Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making porous product
Patent
1991-04-08
1992-06-30
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making porous product
419 49, 501 80, G22F 300
Patent
active
051261030
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for modifying a ceramic and/or metallic porous material having open cells necessary for the material to serve the function of a gas diffusing material, filter material or the like.
BACKGROUND ART
The cells forming porous materials include open cells and closed cells. The closed cells, the latter, are completely held out of communication with the outside, while the former, i.e., the open cells, are predominantly through voids permitting the passage of fluids therethrough and also include open voids having an inlet but no outlet. The ratio of the volume of open cells of the porous material to the volume of its mass will be referred to as an open cell ratio, which can be determined by experiments.
Processes for producing porous materials having such open cells (hereinafter referred to as "open-cell porous materials") include, first, a process comprising sintering a green molding of ceramic and/or metallic particles or fibers while producing open cells at the interstices between the particles or fibers, second, a process for vitrifying a green molding of ceramic and/or metallic particles and a vitrifying binder admixed with the particulate material while producing open cells at the interstices between the particles, third, a process for sintering a green molding of ceramic particles and a large quantity of combustible organic material admixed therewith while burning the organic material to form open cells, fourth, a process comprising heat-treating a melt of glass composed of a component insoluble in a chemical and a component soluble therein at a phase separation temperature and further dissolving out the soluble component with the chemical for removal to form open cells, etc.
These open-cell porous materials must have satisfactory gas or liquid permeability, which in turn requires a high open cell ratio. Further these open-cell porous materials are used under versatile conditions which require high strength. However, the conventional production techniques have encountered difficulties in giving both a high open cell ratio and high strength to open-cell porous materials since these characteristics are in conflict with each other.
Generally in producing open-cell porous materials, the open cell ratio increases but the strength decreases when the sintering temperature or vitrifying temperature is lowered, whereas the strength improves but the open cell ratio decreases when the sintering temperature or vitrifying temperature is conversely raised. On the other hand, the open cell ratio increases but the strength decreases when the molding density of green products is lowered, whereas a higher molding density results in improved strength but a decreased open cell ratio. Further when the proportion of the combustible organic material or of the soluble component of glass serving as a cell forming agent is increased, the open cell ratio increases but the strength lowers, whereas a decreased proportion of the cell forming agent entails improved strength but a decreased open cell ratio.
Thus, in the conventional techniques for producing open-cell porous materials, the increase in the open cell ratio and the improvement in the strength are conflicting characteristics. An object of the present invention, which has been accomplished in view of this problem, is to provide a process for giving an open-cell porous material an increased open cell ratio and improved strength.
DISCLOSURE OF THE INVENTION
To fulfill the above object, the open-cell porous material modifying process of the present invention is characterized in that a ceramic and/or metallic porous material having open cells is subjected to hot isostatic pressing at a temperature at which the base portion of the porous material softens or melts to compact or homogenize the base portion.
The material to be thus treated is preferably a porous material having an open cell ratio of 20 to 90%. As a hot isostatic pressing condition, the treating pressure is preferably not lower than 0.1 MPa to not higher t
REFERENCES:
patent: 4644942 (1987-02-01), Sump
patent: 4659546 (1987-04-01), Kearns
Fujikawa Takao
Ishizaki Kozo
Okada Shojiro
Takata Atsushi
Kabushiki Kaisha Kobeseikosho
Lechert Jr. Stephen J.
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