اوروپيوم

(تم التحويل من Europium)
63 ساماريوماوروپيومگادولينيوم
-

Eu

Am
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صفات عامة
الإسم, الرقم, الرمز اوروپيوم, Eu, 63
سلاسل كيميائية لاناثانيدات
المجموعة, الدورة, المستوى الفرعي f, 6, n/a
المظهر أبيض فضي
Eu,63.jpg
كتلة ذرية 151.964(1) g/mol
شكل إلكتروني [Xe] 4f7 6s2
عدد الإلكترونات لكل مستوى 2, 8, 18, 25, 8, 2
خواص فيزيائية
الحالة صلب
كثافة عندح.غ. 5.264 ج/سم³
كثافة السائل عند m.p. 5.13 ج/سم³
نقطة الإنصهار 1099 ك
826 م °
1519 ف °
نقطة الغليان 1802 ك
1529 م °
2784 ف °
حرارة الإنصهار kJ/mol 9.21
حرارة التبخر kJ/mol 176
السعة الحرارية (25 27.66 C (م) ° ( J/(mol·K
ضغط البخار
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 863 957 1072 1234 1452 1796
الخواص الذرية
البنية البللورية مكعب بسيط (body centered)
حالة التأكسد 3,2
(اكسيد قاعدي باعتدال)
سالبية كهربية ? 1.2 (مقياس باولنج)
طاقة التأين
(المزيد)
1st: 547.1 kJ/mol
2nd: 1085 kJ/mol
3rd: 2404 kJ/mol
نصف قطر ذري 185 pm
نصف قطر ذري (حسابيا) 231 pm
متفرقة
الترتيب المغناطيسي لا توجد بيانات
مقاومة كهربائية (د.ح.غ.) (poly) 0.900 µΩ·م
توصيل حراري (300 K ك ) est. 13.9
(W/(m·K)
معامل التمدد (د.ح.غ.) (poly)
35.0 µm/(m·K)
معامل يونج 18.2 GPa
معامل القص 7.9 GPa
معاير الحجم 8.3 GPa
نسبة بواسون 0.152
رقم فيكرز للصلادة 167 MPa
رقم التسجيل 7440-53-1
النظائر المهمة
المقالة الرئيسية: نظائر الاوروپيوم
نظ ت.ط. عمر النصف طر.إ. طا.إ.MeV ن.إ.
150Eu syn 36.9 y ε 2.261 150Sm
151Eu 47.8% 5×1018 س α   147Pm
152Eu syn 13.516 y ε 1.874 152Sm
β- 1.819 152Gd
153Eu 52.2% Eu يكون ثابت وله 90 نيوترون
المراجع

الاوروپيوم أو اليوروپيوم Europium هو عنصر كيميائي رمزه Eu ورقمه الذري 63. وسـُمي على اسم قارة اوروپا.

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الخصائص المميزة

الاوروپيوم هو أكثر العناصر الأرضية النادرة تفاعلاً; فهو يتأكسد بسرعة في الهواء, ويشبه الكالسيوم في تفاعله مع الماء; وشحنات العنصر الفلزي في صيغة صلبة, حتى عند تغطيتها بطبقة واقية من الزيت المعدني, فهي نادراً ما تكون براقة. ويشتعل الالاوروپيوم في الهواء عند درجة حرارة 150 °م إلى 180 °م. وله تقريباً نفس صلادة الرصاص وهو مطيل بدرجة كبيرة.


الاستخدامات

هناك القليل من الاستخدامات التجارية لفلز الالاوروپيوم, إلا أنه قد استـُعمل to dope بعض أنواع الزجاج لصناعة ليزرات, كما يـُستخدم في الكشف عن متلازمة داون وبعض الأمراض الجينية الأخرى. وبسبب قدرته على امتصاص النيوترونات, فيجري دراسة استخدامه في المفاعلات النووية. اكسيد الالاوروپيوم (Eu2O3) يـُستعمل على نطاق واسع كفوسفور أحمر في أجهزة التلفزيون و مصابيح الفلوسنت, وكمنشط للفوسفورات المصنوعة من الإتريوم. وبينما الاوروپيوم ثلاثي التكافؤ يعطي فوسفورات حمراء, فالاوروپيوم ثنائي التكافؤ يعطي فوسفورات زرقاء. مجموعتا فوسفور الاوروبيوم, مجموعتان مع فوسفورات التربيوم الصفراء/الخضراء, يعطون أضواءً "ثلاثية الألوان trichromatic" وهي التي أصبحت هامة جداً للحصول على إضاءة اقتصادية. ويـُستخدم أيضاً كعامل في صناعة زجاج الفلورسنت. ويستخدم استشعاع الاوروپيوم لفحص التفاعلات الجزيئية الحيوية في غرابيل اكتشاف العقاقير. ويستخدم كذلك في فوسفورات مكافحة التزوير في الأوراق النقدية لليورو. [1]

ويستخدم الاوروپيوم بنسب ضئيلة جداً في دراسات الكيمياء الأرضية و الپترولوجيا فهم العمليات المكونة للصخور النارية (الصخور التي بردت من magma أو الحمم). وطبيعة europium anomaly found تستخدم للمساعدة في اعادة بناء العلاقات داخل مجموعة من الصخور النارية.

التاريخ

Europium was first found by Paul Émile Lecoq de Boisbaudran in 1890, who obtained basic fraction from samarium-gadolinium concentrates which had spectral lines not accounted for by samarium or gadolinium; however, the discovery of europium is generally credited to French chemist Eugène-Anatole Demarçay, who suspected samples of the recently discovered element samarium were contaminated with an unknown element in 1896 and who was able to isolate europium in 1901. When the europium-doped yttrium orthovanadate red phosphor was discovered in the early 1960s, and understood to be about to cause a revolution in the color television industry, there was a mad scramble for the limited supply of europium on hand among the monazite processors. (Typical europium content in monazite was about 0.05%.) Luckily, Molycorp, with its bastnäsite deposit at Mountain Pass California, whose lanthanides had an unusually "rich" europium content of 0.1%, was about to come on-line and provide sufficient europium to sustain the industry. Prior to europium, the color-TV red phosphor was very weak, and the other phosphor colors had to be muted, to maintain color balance. With the brilliant red europium phosphor, it was no longer necessary to mute the other colors, and a much brighter color TV picture was the result. Europium has continued in use in the TV industry ever since, and, of course, also in computer monitors. California bastnäsite now faces stiff competition from Bayan Obo, China, with an even "richer" europium content of 0.2%. Frank Spedding, celebrated for his development of the ion-exchange technology that revolutionized the rare earth industry in the mid-1950s once related the story of how, in the 1930s, he was lecturing on the rare earths when an elderly gentleman approached him with an offer of a gift of several pounds of europium oxide. This was an unheard-of quantity at the time, and Spedding did not take the man seriously. However, a package duly arrived in the mail, containing several pounds of genuine europium oxide. The elderly gentleman had turned out to be the Dr. McCoy who had developed a famous method of europium purification involving redox chemistry.

التواجد

ولا يتواجد الاوروپيوم في الطبيعة كعنصر حر; إلا أن هناك العديد من المعادن التي تحتوي على الاوروپيوم, وأهم المصادر هي باستناسيت و مونازيت. Europium has also been identified in the spectra of the sun and certain stars. Depletion or enrichment of europium in minerals relative to other rare earth elements is known as the europium anomaly.

الاوروپيوم ثنائي التكافؤ بكميات صغيرة وُجد أنه المنشط للاستشعاع الأزرق الساطع لبعض العينات من فلوريتات المعادن (ثنائي فلوريد الكالسيوم). The most outstanding examples of this originated around Weardale, and adjacent parts of northern England, and indeed it was this fluorite that gave its name to the phenomenon of fluorescence, although it was not until much later that europium was discovered or determined to be the cause.

المركبات

مركبات الاوروپيوم تتضمن:

Europium(II) compounds tend to predominate, in contrast to most lanthanides: (which generally form compounds with an oxidation state of +3). Europium(II) chemistry is very similar to barium(II) chemistry, as they have similar ionic radii. Divalent europium is a mild reducing agent, such that under atmospheric conditions, it is the trivalent form that predominates. Under anaerobic, and particularly under geothermal conditions, the divalent form is sufficiently stable such that it tends to be incorporated into minerals of calcium and the other alkaline earths. This is the cause of the "negative europium anomaly", that depletes europium from being incorporated into the most usual light lanthanide minerals such as monazite, relative to the chondritic abundance. Bastnaesite tends to show less of a negative europium anomaly than monazite does, and hence is the major source of europium today. The accessible divalency of europium has always made it one of the easiest lanthanides to extract and purify, even when present, as it usually is, in low concentration. See also europium compounds.


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النظائر

Naturally occurring europium is composed of 2 isotopes, 151Eu and 153Eu, with 153Eu being the most abundant (52.2% natural abundance). While 153Eu is stable, 151Eu was recently found to be unstable to alpha decay with half-life of yr[2], in reasonable agreement with theoretical predictions. Besides natural radioisotope 151Eu, 35 artificial radioisotopes have been characterized, with the most stable being 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, and 154Eu with a half-life of 8.593 years. All of the remaining radioactive isotopes have half-lives that are less than 4.7612 years, and the majority of these have half-lives that are less than 12.2 seconds. This element also has 8 meta states, with the most stable being 150mEu (t½ 12.8 hours), 152m1Eu (t½ 9.3116 hours) and 152m2Eu (t½ 96 minutes).

The primary decay mode before the most abundant stable isotope, 153Eu, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 153Eu are isotopes of samarium (Sm) and the primary products after are isotopes of gadolinium (Gd).

اوروپيوم كناتج عن الانشطار النووي

مقاطع عرضية للإمساك الحراري للنيوترونات
النظير 151Eu 152Eu 153Eu 154Eu 155Eu
Yield ~10 low 1580 >2.5 330
Barns 5900 12800 312 1340 3950
Medium-lived
fission products
Prop:
Unit:
t½
a
Yield
%
Q *
keV
βγ
*
155Eu 4.76 .0803 252 βγ
85Kr 10.76 .2180 687 βγ
113mCd 14.1 .0008 316 β
90Sr 28.9 4.505 2826 β
137Cs 30.23 6.337 1176 βγ
121mSn 43.9 .00005 390 βγ
151Sm 96.6 .5314 77 β

الاوروپيوم يتم انتاجه في الانشطار النووي, ولكن fission product yields of europium isotopes are low near the top of the mass range for fission products.

Like other lanthanides, many isotopes, especially isotopes with odd mass numbers and neutron-poor isotopes like 152Eu, have high cross sections for neutron capture, often high enough to be neutron poisons.

151Eu is the beta decay product of Sm-151, but since this has a long decay half-life and short mean time to neutron absorption, most 151Sm instead winds up as 152Sm.

152Eu (half-life 13.516 years) and 154Eu (halflife 8.593 years) cannot be beta decay products because 152Sm and 154Sm are nonradioactive, but 154Eu is the only long-lived "shielded" nuclide, other than 134Cs, to have a fission yield of more than 2.5 parts per million fissions.[3] A larger amount of 154Eu will be produced by neutron activation of a significant portion of the nonradioactive153Eu; however, much of this will be further converted to 155Eu.

155Eu (halflife 4.7612 years) has a fission yield of 330 ppm for U-235 and thermal neutrons. Most will be transmuted to nonradioactive and nonabsorptive Gadolinium-156 by the end of fuel burnup.

Overall, europium is overshadowed by Cs-137 and Sr-90 as a radiation hazard, and by samarium and others as a neutron poison.


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المحاذير

سمية مركبات الاوروپيوم لم تـُدرس بالكامل بعد, but there are no clear indications that europium is highly toxic compared to other heavy metals. The metal dust presents a fire and explosion hazard. Europium has no known biological role.

عزل الاوروپيوم

Europium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln denotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most common lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and yttrium which makes handling difficult since thorium and its decomposition products are radioactive.

For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulfuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.

Pure europium is available through the electrolysis of a mixture of molten EuCl3 and NaCl (or CaCl2) in a graphite cell which acts as cathode using graphite as anode. The other product is chlorine gas.

هامش

  1. ^ Europium and the Euro [1]
  2. ^ Search for α decay of natural Europium, P. Belli, R. Bernabei, F. Cappell, R. Cerulli, C.J. Dai, F.A. Danevich, A. d'Angelo, A. Incicchitti, V.V. Kobychev, S.S. Nagorny, S. Nisi, F. Nozzoli, D. Prosperi, V.I. Tretyak, and S.S. Yurchenko, Nucl. Phys. A 789, 15 (2007) DOI:10.1016/j.nuclphysa.2007.03.001
  3. ^ ORNL Table of the Nuclides

المصادر

وصلات خارجية