Gemini VII 2390

Overview – Gemini VII 2390 Surface Area Analyzer


Unique Design – The secret of Gemini’s unique capabilities lies in the innovative use of sample and balance tubes. These tubes are identical in every aspect, including their thermal environment. The sample and reference reservoirs, like their associated tubes, are physically identical and are initially charged to the same pressure. During an analysis, differential pressure between reservoirs is monitored. This common mode technique assures that any differential pressure is solely due to adsorption by the sample and not to factors that lead to variations in free space during an analysis.

  • The Windows version includes easy-to-follow installation videos and system verification tests to ensure optimum performance and reliability. How-to videos provide on-screen instruction on instrument operation.
  • The patented twin-tube design negates free-space errors introduced by thermal gradient variations or by initial mis-measurement of free space
  • Permits low surface area measurements without requiring krypton by essentially eliminating free-space error, the limiting factor in typical static volumetric systems.
  • Accelerates delivery of the analysis gas because sample uptake controls the rate at which the gas is delivered to the sample. This results in a surface area analyzer that is as fast as the physics of adsorption allows
  • The use of a servo valve to control the rate of gas flow into the sample tube assures accurate attainment of target pressures without pressure overshoot
  • Three choices of software control: embedded software with a keypad enabling the Gemini VII to be operated without an external PC, Windows XP or Vista operating system, or theGemini VII confirm™ 21 CFR Part 11 option.



✔ Low Cost

✔ System verification tests

✔ Fully automatic operation

✔ High throughput – up to four Geminis can be operated with single computer

✔ Capable of measuring low surface area materials

✔ Keypad- or computer-operated with Windows-driven software

✔ Choice of analysis mode (scan or equilibrate)

✔ No pressure overshoot

✔ Common mode rejection of free-space error effects

✔ No thermal-diffusion errors

✔ Optional stainless-steel Dewars

✔ 21 CFR Part 11 software option

✔ IQ/OQ Validation service (optional)


Three Model Options:

Gemini VII 2390aIdeal for rapid and accurate surface area determinations by single-point and multipoint BET and Langmuir methods. In addition, provides standard methods for total pore volume, micropore analysis by the t-method, and much more. Included is the capability to determine statistical thickness surface area (STSA) of carbon blacks. (Refer to ASTM D 6556, ASTM D 3765, ISO/DIS 18852.2, or ISO/CD 4652-2/3.) Gemini VII 2390pProvides additional precision with the addition of a saturation pressure (P0) tube that allows the system to monitor the saturation pressure of the adsorptive on a continuous basis during an analysis. This design feature permits a rapid measurement of the adsorption isotherm to near-saturation, as well as determination of pore size distribution. Gemini VII 2390tHas all the ability of the 2390p, including a P0 tube, with the addition of a larger Dewar and longer sample tubes for extended analyses. This provides the additional capability to measure the total adsorption-desorption process. With this data set, one can perform a BJH or Dollimore-Heal pore size distribution using up to 1000 data points.


  1. Gemini VII 2390 Software and Reporting

    Superior Data Presentation Capability

    Operating Software

    Gemini analyzers can be operated from a keypad by way of embedded software or from a computer using the more-powerful and versatile Gemini Windows optional software.

    The embedded software includes:

    • System verification tests
    • Single- and Multipoint BET (Brunauer, Emmett, and Teller) surface area
    • Langmuir surface area
    • Total pore volume
    • Total micropore volume and area by the t-Plot method using Halsey, Harkins-Jura, or Carbon Black STSA thickness curves
    • Horvath-Kawazoe for micropore distribution
    • BJH pore size distribution using adsorption isotherm (Gemini 2390p and 2390t only)
    • BJH adsorption and desorption isotherm, 1000 data points (Gemini 2390t only)

    Optional Gemini Windows Software

    The easy-to-use Gemini Windows XP or Vista interface enhances the capabilities to plan, launch, and control the analysis. You can collect, organize, archive and reduce raw data, and store standardized sample information and analysis conditions for easy access during later applications. Finished reports may be generated to screen, paper, or to files in various formats. Features include cut-and-paste graphics and tables, scalable-and-editable graphs, and customizable report formats. Using computer control, you can operate up to four Gemini analyzers simultaneously from a single computer.

    Gemini Windows Features

    Gemini Windows software provides additional features not included with the embedded software.

    As examples:

    • Installation and how-to videos
    • Reduction of user-entered data
    • Automatically generated pressure tables with user-selected endpoints
    • User-defined pressure table
    • Summary report
    • Sample log
    • Isotherm plot overlays
    • Autoscaling x- and y-axes
    • Cut-and-paste graphics and tables
    • Data export to ASCII and spreadsheet formats
    • User-defined thickness curve (manually entered or from data file)
    • Fixed pore size tables
    • Linear and log plots (isotherm, pore volume, pore area)
    • Cumulative and differential data
    • Broekhoff-de Boer thickness curve

    21 CFR Part 11 Option

    Also available is confirm™ software, which addresses the many requirements specified by 21 CFR Part 11 validation, security, audit trails, reporting, and more.

    Link: DataMaster™ and DFT Plus®Data Reduction Technique (NLDFT)

    ReportsThe Gemini VII 2390 Series analyzers provide rapid surface area analysis. The unique balanced design allows BET surface area to be measured using nitrogen for a broad range of materials. The Gemini offers precise measurements of low surface area materials using nitrogen. The determination of micropore volume, micropore surface area, and external surface area is available on all Gemini models using the standard t-plot calculations.
    The Gemini VII 2390p includes a dedicated transducer for continuously monitoring the saturation pressure of the cryogenic bath. This allows the Gemini VII 2390p to rapidly measure adsorption isotherms and determine the pore volume, area, and size distribution of mesoporous materials.
    The Gemini VII 2390t features extended operation to facilitate the determination of the total isotherm. Both adsorption and desorption measurements may be obtained; this allows users the capability to determine the pore volume, area, and size distributions using BJH or Dollimore-Heal reports.

    Micromeritics Gas Adsorption Reports:

    Windows software with all Micromeritics’ gas adsorption instruments contains the following reports:

    Isotherm Reports:

    • tabular
    • graphical
    • pressure composition isotherm

    Isotherm modeling and surface area:

    • BET
    • Langmuir
    • Temkin
    • Freundlich

    Standard isotherm models:


    • t-plot – micropore volume, micropore area, external surface area
    • alpha-s method
    • f-ratio method

    Classic models for mesopore volume, area, and distribution:


    • BJH*
    • Dollimore-Heal*

    Classic models for micropore distribution:


    • Dubinin-Radushkevich and Astakhov
    • Horvath-Kawazoe
    • Saito-Foley
    • Cheng-Yang
    • MP method

    Density Functional Theory for pore size modeling:


    • Slit-shaped pores using N2, Ar, or CO
    • Cylindrical pores for alkaline- exchanged zeolites using N2 or Ar
    • Cylindrical pores for hydrogen- or ammonium-exchanged zeolites using N2 or Ar
    • Windows-shaped model for pillared clay

    Density Functional Theory for surface energy:


    • Surface area and energy distributions using nitrogen at 77 K
    • Surface area and energy distributions using argon at 87 K

    *BJH and Dollimore-Heal require the Gemini VII 2390t to take full advantage of pore size reports based upon the desorption isotherm

  2. Gemini VII 2390 Applications

    Gemini Applications

    Pharmaceuticals – Surface area and porosity play major roles in the purification, processing, blending, tableting, and packaging of pharmaceutical products as well as the drug’s useful shelf life, its dissolution rate, and bio-availability.
    Ceramics – Surface area and porosity affect the curing and bonding of greenware and influence strength, texture, appearance, and density of finished goods. The surface area of glazes and glass frits affects shrinkage, crazing, and crawling.
    Adsorbents – Knowledge of surface area, total pore volume, and pore size distribution is important for quality control of industrial adsorbents and in the development of separation processes. Surface area and porosity characteristics affect the selectivity of an adsorbent.
    Activated Carbons – Surface area and porosity must be optimized within narrow ranges to accomplish gasoline vapor recovery in automobiles, solvent recovery in painting operations, or pollution controls in wastewater management.
    Carbon Black – The wear lifetimes, traction, and performance of tires are related to the surface area of carbon blacks used in their production.
    Catalyst – The active surface area and pore structure of catalysts influence production rates. Limiting the pore size allows only molecules of desired sizes to enter and exit, creating a selective catalyst that will produce primarily the desired product.
    Paints and Coatings – The surface area of a pigment or filler influences the gloss, texture, color, color saturation, brightness, solids content, and film adhesion properties. The porosity of a print media coating is important in offset printing where it affects blistering, ink receptivity, and ink holdout.
    Projectile Propellant – The burn rate of propellants is a function of surface area. Too high a rate can be dangerous; too low a rate can cause malfunctions and inaccuracy.
    Medical Implants – Controlling the porosity of artificial bone allows a better imitation of real bone that is more acceptable to the body for tissue growth.
    Cosmetics – Surface area is often used by cosmetic manufacturers as a predictor of particle size when agglomeration tendencies of the fine powders make analysis with a particle-sizing instrument difficult.
    Aerospace – Surface area and porosity of heat shields and insulating materials affect weight and function.
    Electronics – By selecting high surface area material with carefully designed pore networks, manufacturers of super-capacitors can minimize the use of costly raw materials while providing more exposed surface area for storage of charge.
    Fuel Cells – Fuel cell electrodes require high surface area with controlled porosity to produce adequate power density.
    Geoscience – Porosity is important in groundwater hydrology and petroleum exploration because it relates to the quantity of fluid that a structure can contain as well as how much effort will be required to extract it.

    More Applications

    • Adhesives
    • Alloys
    • Abrasives
    • Carbonates
    • Cements
    • Clays
    • Detergents
    • Fibers
    • Films
    • Fertilizers
    • Filters
    • Glass
    • Food Additives
    • Graphite
    • Minerals
    • Paper
    • Polishing Compounds
    • Polymers
    • Resins
    • Soils and Sediments
  3. Techniques Overview

    Gemini Technique Overview

    Unique Design

    Micromeritics’ Gemini utilizes an adaptive rate, static volumetric technique. It is the first gas sorption method that adapts the rate at which gas is delivered to the sample to the rate at which it is adsorbed. Each pressure point is allowed to equilibrate before the next point is taken. The Gemini has two gas reservoirs which are filled with equal volumes of the desired adsorptive, usually nitrogen. From the reservoirs, gas is metered into the sample and balance tubes by way of a servo valve that reacts to the rate of adsorption. A transducer monitors pressure within the sample tube. In a typical dose-and-wait analytical system, pressure within the sample tube decreases after each dose as the sample adsorbs gas. This is not the case with the Gemini. Transducer causes a fast response servo valve to increase or restrict the flow of gas to the sample tube as necessary to maintain a constant equilibrium pressure within the sample tube as adsorption occurs. Transducer located between the sample and balance tubes detects any pressure difference between the two tubes and causes another servo valve to adjust the pressure within the balance tube to negate any pressure differential. A third pressure transducer monitors the pressure between the two reservoirs to determine the differential quantity of gas, the difference being the quantity that is adsorbed on the sample. These methods of dosing and differential quantity detection enable the Gemini to accurately determine adsorption characteristics at a speed and sensitivity level unsurpassed by other static volumetric instruments.

  4. Sample Preparation Systems

    Sample Preparation Systems for Physisorption Instruments

    Micromeritics’ sample preparation devices prepare batches of samples for surface area and pore volume analysis. They combine flowing gas and/or vacuum with heat to remove atmospheric contaminants, such as water vapor and adsorbed gas, from the surface and pores of the sample. The quality of the data produced by surface area and pore volume analyses depends greatly on the cleanliness of the sample surface. All Micromeritics’ sample preparation devices accept helium, nitrogen, argon, and other non-corrosive gases.



    The SmartPrep™ 065 is a flowing-gas degassing unit which removes adsorbed contaminants from the surface and pores of a sample in preparation for analysis. It contains six sample ports, each one independently temperature-controlled for greater flexibility. It contains two serial ports, one for connecting to the computer and the other available for connection of an additional SmartPrep. The temperature, ramp rates, and soak times of each sample are individually controlled by the computer. Up to five ramps and soaks are allowed. All degas information is integrated into the sample data file for future reference.
    SmartPrep 065 Web page and Specifications

    The VacPrep™ 061 offers two methods for removing contaminants. In addition to flowing gas, it provides vacuum to prepare samples by heating and evacuation. This combination allows you to choose the preparation method that is best suited to your material or application. The VacPrep features six degassing stations, and a choice of vacuum or gas flow preparation on each of the six stations. Needle valves are also provided allowing you to introduce the flowing gas or vacuum slowly to prevent fluidization of samples.
    VacPrep 061  Web page and Specifications

    The FlowPrep™ 060 applies both heat and a stream of inert gas to the sample. The heat causes contaminants to desorb from the surface and the stream of inert gas sweeps them out of the sample tube. It lets you choose the temperature, gas, and flow rate best suited for your sample material and application. Needle valves allow you to introduce the flowing gas slowly to prevent fluidization of samples.
    FlowPrep 060 Web page and Specifications

    The Model 021 LN2 Transfer System allows you to transfer liquid nitrogen or liquid argon from a nonpressurized storage Dewar into smaller containers as needed in laboratory experiments. The system was specifically developed for conveniently filling Dewars for gas adsorption instruments but also can be used for other cryogen applications. The Model 021 can discharge cryogens at adjustable rates up to 3 liters/min. The roller base makes it easy to move the 021 System to the location where the cryogen is needed. The nozzle and insulated, flexible hose enable convenient filling and refilling of analysis Dewars. The system can hold liquid nitrogen or argon up to 30 days allowing cost-efficient use of your cryogen.
    Model 021 Liquid Nitrogen transfer system  Webpage

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