Crystal Slurries Research Articles

The Petrogenesis of the Lower Critical Zone and Lower Group Chromitites, Eastern Bushveld Complex: Incremental Development of Igneous Layering and Injection of Chromite Slurries

Abstract The petrogenesis of the mafic-ultramafic layered rocks of the Bushveld Complex, South Africa, remains uncertain despite more than a century of intensive research. There is little evidence for the existence of a shallow crustal magma chamber, a principle entrenched in the scientific literature for many years, and we prefer an alternative hypothesis in which igneous layering developed from successive intrusive events. Geochemical discontinuities are explained by radical switches in the composition of intruding parental magmas. Here we investigate the origin of the Lower Critical zone, a sequence of five pyroxenitic and two peridotitic units containing the Lower Group (LG) of chromitites, of which LG6 is a major resource for chromium ore in the eastern limb. The pyroxenitic and peridotitic units are not part of magmatic cycles. Two discrete lineages of parental magma are recognized: a pyroxenitic magma sourced from deep crustal staging chambers, and a mantle-derived peridotitic magma. The pyroxenitic units reveal an absence of modal layering (with the exception of the 0.1- to 1-m-thick layers of chromitite) and limited height-related fractionation trends (enstatite: En86–811). Magma was fed as thin laminae. Intrusion rates were insufficient to create a magma reservoir because the supply of magma matched the rate of batch crystallization. There is little evidence of a fractionated residue having been removed. The recognition of minor geochemical trends of Mg- and Fe-enrichment in the pyroxenitic units reflects minor oscillations in the composition of the parental magma. The composition of the orthopyroxene and of the Cr spinel was primarily established at depth. The anomalous concentrations of chromite are explained by the introduction of pyroxenitic magmas containing crystals of Cr spinel, sufficiently abundant in some cases as to have created crystal slurries. The Cr spinel was entrained at depth, in the staging chambers. Each layer of chromitite is related to injection of a crystal slurry. The tiny size of the rounded xenocrysts of Cr spinel facilitated the mobile and dynamic nature of slurries. Coarse-grained mosaics of Cr spinel developed in the compacted layers of chromitite from prolonged periods of annealing. The irregular spacing of the chromitites, and occurrence of variable concentrations of disseminated Cr spinel in the pyroxenites, is explained by fluctuations in the proportion of entrained xenocrysts, rather than changes in the composition of the melt fraction of the magma. The peridotitic units are interpreted as sills, the chromitite layers having been inherited from the earlier formed pyroxenitic stratigraphy. The most primitive layers of dunite and harzburgite (olivine: Fo90-85 in which Fo = forsterite) accumulated in the center of sills, where a high magma flux facilitated growth of pegmatitic oikocrysts.

Variscan lithotectonic units of the Suchý massif in the Strážovské vrchy Mts., Western Carpathians – products of sedimentary, tectonometamorphic and granite forming processes

The present geological investigation of the Pre-Alpine structure of the western part of Strážovské vrchy Mts (the Suchý massif; Western Carpathians) has distinguished three lithologically distinct Variscan lithotectonic units, which originated (1) in the deeper parts of oceanic basin (prevailingly metapelites with different content of organic matter, metabasalts, metacarbonates?); (2) sediments of the continental slope (flyschoid sediments with a predominance of greiwacke sediments; both VmD0); (3) a unit of continent basement primarily of pre-VmD0 granitic composition (orthogneiss). These rock sequences of differing geotectonic provenances were amalgamated and metamorphosed in the pre-intrusive (Pre-Mississipian) stage; pre-VmD2). Regarding the Variscan polyorogenic evolution, Variscan processes in Tatricum represent the Meso-Variscan evolution (VmD). The maximum P-T conditions of orogenic (regional) metamorphism (up to 610 °C and 7.5–8.5 kbar) were not sufficient for more extensive anatexis. Field observations indicated that the production of a limited volume of granitoid melts occurred mainly at the contacts of amalgamated lithotectonic units. Probably due to the heat, produced by the hot line below the collisional orogen and contributing also to unroofing processes (in orogenic phase VmD2) there started new granitization process. This stage of Mississippian VmD2 granite formation is associated with the emplacement of various types of granitoid magma, encompassing the oldest granodiorites with frequent schliers, representing a poorly differentiated and poorly mobile crystal slurry (present in the SE part of the territory). In the highly evolved collision phase, masses of leucogranites intruded comformably with the deformation plan in the metamorphic complexes, interacting with surrounding metamorphic rocks in shallower crustal conditions and causing their contact metamorphic overprint (up to 590 °C and 3–4 kbar). The syn-deformation character of leucocratic granites is proved by the orientation of biotite flakes parallel to the deformation plane of surrounding metamorphites. Part of leucogranites, especially in the central parts of the bodies, is omnidirectional. The stress field acted not only during the intrusion of the leucogranite magma, but also in the subsolidus stage. The final stage of this process is the formation of large bodies of pegmatites in extensional VmD2 fractures oriented at a large angle to the main stress component. The texture of the grey blocky K-feldspar pegmatites and the lack of H2O-bearing minerals point to pneumatolytic fracturing in a subsequently opened environment in VmD2. The final stage of VmD2 is represented by intrusions of I-type granodiorites with indications of magma mixing, or mingling. The chemical dating of monazites in granitoids allowed to date individual phases of granitization process in the range of 360–345 Ma, which youngest ages correspond with the formation of pegmatites. Dating of monazite in metamorphic rocks points to their thermal overprint during granitization process (360–350 Ma), having already earlier metamorphic overprint (380–370 Ma). The scenario of placement of granitoid intrusions is consistent with the decompression regime (in VmD2) after the end of VmD1c crustal thickening until the fracturing of the crustal block with of I-type magma intrusions of deeper origin. After this period, the exhumation of crystalline blocks, partial diaphtoresis and later surface erosion continue until the Lower Triassic. The re-submergence of the crystalline complexes is associated with a low degree of Alpine metamorphic reworking.

Deep-learning based in-situ micrograph analysis of high-density crystallization slurry using image and data enhancement strategy

Process analytical technology (PAT) plays a crucial role in optimizing crystalline powder product qualities, improving process stability, and reducing experimental costs by enabling real-time monitoring and control of process variables during the crystallization process. In-situ process imaging and analysis have gained significant attention due to their capacity to provide abundant information through images, leading to remarkable advancements in image processing technology, particularly with the support of artificial intelligence. However, the performance suffers when processing high-density slurry images due to challenges such as defocusing, overlapping, background and crystal edges blurriness, and inconsistencies in crystal scales. To address these challenges and explore research strategies based on deep learning for segmenting and analyzing high slurry density images effectively, this study constructed a specific dataset that contains high-density slurry crystal images which is well-labeled, and introduced state-of-the-art neural networks including YOLOv8, U2-net, and Mask R-CNN combined with image and data enhancement strategies. Comparative analysis revealed that YOLOv8 outperformed Mask R-CNN and U2-net by capturing multi-dimensional information in high-density crystal slurry scenarios. Finally, based on the segmentation results of the practical taurine crystallization process using proposed strategy, 1D crystal size, aspect ratio along with 2D size distributions were extracted for further evaluation of crystallization kinetics and crystal properties accurately and quickly.

Emplacement and ore potential of the Permian Pobei mafic–ultramafic complex, NE Tarim, NW China

A number of mafic–ultramafic intrusions with variable degrees of Ni-Cu sulfide mineralization occur in the northeastern Tarim Block and East Tianshan Orogenic Belt (NW China). Among them, the Pobei complex is composed of a gabbro body intruded by several ultramafic bodies including Poyi and Poshi. These bodies have similar mineralogy and chemical compositions and were derived from a common magma. Olivine crystals from the Poyi and Poshi bodies generally have high Fo contents with the highest Fo value of 89.5 and Ni up to 3300 ppm Ni, indicative of crystallizing from Ni-undepleted, high-Mg basaltic magmas. Sr-Nd-Pb isotopic compositions show that more mafic rocks show relatively low degrees of crustal contamination, whereas more evolved rocks experienced higher degrees of contamination, especially in the upper part of the complex. Olivine crystals from both the Poyi and Poshi bodies show sharp decrease of Ni with decreasing Fo values, indicating sulfide segregation in these two bodies. Gabbros may have potential of reef-type chromite mineralization at the deep level, and V-bearing magnetite mineralization at higher stratigraphic level corresponding to the current surface level, but the potential of PGE mineralization is low. We propose that the ultramafic bodies of the Pobei complex may have been formed from the injection of olivine- and sulfide-laden crystal slurry from the bottom of a large magma chamber. The Ni-Cu mineralization was triggered by the crustal contamination. The Pobei complex was formed by the multiple intrusions of magmas to form the current complex.

Digital design of an integrated purification system for continuous pharmaceutical manufacturing

In this work dynamic models of the continuous crystallization, filtration, deliquoring, washing, and drying steps are introduced, which are developed in the open-source pharmaceutical modeling tool PharmaPy. These models enable the simulation and digital design of an integrated continuous two-stage crystallization and filtration-drying carousel system. The carousel offers an intensified process that can manufacture products with tailored properties through optimal design and control. Results show that improved crystallization design enhances overall process efficiency by improving critical material attributes of the crystal slurry for downstream filtration and drying operations. The digital design of the integrated process achieves enhanced productivity while satisfying multiple design and product quality constraints. Additionally, the impact of model uncertainty on the optimal operating conditions is investigated. The findings demonstrate the systematic process development potential of PharmaPy, providing improved process understanding, design space identification, and optimized robust operation.

Crystallization of sucrose by using microwave vacuum evaporation

Sucrose crystallization was performed by using a custom designed microwave vacuum evaporation system. Process was designed to mimic a semi-batch crystallization starting from beet syrup concentration to crystal slurry formation. The effect of microwave power and feeding time on the process yield and product attributes (particle size, solution color and turbidity) were investigated. Microwave treatment was shown to affect the sucrose crystal morphology and the quality parameters significantly. Process yield was significantly affected by both crystallization power and feeding time (p < 0.05). Longer feeding time (15 min) and medium microwave power (30%) resulted in the highest process yield (∼55%). The results revealed that microwave processing can be a promising alternative over commercial crystallization.

Evidence for the incremental assembly of the Pyroxenite Marker, Bushveld Complex, by the emplacement of crystal slurries

Evidence for the incremental assembly of the Pyroxenite Marker, Bushveld Complex, by the emplacement of crystal slurries

Investigation of natural gas hydrate formation and slurry viscosity in non-emulsifying oil systems

At a later stage of oilfield development, there will be more free water in the pipeline, which may engender the phase inversion of water-in-oil emulsions, thereby augmenting the risk of hydrate plugging. In a novel 30 L high-pressure autoclave, the effects of wax content, water cut, temperature, initial pressure, and rotation speed on hydrate crystallization nucleation and slurry viscosity were examined. Results demonstrated that in systems with wax content greater than or equal to 2 wt%, at the onset of the swift hydrate growth stage, the aggregation of wax and hydrate will impair the gelling structure of wax-containing oil, inducing an abrupt fall in slurry viscosity. Consideration is given to the solubility fluctuation of the natural gas in oil, and an empirical prediction formula for gas consumption during hydrate formation in wax-containing systems is established. The presence of wax hinders the crystalline nucleation and growth of hydrates. Notwithstanding, the hydrate slurry viscosity of the wax-containing system is greater because the wax-hydrate aggregates have a more conspicuous effect on the slurry viscosity than the hydrate volume fraction. The water cut of 70% is a critical upper limit, above which the viscosity of hydrate slurry would increase dramatically. Higher rotation speed and initial pressure can significantly enhance the viscosity of hydrate slurries, but their effects on the hydrate nucleation induction time are more perplexing.

A novel visible-light catalyzed assisted single crystal diamond chemical mechanical polishing slurry and polishing mechanism

Single crystal diamond has significant chemical and mechanical stability, which makes it challenging to efficiently obtain high quality single crystal diamond surface. In this study, the effect of four different sets of chemical mechanical polishing (CMP) slurries on the surface roughness Ra and the material removal rate MRR was investigated. The optimum slurry consisted of hydrogen peroxide, diamond micro-powder, synthesis product of nanodiamond and CuFe-layered double hydroxide (ND/LDH), oxalic acid and deionized water. After CMP by the optimum slurry, the average Ra value of three scanning ranges of 868 µm× 868 µm was 0.112 ± 0.003 nm and the average MRR value of three measurements was 416 ± 5 nm/h. High efficiency to obtain high quality single crystal diamond surface was achieved. The variation of hydroxyl radicals (·OH) concentration in the optimum slurry with time was measured. The optimum slurry CMP mechanism was elucidated by X-ray diffractometry (XRD) and X-ray photoelectron spectrometer (XPS). Visible-light photoelectrons and the rapid oxidation of C2O4·- radicals were accelerated the redox cycle of Fe3+/Fe2+ and Cu2+/Cu+ to produce·OH. The·OH oxidised the C atoms on the single crystal diamond surface to form -C-O-C-, -C-O-H and -CO. Finally, they were removed by diamond micro-powder abrasive, obtaining an ultra-smooth surface.

The petrogenesis and emplacement mechanism of layered ultramafic-mafic complexes of the Barberton Greenstone Belt: Insights from the Stolzburg Complex, South Africa

Abstract Ultramafic-mafic layered complexes are important but not-well studied components of Archaean granitoid-greenstone terranes. In the vicinity of the Barberton Greenstone Belt (BGB), at least 27 such complexes are intimately associated with the supracrustal succession. The petrogenesis of one of these layered bodies, the Stolzburg Complex (SC), is explored, together with its relationship to the surrounding Barberton volcanic succession. Previous models for the origin of Barberton layered complexes proposed a variety of mechanisms, such as single chamber subvolcanic sills, ponded lavas, and alpine-type tectonites. In contrast, the present work suggests that emplacement mostly occurred as sheeted sills of crystal slurries into the country rocks. Unlike the subvolcanic sills model, whereby each complex grew through repetitive magma injection and differentiation in a single chamber, the preferred model regards the layered bodies as ‘stacks’ of discrete intrusions, where each magmatic unit represents a distinct sill. Through comparison of trace element geochemistry (i.e., trace element ratios and patterns), the Lower and Upper divisions of the SC are inferred to be petrogenetically related, but compositionally distinct from the enveloping Nelshoogte volcanic rocks. The trace element geochemistry of the Lower and Upper divisions of the complex is indistinguishable. While the SC ultramafic rocks display an Al-undepleted character, Nelshoogte metavolcanics can be classified as Al-depleted komatiites and komatiitic basalts.

Co-flow injection for serial crystallography at X-ray free-electron lasers.

Serial femtosecond crystallography (SFX) is a powerful technique that exploits X-ray free-electron lasers to determine the structure of macro-molecules at room temperature. Despite the impressive exposition of structural details with this novel crystallographic approach, the methods currently available to introduce crystals into the path of the X-ray beam sometimes exhibit serious drawbacks. Samples requiring liquid injection of crystal slurries consume large quantities of crystals (at times up to a gram of protein per data set), may not be compatible with vacuum configurations on beamlines or provide a high background due to additional sheathing liquids present during the injection. Proposed and characterized here is the use of an immiscible inert oil phase to supplement the flow of sample in a hybrid microfluidic 3D-printed co-flow device. Co-flow generation is reported with sample and oil phases flowing in parallel, resulting in stable injection conditions for two different resin materials experimentally. A numerical model is presented that adequately predicts these flow-rate conditions. The co-flow generating devices reduce crystal clogging effects, have the potential to conserve protein crystal samples up to 95% and will allow degradation-free light-induced time-resolved SFX.

A novel modified LiCl solution for three-phase absorption thermal energy storage and its thermal and physical properties

• A novel LiCl solution for three-phase absorption thermal energy storage is proposed. • The energy storage density of the solution is enhanced by adding two types of additives. • The LiCl crystal slurry overcomes the fluidity problem caused by crystallization. • Thermal and physical properties of the modified solution are measured by experiments. Absorption thermal energy storage (TES) is gaining increasing attention due to its large energy storage density (ESD), mobility and long-term thermal storage capability. Expanding the working concentration difference of a solution can significantly enhance its ESD; however, this may result in crystallization, influencing fluidity and blocking flow channels in a TES device. Furthermore, bulky crystals are difficult to dissolve during energy discharge. In this paper, a novel modified LiCl solution is proposed for three-phase absorption TES, which allows the growth of fine crystals and the formation of well suspended slurry. For the first time, two types of additives with competing mechanism are introduced into the solution: ethylene glycol as a crystallization inhibitor and SiO 2 nanoparticles (SNPs) as a nucleating agent. Compared with traditional working fluids, the proposed solution has a larger ESD and good fluidity. The expanded concentration difference is determined by experiments on solubility and suspension. The optimal mass ratio of the LiCl solution, ethylene glycol and SiO 2 nanoparticles are obtained considering both ESD and fluidity. Heat and cold storage density using this novel LiCl crystal slurry can be enhanced by 24.8% and 156.0% respectively. Measurements on thermal and physical properties including vapor pressure, density and viscosity are also carried out.

Serial crystallography using automated drop dispensing.

Automated, pulsed liquid-phase sample delivery has the potential to greatly improve the efficiency of both sample and photon use at pulsed X-ray facilities. In this work, an automated drop on demand (DOD) system that accelerates sample exchange for serial femtosecond crystallography (SFX) is demonstrated. Four different protein crystal slurries were tested, and this technique is further improved here with an automatic sample-cycling system whose effectiveness was verified by the indexing results. Here, high-throughput SFX screening is shown to be possible at free-electron laser facilities with very low risk of cross contamination and minimal downtime. The development of this technique will significantly reduce sample consumption and enable structure determination of proteins that are difficult to crystallize in large quantities. This work also lays the foundation for automating sample delivery.

A spatially resolved model for pressure filtration of edible fat slurries

AbstractA spatially resolved one dimensional pressure filtration model was developed for a slurry of edible fat crystals. The model focuses on the expression step in which a cake is compressed to force the liquid through a filter cloth. The model describes the local oil flow in the shrinking cake modeled as a porous nonlinear elastic medium existing of two phases, viz. porous aggregates and interaggregate liquid. Conservation equations lead to a set of two differential equations (vs. time and vs. a material coordinate ω) for two void ratios, which are solved numerically by exploiting a finite‐difference scheme. A simulation with this model results in a spatially resolved cake composition and in the outflow velocity, both as a function of time, as well as the final solid fat contents of the cake. Simulation results for various filtration conditions are compared with experimental data collected in a pilot‐plant scale filter press.

Mathematical modeling and digital design of an intensified filtration-washing-drying unit for pharmaceutical continuous manufacturing

This paper introduces a comprehensive mathematical model of a novel integrated filter-dryer carousel system, designed for continuously filtering, washing and drying a slurry stream into a crystals cake. The simulator includes models for dead-end filtration, cake washing and convective cake drying, based on dynamic multi-component mass, energy and momentum balances. For a set of feed conditions and control inputs, the model allows tracking the solvents and impurities content in the cake (critical quality attributes, CQAs) throughout the whole process. The filtration and drying model parameters were identified for the isolation of paracetamol from a crystallization slurry. The calibrated model was used for designing the isolation of paracetamol from a multi-component slurry, containing a non-volatile impurity, too. The probabilistic design space, expressing the combinations of the carousel feed conditions and control inputs for which the probability of meeting the target CQAs is acceptable, and the maximum throughput were identified.

Exploring the Role of Anti-solvent Effects during Washing on Active Pharmaceutical Ingredient Purity.

Washing is a key step in pharmaceutical isolation to remove the unwanted crystallization solvent (mother liquor) from the active pharmaceutical ingredient (API) filter cake. This study looks at strategies for optimal wash solvent selection, which minimizes the dissolution of API product crystals while preventing the precipitation of product or impurities. Selection of wash solvents to avoid both these phenomena can be challenging but is essential to maintain the yield, purity, and particle characteristics throughout the isolation process. An anti-solvent screening methodology has been developed to quantitatively evaluate the propensity for precipitation of APIs and their impurities of synthesis during washing. This is illustrated using paracetamol (PCM) and two typical impurities of synthesis during the washing process. The solubility of PCM in different binary wash solutions was measured to provide a basis for wash solvent selection. A map of wash solution composition boundaries for precipitation for the systems investigated was developed to depict where anti-solvent phenomena will take place. For some crystallization and wash solvent combinations investigated, as much as 90% of the dissolved PCM and over 10% of impurities present in the PCM saturated mother liquor were found to precipitate out. Such levels of uncontrolled crystallization during washing in a pharmaceutical isolation process can have a drastic effect on the final product purity. Precipitation of both the product and impurities from the mother liquor can be avoided by using a solvent in which the API has a solubility similar to that in the mother liquor; for example, the use of acetonitrile as a wash solvent does not result in precipitation of either the PCM API or its impurities. However, the high solubility of PCM in acetonitrile would result in noticeable dissolution of API during washing and would lead to agglomeration during the subsequent drying step. Contrarily, the use of n-heptane as a wash solvent for a PCM crystal slurry resulted in the highest amount of precipitation among the solvent pairs evaluated. This can be mitigated by designing a multi-stage washing strategy where wash solutions of differing wash solvent concentrations are used to minimize step changes in solubility when the mother liquor and the wash solvent come into contact.

Structural Effects of Gas Hydrate Antiagglomerant Molecules on Interfacial Interparticle Force Interactions.

Gas hydrate interparticle cohesive forces are important to determine the hydrate crystal particle agglomeration behavior and subsequent hydrate slurry transport that is critical to preventing potentially catastrophic consequences of subsea oil/gas pipeline blockages. A unique high-pressure micromechanical force apparatus has been employed to investigate the effect of the molecular structure of industrially relevant hydrate antiagglomerant (AA) inhibitors on gas hydrate crystal interparticle interactions. Four AA molecules with known detailed structures [quaternary ammonium salts with two long tails (R1) and one short tail (R2)] in which the R1 has 12 carbon (C12) and 8 carbon (C8) and saturated (C-C) versus unsaturated (C═C) bonding are used in this work to investigate their interfacial activity to suppress hydrate crystal interparticle interactions in the presence of two liquid hydrocarbons (n-dodecane and n-heptane). All AAs were able to reduce the interparticle cohesive force from the baseline (23.5 ± 2.5 mN m-1), but AA-C12 shows superior performance in both liquid hydrocarbons compared to the other AAs. The interfacial measurements indicate that the AA with an R1 longer alkyl chain length can provide a denser barrier, and the AA molecules may have higher packing density when the AA R1 alkyl tail length is comparable to that of the liquid hydrocarbon chain on the gas hydrate crystal surface. Increasing the salinity can promote the effectiveness of an AA molecule and can also eliminate the effect of longer particle contact times, which typically increases the interparticle cohesive force. This work reports the first experimental investigation of high-performance known molecular structure AAs under industrially relevant conditions, showing that these molecules can reduce the interfacial tension and increase the gas hydrate-water contact angle, thereby minimizing the gas hydrate interparticle interactions. The structure-performance relation reported in this work can be used to help in the design of improved AA inhibitor molecules that will be critical to industrial hydrate crystal slurry transport.

The Rustenburg Layered Suite formed as a stack of mush with transient magma chambers

The Rustenburg Layered Suite of the Bushveld Complex of South Africa is a vast layered accumulation of mafic and ultramafic rocks. It has long been regarded as a textbook result of fractional crystallization from a melt-dominated magma chamber. Here, we show that most units of the Rustenburg Layered Suite can be derived with thermodynamic models of crustal assimilation by komatiitic magma to form magmatic mushes without requiring the existence of a magma chamber. Ultramafic and mafic cumulate layers below the Upper and Upper Main Zone represent multiple crystal slurries produced by assimilation-batch crystallization in the upper and middle crust, whereas the chilled marginal rocks represent complementary supernatant liquids. Only the uppermost third formed via lower-crustal assimilation–fractional crystallization and evolved by fractional crystallization within a melt-rich pocket. Layered intrusions need not form in open magma chambers. Mineral deposits hitherto attributed to magma chamber processes might form in smaller intrusions of any geometric form, from mushy systems entirely lacking melt-dominated magma chambers.

Dynamic Structural Biology Experiments at XFEL or Synchrotron Sources.

Macromolecular crystallography (MX) leverages the methods of physics and the language of chemistry to reveal fundamental insights into biology. Often beautifully artistic images present MX results to support profound functional hypotheses that are vital to entire life science research community. Over the past several decades, synchrotrons around the world have been the workhorses for X-ray diffraction data collection at many highly automated beamlines. The newest tools include X-ray-free electron lasers (XFELs) located at facilities in the USA, Japan, Korea, Switzerland, and Germany that deliver about nine orders of magnitude higher brightness in discrete femtosecond long pulses. At each of these facilities, new serial femtosecond crystallography (SFX) strategies exploit slurries of micron-size crystals by rapidly delivering individual crystals into the XFEL X-ray interaction region, from which one diffraction pattern is collected per crystal before it is destroyed by the intense X-ray pulse. Relatively simple adaptions to SFX methods produce time-resolved data collection strategies wherein reactions are triggered by visible light illumination or by chemical diffusion/mixing. Thus, XFELs provide new opportunities for high temporal and spatial resolution studies of systems engaged in function at physiological temperature. In this chapter, we summarize various issues related to microcrystal slurry preparation, sample delivery into the X-ray interaction region, and some emerging strategies for time-resolved SFX data collection.

Studying Membrane Protein Structures by MicroED.

Microcrystal electron diffraction (MicroED) enables atomic resolution structures to be determined from vanishingly small crystals. Soluble proteins typically grow crystals that are tens to hundreds of microns in size for X-ray crystallography. But membrane protein crystals often grow crystals that are too small for X-ray diffraction and yet too large for MicroED. These crystals are often formed in thick, viscous media that challenge traditional cryoEM grid preparation. Here, we describe two approaches for preparing membrane protein crystals for MicroED data collection: application of a crystal slurry directly to EM grids, and focused ion beam milling in a Scanning Electron Microscope (FIB-SEM). We summarize the case of preparing an ion channel, NaK, and the workflow of focused ion-beam milling. By milling away the excess media and crystalline material, crystals of any size may be prepared for MicroED. Finally, an energy filter may be used to help minimize inelastic scattering leading to lower noise on recorded images.