CERAMICS JOHN H. KOENIG AND ROBERT H. THOMAS Rutgera University, New Brunawick, N. J.
T
HIS report deals eseentially with the developments during the past year in a number of different types of ceramics, enamel and glass products, whitewares, refractories, and structural claywares. ENAMELED PRODUCTS
During the past 3 or 4 years titanium enamels have gained general acceptance in the industry due to high opacity and good acid redstance (49). The chief advantage of these enamels is that they may be applied as thinner coatings than the sirconia-or tin oxide-opacified enamels, and hence, are more resistant to ohipping aa well aa being smoother and of greater reflectance. Twenty yeara ago ceramic enamels-on-steel were about 0.030 inch thick. Manufacturera could normally expect an 18% lom of their products in handling due to the chipping of such a heavy application. Ten yeara ago this loas had been reduced to 1% by the development of improved techniques and materials resulting in coatings about 0.016inch thick. Ence World War 11, coating thicknhave been reduced to 0.010 inch with the advent of titaniwpacified covemoat enamels applied over the conventional cobalt-blue ground coats (8). The recent development of a special enameling steel has made possible the complete elimination of the ground coat, and consequently a further reduction in enamel thickness to 0.0066 inch. This steel is a completely deoxidized--"killed"--steel containing from 0.20 to 0.60% titanium. Although a nickel flash on the base metal is still neceaaary to promote optimum adherence, the complete deoxidation of the metal prior to enameling has eliminated surface defects such as reboiling which can often be traced to the evolution of gas by the metal at temper3tures necessary for maturing the enamel coating (10). In addition to the greater durability of titania-opacified enamels, they serve also to satisfy the demands of the enameling industry to cut costa by producing a superior enamel with a loiver maturing temperature. Thew enamels fire a t 1460" F. compared with the rirconia-opacified enamels which require 1620' F. The new titania enamels have a reflectance of about 85%, which repre&nts an improvement over the older types for the same thickness of coating. They are also less critical to control from the standpoint of weight of application or firing temperature, and have a greater color stability, acid resistance, scratch resistance, and thermal shock resistance (61). The opacity and color of porcelain enamels are of primary importance to the consumer of these products. While other properties might be of greater functional importance, it is the color and opacity which largely determine his choice. The enamel industry must continually improve the color, color stability, and opacity of its products. Factors affecting these properties have been studied for titania-opacified enamels (61,W). Anatase is the crystalline phase responsible for opacity and it produces better spectrophotometric properties in titania enamels than does rutile. Any factor that inhibits the rate of crystal growth and/or rate of inversion of anatase to rutile will tend to increase the color stability of titania enamels under different firing conditions. Careful control of the melting operation under oxidiaing conditions, and as low a temperature as possible provide the proper environment for anatase nucleation (66). The type of clay and the electrolyte used in the mill addition have an important bearing on the rdectance, color, and acid resistance of the finished
product (66). Small amounts of titania can be added as a mill addition to increase the adherence of sheet-steel ground coata (87). The effect of soda, potash, and lithia on the physical properties of titania cover enamels has been reported (88). A syetematic study has resulted in the development of a number of simple titaniebearing porcelain enamels (87). For many years enamelers have attempted to apply a white enamel directly on a sheetateel base, f i e the ware once, and have a finished product. The problems encountered and the progress accomplished have been reported (4.8). The use of one fire white enamels may require special steel, frit, and treatment, or a combination of special and ordinary methods and materials. The most satisfactory combinations economically are hard to predict; the beet for one plant may not be suitable for another. The competition of two-fire enamels, especially for premium ware, remains keen. It is too soon to determine the place for onafire enamels, but they offer considerable promise. Enameled, thin gage steel in a variety of colors has been placed on the market for use aa a wall paper. The paper can be bent without damage and cut with ordinary shears. In industrial buildings, such wall panels can be easily cleaned without deterioration, will maintain a smooth, pleasing appearance which is unaffected by moisture or dirt, and they possess good abrasion resistance (9). The introduction of ceramic enamel-on-aluminum for use under adverse weather conditions has attracted attention to this new material as highway markers, road signs, etc. (7). These are one-coat, low-firing enamels which produce a very light-weight product. The material can also be cut with a hack saw with little or no chipping a t the edges. If any chips occur or if raw edges are left by the sawing operation, the metal doe6 not rust. Ordinary enameling iron rusts readily whenever it is unprotected by enamel. Once rusting begins, the oxidation spreads beneath the ceramic and soon causes discoloration if not a spalling of the enamel. These enamels have a superior adherence and fire at 1oOO' to 1100' F. This is rather close to the temperature of failure for alumlnum, hence, sagging and warpage is a disadvantage until lower temperature coatings for this metal are developed. Ordinarily, a t least three firing operations are necessary: pickel fired, ground coat, and cover coat. The excellent adherence permits extreme bending of the metal without loss of adherence (19). New usea for enamel finish- already in production or well along in the development stage include power line transformers, freezer plates, household furnaces, radiators, space heaters, compression fins, and heater coils and baffles (11, 64). Enamel finishes are well suited to these uses owing to the high emissivities of such coatings, The following table illustrates the relative emissivities of seqeral materials: Porcelain enamel (white) Stainlesa steel Aluminum
0.77 0.13-0.16
0.M
A comprehensive report was made of porcelain enamel household construction (46). During the past year similar applications have been placed in production such as porcelain enamel finishes on escalator ribs, interior trim such as door frames, window trim, picture molding, and even conveyor chutes (33, 41, 6.9, 84). These finishes are being produced in various colore which are durable and smooth. The high abrasion resistance,
1981
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1962
Vol. 42, No. IO
TABLE I. PROPERTIES OF REPREU per Working Ternrjeiatiires
Qlass Code
Forms Usually .4vaiiable" T T BMT TIM BP BP BPU
(Mecganical CoSLderations Only) Annealed Tenpered Nornal Extreme Norpal Ertrerne servlce. limit, service. limit, ' C. C. C. C.
'rh$IsEi,
Annealedd inch i / d inch inch thick, thick, thick, C. C. C. 63 50 35 70 40 60 65 35 50 65 35 50 135 115 75 70 60 40
I/g
Color Principal Use Clear Lamp tubing 91 x lo-; 110 380 ... 110 84 X 10Clear ThermomQters 400 ... 110 92 x lo-; 22Q Clear Lanip bulbs 460 250 0080 110 89 x 10Clear Lamp tubing 380 ... 0120 200 650 Clear Cooking iitensili 42 x 10-7 400 460 1710 110 Generai 82 x 10-7 450 250 Clear 220 1770 General 200 480 43 x lo-; Red 135 115 75 2405 T A-eon signs 110 440 Red 91 x 1065 35 50 2475 T 200 Green Sealing 40 X 10-7 470 135 115 75 3321 110 SI gnalware BPU Green 90 x 10-7 460 ... 65 35 50 ... 4407 r 110 General White 80 x 10-7 480 220 275 70 60 40 6720 opaque Lightingware 220 White 87 x 10-7 110 BPR 420 220 65 50 35 6750 OPd op aq I i e B 1'R 69 X 10-7 Lightingware 120 470 White 240 270 85 70 4; 6810 O P d opaque T Series sealing 46 X lo-. Clear 440 235 125 100 70 7050 Borosilicate 420 46 X 10-7 Rovar sealing 210 125 Clear 70 100 7052 Borosilicate Low loss electrical 430 32 x 10-7 Clear 150 230 180 100 7070 Borosilicate Bakingware 460 Clear 36 x 10-7 260 160 90 130 7250 Borosilicate m I 510 67 X 10-7 Gage glass 310 a5 Clear 45 70 7340 Borosilicate BP'I' 38 x 10-7 460 Electrical 260 160 Clear 90 130 7720 Borosilicate 32 X 10-7 BPSTU General 290 490 Clear 100 160 180 7740 Borosilicate BP 450 34 x lo-; Electrical 250 160 Clear 90 130 7760 Borosilicate HPTU 1090 High temp. 8 X 10... 1250 Clear ... 1000 750 7900 Ll 1250 1090 8 X 10-7 ,.. High temp. 1000 750 7900 96 silica (multi- White ... fd;m) opaque 7910s 96% siliea Clear UJtr++olet transB'I'U 8 x 10-7 800 1090 ,, ... 1250 1000 750 mission 7911 i 96% silica Clear Ultraviolet transT s x 10-7 800 1090 ., . .., 1250 1000 750 inission 8870 High lead Clear Sealingorelectrical M T U 91 X 10-7 110 380 180 180 65 50 35 , , . Clear Ultraviolet transTU 37 x 10-7 no 500 , .,, 150 120 80 9700 mission 9741 Clear Ultravjolet transBUT 39 X 10-7 200 390 , 150 120 80 rmssion 0 B blownware. b4 multiformware; P, pressedware; R , rolled sheet: S, plate glass; T , tubing a n d rod; U, panels. b Fiom Oo t o 3d0° d:, inch/inch/O C. or cm./cm./" C. e These data approximate only. Freedom from excessive thermal shock is ausumed. See column headed Thermal Shock Resistant Plates. At extreme limits annealed glass will be very vulnerable t o thermal shock. Recommendations in this range are based on mechanical considerations only. Tests should be made before adaptiqg final designs. d These d a t a approximate only. Based on plunging sample into cold water after oven heating. Resistanae of loOD C. meam no breakage if heated t o 1100 C. and plunged into water st 10" C. Tempered samples have over twice the resistance of annealed glass. Glasses 7900,7910,7911 cannot be tempered.
0010 0041
Type Potash soda lead Potash soda lead Soda lime Potash soda lead Hard lime Soda lime Hard red Soft red Hard green sealing Soft green Opal
Therniai Expansion Coefficient per ' C.b
g67i
.
.. ..
...
corrosion resistance, and heat resistance make them particularly ' advantageous for use in public buildings Proceases for de-enameling have been reviewed (80). A recently developed technique involves the use of a molten caustic bath. The method is very rapid and the life of the bath is eytended indefinitely. New mottled enamel finishes have been produced in cover coats by precipitation of various color-producing salts in the enamel slips (74). GLASS
Recent developments of glrtss for the chemical industry were reported previously (71). A review of the glass product developments during the past year has been published (73). Plate glass which excludes more than 99% of the sun's ultraviolet rays has been developed. A new glare and heat-reducing glass produced as a safety plate for windshields is now available. Glass is now serving as an aid to convenient electric heating. Radiant glass heating accomplished by passing electricity through an aluminum element fused into glass a t high temperatures is now practical and usable under varied climatic conditions. Improvements have been noted in the field of glass insulation. A definite improvement has been reported in the quality and durability of heat-resistant glasses. This has been effected by increased mechanization. Some progress h a been reported in the development of a technique of sealing glasses together by means of suitable soft glass enamel which acts as a solder, and the sealing can be accomplished without deformation of the glass parts themselves. Glasses particularly applicable are the lead borate type covering the range 50 to 90% lead oxide ahd the remainder boron oxide (boric anhydride). With the recent trend toward miniaturization in the expanding field of electronics, considerable improvement has been required
...
and achieved in glass-to-metal and ceramic-to-metal seals (68,67). As the physical size of the component is decreased, the stresses on the component parts necessarily are increased. Many electronic components require hermetic sealing. The present c e ramic-to-metal seals may be divided into five general classes: matched seals, unmatched seals, soldered seals, brazed seals, and mechanical seals. Great improvement has been made in ail types during the past several years. Recent work in the glass-formation region of the system lead oxide-tungsten trioxide-phosphorus pentoxide has disclosed that glasses of this system have an unusually high x-ray and 7-ray absorption and are not readily discolored when exposed to x-rays (66).
A recent publication concerns the properties of glasses in the systems lithia-beryllia-boron oxide and sodium oxide-berylliaboron oxide which are transparent to x-rays (47). Photosensitive glass is now being produced in sizes ranging from jewelry miniatures to several square feet (IS). The major difference between photosensitive glass and an ordinary photographic plate is that in the former the image is developed within the glass. Furthermore, the photosensitive glass is a true solution of the metallic materials in a homogeneous, clear glass and not a suspension as in a photographic emulsion. This special glass is sensitive to ultraviolet light in the 260 to 360 pp wave length range and also to x-rays and @-rays. Ordinarily, however, a high-powered carbon or mercury arc is employed. By the proper selection of filters and exposure time, the color, depth of penetration, intensity, and contrast can be varied and controlled. After exposure the glass is heated to 580' to 650' C. for periods of time ranging from 15 to 60 minutes. Since this is above the annealing temperature of the glass, care must be taken to prevent deformation. The heat precipitates the metal and forms the image. These metal particles are less than 10 mp in size and may be even an
Oatober 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
1963
SENTATIVD I N D U S ~ IGLASSES AL (87)
Thermal Viscosity Datal Impact Streaa Strain Annealinn Soften- Working Abrasion Density Reaietance, point, point, -inspoint, , point; Resist- (SP. Gr.), O c. C. 0c.e * c. c. ancea G./Cc. 397 19 428 626 970 2.85 460 426 19 2.89 648 510 2.47 696 478 1600 1.2 17 433 400 630 3.05 975 17 672 2:o 29 712 915 2.53 1200 710 2.40 470 503 19 ... 802 2.50 506 537 36 . . . 693 2.56 466 501 .. 17 . . . 497 535 780 2.27 39 695 2.53 518 486 17 .. ... 531 775 2.58 499 19
.... *.
.. .. .
I
.. *. ..
... ... ... ...
........
..
672
529
768
34 34 70 43 20 45 48 51 200 200
461 438 455 486 538 484 515 475 820 820
496 475 490 524 575 618 656 515 910 910
703 708 775 786 766 820 780 1500 1500
1220 1210
3.1
....
3:6 3.5
2.25 2.28 2.13 2.24 2.43 2.35 2.23 2.23 2.18 2.18
200
820
910
1500
..
3.5
2.18
200
820
910
1500
..
3.5
2.18
22 42
398 517
429 558
580 804
1 i95
0.6
...
4.28 2.26
40
407
442
705
,.
...
2.16
iiio
3.2
3:a
.. .. ..
2.66
475
496
i: i
........ ........ .......
12:4 17+ 17+
2.63
445
..
io6
........ 12.7 X 106
.. .. ..
18
iii5 1100
0:s.X
......... ...... ........
23
...
Modu!ys of Elastiarty Lb./Sq. Inoh' 8 . 0 X 106
Lo io pf Volume iteaistivityh 25' C. 250' C. 350° C. 17+ 8.9 7.0
........
.
#
6:4 10.1 11.4
.. .. .. .. ..
..
...
5.1 8.0 9.4
...
... ...
... ...
...
..
Refractive Index Dielectrio Propertiea Sodipm a t 1 Mo. and 20° C. D Line Power Dieleotrie LUSS (0.5893 factor, % oonatant faotor. % Microns) 0.16 6.6 1.1 1.539 1.545 1.512 0:9' 7:Z 615' 0.16 6.6 1.1 1.560 0.37 8.3 2.3 1.534 1.496 ... ... .. 1.508 ... ... .. ... ... 1.511
...
... ... ... ... ...
0.33 0.26 0.06 0.28
4.9 5.1 4.0 4.7
0.27 0.46 0.18 0.05 0.05
4.6 4.5 3.8 3.8
2.1 0.79 0.19 0.19
... ...
... I . .
........ ........ 6.8 X 106
.
I
..
:
.,
1 525 1.507
...
1.513
..
... 1.6
1.3 0.24 1.3
1.508 1.479 1.484 1.489 1.475 1 ,506 1.487 1.474 1.473 1.458 1.458
1i:6'X 9.5 x 9.8 x 9.1 x 9.7 x 9.7 x
loa lo*
x 9.7 x
106
17f
11 2
9.2
0.024
3.8
0.091
1.458
106
17+
11 7
9.6
0.019
3.8
0.072
1 458
17415
11 8
8 0
9.7 6.5
0.09
...
9.5
...
0.85
..
1.698 1.478
17f
9 4
7.8
...
...
...
...
9.7
...
101
106 10' 10'
7.6 X 106
........ ........
4:f
1:3'
Resistance in C. is the temperature differential between the two surfaces of a tube or a constrained plate that will cause a tensile stress of 1000 1 b . h . inch on the oooler surface. I These data subject to normal manufaoturing variations. D Data show relative resistance to sandblasting. Data a t 25O C. extrapolated from high tam eraturc readings and are approximate only. s Eleotncal properties measured on lamp-wor?ced speoimens. e
atomic dispersion. The lack of turbidity and small grain size make the resolution of such reproduction extremely high. Since the image is inside the glass it cannot be scratched or defaced. I n fact sboy scratches on the plate may be removed without affecting the image once the image is formed. Further radiation has no effect on the glass or the image, nor does the image tend to fade unless the glass is again heated. New adaptation of photosensitive glass has produced an improved form of louver panel that gives promise of improving illumination considerably (78). The buvers in the form of planes are ingrained throughout a thick pane of glass, providing a more permanent and acceptable type of shield for lighting fixtures. A recent review waa made on technical glaaa as an engineering material from the viewpoint of the designer (88). Within fairly close dimensional limits glass may be pressed, blown, or drawn to innumerable custom shapes; heat treated to increase resistance to fracture; precisely controlled for critical color work, and formulated for a wide range of electrical properties. GLASS DEVELQPMENTS M)R INDUSTRY
Some time ago Corning Glass Works (89) prepared data on the properties of a representative group of their 4Wodd standard glasses. All glasses in this group have technical applications in industry. These data are shown in Table I (97). The range of glass compositions covered is sufficiently wide so that this table is also representative of the physical properties available in commercial glasses, with the exception of some of the optical glasses and certain unusual glasses used for very special purposes. Of the viscosity reference points, the softening temperatures and the annealing temperature are self-explanatory. The strain point represents the temperature a t which the viscosity is so high that, in cooling below this temperature, the glass becomes, for all
practical purposes, a solid body. The coefficient of linear expansion with temperature is of particular importance as an indication of the stresses set up by temperature differentials within the body of the glass. It is not usually practicable to select glasses for special applications from such tables of properties alone. During the past 2 years, the developments in glass as a material for industry have been mainly along lines of improvements of existing products for both greater serviceability and greater convenience to the user. An exception to this has been the introduction of electrically conducting glass for heating applications. Further details on specific products are given below. Piping. The improvements in glass piping, consisting of the reduction of dimensional tolerances and the strengthening of fittings and the conicat flaoges by tempering, to which reference has already been made (72), have demonstrated their advantages. Both straight sections and fittings being fabricated in special jigs are held to dimensions which facilitate lining up the piping on installation, and also the replaoement of parts. The tempering of those sections which are subjected to the highest stresses when installed has raised the strength level of the piping as a whole. The conditions under which glass pipe lines are installed and operated have been analyzed in some detail from the standpoint of satisfactory service and reliability, In doing this, special consideration has been given tho unusual properties of glass which influence such conditions. The results of this study are being published (70). Outstanding interest is being shown by the dairy industry in the use of glass piping as a means of attaining higher standards of sanitation in their plants. Information gathered in past years from tests of glass pipe lines in actual service conditions in dairy plants has demonstrated that methods developed for cleaning glass lines in place are more effective from the standpoint of sanitation than the current methods of dismantling and brushing required for sanitary metal pipe lines.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42. No. 10
steel of eudc qu;tlit,y and of A.S.T.M. specific&ma. Preysun vesw!Is me built in neeordance with A.8.M.E.-A.P.I. code8 for
unfired pressure YCSSCIS. Thc nurmnl thieknesles of steel d range up to 1 inch and, for special applications, even gleater. Vessels w d reactom are built for either internal pressure or external jacket pressure or fur both pressures aetingsimultaneoudy. The gliLsses used for application in the chemieul industry are usually sodium brosiliestes with the following physics1 prnperticx:
The chemical durnbility of these gl-s when exposed to acids at boiling temperalum
several typical mineral and or8:anic ix ihowm in the folliwing tablo:
Figure 1.
Cascade-Typo Unit G h > s Ileal Exchanger with Weir,
Heat Exchangers. Unit hmt exchangers, complete aith up ports, weirs for the cnvei~detype, itiid outer steel piping and st&ing box
