DATA AND RESULTS. To determine the effect of size of grain of the kaolin, a series was made up of 0.2, 5, 7.5, and 10 per cent of each of the sizes Nos. 2, 3, and 4 of kaolin and fired as a preliminary burn. No difference could be distinguished between the three, and so kaolin No. 3 was used throughout the rest of the determination. Kaolin was added to feldspar in 1 per cent intervals, from 0 to 16 per cent. Beyond this the kaolin percentages were 25, 30, 35, 40, and 45. The average of 9 burns is given in figure 8. Feldspar-----100 99 Kaolin-------0 Cone Cone Cone 10 This chart indicates that— 1. The pure feldspar deforms between cone 8 and cone 9, being closer to the latter. 2. Around 2 and 3 per cent kaolin the start of deformation is late, the rate is fast, and the end is before that of pure feldspar. 3. At 5 and 6 per cent the rate decreases until it is about that of the pure feldspar, but the start and end of deformation is behind that of the latter. 4. In the 9 to 11 per cent region there is another slow starting, a rapid rate, and quick finish to deformation. The rate here is faster than any other. 5. Beyond 10 per cent kaolin, normal conditions are gradually resumed, the start and finish progressing toward higher temperatures with the increase of kaolin. Cones in which the kaolin impurity varies only by 1 per cent do not show much difference in their deformation. Hence regions, instead of definite percentages, must be used in terming these indicated eutectics. FIGURE 9.-Diagram showing relation of rate of deformation to proportion of kaolin. Vertical distance between lines represents rate of deformation of pure feldspar. Figure 9 shows in a more general way the rate of deformation, that being designated by vertical distances between the two curves. The normal rate-that is, that of pure feldspar-is represented by the vertical distance between the two dotted lines dropping to the right as the kaolin content increases. CONCLUSIONS. The results of these two charts show that there are two indicated deformation eutectics, the lesser in the region of 2 to 3 per cent kaolin and 98 to 97 per cent feldspar, and the greater at 9 to 11 per cent kaolin and 91 to 88 per cent feldspar. Correspondingly, 5 to 6 per cent kaolin and 95 to 94 per cent feldspar is a region which may be termed a deformation compound. When we speak of regions, it is meant that in the limits given there is a definite percentage at the maximum or minimum point which should be termed the deformation eutectic, or compound, but that it has not been accurately determined. REFIRING. A final determination was made to this phase of the study by grinding up the deformed cones to pass 150 mesh, mixing with dextrine, reforming into cones and firing again; 0, 2, 4, 6, 7, 5, 10, 12.5 per cent of kaolin were used. The results as given in figure 10 in general check the above results, the deformation, how ever, taking place from two to three cones lower-close to cone 6. Pure feldspar started about the same time as the others, but was slow in deforming. Two, 4, 7.5, and 10 per cent were practically the same and deformed more rapidly than pure feldspar. Six per cent kaolin was slightly behind 2 and 10 per cent and dropped more like 0 per cent, thus indicating the higher region of 4 to 6 per cent. KAOLIN-FELDSPAR-QUARTZ TESTS. Kaolin was added to a 1 to 9 mixture of quartz-feldspar in the percentages 0, 2, 4. 6, 8, and 10. The results of two burns are given in figure 11. The deformation took place with cones 8 and 9, the same as with kaolin and feldspar alone. With 8 per cent kaolin went the most rapid deformation, 10 per cent and 0 per cent kaolin FIGURE 11.-Deformation of kaolin-feldspar-quartz cones. came next, with a lesser rate, leaving 2 to 4 per cent as the "high" region and the slowest to deform. Hence, in a general way, the feldspars with both quartz and kaolin impurities may be made to deform with and before pure feldspar, especially when in the region of 8 to 10 per cent kaolin, 9.2 to 9 quartz, and 82.8 to 81 per cent feldspar. MIXTURES HIGH IN KAOLIN. Dr. Simonis (Sprechsaal, 1907, vol. 2) gives the following table for the deformation of kaolin-feldspar mixtures: Deformation points of kaolin-feldspar mixtures. As is shown by figure 12, we partly checked this with our kaolin and feldspar, the slight variations being probably due as much to furnace irregularities as to anything else. Standard sized cones were made of the different mixtures and tested with standard cones in a small gas-fired muffle furnace. In the figure the dotted lines show where our results disagree with those of Simonis. Notice the rise in deformation of 12 cones between the limits of 30 to 40 per cent kaolin. GRAPHIC GRANITES AS A SOURCE OF FELDSPAR. As the exposed deposits of pure feldspar in the United States are rapidly being worked out and the locating of new deposits of pure material is a matter of more or less uncertainty, it seems wise to seriously consider the available sources of feldspar which is not pure but contains no impurity that would make the feldspar unfit for ceramic uses. The most fruitful source of such investigation is the graphic granites or graphic pegmatites. The pure feldspar has been obtained from isolated lenses in these pegmatite dikes, and in mining it vast quantities of pegmatite rich in feldspar and containing little or no impurity, except quartz, were quarried. This was rejected as waste. When the lenses of pure material were becoming exhausted, the operator began to work over these waste heaps and also to quarry the walls adjoining the pure feldspar lenses, and he found there much material free from other impurity except quartz. This material was sorted, and the portion in which the quartz content did not exceed 10 or 15 per cent was accepted and mixed with the pure feldspar. No serious difficulty resulted from the replacement of 5 or 10 per cent of the feldspar by quartz, as this amount of variation in the ordinary pottery body might often occur through the use of material in which an excess of moisture existed. However, each year the supply of available pure feldspar becomes less, and also the part of the graphic granites which is richest in feldspar is being used up, leaving a poorer assortment from which to select. Owing to the gradual hardening of the commercial grade of New England feldspars, which is not due to any change in the feldspar 60 50 40 30 20 10 0 Feldspar, per cent 100 90 80 70 FIGURE 12.-Deformation curve of kaolin-feldspar series. After Simonis. Dotted lines show where results of Wilson's tests disagree with those of Simonis. itself, but merely to the increased quartz content, many users have turned to other sources of supply, thus fortunately leaving the New England feldspars to those manufacturers who found their use essential to proper color in their wares. This is especially true of the Maine feldspars, which are recognized as being superior in color to any other American feldspar except the North Carolina feldspars, the cost of which is prohibitive in many industries. |