United States Patent Office Patented May 16, 1961 1
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2,984,576 United States Patent Office Patented May 16, 1961 1. 2 say, 100 millimicrons or more can be concentrated to as much as 50 percent ZrO2 or HfO. Sols can be con centrated beyond the ranges stated and they become 2,984,576 viscous or even paste-like. In preparing compositions USES OF ZIRCON A SOLS of the invention the concentrated sols, dilute sols, or even the paste-like products can be used depending upon Guy B. Alexander and John Bugosh, Wilmington, Del, assignors to E. I. du Pont de Nemours and Company, the specific final product, Wilmington, Del, a corporation of Delaware If the autoclaving and hydrolysis process was conducted on a rather concentrated solution, then particularly at No Drawing. Filed Oct. 10, 1956, Ser. No. 615,003 0. higher temperatures and for longer periods of time, the 4 Claims. (C. 106-55) product of the hydrolysis will be a precipitate. Super natant liquid can be removed, excess acid can be re moved as by ion exchange to yield a product in the pH ranges previously indicated. The precipitated zirconia This invention relates to compositions which contain 15 or hafnia peptizes and upon standing forms sols which as a binding agent a metal oxide selected from the group are similar or identical to those prepared by hydrolysis consisting of zirconia and hafnia in the form of particles of more dilute solutions. having a surface area from 5 to 400 m2/g., being com The aqua-sols prepared as above described can be posed of ultimate particles of 5 to 200 millimicrons converted to organosols which can contain more or less average diameter and which when dispersed in a liquid 20 water as described. The sols can be transferred to or medium forms a dispersion in which the percent of solids ganic solvents by mixing them with a solvent which forms in the dispersed phase is at least 30. The invention is . an azeotrope with water and removing the water by further directed to processes for preparing such compo azeotropic distillation. It is preferred to use polar, sitions. water-miscible organic solvents. Preferred solvents in Zirconia and hafnia sols or finely divided powders can clude normal or isopropanol, ethylene glycol, dimethyl be used as binding agents in a wide variety of applica formamide "Cellosolve,” and the like. tions. These can range from refractories in which the The organosols can be concentrated to form very thick zirconia or hafnia serve to bind components together to dispersions or even pastes. They can be completely dried plastic material in which they serve a similar function. to produce dry powders which can be used in making Likewise, they can be used to bind organic acids or other 30 products of the invention. The organic solvent can, if organic compounds such as dyes. The above and further desired, be removed above the critical pressure to pro compositions of the invention will be described here duce products which are somewhat more voluminous. after. The zirconia or hafnia particles can also be dried from The zirconia and hafnia sols and products employed water or from non-aqueous systems. There is somewhat in compositions and processes of the invention and proc 35 more aggregation when the sols are dried from water esses for their preparation are described in our copend than when dried from organic solvents, but the dry ing application Serial No. 625,188, filed November 29, products can be incorporated into compositions of the 1956, as a continuation-in-part of our then copending invention by thorough mixing or milling, with or with application Serial No. 566,969, filed February 21, 1956, out the addition of water or other liquids. now abandoned. 40 The sols and dry dispersible powders to be used in Briefly, an aqueous solution of a basic zirconium or compositions of the invention are characterized by con hafnium salt is heated under pressure. There can be taining ultimate zirconia or hafnia particles which are used zirconium oxychloride ZrOC28H2O, zirconium at least 5 millimicrons in diameter and which are in oxynitrate ZrO(NO3)22H2O, their corresponding half the colloidal size range and which additionally are dense. nium salts and other basic zirconium and hafnium salts Thus the particles can range in size between 5 milli in which the anion corresponds to a strong monobasic 45 microns and the upper limit of colloidal size, about 150 acid. Thus the anion can be that of the strong mono millimicrons. More broadly, the particle size can range basic acids, namely, those which have a dissociation con upwardly to 200 millimicrons in diameter. At this di M. stant greater than 0.1 at 25 C. mension there will be a considerable tendency for the The basicity of the zirconium and hafnium salts can particles to settle. vary from, broadly, a mol ratio of anion:zirconium or 50 The ultimate particle size of the individual zirconia anion:hafnium from 0.5:1 to 4:1. It is preferred to use . and hafnia particles, which may occur as loose aggre mol ratios between 1:1 and 2:1. The zirconium or gates in sols or powders to be used in compositions of hafnium salt is hydrolyzed under pressure to produce a the invention, are best determined by nitrogen surface zirconia or hafnia sol. The temperature will range from area determination, although their general character may about 120 to 300 C. though it is preferred to use a tem 55 be ascertained by use of the electron microscope. perature between 120 and 150° C. At 125 C. about one When the products are prepared at about 150° C. the hour is sufficient to effect substantially complete hy particles and particularly their aggregates will be found drolysis. A time from about 1 to 4 hours will be re to be irregular in shape. By electron diffraction the quired depending upon conditions and the degree of hy zirconia particles show a pattern similar to the mineral drolysis desired. 60 baddeleyite. When the products are prepared at tem Excess acid can be removed by dialysis, precipitation, peratures below 150° C. the particles are amorphous. ion exchange, or in any other suitable manner. The re In referring to the ultimate particles as having a diam moval of acid can for example be effected by a pro eter of 5 millimicrons, for example, it is intended to cedure as described in Rule U.S. Patent 2,577,485, refer to the smallest average dimension of the ultimate column 8, beginning at line 46. The final pH can range 65 particle. Also, in speaking of the particles as having broadly from about 2 to 6 while more specifically it is a certain diameter, it is intended, as will be apparent, preferred that the pH be from about 3 to 5. to refer to the average diameter of all particles in the Sols as prepared by hydrolysis followed by the removal sol or product. of excess acid can be concentrated. Sols with particles O As indicated above the particle size and character of around 5 millimicrons can be concentrated to about 25 the sols and dry powders can be defined by nitrogen ad percent ZrOa or HfC) Sols containing larger particles, sorption. A method for determining nitrogen adsorp 2,984,576 3 4. tion is described in "A New Method for Measuring the mate of the percent zirconia or hafnia by weight in the Surface Areas of Finely Divided Materials and for dispersed colloidal particles from the relation: Determining the Size of Particles,' by P. H. Emmett, in "Symposium on New Methods for Particle Size Deter mination in the Subsieve Range' in the Washington 2. Spring Meeting of A.S.T.M., March 4, 1941. The sol (3) to be measured is deionized, transferred to propanol by S (1-0.00825Z)--0.008252 distillation, and dried in a vacuum oven. The prefered zirconia and hafnia ultimate particles are O where S is the percent ZrO2 or HfOa in the dispersed phase in the size range of 5 to 25 millimicrons. The surface and Z is the percent ZrO2 or HfO2 in the sol as measured area of the ultimate particles in m2/g, A, is related to by quantitative analysis. the average diameter, D, as measured by electron mi As noted above, the percent of solids in the dispersed crograph by the range phase, S, is at least 30 for products of the invention. 15 The value of S, as calculated by the above relationship, is in the range of 45 to 80 for preferred products to be used in composition of the invention. It is noted that 1000 2000 the value of S of about 80 is equivalent to 100 because to ri of errors in the assumption that the particle is spherical for zirconia particles. Because of the higher density of and because of the presence of a monolayer of Water on HfO2, the relationship is 20 the particle. Thus, with true spheres the value for S would be a maximum at about 90. The concentration of aqua-sols to be used in prepar ing compositions of the invention can vary widely. Sols A-600 to 1200 25 prepared as above described can be concentrated to 10 D D percent ZrO or HfO or more as desired. They can be concentrated to 50 percent ZrO2 or HfC), or more with out gelation particularly where the particle size is rela tively large. It is generally preferred that the sols con The particles of the sols and dry powders to be used 30 tain at least 10 percent ZrO2 or HfO2.