I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1044
and silver. The precipitation after the first 3 days is retarded by the presence of nickel. Figure 6 shows that concentrations of the third element of from 0 to 0.01 per cent are most effective in changing the rate of precipitation of excess antimony and that increments beyond 0.01 per cent do not produce proportionately increasing effects. Discussion
The data presented in this paper definitely show that small quantities of certain elements when added to lead-1 per cent antimony alloys have a very marked effect on the rate a t which antimony is precipitated from supersaturated solid Bolution. Some suggestions of the mechanism of this change can be had from a consideration of the experimental findings in conjunction with the pertinent equilibrium diagrams. Although the literature shows that the third elements studied are insoluble in lead in the solid phase, no results have been reported on alloys containing these elements in very low concentrations. Even though they should be insoluble in lead, antimony may so change the lead lattice that they become soluble in lead-antimony. Furthermore, since these elements form either compounds or solid solutions with antimony, there are forces of attraction between them which may be strong enough to carry small quantities of the third elements, along with the antimony, into solid solution in the lead. The resulting ternary solutions, by their different energy relations, may cause the observed effects on the rate of precipitation of antimony.
Vol. 21, No. 11
Another explanation of the observed effects can be based on insoluble third constituents. Low concentration of third elements may be sufficient to form a large number of small particles distributed throughout the alloy. These particles may set up a great local stress tending to change the normal rate of precipitation. Higher concentrations of third elements may produce fewer and larger particles, setting up a comparatively smaller stress and not having so great an effect. There is an objection to this theory, however, because it is difficult to see how insoluble partides could cause the precipitation of antimony to be retarded, such as happens with the alloys containing nickel. Then again, if antimony forms compounds with the third elements in the ternary alloy, different conditions will be set up and the normal precipitation of antimony may be affected. The binary diagrams of copper, silver, manganese, and nickel with antimony show compounds, but since only the alloys containing nickel have low initial resistances (Figure 4), it seems probable that, if any compounds form a t all, only the nickel antimony compound NiSb remains insoluble in the ternary alloy when annealed a t 240" C. Nofe-If 0.100 per cent nickel is used i n forming an insoluble compound NiSb, it would remove approximately 0.2 per cent antimony from solid solution. This would cause a decrease in the initial resistance of the alloy to the value shown in Figure 4.
Literature Cited (1) International Critical Tables, Vol. 11, p. 415. (2) Schumacher and Bouton, J . A m . Chcm. Soc., 49, 1667 (1927) (3) Seljesater, Trans. A m . Ins;. M i n . Met. Eng., 76, 573 (1929).
Developments in Nitrocellulose Production' Everett P. Partridge 1440 EASTPAREPLACE,ANN ARBOR,MXCH
ITROCELLULOSE is an important material in the manufacture of many modern products. Rayon, artificial leather, lacquers, celluloid, photographic film, and smokeless powder are all related to each other by virtue of their production from cellulose that has been nitrated to a higher or lower degree. The rapid growth of the industries making these products and the increasing importance of these products in contemporary life are well known. One of the indications that cellulose has spread from the domain of forestry and agriculture to that of chemical engineering is the rate a t which the use of nitrocellulose lacquers has increased. Figure 1, drawn from the semiannual figures published by the Department of Commerce, shows the production of these lacquers in the United Statea from 1923 through the first half of 1928. At the time of writing there is no indication of any slackening in the upward climb of this production curve. * Inspection of Figure 1 shows that the production of nitrocellulose lacquers during the first six months of 1924 was somewhat under a million and a half gallons, while the production for the first six months of 1928 was slightly above twenty and a quarter million gallons. This very rapid increase in lacquer manufacture, caused largely by the demand of the automobile and other industries for quick-drying finishes suited to mass-production methods, and made possible by the post-war availability of large quantities of butyl alcohol, necessitated a simultaneous rapid development in the manufacture of nitrocellulose. This development was along
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Received July 12, 1929.
two chief lines-the expansion of manufacturing facilities to increase production, and the search for methods of reducing the viscosity of nitrocellulose solutions so that they might be utilized in higher concentrations than had previously been possible, thus reducing the number of coats required to produce a desired thickness of lacquer. These two lines of development are evident in the presentday operation of the Union plant of the Hercules Powder Company, which has produced an important fraction of the nitrocellulose used in lacquer manufacture. Some of the details of nitrocellulose production a t the Union plant are described in this article, together with the more important changes made during the period of rapid development. The different types of nitrocellulose produced will first be briefly mentioned. Types of Nitrocellulose Produced
Industrial nitrocellulose might be defined as a mixture of the nitric esters of cellulose together with such nitrated cellulose derivatives as are not completely removed in the process of purification subsequent to nitration. The properties of nitrocellulose differ with the degree of nitration, which, in turn, is controlled by the concentration of the mixed acids used in the nitration process and by the duration of this process. Products of different degrees of nitration are required for different purposes, as indicated approximately in Table I. The properties of nitrocellulose that are most important from the standpoint of utilization are: (1) solubility in
qiecifio solvents, (2) oaity of the solut.ions produced with these solvents, timi (3) the stability OF the filins rrsiilting from the evapor:ition OS these solutions. The solubility of nitrocellulose in a spccific solvent is a function of the degree and method of nitrntion, while the viscosity is controlled over quite a wide range by varying tlie niaiiufacturing processes subsequent to nitration. The stability of nitrocellulosc fihs appears to be hrgely depcnilcnt upon tlie dcgree of removnl during nianufacture OF substances other than nitrocellulose.
cosities, spccially prcparcd to hold bronze powders without curdling. (ti) Siber Lacquer Nitrocrlluloie, in 20bsecond and 70-second viscoeitics. for the prodisction of lacquers giving thin transparent films tor the protection of polished rnctal surlaces against tarnishing. (7) Dope Nitrocellulose, in viscosities from 20 seconds to 200 seconds, for the manufacture of artificial leather, waterproofing compounds. airplane-wing dopes, gas mantles, belt and film cements, and other nitroceI1ulose products. (8) Nitrocellulose especially prepared for the manufacture of pyroxyliii plastics.
All of these types of nitrocdlulose are made from the same raw tnatcrials and iii tire same p h t , the different properties being riroduced by vnriatkin of the tiitration and purification processes. Raw Materials Used in Manufacture
Fiaure I-Pruducflon of Nlrroeellulose I,'ac~"ers In the IInifed Stases In MiIIIOnSOf Gallons per IIalf-Year Period since 1923
Cellulose, nitric acid, and sulfuric acid are used in the nitration process. Large arnoonts of extremely pure water are required for waslring during tlie purification of the nitrated cellulose. ConsidertLble aniounts of ethyl, isopropyl, and butyl alcoliol w e required during the subsequent dehydration and in the shipping of the final product. The cellulose used a t the Union plant is supplied in t.he form of purified cotton linters by the Virginia Cellulose Company. As this company is a subsidiary, accurate control may he readily maintained over the raw material. This is important, since the properties of the finished nitrocellulose are affected quite considerably by tlie cliaracteristics of the raw linters, as determined by such factors as climatic and soil conditions and by t.lie cornpleteness OF the linter purification process.
(Drawn from Department of Commerce estimates.)
Tlie viscosity of nitrocellulose is referred to industrially in terms of the control test used during manufactiire. This test is of the falling-hall t,ype, a standard P/&ch hall-hearing being allowed to fall tlirongb a column of nitrocellulose solution contained in a glass tube 1 inch in diameter and 14 inches high. The time required for tlie ball to fall tlirougli the central 10 inches of solution ia taken as u measure of the riscosity, and the nitrocellulose is accordingly spoken OF as '%second" or "half-second" or oilier specification product. Tlie solution used is 12.2 per cent nitrocellulose (dry weight), 22 per cent denatured alcohol, 17.5 per cent ethyl acetate, and 48.3 per cent benzol, arid the teat is made a t 25" C. Table I-Indusfrid NlTROCP" CONTiiNT
Uses of NifrocelluleBE of Different
Nitration
sor.vznrs
Degrees of
cam* u5aY
USUD
P I , ten,
lU.7 to 11.2
11.2 to 11.7
Alcuhul~c.ainphorinlxturei l?flir.r-iilcol~ol rnixisires, methanol. ethyl acetate, nreioiiP, etc.
11.8 to 12.3
All common essei solvents. as ethyl. butyl, and iirlyl aceiaLe: nnd methanol. acetone. and a1roho:Letlirr
Cclliiloid plarlics PhoioXiriphiC tiinis. altot,olLs"luble 1IIcq"CTs.
n r t i k i r l silk Lacquers, r r t i f i c i o l teafhere, photosmphic films
mixtiires
hpprar. 13.0
Acetone
Smokclrrr lmwder, exploSiYW
The staridard types of nitrocellulose are: (1) Hel/-Second. which is widely used for automobile sud wood-finishing lacquers. (2) Four-Second, used for the same type of product where somewhat thinner final coats of lacquer are desired. (3) Eight-Sexed, used iii wood lacquers. (4) Fifteen-Second, used far lacquers for thin films, and for bodying lacquers or imparting waterproofing properties to shellac solutions. (5) B,onzii&g Nilroceilzrlore. in 40-second and 70-second vis-
Figure Z--Raw Maferial for Nifrocdlulose ManufactYre "deroi puritird ~ o i t o nlinters being cut and fed
10 nieclirnicrt
pickers
The linter purification is accompliahetlby pressure digestion in caustic solutions, using the mitterinl obtained as a hyproduct, from cottonseed oil mills. After digestion under specified conditions the linters are washcd hot and tlien cold, and are bleached. A second wash follows the bleaciring, after wliicli the piirified and bleached lint passes through continuous driers to baling and storage. A requisite of the linter purifieation process is a supply of pure water. Approximately 30,000 gallons of wat.er arc used per ton OS material. The preceding operat.ionis carried out at the Hopewell, Va., plant of the Virginia Cellulose Conipany. All the remaining steps in the manufacture of nitrocellulose, including the prcduction of the nitric acid used for nitration, are carried out at
alcohol while under a pressure of spproxirnately 2000 pounds per square inch. T h i s step is cnrried out. in lrydraulic prt such as the one illustrated in Figure 5 , The block of 11 crlliilosc, wet nox aitli nlculiol inste:d oi rrlitrr, is t,lien traiisierrcd by h m d t u a 1nee1i:inie:rl brealcer. The disintegriited mnterial frolo t,lie,bmiker is then packed in steel b:irrels with full rcniovable liexls and is sent to dlie storage and sliipping r00111. The nitrocellulose is iiow s:implcd and sent to the laboratory for coompkte esiimination. All through the operations tlie lots h a ~ ebeen kept separate and records are licpt of how ench lot h i s been trentcil. The weight and alcohol eontiant arc cheeked :it t,liis point, nnd alcoliol is added to bring the content up to 30 per cent, in wliicli state it may be shipped by either Freight or express under the 1nterst:itc Commerce Commission classificat.ion oi "lnflammable Liquid." The alcohol used in tlie dehydration process for disp1:iccnrcnt of the water is diluted in this process. It pnsscs from t,lx hydriiulic presses to a still phiit, wlicre it is rectified for use in the same process.
vading t l ~ cnitrat,ilig house. Whereas the steel sliell of a uieclrauiciil dipper hsts only about one year uiider sen-ice condibions, an csperiinent:il chrome-iron shell in use for two years gives evideiii:c :it the present time of an indefinitely long life. With the I:itt,er slioll eostinx :tpproximately five times as muell )IS the oiic in:ide oi st,i:c4, the lis(: of chronic iron for tlie dipping cqiiipnlent, ms ecmiouric:illy justified.
Improvements i n Manufircturing Operations
'PIP TJnion plant w:rs built in I915 for tlie production of nitrocrllrrlose for sniokelrss powder and for the production of smokeless powder. In 1919 that p i r t having to do with tlie pmihiction of smokeless powcler was dismantled :ind tlie rcmainder altered to mnnufacture nitrocellulose for industrid uses. Since that time a gr:rdud replncement oi buildings nnd equipment hiis taken place, so that now the entire p h n t is housed in permiinexit steel brick and concrete buildings. The improvements in manufacture have bcen made :ilorig four m:iin lines: (1) iricreasc in capacity by the repl:icement I'lCure S - - D e h y d r a r l n C Prel(~In W h i c h Wafer Is of small-capacity units by I:irge-cnpacity units, rather thmi P i c a a e d Out of Nirrocelluluae and Replaced by Alcohol by the dup1ic:rtion of the original small u n i t s ; (2) improvements in methods of material handling between steps in t,lie (>Imiiiii:iron hw :&I beori applied at many individual proccss; (3) utilizntioii of special materials, psrticuhdy poitits in t,he makiiig of nitr~~celhilosc.For example, the chrome iron, in the construction of eqoipmcnt in order tu eliminate cont:imin:it.ion of the product; and (4) impruve- nibrow fumes euh:rust,ed from the niechanical dippers were originnlly l~:iudletiby a fan composed of ;in aluminum runner ment in the degree of chemical control during processing. The change from small to large units is wcll illustrated by in i i case of asphnlt-covered wood. 'Phis fan, which broke the fact that the boiling tnbs used in the stabilizing processes down about once a month from one ciinse or another, has now used to be 8 by 8 feet, with a capacity of 1500 pounds, while been replaeed by a fan iabric;ited t.nt.ire1.y froni chrome iron, the r:ap:icity oi crrcli OS t,Iie present 18 by 12 foot tubs is 12,000 which has given no trouble at all in over it year of service. The pressure digesters used for the stabilizat,ion of low-vispounds. Materid handling has becii riintle largely mccli;inical. eosity uitrorellulose have also been eqitipped with chrome-iron Mamirrl labor is still iised for five transfer oper:itions, howeser. thenno-siphons to replace those made from extnt-heavy brass Ilnled cotton linters :ire cut and fed by hand to the meohnriicsl pipe, which used to fail with great regularity every three pickers, tlrc lint is similarly weighed out and chitrgcd to the weeks. As a result of the various improvements in rnethmxls of mechanical dippers, and a t the end of tlic irianufacturiiig cycle nitrated cotton is fed to tlie liydraulic presses by liund, the operation a t l l i c Union plant, comprising expansion of equip compressed cake is removed and transferred to t,liemcch;ruical nicnt, installntion of conveyirig dcvices, utilization of special bre:iker in tlie same may, and the disiiitograted materinl from materials of constrootion, and perfected chemical control, it the bre:iker is again transferred by hand to the shipping has been possible tu better the working conditions and the bsrrels. Throughout the rest of tlie operation all hnndling is wages paid to employees, to improve tho qmrlity of the prodmcchanicnl, wit11 tlie exception noted previously of tile scrap- uct, and a t tlre Same time to make timely and consistent reing out of the "wringer" into water. I'reccding nitration all ductions in tlie selling price of the product. handling is accomplished by means of continuous conveyors while subsequent to nitration the msterial is trtuisferred in suspensim in miter in closed systems. The thanks of the writer are due to the executives and The devclopmcnt of chrome-iron alloys has been of great euginecrs of the Hercules Pomicr Company for iuformation benefit in nitroeelinlose manufacture, because the use of these and assist.ance in the preparation of this article. materials not only reduces replacement labor and shutdown charges, but more especinlly because it tiids in producing a clear colorless product for iise in lacquers. While wooden tubs am1 brass pipe have always been used extensively, the advent oi chrome iron has caused a marked improvement. ihe Bureau of Mines, i n conperation with t h e University df The lining of the boiling tnbs with thin sheet chroiiie iron has Colorado, according to a stateement made public by the Departwell repaid the initial investment. Chrome iron is also in- meat of Commerce.
