摘要:
The present invention relates to a method of making a porous preform in silicon carbide with controlled porosity. The method comprises the operating steps: - a) forming a mass of silicon carbide powders in a mould obtaining a semi-finished preform with an initial porosity ϕ1 - b) pre- sintering said semi-finished preform in an inert atmosphere at a temperature in the range of 1,600°C to 2,000°C, obtaining a pre-sintered preform with an intermediate porosity (ϕ2) higher than the initial porosity ( ϕ1); - c) subjecting said pre- sintered preform to one or more heat treatment cycles. Each heat treatment cycle comprises in sequence: - a sub- phase c1) of oxidation in air at a temperature in the range of 700°C to 1, 250°C; and - a sub-phase c2) of partial sintering at a temperature in the range of 1,600°C to 2,000°C. After the aforesaid step c) a porous preform in at least partly sintered silicon carbide is obtained with a final porosity ϕ3 higher than the intermediate porosity ϕ2 of said sintered preform. Each heat treatment cycle causing a progressive increase of the porosity of said preform. The number of heat treatment cycles to be performed on said pre-sintered preform is defined as a function of the value of final porosity ϕ3 to be obtained in the porous preform of at least partially sintered silicon carbide so as to control the final porosity value ϕ3 of the porous preform.
摘要:
A method is disclosed for plugging selected cells of a honeycomb monolith so as to form a fluidic reactor, the method comprising contacting selected cells of a honeycomb monolith with a melted or softened plug material, the material comprising at least one sinterable particulate and a binder, the binder comprising at least one thermo-setting component and at least one UV-radiation curable polymer, the contacting performed such that a portion of the material remains in contact with the selected cells and plugs the selected cells; cooling the melted or softened plug material such that the thermo-setting component sets; after cooling, irradiating the portion of the material so as to at least partially cure the radiation curable polymer; and after irradiating, debinding or debinding and sintering the portion of the material so as to remove the binder or s as to debind and sinter the at least one sinterable particulate, wherein the step of debinding or debinding and sintereing is performed with the cells of the monolith in a vertical orientation resting on a flat surface with a compatible ceramic or other refractory material felt covering the openings below and above and with a weight resting on the upper face, with optional shims defining the distance between the felt and the end faces.
摘要:
A catalyst comprising palladium supported on a titania-alumina extrudate is disclosed. The extrudate comprises at least 80 wt% titania and 0.1 to 15 wt% alumina. A palladium catalyst prepared from the titania-alumina extrudate has significantly higher crush strength. Its catalytic performance in vinyl acetate production is improved.
摘要:
. Structure poreuse et filtre catalytique, pour le traitement des particules solides et des polluants gazeux issus des gaz de combustion d'un moteur à combustion interne, comprenant une matrice poreuse formant un ensemble de canaux longitudinaux séparés par des parois poreuses constituées de carbure de silicium, lesdites parois étant constituées de grains reliés les uns aux autres par des joints de grains pour délimiter un réseau de pores interconnectés, ladite structure se caractérisant en ce que lesdits grains et/ou les joints de grains constituant lesdites parois poreuses sont recouverts, sur au moins 1% de leur surface, par une texturation, ladite texturation consistant en un matériau disposé à la surface des grains et/ou des joints de grains sous forme d' irrégularités réparties en une pluralité de bandes continues de largeur moyenne, à la surface desdits grains et/ou joints de grains, comprise entre 100 nm et 5 microns, d'épaisseur moyenne à la surface desdits grains et/ou joints de grains inférieure à 1 micron, le matériau constituant lesdites bandes à la surface des grains et/ou des joints de grain étant constitué principalement d'oxyde de silicium.