Showing papers on "Cerium published in 1991"
TL;DR: In this article, the ground state of diπ−cyclooctatetraene cerium (cerocene) was predicted to be in a 4f1 configuration corresponding to Ce3⊕(C8H1.5■8)2.
Abstract: Quantum chemical calculations are presented which predict that in the ground state of di‐π‐cyclooctatetraene cerium (cerocene) the Ce ion is almost entirely in a 4f1 configuration corresponding to Ce3⊕(C8H1.5■8)2. The 4f electron forms with an electron of the ligand e2u highest‐occupied molecular orbital a 4f1e32u singlet in close analogy to a Kondo ion in a metal. Due to coupling of the 4f1e32u with the 4f0e42u configuration, the latter corresponding to Ce4⊕(C8H2≤8)2, the splitting between the ground state singlet and the first excited triplet is of the order 0.5 eV. The self‐consistent‐field and multiconfiguration self‐consistent‐field parts of the calculations are done by employing recently developed pseudopotentials for cerium using basis sets of up to 626 basis functions. The correlation energy is accounted for by means of various correlation‐energy density functionals and also by limited coupled electron‐pair approximation calculations. Similar results are found in both cases.
169 citations
TL;DR: In this article, X-ray absorption near edge structure (XANES) was used to detect 3-and 4-valent cerium-containing films on aluminum and Alloy 5052.
168 citations
1 Jun 1991
TL;DR: In this article, an electrically conducting polypyrrole coatings on inorganic cores were obtained by deposition of pyrrole on catalytically active particles, where the degree of polymer coverage could be controlled by varying the aging time and the properties of the carrier particles.
Abstract: Electrically conducting polypyrrole coatings on inorganic cores were obtained by deposition of pyrrole on catalytically active particles. The finely dispersed core materials were hematite (polyhedral and spindle-type), silica coated with hematite, and cerium(IV) oxide. The degree of polymer coverage could be controlled by varying the aging time and the properties of the carrier particles. The so prepared coated powders were examined by transmission electron microscopy and further characterized by elemental and thermogravimetric analyses, as well as by electrophoresis, X-ray diffraction, and conductivity measurements. The conductivities were comparable to those reported for pure polypyrrole and they increased with pressure.
153 citations
TL;DR: In this paper, the authors show that lanthanide and group 3 carbyls are active precursors for the oligomerization of terminal alyknes HC = CR (R = alkyl, aryl, SiMe3).
149 citations
TL;DR: By using a thermal gravimetric balance reactor and a temperature-programmed reaction technique, this paper found that carbon deposition on cerium oxide-containing nickel catalysts was decreased in both the induction and the constant carbon growth periods Meanwhile the catalysts maintained activity for the steam reforming reaction.
146 citations
TL;DR: In this paper, the authors tried to find a general approach to the non-radiative transitions in a diverse series of Ce(III)-containing samples and found that Ce(3) luminescence will appear if the optical absorption of its surroundings is at high energy, preferentially in the vacuum ultraviolet.
117 citations
TL;DR: In this article, the thermal quenching of light emission from (La,Ce)PO 4 :Tb is greatly improved by substituting borate for a small part of phosphate or doping with thorium.
99 citations
TL;DR: In this article, X-ray absorption near edge structure (XANES) was used to detect 3-and 4-valent cerium-containing films on aluminum and Alloy 5052.
Abstract: Cerium-containing films on aluminum and Alloy 5052 have been investigated using XANES (X-ray Absorption Near Edge Structure). The Ce L III and Ce L I absorption edges allow a clear distinction to be made between 3- and 4-valent cerium. Measurements were made of the fluorescent X-ray signal with X-rays incident at glancing angles to give surface sensitivity. Cerium in the 3-valent state was deposited by galvanostatic reduction from solutions of sufficiently high pH for oxygen to oxidize the cerium to a 4-valent state. From XANES measurements, it was determined that these films contained cerium mainly in the 3-valent state. Exposure of these films to a NaCl solution converted the cerium to the 4-valent state. Open circuit exposure of aluminum to low concentrations of cerium ions gave films with either 3- or 4-valent cerium depending on the exposure time.
93 citations
TL;DR: In this article, the temperature dependence of epitaxial growth of cerium dioxide (CeO2) layers on (111) silicon substrates was studied using ultra-high-vacuum evaporation, varying the substrate temperature in the range between 150 and 900 °C.
Abstract: The temperature dependence of the epitaxial growth of cerium dioxide (CeO2) layers on (111) silicon substrates was studied using ultra‐high‐vacuum evaporation, varying the substrate temperature in the range between 150 and 900 °C. Characterization using Rutherford backscattering spectrometry and reflection high‐energy electron diffraction proved that a CeO2 layer on (111) silicon has considerably good crystalline quality in the range between 200 and 850 °C. It is clarified that the epitaxy can be attained even at surprisingly low temperatures (less than 200 °C). A substrate temperature above 850 °C leads to rather poor crystallinity due to an exponential increase of residual gas pressure. Refractive indices of the epitaxial layers were measured by ellipsometry to be in the range of 2.19–2.79.
91 citations
87 citations
TL;DR: In this article, a vibrating probe technique for measuring the current density distribution over a corroding steel surface has been used to investigate corrosion inhibition by cerium salts, and it has been concluded that at least for steels, cerium acts as an anodic inhibitor.
Abstract: This paper reports on a vibrating probe technique for measuring the current density distribution over a corroding steel surface has been used to investigate corrosion inhibition by cerium salts. The probe vibrations enables the current magnitude and direction in a plane perpendicular to the steel surface to be measured. Contrary to published data, it has been concluded that, at least for steels, cerium acts as an anodic inhibitor.
TL;DR: In this article, a high-precision analytical method for the measurement of 138 Ce 142 Ce ratios was reported using static multicollection mass spectrometry, which reduced the data acquisition time for 2 hours and improved analytical reproducibility to ± 0.002% (n-16) and precision to ±0.002-0.003%.
TL;DR: In this article, the influence of varying cerium, neodymium, cobalt, and silicon concentrations on the magnetic properties of Ce•Fe•B type magnets was investigated, and the results indicated that magnets containing 13.5 at.% of cerium exhibits superior magnetic properties to those exhibited by magnets with higher rare earth element compositions.
Abstract: The influences of varying cerium, neodymium, cobalt, and silicon concentrations on the magnetic properties of Ce‐Fe‐B type magnets were investigated. The results indicated that magnets containing 13.5 at.% of cerium exhibits superior magnetic properties to those exhibited by magnets with higher rare‐earth element compositions. High‐temperature annealing of the cast alloy containing 13.5 at.% cerium at 1010 °C for 120 min results in the elimination of the α‐Fe phase. Increasing the cobalt concentration from 0 to 17 at.% raises the Curie point from 174 °C to 324 °C. The addition of 1 at.% of silicon to the alloy improves intrinsic coercivity by up to 100%. The substitution of up to 5.4 at.% of cerium by neodymium increases magnetic properties of sintered magnets with a 13.5 at.% total rare‐earth content. Neodymium contents exceeding 5.4 at.% decrease coercivity. The highest maximum energy product of 27.2 MGOe was exhibited by magnets with a composition of Ce8.1Nd5.4Fe62Co17SiB6.5.
Patent•
15 Oct 1991
TL;DR: In this paper, the authors proposed to enhance O 2 absorbing and releasing ability by forming the precipitate of cerium carbonate from an aq. soln. having 30-200 g/l concn. contg.
Abstract: PURPOSE: To enhance O 2 absorbing and releasing ability by forming the precipitate of cerium carbonate from an aq. soln. contg. cerium nitrate and NH 4 HCO 3 , hydrothermally treating the precipitate and firing the resulting basic carbonate and/or monoxycarbonate. CONSTITUTION: An aq. cerium nitrate soln. having 30-200 g/l concn. is mixed with an aq. NH 4 HCO 3 soln. having 50-200 g/l concn. in 1.4-3 weight ratio of cerium nitrate to NH 4 HCO 3 and the precipitate of cerium carbonate such as Ce 2 (CO 3 ) 3 .XH 2 O is formed. Basic carbonate such as Ce(OH)(CO 3 ).xH 2 O and/or monoxycarbonate such as Ce 2 O(CO 3 ) 2 .XH 2 O is then formed by hydrothermally treating the precipitate at 100-150°C for about 0.5-2hr and CeO 2 having ≥100μmol/g O 2 absorbing and releasing ability at 400-700°C in a reducing or oxidizing atmosphere is obtd. by firing the basic carbonate and/or monoxycarbonate at ≥300°C, preferably 300-400°C for about 4-10hr. COPYRIGHT: (C)1993,JPO&Japio
Patent•
27 Sep 1991
TL;DR: In this paper, a method of providing a protective coating on the surface of aluminum or aluminum alloys, comprising of removing contaminants from the surface, exposing the surface to water at 50° to 100° C.
Abstract: An method of providing a protective coating on the surface of aluminum or aluminum alloys, comprising: removing contaminants from the surface; exposing the surface to water at 50° to 100° C. to form a porous boehmite coating on the surface; and exposing the boehmite-coated surface to an aqueous solution comprising a cerium salt and a metal nitrate at a temperature of 70° to 100° C. Oxides and hydroxides of cerium are formed within the pores of the boehmite to provide the protective coating, which provides corrosion resistance and improved paint adhesion.
Patent•
22 Jun 1991
TL;DR: In this paper, an alumina-modified cerium oxide was obtained by impregnating a water-insoluble cerium compound with at least one member selected from the group consisting of water-soluble aluminum compounds and alumina hydrates and calcining the product of impregnation.
Abstract: A catalyst for purifying exhaust gas, having deposited on a monolithic honeycomb carrier a catalyst composition comprising an alumina-modified cerium oxide obtained by impregnating a water-insoluble cerium compound with at least one member selected from the group consisting of water-soluble aluminum compounds and alumina hydrates and calcining the product of impregnation, at least one precious metal selected from the group consisting of platinum, palladium, and rhodium, and active alumina.
TL;DR: Graft copolymerization of vinyl compounds onto chitin was studied, and an efficient and reproducible procedure has been established, cerium (IV) being used as the initiator as mentioned in this paper.
Abstract: Graft copolymerization of vinyl compounds onto chitin was studied, and an efficient and reproducible procedure has been established, cerium (IV) being used as the initiator. The reactions with acrylamide and acrylic acid onto powdery chitin were carried out under various conditions to elucidate the polymerization behavior in terms of grafting percentage. The amount of cerium (IV) affected the polymerization most strikingly, and grafting percentages showed maxima with suitable amounts of initiator for both the monomers. As a solvent water proved to be superior to aqueous nitric acid except the reaction with a small amount of initiator. Under appropriate conditions, around 240 and 200% grafting percentages were achieved for acrylamide and acrylic acid, respectively. The resulting graft copolymers showed much improved affinity for solvents and hygroscopicity compared to the original chitin.
TL;DR: In this article, the formation heats of aluminum and cerium were studied using a differential direct isoperibol calorimeter, and the composition and equilibrium state of the samples were confirmed by metallographic and X-ray analyses.
Abstract: The formation heats of the intermetallic compounds of aluminum and cerium were studied using a differential direct isoperibol calorimeter. The composition and equilibrium state of the samples were confirmed by metallographic and X-ray analyses. For the various compounds, the ΔHform (for the reaction in the solid state at 300 K) was determined as follows (kJ/mol of atoms): Ce3Al: -27.0 ± 2; CeAl: -46.0 ± 3; CeAl2: -50.0 ± 2; and Ce3Al11: -41.0 ± 2. The results are discussed and compared with the values which can be found in literature.
TL;DR: In this paper, the interactions of Ce with 20 to 200-A-diameter particles of Pt and Rh on planar Si0 2 were examined using transmission electron microscopy (TEM) and reactivity measurements following treatment in H 2 and O 2 atmospheres.
TL;DR: In this article, the crystal structure of the tetrahydrothiophene derivative was determined by X-ray diffraction, which showed it to consist of discrete [Cp*2Ce(THT)2]+ and BPh4ovbar ions.
TL;DR: In this paper, α-β-Sialon materials were prepared with a constant molar addition of Y2O3 + CeO2 sintering aid with varied composition: 0, 25, 50, 75 and 100 mol% Y 2O3.
Abstract: α-β-Sialon materials were prepared with a constant molar addition of Y2O3 + CeO2 sintering aid with varied composition: 0, 25, 50, 75 and 100 mol% Y2O3. The α-sialon grains formed in the microstructure were carefully investigated by analytical and high-resolution electron microscopy. It was found that the α-sialon structure can accept a small amount of cerium to enter the large interstitial cages, if it is stabilized by simultaneous additions of yttrium. Extended crystal defects were found to occur in the α-phase framework; this has not been observed with only yttrium added.
Patent•
13 Mar 1991
TL;DR: In this article, mixed strontium and lanthanide oxides and a laser using monocrystals of these oxides were used to construct a magnetolead type crystalline structure.
Abstract: Mixed strontium and lanthanide oxides and a laser using monocrystals of these oxides. These oxides with a magnetolead type crystalline structure have the following formula: Sr.sub.x Ln1.sub.y1 Ln2.sub.y2 Ln3.sub.y3 M.sub.z A.sub.a B.sub.b O 19--k in which Ln1 represents at least one trivalent element selected from lanthane, gadolinium and yttrium; Ln2 represents at least one trivalent element selected from neodymium, praseodymium, erbium, holmium and thulium; Ln3 represents an element selected from bivalent europium or trivalent cerium with retention of electric neutrality by virtue of oxygen holes; M represents at least one bivalent metal selected from magnesium, manganese and zinc; A represents at least one trivalent metal selected from aluminum and gallium; B represents a trivalent transition metal selected from chromium and titanium; x, yl, y2, y3, z, a, b and k represent numbers so that 0
TL;DR: In this paper, a metastable cubic phase was formed for ZrO2 modified with 10 mol.% lanthanum, neodymium and samarium by heating at 600°C.
Abstract: ZrO2 catalyst supports modified with rare earth elements were prepared by coprecipitation from an aqueous solution of zirconium oxychloride and rare earth chlorides. The crystallization of amorphous hydrous ZrO2 was inhibited by doping with rare earths; the crystallization temperature was elevated as the amount and ionic radius of the rare earth modifiers was increased. Only modification using cerium had no effect on the crystallization process. The behavior of cerium was different from that of other rare earth elements with valency + 3. A metastable cubic phase was formed for ZrO2 modified with 10 mol.% lanthanum, neodymium and samarium by heating at 600°C. X-ray diffraction and Raman data indicated that the metastable phase had large microstrain and short-range ordering similar to tetragonal symmetry. Rare earth modified ZrO2 showed a large surface area and good thermal stability as a catalyst support. The carbon monoxide oxidation activity of iron was enhanced by modification with neodymium of ZrO2 supports. The results suggest the effectiveness of rare earth modified ZrO2 as catalyst supports.
TL;DR: Cerium dioxide was employed as a gate insulator for an enhancement-type n-channel metal-oxide-semiconductor (MOS) transistor as mentioned in this paper, which yielded a low positive threshold voltage with negligible interface charge effects.
Abstract: Cerium dioxide was employed as a gate insulator for an enhancement‐type n‐channel metal–oxide–semiconductor (MOS) transistor. Cerium was evaporated in a tungsten boat and immediately oxidized for oxide uniformity. The use of CeO2 as a gate oxide in MOS transistor yielded a low positive threshold voltage with negligible interface charge effects. This resulted in the transistor performing as an enhancement type device.
01 Oct 1991-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the radiation resistivity of a fast and high-intensity scintillator GSO(Ce) was measured for 60 Co γ-rays of 10 4 −10 9 rad.
Abstract: Radiation-resistivity of a fast and high-intensity scintillator GSO(Ce) was measured for 60 Co γ-rays of 10 4 −10 9 rad. No sizable radiation-damage was observed up to 10 9 rad irrespective of the amount of cerium between 0.5% and 2.5% in mol.
TL;DR: In this paper, the hydrogenation reactions of but-1-ene, buta-1,3-diene and but- 1-yne have been studied on a series of REPd3 intermetallic compounds (RE = La, Ce, Pr, Nd, Sm) in a powdered form.
Abstract: The hydrogenation reactions of but-1-ene, buta-1,3-diene and but-1-yne have been studied on a series of REPd3 intermetallic compounds (RE = La, Ce, Pr, Nd, Sm) in a powdered form. Because the catalytic pretreatments were found to change activities and selectivities, bulk and surface characterisations were performed by XRD and XPS, before and after the catalytic tests. After 15 h pretreatment with H2 at 573 K, these catalysts showed stable and reproducible activities and selectivities with characteristic changes throughout the series when compared to Pd/pumice catalysts. LaPd3 was the most easily decomposed and its behaviour resembled that of a Pd/La2O3 catalyst. CePd3 was only partly decomposed, the surface becoming partially transformed to metallic palladium and the catalytically active cerium compound, producing a highly active catalyst of low selectivity. Conversely, Pr(Nd,Sm)Pd3 were not decomposed in the bulk and they were more selective than Pd/pumice. Typical trends in the hydrogenation rate ratios of but-1,3-diene to but-1-yne were also observed. Different electronic effects were proposed to explain the different catalytic behaviour of these palladium catalysts.