Porous structure such as for filters, and making the same

1 . A method of making a porous structure configured for use in a particulate filter, comprising:

bonding a plurality of glass bubbles to one another, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but no more than 100 micrometers, wherein the plurality comprises at least 1000 of the glass bubbles;

heating the plurality of glass bubbles to at least a softening temperature of the glass bubbles; and

breaching the glass bubbles, wherein the breaching occurs concurrently with the heating;

wherein, in aggregate, the bonded, breached glass bubbles form the porous structure, and wherein voids within individual breached glass bubbles open into one another to form cavities that extend through the porous structure and to surfaces thereof.

2 . The method of claim 1 , further comprising devitrifying at least some glass of the glass bubbles to form crystals.

3 . The method of claim 2 , wherein the breaching includes flowing amorphous glass of the glass bubbles relative to the crystals.

4 . The method of claim 2 , wherein the devitrifying occurs during the heating.

5 . The method of claim 4 , wherein the devitrifying results in the porous structure having over 45% crystallinity by weight.

6 . The method of claim 1 , wherein the heating is such that adjoining glass bubbles sinter to one another.

7 . The method of claim 1 , further comprising cooling the plurality of bonded, breached glass bubbles.

8 . The method of claim 1 , further comprising, prior to the heating, extruding green material comprising the glass bubbles and an organic binder, wherein most of the glass bubbles survive the extruding without fracturing.

9 . The method of claim 8 , wherein the extruding comprises extruding thousands of the glass bubbles coupled to one another with the organic binder.

10 . The method of claim 9 , wherein the heating burns out or chemically changes most of the organic binder in terms of weight.

11 . The method of claim 1 , wherein, during the heating, before reaching the softening temperature, the glass bubbles are heated to a first temperature range for a first dwell time, and then the heated to a second temperature range for a second dwell time;

wherein the first temperature range is from 300° C. to 400° C.; and

wherein the first dwell time is in a range from 1 to 10 hours.

12 . The method of claim 11 , wherein, during the heating, the second temperature range is from 600° C. to 1200° C.; and

wherein the second dwell time is in a range from 1 to 10 hours.

13 . The method of claim 11 , wherein, during the heating, the second temperature range is above 400° C. and below the softening temperature of the glass bubbles;

wherein the second dwell time is in a range from 1 to 10 hours;

wherein, during the heating, the glass bubbles are heated to a third temperature range for a third dwell time;

wherein the third temperature range is lower-bounded by the softening temperature of the glass bubbles; and

wherein the third dwell time is in a range from 1 to 10 hours.

14 . The method of claim 1 , wherein the glass bubbles comprise more than 6.5% CaO by weight.

15 . The method of claim 14 , wherein the composition of the glass bubbles further comprises greater than 0 but less than 7% B 2 O 3 by weight, greater than 0 but less than 1% Al 2 O 3 by weight, and greater than 0 but less than 2.5% Na 2 O by weight.

16 . The method of claim 1 , wherein the glass bubbles have a D50 particle size of at least 1 micrometer but less than 40 micrometers.

17 . The method of claim 1 , wherein the glass bubbles have a composition that comprises more than 74% SiO 2 by weight.