Influence of Latvian dolomites and clays on the formation and properties of cordierite ceramics | Latvijas dolomītu un mālu ietekme uz kordierīta keramikas veidošanos un īpašībām

English. Cordierite ceramics can be obtained from both synthetic and natural raw materials. The purpose of this work was to obtain ceramics with cordierite as the main crystalline phase by substituting a part of the necessary raw materials with various dolomites from different regions of Latvia and clay from Usma deposit. Ceramic properties of the obtained samples have been determined with hydrostatic weighing method and the crystalline phase composition has been studied by XRD. Compressive strength, for individual samples, has been determined and evaluated. Investigations show that samples, obtained at 1150 ºC, have a high water absorption and porosity, together with low apparent density. Both water absorption and porosity tend to decrease with increasing of firing temperature, while apparent density increases. Addition of clay to samples, with exceptions, increases both water absorption and porosity while lowers their apparent density. According to XRD analysis, cordierite begins to form at temperature of 1200 ºC but the addition of clay increases required firing temperature to 1250 ºC. Depending on the sintering temperatures, spinel, corundum and anorthite crystalline phases are also present in addition to the main cordierite phase. Anorthite crystalline phase is stable until sintering at 1350ºC, where it converts into amorphous state. Small traces of quartz and diopside crystaline phase have been detected for samples sintered at lower temperatures. Compressive strength has been evaluated for samples fired at 1250 ºC. It is determined that the addition of clay, in most cases, reduces compressive strength of samples. Compressive strength of the obtained samples is much smaller in comparison with the reported in literature.

Latvian. Kordierīta keramikas iegūšanai ir iespējams izmantot gan sintētiskas, gan dabiskas izejvielas. Darbā ir parādīta kordierīta keramikas iegūšana, aizstājot daļu nepieciešamo sintētisko izejvielu ar dažādiem Latvijas atradņu dolomītiem un mālu. Iegūto paraugu, kas apdedzināti dažādās temperatūrās, keramiskās īpašības noteiktas ar hidrostatiskās svēršanas metodi, to kristālisko fāžu sastāvs pētīts ar rentgenfāžu analīzi. Paraugiem noteikta un izvērtēta spiedes izturība. Ir noteikts, ka kordierīts sāk veidoties 1250 ºC temperatūrā, bet dolomītu un mālu pievienošana pazemina nepieciešamo apdedzināšanas temperatūru līdz 1150-1200 ºC. Bez kordierīta kristāliskās fāzes, atkarībā no apdedzināšanas temperatūras, veidojas arī špinelis, korunds un anortīts. Noteikts, ka mālu pievienošana, lielākajā daļā gadījumu, samazina paraugu spiedes izturību.