Sintered Pyrex and Soft Glass Sections
in Tubes and Crucibles G. N. QUAM AND JOHANNA H E N " b n g Island University, Brooklyn,N. Y.
S
INCE the report on porcelain filter mats (10) and Pyrex filter mats (ff), many contributions have appeared on the construction and use of Pyrex sintered ware. In general the procedures suggested have involved sealing in place a prepared and shaped disk of sintered Pyrex, porcelain, or Aluadum under controlled heating in a furnace (1, 8, 8, 6,7, 8). In others the sintered-glass sections are prepared in tubes in open flames
(4, 6, 9).
The reason for so many contributions is no doubt the efficiency and ease of use of sintered-glass or porcelain ware in gas dispersers, gas wash bottles, mercury filters and valves, stills, absorbers, extraction thimbles, filters for fine precipitates, and aerators. The advantages of construction of a sintered mat directly in the tube or crucible in one operation have been demonstrated by the senior author. The graded glass may be packed in any part of the tube and sintered in place. The authors have not observed any reference to their method and therefore add this report on procedure and technique for the benefit of those who wish to construct their own apparatus for preliminary or exploratory observations.
Preparation The glass was ground in a steel mortar and graded by means of a set of sieves, 10- to 200-mesh. The graded lass was treated with 6 N hydrochloric acid, washed, and driefi For the first heatin the mat waa prepared by placing an asbestos disk at the lower kvel and holding it in place by fine asbestos fiber packed from below. The graded glass was poured on to the desired thickness. For the construction of a filter mat this 6rst layer consisted of a mixture of 40 r cent of &mesh, 35 per cent of 80-mesh, and 25 r cent oE20-mesh. The mat was wetted with a few drops o r N sodium hydroxide (sodium silicate solution, 8 cific gravity 1.036, also served a smtable flux). Without tE flux many mats failed to fuse uniformly to the wall of the tube or crucible. After this sturdy mat had been sintered in place, the process of controlling porosity followed. The h e r radee (130- to 200-mesh) .were kept suspended in the diluted &ng solution and pulled into the interstices by suction thus buldmg up an effective filter bed. The smaller particfes were then sintered.
minutes and with Pyrex when the temperature was held at 745" C. for 25 minutes,
Cleaning of Sintered Mats The sintered mats were washed with water, dried, and wei hed (weight A, Table I). Any solub!e substances remaining from the sodium hydroxide or sodium sihcate treatment were extracted with 6 N hydrochloric acid in the following manner: The mat was laced in the acid for 24 hours, then washed, dried, and weigged (weight B, Table I the proceea was repeated to determine further low (weight Pressing the mats with a itirring rod indicated no a parent loss in sturdinese from the acid extraction. Walls of spEt mats examined under a low-power microscope, equipped with an illuminator, showed that the porosity was uniform and that the structure was continuous.
&
The method of preparing built-in sintered mats has been successful for a wide variety of grades of powdered glass. Sections limited by the size of mu5e of the furnace can be joined to larger pieces of glass. The coarser grades can be heated to slightly higher temperature with resulting increase in sturdinees. The authors suggest thia method only as a device for preparing sintered-glaes mats during exploratory experimentation in regular laboratory procedure or research. The amateur g l w worker should rely on experts for the construction of permanent glass equipment of special design.
TABLEI. WEIGETLOSSEBFROM HYDROCHLORIC Acn, TREATMENT Thickneas of Mat
Cm.
Weight B Gram
L w Mg.
Weight C &am
L a Ma.
Soft g l w 0.0 -0.1 0.0
-0.1
Pyrex 0.7 0.5
0.7 1.0
Control of Sintering Process The approximate tem rature or cone number required for sintering waa determinerwith cones made from the glasa by drawinq a short section of tubing to a point. These g l w "cones' were placed in the furnace along m t h a selected series of pyrometric cones, or a thermocouple. The approximate temperature at which the glass would sinter was thus determined in terms of cone number or thermocouple ranp. For the work reported here cone No. 0.020 was found smtable for the soft glass and cone No. 0.015 for the Pyrex, while 625' C. (thermocou le) was suitable for the soft law and 745' C. for Pyrex. &e gleesware was.made reafy for the f v e by packing the glass tubes or crucibles in 6re-clay crucibles wlth fine asbestos fiber. Distortion was reduced to a minimum by maintaining the tubes in a vertical position by loose uniform packing. Sturdy sintered mats were obtained with soft glass when the temperature was allowed to rim slowly to 625" C. and held there for 15 1
Weight A Grama
0.a704 5.8145 4.8001 8.1299
0.3090
5.8151 4.8647 8.1278
1.4 1.4 1.4 2.1
6.3090 5.8130 4.8648 8.1277
0.0 0.1 -0.1 0.1
Literature Cited (1) Bruce, W. F., and Bent, H. E., J . Am. Chum. SOC.,53, !JOO (1931). (2) Degering, E. F.,IND.ENG.CHIM.,24, 181 (1932). (3) Holmes, F. E., J. Chum. Education, 18,311 (1941). (4) e k , P. L.,IND.ENG.CHW., ANAL.ED.,7, 135 (1935). (5) Kirk, P.L., Craig, Roderick, and Rosenfels, R. S.,Ibid., 6, 164 (1934). (6) Laitinen, 11. A., Zbid., 13, 393 (1941). (7) Prausnite, Paul H.,IND.ENG.CHIM., 16, 370 (1924). ( 8 ) Roswell, C.A., IND.ENG.CHEM.,ANAL.ED,, 12,350 (1940). (9) Shatenshtein, A. E., J. Chem. I d . (Moscow), 6, 1800 (1929). (10) Sweeney, 0.R., and Quam, G. N., J . Am. C h m . Soo., 46,968 (1924). (11) Wilkinaon, J. A., and Quam, G. N., private communications. August, 1924.
P r m t addreu, Iowa S b t a College, Ama, Iork
766
