This invention is generally directed to improved processes for obtaining chalcogenide alloys; and more specifically, the present invention is directed to a substantially pollution free process for obtaining high purity selenium alloys by the solution coreduction of the corresponding respective acids thereof. In accordance with the simple, direct, economically attractive process of the present invention, there is generated, in a purity of 99.99 percent, alloys of selenium, inclusive of selenium arsenic alloys with small particle sizes. High purity alloys prepared in accordance with the process of the present invention are particularly useful as photoconductive members in xerographic imaging processes. Also, the process of the present invention enables alloy products of a small particle size diameter, less than for example one micron, permitting their rapid dispersion in polymeric binder compositions.
The art of xerography as presently practiced requires the formation of an electrostatic latent image on a photoconductive member. Materials commonly selected for the photoconductive member are amorphous selenium, amorphous selenium alloys, halogen doped amorphous selenium substances, and halogen doped amorphous selenium alloys. These photoconductive substances must usually have a purity of 99.99 percent or greater since the presence of contaminants has a tendency to adversely effect the electrical properties thereof resulting in relatively poor copy quality. Numerous complex physical and chemical processes are known for obtaining the aforementioned photoconductive substances. Flexible photoreceptor devices with photoconductive substances, such as selenium, prepared in accordance with these processes have a tendency to deteriorate over a period of time; therefore, the costly selenium or selenium alloy used must be recovered and recycled. Various methods are available for recovering selenium and its alloys from the substrate on which it is deposited including heat stripping, water quenching, ultrasonics, and bead blasting.
Many of the prior art processes, including the chemical processes for obtaining high purity materials of selenium and selenium alloys from contaminated source materials with these substances, involve a number of method steps, and undesirably high temperature distillations. Additionally, in many of these processes the recycling of reactants is not achieved. Further, in most instances, the prior art processes for recovering selenium, selenium alloys, or other metallic elements from contaminated source materials is complex, economically unattractive, and causes environmental contamination in that, for example, vaporous oxides are formed and must be eliminated. Also, many of these processes result, for example, in the recovery of selenium or selenium alloys, which nevertheless contain impurities that can, over an extended period of time, adversely effect their photoconductivity.
There is, for example, described in U.S. Pat. No. 4,047,973 a physical method for recovering selenium, or an alloy thereof from the surface of an endless xerographic belt with a metal substrate having deposited thereon a thin layer of an organic resinous material which is overcoated with a relatively thicker layer of selenium or a selenium alloy by subjecting the surface of the belt to jets of high water pressure for the purpose of stripping the selenium or selenium alloy without substantially effecting the layer of organic resinous material. According to the disclosure of this patent, subsequent to removal of the water from the slurry, there is obtained substantially pure selenium or an alloy thereof.
Also, in U.S. Pat. No. 4,009,249 there is disclosed a process for precipitating stable red amorphous selenium, which may include halogen with hydrazine from a solution of selenious acid in methanol or ethanol. The process is accomplished at a temperature of between about -20.degree. C. and the freezing point of the solution selected. The resulting precipitate is maintained at a temperature of about -13.degree. C. to about -3.degree. C. until a red color appears. A similar teaching is presented in U.S. Pat. No. 4,007,255 with the exception that there is disclosed a process for producing a stable red amorphous selenium thallium material. There is reference in both of these patents to processes for precipitating selenium by reducing selenious acid in an aqueous solution with sulfur dioxide or sulfurous acid as described in British Pat. No. 515,676, and U.S. Pats. Nos. 2,186,085 and 3,130,012. Further, it is indicated in these patents that a process for precipitating selenium from an aqueous solution of selenious acid with sulfur dioxde, hydroxylamine hydrochloride, or hydrazine sulfate at 6.degree. to 45.degree. C. is described in U.S. Pat. No. 2,860,954.
Moreover, there is described in U.S. Pat. No. 4,411,698, the disclosure of which is incorporated herein by reference, an improved process for obtaining in high purity photoconductive compositions of selenium, tellurium, and arsenic, which comprises converting a source material into a mixture of corresponding oxides, converting the oxides to pure esters, and subsequently affecting reduction of the esters. More specifically, there is described in this patent an improved process for reclaiming or recovering selenium, tellurium, or arsenic in high purity, 99.99 percent, which comprises providing a source material such as a scrap alloy with these elements and other substances; converting this material into a mixture of the corresponding oxides of the elements; reacting the resulting oxides with an alcohol or a diol followed by separation of the esters from the reaction mixture; and subjecting, subsequent to purification by distillation or recrystallization, the esters to a coreduction reaction. The invention of the present application is directed to a similar process with the important exception that the formation of the esters is eliminated.
Moreover, illustrated in a copending application U.S. Ser. No. 594,626, entitled Process For Reclamation of High Purity Selenium From Scrap Alloys, the disclosure of this application being totally incorporated herein by reference, is an improved process for attaining high purity selenium, which comprises converting a source material into a solution mixture of the corresponding oxides, and subsequently adding a reducing composition thereto. More specifically, there is disclosed in the copending application an improved process for reclaiming or recovering selenium in high purity, 99.99 percent, which comprised providing a scrap selenium alloy; converting this alloy into a mixture of the corresponding oxides of the elements; separating the resulting selenium oxides by selective alcoholic dissolution; followed by subjecting the solution mixture of selenium oxides to a reduction reaction; and thereafter separating the selenium product from the solution. In one specific illustrative embodiment, there is disclosed in the copending application a process which comprised converting a scrap alloy with selenium to a mixture of corresponding oxides, followed by treating the mixture with an alcohol for the primary purpose of dissolving the selenium oxide formed. Subsequently, the resulting solution is treated with a reducing substance, and a selenium precipitated product is obtained in solution. Also, disclosed in U.S. Pat. No. 4,484,945, the disclosure of which is totally incorporated herein by reference, is a solution reduction process for the preparation of selenium alloys. In this process, there is initially provided a mixture of selenium alloys, followed by converting this mixture to oxides, and subsequently subjecting the oxide mixture to a reduction reaction. More specifically, there is disclosed in this patent a process for the preparation of chalogenide alloys in high purity which comprises providing a solution mixture of oxides of the desired chalcogens, and subsequently subjecting this mixture to a simultaneous coreduction reaction.
Accordingly, there continues to be a need for improved processes for obtaining chalcogenide alloys, inclusive of selenium, arsenic, and tellurium alloys, by a solution reduction procedure. Additionally, there continues to exist a need for an improved simple low temperature chemical process for obtaining selenium alloys, inclusive of selenium tellurium in high purities from the corresponding acids. There also continues to be a need for improved processes for obtaining selenium alloys in high purity, which processes involve a minimum number of operations, and do not require high temperature distillations. Furthermore, there continues to be a need for improved pollution free processes for obtaining selenium alloys in high purity. Also, there continues to be a need for improved processes for obtaining in high purity selenium alloys useful as photoconductive elements by the solution reduction of the appropriate acids of selenium, and other metallic elements. Furthermore, there is a need for processes for generating selenium alloys of a particle diameter of less than about 10 microns by the solution reduction of specific metallic acids.
Moreover, while numerous processes are known for the preparation and purification of selenium alloys, there continues to be a need for improved processes that permit the production of high purity selenium alloys at low temperatures. Further, there is a need for improved processes for obtaining selenium tellurium alloy photoconductive substances and selenium arsenic by subjecting to a reduction reaction a solution containing therein the acids of selenium and tellurium, or selenium and arsenic.