, W., Cornelius, H., and Menzen, P.,’Ibid., 14, 217-21 (1940). (10) Eilender, W., Fry, A,, and Gottwald, A . , Stahl u. E b e n , 54, 55464 (1934). (11) Epstein, S., “Alloys of Iron and Carbon, Vol. I, Constitution,” pp. 371-96, New York, McGraw-Hill Book Co., 1936. (12) Epstein, S., Proc. Am. SOC.Testing Materials, 32, Part 11, 293379 (1932). (13) Epstein, S., and Rawdon, H. S., J . Research NatE. Bur. Standards, 1, 423-56 (1928). (14) Graham, H. W., Year Book American Iron Steel Inst., 22, 69114 (1932). (15) Graham, H. W., and Work, H. K., Proc. Am. Soc. Testing Materials, 39, 571-82 (1939). (16) Grossman, M. A,, Trans. Am. Sac. Steel Treaters, 16, 1-56 (1929); 18, 601-31 (1930). (16a) Hague, J. L., Paulson, R. A,, and Bright, H. A., J . Research NatE. Bur. Standards, 43, 201-7 (1949). (17) Halley, J. W., Trans. Am. Inst. Mining Met. Engra., 167, 224-36 (1946). (18) Holloman, J. If., and Jaffee, L. D., “Ferrous Metallurgical Design,” p. 18, New York, John Wiley & Sons, 1949. (19) Houdremont, E., and Schrader, H., Arch. Eisenhiittenw., 12, 393404 (1939). (20) Jungbluth, H., Ibid., 4, 533-6 (1931). (21) Kenyon, R. L., and Burns, R. S., “Age Hardening of Metals,” pp. 262-313, American Society for Metals, 1940. (22) Kenyon, R. L., and Burns, R. S., Proc. Am. Soc. Testing Materials, 34, Part 11, 48-58 (1934). (23) Koster, W., Arch. Eisenhiittenw., 2, 503-22 (1929) (24) Ibid., 3, 637-58 (1930). (25) Low, J. R., Jr., and Gensamer, M., Trans. Am. Inst. Minino Met. Engrs., 158, 207-49 (1944). (26) Lundell, G . E., Hoffman, J. I., and Bright, H. A., “Chemical Analysis of Iron and Steel,” pp. 404-25, New York, John \Tiley & Sons, 1931. (27) McQuaid, H. W., and Ehn, E. W., Trans. Am. Inst. Minino Met. Enors., 67, 341-91 (1922). (28) Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. VIII, p. 114, New York, Longmans, Green and Co., 1931. (29) Ott, H., 2.Physik, 22, 201-14 (1924). (30) Swinden, T., and Bolsover, G. R., J . Iron Steet Inst. (London), 134, 457P-546P (1936). (31) Work, H. K., and Case, S. L., Trans. Am. SOC.Metals, 27, 771-83 (1939). (32) Work, H. K., and Enzian, G. H., Trans. Am. Inst. Mining Met. E n g ~ s .162, , 723-33 (1945). RECEIVED .Tune 13. 1949.
