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سریم

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سریم

( Cerium)
نام: سریم
نماد:Ce
عدد اتمی:58
عدد جرمی:140
جرم اتمی:140.116gr/mol
آرایش الکترونی: [Xe]6s²4f²
چگالی:6.77 gr/cm³
دمای ذوب:°795 سلسیوس
دمای جوش:°3443 سلسیوس
 دومین عضو از گروه لانتانید ها است. این فلز دارای جلای زرد فلزی است. درون نفت نگه داشته میشود.
سریوم عنصر فلزی خاکستری رنگی است که به گروه لانتانیدها تعلق دارد. این عنصر در برخی از آلیاژهای غیرمتداول در طبیعت، به کار می‌رود و شکل اکسید شده آن در صنعت شیشه مورد استفاده قرار می‌گیرد. از نظر رنگ و درخشش شبیه آهن است، اما هم نرم بوده و هم چکش‌خوار و انعطاف‌پذیر است. در بین عناصر خاکی کمیاب، تنها اروپیم واکنش پذیرتر از سریوم است. محلول‌های قلیایی رقیق و اسیدهای غلیظ به سرعت به این فلز حمله می‌کنند. در صورت خراش نوع خالص این فلز با چاقو احتمال سوختن آن وجود دارد. سریوم در آب سرد به آرامی و در آب گرم به سرعت تجزیه می‌شود. به علت نزدیکی نسبی ۴f و اربیتال‌های مدار بیرونی در سریوم، این عنصر خواص شیمیایی جالب توجهی دارد. مثلاً فشردن این عنصر وقتی که در حال سرد شدن است، حالت اکسیداسیون آن را از تقریباً ۳ به ۴ تغییر می‌دهد. سریوم در حالت اکسیداسیون ۳+ cerous و در حالت اکسیداسیون ۴+ ceric نامیده می‌شود. نمک‌های سریوم (IV) نارنجی، قرمز یا زردفام هستند، درحالی که نمک‌های سریوم (III) معمولاً سفیدند.
موارد استفاده از سریوم:
در متالورژی:
سریوم در ساخت آلیاژهای آلومینیوم و برخی از فولادها و آهن‌ها به کار می‌رود.
افزودن سریوم به چدن مانع تشکیل گرافیک به هنگام انجماد شده و باعث به دست آمدن نوعی چدن چکشخوار (مالیبل) می شود.
سریم ، فراوان‌ترین عنصر خاکی کمیاب است که 0,0046 درصد پوسته زمین را تشکیل می‌دهد. سریم در تعدادی کانی از جمله آلانیت ( بعنوان orthite هم شناخته می‌شود ) (Ca, Ce, La, Y)2(Al, Fe)3(SiO4)3(OH). مونازیت و باستناسیت در حال حاضر مهمترین منابع سریم می‌باشند
در بین عناصر خاکی کمیاب ، تنها اروپیم واکنش پذیرتر از سریم می‌باشد. محلولهای قلیایی رقیق و اسیدهای غلیظ به‌سرعت به این فلز حمله می‌کنند. در صورت خراش نوع خالص این فلز با چاقو احتمال سوختن آن وجود دارد. سریم در آب سرد به‌آرامی و در آب گرم به‌سرعت تجزیه می‌شود.
به‌علت نزدیکی نسبی 4f و اوربیتالهای مدار بیرونی در سریم ، این عنصر خواص شیمیایی جالب توجهی از خود نشان می‌دهد، مثلا” فشردن این عنصر وقتیکه در حال سرد شدن است، حالت اکسیداسیون آنرا از تقریبا” 3 به 4 تغییر می‌دهد. سریم در حالت اکسیداسیون 3+، cerous و در حالت اکسیداسیون 4+، ceric نامیده می‌شود.
خطرات
مانند تمامی فلزات خاکی کمیاب دارای میزان سمی بودن ضعیف تا متوسط است. این عنصر ، یک عامل کاهنده قوی است و خودبخود در حرارت 80-65 درجه سانتی‌گراد در هوا می‌سوزد. واکنش این عنصر با روی ممکن است بصورت انفجاری باشد و با بیسموت و آنتیموان واکنشهای بسیار گرمازایی دارد. دود حاصل از سوختن این عنصر سمی است. برای جلوگیری از سوختن این عنصر نباید از آب استفاده کرد، چون سریم با آب برای تولید گاز هیدروژن واکنش می‌دهد.
کارگرانی که با سریم سروکار دارند، مواردی مثل خارش ، حساسیت به گرما و آسیبهای بدنی را تجربه کرده‌اند. حیواناتی که به آنها مقدار زیادی سریم تزریق شده است، بعلت ضایعه‌های قلبی و رگی از بین رفته‌اند. اکسیداین عنصر (IV) در درجه حرارت بالا عامل اکسید کننده قوی است و با مواد آلی قابل احتراق واکنش دارد. وقتی سریم رادیواکتیو نباشد، عیار تجاری ناخالص آن ممکن است حاوی مقادیر کمی توریم باشد که رادیواکتیو است. سریم کاربرد بیولوژیک شناخته شده ای ندارد .

سریم

سریم

اگزالات این عنصرce2c2o4

کلراید این عنصر cecl2

سولفات این عنصر ceso4

 
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