CMS is one of the four experiments being constructed for the LHC. The electromagnetic calorimeter (ECAL) is made of lead tungstate (PbWO 4 ) crystals. Scintillation light from the crystals in the ...barrel is detected by avalanche photo diodes (APD). The number of scintillation photons emitted by the crystals and the amplification of the APD are both temperature dependent. Keeping the constant term of the energy resolution (the contribution to the fractional energy resolution which is independent of energy) below a few tenths of percent requires the temperature of the the crystals and APDs to be stabilized to within 0.1 K while for example previously built L3 detector using another type of crystals had a temperature stability around 1 K which is the standard requirement for cooling systems at CERN. In this contribution, we describe the innovative solutions which have been developed and implemented to achieve this performance.
Different perovskite compositions made of (La,Ca/Sr)CrO3-delta, La(Cr,Mg)O3-delta, La(Cr,Mg/Cu/Co,Al)O3-delta, and (La,Ca)(Cr,Al)O3-delta were investigated. Defect models were evaluated to describe ...the oxygen vacancy formation and the respective thermodynamic data were determined. The results are used to explain existing literature data on the isothermal expansion of LaCrO3 based perovskites under reducing conditions. Complementary mechanical measurements with selected perovskite compositions revealed that lower oxygen partial pressure causes higher stiffness, strength and fracture toughness. The change in properties is discussed in terms of the observed ferroelastic domains and the interaction of the domain wall motion with the oxygen vacancies. 30 refs.
The steady state demixing of an initially homogeneous oxide solid solution (A,B)O in an electric field is studied theoretically and experimentally. A formal solution of the transport problem and ...first experimental results in the system (Co,Ni)O are presented.
In the following, a contacting variant for solid oxide fuel cells will be presented in which the conductivity of the interconnect is ensured by contact elements made of fine silver. To this end, the ...interconnect has holes through which the contact elements of fine silver (99.9 wt% Ag) are introduced and then pressed. This pressing process and the thermal expansion of the silver during heating leads to a gastight joint. The silver penetrations are additionally soldered to render them capable of withstanding temperature cycling. Contact resistance measurements and corrosion studies at 800 °C in air or Ar/4 vol.% H2/3 vol.% H2O demonstrate the functionality of the contacting variant under the described conditions. The experimental results indicate that contacting by means of silver contact elements ensures long-term stability up to operating temperatures of 800 °C. Current transmission via the silver contact elements means that a large number of materials are conceivable as the interconnect material. In the following application, an FeCrAl steel (1.4767, Aluchrom Y Hf—trade name Krupp Thyssen Nirosta) with 5.7 wt.% aluminium was used. At the operating temperature, a dense aluminium oxide layer forms on its surface which prevents the vaporization, for example of chromium oxide species, during fuel cell operation.
The steady state demixing of an initially homogeneous oxide solid solution (A,B)O in an electric field is studied theoretically and experimentally. A formal solution of the transport problem and ...first experimental results in the system (Co,Ni)O are presented.
The time evolution of the unmixing process in a semiconducting mixed oxide, (A,B)O, under an electric field was calculated by establishing the continuity equations in a phenomenological way and ...solving them numerically by means of a finite difference method. Temporal variations of composition and defect distribution, and boundary motions were obtained, and therefrom, the distribution of oxygen chemical potential inside the oxide was evaluated. It was found that, sluggish defect relaxation during the unmixing process might induce a gradient of the oxygen chemical potential in addition to the electrotransport-induced composition gradient. General aspects of an electrotransport-induced unmixing process are discussed.
The time evolution of the demixing process in a transition metal oxide solid solution, (A,B)
1−
δ
O, under a stationary oxygen potential gradient is calculated by solving the governing continuity ...equations numerically with a finite difference technique. The transient solution of the chemical diffusion process of a monoxide is also computed. From the time variations of the demixing profile and the spatial distribution of the chemical potential of oxygen in the oxide, it is found that two transient processes are involved in demixing leading to the steady state: (1) the establishment of a gradient in the chemical potential of oxygen across the system oxide; and (2) the redistribution of the cations leading to demixing.
CMS is one of the four experiments being constructed for the LHC. The electromagnetic calorimeter (ECAL) is made of lead tungstate (PbWO 4 ) crystals. Scintillation light from the crystals in the ...barrel is detected by avalanche photo diodes (APD). The number of scintillation photons emitted by the crystals and the amplification of the APD are both temperature dependent. Keeping the constant term of the energy resolution (the contribution to the fractional energy resolution which is independent of energy) below a few tenths of percent requires the temperature of crystals and APDs to be stabilized to within 0.057 K. In this contribution, we describe the innovative solutions which have been developed and implemented to achieve this performance.
In solid oxide fuel cells (SOFCs) the interconnects electrically link air and fuel electrodes on either side to produce a practical electrical power output. The long-term stability of intermediate ...temperature (650–800 °C) SOFC operation strongly depends on the composition of the ferritic steel interconnection material and the steel/ceramic interface. During high-temperature operation the Cr-containing ferritic steel forms an oxide scale at its surface, thereby causing high ohmic electrical contact resistance when connected to the surface of an electronically conducting ceramic cathode material. In the long run, the vaporization of Cr species from these oxide scales also affects the cathode activity, eventually leading to cell deterioration. One way of overcoming the problem is to incorporate another electronically conducting ceramic compliant layer, commonly known as the contact layer, between the cathode and metallic interconnect. In this contribution, LaNi0.6Fe0.4O3 was tested as a cathode contact material. Its performance at 800 °C in the form of a ~50 µm thick film applied on two ferritic steel compositions was examined. After 600 h of testing, contact resistances of 60 and 160 mΩ cm2 were obtained. The different values are explained by the variation in steel composition.
The steady state demixing of an initially homogeneous oxide solid solution in an electrical potential gradient is studied theoretically and experimentally. Experiments were performed with single ...crystalline (CoxNi1-x)1-δO exposed to electrical potential gradients of different strength. With respect to the oxide sublattice one can observe a crystal drift towards the cathode, where an enrichment of Co is found, due to its higher mobility compared to Ni (DCo > DNi > > Do). The demixing increases with increasing strength of the electrical potential gradient. For the steady state conditions a formal treatment is given, which considers the diagonal elements LAA and LBB of the transport coefficient matrix. The predicted demixing profile corresponds well to the experimental one.
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