Partial Phase Separation Research Articles

A Cu-Pd alloy catalyst with partial phase separation for the electrochemical CO2 reduction reaction

Cu catalysts can convert CO2 through an electrochemical reduction reaction into a variety of useful carbon-based products. However, this capability provides an obstacle to increasing the selectivity for a single product. Herein, we report a simple fabrication method for a Cu-Pd alloy catalyst for use in a membrane electrode assembly (MEA)-based CO2 electrolyzer for the electrochemical CO2 reduction reaction (ECRR) with high selectivity for CO production. When the composition of the Cu-Pd alloy catalyst was fabricated at 6:4, the selectivity for CO increased and the production of multi-carbon compounds and hydrogen is suppressed. Introducing a Cu-Pd alloy catalyst with 6:4 ratio as the cathode of the MEA-based CO2 electrolyzer showed a CO faradaic efficiency of 92.8% at 2.4 Vcell. We assumed that these results contributed from the crystal planes on the surface of the Cu-Pd alloy. The phases of the Cu-Pd alloy catalyst were partially separated through annealing to fabricate a catalyst with high selectivity for CO at low voltage and C2H4 at high voltage. The results of CO-stripping testing confirmed that when Cu partially separates from the lattice of the Cu-Pd alloy, the desorption of *CO is suppressed, suggesting that C–C coupling reaction is favored.

Design Rules for Binary Bisamide Gelators: toward Gels with Tailor-Made Structures and Properties.

This study intends to develop design rules for binary mixture of gelators that govern their assembly behavior and subsequently explore the impact of their supramolecular assembly patterns on the gels' rheological properties. To achieve these goals, nBA gelators with odd and even parities [n-methylene spacers between the amide groups (n = 5-10) and 17 carbons at each end] were blended at different ratios. Such bisamides with simple structures were selected to study because their different spacer lengths offer the possibility to have matching or non-matching hydrogen bonds. The results show that the assembly behavior of binary mixtures of bisamide gelators is the same in the solid and gel states. Binary mixtures of gelators, which only differ two methylene moieties in the spacer length, form compounds and co-assemble into fibers and sheets observed for (5BA)1(7BA)1 and (6BA)1(8BA)1 mixtures, respectively. Binary gelator mixtures of the same parity and a larger spacer length difference still lead to mixing for the odd parity couple (5BA)1(9BA)1), but to partial phase separation for the even parity mixture (6BA)1(10BA)1. Binary mixtures of gelators of different parities gave complete phase separation in the solid state, and self-sorted gels consisting of discrete fibers and sheets in the gels of (5BA)3(6BA)1 and (5BA)3(10BA)1. The even-even binary gels (20 wt %) consisting of co-assembled sheets show higher G' than odd-odd binary gels (20 wt %) consisting of co-assembled fibers. In general, the self-sorting of odd and even molecules into the separate primary structures results in a dramatic decrease of G' compared to the co-assembled gels (20 wt %), except for (5BA)1(9BA)1 gel (20 wt %). It might be due to larger woven spheres in (5BA)1(9BA)1 gel (20 wt %), which probably have a less entangled gel network.

Alloying bulk-immiscible metals at the nanoscale: An XPS/STM study of bimetallic Ag-Pt/HOPG nanoparticles

The intentional tailoring of surface structure in bimetallic nanoparticles is of high interest for academic research and industry, and many attempts have been made to improve the control over the distribution mode of the constituent elements which ranges from homogeneously mixed nanoalloys to core–shell nanostructures. However, some metal combinations exhibit a wide miscibility gap in the bulk, which nonetheless could be overcome under definite conditions at the nanoscale due to size effects. Here we present the detailed XPS/STM investigation of alloying capability of bulk-immiscible metals on the example of the Ag-Pt/HOPG bimetallic system prepared by thermal vacuum deposition. We found out that partial alloying of Ag and Pt occurs already at the preparation stage, and the following thermal annealing of the Ag-Pt/HOPG samples at 300–400 °C does not help to enhance the alloying degree owing to thermodynamically driven surface segregation of silver. Increasing the annealing temperature ruins the structure of Ag-Pt bimetallic nanoparticles due to silver sublimation, while even longer annealing time leads to partial phase separation. Our results demonstrate a limited alloying capability of Pt and Ag at the nanoscale which will be relevant for further research on the design and functioning of bimetallic catalysts containing bulk-immiscible metals.

Dolomite catalyst for fast pyrolysis of waste cooking oil into hydrocarbon fuel

Dolomite as the catalyst for pyrolysis of waste cooking oil (WCO) was investigated to produce hydrocarbon fuels. Optimization of pyrolysis parameters i.e. time, temperature and catalysts loading, achieved high selectivity of WCO to diesel hydrocarbon, compared to thermal pyrolysis that produced mainly carboxylic acids. Dolomite catalysed deoxygenation of fatty acid in WCO into hydrocarbon, consequently accelerating the pyrolysis time to 75 min. Bio-oil at 68.06% yield with 57.27% selectivity towards diesel and gasoline hydrocarbons was obtained at 450 °C while using 6% of dolomite. Dolomite exhibited partial phase separation into dolomite/CaCO3 mixtures within 15 min of pyrolysis, initiated by the generated CO2 during pyrolisis of WCO. The catalyst is stable for up to three reaction cycles suggesting the activity was achieved from the synergy between the dolomite/CaCO3 phases.

Role of Nanoscale Morphology on the Efficiency of Solvent-Based Desalination Method

Brine desalination is important for minimizing the environmental impact of contaminated wastewater, yet current desalination techniques have high energy requirements. Solvent-based desalination (SBD) method, which is the process of extracting fresh water using an organic solvent, has existed for decades, yet has not reached competitive efficiencies. In this work, 10 organic solvents were tested for SBD efficacy via synergetic studies using bench-scale extraction experiments and molecular dynamics (MD) simulations. The SBD effectiveness was correlated to the computationally observed ability of the solvent to form one of the three morphologies in water: ordered, disordered, or partial nanoscale. We correlated that solvents that form ordered and disordered morphologies were not able to clean up the water. Solvents that were able to cause low salinity in water showed computationally observed partial nanoscale phase separation, where nanometer-scale aggregated solvent phases were able to effectively reject salt ions while capturing comparatively large amounts of water molecules. The formation of a partial nanoscale phase is likely driven by the solvent structure with bulky hydrocarbons adjacent to hydrophilic end groups. Our results make a step toward the rational design of solvents that may allow for efficient SBD and thus a low-cost source of fresh water.

Magnetic properties and thermal stability of ultrathin TbFeCo films encapsulated by heavy metals Pt and W

Amorphous rare earth (RE)-transition metal (TM) ferrimagnetic alloy films have been intensively studied recently in spintronics and ultrafast information storage due to the large perpendicular magnetic anisotropy (PMA), ultrafast magnetization switching, and the presence of magnetization compensation and angular momentum compensation. In this work, we fabricate <i>X</i>/Tb<sub><i>x</i></sub>(Fe<sub>0.75</sub>Co<sub>0.25</sub>)<sub>1–<i>x</i></sub>/<i>X</i> (0.13 ≤ <i>x</i> ≤ 0.32, <i>X</i> = SiO<sub>2</sub>, Pt and W) trilayers by magnetron sputtering, and systematically investigate the magnetic properties and thermal stabilities of the ultrathin TbFeCo films encapsulated by heavy metals Pt and W at room temperature. The 5–50-nm-thick TbFeCo films sandwiched by SiO<sub>2</sub> exhibit PMA with magnetic compensation occurring in Tb concentration <i>x</i> between 0.21 with 0.24. For 3-nm- and 5- nm-thick TbFeCo ultrathin films encapsulated by Pt, however, there is no magnetic compensation observed throughout the composition range 0.13 ≤ <i>x</i> ≤ 0.32 with the film magnetization dominated by the FeCo moment. Nevertheless, the weakened PMA for the Pt/ultrathin TbFeCo/Pt trilayers is completely destroyed after annealing at 250 ℃. When the buffer layer and capping layer of Pt are replaced by W, the ultrathin TbFeCo films show magnetic compensation at 0.21 < <i>x</i> < 0.24, so do the thick TbFeCo films. The effective PMA field (<i>H</i><sub>K</sub>) exceeds 11.5 T for the W/ultrathin TbFeCo/W films near the compensation composition, and remarkably, the <i>H</i><sub>K</sub> decreases slowly on annealing, with PMA maintained even after annealing at 350–400℃. We further prepare [Pt/TbFeCo]<sub>5</sub>/Pt and [W/TbFeCo]<sub>5</sub>/W multilayers to clarify the origin of the huge difference between Pt/ultrathin TbFeCo/Pt and the W counterpart. It is found that there are partial recrystallization and phase separation for TbFeCo layer around the Pt/TbFeCo interface, leading to the disappearance of magnetic compensation and the deterioration of the PMA in the Pt/ultrathin TbFeCo/Pt films. With large PMA, W/ultrathin TbFeCo/W films show the presence of magnetic compensation, and excellent thermal robustness. The present study provides a promising heavy metal/RE-TM heterostructure for spintronic applications.

Pattern formation and flocking for particles near the jamming transition on resource gradient substrates.

We numerically examine a bidisperse system of active and passive particles coupled to a resource substrate. The active particles deplete the resource at a fixed rate and move toward regions with higher resources, while all of the particles interact sterically with each other. We show that at high densities, this system exhibits a rich variety of pattern-forming phases along with directed motion or flocking as a function of the relative rates of resource absorption and consumption as well as the active to passive particle ratio. These include partial phase separation into rivers of active particles flowing through passive clusters, strongly phase separated states where the active particles induce crystallization of the passive particles, mixed jammed states, and fluctuating mixed fluid phases. For higher resource recovery rates, we demonstrate that the active particles can undergo motility-induced phase separation, while at high densities, there can be a coherent flock containing only active particles or a solid mixture of active and passive particles. The directed flocking motion typically shows a transient in which the flow switches among different directions before settling into one direction, and there is a critical density below which flocking does not occur. We map out the different phases as function of system density, resource absorption and recovery rates, and the ratio of active to passive particles.

Phase State and Relative Humidity Regulate the Heterogeneous Oxidation Kinetics and Pathways of Organic-Inorganic Mixed Aerosols.

Inorganic species always coexist with organic materials in atmospheric particles and may influence the heterogeneous oxidation of organic aerosols. However, very limited studies have explored the role of the inorganics in the chemical evolution of organic species in mixed aerosols. This study examines the heterogeneous oxidation of glutaric acid-ammonium sulfate and 1,2,6-hexanetriol-ammonium sulfate aerosols by hydroxyl radicals (OH) under varied organic mass fractions (forg) and relative humidity in a flow tube reactor. Coupling the oxidation kinetics and product measurements with kinetic model simulations, we found that under both low relative humidity (RH, 30-35%) and high RH conditions (85%), the decreased forg from 0.7 to 0.2 accelerates the oxidation of the organic materials by a factor of up to 11. We suggest that the faster oxidation kinetics under low-RH conditions is due to full or partial phase separation, with the organics greatly enriched at the particle outer region, while enhanced "salting-out" of the organics and OH adsorption caused by higher inorganics could explain the observations under high-RH conditions. Analysis of the oxidation products reveals that the dilution of organics by the inorganic salts and corresponding water uptake under high-RH conditions will favor alkoxy radical fragmentation by a factor of 3-4 and inhibit its secondary chain propagation chemistry. Our results suggest that atmospheric organic aerosol oxidation lifetime and composition are strongly impacted by the coexistent inorganic salts.

Exploring multiphase liquid crystal polymeric droplets created by a partial phase-separation

HypothesisPolymerization of the monomers lowers the miscibility of the polymer. Therefore, a partial phase separation phenomenon can be induced depending on the polymerization conditions. Based on this, usage of anisotropic material has advantages to precisely control the internal structure as well as the external shape. ExperimentsJanus liquid crystal polymer (LCP) droplets and particles with unusual complex shapes were prepared via two steps, thermal- and photo-polymerization using the reactive mesogen(RM) mixture. The internal configuration of mesogens in the droplets and their assembly behaviors were controlled by varying surface condition. Janus LCP particles with complex shapes were formed by anisotropic deswelling and characterized via optical and electron microscopes. FindingsThe partial phase separation in the RM mixture induced the density gradient throughout the droplet, forming the Janus droplets with a certain nematic configurations in each compartment. LCP Janus droplets show not only easy-control of colloidal assembly with surface condition and also complex external structures that is hardly obtained in typical ways using isotropic materials. This report demonstrates for the first time a high availability of anisotropic materials for generation of multiphase microparticles controlled with internal and external structures.

Plasma-Assisted Molecular Beam Epitaxy of In-Rich InGaN: Growth Optimization for Near-IR Lasing

Near-infrared stimulated emission (SE) from InGaN layers grown by plasma-assisted molecular beam epitaxy has been studied, and the influence of the growth temperature (T gr) on the SE threshold has been revealed. The obtained experimental data strongly suggest a two-layer model for the grown InGaN structure with a thin defect-rich interface layer and a relatively pure InGaN bulk responsible for light emission. For the latter, the crystalline quality appears to be unaffected by the growth temperature, at least in terms of free electron concentration, which is supported by the similar spontaneous luminescence intensities measured throughout the entire T gr range of 430 °C–510 °C. However, the quality of the interface layer improves with increasing T gr, leading to a decrease in the SE threshold down to ∼10 kW cm−2 at T = 77 K for the samples grown at T gr = 470 °C–480 °C. For the higher growth temperatures (T gr ≥ 490 °C), the SE threshold increases rapidly with T gr, apparently related to the strong waveguide losses due to the increasing surface roughness of the InGaN layer, and SE vanishes completely at T gr = 510 °C, further suppressed by the partial phase separation of the InGaN alloy.

Conductive, self-healing and recyclable electrodes for dielectric elastomer generator with high energy density

Dielectric elastomer generator (DEG), consisting of highly deformable dielectric elastomer (DE) film sandwiched between two compliant electrodes, can convert mechanical energy into electrical energy. To achieve high energy harvesting performance and practical durability, electrode material with high stability of electrical conductivity (EC) and self-healing/recycling capability is required. In this study, we designed and prepared conductive rubber electrode with high EC, high stability of EC at high strain and high durability during cyclic stretching, self-healing and recycling ability for DEG by synthesizing a hydrogen bond crosslinked supramolecular network of silicone rubber (SiR-SN) followed by introducing a commercially available, highly conductive carbon black (CB) and carbon grease (CG) into SiR-SN matrix. The addition of CG composed of silicone oligomer (SO) and CB can induce the partial phase separation of polar SiR-SN and the formation of segregated conductive network, leading to the significantly enhanced EC and stability of EC at high strain. The presence of SO chains also increases the chain mobility, leading to the high durability, self-healing ability and recyclability of the electrode. Compared with CG electrode commonly used in laboratory, the energy loss at 3 kV and 400% strain of DEG using the 5 phr CB/60 phr CG/SiR-SN electrode is reduced by 83.5%, and the harvested energy density increases by 73.1%, which reaches 23 mJ/cm3, much higher than that reported in previous studies. Meanwhile, this electrode shows high self-healing efficiency of conductivity (92% at 60 °C for 4 h), and can be recycled for 5 times without negative effect on performance.

Properties of the konjac glucomannan and zein composite gel with or without freeze-thaw treatment

In this study, a novel composite gel was fabricated from Konjac glucomannan (KGM) combined with zein, while its properties and structure were characterized. The effect of the KGM/zein ratios and freeze-thaw treatment on the composite gels was investigated. The storage modulus (G′) of the KGM gel increased even when the zein content was below 20%, while partial phase separation occurred when the zein content exceeded 50%. The initial decomposition temperature of the gels was improved by adding zein or freeze-thaw treatment. The presence of zein strengthened the effect of freeze-thaw treatment on the improvement of G′ of the gels. These findings helped clarify the influence of hydrophobic proteins on hydrogel, determined the target characteristics ratio of the final product when preparing composite gels, and elucidated the effect of freeze-thaw treatment on the structure and properties of these gels.

Control of Particle Size in the Self-Assembly of Amphiphilic Statistical Copolymers.

A range of amphiphilic statistical copolymers is synthesized where the hydrophilic component is either methacrylic acid (MAA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic component comprises methyl, ethyl, butyl, hexyl, or 2-ethylhexyl methacrylate, which provide a broad range of partition coefficients (log P). Small-angle X-ray scattering studies confirm that these amphiphilic copolymers self-assemble to form well-defined spherical nanoparticles in an aqueous solution, with more hydrophobic copolymers forming larger nanoparticles. Varying the nature of the alkyl substituent also influenced self-assembly with more hydrophobic comonomers producing larger nanoparticles at a given copolymer composition. A model based on particle surface charge density (PSC model) is used to describe the relationship between copolymer composition and nanoparticle size. This model assumes that the hydrophilic monomer is preferentially located at the particle surface and provides a good fit to all of the experimental data. More specifically, a linear relationship is observed between the surface area fraction covered by the hydrophilic comonomer required to achieve stabilization and the log P value for the hydrophobic comonomer. Contrast variation small-angle neutron scattering is used to study the internal structure of these nanoparticles. This technique indicates partial phase separation within the nanoparticles, with about half of the available hydrophilic comonomer repeat units being located at the surface and hydrophobic comonomer-rich cores. This information enables a refined PSC model to be developed, which indicates the same relationship between the surface area fraction of the hydrophilic comonomer and the log P of the hydrophobic comonomer repeat units for the anionic (MAA) and cationic (DMAEMA) comonomer systems. This study demonstrates how nanoparticle size can be readily controlled and predicted using relatively ill-defined statistical copolymers, making such systems a viable attractive alternative to diblock copolymer nanoparticles for a range of industrial applications.

Crystallization properties of melt-quenched Ge-rich GeSbTe thin films for phase change memory applications

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs.

Effect of hydrogen-bond strength on photoresponsive properties of polymer-azobenzene complexes

Supramolecular complexation between photoresponsive azobenzene chromophores and a photopassive polymer host offers synthetic and design advantages compared with conventional covalent azo-containing polymers. In this context, it is important to understand the impact of the strength of the supramolecular interaction on the optical response. Herein, we study the effect of hydrogen-bonding strength between a photopassive polymer host [poly(4-vinylpyridine), or P4VP] and three azobenzene analogues capable of forming weaker (hydroxyl), stronger (carboxylic acid), or no H-bonding with P4VP. The hydroxyl-functionalized azo forms complete H-bonding complexation up to equimolar ratio with VP, whereas the COOH-functionalized azo reaches only up to 30% H-bond complexation due to competing acid dimerization that leads to partial phase separation and azo crystallization. We show that the stronger azo-polymer H-bonding nevertheless provides higher photoinduced orientation and better performance during optical surface patterning, in terms of grating depth and diffraction efficiency, when phase separation is either avoided altogether or is limited by using relatively low azo contents. These results demonstrate the importance of the H-bonding strength on the photoresponse of azopolymer complexes, as well as the need to consider the interplay between different intermolecular interactions that can affect complexation.

Development of phases in the sol-gel derived mixed-metal-oxide (Al2O3–TiO2–ZnO) functional sorbent material

Aluminium-Titanium–Zinc mixed-metal-oxide system was investigated in order to elucidate appropriate sorbent material for the High-Temperature Gas-Desulphurisation (HTGD) in the Integrated Gasification Combined Cycle (IGCC). Conceptually, Zn-based constituent phases support sorption functionality, Ti-based constituent phases support chemical stability and Al-based constituent phases support mechanical durability. Samples were prepared using sol-gel synthesis in a broad compositional range from gahnite to Zn-titanate spinel; i.e. gahnite was Ti-doped on the account of Al (0–100%). Complexing agent was used to control the hydrolysis rate. We monitored the thermal and structural evolution in order to observe and clarify different mechanisms of phase formation, as a function of the doping and temperature conditions. The significance of this work lies within insight in the stability ranges of the observed solid-solutions, whereas gahnite spinel and zinc titanate spinels can interchange cations only in limited amounts, depending on the conditions, as confirmed from the structure refinement. It was observed that these solid-solution phases exhibit quite different stability when thermally treated. More importantly, observed partial phase-separation at low-temperature thermal treatment (which occur on behalf of different hygroscopic properties of the (Al,Ti)–Zn gels) significantly precludes the mechanisms of phase development at high-temperatures. Thereof, intermediate Zn-based phase was found to be responsible for the facilitated early zincite crystallisation. Microstructural and textural changes were correlated according to structural changes. Characterisation results allowed understanding of compositional and treatment conditions necessary for the selection of sorbent best with best functionality.

Distribution of elements in Ge–Se bulk glasses and optical fibers detected by inductively coupled plasma atomic emission spectrometry

The elemental composition of Ge–Se glasses prepared by different methods and the distribution of Ge and Se along the bulk sample length are investigated by inductively coupled plasma atomic emission spectrometry. The estimated uncertainty of Ge and Se content measurement is 0.02–0.05 at.% (P = 0.95). To date, these results are the most accurate for determining the elemental composition of optical Ge-based chalcogenides. The minimum required mass of the analyzed glass samples does not exceed 1 mg. Partial phase separation in the Ge–Se system leads to a significant (±2 at.%) deviation of the chemical composition of Ge–Se glasses along the length of the bulk sample from the specified value. This is the first time that the elemental composition of single-index Ge–Se fibers along the fiber length has been studied. The rod drawing method allows the fabrication of optical fibers with composition deviation along the length of 0.03–0.05 at.%. In the case of drawing by the crucible method, the deviations of the fiber composition can reach 0.16 at.% compared with the initial glass sample.

Simulation study of the effects of phase separation on hydroxide solvation and transport in anion exchange membranes.

Anion exchange membranes (AEMs) can be cheaper alternatives than proton exchange membranes, but a key challenge for AEMs is to archive good ionic conductivity while maintaining mechanical strength. Diblock copolymers containing a mechanically strong hydrophobic block and an ion-conducting hydrophilic block have been shown to be viable solutions to this challenge. Using our recently developed reactive hydroxide model, we investigate the effects of block size on the hydroxide solvation and transport in a diblock copolymer (PPO-b-PVBTMA) in its highly hydrated state. Typically, both hydroxide and water diffusion constants decrease as the hydrophobic PPO block size increases. However, phase separation takes place above a certain mole ratio of hydrophobic PPO to hydrophilic PVBTMA blocks and we found it to effectively recover the diffusion constants. Extensive analyses reveal that morphological changes modulate the local environment for hydroxide and water transport and contribute to that recovery. The activation energy barriers for hydroxide and water diffusion show abrupt jumps at the same block ratios when such recovery effects begin to appear, suggesting transformation of the structure of water channels. Taking the advantages of partial phase separation can help optimize both ionic conductivity and mechanical strength of fuel cell membranes.

Unravelling local environments in mixed TiO2–SiO2 thin films by XPS and ab initio calculations

Mixed TixSi1−xO2 oxide can exhibit a partial phase separation of the TiO2 and SiO2 phases at the atomic level. The quantification of TiO2–SiO2 mixing in the amorphous material is complicated and was so far done mostly by infrared spectroscopy. We developed a new approach to the fitting of X-ray photoelectron spectroscopy data for the quantification of partial phase separation in amorphous TixSi1−xO2 thin films deposited by plasma enhanced chemical vapour deposition. Several fitting constraints reducing the total number of degrees of freedom in the fits and thus the fit uncertainty were obtained by using core electron binding energies predicted by density functional theory calculations on TixSi1−xO2 amorphous supercells. Consequently, a decomposition of the O1s peak into TiO2, SiO2 and mixed components was possible. The component areas ratios were compared with the ratios predicted by older theoretical models based on the atomic environment statistics and we also developed several new models corresponding to more realistic atomic structure and partial mixing. Based on the comparison we conclude that the studied films are mostly disordered, with only a moderate phase separation.

Effect of Al2O3 on phase separation and microstructure of R2O-B2O3-Al2O3-SiO2 glass system (R = Li, Na)

The investigation of selected properties in non-porous and porous R2O-B2O3-Al2O3-SiO2 (R = Li, Na) glasses indicates different effects of Al2O3 on phase separation and microstructure. Decrease of [BO4]− units in Na2O-B2O3-SiO2 glass system reveals a constant inhibition of phase separation with addition of Al2O3. In Li2O-B2O3-SiO2 glass system, the addition of Al2O3 leads to a non-linear behaviour. XRD pattern and MAS-NMR studies display a microstructure-dependence on partial crystallization and phase separation. An addition of up to 4 mol.-% Al2O3 changes the microstructure from isolated into bimodal and monomodal interconnected phases. Based on the analysed properties a simplified model is set up which explains the influence of Al2O3 on phase separation, crystallization and microstructure in Li2O-B2O3-Al2O3-SiO2 glasses.