Glass bubbles, composites therefrom, and method of making glass bubbles

Abstract

The present disclosure provides a plurality of glass bubbles having an average true density of up to about 0.55 grams per cubic centimeter and a size distribution including a median size in a range from about 15 micrometers to 40 micrometers. A hydrostatic pressure at which ten percent by volume of the plurality of glass bubbles collapses is at least about 100 megapascals. In some embodiments, the plurality of glass bubbles is a graded fraction preparable by classifying a second plurality of glass bubbles, wherein the second plurality of glass bubbles has a higher percentage of glass bubbles with a size of up to ten micrometers than the first plurality of glass bubbles. Composites including the plurality of glass bubbles are also disclosed.

What is claimed is: 
     
         1 . A method of making a graded fraction of glass bubbles, the method comprising:
 providing a second plurality of glass bubbles having a second size distribution comprising a median size, a number of glass bubbles up to ten micrometers in size, and a number of glass bubbles at least 40 micrometers in size;   removing at least a portion of the glass bubbles at least 40 micrometers in size;   removing at least a portion of the glass bubbles up to ten micrometers in size,   wherein after removing at least a portion of the glass bubbles at least 40 micrometers in size and removing at least a portion of the glass bubbles up to ten micrometers in size, a first plurality of glass bubbles remains, wherein the first plurality of glass bubbles has a number of glass bubbles up to ten micrometers in size that is lower than the number of glass bubbles up to ten micrometers in size of the second plurality of glass bubbles, and wherein one of the following conditions is met:   the first plurality of glass bubbles and the second plurality of glass bubbles have equivalent densities, but the first plurality of glass bubbles is higher in strength than the second plurality of glass bubbles;   the first plurality of glass bubbles and the second plurality of glass bubbles have equivalent strengths, but the first plurality of glass bubbles is lower in density than the second plurality of glass bubbles; or   the first plurality of glass bubbles is both lower in density and higher in strength than the second plurality of glass bubbles.   
     
     
         2 . The method of  claim 1 , wherein the first plurality of particles has an average true density of up to 0.55 grams per cubic centimeter, and wherein the first plurality of particles has a median size by volume in a range from 15 micrometers to 40 micrometers. 
     
     
         3 . The method of  claim 2 , wherein the first plurality of particles has an average true density of up to 0.54 grams per cubic centimeter. 
     
     
         4 . The method of  claim 2 , wherein the first plurality of particles has an average true density of up to 0.53 grams per cubic centimeter. 
     
     
         5 . The method of  claim 2 , wherein the median size is in a range from about 15 micrometers to about 25 micrometers, and wherein the size distribution further comprises up to twenty percent by number of the glass bubbles having a size of up to ten micrometers. 
     
     
         6 . The method of  claim 2 , wherein the first plurality of particles has an average true density of up to 0.45 grams per cubic centimeter, and wherein the first plurality of particles has a median size by volume in a range from 15 micrometers to 25 micrometers. 
     
     
         7 . The method of  claim 6 , wherein the size distribution further comprises up to forty percent by number of the glass bubbles having a size of up to ten micrometers. 
     
     
         8 . The method of  claim 1 , wherein the first plurality of particles has an average true density of up to 0.35 grams per cubic centimeter, and wherein a hydrostatic pressure at which ten percent by volume of the first plurality of glass bubbles collapses is at least 75 megapascals. 
     
     
         9 . The method of  claim 1 , wherein a hydrostatic pressure at which ten percent by volume of the first plurality of glass bubbles collapses is at least 100 megapascals. 
     
     
         10 . The method of  claim 1 , wherein removing at least a portion of the glass bubbles at least 40 micrometers size comprises collecting glass bubbles that passed through a 32-micrometer screen. 
     
     
         11 . The method of  claim 1 , wherein removing at least a portion of the glass bubbles up to ten micrometers in size comprises collecting glass bubbles that were retained on a 20-micrometer screen. 
     
     
         12 . The method of  claim 1 , wherein removing at least a portion of the glass bubbles at least 40 micrometers in size comprises at least one of screening, air classifying, fabric filter classifying, settling classifying, centrifugal classifying, electrostatic classifying, and wet scrubbing classifying. 
     
     
         13 . The method of  claim 1 , wherein removing at least a portion of the glass bubbles up to ten micrometers in size comprises at least one of screening, air classifying, fabric filter classifying, settling classifying, centrifugal classifying, electrostatic classifying, and wet scrubbing classifying 
     
     
         14 . The method of  claim 1 , wherein the glass bubbles have a glass composition comprising an alkaline earth metal oxide and an alkali metal oxide in a weight ratio in a range from 1.2:1 to 3:1. 
     
     
         15 . The method of  claim 1 , wherein the glass bubbles have a glass composition comprising B 2 O 3  in a range from 2 to 6 percent by weight, based on the total weight of the glass bubbles. 
     
     
         16 . The method of  claim 1 , wherein the glass bubbles have a glass composition comprising up to 5 percent by weight Al 2 O 3 , based on the total weight of the glass bubbles. 
     
     
         17 . The method of  claim 1 , wherein the glass bubbles have a glass composition comprising SiO 2  in a range from 70 to 80 percent by weight, alkaline earth metal oxide in a range from 8 to 15 percent by weight, and alkali metal oxide in a range from 3 to 8 percent by weight, each percent by weight based on the total weight of the glass bubbles. 
     
     
         18 . The method of  claim 1 , wherein the glass bubbles are treated with a coupling agent. 
     
     
         19 . The method of  claim 1 , wherein the first plurality of glass bubbles and the second plurality of glass bubbles have equivalent strengths, but the first plurality of glass bubbles is lower in density than the second plurality of glass bubbles. 
     
     
         20 . The method of  claim 1 , wherein the first plurality of glass bubbles is both lower in density and higher in strength than the second plurality of glass bubbles.