أوروبيوم

Europium, ₀₀Eu

Europium
المظهر	silvery white, with a pale yellow tint; but rarely seen without oxide discoloration
الوزن الذري العياري Ar°(Eu)
Europium في الجدول الدوري
– ↑ Eu ↓ Am samarium ← europium → gadolinium
الرقم الذري (Z)	63
المجموعة	n/a
الدورة	period 6
المستوى الفرعي	f-block
التوزيع الإلكتروني	[Xe] 4f7 6s2
الإلكترونات بالغلاف	2, 8, 18, 25, 8, 2
الخصائص الطبيعية
الطور at د.ح.ض.ق	solid
نقطة الانصهار	1099 K ​(826 °س، ​1519 °F)
نقطة الغليان	1802 K ​(1529 °س، ​2784 °ف)
الكثافة (بالقرب من د.ح.غ.)	5.244 ج/سم³
حين يكون سائلاً (عند ن.إ.)	5.13 ج/سم³
حرارة الانصهار	9.21 kJ/mol
حرارة التبخر	176 kJ/mol
السعة الحرارية المولية	27.66 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
الخصائص الذرية
الكهرسلبية	مقياس پاولنگ: 1.2
طاقات التأين	الأول: 547.1 kJ/mol الثاني: 1085 kJ/mol الثالث: 2404 kJ/mol
نصف القطر الذري	empirical: 180 pm
نصف قطر التكافؤ	198±6 pm
الخطوط الطيفية
خصائص أخرى
البنية البلورية	​body-centered cubic (bcc)
سرعة الصوت قضيب رفيع	est. 13.9 W/(m·K)
التمدد الحراري	poly: 35.0 µm/(m⋅K) (at r.t.)
المقاومة الكهربائية	poly: 0.900 µΩ⋅m (at r.t.)
الترتيب المغناطيسي	paramagnetic
القابلية المغناطيسية	+34000.0×10−6 cm3/mol
معامل يونگ	18.2 GPa
معامل القص	7.9 GPa
معاير الحجم	8.3 GPa
نسبة پواسون	0.152
صلادة ڤيكرز	165–200 MPa
رقم كاس	7440-53-1
التاريخ
التسمية	after Europe
الاكتشاف وأول عزل	Eugène-Anatole Demarçay (1896, 1901)
نظائر الeuropium

يروپيوم أو أوروپيوم أو اليوروپيوم Europium هو عنصر كيميائي رمزه Eu ورقمه الذري 63. وسـُمي على اسم قارة اوروپا. It is a silvery-white metal of the lanthanide series that reacts readily with air to form a dark oxide coating. Europium is the most chemically reactive, least dense, and softest of the lanthanides. It is soft enough to be cut with a knife. Europium was discovered in 1896, provisionally designated as Σ; in 1901, it was named after the continent of Europe. Europium usually assumes the oxidation state +3, like other members of the lanthanide series, but compounds having oxidation state +2 are also common. All europium compounds with oxidation state +2 are slightly reducing. Europium has no significant biological role but is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the rarest of the rare-earth elements on Earth.

 أصل الاسم

مكتشف العنصر، أوجين-أناتول ديمارساي، سمّاه على اسم قارة أوروپا.

 الخصائص الطبيعية

نحو 300 جرام من أوروبيوم الشجيري المتسامي بنقاء 99.998% يتم التعامل معه في صندوق قفاز

أوروبيوم مؤكسد، مكسو بـكربونات الأوروبيوم الثنائي الصفراء

الأوروبيوم هو فلز مطيل بصلادة مماثلة للرصاص. ويتبلور في شبكة مكعبة موسطنة حول الجسم. ومن بين اللانثانيدات، فإن الأوروبيوم مع الإيتربيوم لديهما أكبر حجم لمول الفلز. وتقترح القياسات المغناطيسية أن ذلك هو نتيجة لكون تلك الفلزات فعلياً ثنائية التكافؤ بينما اللانثانيدات الأخرى هم فلزات ثلاثية التكافؤ.^:1700

الأوروپيوم 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 الاوروپيوم في الهواء عند درجة حرارة 150 °م إلى 180 °م.

 الخصائص الكيميائية

The chemistry of europium is broadly lanthanoid chemistry, but Europium is the most reactive lanthanoid.^:1703 It rapidly oxidizes in air, so that bulk oxidation of a centimeter-sized sample occurs within several days. Its reactivity with water is comparable to that of calcium, and the reaction is

2 Eu + 6 H
2O → 2 Eu(OH)
3 + 3 H
2

Because of the high reactivity, samples of solid europium rarely have the shiny appearance of the fresh metal, even when coated with a protective layer of mineral oil. Europium ignites in air at 150 to 180 °C to form europium(III) oxide:

4 Eu + 3 O
2 → 2 Eu
2O
3

Europium dissolves readily in dilute sulfuric acid to form pale pink solutions of [Eu(H
2O)
9]³⁺:

2 Eu + 3 H
2SO
4 + 18 H
2O → 2 [Eu(H
2O)
9]³⁺ + 3 SO2−
4 + 3 H
2

 Eu(II) vs. Eu(III)

Although usually trivalent, europium readily forms divalent compounds. This behavior is unusual for most lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has an electron configuration 4f⁷ because the half-filled f-shell provides more stability. In terms of size and coordination number, europium(II) and barium(II) are similar. The sulfates of both barium and europium(II) are also highly insoluble in water. Divalent europium is a mild reducing agent, oxidizing in air to form Eu(III) compounds. In anaerobic, and particularly geothermal conditions, the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline earths. This ion-exchange process is the basis of the "negative europium anomaly", the low europium content in many lanthanide minerals such as monazite, relative to the chondritic abundance. Bastnäsite tends to show less of a negative europium anomaly than does monazite, and hence is the major source of europium today. The development of easy methods to separate divalent europium from the other (trivalent) lanthanides made europium accessible even when present in low concentration, as it usually is.

 المركبات

Europium(III) sulfate, Eu₂(SO₄)₃

Europium(III) sulfate fluorescing red under ultraviolet light

Europium compounds tend to exist in a trivalent oxidation state under most conditions. Commonly these compounds feature Eu(III) bound by 6–9 oxygenic ligands. The Eu(III) sulfates, nitrates and chlorides are soluble in water or polar organic solvents. Lipophilic europium complexes often feature acetylacetonate-like ligands, such as EuFOD.

 الهاليدات

Europium metal reacts with all the halogens:

2 Eu + 3 X₂ → 2 EuX₃ (X = F, Cl, Br, I)

This route gives white europium(III) fluoride (EuF₃), yellow europium(III) chloride (EuCl₃), gray europium(III) bromide (EuBr₃), and colorless europium(III) iodide (EuI₃). Europium also forms the corresponding dihalides: yellow-green europium(II) fluoride (EuF₂), colorless europium(II) chloride (EuCl₂) (although it has a bright blue fluorescence under UV light), colorless europium(II) bromide (EuBr₂), and green europium(II) iodide (EuI₂).

 الكالكوجينيات والپنيكتوجينات

Europium forms stable compounds with all of the chalcogens, but the heavier chalcogens (S, Se, and Te) stabilize the lower oxidation state. Three oxides are known: europium(II) oxide (EuO), europium(III) oxide (Eu₂O₃), and the mixed-valence oxide Eu₃O₄, consisting of both Eu(II) and Eu(III). Otherwise, the main chalcogenides are europium(II) sulfide (EuS), europium(II) selenide (EuSe) and europium(II) telluride (EuTe): all three of these are black solids. Europium(II) sulfide is prepared by sulfiding the oxide at temperatures sufficiently high to decompose the Eu₂O₃:

Eu₂O₃ + 3 H₂S → 2 EuS + 3 H₂O + S

The main nitride of europium is europium(III) nitride (EuN).

 النظائر

المقالة الرئيسية: نظائر الأوروبيوم

Naturally occurring europium is composed of two isotopes, ¹⁵¹Eu and ¹⁵³Eu, which occur in almost equal proportions; ¹⁵³Eu is slightly more abundant (52.2% natural abundance). While ¹⁵³Eu is stable, ¹⁵¹Eu was found to be unstable to alpha decay with a half-life of 4.6×10¹⁸ years, giving about one alpha decay per two minutes in every kilogram of natural europium. Besides the natural radioisotope ¹⁵¹Eu, 39 artificial radioisotopes have been characterized from ¹³⁰Eu to ¹⁷⁰Eu, the most stable being ¹⁵⁰Eu with a half-life of 36.9 years, ¹⁵²Eu with a half-life of 13.516 years, ¹⁵⁴Eu with a half-life of 8.592 years, and ¹⁵⁵Eu with a half-life of 4.742 years. All the others have half-lives shorter than 100 days, with the majority shorter than 3 minutes.

This element also has 27 meta states, with the most stable being ^150mEu (12.8 hours), ^152m1Eu (9.3116 hours) and ^152m5Eu (96 minutes). The primary decay mode for isotopes lighter than ¹⁵³Eu is electron capture to samarium isotopes, and the primary mode for heavier isotopes is beta minus decay to gadolinium isotopes.

 الأوروپيوم كناتج عن الانشطار النووي

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

Europium is produced by nuclear fission: ¹⁵⁵Eu (half-life 4.742 years) has a fission yield of 0.033% for uranium-235 with thermal neutrons. The fission product yields of europium isotopes are low, as they are near the top of the mass range of fission products.

As with other lanthanides, many isotopes of europium have high cross sections for neutron capture, often high enough to be neutron poisons.

مقاطع عرضية للإمساك الحراري للنيوترونات

النظير	151Eu	152Eu	153Eu	154Eu	155Eu
Yield	~10	low	1580	>2.5	330
Barns	5900	12800	312	1340	3950

¹⁵¹Eu is the beta decay product of samarium-151 (not included in above yield), but since this has a long decay half-life and short mean time to neutron absorption, most ¹⁵¹Sm instead ends up as ¹⁵²Sm.

¹⁵²Eu (half-life 13.517 years) and ¹⁵⁴Eu (half-life 8.592 years) cannot be beta decay products because ¹⁵²Sm and ¹⁵⁴Sm are non-radioactive, 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. A larger amount of ¹⁵⁴Eu is produced by neutron activation of a significant portion of the non-radioactive ¹⁵³Eu; however, as shown by the cross-sections, much of this is further converted to ¹⁵⁵Eu and ¹⁵⁶Eu, ending up as gadolinium.

 الاستخدامات

Europium is one of the elements involved in emitting red light in CRT televisions.

هناك القليل من الاستخدامات التجارية لفلز الأوروپيوم, إلا أنه قد استـُعمل to لتطعيم 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 الأوروپيوم (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.

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

Monazite

لا يتواجد الأوروپيوم في الطبيعة كعنصر حر؛ إلا أن هناك العديد من المعادن التي تحتوي على الأوروپيوم, وأهم المصادر هي باستناسيت و مونازيت وxenotime and loparite-(Ce).

Depletion or enrichment of europium in minerals relative to other rare-earth elements is known as the europium anomaly. Europium is commonly included in trace element studies in geochemistry and petrology to understand the processes that form igneous rocks (rocks that cooled from magma or lava). The nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks. The median crustal abundance of europium is 2 ppm; values of the less abundant elements may vary with location by several orders of magnitude.

الاوروپيوم ثنائي التكافؤ بكميات صغيرة وُجد أنه المنشط للاستشعاع fluorescence الأزرق الساطع لبعض العينات من فلوريتات المعادن (ثنائي فلوريد الكالسيوم CaF₂). The reduction from Eu³⁺ to Eu²⁺ is induced by irradiation with energetic particles. The most outstanding examples of this originated around Weardale and adjacent parts of northern England; it was the fluorite found here that fluorescence was named after in 1852, although it was not until much later that europium was determined to be the cause.

In astrophysics, the signature of europium in stellar spectra can be used to classify stars and inform theories of how or where a particular star was born. For instance, astronomers used the relative levels of europium to iron within the star LAMOST J112456.61+453531.3 to propose that the accretion process for the star occurred late.

 النظائر

•  مقالة مفصلة: نظائر الاوروپيوم

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 $5_{-3}^{+11}\times 10^{18}$ yr, 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 (t_½ 12.8 hours), ^152m1Eu (t_½ 9.3116 hours) and ^152m2Eu (t_½ 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).

 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.

 المصادر

• Los Alamos National Laboratory - Europium

 وصلات خارجية

• WebElements.com - Europium
• It's Elemental - Europium