L05~6Z , . , The present invention is directed to substrate ; treatment. ; The high surface area gamma-alumina generally used to coat a substrate used for a catalytic converter is - in the form of an aqueous colloidal suspension. To deposit `~ ,` the alumina within the passageways of the substrate, the ,- substrate is dipped into the colloidal alumina, the excess ~-- of the colloidal material thereafter being blown from the passageways with a stream of air. The substrate is dried - 10 and calcined at a high temperature in air. In placing a high surface material on the substrate in the following ~- manner, the uniformity of deposition is poor as the solution - tends to wick to the ends of the substrate during drying. ;~ Variations of up to 40~ in the uniformity of deposit are ~-- found in the direction along the axis of the substrate. ~ ., ~ - The method of this invention is initiated by .: ,, . preparing an aqueous colloidal suspension of gamma-alumina, the prepared suspension having a pH less than about 7O A substrate having passageways extending in an axial direction through the entire length of the substrate is submerged in ;i.,: :, the colloidal suspension for a time sufficient to permit the ` passageways of the substrate to become filled with the ~. ~, . . suspension. The substrate is removed from the colloidal .~; suspension and the excess suspension is removed from the.-,.;-, - ~` passageways of the substrate. The pH of the colloidal ~. -,. . ~i suspension within the passageways of the substrate is ~;; increased to a pH greater than 10 by flowing an ammonia i, containing gas through the passageways of the substrate. This .,.;~. . . .~ action changes the coIloidal suspension to a thixotropic gel. ~,.?.: 30 Thereafter the substrate is dried in air to develop a sub- strate with a uniform coating of gamma-alumina throughout . ,~ . . "' - 2 - ~ ' lB '' ~-- - - . : , - . . . . r''' , . , ' ~ . '. ' ~44~;2 . .- -. the passageways thereof. The increasing of the pH of the colloidal suspension to form a thixotropic gel is the step . ,; -`~- which assures that the material is uniformly deposited .;.; . throughout the substrate and remains uniformly deposited , . during the period of time in which the gamma-alumina is ` being dried onto the substrate passageways. A honeycomb structure of the type used in a catalytic converter is selected for the substrate. The - honeycomb structure is formed from a ceramic material and '- 10 has passageways extending in an axial direction through the ; entire length of the substrate. Such substrates are available - from the American Lava Corporation. ' - The substrate is submerged in a gamma-alumina : - suspension (30% gamma-alumina in water such as "ALON" (Trade Mark) 30-D colloidal alumina sold by the Cabot Corporation). 1 . , - The substrate is removed from the suspension and inverted and ~- placed again in the alumina suspension to insure that all of :: . the passageways through the substrate are filled with the ~: alumina. :', . ~ 20 The substrate is removed from the suspension. ~` A stream of clean air is passed through the substrate at a ,; . . , low velocity in order to remove any excess alumina suspension - ... . ; from the passageways of the substrate. During the preceding . . t steps, the suspension has a pH of about 2. The suspension 5~i~ is acidic because acid is added to the alumina suspension. : :.: ~, ~fter the above discussed steps, pure anhydrous ''`'`"''I . . ammonia (NH3), (or mixtures of NH3 and an inert gas) is passed through the passageways of the substrate. Sufficient ,- NH3 is used to cause a change in the pH of the alumina suspension to a pH of 10 or above. This step causes a large ' increase in the viscosity of the alumina suspension and the ''.. :'' L~ .. ~ `~ B ~ ~ 3 ~ ..~.'- ;-` 105~462 ...~.. v suspension becomes a thixotropic gel securely attached t.o the passageways of the substrate in a substantially .~ uniform manner. . ~ . `"',": ~ ' ': ':: . ;, . ... . , . ~ ' :.'; ~ . . . . `` '' 1,- ~ ~,,. ~ . ,~ .`.'''' ~ :;; . ,.,. . : . ..... ~.; ...................... . , . ~,, . ,, . ,~;, . . i; - :,.. . .. .,~,.,.~ . . " .~ ; ::, . . s ,,;. : n: . ~ ., . ~ ~' . ~ 3a - . . ~ ! ~` ' ` ~: : ~` ` ~544~: '': ` The substrate is placed in a furnace having an air ambient. The substrate is heated in the furnace to a temperature of about 500C for several hours. The heating - may take place for a period of from 1 to 5 hours. This action dries the substrate and removes the ammonia leaving - behind a uniform coating of gamma-alumina throughout the passageways of the substrate. A first three inch long by five inch diameter sub- strate was treated with a 30% solution of Alon 30-D washcoat . . - 10 as described in the Preferred Embodiment and a second such substrate was treated as described in the Background of the Invention section of this specification. An axial section .: : was taken near the outer circumference of each substrate , and divided into five equal test samples, #1 and #5 being - at opposite ends and #3 being in the middle of the test section. BET surface area tests were carried out on samples :. . #1, #3 and #5. The substrate treated by the method of this - invention had BET surface area in sample #1 of 11.80, in sample #3 of 12.73, and in sample #5 of 12.78. On the other r ~:. hand, the substrate treated as described in the Background of the Invention in Sample ~1 had 15.72 at sample #3 had ,;..- 7.54, and at sample #5 had 12.70. It is readily apparent : :~ ;- from these figures that the method of the present invention . provides a uniform coating from one to the other of the substrate. As an additional indication of this uniformity, ,-.-. . -~ samples along the central axis of the substrate treated in s-~ accordance with this invention had the following sET surface ` areas: at sample #1 12.02, at sample ~3 12.03, and at sample ` ;: :-,. . #5 12.17. ; ; 30 There has been described herein a method of forming `~ a high surface area material on a honeycomb. Modifications ',:. . ~, . .~ : ~OS4462 of this invention will be apparent to those skilled in the ~ : art in view of this specification. It is intended that all '`~ such modifications which fall wi.thin the true spirit and ; . i ~ scope hereof be included within the appended claims. . . . ,... ... ':~ '- - , . , ,s. , .. -,: , . ~ :~.. , :, f . ;, ,.'.'. ' ' ~.`'' ' :''' f;,~`'' .' ~ ` r,~,, ` ~: ' .'; '`'. ,.' ~ ' , \' S;" "', :; ' .'. ., ~ . . ~`; .,. '~ .~' ,. ~, . ~ ''~ ~`'`,................................................................... .' .;r~ ~- ,, .,.,.. -~ . ., .,-,', ~. '~ :, , ' s.'..~ ,, ~, - i~'`,'.'~'-. ! -~ ` .. `. s~