Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/24—Chromium, molybdenum or tungsten
  • B01J23/26—Chromium
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G37/00—Compounds of chromium
  • C01G37/02—Oxides or hydrates thereof
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity
  • C01P2006/82—Compositional purity water content
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/90—Other properties not specified above

Definitions

• This invention relates to a method for making anhydrous chromium sesquioxide by reducing a hexavalent chromium compound which is not thermally decomposed at a temperature of less than 300 C., preferably chromic anhydride.
• a first case here involves the production of chromium sesquioxide catalysts on a porous support, for example, a support made of alumina, on the basis of reducible hexavalent compounds of chromium.
• a porous support for example, a support made of alumina
• Supports, soaked in a solution of a hexavalent compound, for example, chromic anhydride are heated up to the complete transformation of the latter into chromium sesquioxide.
• a hexavalent compound for example, chromic anhydride
• Another case involves a treatment process for porous ceramic masses, which are partially fused at low temperatures or substrate coatings using successive cycles of chromic anhydride impregnation and the transformation of the latter (chromic anhydride) into chromium sesquioxide, in situ, with a view to the production of hard ceramic masses or hard coatings, by the methods set forth in French Pat. No. 1,580,247, dated May 3, 1968, and Belgian Pat. No. 726,180, of the Kaman Sciences Corporation.
• these treatments can, in certain cases involving narrow tolerances or particular configurations, bring about unacceptable deformations or differences in the sides, particularly in the case of coatings on metal substrates. In this case, likewise, the metal can undergo harmful changes in terms of structure, texture, or mechanical properties.
• a reduction of the treatment temperature by several hundred degrees would thus be extremely worthwhile and would furthermore make it possible to impregnate porous products or to coat substrates, which could not stand up under treatment at 600 or 700 C. because of their low fusion or degradation temperature.
• An object of the invention is to remedy the inconveniences in the known methods. Its primary purpose is to reduce the temperature used in obtaining anhydrous chromium sesquioxide using a hexavalent compound of chromium, preferably chromic anhydride, CrO below 300 C., with sufliciently short reaction durations.
• Another object is to transform the hexavalent compound of chromium into chromium sesquioxide without any explosive effect.
• Another object of the invention is to apply this reaction in the production of catalysts involving a layer of chromium sesquioxide.
• Another object of the invention is to apply this reaction to methods for making hard refractory ceramic substances, as described in French Pat. No. 1,580,247, and Belgian Pat. No. 726,180.
• the method involved in this invention is characterized by first of all subjecting the hexavalent compound of chromium to heating in a non-reducing atmosphere between 197 and 280 C., approximately, and secondly, to heating in a reducing atmosphere between about 250 and 350 C.
• a small quantity of a reduction catalyst consisting of an amine containing organic compound, preferably pyridine, is added to the hexavalent compound of chromium.
• Heating in non-reducing atmosphere is accomplished by raising the temperature to about 240 C.,' followed by maintaining this temperature for about 1 hour.
• the reducing atmosphere contains hydrogen.
• the reducing atmosphere is made up of a mixture of hydrogen and an inert gas, and the reduction takes place at a temperature of about 340 C.
• the reducing atmosphere is pure hydrogen.
• the hydrogen is introduced progressively, first of all, in a mixture with an inert gas, and then as pure hydrogen. I Heating in the presence of hydrogen is accomplished by raising the temperature to about 280 C., after which this temperature is maintained for about 1 hour.
• EXAMPLE 1 A small alumina stick, partially fused so as to present a porosity of 50% by volume, is subjected to impregnation in a solution of 1 kg./ liter of CrO The small rod is dried for 3 hours at 170-180 C. in a hot air oven, it is then placed in a sealed furnace whose temperature is raised up to 240 C., and it is then kept at this temperature for an hour. A current of hydrogen is then brought in at the same time that the temperature is increased to 280 C. small rod is pulverized and analyzed. The analysis reveals for an hour. After the treatment has been completed, the no trace of soluble CrO or hexavalent chromium salts.
• EXAMPLE 2 A certain number of small rods identical to those in Example 1 are distributed in two portions: one portion is subjected to the treatment described in Example 1, repeated until no further weight loss is registered. The other portion is subjected to the same number of impregnations, followed by a baking treatment in air at 670 C. Analysis does not reveal any appreciable difference between the two portions. The surface hardness obtained on the rods treat-.
• the hydrogen is introduced, drop by drop, stopping the flow of nitrogen, and the temperature is increased to 280 C. This temperature is maintained for /2 hour.
• the hydrogen is scavenged to remove the residual nitrogen and then to the drop by drop introduction of the hydrogen is again begun, maintaining the temperature at 280 C. for /2 hour.
• a hardness of 96 Rockwell 15 N or 85 Rockwell 45 N is obtained, and a bending-resistance of 3000 kg./cm. measured on. rods with a diameter of 5 mm.
• the reduction speed is much a slower, it decreases as the hydrogen content decreases;
• the heating temperature in the reducing atmosphere is slightly raised and brought up to about 340 C.
• trogen and 20% by volume of hydrogen introduced at a flow rateiif 20 liters per hour (the volume of the furnace was 4 liters).
• the temperature was raised to 340 C.
• EXAMPLE 5 The same rod samples as in Example 4 were'subjected to the same impregnation and drying treatment and to the first baking phase.
• the second baking phase was performed in an atmosphere involving a mixture of 99% by volume of nitrogen and 1% by volume of hydrogen, at 340 C., with one .8 hour stage at this temperature.
• EXPERIMENT 2 Absence of the first treatment stage at 197-280 C., in an oxidizing atmosphere, with treatment under hydrogen at 280 C., with a catalyst
• the solution indicated in Example 3 containing the addition of g./liter to a solution of 1 kg./ liter 010 was used.
• the rods were weighed before and after they had spent an hour in a kiln at 670 C. Weight loss was found and it amounted to 10.6% of the unreduced CrO EXPERIMENT 3 Increase in temperature of first treatment phase After drying the rods, impregnated as in Experiment 1, at 178 to 180 C., these rods were heated in the first phase in air at 280 C.
• the impregnation solution comprises a solution of CrO and a solution or suspension of oxides such as Cr O ZnO, MgO, A1 0 CiO and the like.
• said reducing atmosphere comprises a mixture of hydrogen and an inert gas and said heating in said reducing atmosphere is at a temperature of about 340 C.
• the method of making a porous mass impregnated with chromium sesquioxide comprising impregnating a porous mass with a solution of a hexavalent chromium compound non-decomposable into said anhydrous chromium sesquioxide at a temperature of less than 300 C., subjecting the porous mass to heating at substantially atmospheric pressure, first in a dry non-reducing atmosphere between about 197 C. and 280 C., then in a reducing atmosphere between about 250 and 350 C.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Catalysts (AREA)
• Chemical Treatment Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=9055184

Family Applications (1)

Country Status (11)

Cited By (4)

Family Cites Families (3)

• 1970
  • 1970-05-06 FR FR7016592A patent/FR2104656B1/fr not_active Expired
• 1971
  • 1971-04-29 CH CH637771A patent/CH531990A/fr not_active IP Right Cessation
  • 1971-04-29 BE BE766446A patent/BE766446A/xx unknown
  • 1971-05-04 US US00140274A patent/US3749595A/en not_active Expired - Lifetime
  • 1971-05-05 CA CA112279A patent/CA932124A/en not_active Expired
  • 1971-05-05 DE DE19712122299 patent/DE2122299A1/de active Pending
  • 1971-05-05 ES ES390901A patent/ES390901A1/es not_active Expired
  • 1971-05-05 IT IT68483/71A patent/IT939715B/it active
  • 1971-05-05 LU LU63108A patent/LU63108A1/xx unknown
  • 1971-05-06 GB GB1357071*[A patent/GB1341607A/en not_active Expired
  • 1971-05-06 NL NL7106248A patent/NL7106248A/xx unknown

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