Role Of Cerium Research Articles

On the role of cerium in a chromium-ytterbium-erbium phosphate glass

The influence of cerium oxide on photo- and gamma-stability of chromium-ytterbium-erbium phosphate glasses is studied. It is found that UV irradiation does not cause any noticeable changes in the glass independently of the presence of cerium. Gamma rays produce colour centres in glasses without cerium and their lasing properties deteriorate. Doping glasses with an optimum amount of cerium oxide improves their radiation resistance with respect to gamma rays.

Cerium and lanthanum promote floral initiation and reproductive growth of Arabidopsis thaliana

The effects of cerium and lanthanum on the vegetative growth, floral initiation and reproductive growth of Arabidopsis thaliana were studied. Addition of cerium nitrate (0.5–10 μM) or lanthanum nitrate (0.5–50 μM) to the culture medium significantly increased the lengths of primary roots, but had no significant effects on the number of rosette leaves produced per plant, plant heights and dry weights during the vegetative growth stage (17 days after seed germination). The percentage of plants bolted was significantly increased with the addition of 0.5–10.0 μM cerium nitrate or lanthanum nitrate. The combination of 0.5 μM cerium nitrate and 0.5 μM lanthanum nitrate was found to be most effective on the induction of floral initiation. The height, dry weight and average number of flower numbers of 35-day-old plants growing in media containing cerium nitrate or/and lanthanum nitrate (0.5–10.0 μM) were found to be significantly higher than those in the control medium. The endogenous levels of cytokinins (zeatin riboside, dihydrozeatin riboside and isopentenyl adenosine) and carbohydrates (sucrose, glucose and fructose) in leaf and root tissues of plants growing in the medium supplemented with 0.5 μM cerium nitrate and 0.5 μM lanthanum nitrate were not significantly different from those of plants in the control medium. Application of 0.5 μM cerium nitrate and 0.5 μM lanthanum nitrate enhanced the effects of 10 −6 M IPA on root growth, plant height and flowering. The role of cerium and lanthanum in promoting floral initiation and reproductive growth and the possibility of developing non-hormonal flowering promoting agents are discussed.

Role of cerium in lithium niobate for holographic recording

Cerium-doped lithium niobate crystals are tested for holographic recording. A photochromic effect is observed in crystals doped with cerium and manganese. But two-center recording in the sample is not as effective as in iron and manganese doubly doped crystals. Photocurrent measurements in cerium and iron singly doped crystals indicate that the photovoltaic constant in the cerium-doped crystal is only one third of that of the iron-doped one. This is the main reason accounting for the low sensitivity of cerium-doped lithium niobate crystals. However, in the diffusion dominated case, i.e., for reflection geometry, cerium-doped lithium niobate may give a strong effect.

Oxidative coupling of methane on Ce/Na/CaO catalysts

Oxidative coupling of methane was investigated on Na/CaO and Ce/Na/CaO catalysts with different sodium and cerium contents. The reaction was carried out in a micro fixed-bed flow reactor operating at atmospheric pressure, at 700 and 750°C and molar ratio feed of CH4 : O2 : N2 = 50 : 10 : 40. Catalysts were compared at isoconversion and were characterized by BET, XRD and XPS. The addition of cerium to Na/CaO catalyst increased the specific activity by a factor of eight. These catalytic and characterization results were related to the presence not only of Na+O- active sites, formed by the introduction of Na+ in the CaO lattice, but also to peroxide active sites. A mechanism is proposed to explain the role of cerium in increasing the rate of the regeneration step of the O s – and Na2O2 sites.

The Role of Cerium in the Resistance of an MoS2-Containing Composite Brush Plating Layer to Humid Atmosphere

MoS2 is an excellent solid lubricant widely used for reducing friction. However, moisture is very harmful to its solid lubrication property because MoS2 is easily oxidized to form Mo6+ and S6+ in a humid atmosphere. In order to improve its oxidation resistance, a study on the role of a rare earth element Ce in the resistance of a Ni-Cu-P/Mo2 brush plating layer to the humid atmosphere was carried out. It was found that cerium can effectively stabilize the solid lubrication property of MoS2 due to its preferential adsorption on the surface of MoS2 particles, the adsorbed layer serving as a barrier to oxidation. This study shows that the rare earth element Ce can be deposited from a water plating solution.

ChemInform Abstract: The Role of Cerium in Potassium Titanyl Phosphate (KTiOPO4)

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The role of cerium in potassium titanyl phosphate (KTiOPO 4)

The role of cerium in potassium titanyl phosphate (KTiOPO 4), where it increases its optical transmission in the visible region, is explained. A comparison with the afterglow-reducing role of cerium in phosphors for computed tomography is made.

Understanding the role of cerium during VIM refining of nickel-chromium and nickel-iron alloys

The effect of cerium addition on the VIM refining process of oxygen, sulfur, and nitrogen in a nickel-chromium alloy and the Udimet 901 iron-nickel-base superalloy is presented. It was found that cerium reduces sulfur and oxygen content effectively through the formation of cerium oxides, sulfides, and oxysulfides but did not reduce the already low nitrogen content. The kinetics of oxygen and sulfur depletion in the VIM heats follow the first order reaction rate theory and the proposed mechanism is that of the drift of inclusions to crucible skulls. The maximum addition of cerium to iron-nickel-base alloys is limited by segregation effects that lead to hot shortness.

Thermoluminescence due to intrinsic point defects in polycrystalline calcium sulphide

A predominant glow peak at 226+or-3K in calcium sulphide, reported here, is thought to be due to sulphur vacancies acting as electron traps. In all, there are four predominant glow peaks in pure and cerium-activated CaS, two of which have been previously reported by the authors. These exhibit a significant behaviour which has been analysed to reveal the presence of hole traps as well as deep electron traps due to intrinsic point defects in CaS. Cerium has been used primarily to enhance thermoluminescence emission of CaS. However, in view of the fact that the role of cerium in producing compensating defects in CaS is still highly controversial, its role in the present work has been examined.

Radiation induced color centers in multicomponent glasses

This paper discusses, in some detail, the nature of color centers induced by radiation in different borate, silicate and phosphate glasses; using optical and ESR techniques. The role of cerium and other multivalent ions in suppression of some of these centers and in studying their nature is also discussed. In most glasses, the visible induced absorption was associated with positive hole centers. However, at certain compositions, an electron trap center which absorbs in the visible is also induced by radiation, and was associated with certain structural defects, e.g. a non-bridging oxygen ion vacancy neighboring the alkai ions in diborate or disilicate glasses, Pb 2+ ions (or other isoelectronic ions) taking network modifying positions, or Ce 3+ ions in relatively high concentrations. Some examples of the use of radiation induced optical absorption and electron spin resonance as a tool for studying structural changes are also discussed.

Role of Cerium in Suppression of Gamma‐Ray Induced Coloring of Borate Glasses

The role of cerium in the suppression of gamma‐ray induced coloration in glass has been found to depend on the relative concentration of Ce3+ to Ce4+ ions as well as on the total cerium content. In a borate glass having high ultraviolet transmission, it has been found that both Ce3+ and Ce4+ ions are necessary to suppress the optical absorption bands induced in the visible region. The role of cerium can be explained on the basis of a change in its oxidation state as a result of gamma irradiation. It is postulated that the cerous ions, by the reaction Ce3+→ Ce4++e, suppress the induced visible band at 2.36 ev (525 mμ), which may result from positive hole centers. High cerous ion concentration results, however, in an induced center (Ce3++e) which absorbs in the visible at about 1.9 ev (650 mμ). The presence of Ce4+ ions near Ce3+ prevents the formation of this center possibly by the reaction Ce4++e→ Ce3+. These induced opposite changes in the oxidation state of cerium tend to maintain a balance in the ratio of Ce3+ to Ce4+ ions in the glass during irradiation, and the suppression of the visible bands depends on this ratio.