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ISOSTERIC HEAT OF ADSORPTION Heat   of   adsorption   is   a   measure   of   the   strength   of   interaction   between an   adsorbate   gas   or   liquid   and   a   solid   adsorbent   surface.   Adsorption   is an    exothermic    process    and    the    heat    of    adsorption    is,    therefore,    the energy     released     during     the     process     of     adsorption.     The     heat     of adsorption   is   a   fundamental   thermodynamic   feature   of   the   adsorption process   and   its   value   can   be   utilised   practically   when   developing   and assessing   materials   for   a   specific   adsorption   process.   For   applications   of adsorbents,   separation   processes,   gas   storage   and   catalysis   it   is   often desirable    to    select    or    develop    materials    with    an    affinity    to    adsorb    a certain   gaseous   species.   Measurement   of   the   heat   of   adsorption   of   the specific   gas   onto   the   material   is   then   a   very   important   consideration   and is complimentary to knowledge of the porosity of the material. Measurement   of   the   isosteric   heat   of   adsorption   is   a   common   technique for   the   calculation   of   the   heat   of   adsorption.   At   least   two   adsorption isotherms     are     measured     at     different     temperatures     from     which adsorption   isobars   can   be   derived.   The   isosteric   heat   of   adsorption   is then   calculated   using   the   Clausius-Clapeyron   equation,   applied   across an   adsorption   pressure   range   for   which   adsorption   quantities   of   the isotherms   are   common.   Since   isotherms   covering   a   range   of   adsorption pressures   are   collected,   a   plot   of   heat   of   adsorption   as   a   function   of surface coverage is also plotted .    Key Information: • Isosteric heat of adsorption measurement • Range of adsorbates available • CO2, H2, N2, Ar, O2 and CO commonly applied • Measurements from low pressure to saturation • Number of isotherms variable from 2 upwards • Wide range of analysis temperatures • Isotherms close to ambient commonly measured • Cryogenic temperature analysis also available • Numerical and graphical report formats • Heat of adsorption as function of coverage At   MCA   Services   we   use   our   Micromeritics   3Flex   Micropore   instrument for   all   heat   of   adsorption   measurements.   A   wide   range   of   temperatures can   be   applied   to   the   measurement   of   isotherms,   enabling   conditions which    replicate    the    intended    application    to    be    selected.    For    many applications,   temperatures   close   to   ambient   are   required   and   our   iso- controller   unit   is   used   to   maintain   a   selected   temperature   between   -5   °C and    +50    °C    with    excellent    stability.    Alternatively,    temperatures    below ambient, to 77 K and temperatures above ambient can also be applied. The    adsorption    pressures    measured    commence    at    very    low    relative pressures,    below    atmospheric,    and    usually    extend    to    saturation.    The heat    of    adsorption    plot    therefore    represents    the    adsorption    process from   low   coverage   to   saturation   and   is   directly   applicable   to   applications conducted   at   or   around   atmospheric   pressure.   The   heat   of   adsorption values   at   low   coverage   are   very   useful   where   further   thermodynamic calculations are being undertaken.