Initial Si Research Articles

2297-PUB: The Shape of Glucose Response Curve during Oral Glucose Tolerance Tests (OGTT) and Long-Term Near-Normoglycemia Remission in African Americans Presenting with Hyperglycemic Crises

Approximately 70% of obese African American (AA) patients with new-onset diabetic ketoacidosis (DKA) and severe hyperglycemia (SH) achieve near-normoglycemia remission (defined as HbA1c <7%, fasting blood glucose [BG]< 130 mg/dl, and off insulin for 1 month) with intensive insulin treatment. The shape of glucose response curve during OGTT has been shown predictive of future glycemic failure and beta(β)-cell function in adolescents with diabetes and adults. Biphasic (Bφ) curves showing better glycemic control and β-cell function compared to monophasic (Mφ) or incessant rise (IR) curves. We hypothesize that in AA patients with new-onset DKA and SH, Bφ shape at remission is associated with lower hyperglycemia relapse compared to Mφ or IR curves. Seventy AA patients underwent a 75g two-hour OGTT after near-normoglycemia remission and at end of study (median follow-up, 392 days). Insulin sensitivity (Si, oral minimal model) and β-cell function (AUCi: incremental area under the curve of insulin), and disposition index (Di= Si x AUCi) were compared among the different OGTT response curves. Hyperglycemia relapse-free survival (fasting BG > 130 mg/dl, 2 random BG > 180 mg/dl or HbA1c > 7%) was calculated with Kaplan-Meier curve. At remission, initial OGTT showed 56% of patients with Mφ, 16% with Bφ, and 29% with IR curve shape. Baseline characteristics did not differ. Even though, more patients in the Bφ group (88%) sustained remission than the Mφ (57%) and IR (53%), hyperglycemia relapse-free survival did not differ by curve shape (log rank, p=0.26). On initial OGTT, Si (p=0.09), AUCi (p=0.12) and Di (p=0.06) did not differ between curve shapes. At last OGTT, Si (p=0.43), AUCi (0.47) and Di (p=0.22) did not differ. In obese AA patients with new-onset DKA and SH, the shape of the glucose response curve during OGTT does not predict long-term glycemic control or β-cell function. Disclosure L. Cotten: None. D. Stefanovski: None. O. Oladejo: None. G.E. Umpierrez: None. P. Vellanki: Consultant; Self; Boehringer Ingelheim Pharmaceuticals, Inc. Funding National Institutes of Health (K08DK0830361, K23DK113241-01A1, UL1TR002378, 1P30DK111024-01)

Diversity of silicon release rates among tropical tree species during leaf-litter decomposition

Leaf-litter is a significant source of biogenic Si, and differences among tree species in Si release rates during litter decomposition are important for quantifying Si cycles in forest ecosystems. We conducted two experiments to improve mechanistic understanding of Si release rates from dead leaves, using lowland tropical trees of Sarawak, Borneo. In the first experiment, we assessed Si leaching from leaf litter when they were shaken in water for four hours. In the second experiment, leaf litter samples were allowed to decompose in mesh bags in growth chambers for two months, in order to determine rates of decomposition and Si release, and to explore a relationship between decomposition rate and initial litter chemistry. Among the 12 species with large differences in initial leaf-litter Si concentration (0.72–80.0 mg Si g−1), Si leaching to water varied widely (0.04–0.16 mg Si g−1) and positively correlated with the initial Si concentration (R2 = 0.87; P < 0.001). Si release per unit leaf dry weight in the decomposition experiment was also positively correlated with initial litter Si concentration among six species (R2 = 0.998; P < 0.001). In contrast, proportion of initial Si content released did not exhibit a significant relationship with their decomposition rates, which were correlated with labile carbon content in leaf litter (e.g. hemicellulose). Our results suggest that Si release rates from decomposing leaf litter cannot be simply predicted from decomposition rates. The species differences in locations and stability of opal phytoliths and their resulting effects on Si dissolution rates should be considered.

Покрытие наноструктурированной профилированной поверхности Si слоем SiC

The method has been developed for coating of a profiled Si surface with a SiC lay-er, which completely preserves its original morphology of the Si surface. The SiC synthesis conditions are determined under which the initial Si surface profile is transformed into a profile coated with a SiC layer without geometric distortions. It has been experimentally proved that the critical synthesis temperature at which this coating is formed is a temperature equal to 1050ºC.

Design and application of gas cluster accelerator for surface smoothing and nanostructures formation

A custom-built gas cluster ion source with energy up to 50 keV is constructed, and Ar, CO&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;, and O&lt;sub&gt;2&lt;/sub&gt; are used as the working gases. The clusters are formed by a metal supersonic conical nozzle with critical diameter in a range of 65–135 μm and a cone angle of 14°. The nozzle is powered in the pulsed mode, which improves the pumping conditions, and also makes it possible to increase the gas pressure in the stagnation zone to 15 atm and thereby obtain larger clusters. Based on the principle of ultrasonic expansion, gas cluster ions with an average size of 3000 atoms are obtained. The cluster beam current of 50 μA is obtained. The Ar cluster beam, which is less reactive, is used for treating surface, namely, surface smoothing and formation of self-assembled nanostructures. The Ar cluster bombardment perpendicular to the surface of the substrate is used to demonstrate the smoothing of the surface of Si wafers, Ti coating, and Au film. For the initial Si wafer, its root-mean-square (RMS) roughness of 1.92 nm decreases down to 0.5 nm after cluster beam treatment. The cleaning effect of the cluster beam is also observed very well. The one-dimensional (1D) isotropic power spectral density of the Si surface topography before and after smoothing are also discussed. The off-normal irradiation Ar cluster beam is also used to form self-assembled surface nanoripple arrays on the surface of flat ZnO single crystal substrates. The ripple formation is observed when the incident angle of the cluster beam is in a range of 30°–60°. The process of nanoripple fabrication is significantly governed by the cluster beam incident angle, energy and dose. The nano-ripples formed on the flat substrates remain eolian sand ripples and their formation starts at the incident angle of 30°. The most developed nanoripples are observed at the incident angle within a range of 45°–60°. The surface morphology and characteristic distribution of the nano-structures on the flat ZnO substrate are also analyzed by the two-dimensional (2D) power spectral density function. Next, Ar cluster beam is used for irradiating the ZnO nanorod arrays grown on the Si substrate. Due to various angles between the nanorod’s axis and the substrate normal, the conditions of the ripple formation on the nanorod facets are also realized. The dependence of wavelength on the accelerating voltage of the cluster ions and the dose are studied. Similar dependence of wavelength on accelerating voltage and dose are found for nanorods. Comparing with the flat ZnO surface, nanoripples on the ZnO nanorod faces at high irradiation doses demonstrate an ordering effect, and morphology of the ripples resembles that of more parallel steps rather than eolian ripples.

Silicon Mobilization in Soils: the Broader Impact of Land Use

Dissolved Si (DSi) provision from land systems triggers diatom growth and CO2 sequestration. Soils and ecosystems act as a Si “filter”, transforming DSi originated from mineral weathering into biogenic Si (BSi) after DSi uptake by plants, or into other pedogenic forms of Si (non-BSi). Land use changes the quantity of BSi and non-BSi pools along the soil profile. However, methods used to isolate Si pools include chemical extractions at high temperatures and alkaline environments and therefore are unable to provide information concerning the dissolution potential of BSi and non-BSi pools under normal conditions of temperature and pH. Here, we conducted a batch experiment where forest, pasture and cropland soil samples were mixed with water at 25 °C and pH 7. The soil samples were collected from a temperate land use gradient located in the Belgian Loess Belt. We measured dissolved Si and aluminium (Al) during 80 days. BSi and non-BSi pool contents along the soil profile were known, as they had been established previously through chemical extraction. Results show that BSi and non-BSi enriched samples present distinct Si and Al dissolution curves. While non-BSi pools contribute significantly with immediate availability of Si, BSi pools present an initial slow dissolution. Therefore, croplands that were depleted of phytoliths and had poorly organic horizons display higher concentrations of initial dissolved Si, while pastures and forests, where pedogenic pools dominate only at depths below 40 cm, have more limited initial Si release.

Formation of extracellular β-chitin nanofibers during batch cultivation of marine diatom Cyclotella sp. at silicon limitation

Diatoms are unicellular algae that make nanostructured biosilica shells called frustules possessing ordered pore arrays. Dissolved silicon (Si) in the form of Si (OH)4 is the required substrate for cell wall biosynthesis and cell division. The extracellular formation of β-chitin nanofibers by the centric diatom Cyclotella sp. was followed during batch cultivation of the cell suspension within a bubble-column photobioreactor at a low initial Si concentration (0.25 mM) leading to 1–2 cell divisions, and high Si concentration (1.7 mM) leading to 4–5 cell divisions. Fibers were excreted from 20 specialized pores (fultoportulae) lining the rim of each frustule valve face. In Si-limited batch cultivation, 80% of the fibers formed during the last cell division after dissolved Si was depleted from the medium. Within 24 h after the final cell division, fibers were nominally 56 nm diameter and 60 μm length, with 85% of the fibers between 20 and 80 μm, and one fiber per fultoportula was formed. After the final cell number density was maintained for 72 h, a second fiber per fultoportula was formed, presumably after breakage or scission of the first fiber from the cell. X-ray diffraction (XRD) analysis confirmed that isolated fibers were composed of pure β-chitin. The unprecedented length and purity of the β-chitin nanofibers suggest future advanced material applications.

Oxidation-induced stress in Si nanopillars

In this work, we investigate the microstructure and oxidation of Si nanopillars and report that the oxidation at the sidewall of Si pillars is initially retarded (the so-called self-limiting) and eventually stops altogether at a certain size (stopping size), and further oxidation causes cracks at the bottom of the pillars, that depends on the initial Si nanopillar diameter and the experimental conditions. The diffusion of oxidant in the oxide and the compressive stress due to volume expansion from Si to SiO2 caused by the old oxide are insufficient to explain the above phenomenon. Herein, the chemical reaction (breaking of Si–Si bonds) that causes the remaining Si–Si bonds to shrink is introduced; this new model well explains the oxidation of Si nanopillars with the evidence of the change in crystal planes distances observed from transmission electron microscope. The present work contributes to the intrinsic understanding and precise controlling of oxidation in Si nanopillars for future device fabrication.

Complementary etching behavior of alkali, metal‐catalyzed chemical, and post‐etching of multicrystalline silicon wafers

AbstractBoth alkali and metal‐catalyzed chemical etching (MCCE) of multicrystalline silicon (mc‐Si) wafer show anisotropic etching behavior, resulting in different morphologies among the different grains. However, by combining alkali etching, MCCE, and a post‐etching process, homogeneous microstructures can be obtained on the surface of mc‐Si wafer. After the first alkali etching, there are three typical morphologies of upward pyramids, terraces, and tilt planes, and relative to the initial Si(100), Si(110), and Si(111) dominated grains, these show low, moderate, and high reflection, respectively. After MCCE and the post‐etching process, the microstructures on the different grains have converged to a similar morphology and reflection. Mc‐Si solar cells fabricated by complementary alkali etching, MCCE, and post‐etching have a good appearance and high efficiency of ~19.4%. Moreover, the cells with submicrometer texture have the advantages of reverse current‐voltage characteristics and weak light response over traditional cells with micrometer texture.

Quantification and isotherm modelling of competitive phosphate and silicate adsorption onto micro-sized granular ferric hydroxide.

Adsorption onto ferric hydroxide is a known method to reach very low residual phosphate concentrations. Silicate is omnipresent in surface and industrial waters and reduces the adsorption capacity of ferric hydroxides. The present article focusses on the influences of silicate concentration and contact time on the adsorption of phosphate to a micro-sized iron hydroxide adsorbent (μGFH) and fits adsorption data to multi-component adsorption isotherms. In Berlin drinking water (DOC of approx. 4 mg L−1) at pH 7.0, loadings of 24 mg g−1 P (with 3 mg L−1 initial PO43−–P) and 17 mg L−1 Si (with 9 mg L−1 initial Si) were reached. In deionized water, phosphate shows a high percentage of reversible bonds to μGFH while silicate adsorption is not reversible probably due to polymerization. Depending on the initial silicate concentration, phosphate loadings are reduced by 27, 33 and 47% (for equilibrium concentrations of 1.5 mg L−1) for 9, 14 and 22 mg L−1 Si respectively. Out of eight tested multi-component adsorption models, the Extended Freundlich Model Isotherm (EFMI) describes the simultaneous adsorption of phosphate and silicate best. Thus, providing the means to predict and control phosphate removal. Longer contact times of the adsorbent with silicate prior to addition of phosphate reduce phosphate adsorption significantly. Compared to 7 days of contact with silicate (c0 = 10 mg L−1) prior to phosphate (c0 = 3 mg L−1) addition, 28 and 56 days reduce the μGFH capacity for phosphate by 21 and 43%, respectively.

Mechanical alloying of iron-coated NbC and Si in stirred media mill

In the current research, the effect of mechanical alloying (MA) of iron-coated NbC and Si on the material?s fineness and crystal structure was investigated. The MA experiments were carried out in a batch-type laboratory scale stirred media mill for various residence times up to 240 min in isopropanol. During MA, milling energy was measured, and stress energy (SE) was calculated. Morphology and material structural changes, during the mechanical alloying process, were determined by means of scanning electron microscopy (SEM) and powder X-ray diffraction (XRD), respectively. The particle size distribution of the product was measured by a Horiba 950 LA laser particle size analyser. Evolution of phases during highenergy milling of NbC, Al-Fe-carbide, Fe, and Si was studied as a function of specific milling energy. Transformations in the crystal structure were revealed, namely the generation of cementite and Nb-Si-carbide, which was proved by XRD results and thermodynamic calculations. As result of the experiments, optimum MA conditions were determined. The application of the mechanical alloying method gives the opportunity to produce nanocrystalline phase from the initial ironcoated NbC and Si powder

Effects of silicon content on the separation and purification of primary silicon from hypereutectic aluminum–silicon alloy by alternating electromagnetic directional solidification

Hypereutectic aluminum (Al)–silicon (Si) alloys with different Si contents were used to evaluate the effects of Si content on separation and purification by alternating electromagnetic directional solidification (AEM–DS) at 3 kHz. A relatively high pulling speed of 40 µm/s was used for improved energy efficiency. After cooling, samples underwent AEM–DS, and efficient separation was obtained. The Si content in Si-rich areas exceeded 85 wt.% (considerably higher than the content in others) and exhibited not a slight relevance with the original Si contents in the hypereutectic Al–Si alloy. With regard to purification, impurities— particularly metallic impurities (Fe, Ti, and Ca)—can be removed to a low level. Electron probe microanalysis (EPMA) indicated that B content was lower in the Si-rich area than in the Al–Si alloy, suggesting that the segregation of B in solid primary Si was higher than that in Al–Si melt during AEM–DS. Moreover, the contents of metallic impurities (Fe, Ti, and Ca) and B decreased when the initial Si content in the Al–Si melt decreased. This finding was attributed to a lower silicon content, which indicated a lower melt temperature, thus allowing segregation at a lower temperature.

Processing of silicon-derived silica-bonded silicon carbide membrane supports

Silicon-derived silica-bonded SiC membrane supports were fabricated by oxidizing the SiC-Si compacts at 1250–1400 °C in air. The effects of initial Si content and sintering temperature on the porosity, pore size, permeability, and mechanical strength of the SiC membrane supports were investigated. The addition of Si into SiC powder compact increased the silica content and flexural strength, but decreased porosity, pore size, and permeability. The strength of silica-bonded SiC membrane supports showed excellent chemical durability (5% and 8% strength degradation after exposure to acidic and alkaline solutions for 63 days, respectively). The excellent chemical durability of silica-bonded SiC membrane supports was attributed to the absence of alkali and alkaline earth elements in its bonding phase. Typical porosity, pore size, permeability, and flexural strength of Si-derived silica-bonded SiC membrane supports (sintered with 30 wt% Si at 1350 °C) are 40%, 1.3 µm, 4.7 × 10–14 m2, and 62 MPa, respectively.

Sugarcane yield response to calcium silicate on Florida mineral soils

Silicon (Si) is a beneficial nutrient for sugarcane (Saccharum spp.) and yield responses to Si amendment have been determined on soils with low soluble Si. Because a soil test Si calibration has not been published for sugarcane grown on Florida mineral soils, the objectives were to determine sugarcane yield response to silicon soil amendment on two mineral soils (Entisol and Spodosol) and to relate sucrose yield to soil-extractable Si. Calcium silicate application rates were 0, 3.4, and 6.7 Mg ha−1 (Site 1) and 0, 2.2, 4.5, and 6.7 Mg ha−1 (Site 2) in small-plot (120 m2 plot−1) experiments, with Si application resulting in significant increases in biomass and sucrose ha−1. Calcium silicate requirements of 6.7 and 4.3 Mg ha−1 were determined with initial acetic acid-extractable Si of 21 and 46 g m−3, respectively. Nonlinear models indicated that Si amendments will be required with acetic acid-extractable Si <105 g m−3.

Determination of Critical Soil Silicon Levels for Rice Production in Louisiana Using Different Extraction Procedures

ABSTRACTWhile silicon (Si) fertilization is widely practiced in rice production, establishing critical soil Si levels has remained understudied. Field trials were established at 12 sites across Louisiana from 2013 to 2015 to determine critical soil Si for rice cultivation. Five silica slag (14% Si) rates at 0, 1, 2, 4, 6, and 8 Mg ha−1 and two lime rates (2 and 4 Mg ha−1) were arranged in randomized complete block design with four replications. Post harvest soil samples were analyzed for Si using seven extraction procedures. The critical soil Si levels established by the linear plateau model using 0.5 M acetic acid-1 hr (OAc-1) extraction procedure were 36, 41 and 50 mg kg−1 for plant Si uptake, grain yield, and relative yield as response variables, respectively. Generally, soils having high initial Si and pH had minimal responses to Si fertilization, whereas Si content of soils with low initial Si was significantly increased.

Solar Cells Based on Laser-Modified Silicon

The fabrication of solar cells based on laser-modified silicon (LMS) has been experimentally investigated. Laser ablation of single-crystal Si in air results in the formation of a quasi-periodic array of microcones. After removing the oxide layer, this array is coated by a transparent conducting tin oxide layer. A comparison of the spectral dependence of the mirror reflection of laser-modified Si with that of the initial flat Si surface shows a 10 to 15% drop in reflectivity. The light-to-electricity conversion efficiency is shown to exceed that of the initial flat Si surface by more than 20%.

SILICON BEHAVIOR IN SOILS CONTAINED DIFFERENT SILICON AND PHOSPHORUS CONCENTRATIONS USING ADSORPTION MODELS [

Silicon (Si) is an element, not essential, but is beneficial for some plants. The Freundlich model was used to describe Si adsorption on soil samples incubated with different Si and phosphorus (P) concentrations. Soil incubated samples were: T1 soil had no Si or P (control); T2, T3 and T4 soils contained 50, 100, and 200 mg Si L-1, respectively. T5 and T6 soils contained 50 mg Si L-1 in combined with either 7 or 10 mg P L-1 along with T7 and T8 soil contained 100 mg Si L-1 in combined with either 7 or 10 mg P L-1. In final, T9 and T10 soil contained 200 mg Si L-1 in combined with either 7 or 10 mg P L-1. A series of adsorption experiments were performed using sodium metasilicate pentahydrate (Na2O3Si.5H2O) solution prepared to have concentrations representing 0, 14, 28, 42 and 56 mg Si L-1. The supernatant of Si concentration was determined. The amount of element adsorbed was calculated as the difference between applied element concentrations and that remaining in solution after equilibration. Adsorption isotherms were determined at room temperature (25 oC±1). Results revealed that a positive trend was generally found; increases in amount of adsorption onto soil with increasing Si concentration and equilibrium concentration in concerned solution either applied separately or applied + initial available Si concentration in soil. The Freundlich equation provides a good fit to the sorption data for all incubated soil samples and R2 values were ranged from 0.82 to 0.97. Present study indicated that adsorption capacity value (Kf) decreased from T1 to T3 soil samples then increased at T4 sample, and intensity adsorption values (1/n) gave almost an opposite trend to that of capacity adsorption (Kf) values. Moreover, adsorption of Si onto soil incubated with different Si concentrations in combined with P2 decreased as compared to P1. Opposite trend was obtained with equilibrium Si concentration in concerned solution. Also, present study showed that the higher values of Kf obtained in P1 soils (T5, T7 and T9), compared to Kf values of P2 soils (T6, T8 and T10), and intensity adsorption values (1/n) gave almost an opposite trend to that of capacity adsorption (Kf) in both P1 and P2 soils. Finally, large Si sorption capacity and low Si affinity for the surface sites were observed in soil incubated with high Si concentration compared to soil incubated with low ones.

Numerical Investigation of Desulfurization Kinetics in Gas-Stirred Ladles by a Quick Modeling Analysis Approach

A quick modeling analysis approach for predicting the slag-steel reaction and desulfurization kinetics in argon gas-stirred ladles has been developed in this study. The model consists of two uncoupled components: (i) a computational fluid dynamics (CFD) model for predicting the fluid flow and the characteristics of slag-steel interface, and (ii) a multicomponent reaction kinetics model for calculating the desulfurization evolution. The steel-slag interfacial area and mass transfer coefficients predicted by the CFD simulation are used as the processing data for the reaction model. Since the desulfurization predictions are uncoupled from the CFD simulation, the computational time of this uncoupled predictive approach is decreased by at least 100 times for each case study when compared with the CFD-reaction kinetics fully coupled model. The uncoupled modeling approach was validated by comparing the evolution of steel and slag compositions with the experimentally measured data during ladle metallurgical furnace (LMF) processing at Nucor Steel Tuscaloosa, Inc. Then, the validated approach was applied to investigate the effects of the initial steel and slag compositions, as well as different types of additions during the refining process on the desulfurization efficiency. The results revealed that the sulfur distribution ratio and the desulfurization reaction can be promoted by making Al and CaO additions during the refining process. It was also shown that by increasing the initial Al content in liquid steel, both Al oxidation and desulfurization rates rapidly increase. In addition, it was found that the variation of the initial Si content in steel has no significant influence on the desulfurization rate. Lastly, if the initial CaO content in slag is increased or the initial Al2O3 content is decreased in the fluid-slag compositional range, the desulfurization rate can be improved significantly during the LMF process.

Effect of Si Content on Oxide Formation on Surface of Molten Fe-Cr-C Alloy Bath During Oxygen Top Blowing

Using a direct observation experimental method, the oxide formation behavior on the surface of Fe-Cr-5 mass pct C-Si alloy baths during decarburization by a top-blown Ar-O2 mixture was studied. The effects of the initial Si and Cr content of the alloy, temperature, and oxygen feed ratio on oxide formation were investigated. The results showed that, for alloys without Si, oxide particles, unstable oxide films, and stable oxide films formed sequentially. The presence of Si in the alloy changed the formation behavior of stable oxide film, and increased the crucial C content when stable oxide film started to form. Increasing the temperature, decreasing the initial Cr content, and increasing the ratio of the diluting gas decreased the critical C content at which a stable oxide film started to form. In addition, the P CO and $$ a_{{{\text{Cr}}_{2} {\text{O}}_{3} }} $$ values at which oxides started to form were estimated using Hilty’s equation and the equilibrium relation to understand the formation conditions and the role of each parameter in oxide formation.

Si Purification by Removal of Entrapped Al during Electromagnetic Solidification Refining of Si-Al Alloy

To investigate the effect of the removal of entrapped Al on Si purity during Al-Si electromagnetic solidification refining, the formation mechanism and removal principle of entrapped Al in primary Si were studied. The results showed that the agglomeration and irregular shape of primary Si crystals during electromagnetic solidification were the main reasons for the formation of entrapped Al; a higher initial Si content in an Al-Si alloy may result in higher amounts of entrapped Al. The entrapped Al can be effectively removed by first grinding the primary Si to powder particles of ~20 μm and then leaching the particles with acid, which can simultaneously remove other impurities concentrated in the entrapped Al such as Fe, Ca, Ti, and B. Hence, it is proposed that the combination of electromagnetic solidification, acid leaching, and vacuum directional solidification could be used to obtain solar-grade silicon.

Cage-based small-pore catalysts for NH3-SCR prepared by combining bulky organic structure directing agents with modified zeolites as reagents

It has been possible to efficiently synthesize high-silica ERI and AFX zeolites with nano-sized primary crystallites (30–200nm). This was achieved by using a dicationic and rigid organic structure directing agent (OSDA) that fits within the large cavities of these zeolites, and the use of FAU zeolites as initial Si- and Al-sources. Cu- and Fe-based ERI and AFX materials were prepared following both post-synthetic cation exchange and direct synthesis methodologies, showing good activity for the selective catalytic reduction (SCR) of nitrogen oxide using ammonia. Accelerated hydrothermal ageing of the zeolites at high temperature (i.e. 750°C) shows the necessity of removing the alkali cations remaining in the zeolites to obtain stable materials. Furthermore, the catalytic performance of the prepared Cu- and Fe-containing AFX catalysts, both before and after ageing treatment, approaches the catalytic activity of Cu- and Fe-CHA.