Showing papers by "Markus Janousch published in 2010"

In Situ XAS and XRPD Parametric Rietveld Refinement To Understand Dealumination of Y Zeolite Catalyst

Abstract: Dealumination of NH4−Y zeolite during steaming to 873 K was investigated with in situ, time-dependent, synchrotron radiation XRPD and in situ Al K-edge XAS. Water desorption is complete at 450 K, and ammonium decomposition occurs between 500 and 550 K. Only a small fraction of Al3+ species (5%) leaves the framework during heating from 710 to 873 K; these species occupy site I′ inside the sodalite cage. This fraction increases up to 8% in the first 50 min at 873 K and remains constant for the following 70 min isotherm and during the high-temperature part of the cooling experiment. During cooling from 500 to 450 K, the electron density at site I′ increases suddenly, corresponding to a fraction of 30−35% of the total Al, confirmed by ex situ 27Al MAS solid-state NMR. At that temperature, in situ Al K-edge XAS indicates a change in Al coordination of a large fraction of Al, and thermogravimetric (TG) data show the first water molecules start to repopulate the pores. Such molecules drive the dislodgment of mos...

Synchrotron and ion beam studies of the bone-cartilage interface

Abstract: The investigations reported herein concern the bone and overlying cartilage in thin sections of articular joints. The focus is on essential and trace elemental distribution and the structural organization of the component collagen fibres. Use is made of several nuclear analytical techniques (NATs), including micro-proton induced x-ray emission (mu-PIXE), Rutherford back scattering technique (RBS), micro proton-induced gamma emission (mu-PIGE), synchrotron radiation micro x-ray fluorescence (SR-muXRF) and synchrotron radiation small angle x-ray scattering (SR-SAXS). Sections of healthy and diseased human femoral heads were examined by a combination of mu-PIXE, RBS and PIGE to investigate the accumulation of some essential and trace elements such as zinc (Zn), calcium (Ca), phosphorus (P), sulfur (S), sodium (Na) and potassium (K) and their concentrations in these sections. Enhanced accumulations of these elements were noted at the bone-cartilage interface in both normal and diseased sections, and suggest an increased activity of bone/cartilage formation and degrading enzymes whose function rely on the presence of Zn, Ca, K and P as co-enzymes. Their high concentrations in the calcified zone of cartilage affected by OA may reflect an enhanced metabolic activity of chondrocytes that are associated with their reparative response to osteoarthritis and also as an indicator of bone growth. SR-muXRF has also been employed in mapping the distribution of Ca, P, K, S, Na and Cl in equine metacarpophalengeal joint, the samples comprising healthy and diseased tissues at the bone-cartilage interface. Of interest was that the mu-SXRF technique showed for the first time the change in shape of the tidemark and cement line in accord with the expectation of an abraded cartilage surface. To investigate the molecular and structural features of bone and cartilage on the nanometre scale, a Pilatus 2M detector was used for the first time in investigation of collagen fibres arrangements in diseased calcified human femoral head sections. Well defined intensity and orientation maps were obtained The findings of this study have shown that the use of these physical techniques in qualitative analysis and quantification of the elemental content and collagen orientation in bone and cartilage tissues offer the ability to make an assessment of the initiation and progress of OA at the micro and nanometre scale.