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Bioactive materials XX, S2452199X21005077 (2021). doi:10.1016/j.bioactmat.2021.10.041, Biodegradable magnesium (Mg) alloys can revolutionize osteosynthesis, because they have mechanical properties similar to those of the bone, and degrade over time, avoiding the need of removal surgery. However, they are not yet routinely applied because their degradation behavior is not fully understood.In this study we have investigated and quantified the degradation and osseointegration behavior of two biodegradable Mg alloys based on gadolinium (Gd) at high resolution.Mg-5Gd and Mg-10Gd screws were inserted in rat tibia for 4, 8 and 12 weeks. Afterward, the degradation rate and degradation homogeneity, as well as bone-to-implant interface, were studied with synchrotron radiation micro computed tomography and histology. Titanium (Ti) and polyether ether ketone (PEEK) were used as controls material to evaluate osseointegration.Our results showed that Mg-5Gd degraded faster and less homogeneously than Mg-10Gd. Both alloys gradually form a stable degradation layer at the interface and were surrounded by new bone tissue. The results were correlated to in vitro data obtained from the same material and shape. The average bone-to-implant contact of the Mg-xGd implants was comparable to that of Ti and higher than for PEEK. The results suggest that both Mg-xGd alloys are suitable as materials for bone implants., Published by Elsevier B.V., [Amsterdam]

This study introduced a rat model for preclinical investigation of magnesium-based biodegradable materials in bone fracture conditions, allowing longitudinal in vivo monitoring of fracture healing and implant degradation with multimodal imaging.

The corrosion performances of the as-cast and solution-treated Mg-0.5Zn samples were investigated in 0.9% NaCl solution and compared. From the electrochemical measurement results and corrosion morphology observations, it is found that the corrosion resistance of Mg-0.5Zn deteriorated with the extension of solution treatment duration. The main reason was the formation of Fe-Si precipitates with higher Fe concentrations during heat treatment. The Fe-Si precipitates, especially the ones with high Fe contents influenced the corrosion initiation and propagation significantly. In regard of corrosion performance, the solution-treated and then extruded sample was also performing not as good as the cast and then directly extruded sample.

Novel biodegradable metal alloys are increasingly used as implant materials. The implantation can be accompanied by an inflammatory response to a foreign object. For studying inflammation in the implantation area, non-invasive imaging methods are needed. In vivo imaging for the implanted area and its surroundings will provide beneficiary information to understand implant-related inflammation and help to monitor it. Therefore, inflammation-sensitive fluorescent liposomes in rats were tested in the presence of an implant to evaluate their usability in studying inflammation. The sphingomyelin-containing liposomes carrying alpha-melanocyte-stimulating hormone (α-MSH)-peptide were tested in a rat bone implant model. The liposome interaction with implant material (Mg-10Gd) was analyzed with Mg-based implant material (Mg-10Gd) in vitro. The liposome uptake process was studied in the bone-marrow-derived macrophages in vitro. Finally, this liposomal tracer was tested in vivo. It was found that α-MSH coupled sphingomyelin-containing liposomes and the Mg-10Gd implant did not have any disturbing influence on each other. The clearance of liposomes was observed in the presence of an inert and biodegradable implant. The degradable Mg-10Gd was used as an alloy example; however, the presented imaging system offers a new possible use of α-MSH-SM-liposomes as tools for investigating implant responses.

Electrical resistance testing offers a fast and non-destructive method, which is very sensitive to microstructural features and crystal defects. The influence of the mechanically introduced strain, the alloy concentration and solution state as well as the grain size is shown and discussed based on cold-drawn magnesium wires containing 0.45, 0.91 and 1.42 at.% silver. The condition of the material can be quantified by linear increase of 8.96 ± 0.17 nΩm per unit strain and 6.58 ± 0.06 nΩm/at.% with silver content. This enables the classification of the deformation state and work hardening to push the process limits and allow adjusting the mechanical properties for their application.

The effect of Ag in solid solution on the microstructure, texture and the deformation behaviour of indirectly extruded Mg was investigated. Ag as a solid solution strengthener affects the behaviour during extrusion, resulting in enhanced deformation related heating and corresponding coarser grained microstructures. No substantial effect on the texture development is revealed. The mechanical properties simultaneously increase in stress and strain levels with increasing Ag content, especially in tension as a result of the changing impact of the slip modes which can be associated with a decrease of the lattice parameters as well as the c/a ratio of the hcp lattice structure. In compression tests with twin dominated flow, the impact is much smaller on the compressive yield stress but higher with respect to the twinning related strain hardening rate. Solid solution strength functions for Fleischer and Labusch were determined, also confirming the anisotropic behaviour of the extruded Mg alloys.

Rodent models are commonly used in pre-clinical research of magnesium (Mg)-based and other types of biomaterials for fracture treatment. Most studies selected unstable fixation methods, and there is a lack of multimodal longitudinal

Biodegradable magnesium (Mg) alloys can revolutionize osteosynthesis, because they have mechanical properties similar to those of the bone, and degrade over time, avoiding the need of removal surgery. However, they are not yet routinely applied because their degradation behavior is not fully understood. In this study we have investigated and quantified the degradation and osseointegration behavior of two biodegradable Mg alloys based on gadolinium (Gd) at high resolution. Mg-5Gd and Mg-10Gd screws were inserted in rat tibia for 4, 8 and 12 weeks. Afterward, the degradation rate and degradation homogeneity, as well as bone-to-implant interface, were studied with synchrotron radiation micro computed tomography and histology. Titanium (Ti) and polyether ether ketone (PEEK) were used as controls material to evaluate osseointegration. Our results showed that Mg-5Gd degraded faster and less homogeneously than Mg-10Gd. Both alloys gradually form a stable degradation layer at the interface and were surrounded by new bone tissue. The results were correlated to

Metals 11(9), 1422 (2021). doi:10.3390/met11091422, Magnesium–silver alloys are of high interest for the use as temporary bone implants due to their antibacterial properties in addition to biocompatibility and biodegradability. Thin wires in particular can be used for scaffolding, but the determination of their degradation rate and homogeneity using traditional methods is difficult. Therefore, we have employed 3D imaging using X-ray near-field holotomography with sub-micrometer resolution to study the degradation of thin (250 μm diameter) Mg-2Ag and Mg-6Ag wires. The wires were studied in two states, recrystallized and solution annealed to assess the influence of Ag content and precipitates on the degradation. Imaging was employed after degradation in Dulbecco’s modified Eagle’s medium and 10% fetal bovine serum after 1 to 7 days. At 3 days of immersion the degradation rates of both alloys in both states were similar, but at 7 days higher silver content and solution annealing lead to decreased degradation rates. The opposite was observed for the pitting factor. Overall, the standard deviation of the determined parameters was high, owing to the relatively small field of view during imaging and high degradation inhomogeneity of the samples. Nevertheless, Mg-6Ag in the solution annealed state emerges as a potential material for thin wire manufacturing for implants., Published by MDPI, Basel

We have studied the degradation of pure magnesium wire in simulated body fluid and its subsets under physiological conditions to enable the prediction of the degradation rate based on the medium's ionic composition. To this end, micro-computed tomography and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used, followed by a tree regression analysis. A non-linear relationship was found between degradation rate and the precipitation of calcium salts. The mean absolute error for predicting the degradation rate was 1.35 mm/yr. This comparatively high value indicates that ionic interactions were exceedingly complex or that an unknown parameter determining the degradation may exist.

Several material parameters affect degradation characteristics of Mg and its alloys under physiological conditions. Porous Mg materials are interesting for their simultaneous degradation and drug delivery capabilities. However, an increase in pore surface area is detrimental to both degradation resistance and subsequent mechanical properties. The present work aims at determining the threshold porosity value in Mg–0.6Ca specimens produced by powder metallurgy (PM) below which low degradation rates persist with acceptable mechanical properties. Seven different porous Mg–0.6Ca specimens containing both closed and open pore structures were fabricated with porosities ranging from 3% to 21%. Degradation profiles were obtained via a semi static immersion test over 16 days under physiological conditions using Dulbecco\'s modified Eagle\'s medium with Glutamax and 10% fetal bovine serum as supplements. The results are related to morphological pore parameters like pore size distribution, pore interconnectivity and pore curvatures that were quantified using an ex situ µCT analysis. In general, with decreasing porosity a decrease in pore interconnectivity is seen followed by rounding of the pores. Low degradation rates (MDR < 0.3 mm/year) are observed in specimens until 10% porosity, however, the upper bound for reproducible degradation is observed to be in specimens until 12% porosity. This porosity level also marks the transition from closed to open pore nature with a simultaneous change in pore interconnectivity from less than 10% to greater than 95%, below and above this porosity level, respectively. The tensile strength and elongation to failure recorded for specimens with 10% porosity were 70 MPa and 2%, respectively displaying positive traits of both homogenous degradation and mechanical properties. The results suggest that high pore interconnectivity is the dominant factor controlling degradation and mechanical properties in porous Mg-0.6Ca specimens. The results also indicate a good sintering response of Mg-0.6Ca specimens providing further material development towards biomaterial applications.

Journal of magnesium and alloys 9(6), 2207-2222 (2021). doi:10.1016/j.jma.2021.07.029, Biodegradable implants are taking an increasingly important role in the area of orthopedic implants with the aim to replace permanent implants for temporary bone healing applications. During the implant preparation process, the material's surface and microstructure are being changed by stresses induced by machining. Hence degradable metal implants need to be fully characterized in terms of the influence of machining on the resulting microstructure and corrosion performance.In this study, micro-computed tomography (��CT) is used for the quantification of the degradation rate of biodegradable implants. To our best knowledge, for the first time quantitative measures are introduced to describe the degradation homogeneity in 3D. This information enables a prediction in terms of implant stability during the degradation in the body.Two magnesium gadolinium alloys, Mg-5Gd and Mg-10Gd (all alloy compositions are given in weight% unless otherwise stated), in the shape of M2 headless screws have been investigated for their microstructure and their degradation performance up to 56 days. During the microstructure investigations particular attention was paid to the localized deformation of the alloys, due to the machining process. In vitro immersion testing was performed to assess the degradation performance quantified by subsequent weight loss and volume loss (using ��CT) measurements.Although differences were observed in the degree of screw's near surface microstructure being influenced from machining, the degradation rates of both materials appeared to be suitable for application in orthopedic implants. From the degradation homogeneity point of view no obvious contrast was detected between both alloys. However, the higher degradation depth ratios between the crests and roots of Mg-5Gd ratios may indicated a less homogeneous degradation of the screws of these alloys on contract to the ones made of Mg-10Gd alloys. Due to its lower degradation rates, its more homogeneous microstructure, its weaker texture and better degradation performance extruded Mg-10Gd emerged more suitable as implant material than Mg-5Gd., Published by Elsevier, Amsterdam [u.a.]

The study is focussing towards Metal Injection Moulding (MIM) of Mg-alloys for biomedical implant applications. Especially the influence of the sintering processing necessary for the consolidation of the finished part is in focus of this study. In doing so, the chosen high strength EZK400 Mg-alloy powder material was sintered using different sintering support bottom plate materials to evaluate the possibility of iron impurity pick up during sintering. It can be shown that iron pick up took place from the steel bottom plate into the specimen. Despite the fact that a separating boron nitrite (BN) barrier layer was used and the Mg-Fe phase diagram is not predicting any significant solubility to each other. As a result of this study a new bottom plate material not harming the sintering and the biodegradation performance of the as sintered material, namely a carbon plate material, was found., Graphical abstract Image 1

Acta biomaterialia 101, 637 - 645 (2020). doi:10.1016/j.actbio.2019.11.030, Magnesium alloys are increasingly researched as temporary biodegradable metal implants in bone applications due to their mechanical properties which are more similar to bone than conventional implant metals and the fact that Magnesium occurs naturally within the body. However, the degradation processes in vivo and in particular the interaction of the bone with the degrading material need to be further investigated. In this study we are presenting the first quantitative comparison of the bone ultrastructure formed at the interface of biodegradable Mg–5Gd and Mg–10Gd implants and titanium and PEEK implants after 4, 8 and 12 weeks healing time using two-dimensional small angle X-ray scattering and X-ray diffraction. Differences in mineralization, orientation and thickness of the hydroxyapatite are assessed. We find statistically significant (p < 0.05) differences for the lattice spacing of the (310)-reflex of hydroxyapatite between titanium and Mg–xGd materials, as well as for the (310) crystal size between titanium and Mg–5Gd, indicating a possible deposition of Mg within the bone matrix. The (310) lattice spacing and crystallite size further differ significantly between implant degradation layer and surrounding bone (p < 0.001 for Mg–10Gd), suggesting apatite formation with significant amounts of Gd and Mg within the degradation layer., Published by Elsevier, [Amsterdam]

The effects of micro-addition (0.2 wt.%) of Ca, Sr, Ag, In and Cu on the microstructure and corrosion properties of the as-cast Mg-0.5Zn alloy were systematically studied. It is found that the grain refinement efficiency and intermetallics forming ability differed greatly among these elements. Si impurity also played a vital role in the precipitates formation in all systems. It is generally observed that Mg-Zn-Ca possessed the highest corrosion resistance due to the refined grain size, limited intermetallics and uniform corrosion, whereas Mg-Zn-Cu showed the highest corrosion rate due to the coarse grains, intermetallics activity and severe pitting corrosion. With the exception of Mg-Zn-Cu, the corrosion performances of Mg-0.5Zn(-0.2X) alloys were comparable with the higher concentrated systems from literature, indicating the feasibility of these micro-alloying systems for biomedical applications.

The effect of equal-channel angular pressing (ECAP) on the microstructure, texture, mechanical properties, corrosion resistance and cytotoxicity of two magnesium-silver alloys, Mg-2.0%Ag and Mg-4.0%Ag, was studied. Their average grain size was found to be reduced to 3.2 &plusmn, 1.4 &mu, m and 2.8 &plusmn, 1.3 &mu, m, respectively. Despite the substantial grain refinement, a drop in the strength characteristics of the alloys was observed, which can be attributed to the formation of inclined basal texture. On a positive side, an increase in tensile ductility to ~34% for Mg-2.0%Ag and ~27% for Mg-4.0%Ag was observed. This effect can be associated with the activity of basal and prismatic slip induced by ECAP. One of the ECAP regimes tested gave rise to a drop in the corrosion resistance of both alloys. An interesting observation was a cytotoxic effect both alloys had on tumor cells in vitro. This effect was accompanied with the release of lactate dehydrogenase, an increase in oxidative stress, coupled with the induction of NO-ions and an increase in the content of such markers of apoptosis as Annexin V and Caspase 3/7. Differences in the chemical composition and the processing history-dependent microstructure of the alloys did not have any significant effect on the magnitude of their antiproliferative effect.

Mg-xGd alloys show potential to be used for degradable implants. As rare earth containing alloys, they are also of special interest for wrought products. All applications from medical to engineering uses require a low and controlled degradation or corrosion rate without pitting. Impurities from fabrication or machining, like Fe inclusions, encourage pitting, which inhibits uniform material degradation. This work investigates a suitable etching method to remove surface contamination and to understand the influence of etching on surface morphology. Acetic acid (HAc) etching as chemical surface treatment has been used to remove contamination from the surface. Extruded Mg-xGd (x = 2, 5 and 10) discs were etched with 250 g/L HAc solution in a volume of 5 mL or 10 mL for different times. The microstructure in the near surface region was characterized. Surface characterization was done by SEM, EDS, interferometry, and ToF-SIMS (time-of-flight secondary ion mass spectrometry) analysis. Different etching kinetics were observed due to microstructure and the volume of etching solution. Gd rich particles and higher etching temperatures due to smaller etchant volumes promote the formation of pits. Removal of 2–9 µm of material from the surface was sufficient to remove surface Fe contamination and to result in a plain surface morphology.

Magnesium (Mg) and its alloys degrade under physiological conditions. But how strong is the connection between the implant, the corrosion layer and the surrounding tissue, namely bone? Biomechanical tests like push-out tests have shown that a degraded Mg-pin is surprisingly well integrated with the bone “as reported by Castellani et al. (Acta Biomater 7(1):432–440, 2011) [1]”. High-resolution synchrotron tomography offers a deep look into the microstructure of the material as well as of the bone during deformation until fracture happens. Here we present first data from an in situ tomography experiment of a biodegradable Mg-based implant under compressive load showing how Mg implants are incorporated into bone.

Magnesium alloys attract attention as degradable implant materials due to their adjustable corrosion properties and biocompatibility. In the last few decades, especially wrought magnesium alloys with enhanced mechanical properties have been developed, with the main aim of increasing ductility and formability. Alloying and processing studies allowed demonstrating the relationship between the processing and the microstructure development for many new magnesium alloys. Based on this experience, magnesium alloy compositions need adjustment to elements improving mechanical properties while being suitable for biomaterial applications. In this work, magnesium alloys from two Mg-Zn series with Ce (ZE) or Ca (ZX) as additional elements and a series of alloys with Ag and Ca (QX) as alloying elements are suggested. The microstructure development was studied after the extrusion of round bars with varied processing parameters and was related to the mechanical properties and the degradation behavior of the alloys. Grain refinement and texture weakening mechanisms could be improved based on the alloy composition for enhancing the mechanical properties. Degradation rates largely depended on the nature of second phase particles rather than on the grain size, but remained suitable for biological applications. Furthermore, all alloy compositions exhibited promising cytocompatibility.

The corrosion behaviour of as-cast and solution-annealed Mg-0.5Zn-0.2Ca alloy containing 150 ppm Si was investigated in 0.9% NaCl solution. The main secondary phases in the as-cast state are isolated MgCaSi and a coexisting intermetallic particle which consists of Mg2Ca and Ca2Mg6Zn3. A quasi-in situ approach is applied to investigate the corrosion initiation and development. It is proved that Mg2Ca phase is anodic and preferentially corrodes within the first hour of immersion. Whereas, Ca2Mg6Zn3 and MgCaSi phases continuously act as cathodes until 24 h. After solution annealing, the more homogeneous microstructure and reduced galvanic corrosion result in a higher corrosion resistance.

Developments in X-Ray Tomography XI : [Proceedings] - SPIE, 2017. - ISBN 9781510612396 - doi:10.1117/12.2275121 Developments in X-Ray Tomography XI, San Diego, United States, 6 Aug 2017 - 10 Aug 2017; Proceedings of SPIE 10391, 103910 (2017). doi:10.1117/12.2275121, Permanent implants made of titanium or its alloys are the gold standard in many orthopedic and traumatological applications due to their good biocompatibility and mechanical properties. However, a second surgical intervention is required for this kind of implants as they have to be removed in the case of children that are still growing or on patient’s demand. Therefore, magnesium-based implants are considered for medical applications as they are degraded under physiological conditions. The major challenge is tailoring the degradation in a manner that is suitable for a biological environment and such that stabilization of the bone is provided for a controlled period. In order to understand failure mechanisms of magnesium-based implants in orthopedic applications and, further, to better understand the osseointegration, screw implants in bone are studied under mechanical load by means of a push-out device installed at the imaging beamline P05 of PETRA III at DESY. Conventional absorption contrast microtomography and phasecontrast techniques are applied in order to monitor the bone-to-implant interface under increasing load conditions. In this proof-of-concept study, first results from an in situ push-out experiment are presented., Published by SPIE, Bellingham, Wash.

This report reviews the effects of chemical, physical, and mechanical surface treatments on the degradation behavior of Mg alloys via their influence on the roughness and surface morphology. Many studies have been focused on technically-used AZ alloys and a few investigations regarding the surface treatment of biodegradable and Al-free Mg alloys, especially under physiological conditions. These treatments tailor the surface roughness, homogenize the morphology, and decrease the degradation rate of the alloys. Conversely, there have also been reports which showed that rough surfaces lead to less pitting and good cell adherence. Besides roughness, there are many other parameters which are much more important than roughness when regarding the degradation behavior of an alloy. These studies, which indicate the relationship between surface treatments, roughness and degradation, require further elaboration, particularly for biomedical Mg alloy applications.

The phase dissolution and evolution during the melting and the solidification of Mg containing 10 wt.% CaO was investigated in the temperature range of 20-680 °C. The dissolution of CaO and the formation of Mg2Ca were detected with in situ synchrotron radiation diffraction. The dissolution of CaO was observed at ∼407 °C with the detection of a peak unique to the Mg2Ca phase prior to melting of Mg. After the solidification no CaO was detected, and Mg2Ca and MgO phases were observed.

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Materials letters 102-103, 62 - 64 (2013). doi:10.1016/j.matlet.2013.03.110, In situ synchrotron diffraction experiments were performed during the solidification of a Mg4Y3Nd alloy. The material was melted and solidified inside a sealed stainless steel crucible in the chamber of a Bähr 805 A/D dilatometer. The sample was heated up to 680 °C and kept at this temperature for 5 min to ensure it is molten. Afterwards it was cooled down to the fully solidified state with a cooling rate of 10 K/min. During the T(t) program diffraction patterns were acquired continuously in every 25 s (∼5 K). The forming phases were identified as α-Mg at 625 °C, Mg$_{12}$Nd and Mg$_{14}$Y$_{4}$Nd at 545 °C, and Mg$_{24}$Y$_{5}$ at 320 °C. The experimental results were correlated with simulations based on thermodynamic databases., Published by Elsevier, New York, NY [u.a.]

A sensitive and selective bioanalytical liquid chromatographic method for diclofenac is described. The drug was detected as a flourescent derivative, which was demonstrated by 1H NMR and mass spectrometric studies to be carbazole acetic acid. Diclofenac was derivatized by UV irradiation of the substance performed as a post-column photoreaction. The reactor was a PTFE capillary wound around a 254-nm UV lamp. Diclofenac was isolated from the plasma samples by precipitation of the proteins with acetonitrile. A 50-microliters volume of the supernatant was injected onto a Nucleosil C18 column. The mobile phase was 32% acetonitrile in pH 6.6 buffer. Carbazole acetic acid was detected by a fluorescence detector using an excitation wavelength of 288 nm and an emission wavelength of 360 nm. The recovery was 92%, the standard curve was linear in the range 10-5500 ng diclofenac per ml plasma, and the relative standard deviation at 10 and 5000 ng of diclofenac per ml plasma was 9.0% and 3.3%, respectively. The limit of detection was 6 ng/ml at an injection volume of 50 microliters. Chromatograms of human and rat plasma containing diclofenac are shown.

The water in different parts of a plant forms a continuum throughout the plant body. This makes it possible to record changes in the water content as changes in thickness of any part of the plant. A leaf kept in darkness has been found to change its thickness to a sufficient degree for recordings of changes in transpiration from the rest of the plant. The rapidness of the changes makes it probable that they are mirroring the stomatal movements. The method has been used for recording of influences of SO as air pollutant. It has a couple of advantages over direct measurements of changes in transpiration. One is that the measurement can be used without enclosing the plant in a cuvette. Another is that possibly occurring effects on the hygrometer are eliminated. The method has until now mainly been used for wheat plants but also woody plants as and have been tested.2PinusSalix

A new TEXAS alloy system (Mg-Sn-Nd-Ca-Al-Si) is presented in order to extend the range of applications for magnesium alloys. The alloy has been produced by permanent mould direct chill casting, a process that provides a homogenous distribution of alloying elements throughout the entire casting. This work presents microstructural features and a new Mg-Sn-Ca phase with the morphology of hexagonal platelets. Additionally mechanical properties and the corrosion behaviour of TEXAS alloys are presented in as cast and heat treated conditions.

Mg-RE alloys have a good potential to be used in bio-applications as degradable implants. Their macroscopic characteristics are strongly dependant on the microstructure, which can be tailored through the alloy composition and the solidification parameters. In situ synchrotron diffraction provides a unique tool to follow the phase formation, possible meta-stable and stable phase transformations and grain growth during cooling. In the present study Mg alloys containing Gd, Y and Nd were investigated to characterize the solidification phenomenon during cooling from 680°C to room temperature. Samples were melted and solidified in a Bähr 805 dilatometer modified for in situ synchrotron measurements. The molten samples were contained in steel crucibles, and the temperature was controlled by type S thermocouples during cooling. The results provide an experimental validation of thermodynamic calculations; and provide experimental input for refining the thermodynamic models, which contribute to the better understanding of the microstructure evolution to control desirable macroscopic characteristics.

Mg-RE alloys have potential to be used for bio-applications as degradable implant materials. For the production of these alloys casting plays an important role: Phase formation and microstructure evolution are at first determined during solidification. In situ synchrotron radiation diffraction is a unique tool to follow phase formation, phase transformations and grain growth during solidification. The measurements were performed at the High Energy Materials Science beamline P07 at PETRA III at the Deutsches Elektronen-Synchrotron (DESY, Hamburg, Germany). In the present study Mg4Y, Mg4YlGd and Mg4Y4Gd alloys were investigated to characterize their solidification behavior during cooling from 800°C and 680°C to 450°C, respectively with a cooling rate of 20 K/min. The samples were held in graphite crucibles and were molten in a modified Bahr 805 dilatometer under Ar atmosphere, while the temperature was controlled by type S thermocouples. The results are compared with thermodynamic simulations using Pandat 8™ software.

Previous investigations show that CaO additions have an effect on the microstructure and mechanical properties of commercial Mg alloys. Addition of CaO to pure Mg and Mg alloys results in the dispersion of Ca in the molten and solid Mg with no evidence of CaO. This paper reports on the reactions between Mg, Al and CaO measured by means of in situ synchrotron radiation diffraction during melting and solidification. The experiment was conducted on Mg-3A1 wt% with CaO concentrations between 3 wt% and 10 wt% to study the effect of different Al:CaO ratios. The initial sample contained Mg, Al and CaO in powder state, pressed to cylindrical samples. The melting, the solidification and associated phase transformations were measured in a Bahr 805A/D dilatometer inside a sealed stainless steel crucible at the High Energy Materials Science Beamline P07 at PETRA III, DESY.

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