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<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Susan Russell-Robinson</dc:contributor>
  <dc:contributor>Bruce S. Hemingway</dc:contributor>
  <dc:creator>Richard A. Robie</dc:creator>
  <dc:date>1989</dc:date>
  <dc:description>&lt;p id=""&gt;Heat capacities of K&lt;sub&gt;2&lt;/sub&gt;Mg&lt;sub&gt;2&lt;/sub&gt;(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;&amp;nbsp;(langbeinite) and CaSO&lt;sub&gt;4&lt;/sub&gt;&amp;nbsp;(anhydrite) were measured from approximately 8 to 1000 K by combined adiabatic shield calorimetry (8-365 K) and differential scanning calorimetry (350-1000 K). Heat capacities were also measured on natural crystals of gypsum (CaSO&lt;sub&gt;4&lt;/sub&gt;&amp;nbsp;&amp;middot; 2H&lt;sub&gt;2&lt;/sub&gt;O) between 8.1 and 323.5 K. The molar entropies at 298.15 K,&amp;nbsp;&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;m&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;(298.15 K), are 378.8 &amp;plusmn; 0.6, 107.4 &amp;plusmn; 0.2 and 193.8 &amp;plusmn; 0.3 J K&lt;sup&gt;&amp;minus;1&lt;/sup&gt;&amp;nbsp;mol&lt;sup&gt;&amp;minus;1&lt;/sup&gt;&amp;nbsp;for langbeinite, anhydrite and gypsum, respectively. The heat capacity in J K&lt;sup&gt;&amp;minus;1&lt;/sup&gt;&amp;nbsp;mol&lt;sup&gt;&amp;minus;1&lt;/sup&gt;&amp;nbsp;of langbeinite can be represented by the equation&amp;nbsp;&lt;i&gt;C&lt;/i&gt;&lt;sub&gt;p,m&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;(K&lt;sub&gt;2&lt;/sub&gt;Mg&lt;sub&gt;2&lt;/sub&gt;(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;&lt;i&gt;T&lt;/i&gt;) = 535.9 + 0.11011&lt;i&gt;T&lt;/i&gt;-1.0200 &amp;times; 10&lt;sup&gt;6&lt;/sup&gt;/&lt;i&gt;T&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt;-4.909 &amp;times; 10&lt;sup&gt;&amp;minus;5&lt;/sup&gt;&lt;i&gt;T&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt;&amp;nbsp;-4040.2/&lt;i&gt;T&lt;/i&gt;&lt;sup&gt;0.5&lt;/sup&gt;&amp;nbsp;between 300 and 1000 K with an average deviation of &amp;plusmn; 0.4%. For anhydrite the heat capacity between 300 and 1000 K is given by&amp;nbsp;&lt;i&gt;C&lt;/i&gt;&lt;sub&gt;p,m&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;(CaSO&lt;sub&gt;4&lt;/sub&gt;,&lt;i&gt;T&lt;/i&gt;) = 372.8 - 0.1574&amp;nbsp;&lt;i&gt;T&lt;/i&gt;&amp;nbsp;+1.695 &amp;times; 10&lt;sup&gt;6&lt;/sup&gt;/&lt;i&gt;T&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt;&amp;nbsp;+ 7.993 &amp;times; 10&lt;sup&gt;&amp;minus;5&lt;/sup&gt;&lt;i&gt;T&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt;&amp;nbsp;- 4330.8/&lt;i&gt;T&lt;/i&gt;&lt;sup&gt;0.5&lt;/sup&gt;&amp;nbsp;with an average deviation of &amp;plusmn;0.4%.&lt;/p&gt;
&lt;p id=""&gt;Combining our heat-capacity and entropy data with the solution calorimetric results of Kelley et al. (U.S. Bur. Mines Tech. Paper, 625, 1941) yields an equilibrium temperature for the reaction gypsum &amp;rarr; anhydrite + 2 water of 314.7 K (41.5 &amp;deg; C).&lt;/p&gt;
&lt;p id=""&gt;Our observations are in agreement with the conclusions of Speer and Salje (Phys. Chem. Miner., 13 (1986) 17); we see no evidence in our heat capacity measurements for the transformation of cubic langbeinite (P2&lt;sub&gt;1&lt;/sub&gt;3) to a low temperature orthorhombic (P2&lt;sub&gt;1&lt;/sub&gt;2&lt;sub&gt;1&lt;/sub&gt;2&lt;sub&gt;1&lt;/sub&gt;) form as is seen in the isostructural Co, Zn, Ca, Mn and Cd langbeinites.&lt;/p&gt;
&lt;p id=""&gt;Although Bond (Bell Sys. Tech. J., 22 (1943) 145) reported that langbeinite was piezoelectric at room temperature, we found no evidence in our&amp;nbsp;&lt;i&gt;C&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&amp;nbsp;measurements for a Curie temperature above which langbeinite would no longer be piezoelectric.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/0040-6031(89)87010-8</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>Heat capacities and entropies from 8 to 1000 K of langbeinite (K&lt;sub&gt;2&lt;/sub&gt;Mg&lt;sub&gt;2&lt;/sub&gt;(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;), anhydrite (CaSO&lt;sub&gt;4&lt;/sub&gt;) and of gypsum (CaSO&lt;sub&gt;4&lt;/sub&gt;·2H&lt;sub&gt;2&lt;/sub&gt;O)</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>