The conversion of hematite to magnetite was investigated in a mixture of h2, h2o, and n2. In the te perature range of 500 deg. to 700 deg. C, the magnetic roast reaction gives a sigmoidal kinetic curve with a finite induction time. The induction time decreases with rise in temperature and increases in the presence of alkali and alkaline earth oxides. The magnetic roast reaction was also studied in the presence of low concentrations of silica (quartz structure) and alumina (5.0 and 4.3 wt-pct, respectively, which correspond to 8.4 X 10-4 g atom of si or al per gram of mixture). The addition of sio2 to hematite decreases the induction time. At temperatures below 550 deg. C, alumina increases the induction time; at higher temperatures, it has about the same effect as silica. For pellets containing sio2, a maximum in the relative decrease in induction time, a, was observed at 578 deg. C; for pellets containing al2o3, there was a steady increase in a with increasing temperature. Because the a<-/->b quartz transition occurs at 575 deg. C, the enhanced surface activity at 578 deg. C in the presence of quartz is attributed to the hedvall effect of solid-state chemistry. The induction period of the magnetic roast reaction was exceptionally prolonged in the presence of lithia. Mixing of hematite with silica, alumina, and lithia (8.4 X 10-4 atom, respectively, per gram of mixture) was found to eliminate the beneficial effect of quartz by inhibiting its a<-/->b transformation.
We take your privacy seriously. You can review and change the way we collect information below.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
Cookies used to make website functionality more relevant to you. These cookies perform functions like remembering presentation options or choices and, in some cases, delivery of web content that based on self-identified area of interests.
Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data.
Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. These cookies may also be used for advertising purposes by these third parties.