Title:
PRECIPITATION OF METAL SALTS
United States Patent 3790387
Abstract:
Improved precipitation processes for forming metal salt crystals are disclosed wherein crystals of metal salts are made by forming nuclei of the metal salt at a high temperature and the remainder of the crystal growth procedure is continued at a lower temperature. In one preferred embodiment, relatively large crystals having a narrow size distribution can be produced, especially when making photographic silver halide emulsions.
US Patent References:
Method of making silver iodide crystals
Watson - December 1952 - 2620264
Direct positive photographic emulsion
De Maria - March 1961 - 2976149
Crystallizing apparatus and method of operating the same
Ebner - June 1964 - 3137544
Process for producing finely divided rounded particles
Markels - December 1965 - 3222231
METHOD FOR PRODUCING HIGH-PURITY CRYSTALS USING SERIALLY CONNECTED CRYSTALLIZATION ZONES
Hays - December 1970 - 3547597
Method of making silver iodide crystals
Watson - December 1952 - 2620264
Direct positive photographic emulsion
De Maria - March 1961 - 2976149
Crystallizing apparatus and method of operating the same
Ebner - June 1964 - 3137544
Process for producing finely divided rounded particles
Markels - December 1965 - 3222231
METHOD FOR PRODUCING HIGH-PURITY CRYSTALS USING SERIALLY CONNECTED CRYSTALLIZATION ZONES
Hays - December 1970 - 3547597
Application Number:
05/236219
Publication Date:
02/05/1974
Filing Date:
03/20/1972
View Patent Images:
Export Citation:
Assignee:
Eastman Kodak Company (Rochester, NY)
Primary Class:
Other Classes:
23/295R
International Classes:
G03C1/015; G03C1/02; G03C1/28
Field of Search:
96/94,114.7,107 23/295,301
Other References:
"Nucleation and Growth of Crystals in Gels," J. Electrochem. Soc., Dennis, J., Vol. 114, No. 3, 1967, pp. 263-266..
Primary Examiner:
Torchin, Norman G.
Assistant Examiner:
Suro Pico, Alfonso T.
Attorney, Agent or Firm:
Robert, Hampton Et Al W.
Parent Case Data:
This is a division of copending application Ser. No. 31,351 filed Apr. 23, 1970, now abandoned.
Claims:
1. In a process for precipitating silver halide crystals in an aqueous medium in the presence of an organic thioether wherein a solution of silver nitrate is mixed with a solution of a soluble halide salt, said halide being selected from the group consisting of chlorides, bromides, iodides and mixtures thereof, and maintaining the crystals in contact with the mother liquor throughout the entire precipitation, the improvement comprising forming the initial silver halide nuclei at a temperature greater than about 55° C and carrying out the remainder of the crystal formation at a temperature less than 70° C and at least about 20° C cooler than the initial precipitation while maintaining the pAg and pH of the precipitation medium substantially constant
2. A process according to claim 1 wherein the forming of the initial silver halide nuclei and remainder of the crystal formation are carried out in an
3. A process according to claim 1 wherein the silver halide is precipitated in the presence of a hydrophilic colloid.
2. A process according to claim 1 wherein the forming of the initial silver halide nuclei and remainder of the crystal formation are carried out in an
3. A process according to claim 1 wherein the silver halide is precipitated in the presence of a hydrophilic colloid.
Description:
This invention relates to an improved method of forming crystals of a salt. In one aspect, this invention relates to improved silver salt precipitation processes. In another aspect this invention relates to a salt precipitation process wherein the crystal-growth procedure is continued at a lower temperature and preferably in the same vessel in a continuous precipitation process. Another aspect of this invention relates to the formation of dispersions of large monodispersed crystals.
It is known in the art now to precipitate large grains of salts in a liquid medium. However, under most precipitation conditions, small grains nucleate while the large grains are growing, making it difficult to form a precipitate of crystals having a substantially uniform grain size. Moreover, many of the procedures in the prior art required the seeding of a precipitation medium with small nuclei to build up a core-shell or layered structure; however, this procedure is prone to introduce random faults in the crystal structure due to handling between successive precipitations. Therefore, improved precipitation processes are desirable.
I have now discovered an improved process of forming crystals of salts wherein large-grain precipitates can be obtained rapidly and with a substantially uniform grain size. Generally, the improved process utilizes a double-jet precipitation of the salt wherein less than 40 percent of the mass of the crystals is formed at a high temperature greater than about 55° C. and preferably greater than about 70° C.; the remainder of the precipitation is carried out at a temperature at least about 20° C. cooler than the initial precipitation, generally less than 70° C. and preferably less than 55° C. The second cooler part of the precipitation can also include the step of increasing flow rates of reactants to the vessel as disclosed in Wilgus, U.S. Ser. No. 11,838, entitled "Precipitation of Metal Salts," filed Feb. 16, 1970, now abandoned, and a continuation thereof U.S. Ser. No. 244,230 filed Apr. 14, 1972. In certain instances, it is also desirable to add ripening agents such as thioethers, thiocyanates and the like to the precipitation medium to obtain desired grain shapes and distributions.
One preferred embodiment of the invention relates to the production of silver halide grains of up to about 2 micrometers in diameter or having an edge length of up to 2 micrometers.
Another preferred embodiment relates to a double-jet precipitation procedure wherein the first 40 percent and preferably the first 20 percent of the respective salt solutions is added while the precipitation medium is held at a high temperature of at least 55° C. and preferably at least 70° C. and a substantial portion of the remainder of the precipitation is carried out wherein the precipitation medium is maintained at least 20° C. cooler in temperature of less than 70° C. and preferably less than 55° C. In a highly preferred version of this embodiment wherein silver halide is precipitated, the pAg and the pH of the precipitation medium are maintained substantially constant throughout the entire procedure.
In still another preferred embodiment, the metal salt crystals formed by the process of the present invention are maintained in contact with the mother liquor throughout the entire precipitation, i.e., the precipitation is not an interrupted procedure wherein the nuclei are added to the second vessel as seed crystals.
The process of this invention is generally applicable to the production of crystals of any salt. Typical salts which can be precipitated include silver chloride, silver bromide, silver iodide, mixed silver halides, barium sulfate, bismuth sulfate, calcium carbonate, calcium sulfate, lead carbonate, lead iodide, lead sulfate and the like. The process of this invention is especially convenient for forming metal salt crystals with minor amounts of other metal ions occluded within the crystal such as for grains or crystals used in the semiconductor arts or photographic arts. The metal ion can be introduced into the precipitation vessel at any convenient time to obtain foreign metal ion occlusions at predominantly precise locations within the crystals or throughout the crystal structure. Processes of this type are especially suitable for making silver halide grains having occluded lead ions, bismuth ions, iridium ions, gold ions, osmium ions, palladium ions, rhodium ions and the like.
The process preferably is used for the production of monodispersed crystals of salts in a liquid medium where they are insoluble or only slightly soluble. A typical highly preferred embodiment involves the precipitation of a silver halide, including mixed silver halides, in an aqueous medium. However, good results can also be obtained in the precipitation of silver halides in liquid organic solvents.
In the process of precipitation of the silver halide according to the invention, the pH and/or pAg are generally monitored and controlled by apparatus known in the art. Typical useful control apparatus are disclosed in U.S. Pat. No. =b 3,031,304 and in F. H. Claes and W. Peelaers, "Crystal Habit Modification of AgBr by Incorporation of I-Ions," Photographische Korrespondez--103-161, 1967. Automatic control apparatus of this type can be used to control the pH and/or pAg of the emulsion within a range of ±0.04 unit after the first few seconds of the precipitation start-up procedure. In accordance with the invention, the total precipitation procedure can be carried out in an interrupted manner, a continuous manner or a semicontinuous manner.
In preferred embodiments, this process can be used to make monodispersed crystals. Generally, in such emulsions no more than about 5 percent by weight or number of the crystals smaller than the mean grain size and/or no more than 5 percent by weight or number of the crystals larger than the mean grain size vary in diameter from the mean grain size by more than 25 percent and preferably no more than 10 percent. The grain size can be determined by means commonly used in the art which include projective area, electronmicroscopy and the like.
In one preferred typical precipitation procedure, the crystals can be formed by a double-jet apparatus wherein the precipitation vessel is in the shape of a bowl with upwardly extending diverging walls. The diverging-wall container will accommodate small volumes during the initial nuclei formation and will also be adequate to contain the medium under increased flow conditions. A stirrer or agitator can be employed in the vessel and preferably a dispersator such as disclosed in Frame and Johnson, U.S. Pat. No. 3,415,650, can be used. The flow rates can be controlled by peristaltic-type pumps which are in turn hand-controlled or preferably controlled with a continually monitoring proportional controller. The ion concentration can be measured in the usual manner. Preferably, the nuclei are maintained in contact with the mother liquor during the reduction in temperature and throughout the entire precipitation process. Generally, agitation of the vessel is continued throughout the entire precipitation, even though there are periods when the flow of the respective metal salt reactants are stopped for periods of time.
As previously mentioned, generally any metal salt which can be precipitated in a liquid medium from the respective component reactants can be precipitated by the improved procedure of this invention. In certain specific preferred embodiments, silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide or mixtures thereof can be made by this process, including emulsions such as Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether-ripened emulsions such as those described in U.S. Pats. Nos. 2,222,264 by Nietz et al., 3,320,069 by Illingsworth, and 3,271,157 by McBride. Surface-image emulsions may be made or internal-image emulsions such as those described in U.S. Pats. Nos. 2,592,250 by Davey et al., 3,206,313 by Porter et al., 3,367,778 by Berriman and 3,447,927 by Bacon et al. Generally, this process can be used to prepare silver halide grains for negative-type emulsions or direct-positive emulsions such as those described in U.S. Pats. Nos. 2,184,013 by Leermakers, 2,541,472 by Kendall et al., 3,367,778 by Berriman, 2,563,785 by Ives, 2,456,953 by Knott et al. and 2,861,885 by Land; British Patent No. 723,019 by Schouwenaars; and French Pat. No. 1,520,821 =by Illingsworth et al.
The actual precipitation can be carried out in the presence of various peptizers, surfactants or precipitation aids to prevent undesirable physical or chemical effects on the grains such as clumping, etc. In certain embodiments, precipitation aids or peptizers can be introduced with the respective injection of the metal cation or the anion of the salt to be precipitated, or they can be present in the vessel before precipitation is initiated. In the instance of silver halide precipitation, it is generally preferred to carry out the precipitation in the presence of a petizer such as gelatin, synthetic polymeric peptizers such as hydrophilic polymers as disclosed in Perry et al., U.S. Pat No. 3,425,836 issued Feb. 4, 1969, acrylyl or methacrylyl histidine polymers such as disclosed in U.S. Pat. No. 3,419,397 issued Dec. 31, 1968, hydrophilic polymers such as disclosed in Whitely et al., U.S. Pat. No. 3,392,025, interpolymers containing vinylamine units as disclosed in Smith et al., U.S. Pat. No. 3,415,653 issued Dec. 10, 1968, interpolymers such as disclosed in Hollister, U.S. Pat. No. 3,536,677, interpolymers as disclosed in Smith et al., U.S. Pat. No. 3,615,624, and the like.
The metal salts produced in accordance with this invention can be washed, if desired, to remove the soluble salts. Typical useful procedurs involve chill-setting and leaching or coagulation-washing, e.g., by the procedures described in U.S. Pats. Nos. 2,618,556 by Hewitson et al., 2,614,928 by Yutzy et al., 2,565,418 by Yackel, 3,241,969 by Hart et al., and 2,489,341 by Waller et al.
When silver halides are produced by this method, the normal addenda useful in photographic silver halides can be added to the emulsion after completion of precipitation or during the final stages of precipitation, such as chemical sensitizers, spectral sensitizers, development modifiers, antifoggants, fogging agents such as in the case of direct-positive emulsions, developing agents, hardeners, coating aids and the like.
The invention can be further illustrated by the following examples.
Example 1
A 1-mole silver bromoiodide emulsion is prepared by simultaneously adding over a period of 11 minutes 1/8 mole silver nitrate and 1/8 mole halide (98.5 % bromide and 1.5% iodide) in aqueous solutions to a well-stored aqueous solution containing 20 grams of a gelatin derivative and 1 gram of 1,8-dihydroxy-3,6-dithiaoctane as described in McBride, U.S. Pat. No. 3,271,157, at a temperature of 83° C. and maintaining a pAg of 8.9. After precipitation, the emulsion is cooled to 50° C. and held for 5 minutes. The remaining silver nitrate and halide solutions are then added in 33 minutes at 50° C. The emulsion is then washed as described in Yutzy, U.S. Pat. No. 2,614,928.
The resulting emulsion consists essentially of spehrical grains having an average size of about 1.1 microns and a size distribution between 0.9 to 1.3 microns.
Example 2
A procedure similar to Example 1 is followed except the iodide level is decreased to 0.55 mole percent of the salts and the ripening agent is changed to 200 mg. of 1,10-dithia- 4,7,13,16-tetraoxacylooctadecane as described in Dann et al., U.S. Pat. No. 3,062,646.
The resulting emulsion consists essentially of cubic monodispersed grains 1.2 microns in diameter.
Similar results are obtained when precipitating silver chlorobromide and silver chloro-bromoiodide emulsions in the presence of small concentrations of lead ions, osmium ions, bismuth ions or iridium ions.
Example 3
An emulsion is prepared similar to that described in Example 2 except the level of ripening agent is increased to 600 mg. and the nuclei-forming precipitation is for 1 minute at 50° C.
The emulsion consists essentially of spehrical grains from 0.4 micron to 1.2 microns in diameter.
Example 4
An emulsion is prepared similar to Example 3 except the nuclei-forming precipitation is for 1 minute at 83° C.
The emulsion consists essentially of spherical grains from 1.2 microns to 1.6 microns in diameter.
Example 5 =
A pure bromide emulsion is prepared by simultaneously adding over a period of 10 minutes 1/8 mole of silver nitrate and 1/8 mole of potassium bromide, in aqueous solutions, to a well-stirred aqueous solution containing 20 g. of gelatin and 800 mg. of 1,8-dihydroxy-3,6-dithiaoctane at a temperature of 70° C. The nuclei grains are then cooled to 50° C. and held for 5 minutes. The remaining silver nitrate and potassium bromide solutions are then added in 35 minutes at 50° C. The emulsion is then washed as described in Yutzy, U.S. Pat. No. 2,614,928.
The emulsion consists essentially of silver halide grains having a size distribution between 1.0 and 1.4 microns.
Example 6
samples of the emulsions of Examples 1, 3, 4 and 5 are coated on a support, exposed for 1/50 inch on a sensitometer and then developed for 6 minutes in a conventional Elon-hydroquinone developer. After fixing and washing, the following photographic results are obtained:
Example Relative Speed γ Dmin ______________________________________ 1 123 2.40 0.09 3 89 2.58 0.09 4 107 2.17 0.09 5 100 2.77 0.05 ______________________________________
he size distributions of the silver halide grains of the above-described emulsions of Examples 1, 3, 4 and 5 are determined by using photomicrographs of the respective emulsions. The respective emulsions consist essentially of silver halide grains of a size within the range in the table below:
Emulsion Time-Temp. of Nucleation Time-Temp. of Grain Growth Size Distribution (microns) ______________________________________ Example 1 11' 83° C. 33' 50° C. 0.9-1.3 Example 3 1' 50° C. 33' 50° C. 0.4-1.2 Example 4 1' 83° C. 33' 50° C. 1.2-1.6 Example 5 10' 70° C. 35' 50° C. 1.0-1.4 ______________________________________
It is apparent from the above data that silver halide emulsions having improved photographic properties, such as Dmin and photographic speed, can be made by the present invention. It is also interesting to observe that silver halide emulsions having a relatively narrow size distribution can be made by this method. Examples 1, 4 and 5 which employed at least a 20° C. temperature drop in the precipitation medium between nucleation and the main portion of the grain growth result in larger grains with a very narrow size distribution compared to Example 3 wherein nucleation and grain growth occur at the same temperature. The size distribution results obtained are quite unexpected since substantially more silver halide is required in making larger grains as the volume of a grain, i.e., the mass of silver halide needed to make the grain, increases geometrically with the increase in diameter or edge length.
Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention.
It is known in the art now to precipitate large grains of salts in a liquid medium. However, under most precipitation conditions, small grains nucleate while the large grains are growing, making it difficult to form a precipitate of crystals having a substantially uniform grain size. Moreover, many of the procedures in the prior art required the seeding of a precipitation medium with small nuclei to build up a core-shell or layered structure; however, this procedure is prone to introduce random faults in the crystal structure due to handling between successive precipitations. Therefore, improved precipitation processes are desirable.
I have now discovered an improved process of forming crystals of salts wherein large-grain precipitates can be obtained rapidly and with a substantially uniform grain size. Generally, the improved process utilizes a double-jet precipitation of the salt wherein less than 40 percent of the mass of the crystals is formed at a high temperature greater than about 55° C. and preferably greater than about 70° C.; the remainder of the precipitation is carried out at a temperature at least about 20° C. cooler than the initial precipitation, generally less than 70° C. and preferably less than 55° C. The second cooler part of the precipitation can also include the step of increasing flow rates of reactants to the vessel as disclosed in Wilgus, U.S. Ser. No. 11,838, entitled "Precipitation of Metal Salts," filed Feb. 16, 1970, now abandoned, and a continuation thereof U.S. Ser. No. 244,230 filed Apr. 14, 1972. In certain instances, it is also desirable to add ripening agents such as thioethers, thiocyanates and the like to the precipitation medium to obtain desired grain shapes and distributions.
One preferred embodiment of the invention relates to the production of silver halide grains of up to about 2 micrometers in diameter or having an edge length of up to 2 micrometers.
Another preferred embodiment relates to a double-jet precipitation procedure wherein the first 40 percent and preferably the first 20 percent of the respective salt solutions is added while the precipitation medium is held at a high temperature of at least 55° C. and preferably at least 70° C. and a substantial portion of the remainder of the precipitation is carried out wherein the precipitation medium is maintained at least 20° C. cooler in temperature of less than 70° C. and preferably less than 55° C. In a highly preferred version of this embodiment wherein silver halide is precipitated, the pAg and the pH of the precipitation medium are maintained substantially constant throughout the entire procedure.
In still another preferred embodiment, the metal salt crystals formed by the process of the present invention are maintained in contact with the mother liquor throughout the entire precipitation, i.e., the precipitation is not an interrupted procedure wherein the nuclei are added to the second vessel as seed crystals.
The process of this invention is generally applicable to the production of crystals of any salt. Typical salts which can be precipitated include silver chloride, silver bromide, silver iodide, mixed silver halides, barium sulfate, bismuth sulfate, calcium carbonate, calcium sulfate, lead carbonate, lead iodide, lead sulfate and the like. The process of this invention is especially convenient for forming metal salt crystals with minor amounts of other metal ions occluded within the crystal such as for grains or crystals used in the semiconductor arts or photographic arts. The metal ion can be introduced into the precipitation vessel at any convenient time to obtain foreign metal ion occlusions at predominantly precise locations within the crystals or throughout the crystal structure. Processes of this type are especially suitable for making silver halide grains having occluded lead ions, bismuth ions, iridium ions, gold ions, osmium ions, palladium ions, rhodium ions and the like.
The process preferably is used for the production of monodispersed crystals of salts in a liquid medium where they are insoluble or only slightly soluble. A typical highly preferred embodiment involves the precipitation of a silver halide, including mixed silver halides, in an aqueous medium. However, good results can also be obtained in the precipitation of silver halides in liquid organic solvents.
In the process of precipitation of the silver halide according to the invention, the pH and/or pAg are generally monitored and controlled by apparatus known in the art. Typical useful control apparatus are disclosed in U.S. Pat. No. =b 3,031,304 and in F. H. Claes and W. Peelaers, "Crystal Habit Modification of AgBr by Incorporation of I-Ions," Photographische Korrespondez--103-161, 1967. Automatic control apparatus of this type can be used to control the pH and/or pAg of the emulsion within a range of ±0.04 unit after the first few seconds of the precipitation start-up procedure. In accordance with the invention, the total precipitation procedure can be carried out in an interrupted manner, a continuous manner or a semicontinuous manner.
In preferred embodiments, this process can be used to make monodispersed crystals. Generally, in such emulsions no more than about 5 percent by weight or number of the crystals smaller than the mean grain size and/or no more than 5 percent by weight or number of the crystals larger than the mean grain size vary in diameter from the mean grain size by more than 25 percent and preferably no more than 10 percent. The grain size can be determined by means commonly used in the art which include projective area, electronmicroscopy and the like.
In one preferred typical precipitation procedure, the crystals can be formed by a double-jet apparatus wherein the precipitation vessel is in the shape of a bowl with upwardly extending diverging walls. The diverging-wall container will accommodate small volumes during the initial nuclei formation and will also be adequate to contain the medium under increased flow conditions. A stirrer or agitator can be employed in the vessel and preferably a dispersator such as disclosed in Frame and Johnson, U.S. Pat. No. 3,415,650, can be used. The flow rates can be controlled by peristaltic-type pumps which are in turn hand-controlled or preferably controlled with a continually monitoring proportional controller. The ion concentration can be measured in the usual manner. Preferably, the nuclei are maintained in contact with the mother liquor during the reduction in temperature and throughout the entire precipitation process. Generally, agitation of the vessel is continued throughout the entire precipitation, even though there are periods when the flow of the respective metal salt reactants are stopped for periods of time.
As previously mentioned, generally any metal salt which can be precipitated in a liquid medium from the respective component reactants can be precipitated by the improved procedure of this invention. In certain specific preferred embodiments, silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide or mixtures thereof can be made by this process, including emulsions such as Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether-ripened emulsions such as those described in U.S. Pats. Nos. 2,222,264 by Nietz et al., 3,320,069 by Illingsworth, and 3,271,157 by McBride. Surface-image emulsions may be made or internal-image emulsions such as those described in U.S. Pats. Nos. 2,592,250 by Davey et al., 3,206,313 by Porter et al., 3,367,778 by Berriman and 3,447,927 by Bacon et al. Generally, this process can be used to prepare silver halide grains for negative-type emulsions or direct-positive emulsions such as those described in U.S. Pats. Nos. 2,184,013 by Leermakers, 2,541,472 by Kendall et al., 3,367,778 by Berriman, 2,563,785 by Ives, 2,456,953 by Knott et al. and 2,861,885 by Land; British Patent No. 723,019 by Schouwenaars; and French Pat. No. 1,520,821 =by Illingsworth et al.
The actual precipitation can be carried out in the presence of various peptizers, surfactants or precipitation aids to prevent undesirable physical or chemical effects on the grains such as clumping, etc. In certain embodiments, precipitation aids or peptizers can be introduced with the respective injection of the metal cation or the anion of the salt to be precipitated, or they can be present in the vessel before precipitation is initiated. In the instance of silver halide precipitation, it is generally preferred to carry out the precipitation in the presence of a petizer such as gelatin, synthetic polymeric peptizers such as hydrophilic polymers as disclosed in Perry et al., U.S. Pat No. 3,425,836 issued Feb. 4, 1969, acrylyl or methacrylyl histidine polymers such as disclosed in U.S. Pat. No. 3,419,397 issued Dec. 31, 1968, hydrophilic polymers such as disclosed in Whitely et al., U.S. Pat. No. 3,392,025, interpolymers containing vinylamine units as disclosed in Smith et al., U.S. Pat. No. 3,415,653 issued Dec. 10, 1968, interpolymers such as disclosed in Hollister, U.S. Pat. No. 3,536,677, interpolymers as disclosed in Smith et al., U.S. Pat. No. 3,615,624, and the like.
The metal salts produced in accordance with this invention can be washed, if desired, to remove the soluble salts. Typical useful procedurs involve chill-setting and leaching or coagulation-washing, e.g., by the procedures described in U.S. Pats. Nos. 2,618,556 by Hewitson et al., 2,614,928 by Yutzy et al., 2,565,418 by Yackel, 3,241,969 by Hart et al., and 2,489,341 by Waller et al.
When silver halides are produced by this method, the normal addenda useful in photographic silver halides can be added to the emulsion after completion of precipitation or during the final stages of precipitation, such as chemical sensitizers, spectral sensitizers, development modifiers, antifoggants, fogging agents such as in the case of direct-positive emulsions, developing agents, hardeners, coating aids and the like.
The invention can be further illustrated by the following examples.
Example 1
A 1-mole silver bromoiodide emulsion is prepared by simultaneously adding over a period of 11 minutes 1/8 mole silver nitrate and 1/8 mole halide (98.5 % bromide and 1.5% iodide) in aqueous solutions to a well-stored aqueous solution containing 20 grams of a gelatin derivative and 1 gram of 1,8-dihydroxy-3,6-dithiaoctane as described in McBride, U.S. Pat. No. 3,271,157, at a temperature of 83° C. and maintaining a pAg of 8.9. After precipitation, the emulsion is cooled to 50° C. and held for 5 minutes. The remaining silver nitrate and halide solutions are then added in 33 minutes at 50° C. The emulsion is then washed as described in Yutzy, U.S. Pat. No. 2,614,928.
The resulting emulsion consists essentially of spehrical grains having an average size of about 1.1 microns and a size distribution between 0.9 to 1.3 microns.
Example 2
A procedure similar to Example 1 is followed except the iodide level is decreased to 0.55 mole percent of the salts and the ripening agent is changed to 200 mg. of 1,10-dithia- 4,7,13,16-tetraoxacylooctadecane as described in Dann et al., U.S. Pat. No. 3,062,646.
The resulting emulsion consists essentially of cubic monodispersed grains 1.2 microns in diameter.
Similar results are obtained when precipitating silver chlorobromide and silver chloro-bromoiodide emulsions in the presence of small concentrations of lead ions, osmium ions, bismuth ions or iridium ions.
Example 3
An emulsion is prepared similar to that described in Example 2 except the level of ripening agent is increased to 600 mg. and the nuclei-forming precipitation is for 1 minute at 50° C.
The emulsion consists essentially of spehrical grains from 0.4 micron to 1.2 microns in diameter.
Example 4
An emulsion is prepared similar to Example 3 except the nuclei-forming precipitation is for 1 minute at 83° C.
The emulsion consists essentially of spherical grains from 1.2 microns to 1.6 microns in diameter.
Example 5 =
A pure bromide emulsion is prepared by simultaneously adding over a period of 10 minutes 1/8 mole of silver nitrate and 1/8 mole of potassium bromide, in aqueous solutions, to a well-stirred aqueous solution containing 20 g. of gelatin and 800 mg. of 1,8-dihydroxy-3,6-dithiaoctane at a temperature of 70° C. The nuclei grains are then cooled to 50° C. and held for 5 minutes. The remaining silver nitrate and potassium bromide solutions are then added in 35 minutes at 50° C. The emulsion is then washed as described in Yutzy, U.S. Pat. No. 2,614,928.
The emulsion consists essentially of silver halide grains having a size distribution between 1.0 and 1.4 microns.
Example 6
samples of the emulsions of Examples 1, 3, 4 and 5 are coated on a support, exposed for 1/50 inch on a sensitometer and then developed for 6 minutes in a conventional Elon-hydroquinone developer. After fixing and washing, the following photographic results are obtained:
Example Relative Speed γ Dmin ______________________________________ 1 123 2.40 0.09 3 89 2.58 0.09 4 107 2.17 0.09 5 100 2.77 0.05 ______________________________________
he size distributions of the silver halide grains of the above-described emulsions of Examples 1, 3, 4 and 5 are determined by using photomicrographs of the respective emulsions. The respective emulsions consist essentially of silver halide grains of a size within the range in the table below:
Emulsion Time-Temp. of Nucleation Time-Temp. of Grain Growth Size Distribution (microns) ______________________________________ Example 1 11' 83° C. 33' 50° C. 0.9-1.3 Example 3 1' 50° C. 33' 50° C. 0.4-1.2 Example 4 1' 83° C. 33' 50° C. 1.2-1.6 Example 5 10' 70° C. 35' 50° C. 1.0-1.4 ______________________________________
It is apparent from the above data that silver halide emulsions having improved photographic properties, such as Dmin and photographic speed, can be made by the present invention. It is also interesting to observe that silver halide emulsions having a relatively narrow size distribution can be made by this method. Examples 1, 4 and 5 which employed at least a 20° C. temperature drop in the precipitation medium between nucleation and the main portion of the grain growth result in larger grains with a very narrow size distribution compared to Example 3 wherein nucleation and grain growth occur at the same temperature. The size distribution results obtained are quite unexpected since substantially more silver halide is required in making larger grains as the volume of a grain, i.e., the mass of silver halide needed to make the grain, increases geometrically with the increase in diameter or edge length.
Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention.