Apparatus and method for determining the amount of entrapped gas in a

Abstract

An entrapped gas measuring apparatus includes a reservoir housing with a reservoir which is adapted to receive a material sample and to expand according to an expansion of the material sample when a negative pressure is applied externally to the reservoir. A parameter indicating the change in volume of the reservoir during the expansion, such as the actual change of volume of the reservoir or a change in position of a moveable wall which at least in part defines the reservoir, is detected by a detector. A processor coupled to the detector is used to determine the amount of entrapped gas based upon the detected parameter. The amount of entrapped gas determined by the processor may be the percent volume of the entrapped gas in relation to the overall volume of the sample, or may be the actual volume of the entrapped gas in the sample. Based at least in-part upon the measured amount of entrapped gas within the sample, the processor is further adapted to determine at least one of: percent volume of the substrate in the sample in relation to the overall volume of the sample; actual volume of the substrate in the sample; or density of the sample or substrate within the sample. The entrapped gas measuring apparatus may be used to produce a material having a known amount of entrapped gas by: making a first material according to a first method and which has a first amount of entrapped gas; applying a negative pressure to the sample such that the sample expands from a first volume to a second volume; detecting a parameter which is indicative of the change of sample volume under the applied negative pressure; comparing the detected parameter with a predetermined range for the parameter; and, if the detected parameter is not within the predetermined range, making a second material according to a second method which has a second amount of entrapped gas that is within the predetermined range.