AutoPore IV

• Description
• Features
• Analysis Technique
• Technical Specifications

Description

The instrument quickly and accurately gathers the data needed to characterize pore structure. This data set provides the basis for calculating pore area and volume distributions according to size, total pore volume, total pore surface area, median pore diameter, and sample densities (bulk and skeletal). These basic characteristics of the material and its porosity allow other characteristics to be ascertained and reported. Examples include material permeability, tortuosity, pore cavity size, pore cavity to pore throat ratios. These are fundamental to the fluid transport properties of porous materials such as reservoir rocks and catalysts. The AutoPore IV also provides estimates of particle size distributions and the compressibility of materials. The advantages of using mercury porosimetry over other methods to determine these material parameters include speed, accuracy, a broad analytical size range, the ability to perform analysis on a wide variety of materials, and the fact that this versatile technique can characterize materials in a wide variety of dimensions.

Features

The AutoPore IV software lets you enter the precise angle of contact between mercury and a solid sample surface. (For determining the exact contact angle, Micromeritics offers the Contact Anglometer Model 1501.) You can enter different values for the advancing contact angle (intrusion), receding contact angle (extrusion), an important consideration in some applications and in consideration of a number of published theories on hysteresis theory. All mercury parameters (surface tension, density, contact angles) can be entered either before or after the analysis as need dictates.

The AutoPore IV’s low-pressure system permits linear and controllable pumpdown to avoid fluidization of fine, light powders and the resultant contamination of the low-pressure manifold. This same capacity, used in reverse, also provides controlled pressurization for the purpose of acquiring precisely placed and closely spaced low-pressure data points. Attaining high resolution data in the macropore region has gained much interest recently, particularly in the characterization of reservoir rocks, various forms of silica, and plastic foams. Controlled pressure increases in increments as fine as 0.05 psia from 0.2 to 50 psia are what makes the AutoPore IV exceptional in its capability in this pressure range.

Choice of Analysis and Report Parameters

The AutoPore offers various options of obtaining important sample information as quickly as possible and for presenting the data in a format of your own design. Analysis options include choices of analysis parameters and equilibration techniques, as well as the capability to define the pressure points at which data are to be collected. The flexibility to select equilibration techniques is a powerful analytical function especially for research work. When working with unfamiliar samples, one selectable equilibration mode can make 'intelligent' decisions about where porosity is present in the sample and increase the number of data points collected in that area. If no porosity is detected, limited data are collected and time is not wasted taking high-resolution data over areas where there is no uptake of mercury.

A selection of report options lets you arrange many aspects of the data pages. You can select a specific range of data to be used in calculations, arrange columns of tabular data, select cumulative, incremental, or differential plots, scale the X-axis to display in either logarithmic or linear format for pore size, report actual or interpolated data, and select data presentation units such as psia or MPa, diameter or radius, and micrometers or Angstroms.

Data reduction methods include particle size distribution using the Mayer-Stowe method, pore tortuosity, material compressibility, relative pore number, pore cavity to pore throat ratio, pore fractal dimensions, SPC charts, tabular and graphical reports of percentage pore volume vs. diameter, and a summary report of percent porosity in user defined size ranges. The user has the ability to instruct the instrument to average several analyses and use the average value as a reference with which to compare subsequent analyses. Similarly, a user-defined reference analysis may be used for subsequent comparisons. Both are useful features for quality control and calibration verification.

Large Selection of Penetrometers

The penetrometer is both a sample holder and a volume measuring transducer. It consists of a sample cup bonded to a precision-bore, glass capillary stem, the outer surface of the stem being clad with metal. When the penetrometer stem is filled with mercury, the outer metal coating, the metallic mercury in the capillary, and the glass separating the two form a capacitor. As mercury invades the voids in the sample it moves out of the capillary stem. The loss of mercury from the core of the stem results in a change in the electrical capacitance. The AutoPore employs an extremely sensitive capacitance detector to measure the slightest change in capacitance in the penetrometer stem. By this method as little as 0.1 microliters of mercury leaving the capillary (or entering, in the case of extrusion) is detected.

Micromeritics offers a large selection of penetrometer bulbs and stem volumes designed to accommodate most sample forms, shapes, porosities, and quantities. The better the match between the sample, its porosity, and the measurement range of the sample penetrometer, the more sensitive the results.

Safety Systems

The AutoPore features several levels of mechanical and electro-mechanical safety devices. First, the computer will not accept keyboard instructions to overpressurize the system. Second, the high-pressure system is mechanically unable to generate unsafe pressures. Third, a circuit stops generating pressure in the event of a failure in the computer. And fourth, the operating specifications for the pressure systems (low = 50 psia, high = 60,000 psia) are, by design, well below actual safe values. The 33,000 psia units include a rupture disk as a final safety measure.

Analysis Technique

The AutoPore IV analysis technique is based on the intrusion of mercury into a porous structure under stringently controlled pressures. From the pressure versus intrusion data, the AutoPore IV series generates volume and size distributions using the Washburn equation. Since mercury does not wet most substances and will not spontaneously penetrate pores by capillary action, it must be forced into the pores by the application of external pressure. The required pressure is inversely proportional to the size of the pores, only slight pressure being required to intrude mercury into large macropores, whereas much greater pressures are required to force mercury into micropores. Clearly, the more accurate the pressure measurements, the more accurate the resulting pore size data. The AutoPore IV’s unique pressure generating system allows the instrument to deliver remarkable precision.

Operation

An analysis method which is run for the first time on the AutoPore takes just a few minutes to set up. Each analysis will have some unique parameters that must be entered, the sample weight, for example. To run the same method anytime in the future requires only that you assign the stored analysis condition set to the new sample parameters. Not only does this save time, but it helps to assure repeatability and reproducibility by reducing the potential for human error.

The penetrometers, which hold the sample, are weighed and then placed in the low-pressure stations where the samples are degassed under vacuum. User-selectable evacuation rates control powder fluidization and reduce the opportunity for system contamination when light powders are analyzed. After degassing, the penetrometers automatically are filled with mercury and the low-pressure analysis begins. The low-pressure analysis, which proceeds from 0.1 psia upward to any pressure between ambient and 50 psi as prescribed by the operator, provides data for characterization of macropores.

If mesopores or micropores are to be characterized, or if total porosity or skeletal density is to be determined, a high-pressure analysis also is required. The penetrometer(s) then are moved to the high-pressure stations where data are collected at pressures between ambient and as high as 60,000 psig (400 Mpa). A total of up to 2500 low- and high-pressure data points can be collected to provide an extremely high-resolution profile of mercury uptake.

Specifications