CA1281225C - Emulsions and photographic elements containing silver halide grains having hexoctahedral crystal faces - Google Patents

Abstract

EMULSIONS AND PHOTOGRAPHIC ELEMENTS CONTAINING SILVER
HALIDE GRAINS HAVING HEXOCTAHEDRAL CRYSTAL FACES
Abstract of the Disclosure Silver halide photographic emulsions are disclosed comprised of radiation sensitive silver halide grains of a cubic crystal lattice structure comprised of hexoctahedral crystal faces.

Description

~X~ Z5 EMULSIONS AND PHOTOGRAPHIC ELEM~NTS CONTAINING SILVER
HALID~ GRAINS ~AVING ~EXOCTAHED~AL CRYSTAL FACES
Field Qf the Invention This invention relates to photography. More specifically, this invention is directed ~o photographic emulsions containing silver halide grains and to photographic elements containing these emulsions.
~Eief Description of the Drawin~s Figure 1 is an isometric view of a regular cubic silver halide grain;
Figure 2 i9 a schematic diagram of the atomic arrangement at a silver bromide cubic crystal surface;
Figure 3 is an isometric view of a regular octahedral silver halide grain;
Figure 4 is a schematic diagram of the atomic arrangement at a silver bromide octahedral crystal surface;
Figure 5 is an isometric view of a regular rhombic dodecahedron;
Figure 6 is a schematic diagram of the atomic arrangement at a silver bromide rhombic dodecahedral crystal surface;
Figure 7 is an isometric view of a regular cubic silver halide grain, a regular octahedral silver halide grain, and intermediate cubo-octahedral silver halide grains.
Figures 8 and 9 are front and rear isometric views of a regular {321} hexoctahedron;
Figure 10 is a schematic diagram of the atomic arrangement at a silver bromide {321}
hexoctahedral crystal surface; and Figures 11 through 15 are electron micrographs of hexoctahedral silver halide grains.
Back~round of the Invention Silver halide photography has been practiced for more than a century. The radiation sensitive . : .. , ~8~ S

silver halide compositions initially employed for imaging were termed emulsions, since it was not originally appreciated that a ~olid phase ~as present. The term "photographic emulsionl' has remained in uæe, although it has long been known that the radiation sensitive component is present in the form of dispersed microcrystals, typically referred to as grains.
Over the years silver halide grains have been the subject of intense investigation. Although high iodide silver halide grains, those containing at least 90 mole percent iodide, based on silver, are known and have been suggested for photographic applications, in practice photographic emulsions almost always contain silver halide grains comprised of bromide, chloride, or mixtures of chloride and bromide optionally containing minor amounts of iodide. Up to about 40 mole percent iodide, based on silver, can be accommodated in a silver bromide crystal structure 20 without observation of a separate silver iodide phase. However, in practice silver halide emulsions rarely contain more than about 15 mole percent iodide, with iodide well below 10 mole percent being most common.
All silver halide grains, except high iodide silver halide grains, exhibit cubic crystal lattice structures. However, grains of cubic crystal lattice structures can d'iffer markedly in appearance.
In one form silver halide grains when microscopically observed are cubic in appearance. A
cubic grain 1 is shown in Figure 1. The cubic grain is bounded by six identical crystal faces. In the photographic literature these crystal faces are usually referred to as {100) crystal faces, referring to the Miller index employed for designating crystal faces. While the {100} crystal face designation is most commonly employed in connection 1;~81~'~5 with silver halide grains, these same crystal faces are sometimes also referred to as {200} crystal faces, the difference in designation resulting from a difference in the definition of the basic unit of the crystal 3tructure. Although the cubic crystal shape is readily visually identified in regular grains, in irregular grains cubic crystal faces are not always ~quare. In grainæ of more complex shapes the presence of cubic crystal faces can be verified by a combination of visual inspection and the 90 angle of intersection formed by adjacent cubic crystal faces.
The practical importance of the {100}
crystal faces is that they present a unique surface arrangement of silver and halide ions, which in turn influences the grain surface reactions and adsorptions typically encountered in photographic applications.
This unique surface arrangement of ions as theoreti-cally hypothesized is schematically illustrated by Figure 2, wherein the smaller spheres 2 represent silver ions while the larger spheres 3 designate bromine ions. Although on an enlarged scale, the relative size and position of the silver and bromide ions is accurately represented. When chloride ions are substituted for bromide ions, the relative arrangement would remain the same, although the chloride ions are ~maller than the bromide ions. It can be seen that a plurality of parallel rows, indicated by lines 4, are present, each formed by alternating silver and bromine ions. In Figure 2 a portion of the next tier of ions lying below the surface tier is shown to illustrate their relationship to the surface tier of ions.
In another form silver halide grains when microscopically observed are octahedral in appear-ance. An octahedral grain 5 is shown in Figure 3.The octahedral grain is bounded by eight identical crystal faces. These crystal faces are referred to as ~a, ~ X~ 5 {111} crystal faces. Although the octahedral crystal shape is readily visually identified in regular grains, in irregular ~rain6 octahedral crystal faces are not always trian~ular. In grains of more complex shapes the presence of octahedral crystal faces can be verified by a combination of visual inspection and the 109.5 angle of intersection formed by adjacent octahedral crystal faces.
Ignoring possible ion adsorptions, octahedral crystal faces differ from cubic crystal faces in that the surface tier of ions can be theoretically hypothesized to consist entirely of silver ions or halide ions. Figure 4 is a schematic illustration of a {~11} crystal face, analogous to Figure 2, wherein the smaller spheres 2 represent silver ions while the larger spheres 3 designate bromine ions.
Although silver ions are shown at the surface in every available lattice position, it has been suggested that having silver ions in only every other available lattice position in the surface tier of atoms would be more compatible with surface charge neutrality.
Instead of a surface tier of silver ions, the surface tier of ions could alternatively be bromide ions. The tier of ions immediately below the surface silver ions consists of bromide ions.
In comparing Figures 1 and 2 with Figures 3 and 4 it iE' important to bear in mind that both the cubic and octahedral grains have exactly the same cubic crystal lattice structure and thus exactly the same internal relationship of silver and halide ions.
The two grains differ only in their surface crystal faces. Note that in the cubic crystal face of Figure 2 each surface silver ion lies immediately adjacent five halide ions, whereas in Figure 4 the silver ions at the octahedral crystal faces each lie immediately adjacent only three halide ions.

.. .. ..

~X81Z;~S
~5--Much less common than either cubic or octahedral silver halide grains are rhombic dodecahedral silveE halide grains. A rhombic dodecahedral grain 7 is shown in Figure 5. The rhombic dodecahedral grain is bounded by twelve identical crystal faces. These crystal faceæ are referred to as {110} (or, less commonly in reference to silver halide grains, {220}~ crystal faces. Although the rhombic dodecahedral crystal shape is readily visually identified in regular grains, in irregular grains rhombic dodecahedral crystal faces can vary in shape. In grains of more complex shapes the presence of rhombic dodecahedral crystal faces can be verified by a combination of visual inspection and measurement of the angle of intersection formed by adjacent crystal faces.
Rhombic dodecahedral crystal faces can be theoretically hypothesized to consist of alternate rows of silver ions and halide ionæ. Figure 6 is a schematic illustration analogous to Figures 2 and 4, wherein it can be seen that the surface tier of ions is formed by repeating pairs of silver and bromide ion parallel rows, indicated by lines 8a and 8b, respectively. In Figure 6 a portion of the next tier of ions lying below the surface tier is shown to illustrate their relationship to the surface tier of ions. Note that each surface silver ion lies immediately adjacent four halide ions.
Although photographic silver halide emulsionæ
containing cubic crystal lattice structure grains are known which contain only regular cubic grains, such as the grain shown in Figure 1, regular octahedral grains, such as the grain shown in Figure 3, or, in rare instances, regular rhombic dodecahedral grains, such as the grain shown in Figure 5, in practice many other varied grain shapes are also observed. For example, silver halide grains can be cubo-octa-~ , ~ '2Z ~

hedral -that is, formed of a combination of cubic and octahedral crystal faces. This is illustrated in Figure 7, wherein cubo-octahedral grains 9 and 10 are shown along with cubic grain 1 and octahedral grain 5. The cubo-octahedral grains have fourteen crystal faces, six cubic crystal faces and eight octahedral crystal faces. Analogous combinations of cubic and/or octahedral crystal faces and rhombic dodecahedral crystal faces are possible, though rarely encoun-tered. Other grain shapes, such as tabular grains androds, can be attributed to internal crystal irregularities, such as twin planes and screw dislocations. In most instances some corner or edge rounding due to solvent action is observed, and in some instances rounding is so pronounced that the grains are described as spherical.
It is known that for cubic crystal lattice structures crystal faces can take any one of seven possible distinct crystallographic forms. However, for cubic crystal lattice structure silver halides only grains having {100} (cubic~, {111}
(octahedral), or, rarely, {110} (rhombic dodecahedral) crystal faces, individually or in combination, have been identified.
It is thus apparent that the photographic art has been limited in the crystal faces presented by silver hali.de grains of cubic crystal lattice structure. As a result the art has been limited in modifying photographic properties to the choice of surface sensitizers and adsorbed addenda that are wor~able with available crystal faces, in most instances cubic and octahedral crystal faces. This has placed restrictions on the combinations of materials that can be employe~ for optimum photo-graphic performance or dictated accepting less thanoptimum performance.

Relevant Art F. C. Phillips, An Introdu~tion to C~vstallo~raphy, 4th Ed., John Wiley & Sons, 1971, is relied upon as authority for the basic preeepts and terminology of crystallography herein presented.
James, The Theory of the Photographic ~rocess, 4th Ed., Macmillan, New York, 1977, pp. 98 through 100, i3 corroborative of the background of the invention described above. In addition, Jame~ at page 98 in reference to silver halide grains states that high Miller index faces are not found.
Berry, "Surface Structure and Reactivity of AgBr Dodecahedra", Photographic Science and Engineering, Vol. 19, No. 3, May/June 1975, pp. 171 and 172, illustrates silver bromide emulsions containing {110} crystal faces.
Klein et al, "Formation of Twins of AgBr and AgCl Crystals in Photographic Emulsions", Photo-graphische Korrespondenz, Vol. 9~, No. 7, pp. 99-102 (1963) describes a variety of singly and doubly twinned silver halide crystals having {100) (cubic) and {111} (octahedral) crystal faces.
Klein et al is of interest in illustrating the variety of shapes which twinned silver halide grains can assume while still exhibiting only {111} or {100} crystal faces.
A. P. H. Trivelli and S. E. Sheppard, ~h~
Silver Bromi~ Grain of Photographic ~mulsions, Van Nostrand, Chapters VI and VIII, 1921, is cited for historical interest. Magnifications of 2500X and lower temper the value of these observations. Much higher resolutions of grain features are obtainable with modern electron microscopy.
W. Reinders, "Studies of Photohalide Crystals", Kolloid-Zeitschrift, Vol. 9, pp. 10-14 (1911); W. Reinders, "Study of Photohalides III
Absorption of Dyes, Proteins and Other Organic 1 ~ 8 Compounds in Crystalline Silver Chloride", Zeitschrift fur Physik~lische Chemie, Vol. 77, pp. 677-699 (1911);
~irata et al, "Crystal ~abit of Photographic Emulsion Grains", ~. Photog. ~oc. of Japan, Vol. 36, pp.
359-363 (1973); Locker U.S. Patent 4,183,756; and Locker et al U.S. Patent 4,225,666 illustrate teachings of modifying silver halide grain shapes through the presence of various materials present during silver halide grain formation.
Wulff et al U.S. Patent 1,696,~30 and Heki et al Japanese Kokai 58[1983]-54333 describe the precipitation of silver halide in the presence of benzimidazole compounds.
Halwig U.S. Patent 3,519,426 and Oppenheimer et al, "~ole of Cationic Surfactants in Recrystalliza-tion of Aqueous Silver Bromide Dispersions", Smith Particle Growth and ~pension, Academic Press, London, 1973, pp. 159-178, disclose additions of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene to silver chloride and silver bromide emulsions, respectively.
S~mmary of the I--vention In one aspect this invention is directed to a silver halide photographic emulsion comprised of radiation sensitive silver halide grains of a cubic crystal lattice structure comprised of hexoctahedral crystal faces.
In another aspect this invention is directed to a photographic element containing at least one emulsion of the type previously described.
The invention presents to the art for the first time the opportunity to realize the unique surface configuration of hexoctahedral crystal faces in photographic silver halide emulsions. The invention thereby renders accessible for the first time a new choice of crystal faces for modifying photographic characteristics and improving interac-tions with sensitizers and adsorbed photographic addenda.

,~i .~

~ ~ 8~2 Description of Preferred Embodiments The present invention relates to silver halide photographic emulsions comprised of radiation sensitive silver halide gralns of a cubic cry~tal lsttice structure comprised of hexoctahedral crystal faces and to photographic elements including the emulsions.
In one form the silver halide grains csn take the form of regular hexoctahedra. A regular hexoctahedron 11 is shown in Figures 8 and 9. A
hexoctshedron has forty-eight identical faces.
Although any grouping of faces is entirely arbitrary, the hexoctahedron can be visualized as 5iX separate clusters of crystal faces, each cluster containing eight separate faces. In Figure 8 faces 12a, 12b, 12c, 12d, 12e, 12f, 12g, and 12h can be visualized as members of a first cluster of faces. A second cluster of faces is represented by faces 13a, 13~, 13c, 13d, 13e, 13f, and 13g. The eighth face of the cluster, 13h, is shown substantially normal to the field of view. Faces 14a, 14b, 14c, and 14d represent four visible faces of a third cluster of eight faces, and faces 15a and 15b represent two visible faces of a fourth cluster of eight faces.
Two remaining clusters of eight faces each are entirely hidden from view on the opposite slde of the hexoctahedron.
Figure 9 shows a back view of the hexoctahe-dron 11 obtained by 1~0 rotation of the hexoctahe-dron about a vertical axis. Faces 14e, 14f, 14g, and14h of the third cluster are shown. Faces 15c, 15d, 15e, 15f, 15g, and 15h of the fourth cluster are shown. Faces 16a, 16b, 16c, 16d, 16e, 16f, 16g, and 16h forming a fifth cluster are ~hown. Faces 17a, 17b, 17c, 17d, 17e, 17f, 17g, and 17h complete the sixth cluster.

Looking at the hexoctahedron it can be Reen that there are eight intersections of ad~acent faces within each cluster, and there are two face intersec-tions of each cluster with each of the four clusters ad~acent to lt for a total of seventy-two face edge intersections. The relative angles formed by intersecting faces have only three different Yalues.
All intersections of a face from one cluster with a face from snother cluster are identical, forming a first relative angle. All ad~acent faces within each cluster intersect at one of two different relative angles. Looking at one cluster in which all faces are fully visible, the lntersections between feces 12a and 12b, 12c and 12d, 12e and 12f, and 12g and 12h are all at the same relative angle, referred to ~s a second relstive angle. The intersections between faces 12b and 12c, 12d and 12e, 12f and 12g, and 12h and 12a are all at the same relative angle, referred to as a third relative angle, since it is of a different value than both the first and second relstive angles. While the regular hexoctahedron has a distinctive appearance that cfln be recognized by viRual inspection, it should be appreciated that measurement of any one of the three relative angles provides a corroboration of ad~acent hexoctahedral crystal faces.
In cryRtallography measurement of relative angles of ad~acent crystal faces ls employed for pos~tive crystal face identification. Such tech-niqueR are deRcribed, for example, by Phillips, citedabove. Theae techniques can be combined wlth techniques for the microscopic examination of silver halide gr~ins to identify positively the hexoctahe-dral crystal faces of silver halide grains.
Techniques for preparing electron micrographs of silver halide grains are generally well known in the art, as illustrated by B.M. Spinell and C.F. Oster, ~ ;~8~

"Photographic Materials", The EncycloPedia of MicroscopY and Microtechnique, P. Gray, ed., Van Nostrsnd, N.Y., 1973, pp.427-434, note particularly the section dealing with carbon replica electron S microscopy at pages 429 and 430. Employing tech-niques well known in electron microscopy, carbon replicas of silver halide grains are first prepared.
The carbon replicas reproduce the grain shape while avoiding shape altering ~ilver print-out that is known to result from employing the silver halide grains without carbon qhells. An electron scanning beam rather than light is employed for imaging to permit h~gher ranges of magni$ication to be realized than when light is employed. When the grains are sufficiently spread apart that ad~acent grains are not impinging, the grains lie flat on one crystal face rather than on a coign (i.e., a point). By tilting the sample being viewed relative to the electron beam a selected grain can be oriented so that the line of sight i-q substantially parallel to both the line of intersection of two ad~acent crystal faces, seen as a point, and each of the two inter-secting crystal faces, seen as edges. When the grain faces &re parallel to the imaging electron beam, the two corresponding edges of the grain which they define will appear sharper than when the fsces are merely close to beir~g parallel. Once the deslred grain orientation with two intersecting crystal faces presenting a parallel edge to the electron beam is obtained, the angle of intersection can be measured from an electron micrograph of the oriented grain.
In this way ad~acent hexoctahedral crystal faces can be identified. Relative angles of hexoctahedral and ad~acent crystal faces of other Miller indices can also be determined in the same w&y. Again, the unique relative angle allows a positive identifica-tion of the crystal faces. While relative angle 1;~81~:XS

measurements can be definitive, in many, if not most, inRtances visual inspection of grains by electron microscopy allows immediate identification of hexoctahedral cry~tal ~aces.
~eferring to the mutually perpend~cular x, y, and z axes oF 8 cubic crystal lattice, it is well recognized in the art that cubic crystal faces are parallel to two of the axes and intersect the third, thus the {100} Miller index a~signment; octahe-dral crystal faces intersect each of the three axes st an equal interval, thus the 1111} Miller index assignment; and rhombic dodecahedral crystal faces inter~ect two of the three axes at an equal interval and are parallel to the third axis, thu~ the {110} Miller index assignment. For a given definition of the basic crystal unit, there i~ one and only one Miller index assignment for each of cubic, octahedral, and rhombic dodecahedral cryst~l faces.
Hexoctahedral crystal faces include a family of crystfll faces that can have differing Miller index values. Hexoctahedral crystal faces are gener~cally designated as {hkQ} crystal faces, wherein h, k, and Q are each integers greater than 0; h is greater than k; and k i9 greater than Q. The regular hexoctahedron 11 shown in Figures 8 ~nd 9 consists oF {321} cry~tal faces, which corre-sponds to the lowest value that h, k, and Q can each represent. A regular hexoctahedron having {421}, {431}, {432}, {521}, {531}, {532}, {541}, {542}, or {543} crystal faces would appear similar to the hexoctahedron 11, but the higher Miller indices would result in changes in the angles of intersection.
Although there is no theoretical limit on the maximum value~ of the integers h, k, and Q, hexoctahedral crystal faces having a value of h of 5 or less are ~ 8~'~2 5 more easily generated. For this reason, silver halide grains having hexoctahedral crystal faces of the exemplary Miller index value identified above are preferred. With practice one hexoctahedral crystal face can often be distinguished visually from another of a different Miller index value.
Measurement of relative angles permits positive corroboration of the specific Miller index value hexoctahedral crystal faces present.
In one form the emulsions of this invention contain silver halide grains which are bounded entirely by hexoctahedral crystal faces, thereby forMing basically regular hexoctahedra. In practice although some edge rounding of the grains is usually present, the unrounded residual flat hexoctahedral faces permit positive identification, since a sharp intersecting edge is unnecessary to establishing the relative sngle of ad~acent hexoctahedral cry~tal faces. Sighting to orient the grains is still possible employing the residual flat crystal face portions.
The radiation sensitive silver halide grains pre~ent in the emulsions of this invention are not confined to those ~n which the hexoctahedral crystal faces are the only flat crystal faces present. Just as cubo-octahedral sllver halide grains, ~uch as 9 snd 10, exhibit both cubic and octahedral crystal faces and Berry, cited above, reports grains having cubic, octahedral, and rhombic dodecahedral crystal faces in R single grain, the radiation sensitive grains herein contemplated can be formed by hexocta-hedral crystal faces in combination with any one or combination of the other types of crystal faces possible with a qilver halide cubic crystal lattice structure. For example, if conventional Rilver hallds grains having cubic, octahedrsl, and/or rhombic dodecahedral crystal faces are employed as Z~

host grains for the preparation of ~ilver halide grains having hexoctahedral crystal faces, stopping silver halide deposition onto the host grains before the original cryst&l faces have been entirely S overgrown by silver halide under conditions favoring hexoctahedral crystal face formation results in both hexoctahedral crystal faces and residual crystal faces corresponding to those of the original host grain being present. Starting with cubic host grains, the preparation of cubo-hexoctahedral grains is illustrated in the examples.
In another variant form deposition of silver halide onto host grains under conditions which favor hexoctahedral crystal faces can initially result in ruffling of the grain surfaces. Under close examination it has been observed that the ruffles are provided by protrusions from the host grain surface.
Protrusions in the form of ridges have been observed, but protrusions, when present, are more typically in the form of pyramids. Pyramids presenting hexoctahe-dral crystal faces on host gralns initially present-ing {100} crystal faces have eight surface faces. These correspond to the eight faces of any one of the 12, 13, 14, 15, 16, or 17 series clusters described above ln connection with the hexoctahedron 11. When the host grains initially present {111}
crystal faces, pyramids bounded by six surface faces are formed. Turning to Figure 8, the apex of the pyramid corresponds to the coign formed faces 12a, 12h, 13d, 13c, 14b, and 14c. If the host grains inltially present {110} crystal faces, pyramids bounded by four surface faces are formed. Turning to Figure 8, the apex of the pyramid corresponds to the coign formed faces 12a, 12b, 13c, and 13d. The protrusions, whether in the form of ridges or pyramids, can within a short time of initiating precipitation onto the host grains substantially ~8~25 -lS-cover the original host grain surface. If silver hal~de depo~ition is continued after the entire grain ~urface is bounded by hexoctshedral crystal faces, the protrusions become progressiYely larger snd eventually the grains lose their ruffled appearance as they present larger snd larger hexoctahedral crystal faces. It is possible to grow a regular hexoctahedron from a ruffled grain by continuing silver halide deposition.
Even when the grains are not ruff`ied and bounded entirely by hexoctahedral crystal f aces, the grains can take overall shapes differing from regular hexoctahedrons. This can result, for example, from irregularities, such as twin planes, present in the host grains prior to growth of the hexoctahedral crystal faces or introduced during growth of the hexoctahedral crystal faces.
The importsnt feature to note is that if any crystal face of a ~ilver halide grain is a hexoctahe-dral crystal face, the resulting grain presents aunique arrangement of surface silver and halide ions that differs from that presented by all other possible crystal faces for cubic crystal lattice structure silver halides. This unique surface arrangement of ions as theoretlcally hypothesized is schematica:Lly illustrated by Figure 10, wherein a {321} hexoctahedral crystal face is shown formed by silver ions 2 and bromide ions 3. Comparing Flgure 10 with Figures 2, 4, and 6, it is apparent that the surface positioning of silver and bromide ions ln each figure is distinctive. The {321}
hexoctahedral crystal face presents an ordered, but more varied arrangement of surface silver and bromide ions than i~ presented at the cubic, octahedral, or rhombic dodecahedrAl silver bromide crystal faces.
This is a result of the oblique tiering that occurs st the ~321} hexoctahedral crystal face.

Hexoctahedral crystal faces with differing Miller indices also exhibit oblique tiering. The dif~ering Miller indice~ re~ult in analogous, but nevertheless unique surface arrangements of sllver and halide ions.
While Figures 2, 4, 6, and lO all contain bromide ions as the sole halide ions, it is appre-ciated that the same observations as to differences in the crystal faces obtain when each wholly or partially contains chloride ions instead. Although chloride ions are substantially ~maller in effective diameter than bromide ions, a {321~ hexoctshedral crystal surfsce presented by silver chloride would appear similar to the surface sho~n in Figure 10 The cubic crystal lattice structure silver halide grains containing hexoctahedral crystal faces can contsin minor amounts of iodide ions, similarly as conventional silver halide grains. Iodide ions have an effective diameter substantially larger thsn that of bromide ions. As is well ~nown in silver 2Q halide crystallography, this has a somewhat disrup-tive effect on the order of the cry~tal ~tructure, which can be accommodated and actually employed photographically to advantage, provided the iodide ions sre limited in concentration. Preferably iodide ion concentrations below 15 mole percent and optimally below 10 mole percent, based on silver, are employed in the practice of this invention. Iodide ion concentrations of up to 40 mole percent, based on silver, can be present in silver bromide crystals.
Since iodide ions as the sole halide ions in silver halide do not form a cubic crystal lattice structure, their use alone has no applicability to this invention.
It is appreciated that the larger the proportion of the total ~ilver halide grain surface area accounted for by hexoctahedral crystal faces the more distinctive the silver halide grains become. In ~a~ 5 most instances the hexoctahedral crystal faces account for at lesst 50 percent of the total surface area of the silver halide grain~. Where the grains are regular, the hexoctahedral crystal faces can account for all of the flat crystal faces observable, the only remsining grain surfhces being attributable to edge rounding. In other words, silver halide grains having hexoctahedral crystal faces accounting for at least 90 percent of the total grain surface area are contemplated.
It is, however, appreciated that distinctive photographic effects may be reali2ed even when the hexoctahedral crystal faces are limited in areal extent. For exsmple, where in an emulsion containing the silver halide grains ~ photographic addendum is present that shows a marked adsorption preference for a hexoctahedral crystal face, only a limited percentage of the total grain surface may be required to produce a diQtinctive photographic effect.
Generally, if any hexoctahedral crystal face is observable on a silver halide grain, it accounts for a sufficient proportion of the total surface area of the silver halide grain to be capable of influencing photographic performance. Stated another way, by the time a hexoctahedral crystal face becomes large enough to be identified by its relative angle to sdJacent crystal faces, it is already large enough to be capable of influencing photographic performance.
ThuQ, the minimum proportion of total grain surface area accounted for by hexoctahedral crystal faces is limited only by the observer '8 ability to detect the presence of hexoctahedral crystal faces.
The successful formation of hexoctahedral crystal faces on silver halide grains of a cubic crystal lattice structure depends on identifylng silver halide grain growth conditions that retard the surface growth rate on hexoctahedral crystal planes.

z~
It is generally recognized in ~ilver halide crystal-lography that the predominant crystal faces of a silver halide grain are determined by choosing grain growth conditions that are least favorable for the growth of th&t crystal face. For example, regular cubic silver halide grains, such as grain 1, are produced under grain growth conditions that favor more rapid deposition of silver and halide ions on all other available crystal faces than on the cubic crystal faces. Referring to Figure 7, if an octahedral grain, ~uch as regular octahedr~l grain 5 is aub~ected to growth under conditions that least favor deposition of silver and halide ions onto cubic crystal faces, grain 5 during continued silver halide precipitation will progress through the intermediate cubo-octahedral grain forms 9 and 10 before reaching the final cubic grain configuration l. Once only cubic crystal faces remain, then silver and halide ions deposit i~otropically on these surfaces. In other words, the grain shape remains cubic, and the cubic grains merely grow larger as additional silver and halide ions Rre precipitated.
By analogy, grains having hexoctahedral crystal face~ have been prepared by introducing into a silver halide precipitation reaction vessel host grains of conventional crystal faces, such a~ cubic grains, while maintaining growth conditions to favor retarding silver halide deposition along hexoctahe-dral crystsl faces. As silver halide precipltation continues hexoctahedral crystal faces first become identifiable and then expand in area until eventual-ly, if precipitation is continued, they account for all of the crystal faces of the silver halide grains being grown. Since hexoctahedral crystal faces accept additional silver halide deposition at a slow rate, renucleation can occur, creating a second grain population. Precipitation conditions can be ad~usted by techniques generally known in the art to favor either continued grain growth or renucleation.
Failure of the art to observe hexoctahedrsl crystal faces for silver halide grains over decades of intense investigat~on as evidenced by published silver halide crystallographic studies suggests that there i5 not an extensive range of conditions that favor the selective retarding of silver halide deposition along hexoctahedral crystal faces. It has been discovered that growth modifiers can be employed to retard silver halide deposition selectively at hexoctahedral crystal faces, thereby producing these hexoctahedral crystRl faces as the external surfaces of the silver halide grains being formed. The growth modifiers which have been identified are organic compounds. They are believed to be effective by reason of showing an adsorption preference for a hexoctahedral crystal face by reason of its unique arrangement of silver and halide ions. Growth modifiers that have been empirically proven to be effective in producing hexoctahedral crystal faces are described in the examples, below.
These growth modifiers are effective under the conditions of their use in the examples. From empirical screenlng of a variety of candidflte growth modifiers under differlng conditions of silver halide precipitation lt has been concluded that multiple parameters must be satisfied to schieve hexoctahedral crystal faces, including not only the proper choice of a growth modif~er, but also proper choice of other precipitation parameters identified in the e~amples.
Failures to achieve he~octahedral crystal faces with compounds shown to be effective as growth modifiers for producing hexoctahedral crystal faces have been observed when accompanying conditions for silver halide precipitation have been varied. However, it is appreciated that having demonstrated success in ~81~

the preparation~ of silver halide emulsions contain-ing grains with hexoctahedral crystal faces, routine empirical studies sy~tematically varying parameters are likely to lead to sdditional u~eful preparation S techniques.
Once silver halide grain growth conditions are satisfied that selectively retard silver halide deposition at hexoctahedral crystal faces, continued grain growth uQually results in hexoctahedral crystal faces appearing on ell the grains present in the silver halide precipitation reaction vessel. It does not follow, however, that all of the radistion sensitive silver halide grains in the emulsions of the present invention must have hexoctahedral crystal lS faces. For example, silver halide grains having hexoctahedral crystal faces can be blended with any other conventional silver halide grain population to produce the final emulsion. While silver halide emulsions containing any identifiable hexoctahedral crystal face grain surface are considered within the scope of this invention, in most applications the grains having at least one identifiable hexoctahedral crystal face account for st least 10 percent of the total grain population and usually these grains will account for greater than 50 percent of the total grain population.
The emulsions of this invention can be substituted for conventional emulsions to satisfy known photographic applications. In addition, the emulsions of this invention can lead to unexpected photographic advantages.
For example, when a growth modifier is present adsorbed to the hexoctahedral crystal faces of the grains and has a known photographic utility that is enhanced by adsorption to a grain surface, either ~ecause of the more intimate association with the grain surface or because of the reduced mobility ~8'1'~
-2~-of the growth modifier, improved photographic performance can be expected. The reason for this i3 that for the growth modifier to produce a hexoctPhe-dral crystal face it must exhibit an sdsorption preference for the hexoctahedral crystal face that is greater than that exhibited for any other possible crystal face. This can be appreciated by considering growth in the presence of an adsorbed growth modifier of a silver halide grsin having both cubic and hexoctahedral crystal faces. If the growth modifier shows an adsorption preference for the hexoctahedral crystal faces over the cubic crystal faces, deposi-tion of silver and halide ions onto the hexoctahedral crystal faces is retarded to a greater extent than slong the cubic crystal faces, and grain growth results in the ellmination of the cubic crystal f~ces in favor of hexoctahedral crystal fsces. From the foregoing it is apparent that growth modifiers which produce hexoctahedral crystal faces are more tightly adsorbed to these grain surface~ than to other silver halide grain ~urfaces during grain growth, and this enhanced adsorption carries over to the completed emulsion.
To provide sn exemplary photographic application, Locker U.S. Patent 3,989,527 de~cribes improving the speed of a photographlc element by employing an emulsion containing radiation sensitive silver halide grains having a spectral sensitizing dye adsorbed to the grain surfaces in combination with sllver halide grains free of spectral sensitiz-ing dye having an average diameter chosen to maximize light scattering, typically in the 0.15 to 0.8 ~m range. Upon imagewise exposure radiation striking the undyed gr~ins is scattered rather than being absorbed. This re~ults in an increased amount of exposing radiation striking the radiation sensitive imaging grains having a spectral sensitizing dye ~.~8~i~25 adsorbed to their ~urfaces.
A disadvantage encountered with this approach has been that spectral sensitizing dyes can migrate in the emul~ion, RO that to some extent the S initially undyed grains adsorb spectral ~ensitizing dye which has migrated from the lnitially spectrally sensitized grains. To the extent that the initially spectrally sensitized grains were optimally sensi-tized, dye migration away from their surfaces reduces sensitization. At the same time, adsorption of dye on the grains intended to scatter imaging rad~ation reduces their scattering efficiency.
In the examples below it is to be noted that a speciflc spectral sensitizing dye has been identified as a growth modifier useful in forming silver halide grains having hexoctahedral crystal faces. When radiation ~ensitive silver halide grains having hexoctahedral crystal faces and a growth modifier spectral sensitizing dye adsorbed to the hexoctahedral crystal faces are substituted for the spectrally sensitized silver halide grains employed by Locker, the disadvantageous migration of dye from the hexoctahedral crystal faces to the sllver halide grains intended to ~catter llght ls reduced or ellminated. Thus, an improvement in photographlc efficlency can be realized.
To lllustrate another advantageous photo-graphic application, the layer structure of a multicolor photographic element whlch lntroduces dye lmage providing materlals, such as couplers, durlng processlng can be simpllfied. An emulslon lntended to record green exposure~ can be prepared using a growth modifier that is a green spectral sensitizing dye while an emul~ion intended to record red exposures can be prepared uslng a growth modlfier that is e red spectral sensltlzlng dye. Since the growth modlfiers are tlghtly adsorbed to the grains S

and non-wandering, instead of coating the green and red emulslons in separste color forming layer units, as is conventional practice, the two emulsions can be blended and coated ~s a slngle color forming layer unit. The blue recording layer can take ~ny conventional form, and a conventional yellow filter layer can be employed to protect the blended green and red recording emulsions from blue light expo-~ure. Except for blending the green and red recording emulsions in a single layer or group of layers differing in speed in a ~ingle color forming layer unit, the structure and processing of the photographic element is unaltered. If qilver chloride emulsions are employed, the approach described above can be extended to blending in a single color forming layer unit blue, green, and red recording emulsions, and the yellow filter layer can be eliminated. The advantage in either case is a reduction in the number of emulsion layers required as compared to a corresponding conventional multi-color photographic element.
In more 8eneral applications, the substitu-tion of an emulsion according to the invention containing a growth modifier spectral sensitizing dye should produce a more invariant emulqion in terms of spectral properties than a corresponding emulsion containing silver halide grains lacking hexoctahedral crystal faces. Where the growth modifier is capable of inhibiting fog, such as nitrobenzimidazole or 5-carboxy-4-hydroxy-1,3,3a,7-tetraazaindene, shown to be effective growth modifiers in the examples, more effective fog inhibition at lower concentrations may be expected. It ls recognized that a variety of photographic effects, such as photographic sensitivi-ty, minimum background density levelq, latent image~tability, nucleation, developability, image tone, absorption, and reflectivity, are influenced by grain surface interactions with other components. By employing components, such as peptizers, silver halide solvents, sensitizers or desensitizers, supersensi-tizers, halogen acceptors, dyes, antifoggants, stabilizers, latent image keeping agents, nucleating agents, tone modifiers, development accelerators or inhibitors, development restrainers, developing agents, and other addenda that are uniquely matched to the hexoctahedral crystal surface, distinct advantages in photographic performance over that which can be realized with silver halide grains of differing crystal faces are possible.
The silver halide grains having hexoctahedral crystal faces can be varied in their properties to satisfy varied known photographic applications as desired. Generally the techniques for producing surface latent image forming grains, internal latent image forming grains, internally fogged grains, surface fogged grains, and blends of differing grains described in Research Disclosure, Vol. 176, December 1978, Item 17643, Section I, can be applied to the preparation of emulsions according to this invention.
Research Disclosu~ is published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire P010 7DD, England. The silver halide grains having hexocta-hedral crystal faces can have silver salt deposits on their surfaces, if desired. Selective site silver salt deposits on host silver halide grains are taught by Maskasky U.S. Patents 4,463,087 and 4,471,050.
The growth modifier used to form the hexoctahedral crystal faces of the silver halide grains can be retained in the emulsion, adsorbed to the grain faces or displaced from the grain faces.
For example, where, as noted above, the growth modifier i8 also capable of acting as a spectral :` ~
,~1 . .

~ 2 sensitlzlne dye or performin~ some other u eful functlon, it ls ~dvsnta~eous to ret~in the growth modifler ln the emulslon. Where the growth modifier is not relled upon to perform an ~dditional useful photogrsphlc functlon, lts presence in the emulsion csn be reduced or elimlnated, if desired, once its lntended function is performed. This spproach is advants~eous where the F,rowth modifier i~ ~t all dissdvantageous in the environment of use. The growth modlfier can itself be modified by chemical lnteractions, such as oxld~tion, hydrolysis, or ~dditlon reactlons, sccomplished with reagents such a~ bromine water, bsse, or acid -e.~., nitric, hydrochloric, or sulfuric ~cid.
Apart from the novel Brain structures identified above, the radiation sensitive silver ~allde emulsions snd the photogrsphic elements in which they are incorporated of this invention can take any convenient conventional form. The emulsions csn be wsshed ~ described in Research Disclosure, Item 1/643, cited above, Section II.
The radlatlon sensitive silver halide grains of the emulsions csn be surface chemicslly sen~i-tlzed. Noble metal (e.p~., gold), middle chalcogen (e.e., sulfur, selenlum, or tellurium), and reduction sens~tlze~s, employed indivldually or in combination are speciPically contemplated. Typical chemical sensittzers are listed in Research Disclosure, Item 17643, clted above, Section III. From comp~risons of surf~ce hallde snd sllver ion arrangements in genersl the chemical sensitization response of ~ilver halide grains h~vin~ hexoctshedrsl crystal faces should be analogous, but not identical, to thst of cubic and octahedral silver haltde grains. That observ~tion c~n be extended to emulsion addends generally which adsorb to Brsin surface ~ 2 The sllver halide emulslons can be ~pectral-ly sensltlzed with dyes from a variety of classes, Lncluding the polymethine dye cl~ss, which includes the cyanines, merocyanines, complex cyanines snd merocyanlnes (~.e., tri-, tetra-, and polynuclear cyanines and merocyanines), oxonols, hemioxonols, styryls, merostyryls, snd streptocyanines. Illustra-tlve spectral sensLt1zinp, dyes are ~isclosed in Research Disclosure, Item 17643, cited above, Section IV.
The s11ver h~llde emulsions as well as other l~yers of the photographic elements of this invention can contain as vehicles hydrophilic colloids, employed alone or ln combination with other polymeric materials (e.g., latlces). Suitable hydrophilic materials lnclude both naturslly occurring substances such as proteLns, proteln derivatives, cellulose derlvatives -e.e., cellulose esters, gelatLn-e.g., alk~li treated Æelatin (cattle, bone, or hide gel~tLn) or acid treated gelstin (pigskin gelatin), gelatin derlvatives ~e.~ acetylated gelatin, phthalated gelatin, ~nd the like, polyssccharides such as dextran, eum arabic, zein, casein, pectin, collagen derlvatlves, collodlon, sgar-agar, arrow-root, snd albumln. It Is specifically contemplatedto employ hydrophllic collolds which contain a low proportlon of dLvalent sul$ur atoms. The proportion of dlvalent sulfur ~toms can be reduced by treRting the hydrophilLc colloid wlth a strong oxidi~ing ap,ent, such as hydrogen peroxLde. Among preferred hydrophilLc collolds for use as peptizers for the emulslons o$ this inventLon are gelatino-peptizers wh~ch contsln less than 30 micromoles of methionine per gram. The vehicles can be hardened by conven-tionsl procedures. Further detsils of the vehiclesand hardener~ are provided in Research Disclosure, Item 1764~, clted ~bove, Sections IX and X.

~ ~ 81f~2 S
-2~-The silver h~lide photographic elements of this invention can contaLn other sddenda conventional in the photogr&phic art. Useful addend~ are described, for ex~mple, ln Research Disclosure> Item S 17643, cited ~bove. Other conventionsl useful sddenda include antifo~gantq and stabilizers, couplers ~such ~s dye forming couplers, masking couplers and DIR couplers) DIR compounds, anti-stsin agents, Imsge dye stablliæer~, absorbing materials sucil ss filter dyes and UV sbsorbers, light ~catter-ing materials, antlstatic agents, coating aids, and plasticizers and lubricants.
The photogr~phic elements of the present invention can be simple blsck-and-white or monochrome elements compris~ng a support bearing a layer of the silve~ hslide emul~lon, or they csn be multilsyer and/or multicolor element~. The photographic elements produce imaKes rsnBing from low contrast to very high contrast, such ss those employed for produclng half tone imaees in eraphic arts. They can be desip,ned for processing with separate solutions or for ln-c~mera processlng. In the latter instsnce the photographic elements can include conventional image transfer festures, such as those illustrated by Research Dlsclo~ure, Item 1~643, cited above, Section XXIII. Multlcolor element~ contsin dye image forming unlts sensltive to each of the three primary regions of the spectrum. Each unit can be comprised of a slnele emulsion layer or of multiple emulslon layers sensLtive to a glven region of the spectrum. The layers of the element, including the lQyers of the imap,e formine units, can be srrsnged in various orders ss known in the ~rt. In ~n altern~tive format, the emulsion or emulsions can be disposed as one or more segmented layers, e.g., ~5 by the use of microve~sels or mlcrocells, as described in Whitmore U.S. Patent 4,387,154.

1,~81 A preferred multlcolor photographic element sccordlnÆ to this invention contsining incorpor~ted dye image provlding materials comprises a qupport bearin~ st least one blue sensitive silver halide emulsion layer having as oclated therewith a yellow dye formlng coupler, at least one ~reen ~ensit~ve silver halide emulsion lsyer havinK associated therewlth a ma~enta dye forming coupl.er, and at least one red sens:ltlve silver halide emulslon layer having associated therewlth a cyan dye forming coupler, at l.east one of the silver halide emulsion layers contalnlne grain hsvine hexoctahedral cryqtal faces as previously described.
The elements of the present invention can contain addit~onal layers conventional in photo-~raphic elements, such as overcoat layers, spacer layers, fllter leyers, sntihalation layers, and scavenger layers The support can be ~ny suitable ~upport u~ed with photo~raphic elements. Typical supports include polymeri.c filmq, psper (including polymer-coQted paper), glass, and metal supports.
Details re~ardin~ supports and other layers of the photogr~phLc elements of this invention are contained in Research Disclo~ure, Item 17643, cited above, Section XVII.
The photoersph~c elements can be imagewise exposed wlt}l varlous forms of ener~y, which encompass the ultravl.olet, vlslble, and lnfrared regions of the electromagnetic spectrum as well as electron beam and - 30 beta radlation, gamma ray, X ray, alpha particl0, neutron rfldifltLon, and other forms of corpuscular and wave-like radlflnt enerey ln either noncoherent (random phase) forms or coherent (in phase) forms, as produced by l~sers. When the photographic elements sre lntended to be exposed by X rays, they can include features found ln conventional radiographic elements, such as those illustrated by Reseflrch Disclosur.e, Vol. 184, August 1979, Item 18431.

1~81;~

Proceqsine of the imagewi3e exposed photogrflphic elements can be accompli~hed in any convenient conventional msnner. Processing proced-ures, developing aeents, and development modlfiers are illustr~ted by Research Di~closure, Item 17643, cited sbove, Sections XIX, XX, ~nd XXI, respectively.
ExamPles The invention csn be better fippreciated by reterence to the following speclfic ex~mples. In e~ch of the exQmples the term "percent" means percent by welght, unless otherwise indicated, and all ~olutlons, unle~s otherwise indicAted, sre ~queous solut10ns. Dilute nltric scid or dilute sodium hydrox1de wss employed l:or pH ad~ustment, as required.
ExAmPle 1 Thls ex~mple illu~trates the preparstion of ~ hexoctahedr~l ~llver bromide emul~ion hsving the Miller index {32t~, beginning with a cubic host emulsion.
To a reaction vessel supplied with a stirrer W~9 added 0.5 e of bone gelstin dissolved in 28.5 g of wster. To thls W8S sdded 0.05 mole of ~ cubic sllver bromide emulsion of mean grsin size 0.8~m, contsinlng sbout 10 g/Ag mole gelstin, snd h~ving a tots~ welght of 21.6 g. The emulsion wss he&ted to 40C, and 0.8 milllmole/Ag mole of 6-nitrobenz-lmlda201e dissolved in 2 mL. methanol wss sdded. The mlxture wa~ held for 15 mtn. st 40C. The pH W8S
ad~usted to 6.0 at 40C. The emulsion was then heated to 60C, and the pAg ~djusted to 8.5 fft 60C
wLth KBr, ~nd mslntalned st thst value during the precipltatLon. A 2.5M solutton of AgN03 snd ~ 2.5M
solutlon of KBr were then introduced with 8 constant sllver fiddition rste over a period of 50 min., consuming 0.025 mole Ap,. The precipitation was then stopped, and an sdditional 6.0 millimoles/- original Ag mole of 6-nitrobenzimldszole dissolved in 2 ml of ~X~3~225 meth~nol were ~dded. The precipit~tion w~s then continued ~t the s~me r~te 8S before for lO mlnutes, consumIng ~n additional 0.005 mole Ag. At thi stege 8 sample (Emulsion lA) was removed. The precipits-tLon wa~ contlnued for a further 6S min., duringwhich sn ~dditional 0.0325 mole Ag was consumed, to produce Emulsion lB.
A csrbon replic~ electron micrograph (Figure ll) shows Emulslon lA to have a combinstion of cubic snd hexoct~hedral faces. Emulsion lB (Figure 12) hss hexoctahedral faces only. The Miller index of the hexocts}ledr~l faces was determined by measurement of the relatJ.ve anele between two adjacent hexoctahedral crystsl tQces. From thIs sngle, the supplement of t~e relative snele, which is the angle between their respectlve cryst~11Ographic vectors, ~, could be obt~ined, and the M.lller index of the ~d~scent hexoctahedr~l crystal fsces w~s identlfied by comp~rlson of th~s angle ~ wlth the theoreticsl intersecting anele ~ between [hlklQl] and rh2k2Q2~ vectors. The angle e was calculated as described by Phillip~, cited sbove, at pages 218 and 219.
To obtsin the angle ~, a carbon replica of the crystal sRmple wss rotsted on the stage of an electron mIcroscope untll, for a chosen crystal, the an~,le of observatlon wss dlrectly slong the line of lntersectlon of the two ad~acent crystal faces of lnterest. An electron mlcrograph was then made, and the relAtlve ~ngle was me~sured on the microgr~ph wlth a protr~ctor. The supplement of the measured relAtIve ~ngle wss the angle ~ between vectors.
The results for Emulslons lA and lB for esch of the vector sneles correspondin~, to the three different rel.stlve sngles messured sre given below. The number of messurements m~de ls given in psrentheses.
Theoretical Mlller lndlces ~s high ~s {543} were considered.

1~81225 An~le Between Vectors Theoretic~l {321} 31.0~ 21.8 44.4 Mea~ured, Emulsion lA 30.5*1.0(4) 21(1) 45(1) Emulsion lB 32.0~1.9(4) 21(1) `-The emulsions of this exsmple therefore show l3213 hexoctshedral faces, with Emulsion 18, which is composed of re~ul~r hexoct6hedra, showing only { 321~ crystRl faces.
Ex&mPle 2 1~ Thls exsmple illustrates the preparstion of a hexoct~hedral silver bromide emulsion having the MLller lndex ~3217 beginnine with sn octshedral host emulsion.
To a reaction ve~sel suppliPd with 8 stirrer was added 0.10 mole oF sn octshedrAl AgBr emulsion, contalnlne 40 g/A~ mole p,elstin, of mean grain size 1.3~m, dlluted to 55 mL. with water. The emulsion W8S hested to 40~C, and 4.0 millimole/mole Ytsrtup Ag of 6-nitrobenzLmidazole dis~olved in 3 mL. of methanol was added. The mixture wss held 15 min. at 40C. The tempersture was then rsised to 60C. The pAg wss ~dJusted to 8.5 st 60 with KBr and main-tsined at that v~lue durlng the precipitation. The pH was a~justed to 6.0 st bOC and maint~ined at th&t v~lue. A 2.0 M solution of AgN03 snd a 2.0 M
solution oF KBr were simultsneously udded over ~
period oF 400 min., wlth a constsnt silver addition rste consuming O.08 mole Ag.
Fi~llre 13 is sn electron microsrsph showin8 the hexoctahedrsl habit of the emulsion prepared.
The Miller lndex wss observed to be {321}.
ExsmPle 3 This exAmple Illustrstes the prepsrstion of a hexoct~h~dr~l silver bromlde emulsion having the Mlller lndex ~521} be~innine with a cubic host emulsion.

1~8~Z~

To a reactlon ve~sel ~upplled with a stirrer was added 0.05 mole of a cublc ~ilver bromide emulsion of mean grain size O.#~m, containing about 10 g/Ag mole of gelatin. Water was added to make the total weight 50 g. To the emulsion at 40C wa~ sdded 3.0 mlllimole/Ag mole o~ the growth modifier spectral sensit~zing dye 3-carboxymethyl-5-~[3-(3-sulfo-propyl~-2-th~azolidinyl~dene~ethylidene3rhodanine, sodium sslt (structure ~hown below), hereinafter referred to a5 Dye I, dl~solved in 3 mL. of methsnol, 2 mL. water, and 3 drops of triethylamine.
o ~S ~ - -Cl~2 C--OH
lS I ~=CH - C~ Dye I
(CH2)3SO3 Na The emulslon WHS then held for 15 min. at 40C. The pH was adJusted to 6.0 at 40C. The t.em~erature was raLsed to 60C, and the pAg ad~usted to 8.5 at 60C wlth KBr and malntained at th~t value during the precipitation. A 2.5 M solution of AgN03 wa~ introduced at a constant rate over a period of 125 mtn. while a 2.5 M aolution of KBr was added as needed to hold the pAg constsnt. A total of 0.0625 mole Ag was added. An electron micrograph of the resulting hexoctahedrsl emulsion grAins is shown in Figure 14.
The Miller lndex of the hexoctahedra of the prepared emulslon was determined to be ~521} by the method descrlbed for Example 1.
An~le Between Vectors Theoretic~l {521} 21.0 45.6 Measured 22.9~1.4G(10) 45.6~3.2(15 35 Example 4 This exAmple Lllustrates the preparation of ~ hexoctahedra] silver chloride emulsion having the Miller index ~521}.

~ ~ 8 To a reactLon vessel supplied with a ~tirrer W89 ~dded 0.05 mole of 8 cubic silver chloride emulsion of me~n grain size 0.65 ~m ~nd cont~ining 40 g/Ae mole gel~tin~ W~ter was added to m~ke the tot~l weight 48 g. To the emulsion st 40C was added 2.0 millimole/Ag mole of ~ye I di3solved in 3 mL. of methanol 1.5 mL. wster and 2 drops of triethyl-amine. The emulsion W8~ then held for 15 min. st 40C. The tempersture w~s then rsised to 50C. The pll wa~ ad~u~ted to 5.92 at 50C, and maintained ~t about this v~lue durinp the precipitstion by NsOH
sdditlon. The pAg wss sdJusted to 7.7 at 50C with NaCl solution and maintained during the precipit~-tlon. A 2.0 M solution of AgN03 was introduced ~t a con~tant r~te over a period of 200 min., while ~
2.2 M solutton of NaCl wss sdded ag needed to hold the pA~ constsnt. A tot~l of 0.04 mole Ag was added. An electron microer~ph of the resulting hexoctshedral emulsion grains ls shown in Figure 15.
T}le Miller lndex of the ~rsins wss observed to be {521}.
ExsmPle 5 Ihls example lllustrstes additionsl growth modlfiers cspsble of producing hexoctshedral crystsl fsces and ltsts potentisl ~rowth modlflers investi--gsted, but not observed to produce hexoctahedrsl crystsl f~ces.
The grsln growth procedures employed were of two different types:
A. The flrst grsin ~rowth procedure wss ss follows: To a resction vessel supplied with a sti~rer wss sdded 0.5 e of bone gelatin dissolved in 2~.5 e of water. To this wss added 0.05 mole of silver bromlde host ~r&in emulsion of me~n gr~in size O.#~m contsinin~ sbout lOg/Ag mole gelstin, &ndhsving a totsl weight of 21.6 F.- The emulsion wss he~ted to 40C, and 6.0 mlllimoles/Ag mole of di~solved p~rowth modifier were added. The mixture wa~ held for 15 min. at ~0C. The pH was ad~u~ted to 6.0 at 40C. The emul~lon was then heated to 60~C, and the pA~ was ad~usted to 8.5 st 60C with KBr and maintained at tS)at value during the precipi-tatlon. The pll, which shifted to 5.92 at 60C, waR
held at that value thereefter. A 2.5M solution of A~NO3 and 8 2.5M solution of KBr were then lntroduced with a constant silver addition rste over a period of 1~5 min., con~uming 0.0625 mole Ag.
Cubic or octahedral host grains were employed as noted ln Table I. Small sample3 of emulslon were wlthdrawn at intervsl~ during the precipLtatlon for electron microscope examination, any hexoctahedral cry3t~1 faces revealed in such samples are reported in Table I.
B. The Recond Brain growth procedure employed 7.5 mlllLmoles of a freshly prepared very fine graln (approximately 0.02 ~m) AgBr emul~ion to which was added 0.09 mlllimole of grDwth modifier.
In thls proces~ these very ~Lne AgBr grain~ were di~olved and reprecipltated onto the host grains.
The host gcaln emulsion contained 0.8 ~m AgBr 8ra1n9- A l.5 m$111mole portion of the host graln emulsLon wa9 added to the very flne 8rain emulsion.
A pH ot 6.0 snd pAg of 9.3 at 40 C was employed.
The mixture was stlrred at 60~ C for about 19 hour~.
The cry~tal face~ presented by the host gralns are as noted ln Table I. Where both octahe-dral and cubic host grains sre noted using the sameerowth modifier, e mixture of 5.0 millimoles cubic p,raLns of 0.8 ~m and 2.5 mLllimole~ of oct~hedral B~Rln9 of 0.8 ~m was employed ~iving ~pproxlmately the 3ame number of cubic and oct~hedrRl host grains.
In looklng et the grains produced by ripening, those produced by ripenin~ onto the cubic grains were readlly vl~ually dlstlnguished, since they were z~

lsreer. Thus, ~t wa~ po~sible in one ripening process to determine the cry~tal faces produced usln~
both cubic an~ octahedrsl host grains.
Ditferences in indivldu~l procedures sre indicated by footnote. The {hkQ} surface column of Table I refers to those surfaces which satisfy the defLnltlon sbove for hexoctahedral crystal faces.

lX~ 5 T A B L E
{hkQ} Host Growth ModLfier Surfaces Grains Method 1 5-Nitro-o-phenylene-5gu~nidlne nLtrate Yes cubic B
2 Cltric acld, tri-sodlum salt None cubic B
3 5-Nitrolndazole None cubic B
None octahedral B
10 4 l-Phenyl-5-mercaP- None octahedral totetrszole (1)(2) A
5 5-Bromo-1,2,3-benzo- None cubic A
triazole None octahedral 6 6-Chloro-4-nitro-1,2,3-benzotri- None cubic B
szole None octshedral B
7 5-Chloro-1,2,3- None cubic B
benzotriazole None octahedrsl B
8 5-Chloro-6-nitro-1,2,3-benzotri-azole None cubic B
9 3-Methyl-1,3-benzo-thIazolium ~- None cubic B
tol.uenesulfonate None octahedral B
25 lO 4-Hydroxy-6-methyl-1,3,3a,7-tetra-azalndene, sodlum ~elt None octahedral B
11 4-Hydroxy-6-methyl-2-methylmercapto-1,3,3a,7-tetrs-azaIndene None cubic A
12 2,6,8-Trichloro- None cublc B
purtne None octahedr~l B
35 13 2-Mercspto-l-phenyl- None cublc B
benzLmLdazole None octahedral B

T A B L E I (Cont'd) {hkQ} Ho3t Growth Modifier Surface3 Grsin~ Method 14 3,6-Dimethyl-4-hy-droxy-1,2,3a,l- None cubic B
tetraazaindene None octahedral B
15 5-Carboxy-4-hydroxy-1,3,3a,7-tetra- None cubic B
s%s3.ndene None octahedral B
16 5--Carbethoxy--4-hy-droxy-1,3,3a,7-tetraaza~ndene Ye~ cubic A
17 5-Imino-3-thlour- None cubic B
azole None octahedral B
15 18 2-Formamidinothio-methyl-4-hydroxy-6-methyl-1,3,3a,7- None cubic B
tetraazaindene None octahedral B
19 4-Hydroxy~2-8-hy-droxyethyl-6- None cubic B
methyl-1,3,3~,7-tetraazaindene None octahedral B
20 6-Methyl-4-phenyl-mercQpto-1,3,3a,7- None cubic B
25tetrQazaindene None octahedral B
21 2-Mercapto-5-phenyl- None cubic B
1,3,4-oxadlazole None octahedr~l B
22 l,10-Dithla-4,7,13,16-tetra- None cubic B
30oxacyclooctadecane None octahedral 23 2-Mercapto-1,3- None cubic B
benzothiazole None octahedral B
24 6-NLtrobenzimi.dazole ~321} cubic ( 3) A
25 5-Methyl-1,2,3- None cubic B
35benzotriazole None octahedral B
26 UraÆole None cubic B
None octahedral B

T A B L E I (Cont'd) {hkQ} Ho~t Growth Modi~`ier Surface~ Grains Method 27 4,S-Dicarboxy-1,2,3-triazole, mono- None cubic B
pota~slum ~alt None octahedral B
28 3-Mercapto-1,2,4- None cubic B
triazole None octahedral B
29 2-Mercapto-1,3- None cubic B
ben%oxszole None octahedral B
30 6,7-Dthydro-4-meth-yl.-6-oxo-1,3,3a,~- None cubic B
tetraaza:lndene None octahedral B
31 1,8-Dihydroxy-3,6- None cubic B
dithiaoctane None octahedral B
32 5~Ethyl-5-methyl-4-thl.ohyflantoln None cubic A
33 Ethylenet}liourea None cubic A
None octahedral A
20 34 2-Carboxy-4-hydroXY-6-methyl-1,3,3a,7- None cubic B
tetraazaindene None octahedral B
35 Dtthiour~zole None cubic B
None octahedral B
25 36 2-Mercsptolmidazole None cubic A
37 5-Carbethoxy-3-(3-carboxypropyl)-4-m~thyl-4-thla- None cubic B
zoline-2-thione None octahedral B
38 Dlthiourazole-meth-yl vlnyl ketone None cubic B
monosdduct None octahedral B
39 1,3,4-Thiadiazo-lldine-2,5-d~.- None cubic B
thlone None octahedral B

8 ~ 5 T A B L E I (Contld) {hkQ} Ho~t ~.rowth Modifier Surf~ces Grsin4 Method 40 4-Carboxymethyl-4-thl.~zoline-2- None cubic B
thione None oct~hedr~l B
41 1-Phenyl-5-selenol-tetr~zole, pOtflS- oct~hedrsl slum salt None (1)(2) A
10 42 1-Carboxymethyl-5H-4-thiocyclopenta- None octshedral B
(d)ur~cll None cubic B
43 5-Bromo-4-hydroxy-6-methyl-1,3,3a,7-tetra~zaindene None cubic A
44 2-C~rboxymethyl-thio-4-hydroxy-6-methyl-1,3,3a,7-tetraszalndene None cubic B
I-(3-AcetamidoPhen-yl)-5-mercap-totetrazole, sodi.um salt None octahedr~l B
46 5-C~rboxy-6-hydroxy-4-methyl-2-methyl-thio-1,3,3~,7-tetrflaz~indene None oct~hedrsl B
47 5-Carboxy-4-hy-droxy-6-methyl-2-methylthio-1,3,3a,7-tetrR-az~lndene None cub1c A
48 -ThlocRprolactRm None cubic (1) A
49 4-Hydroxy-2-methyl-thio-1,3,3~,7-tetra~zflindene None cubic A

1~3LZ2 T A B L E I ~Cont'd) {hkQ} Host ~rowth Modlfier Sur~aces GraLns Method 50 4-Hydroxy-2,6-di-methyl-1,3,3a,7- NoneoctAhedrAl tetraazsindene (4) A
51 PyrLdine-2-thiol Noneoctahedrsl (1)(8) A
52 4-Hydroxy-6-methyl-l,2,3a,7-tetra- Noneoctahedrsl azaindene (4) A
53 7-Ethoxycarbonyl-6-methyl-2-methyl-thlo-4-oxo-15 1,3,3a,7-tetra-azalndene None cubic B
54 1-(4-Nitrophenyl)-5-mercapto- Noneoctahedral tetr~zole (1)(2) A
55 4-Hydroxy-1,3,3a,7- Noneoctahedral tetraazaindene (4) 56 2-Methyl-5-nitro-1-H-benzlmidazole None octahedral A
57 Ben7~enethiol Noneoctahedrsl (1)(8) A
58 Melsmine None cubic B
Noneoctahedral B
59 1-(3-NLtrophenyl)-5- None cubic B
mercaptotetrszole Noneoctahedral B
30 60 Pyridine-4-thiol Noneoct~hedrsl (1) A
61 4-llydroxy-6-methyl-3-methylthio-1,2,3~,7-tetra-az~:Lndene None cubic A

~ 8~2 ~ 5 T A B L E I (Cont'd) {hkQ~ Ho~t ~rowth Modifler Surface~ Grsin Method 62 4-Methoxy-6-methyl-1,3,3a,7-tetra-az~Indene None oct~hedral A
63 4-Amino-6-methyl-1,3,3~,7-tetra-szalndene None octahedr~l A
64 4-Methoxy-6-methyl-2-methylthio-1,3,3s,7-tetr~-~zs1ndene None cubic A
65 4-Hydroxy-6-methyl-1,2,3,3a,7-pent~-aza5.ndene None oct~hedral A
66 3-Carboxymethyl-rhodanine None cubic (1) A

6/ lH-Ben7imIdazole None octahedr~l A
68 4-N1tro-lH-benz-imldazole None oct~hedral A
69 3~Ethyl-5-t(3-ethyl-2-benzoxazollnyli-dene)ethylidene]-4-phenyl-2-thioxo-3-thIazollnium None cubic B
iodide None octahedral B

30 ~ CH-CHz /

Et 31,2~5 T A B L E I (Cont'd) {hXQ} Ho~t Growth Moditier ,urfacea Grain~ Method 70 3-Ethyl-5-~4-methyl-2-thioxo-3-thia-zolin-5-ylIdene- None cubic methyl)rhodanSne None octahedral B
O Me 10 Et ~--S/ \S~ ~

/1 3,3'-Dlethylthia-cyanine ~-toluene-~ulfonate None cubic (5) A

i ~ -CH= /~

Et Et pts~
72 3-Ethyl-5-(3-ethyl-2-benzothiazolin-ylldene)rhodanine None cubic (5) A

25 1 li ~ .=.~ ~ -Et Et 73 3-Ethyl-5-(3-ethyl-2-benzothiazolin-ylidene)-2-thio-2,4-oxazolidine-dlone None cubic (5) A
o .~ /S ~ / ~ -Et N/ \0/ ~S
Et ~ 8~ S

T A B L E I (Cont'd) {hkQ~ Host Growth Modlfier Sur~ces Grains Method 74 5-(3-Ethyl-2-benzo-thlszolinylidene)-1,3-dlphenyl-2- None cubic B
thLohyd~ntoin None octahedral B
o s\ /~
./ \ ~ \ N/ ~S
Et 75 3-Ethyl-5-(3-ethyl-2-benzox~zolinyli-dene)rhodsnlne None cubic (5) A
o Et Et 76 1-Methyl-4-[(1,3,3-trimethyl-l(H)-2-25indolylidene)-ethylidene]-l-phenyl-2-pyr~- None cubic B
zolln-5-one None octshedr~l B
~e ~e O
\ / l I Me Me T A B L E _ (Cont'd) ~hkQ} Ho~t GrowtSI Mod~fler Surfaces Grsin~ Method 77 5-(1,3-Dithiolan-2-S yl.ldene)-3-ethyl-~hodanlne None cubic (5) A
O

~2-l \ .=./ ~ Et H2--. / \ S/ ~S
78 5-(5-Methyl-3-pro-pyl-2-thiazolinyl-ldene)-3-propyl-rhodani.ne None cubic (5) A

g ~ .=./ ~ CH2-C~2-Me Me 79 3-Carboxymethyl-5-[(3-ethyl--2-benzoxQzolinyli-dene)ethyli.- None cubic B
dene]rhodanlne None oct~hedr~l B
o l~ ll ~ ~-CH--CH=./ ~ -CH2-co2H

Et ~L~8 T A B L E l ~Cont ' d) ~hkQ~ Ho4t Growth Modlfler Surf~ce~ Gr~ins Method #0 5-(3-Ethyl-2-benzo-thi~zolinylidene)-3-~-sulfoethyl-rhodsnine None cubic (5) A
o ~ \./ \ / \~ - Cl~2-CH2-SO3H
~-/ \N/ \ S/ ~S
Et 81 5-Anilinomethylene-3-(2-sulfoethyl)-rhod~nine None cubic (6) o HSO3-CH2-CH2-~ \ ~=CH-N/
S~ \S/
82 3-(2-Csrboxyethyl)-5-[(3-ethyl-2-ben-zothiazolinyli-dene)ethylidene~- None cubic B
rhod~nine None octshedr~l B
o i G =CH-CH=-/ ~--CH2-CH~CO2H
~-/ \N/ \ ~/ ~S

Et s T A B L E I (Cont'd) ~hkQ} Hot~t Growth Modifier Surf~ces Graln~ Method 83 ~.-Ethyl-4-(1-ethyl-S 4-pyridinylidene)- ~, 3-phenyl-2-th10- None cubic B
hydantoi.n None oct~hedral B
o Et ~ _ / \ ~y~

84 Anhydro-3-ethyl-9-methyl-3'-(3-sul-~obutyl)thlRcarbo- None cubic B
cyanine hydroxide None oct~hedral B
/S \ Me / \,/ ~.
I ll +~ -CH=C-CH= \ I! ~!

Et CIH2 CH~
CH - S03e Me 85 3-Ethyl-5-[1-(4-sul-fobutyl)-4-pyrl-di.nylidene]rhod~-nine, plperidine None cubic B
s~lt None oct~hedr~l B
o ~03S-(CH2)4 ~ _ / \ 5/ ~S

H ~\H

~ 2 5 T A B L E I (Cont'd) {hkQ} Host Growth Modifier Surf~ce~ Grain~ Method 86 5-(3-Ethyl-2-benzo-- ¦
5thiszolinylidene)-l-methoxycarbonyl-methyl-3-phenyl-2- None cubic B
thiohydantoin None octahedr~l B
o 0 g~-\ /S\ ~~
~./-~ ~ ~S
Et CH2 C=O

87 3-(2-Csrboxyethyl)-5-(1-ethyl-4-pyr-idinylidene)rho- None cubic d~nine (1)(2) A

o ~-=-\ / \~ -CH -CH CO H
=- \S/ ~S
88 3-Csrboxymethyl-5-{[3-(3-~ulfopro-pyl)-2-thiszoll-dinylidene]ethyli-dene}rhodsnine, sodium q~lt {521~ cubic (1) A
o H2_l ~ =CH-CH=~ CH2-C02H

(CH2)3S03 ~ ~ 8~Z 5 T A B L E I (Cont'd) {hkQ) Ho~t Growth Modlfler Surface3 Gr~in Method 89 3-(3-Carboxypropyl)-5-~[3-(3-sulfo-propyl)-2-thiazol-idinylldene]ethyl-Ldene}rhodanine, sodium sRlt None cubic (7) A

s l!
H2--~ ^--CH--CH=/ \~ ~CH2)3C2H

(CH~)3S03 NA+
3-(2-C~rboxyethyl)--5-~[3-(3-Yulfo-propyl)-2-thiazol-idinylidene]ethyl-i.dene~rhodsnine, cubic B
sodium salt None octahedral B
O
H -~ cH2-cH2co2H
H22_!~ ~ CH CH= \ .

0 +
(CH2)3~,03 N8 91 3-C~rboxymethyl-5-(2-pyrrolino-1-cyclopenten-l-yl-methylene)rhod~-nine, sodium salt None oct~hedr~l A

3 5 ~302C--CH2 11 \N/
\~/ \-=C:H--j~ \
Na+ S~ \S/ \~/

81~ZS

T A B L E I (Cont'd) ~ hkQ } Ho~t Growth Modlfier Surf~ces Gr~ins Method 92 3-Ethyl-5-(3-methyl-2-thi~zolidinyli-dene)rhodsnine None cubic ~5) A
o HH2-¦ \ = / 5 ~ Et Me 93 5-(4-Sulfophenyl-~zo)-2-thiob~r-bituric ~cid, cubic B
sodium s~lt None octahedr~l B
o ~O3S-^~ ~--N=N-~ H
N~+ O~ ~ ~S
H

94 3-C~rboxymethyl-5-(2,6-dimethyl-4(H)-pyr~n-4-yl-idene)rhod~nine None cubic (5) A
o CH2co2H
M~-=' \S/!~S

_50_ ~ 8~2 T A B L E I (Gont'd) lhkQ~ Ho~t Growth Modlfier Surf~ces Grsins Method 95 Anhydro-l,3'-bi~(3-S sulfopropYl)naPh~
tho[l,2-d]-thia-zolothiacy~nine hydroxide, tri-ethylamine ~lt None cubic (5) A
s~ /S\ /S~

(~H2)3 (~H2)3 SO3~ SO3~ HNEt3 96 3-Ethyl-5-[3-(3- 9ul -fopropyl)2-benzo-thiazollnylidene]--rhodanine, tri-ethyl.~m~ne s~1.t None cubic (5) A
o ~ Et 2)3 SO(3~ HNEt3 9~ 3-Ethyl-5-[3-(3-sul-fopropyl)2-benz~
oxazolinylidene]-rhodanine, potas- None cubic B
sium sa1.t None octahedral B
o ~ il \,=,/ ~ Et (CH2)3~~ K~

~ 8~'~

(l) 3 mmole~ of growth modifier/Ag mole of host grain emulsion was employed (2) a pRr of 1.6 w~s employed (3) 9 mmoles of growth modifier/Ag mole of host gr~in emulsion was employed, added in two portions (4) 50C WR~ employed instead of 60C
(5) 2 mmoles of growth modifier/Ag mole of ho~t grain emul~ion was employed ~6) 1.5 mmoles of growth modifier/Ag mole of host gr~in emulsion was employed (7) 4 mmoles of growth modifier/Ag mole of host emulsion was employed ( 8 ) 8 pBr of 2.3 was employed ComParatiVe ExamPle 6 The purpose of this comparative example i~
to report the result of adding 6-nitrobenzimidazole to A ~eactl.on vessel. prior to the precipitstion of silver bromlde, as suRgested by Wulff et al U.S.
Patent 1,696,830.
A react:lon vessel equipped with a ~tirrer was chsrged with 0.75 e of deionized bone gel~tin made up to 50 g wlth water. 6-Nitrobenzimidazole, 16.2 mg (0.3 wei.ght % based on the Ag used), dissolved in lmL of methanol, was ~dded, followed by 0.055 mole of KBr. At 70C 0.05 mole of a ZM
solution of AgN03 w~s sdded at 8 uniform rate over a perlod of 25 min. The ~rains formed were relative-ly thick tablets showing {111} crystal faces.
There W8S no indication of the novel hexoct~hedral crystal faces of the invention.
ComP~rative Example 7 The purpose of thi~ comparstive ex~mple is to report the resul.t of employing 4-hydroxy-6-methyl.--1,3,3~,7-tetraQzaindene, sodium salt during grain preclpltation, 8S sugp,ested by Smith Particle ~rowth and Su~pension, cited sbove.

1~8~225 To lO0 mL of 8 3~ bone gelatin solution were sdded slmultaneously 10 mL of 1.96 M AgN03 and lOmL
of 1.96 M KBr st 50C with stirring over a period of sbout ~0 sec. The A8~r disperslon wss ~ged for 1 min st 50C, then dlluted to 500 m~.. The dispersion was sd~usted to pBr 3 with KBr. I
SamPles 7a, 7b.
To 80mL of lX10- 3 M KBr cont~ining 0.4 mmole/Q of 4-hydroxy-6-methyl-1,3,3a,7-tetrasza-lndene, sodLum sslt ~nd 0.6 mmole/Q of 1-dodecyl-quinolinium bromide W8S sdded 20 mL of the sbove dispersion, which was then stirred at 23C. Ssmples were removed after 15 mln (Sample 7a) snd 60 min (Sample 7b).
SsmPles 7c, 7d Ssmples 7c snd 7d were prepared similarly ss Samples 7a and 7b, respectively, except that 0.8 mmole/ of 4-hydroxy-6-methyl-1,3,3~,7-tetr~Aza-lndene and 0.6 mmole/Q of 1-dodecylquinolinium ~romide were used.
Examination of the grains of esch of the samples revealed rounded cubLc ærsinq. No hexoctshe-dral crystsl ~sces were observed.
ExamPle 8 This ex~mple illustrstes thst a hexocta-hedral emulsion exhibits sn incresse in photogrsphic speed st a given fog level as compsred to sn octshedr~l emulslon of the ssme hslide composition snd grsin volume.
Exsmple Hexoctahedrsl Emulsion (A) To a resction vessel supplied with a stirrer wss sdded 0.4 moles of sn 0.7~m AgIBr (6 mole percent I) oct~hedrsl emulsion contalning ~ag bone gelstin/A~ mole. The contents of the kettle weighed 400p~. The emulsLon wa~ heated to 40~C, and 6.0 mmoles/Ag mole of 6-nitrobenzlmid~zole dissolved in 2~ mL methanol was ~dded. The mixture was held for i~8~ 5 15 min at 40~C. The pH was ad~u~ted to 6.0 at 60C
snd the pAg ed~usted to 8.5 at 60C with NaBr solution, and maintained st these value3 during the precipitation. A 2~5M solution of AgN03 and a S solution 2.48M ln NaBr and 0.5M in NaI were then introduced wlth a constant ~ilver sddition rate over a perlod of 145 mln, consumlng 0.4 moles of Ag. The resulting emul~lon was centrifuged and the solid ~ilver halide phase was re~uspended in 250mL of 3%
bone gelatin solution. Electron micrographs of this emulsion showed grains with distinct hexoctahedrsl crystal faces had been formed.
Control Emulsion_~B) This control emulsion was precipitated identically to the above hexoctahedrsl emulsion, except the 6-nltro-benzimidazole was added after the precipltation was complete, but before the centri-fugation step. After this compound had been added, the emulsion was 4tlrred for 15 min st 40C, then centrlfuged. The re~ultlng grains were octahedrsl in shape .
Sen~itization Emulslons A and B were chemically sen3i-tized, as llsted below, and then coated on acetate support at 1.088 A~/m2, 4.31g bone gelstin/m2, O.Blg of a dispersion of the coupler 2-benz~mido-5-[2-(4-butanesulfonylarnidophenoxy)tetradecan-amido]-4-chlorop}lenol/m , 0.14g saponin/m as spreading agent, and 18mg bis(vinylsulfonylmethyl) ether/g gelatin as hardener.
Coatinp~ Emulsion 1 B heated 10 min at 70C with 2.4mg/Ag mole sodium thlosulfate & 0.8mg/Ag mole pota~sium chloroaurste 2 B heated 10 min at 70C with 4.8mg/Ag mole sodium thiosulfate & 1.6mg/Ag mole potasium chloroaurate ~'~ 8~ 5 3 A heated 10 min at 70C with 2.4mg/Ag mole sodium thiosulfate & 0.8mg/Ag mole potassium chloroaurate These coatings were exposed for 0.1 8 to a 2850K tungsten light source through a variable density tablet. These coatings were then processed for 1 min, 2 min, 3 min, 4 mln, 5 min, 8 min in Kodak C-41TM Color Negative developer at 38C. The results are ~ummarized below in Table II.
Table II
Development Log Relative Coating Time (min.) Fog Speed 1 (Control) 1 0.060.00 2 0.070.19 3 0.080.27 4 0.110.41 0.140.45 8 0.180.64 2 (Control) 1 0.07 2 0.070.27 3 0.070.53 4 0.130.62 0.140.70 8 0.200.92 25 3 (Example~ 1 0.07 0.91 2 0.101.29 3 0.191.38 ; 4 0.30~.46 0.391.49 8 0.671.55 From Table II it is apparent that the example emulsion satisfying the requirements of this invention exhibits higher photographic speeds than the control octahedral emulsion. Further, this increased speed is realized even when the chemical sensitizers are doubled in concentration in the control emulsion.
Whether compared at the same , .. .

~ 5 development time~ or ~t the ssme fog level~, the exsmple emulslon of the invention is in all instsnce~
~uperior in photo~r~phic performsnce.
ExsmPle 9 This example Lllustrates the selective site ~-epitsxial. deposition of a sllver s~lt onto hexoct~-hedrsl grains of an emulslon satisfying the require-ments of this invention.
To a reaction vessel. supplled with ~ stirrer was added 0.05 moles of Emulsion A of Ex&mple 8.
DLstill.ed water was Added to make a tot~l contents welght of 50g. The contents were heated to 40C snd O.92 mmole of NaCl W8S added. A 0.50M solution of AgN03 and ~ 0.52M solution of NaCl were then i.ntroduced with a const~nt silver ~ddition rate over a period of 5 min, consuming 1.25 mmoles of silver.
Durinp, the preclpltatlon, the pAg was held constsnt at 7.5 and the temperature held constsnt at 40C.
A 20,000X carbon replic~ electron microgr~ph of the re~ultlng emulsion showed discrete epitaxial growths on the surfsces of the hexoctshedral host emul.sion grains The host grsins showed some edge rounding sfter epitsxy.
The invention hss been described in detsil with particulsr reference to preferred embodiments thereof, but lt wlll be understood th~t variations snd modlficAtlons csn be ef~ected wlthin the spirit and scope of the invention~

Claims (11)

1. A silver halide photographic emulsion comprised of radiation sensitive silver halide grains of a cubic crystal lattice structure comprised of hexoctahedral crystal faces.

2. A silver halide photographic emulsion according to claim 1 wherein said silver halide grains comprised of hexoctahedral crystal faces are silver bromide grains.

3. A silver halide photographic emulsion according, to claim 1 wherein said silver halide grains comprised of hexoctahedral crystal faces are silver chloride grains.

4. A silver halide photographic emulsion according to claim 1 wherein said silver halide grains comprised of hexoctahedral crystal faces contain at least one of bromide and chloride ions and optionally contain a minor proportion of iodide ions based on total silver.

5. A silver halide photographic emulsion according, to claim 1 wherein said silver halide grains are additionally comprised of at least one of cubic and octahedral crystal faces.

6. A silver halide photographic emulsion according claim 1 wherein said silver halide grains are regular hexoctahedral grains.

7. A silver halide photographic emulsion according, to claim 1 wherein a grain growth modifier is adsorbed to said hexoctahedral crystal faces.

8. A silver halide photographic emulsion according to claim 1 wherein said hexoctahedral crystal faces satisfy the Miller index assignment {hk?}, wherein h, k, and ? are integers greater than 0, h is greater than k, k is greater than ?, and h is 5 or less.

9. A silver halide photographic emulsion according to claim 8 wherein said hexoctahedral crystal faces exhibit a {321} or {521} Miller index.

10. A silver halide photographic emulsion according to claim 9 wherein a grain growth modifier is present in said emulsion chosen from the class consisting of 6-nitrobenzimidazole, 5-nitro-o-phenyleneguanidine nitrate, 5-carbethoxy-4-hydroxy-1,3,3a,7-tetraazaindene, and 3-carbethoxymethyl-5-{[3-(3-sulfopropyl)-2-thiazolidinylidene}ethyli-dene}rhodanine, sodium salt.

11. A photographic element containing an emulsion according to claim 1.