as has been described above , the method for producing bodies of high fluorine , aluminosilicate crystals , in particular bodies containing topaz crystals , comprises two basic steps : first , amorphous powder of the desired composition is generated via chemical vapor deposition ; and second , that powder is heated to sinter it into an integral body and concurrently crystallize it in situ . as was explained above in general terms , the first step involves bringing streams of vaporous materials to a flame wherein those materials react to form a deposit of amorphous powder having the desired high fluorine - containing , aluminosilicate composition . nevertheless , because of the extreme volatility of sif 4 which , when formed , carries away fluorine , the vaporous source of the fluorine must be chosen such that it is strongly bonded to aluminum , thereby inhibiting the formation and subsequent volatilization of sif 4 . this requirement led to the investigation of aluminum organometallic compounds as source materials . it was recognized that there were two critical parameters which such compounds must satisfy : ( 1 ) that they exhibit a high vapor pressure at a reasonable practical operating temperature ; and ( 2 ) that the ligands on the aluminum complex contain a substantial excess of fluorine , i . e ., greater than three fluorines per aluminum , which is needed to achieve the required fluorine uptake . an investigation of compounds satisfying those parameters led to the determination that the β - diketonate aluminum hexafluoroacetylacetonate [ al ( hfa ) 3 ] constitutes the most preferred material because it has the highest vapor pressure and , therefore , does not require a high temperature vapor delivery system . nevertheless , other diketonates such as [ al ( hfa ) 2 ( acac )], [ al ( hfa )( acac ) 2 ], [ al ( tfa ) 3 ], and [ al ( fod ) 3 ] also satisfy the above two criteria . ( acac = acetylacetone ; tfa = trifluoroacetylacetone ; fod = heptafluorodimethyloctanedione ). families of organoaluminum compounds other than the β - diketonates can also exhibit properties recommending their utility . for example , fluorine - substituted aluminum alkyls and fluorinated aluminum alkoxides can contain excess fluorine . much more care must be taken in handling such compounds than the diketonates , however , because of their thermal and air sensitivity . because of ease of use and relatively low cost , sicl 4 was deemed to comprise the most preferred source of si . using those sources of vapors , the production of the desired amorphous powders will be illustrated utilizing the apparatus schematically represented in fig1 . as shown there , al ( hfa ) 3 vapor generator 1 comprises a glass flask containing a charge of liquid al ( hfa ) 3 into which carrier gas delivery tube 2 injects an argon carrier gas from an argon source . the glass flask is heatable by a heating mantel , oil bath , or the like ( not shown ) to raise the vapor pressure of the al ( hfa ) 3 therein to a suitable level (≈ 125 °- 175 ° c ). argon saturated with al ( hfa ) 3 vapors exits flask 1 into delivery line 3 which is heated , e . g ., with electrical heating tape ( not shown ), to prevent vapor condensation therein . sicl 4 vapor generator 4 comprises a stainless steel canister containing liquid sicl 4 into which carrier gas delivery tube 5 injects an oxygen carrier gas from an oxygen source . the canister is likewise heatable by a heating mantel , oil bath , or the like ( not shown ) to raise the vapor pressure of the sicl 4 therein to a suitable level (≈ 20 °- 50 ° c ). oxygen saturated with sicl 4 vapors exits the canister into delivery line 6 , which line is again heated , e . g ., with electrical heating tape ( not shown ), to prevent vapor condensation therein . vapor delivery lines 3 and 6 are passed to burner 7 having a general configuration similar to that illustrated in u . s . pat . no . 4 , 604 , 118 , supra , where they are combined with an argon and / or oxygen fume shield gas line 8 ( not shown ), an oxygen inner shield gas line 9 ( not shown ), a combustible gas ( methane / oxygen ) line 10 ( not shown ), and an oxygen outer shield gas line 11 ( not shown ) to form a unit consisting of six concentric tubes leading into burner 7 and terminating at the face thereof . the oxygen of fume shield gas line 8 retards the interaction between the al ( hfa ) 3 and sicl 4 vapors such that oxidation of those vapors can proceed before they can interact to form undesired fluorides . the inner and outer shields 9 and 11 , respectively , on either side of the combustible gas 10 , are designed to shield the sicl 4 and al ( hfa ) 3 vapors from the effects of the flame until the vapors have traveled a distance away from the face of the burner , thereby precluding a deposit of powder building up on the face thereof . in carrying out the vapor deposition process , the sequence of the four basic steps listed below is customarily followed : ( a ) the stream of combustible gas ( methane / oxygen ) 10 is ignited to preheat the flame oxidation burner 7 ; ( b ) the flows of fume shield 8 , inner shield 9 , and outer shield 11 are begun ; ( c ) al ( hfa ) 3 generator 1 is heated via an oil bath to temperatures above 125 ° c . and sicl 4 generator 4 is heated via a heating mantel to temperatures above 25 ° c . ; and ( d ) carrier gas flow to each of the generators is commenced ; argon being supplied to the al ( hfa ) 3 generator and oxygen being supplied to the sicl 4 generator ; in each case , the carrier gas is preheated to the temperature of the respective generator . with the commencement of vapor flows to the flame oxidation burner , amorphous high fluorine - containing , aluminosilicate powder ( or soot as it is frequently termed ) is formed in and ejected from the flame to be deposited upon a suitable substrate . table i sets forth flow rates of the various gases in terms of liters / minute [ the flow of al ( hfa ) 3 was 1 liter / minute for all the examples ], the temperature of the sicl 4 and al ( hfa ) 3 in ° c ., and the weight percent of al 2 o 3 , sio 2 , and fluorine in the powder as chemically analyzed . table i______________________________________ sicl . sub . 4 al ( hfa ). sub . 3 flame flameexample sicl . sub . 4 ° c . ° c . ch . sub . 4 o . sub . 2______________________________________1 0 . 25 40 140 5 . 4 5 . 02 0 . 35 40 140 5 . 4 5 . 03 0 . 15 30 140 5 . 4 5 . 04 0 . 25 30 140 5 . 4 5 . 05 0 . 25 30 140 5 . 4 5 . 06 0 . 16 30 140 5 . 4 5 . 07 0 . 16 30 140 5 . 4 5 . 08 0 . 16 30 140 5 . 4 5 . 09 0 . 16 25 140 5 . 4 5 . 010 0 . 16 25 140 5 . 4 5 . 011 0 . 16 24 140 6 . 0 5 . 412 0 . 16 24 140 6 . 0 5 . 413 0 . 16 24 140 6 . 0 5 . 414 0 . 16 24 140 4 . 0 3 . 615 0 . 16 24 140 4 . 0 3 . 616 0 . 16 24 140 3 . 5 3 . 217 0 . 16 24 140 4 . 0 3 . 618 0 . 12 30 140 3 . 5 3 . 219 0 . 12 30 140 4 . 0 3 . 620 0 . 16 30 140 3 . 5 3 . 221 0 . 25 30 140 4 . 0 3 . 622 0 . 16 25 145 3 . 5 3 . 223 0 . 16 30 157 3 . 5 3 . 224 0 . 16 30 140 3 . 5 3 . 225 0 . 10 30 163 3 . 5 3 . 226 0 . 25 30 163 3 . 5 3 . 227 0 . 16 30 165 3 . 5 3 . 228 0 . 16 28 145 3 . 5 3 . 2______________________________________ fume inner outer % % % example shield shield shield al . sub . 2 o . sub . 3 sio . sub . 2 f . sub . 2______________________________________1 0 . 6 ar 3 . 8 2 . 4 0 . 3 99 . 0 0 . 032 0 . 6 ar 3 . 8 2 . 4 0 . 3 88 . 0 0 . 043 0 . 6 ar 3 . 8 2 . 4 68 . 1 31 . 5 1 . 784 0 . 6 ar 3 . 8 2 . 4 40 . 0 58 . 0 1 . 955 0 . 6 o . sub . 2 3 . 8 2 . 4 45 . 3 47 . 3 8 . 206 0 . 6 o . sub . 2 3 . 8 2 . 4 60 . 2 28 . 8 6 . 997 1 . 9 o . sub . 2 3 . 8 2 . 4 59 . 0 31 . 0 8 . 008 3 . 0 o . sub . 2 3 . 8 2 . 4 55 . 0 33 . 0 9 . 009 0 . 5 o . sub . 2 3 . 8 2 . 4 51 . 1 27 . 7 6 . 77 0 . 5 ar10 0 . 2 o . sub . 2 3 . 8 2 . 4 53 . 9 37 . 1 6 . 60 0 . 8 ar11 3 . 0 o . sub . 2 1 . 0 3 . 7 49 . 7 31 . 1 12 . 5012 3 . 0 o . sub . 2 3 . 0 3 . 7 54 . 7 30 . 5 9 . 3013 2 . 8 ar 1 . 0 3 . 7 58 . 8 27 . 6 9 . 6014 3 . 0 o . sub . 2 1 . 0 3 . 7 51 . 0 28 . 7 10 . 5015 3 . 0 o . sub . 2 3 . 0 3 . 7 51 . 3 29 . 6 11 . 5016 5 . 0 o . sub . 2 1 . 0 3 . 7 58 . 4 25 . 3 12 . 3017 3 . 0 o . sub . 2 4 . 0 3 . 7 56 . 6 29 . 3 9 . 3018 5 . 0 o . sub . 2 1 . 0 3 . 7 n . a . n . a . 16 . 2019 0 . 3 ar 2 . 4 3 . 7 n . a . n . a . 9 . 6020 5 . 0 o . sub . 2 1 . 0 3 . 7 42 . 6 28 . 5 19 . 2021 0 . 3 ar 2 . 4 3 . 7 n . a . n . a . 10 . 6022 5 . 0 o . sub . 2 1 . 0 3 . 7 53 . 8 26 . 0 16 . 5023 5 . 0 o . sub . 2 1 . 0 3 . 7 38 . 2 39 . 0 16 . 2024 5 . 0 o . sub . 2 1 . 0 3 . 7 36 . 2 42 . 0 15 . 2025 5 . 0 o . sub . 2 1 . 0 3 . 7 70 . 0 11 . 4 14 . 2026 5 . 0 o . sub . 2 1 . 0 3 . 7 72 . 9 11 . 5 14 . 3027 5 . 0 o . sub . 2 1 . 0 3 . 7 64 . 2 12 . 3 16 . 2028 5 . 0 o . sub . 2 1 . 0 3 . 7 48 . 4 21 . 6 21 . 00______________________________________ n . a . = not analyzed several general observations can be made with respect to table i . a highly oxidizing flame is necessary to promote high concentrations of fluorine in the soot . that is , every increase in the oxidizing nature of the flame , whether in the inner shield , the fume shield , or in the outer shield , or in the flow rates thereof , resulted in an increase in the fluorine level in the powder . the nature of the fume shield appears to be especially critical . for example , the retention of fluorine in the powder is generally much less where argon gas comprises the fume shield than where oxygen gas forms the fume shield . there appears to be an inverse correlation between the fluorine content of the amorphous powder and the flow rate of sicl 4 vapor . the temperatures of the sicl 4 and al ( hfa ) 3 vapors as they enter the burner appear to have a minor effect upon the stoichiometry of the powder . the flow rate of the ch 2 / o 2 combustible gas does not appear to exert any substantive effect upon the stoichiometry of the soot . as was explained above in general terms , the sintering step to produce integral bodies of high fluorine , aluminosilicate compositions comprehends subjecting the amorphous soot to a heat treatment involving four parameters : ( d ) although sintering may be carried out in oxidizing and neutral environments , the highest levels of fluorine in the final product , i . e ., to synthesize essentially stoichiometric topaz , are only secured in reducing environments . as was also described above , amorphous powder from the flame was deposited on rectangular samples of stainless steel or a transparent glass - ceramic . nf 3 constituted the preferred fluorine - containing atmosphere , although a combination of sif 4 and h 2 o vapors was also operable for that purpose . finally , the preferred reducing atmosphere consisted of a mixture of co and co 2 . fig2 provides a schematic illustration of a laboratory electrically - heated tube furnace equipped with atmosphere variation and control capabilities . as pictured there , 10 represents generally a glass tube formed from corning code 7690 , a refractory 96 % silica glass marketed by corning incorporated , corning , n . y . under the trademark vycor . tube 10 has a concentrically - reduced end portion 11 providing a port therein and an open end portion which is covered by a replaceable cap 12 . cap 12 , which was also fashioned from corning code 7690 glass , has ports 13 and 14 to permit the exhaust of gases ( through port 13 ) in order to vary the atmosphere within tube 10 , and to permit the movement ( through port 14 ) of sample 15 on sample holder 16 which rests on rod 17 between baffles 18 and 19 , the latter being integral with rod 17 . sample holder 16 and rod 17 were likewise fabricated from corning code 7690 glass . that construction allows the rapid insertion of sample 15 into the hot zone of furnace 20 without opening furnace 20 or disturbing the atmosphere therein . to provide the atmosphere in furnace 20 , nf 3 gas from source 21 was mixed with a combination of co 2 gas from source 22 and co gas from source 23 , and that mixture was passed through port 11 into tube 10 and thence vented out through port 13 . in operation , sample 15 was positioned within tube 10 and cap 12 placed on tube 10 with rod 17 extending thereout through port 14 . sources of 21 , 22 , and 23 were connected to inport 11 and the gases flowed therethrough to purge the atmosphere in tube 10 of air . ( if desired , gaseous nitrogen or argon may be utilized to purge the tube atmosphere and the flows of nf 3 , co 2 , and co thereafter commenced .) the flow of gases was continued until essentially all of the air had been removed , thereby assuring a reducing environment in tube 10 . sample 15 was then quickly introduced via movement of rod 17 into the zone of furnace 20 wherein the desired temperature within the range of 650 °- 925 ° c . is located . after a previously determined exposure period , sample 15 was quickly withdrawn from furnace 20 , but held within tube 10 with cap 12 in place , in order to cool under reducing conditions in an active flow of the gases . table ii sets forth a soot composition example from table i , the sintering temperature in ° c ., the hold time at that temperature in minutes , the gaseous atmosphere within the furnace tube , the flow rate in liters / minute of the gaseous atmosphere within the furnace tube , and the topaz index . in each example except 15 , the sample was quickly introduced into the hot zone of furnace , whereas in example 15 the sample was heated at about 5 ° c ./ minute . stainless steel comprised the substrate in the last three treatments of example 28 ; the above - described transparent glass - ceramic constituted the substrate in all of the other examples . table ii__________________________________________________________________________ex . temp hold flow atmosphere index__________________________________________________________________________15 800 15 1 . 1 0 . 9 air / 0 . 1 nf . sub . 3 0 . 138 700 15 1 . 1 0 . 9 ar / 0 . 1 nf . sub . 3 0 . 338 800 15 1 . 1 0 . 9 ar / 0 . 1 nf . sub . 3 0 . 9016 800 30 1 . 1 0 . 9 ar / 0 . 1 nf . sub . 3 0 . 2518 800 15 1 . 1 ar vol . 21 900 30 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 vol . 21 950 10 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 none22 800 15 0 . 55 0 . 8 he ( hcl )/ 0 . 2 nf . sub . 3 * 0 . 8022 800 15 1 . 1 0 . 49 he / 0 . 01 cl / 0 . 3 o . sub . 2 / 0 . 2 nf . sub . 3 & lt ;& lt ; 0 . 0122 700 15 1 . 1 0 . 5 he / 0 . 3 o . sub . 2 / 0 . 2 nf . sub . 3 & lt ;& lt ; 0 . 0624 650 45 1 . 1 0 . 9 ar ( hcl )/ 0 . 1 nf . sub . 3 & lt ; 0 . 8628 800 10 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 1 . 0028 850 10 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 1 . 0028 850 10 0 . 55 0 . 89 ar / 0 . 01 cl / 0 . 1 nf . sub . 3 1 . 0028 900 10 0 . 55 0 . 89 ar / 0 . 01 cl / 0 . 1 nf . sub . 3 & lt ;& lt ; 0 . 0128 900 10 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 1 . 0028 900 10 0 . 55 0 . 5 ar ( h . sub . 2 o )/ 0 . 5 sif . sub . 4 1 . 0028 900 10 0 . 55 0 . 33 co . sub . 2 / 0 . 17 co + h . sub . 2 o / 0 . 5 sif . sub . 4 1 . 0028 600 15 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 none28 700 15 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 1 . 0028 650 45 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 none28 900 10 0 . 55 0 . 45 co . sub . 2 / 0 . 45 co / 0 . 1 nf . sub . 3 1 . 028 900 10 0 . 55 0 . 6 co . sub . 2 / 0 . 3 co / 0 . 1 nf . sub . 3 1 . 028 900 10 0 . 55 0 . 2 co . sub . 2 / 0 . 72 co / 0 . 07 nf . sub . 3 1 . 0__________________________________________________________________________ * argon bubbled through 6n hcl ** argon bubbled through distilled h . sub . 2 o first , topaz can be synthesized at temperatures of at least 650 ° c ., but below 950 ° c . synthetic topaz could be produced at 650 ° c . in a neutral atmosphere , but complete elimination of extraneous fluorides was not attained ( see example 24 ). topaz is not stable at 950 ° c . and decomposes into a mixture of fluorides with , occasionally , mullite , such as is demonstrated in example 21 . hence , a firing temperature of about 925 ° c . is deemed to constitute a practical maximum . the development of extraneous fluorides appears to be more effectively suppressed in neutral atmospheres when higher firing temperatures are employed , as is exemplified in example 8 at 700 ° c . and example 8 at 800 ° c ., both in ar / nf 3 , with topaz ratios of 0 . 33 and 0 . 90 , respectively . the effect of sintering temperature does not appear to be very significant where reducing atmospheres are utilized , provided that the lower and upper extremes are avoided . hence , fluor - topaz has been generated by sintering ( example 28 ) at temperatures of 700 ° c ., 800 ° c ., 850 ° c ., and 900 ° c . second , sintering times required for the crystallization of topaz are at least about five minutes , but less than one hour , and are generally on the order of 10 - 15 minutes . sintering times will preferably be held below 30 minutes inasmuch as longer times hazard volatilization of fluorine or even of the entire sample ( example 21 ). example 24 utilized long firing times at 650 ° c ., but total elimination of extraneous fluorides was not achieved . third , slow heating rates appear to yield increased proportions of undesired fluorides in the final product , as can be observed in a comparison of example 15 with example 8 . that phenomenon seems to be particularly present when sintering temperatures of 700 °- 800 ° c . are utilized . hence , optimum products appear to result when the samples are plunged into the sintering zone of the furnace . fourth , the absence of fluorine from the furnace atmosphere leads to a loss of fluorine , or even complete volatilization of the soot . that circumstance can be seen through a comparison of example 18 , where all of the sample volatilized , with example 8 having a topaz ratio of 0 . 90 . nevertheless , excess fluorine in the atmosphere can lead to the development of extraneous fluorides in the final product . consequently , the ratio of fluorinated gas to carrier gas must be kept below a prescribed value to suppress this formation of fluorides . as noted above , this value varies with the gas ; for nf 3 it must be ≦ 10 % and for sif 4 ≦ 50 %. fifth , an oxidizing atmosphere appears to exert a very adverse effect upon the level of topaz that will be present in the final product . that fact can be seen in the three treatments of example 22 . whereas , a relatively high concentration of topaz can be formed utilizing a neutral atmosphere , it appears that a reducing atmosphere is necessary to assure the complete elimination of fluorides from the final product .