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Effect of Ca2+ and Mg2+ ions on the sintering and spectroscopic properties of cr‐doped yttrium aluminum garnet ceramics

Przemysław Gołębiewski, Helena Węglarz, Magdalena Nakielska, Anna Wajler

Abstract

In this work, we investigated the effects of Ca2+ and Mg2+ ions and annealing temperature on the spectroscopic parameters of chromium‐doped yttrium aluminum garnet ceramics (Cr:YAG). Samples were obtained with either a separate or a simultaneous addition of calcium and magnesium oxides. To achieve this, aqueous suspensions were prepared using Y2O3, Al2O3, Cr2O3, MgO, and CaO high‐purity powders as raw materials. The obtained suspensions were freeze‐granulated, pressed into pellets, debinded, and subjected to reactive sintering in vacuum at 1715°C for 6 h. Each material was annealed in air with temperatures between 1300 and 1700°C. Samples were also compared to Cr:YAG ceramics with the addition of silica as a sintering aid. All the materials obtained were then exposed to 445 nm excitation, and emission spectra in the visible and infrared wavelengths were recorded. The results showed that the emission spectra of Cr:YAG ceramics varied according to the annealing conditions: as‐sintered samples exhibited strong emissions of around 680 nm and, after air annealing, of around 1400 nm. This phenomenon is attributed to the Cr3+→Cr4+ transition. Samples doped solely with MgO exhibited the highest emission intensity in the infrared region. Thus, Mg2+ ions provided the best conversion efficiency of chromium ions.

Keywords

Cr:YAG, Q‐switching, transparent ceramics, yttrium aluminum garnet

Formulation and evaluation of inhalable microparticles of Rizatriptan Benzoate processed by spray freeze-drying

Mahsa Keyhan shokouh, Homa Faghihi, Majid Darabi, Maryam Mirmoeini, Alireza Vatanara

Abstract

The aim of the current study was to prepare and evaluate inhalable microparticles of Rizatriptan benzoate in order to further benefit from its pulmonary delivery, the expected enhanced bioavailability and accelerated onset of action. The spray freeze drying (SFD) technique was used to produce microparticles consisting of a fixed amount of a sugar which was either mannitol or trehalose and an amino acid component including leucine, phenylalanine or serine. The powders were then characterized for particle size distribution, morphology, thermal properties and in vitro aerosolization performance. It was demonstrated that various formulations of inhalable Rizatriptan could be efficiently aerosolized and offered acceptable fine particle fraction (FPF) ranging up to 61.1%. In particular, a spray-freeze-dried powder composed of trehalose and phenylalanine showed the most superior inhalation performance (FPF = 61.1%), indicating better dispersion properties of those spherical porous microparticles with less adhesion and agglomeration. These results successfully demonstrated that Rizatriptan could be engineered into respirable microparticles to be proposed as a promising delivery system for fast and effective control of migraine attacks.

Keywords

Rizatriptan benzoate. Spray freeze drying, Inhalation, Carbohydrates, Amino acids

Engendering Unprecedented Activation of Oxygen Evolution via Rational Pinning of Ni Oxidation State in Prototypical Perovskite: Close Juxtaposition of Synthetic Approach and Theoretical Conception

Rebecca Pittkowski, Spyridon Divanis, Mariana Klementová, Roman Nebel, Shahin Nikman, Harry Hoster, Sanjeev Mukerjee, Jan Rossmeisl, Petr Krtil

Abstract

Rational optimization of the OER activity of catalysts based on LaNiO3 oxide is achieved by maximizing the presence of trivalent Ni in the surface structure. DFT investigations of the LaNiO3 catalyst and surface structures related to it predict an improvement in the OER activity for these materials to levels comparable with the top of the OER volcano if the La content is minimized while the oxidation state of Ni is maintained. These theoretically predicted structures of high intrinsic OER activity can be prepared by a templated spray-freeze freeze-drying synthesis followed by a simple postsynthesis exfoliation-like treatment in acidic media. These nanocrystalline LaNiO3-related materials confirm the theoretical predictions, showing a dramatic improvement in OER activity. The exfoliated surfaces remain stable in OER catalysis, as shown by an in-operando ICP-OES study. The unprecedented OER activation of the synthesized LaNiO3-based materials is related to a close juxtaposition of the theoretical conception of ideal structural motifs and the ability to engender such motifs using a unique synthetic procedure, both principally related to stabilization and pinning of the Ni oxidation state within the local coordination environment of the perovskite structure.

Keywords

electrocatalysis, oxygen evolution, rational catalyst design, DFT

Particle Size Reduction Techniques of Pharmaceutical Compounds for the Enhancement of Their Dissolution Rate and Bioavailability

Rahul Kumar, Amit K. Thakur, Pranava Chaudhari, Nilanjana Banerjee

Abstract

In pharmaceutical research and development, various new chemical entities (NCE) are found to be poorly water-soluble. Therefore, solubility enhancement, a key factor for higher bioavailability, is a major challenge in pharmaceutical industries. Particle size reduction is one such method that increases the surface area of the pharmaceutical compounds and subsequently leads to a higher dissolution rate and bioavailability. Conventional processes such as milling, high-pressure homogenization, and spray drying are well established and widely used for particle size reduction. However, a few disadvantages such as a broader particle size distribution (PSD) and thermal and chemical degradation of the product are major concerns for the product quality. Non-conventional processes such as liquid anti-solvent crystallization, supercritical anti-solvent process, rapid expansion of supercritical solutions, particles from gas saturated solutions, and pulsed laser ablation are emerging as potential alternatives to overcome the disadvantages of conventional processes. This review critically summarizes the milling, spray drying, high-pressure homogenization, liquid anti-solvent crystallization, spray freeze-drying, supercritical carbon dioxide (SCCO2)–based micronization processes, pulsed laser ablation and combinative techniques. The success of these processes in enhancing the dissolution rate and bioavailability of many active pharmaceutical ingredients (APIs) has been critically examined. The advantages and limitations of these processes are also discussed. Finally, opportunities for future research are also proposed.

Keywords

Anti-solvent, Milling, Particle size reduction, Powder, Spray drying, Supercritical carbon dioxide

Effects of drying method and excipient on the structure and physical stability of protein solids: Freeze drying vs. spray freeze drying

Tarun Tejasvi Mutukuri, Nathan E. Wilson, Lynne S. Taylor, Elizabeth M. Topp, Qi Tony Zhou

Abstract

This study aims to determine the impacts of drying method and excipient on changes in protein structure and physical stability of model protein solids. Protein solids containing one of two model proteins (lysozyme or myoglobin) were produced with or without excipients (sucrose or mannitol) using freeze drying or spray freeze drying (SFD). The protein powders were then characterized using solid-state Fourier transform infrared spectroscopy (ssFTIR), differential scanning calorimetry (DSC), circular dichroism spectrometry (CD), size exclusion chromatography (SEC), BET surface area measurements and solid-state hydrogen deuterium exchange with mass spectrometry (ssHDX-MS). ssFTIR and CD could identify little to no difference in structure of the proteins in the formulation. ssHDX-MS was able to identify the population heterogeneity, which was undetectable by conventional characterization techniques of ssFTIR and CD. ssHDX-MS metrics such as Dmax and peak area showed a good correlation with the protein physical instability (loss of the monomeric peak area by size exclusion chromatography) in 90-day stability studies conducted at 40 °C for lysozyme. Higher specific surface area was associated with greater loss in monomer content for myoglobin-mannitol formulations as compared to myoglobin-only formulations. Spray freeze drying seems a viable manufacturing technique for protein solids with appropriate optimization of formulations. The differences observed within the formulations and between the processes using ssHDX-MS, BET surface area measurements and SEC in this study provide an insight into the influence of drying methods and excipients on protein physical stability.

Keywords

Freeze drying, Spray freeze drying, Protein structure, Biopharmaceutical processing, Solid formulation, Solid-state hydrogen/deuterium exchange with mass spectrometric analysis (ssHDX-MS)

A Kinetic Model for Spray-Freezing of Pharmaceuticals

Abstract

Spray freeze-drying (SFD), which includes spray-freezing into droplets and dynamic vacuum drying, presents a promising alternative approach to manufacture dried pharmaceuticals more efficiently than conventional vial freeze-drying. Without reliable predictive models for the SFD conditions of interest, any respective process development still relies on empirical approaches. In this work, we propose an improved modeling framework to describe the fast freezing (<1 s) that sub-millimeter droplets undergo in the present SFD process. The modeled freezing rate accounts for both the kinetics of ice growth and droplet heat transfer mechanisms. Computational fluid dynamics (CFD) simulations and experiments on bulk spray-freezing are combined to refine and validate the proposed reduced-order model. While this study is limited to water-sucrose solutions, the present modeling approach can be extended to other pharmaceutical excipients. For the cooling rates of interest, model results indicate that droplets with initial sucrose concentration higher than 20% w/w will transit to a glassy state before completion of crystallization and, consequently, devitrification is expected during post spray-freezing manipulation of the bulk material. In practice, such compact model does not only allow quantification of process parameters that cannot be measured in real time but also enable the choice of optimal spraying conditions for production of free-flowing, high-quality frozen droplets that meet the target product profile.

Keywords

Crystallization, Freeze-drying, In silico modeling, Lyophilization, Mechanistic modeling, Microsphere(s), Powder technology(s), Spray freeze-drying, Sucrose

Transparent cobalt‐doped yttrium aluminum garnet (Co2+:YAG) ceramics—An innovatory fast saturable absorber

Agnieszka Szysiak, Kamila Leśniewska‐Matys, Helena Węglarz, Przemysław Gołębiewski, Dariusz Podniesiński, Anna Kozłowska

Abstract

Highly transparent Y3Al5O12 (YAG) ceramics doped with 0.025 and 0.05 at.% Co ions were prepared for the first time by the freeze granulation process and reaction sintering. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) were performed to analyze the microstructure and crystal structure of the samples. The absorption spectra of the Co2+:YAG ceramics were measured at room temperature, and significant absorption bands at 600 nm, as well as at 1535 nm, were observed. The nonlinear behavior of the received material was experimentally demonstrated. Due to the short relaxation time of investigated ceramics, we considered them as fast saturable absorbers. The influence of the postsintering annealing process was examined. The values of saturation intensities of YAG ceramics with different concentrations of cobalt were estimated by fitting experimental data to the theoretical model for fast saturable absorbers.

Keywords

Co:YAG ceramics, Fast saturable absorber, Freeze granulation, Transparent ceramics

Spray freeze granulation of submicrometre α-alumina using ultrasonication

Shaghayegh Ghanizadeh, Prabhu Ramanujam, Bala Vaidhyanathan, Jon Binner

Abstract

Granulation is a key factor towards improvement of the flowability of fine ceramic powders to make them suitable for industrial dry pressing. Controlled granulation of fine alumina particles with a primary particle size of ∼150 nm was carried out using spray-freeze drying, which led to the production of flowable granules with high crushability. The fracture surface of uniaxially die-pressed green bodies made from granules with density values of ≥50 % of theoretical showed a uniform microstructure. Sintering experiments were performed using conventional single- and two-stage radiant heating methods followed by density and grain size measurement and characterisation of the final dense compacts to study the efficiency of two-stage sintering in grain growth elimination. The results have been compared with those of alumina bodies prepared using similar suspension by the slip-casting route.

Photocatalytic Oxidation of HMF under Solar Irradiation: Coupling of Microemulsion and Lyophilization to Obtain Innovative TiO2-Based Materials

Alessandro Allegri, Valeriia Maslova, Magda Blosi, Anna Luisa Costa, Simona Ortelli, Francesco Basile, Stefania Albonetti

Abstract

The photocatalytic oxidation of biomass-derived building blocks such as 5-hydroxymethylfurfural (HMF) is a promising reaction for obtaining valuable chemicals and the efficient long-term storage of solar radiation. In this work, we developed innovative TiO2-based materials capable of base-free HMF photo-oxidation in water using simulated solar irradiation. The materials were prepared by combining microemulsion and spray-freeze drying (SFD), resulting in highly porous systems with a large surface area. The effect of titania/silica composition and the presence of gold-copper alloy nanoparticles on the properties of materials as well as photocatalytic performance were evaluated. Among the lab-synthesized photocatalysts, Ti15Si85 SFD and Au3Cu1/Ti15Si85 SFD achieved the higher conversions, while the best selectivity was observed for Au3Cu1/Ti15Si85 SFD. The tests with radical scavengers for both TiO2-m and Au3Cu1/Ti15Si85 SFD suggested that primary species responsible for the selective photo-oxidation of HMF are photo-generated electrons and/or superoxide radicals.

Keywords

5-hydroxymethyl furfural, spray-freeze drying, photocatalysis, TiO2, microemulsion