Chemicals
APPLICATIONS OF NICKEL COMPOUNDS IN CERAMICS CAMERON G. HARMAN
AND
BURNHAM W. KING
Battelle Memorial Institute, Columbus, Ohio
A
large portion of the nickel consumed by the ceramic industry i s supplied in the form of oxides or sulfates. The utility of these compounds i s based on a relatively small number of their inherent properties. O n e ol the first of these i s the ability of nickel oxide to absorb light selectively, as, for example, when the oxide is used to produce a colored glass or a colored pigment. A second use of nickel depends upon the ease with which nickel can b e replaced by iron, as i n a plating solution. The use of nickel i n porcelain enamel ground coat compositions i s dependent upon the ability of nickel to promote the adherence of the enamel to iron and upon the effect of nickel on the viscous properties of the enamel. Nickel oxide i s used in ferrlte-type compositions as a means of improving the magnetic and electrical properties of these materials. The use of metallic nickel i n the ceramic industry i s due mostly to the properties obtained i n nickel-bearing alloys. Such materials owe their utility to such qualities as good oxidation resistance, high fusion temperature, and good corrosion resistance. Their use i n thermocouples i s dependent upon their high thermoelectric power, which is also proportional to the temperature to which the couple i s exposed. The various uses i n the ceramic industry of nickel and nickel compounds are discussed in some detail. Most of the discussion concerns ceramic products in which nickel compounds form some part of the composition. In addition, a brief review i s given of the use of nickel i n equipment for the production of ceramic products,
HE use of nickel in the ceramic industry is dependent largely on the rather unusual properties of the oxide. In some applications, nickel gives results which cannot be duplicated by any other material. Compounds of nickel probably were first used in the ceramic industry because of the colors which they imparted t o glasses, glazes, or enamels. A review of the literature shows that a wide variety of cokrs have been obtained by adding nickel oxide to glazes. The colors reported include violet, blue, green, yellow, red, brown, and gray. In general, except for the brown or t a n glazes, the colors were rather difficult to reproduce consistently. One old English potter is said t o have advised his son never t o uae nickel for colors. In spite of this advice, nickel is still being used and probably could be used even more where rather unusual decorative glazes are desired. Compared with most colored oxides, nickel oxide is relatively insoluble in most glass compositions and, therefore, lends itself more readily to the spotted or streaked effects sometimes desired in a r t glazes. For more uniform colors, nickel is often used with manganese to give a wide range of browns. One-coat brown porcelain enamels are sometimes produced by the addition of these two materials to the frit. The color may then be further controlled by the addition of a color oxide during milling of the enamel. Nickel can be used in small quantities t o modify another color. Some of the early Chinese blue glazes owe their pleasing effects to the presence of small amounts of nickel, iron, or manganese. Such additions sometimes now are made intentionally t o produce a more desirable color. The explanation of how nickel acts as a colorant in glass has been outlined by Weyl(3). He reports that the state of oxidation of nickel oxide is not affected by a wide variation in the oxygen
pressure over a molten glass, and that nickel is present in solution in the glass as the divalent ion only. However, the color of the glass may range from purple to yellow, depending on the coordination of the nickel ion. For glasses in which the nickel atom is surrounded by four oxygen atoms, the glasses show three absorption peaks, as illustrated in Figure 1. The net effect is that the glass appears purplish. When the nickel atom is surrounded by six or more oxygen atoms, only a single absorption peak a t 440 mp exists, as illustrated in Figure 2. Such glasses appear yellow. Varying the conditions which alter the coordination of the nickel atoms shifts the color from purple to yellow. This is illustrated by the effect of temperature, as shown in Figure 3. Increasing temperature decreases the number of oxygen atoms surrounding the nickel atoms, and the color shifts from yellow to purple. Similar effects can be obtained by changing the glass composition. The rather unusual blues or green produced in the presence of zinc oxide are explained as being oaused by the covalent nature of the bond in this material.
T
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Wavelength, millimicrons Figure 1. Extinction Coefficient versus Wave Length for Glass Nickel atoms surrounded by four oxygen atom I’
lolO-Ecd
I
Nickel oxide-containing glasses show relatively little absorption of ultraviolet light, but relatively high absorption in the visible spectrum. It is possible, therefore, by the use of nickel oxide, to make glass which will transmit ultraviolet light, but absorb visible light. Sometimes this effect is aided by the addition of a small amount of cobalt oxide. Sickel oxide with cobalt oxide has been used to a limited extent as a decolorizer for crystal glass. Very little information has been published regarding the effect of nickel oxide on the properties of glasses other than their lighttransmitting characteristics. Nickel oxide has been shown to increase the surface tension of a soda-lime silica glass. On the other hand, nickel oxide increases the rate a t which a soda-borosilicate will wet iron oxide. Glasses of the latter type will dissolve only between 5 and 10% of nickel oxide without the precipitation of a crystalline phase. A large proportion of the nickel consumed by the ceramic in-
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dustrj is used in the preparation of baths of nickel salts coinmonly employed a8 a means of preparing iron for porcelain enameling. Originally, such nickel treatments provided a little extra insurance in the enameling operation. The presence of a light film of nickel promoted better adherence between the glass and the metal and also reduced minor defects which were caused largely by excessive oxidation of the iron. The baths used contained 4 ounces of double nickel salts per gallon and were operated a t a p H of from 5.6 to 6.4 and a temperature of 160" to 195' F. The usual time of immersion n as 5 to 10 minutes.
Ni
'+
0.5
0.0
400
500
600
W a v e l e n g t h , m iI limicrons Figure 2. Extinction Coefficient versus Wave Length for Glass Nickel atoms rurrounded bv six or more o x w e n atoms I' = IofO-Etd
More recently, there has h e n a shift in practice, and nickel has been used more directly for the promotion of adherence. For this purpose, it has been found desirable to use ll/t ounces of single nickel salts per gallon and to maintain the pH a t about 3 and the temperature a t about 170' F. The time is adjusted to give a deposit of about 0.1 gram of nickel per square foot. This usually requires about 5 minutes. By careful control of the cleaning, pickling, and nickel dipping operations, it is possible to produce satisfactory adherence of porcelain enamels to iron without the use of the customary ground-coat enamel. An operation of this type is commercially practicable if the enameling is done on a nonboiling metal, such as a titanium steel. The Westinghouse Manufacturing Go. has produced enameled range tops on a production scale without using a ground coat. Investigations of these nickel deposits have shown them to consist of a very thin and porous layer of metallic nickel particles. During the firing of the enamel, this layer first partly protects the iron, and then later is wet by the enamel. It is even possible that some of the nickel which is in direct contact with the iron base alloys with it. The net effect is the production of a thin interfacial layer which aids materially the adherence of the enamel. Nickel oxide has been a rather conimon addition to groundcoat enamels as a means of promoting a better bond between the glass and the metal. The amounts used range from 0.5 to 2%. Relatively high nickel contents have been more effective in very low temperature enamels, such as those fired a t 1300" F., whereas 0.5% is more typical of those which are fired a t 1500' F. Ordinarily, nickel oxide is used in conjunction with cobalt oxide and manganese oxide in ground coats, but Some one-coat brown enam1016
els contain only nickel and manganese. The nickel oxide iri enamel compositions is rather easily reduced to the metal. Such a decomposition may take place even in a, neutral atmosphere. I t may be that this propert); is responsible for the usefulness of the oxide as an adherence promoter. Of recent commercial importance has been the developmeiit of ferrites for use in electrical equipment. T h a e oxide materials have many of the properties ordinarily nssociated with mctals. Many of the ferrites, which have the general formula R0.FcL03, are ferromagnetic, and, in addition, they have larger fipccific electrical resistance than metallic alloys. Thus, the eddy-current losses with these materials are relatively lorn. The best known ferrite is magnetite, FeaOa, which can be considered to he a compound of 1 mole of FeO and 1 mole of Fe&. The propertics of this compound can be modified by the substit'ution of other divalent atoms of suitable size for the divalent iron. Of the materials available, nickel oxide or nickel oxide in combination with zinc oxide produce ferrites of very 6escellent properties. The addition of zinc oxide depresses the Curie point to a lit'tle above room temperature, and the addition of nickel oxide produces a material having a high saturation magnetization and a not too high initial permeability. It is also desirable that the RO compounds do not easily lose oxygen a t high temperatures nor take up so much oxygen at l o x t'emperatures m to cause thc ferrite to become unstable. All these conditions are fulfilled by a ferrite-containing nickel and zinc atoms in the ratio of 15:35 and containing iron atoms in a proportion a little less than 50% ( 2 ) . Such materials are now finding wide usage in transformer cores and in choke coils. Single crystals of nickel ferrite were grown by Galt, Matthias, arid Remeika ( 1 ) . These crystals had an initial magnetization of about 260 c.g.s. units. The crystals of nickel ferrite had relatively high electrical conductivity, which prevented the determination of precise dielectric constant values. The dielectric constant reported for liquid air temperatures was about 20. Semiconducting films and glasses are placed on high-voltage insulators to reduce or to prevent radio interference or noise. T n some cases, this has been accomplished by adding nickel oxide and other oxides to a more or less conventional type of porcelain glaze. Satisfactory semiconducting film8 have been prepared from nickel oxide admixed with minor amounts of impurity osides, particularly lithium.
1
1
00
500
I
600
J
700
Wavelength, millimicrons
Fi ure 3.
Extinction Coefficient versus d v e Length for Nickel Containing Glass Heated at 20' to 760" c. I'
= lolO-Brd
In recent years, a great deal of experimental work has been done on ceraniets, which are a combination of a refractory oxide and a metal such as nickel. The metal fills the space between the oxide grains and gives the whole mass greater toughness. It is hoped, thus, to produce a material having the good properties of both a metal and an oxide. T o date, the work on these materials has been largely government sponsored, and no commercial applications have been reported.
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NICKEL-CHEMICALS Metallic nickel or nickel alloys are widely used in the ceramic industry because of their excellent oxidation resistance and their strength at elevated temperatures. Common uses are furnace parts and electric heating elements which are not subjected t o furnace operating temperatures in excess of 2000’ F. The corrosion resistance of nickel alloys has provided a use for nickel in some of t h e chemical processing done in the ceramic industry. Other special nickel alloys serve as parts of thermocouples. For temperatures u p t o 2200’ F., chromel-alumel couples are quite commonly used, and these two alloys consist of 90 and 98% of nickel, respectively. Nickel thus serves a wide variety of uses in the ceramic industry. For many purposes, however, very little information is
available. As more is learned about the properties of nickel and its compounds, a still greater variety of uses is t o be anticipated. ACKNOWLEDGMENT
The authors gratefully acknowledge the permission of Weyl to use figures from his article (S), which are reproduced herein as Figures 1,2,and 3. LITERATURE CITED (1) Galt, J. K., Matthias, B. T., and Remeika, J. P., Phys. Rev.,
79,214(1950). (2) Snoek, J. L., “New Developments in Ferromagnetic Materials,” New York, Elsevier Publishing Co., 1947. (3) Weyl, W. A,, J. Soc. Glass Technol., 28, 128, 231 (1944).
RECEIVED for review October
17, 1951.
ACCEPTED March 13, 1052.
NICKEL DERIVATIVES OF AZO D Y E S NEIL M. MACKENZIE, HENRY E. MILLSON, AND BYRON L. WEST American Cyanamid Co., Calco Chemical Division, Bound Brook, N. J. N i c k e l possesses the property of forming stable coordination compounds with azo dyes containing certain functional groups ortho to the azo bridge. In this respect, it is similar to cobalt, iron, copper, and chromium. The patent literature contains many references to the use of these compounds as wool dyes, direct dyes,.pigments, dyes for synthetic fibers, leather colors, and colors for lacquers and plastics, M a n y show interesting properties. In several instances the fastness to light is reported to be outstanding. Although chromium and copper coordination compounds have important commercial applications, nickel derivatives are not extensively used. However, the application of color is becoming more widespread, and the problems connected with the application of color to various fibers and materials of construction are becoming more complex. Certain nickel coordination compounds of azo dyes, because of their fastness to light, are worthy of consideration for some of these new applications.
VER since the discovery of the first synthetic dye by Perkin,
E
the dye industry- has recognized the necessity for constantly improving the quality of its products. Thousands of pages in the chemical and patent literature are concerned with the production of new and improved dyes and intermediates. Much of this work has been directed toward the production of dyes with better fastness properties-fastness t o light, t o washing, to various conditions encountered in manufacturing processes and to many other specid conditions t o which colored materials are exposed. It was the search for dyes having good fastness properties that led to the discovery t h a t the light and wash fastness of certain appropriately constituted azo dyes could be greatly improved by treating the dye on the fiber with certain metallic salts. It was found that salts of chromium, iron, cobalt, nickel, and copper have the most pronounced effect in improving fastness properties. After many years of research and development by the dye companies and the textile industry, a complete line of fast colors for wool was created. These dyes are the well-known chrome dyes. They are converted into chromium coordination compounds in t h e dyeing process. The chrome dyes were followed by dyes which had been converted t o chromium coordination compounds during manufacture a t the dye factory and then applied by the dyer t o wool h v a one-step process. Dyes which are May 1952
so prepared are known as premetallized dyes. Copper derivatives of certain direct dyes are becoming increasingly important in the production of fast dyeings on cotton, rayon, and other related cellulosic fibers. Information from Germany states that several of the Perlon Echt colors for nylon-type fibers are cobalt coordination compounds ( 4 ) . hIetallized dyes made from chromium, copper, and iron are used for dyeing plastics and leather. Nickel salts will also react with azo dyes to give stable coordination compounds. The patent literature contains numerous references t o the use of nickel derivatives as wool dyes, direct dyes, pigments, leather colors, and colors for lacquers and plastics (29). Many of these compounds show very interesting properties. In several instances the fastness t o light is reported to be outstanding. Nevertheless, nickel compounds up t o the present time haye not found widespread application in industry. However, the use of color has spread t o hundreds of items formerly left uncolored, and the types of fibers and construction materials that must be colored are increasing daily. T h e problems connected with the preparation and application of new dyes are becoming more complex. In view of this state of affairs, it was thought that a brief discussion of the constitution and properties of nickel coordination compounds of azo dyes would be timely and might bring them to the attention of investigators who have a possible use for them. Nickel exists in the divalent form in a large majority of its compounds. As such, it forms two types of compounds. The first type includes the salts, such as nickel sulfate (NiSOP.6H20), which are ionized in water solution t o give the ion Ni++. The members of the second group are not ionized or are ionized to only a very slight extent, such as the red nickel compound of dimethylglyoxime which is used in analysis:
[
CHa-I=N-OH] CH3-
=N-0-
Ni 2
Nickel derivatives of most organic compounds including azo dyes are of the latter type, which are known coordination compounds. They are the connecting link between organic and inorganic chemistry. Early in this century, A. Werner proposed B clear, logical ex-
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