POROUS FLOW RESTRICTOR AND METHODS OF MANUFACTURE THEREOF

1 . A dual density disc comprising:

a dense outer tube comprising a metal oxide having a purity of greater than 92%; and

a porous core comprising a metal oxide of a lower density than a density of the dense outer tube; wherein the porous core has a metal oxide purity of greater than 99%; where the dense outer tube has an inner tapered surface.

2 . The dual density disc of claim 1 , wherein the porous core has a bulk density of 1.00 to 3.0 g/cc and the crush strength is greater than 2000 pounds per square inch when present within the dense outer tube.

3 . The dual density disc of claim 1 , where the porous core contacts the dense outer tube at its inner surface and where the dense outer tube is in continuous contact with the porous core along an entire circumference of the porous core.

4 . The dual density disc of claim 1 , having radial hermiticity, which does not leak from the sides of the porous body and permits flow in only a longitudinal direction.

5 . The dual density disc of claim 1 , wherein the dense outer tube has an outer diameter of 1 to 75 millimeters and an inner diameter of 0.8 to 70 millimeters.

6 . The dual density disc of claim 1 , wherein the dense outer tube has an initial length of 1 to 120 millimeters.

7 . The dual density disc of claim 1 , wherein the porous core is manufactured from a metal oxide powder having an initial purity of greater than 92%.

8 . The dual density disc of claim 1 , wherein the porous core is manufactured from a metal oxide powder having an initial purity of greater than 99%.

9 . The dual density disc of claim 1 , wherein the porous core is manufactured from a metal oxide powder having an initial purity of greater than 99.5%.

10 . The dual density disc of claim 1 , where the metal oxide used in the dense outer tube is alumina.

11 . The dual density disc of claim 1 , where the metal oxide used in the porous core is alumina.

12 . The dual density disc of claim 1 , where the inner threaded surface is located at an inlet, an outlet of the tube or both at the inlet and the outlet of the tube.

13 . The dual density disc of claim 1 , where an inlet, outlet or both an inlet and an outlet of the dual density disc has threads on the tapered surface.

14 . The dual density disc of claim 1 , where an inlet, outlet or both an inlet and an outlet of the dual density disc has a diameter that is greater than a diameter of the porous core.

15 . The dual density disc of claim 1 , where an inlet, outlet or both an inlet and an outlet of the dual density disc has a diameter that is smaller than a diameter of the porous core.

16 . A method comprising:

disposing in a dense outer tube a slurry comprising:

a metal oxide powder and a pore former;

heating the dense outer tube with the slurry disposed therein to a temperature of 300 to 600° C. to activate the pore former;

creating a porous core in the dense outer tube;

sintering the dense outer tube with the porous core at a temperature of 800 to 2000° C. in one or more steps; and

machining threads on an inner surface of the dense outer tube, where the threads are parallel to a longitudinal axis of the tube or inclined to the longitudinal axis of the tube.

17 . The method of claim 16 , where the sintering operation is performed in air, nitrogen, natural gas, argon, hydrogen, or a combination thereof.

18 . The method of claim 16 , where the pore former is an organic pore former.

19 . The method of claim 16 , where the slurry further comprises a solvent.

20 . The method of claim 16 , wherein the sintering is preceded by a first sintering step where the temperature is 1200 to 1600° C.

21 . The method of claim 16 , where the pore former is azobisisobutyronitrile.

22 . The method of claim 16 , where the pore former is gas that is soluble in the metal oxide slurry.

23 . The method of claim 16 , where the pore former is a liquid.

24 . The method of claim 16 , wherein the pore former is an organic polymer.

25 . The method of claim 24 , wherein the organic polymer is a polyacetal, a polyacrylic, a polycarbonate, a poly(meth)acrylate, a polyalkyd, a polystyrene, a polyolefin, a polyester, a polyamide, a polyaramide, a polyamideimide, a polyarylate, a polyurethane, an epoxy, a phenolic, a polyarylsulfone, a polyethersulfone, a polyphenylene sulfide, a polyimide, a polyetherimide, a polytetrafluoroethylene, a polyetherketone, a polyether ether ketone, a polyether ketone, a polybenzoxazole, a polyoxadiazole, a polybenzothiazinophenothiazine, a polybenzothiazole, a polypyrazinoquinoxaline, a polypyromellitimide, a polyguinoxaline, a polybenzimidazole, a polyoxindole, a polyoxoisoindoline, a polydioxoisoindoline, a polytriazine, a polypyridazine, a polypiperazine, a polypyridine, a polypiperidine, a polytriazole, a polypyrazole, a polycarborane, a polyoxabicyclononane, a polydibenzofuran, a polyphthalide, a polyacetal, a polyanhydride, a polyvinyl ether, a polyvinyl thioether, a polyvinyl alcohol, a polyvinyl ketone, a polyvinyl halide, a polyvinyl nitrile, a polyvinyl ester, a polysulfonate, a polysulfide, a polythioester, a polysulfone, a polysulfonamide, a polyurea, a polyphosphazene, a polysilazane, a polyvinylidene fluoride, a polysiloxane, or a combination thereof.

26 . A method comprising:

disposing into a dense outer tube an alumina powder; where the alumina powder does not contain a pore former;

sintering the dense outer tube with the alumina powder disposed therein to a temperature of 800 to 2000° C.;

creating a porous core in the dense outer tube; where the porous core has a purity of greater than 99%; and

machining threads on an inner surface of the dense outer tube; where the threads are parallel to a longitudinal axis of the tube or inclined to the longitudinal axis of the tube.

27 . The method of claim 26 , further comprising heating the dense outer tube with the alumina powder disposed therein to a temperature of 1200 to 1600° C.

28 . A dual density disc comprising:

a dense outer tube comprising a first ceramic having a purity of greater than 92%;

a porous core comprising a second ceramic of a lower density than a density of the dense outer tube; wherein the porous core has a purity of greater than 99%; and

wherein the dense outer tube comprises threads on an inner surface of the dense outer tube; where the threads are parallel to a longitudinal axis of the tube or inclined to the longitudinal axis of the tube.

29 . The dual density disc of claim 28 , wherein the first ceramic is the same as the second ceramic.

30 . The dual density disc of claim 28 , wherein the first ceramic is different from the second ceramic.