Eine Grlaselektrode zur Indizierung der direkten potentiometrischen Kaliumtitration mit Hexafluorosilicat

Zusammenfassung Aus einem Natriumaluminiumsilicat-Glas mit der Synthese-Zusammensetzung (Mol-%) 27% Na₂O, 8% Al₂O₃ und 65% SiO₂ (NAS 27-8) wurden Glaselektroden hergestellt, deren Eignung zur Indizierung der Kaliumtitration mit Zn[SiF₆] in methanoliseher Lösung untersucht wurde. In reinen, schwach sauren Kaliumsalzlösungen erhält man gut auswertbare Titrationskurven. Die Glaselektrode versagt in stark saurer Lösung. Außer den Ionen, die mit Hexafluorosilicat schwerlösliche Salze bilden, stören auch Ca²⁺, Mg²⁺ und Al³⁺, die mit den im Gleichgewicht vorliegenden Fluoridionen reagieren.

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Summary Glass electrodes have been prepared from a sodium-alumina-silica glass of the synthesis composition (mole %) of 27% Na₂O, 8% Al₂O₃, 65% SiO₂ (NAS 27-8) and their suitability for the indication of the potassium titration by means of Zn[SiF₆] in methanolic solution has been studied. With pure potassium salt solutions of low acidity it is possible to obtain well definable titration curves. With strongly acid solutions the glass electrode fails. Apart from ions forming sparingly soluble salts with hexafluorosilicate also Ca²⁺, Mg²⁺, and Al³⁺ are interfering by reaction with the fluoride ions present in equilibrium.

     

Does the valence state of an ion affect its diffusivity? Part I: Oxygen activity dependence of the diffusion of iron in alumina-doped MgO

To investigate whether a change in the valence state of tracer ions affects their diffusivity or not, the iron tracer diffusion in Al₂O₃-doped MgO, in which 0.5% of the cations were Al³⁺ ions, has been studied experimentally. Samples were prepared from high purity aluminum and magnesium nitrates using a chemical solution method and from powders of high purity Al₂O₃ and MgO. Because the concentration of the Al³⁺ dopant ions present in the samples was much larger than that of all other impurities, the concentration of the majority point defects, cation vacancies, was determined by the Al³⁺ concentration. Therefore, when changing the oxygen activity, the diffusivity of iron tracer ions can only be altered by changes in their valence state. Measurements of iron tracer diffusion coefficients were performed as a function of the oxygen activity at 1100 and 1200 °C. The experimental results indicate that the mean diffusivity of iron ions in Al₂O₃-doped MgO increases with increasing oxygen activity at both temperatures, suggesting that Fe³⁺ ions diffuse in Al₂O₃-doped MgO faster than Fe²⁺ ions.     

Laser spectroscopy of chromium(III) in magnesium aluminate spinels and transparent glass-ceramics

Laser excitation at different wavelengths was carried out on Cr³⁺-doped transparent glass-ceramics of composition (mole%) Ac(58.7SiO₂, 16.7 Al₂O₃, 17.8 MgO, 6.7TiO₂, 0.03 Cr₂O₃) and Bc(49.1 SiO₂, 19.7 Al₂O₃, 21.9 MgO, 6.0 TiO₂, 3.2 ZrO₂, 0.03 Cr₂O₃), and in synthetic crystals of composition MgAl₂O₄ (Cr³⁺), Mg₂TiO₄ (Cr³⁺) and Mg₁₂ Ti₀₂ Al₁₆ o₄ (Cr³⁺). Analysis of the emission spectra, excitation spectra and decay curves at 4.4. K and room temperature reveals that Cr³⁺ is essentially situated on distorted single sites and in pairs exchanging Al³⁺ ions in the crystalline phase of glass-ceramics.     

Die langdauernde Luminiszenz von Kieselsäure und Aluminiumoxidhydrat als Gel und als Sol

Zusammenfassung Die langdauernde Lumineszenz von Kieselsäure und Aluminiumoxidhydrat im kolloiden Zustand als Gel und als Sol besitzt zwar ähnliche, aber nicht identische Emissionsspektren im Wellenlängenbereich zwischen 350 und 550 nm. Ihre Anregungsspektren liegen im ultravioletten Bereicht mit den stärksten Maxima bei 220 (Al₂O₃) und 290 nm (SiO₂). Das Lumineszenzspektrum des Al₂O₃ ist abhängig von der Anregungswellenlänge, das des SiO₂ jedoch nicht. Beim Erhitzen auf 900° verlieren beide Gele ihre Fähigkeit zu lumineszieren. Sie wird bei Normaltemperatur sehr langsam zurückgebildet, im Falle des SiO₂ aber nur in Gegenwart von H₂O.Paralleluntersuchungen der Lumineszenz, der Lichtstreuung, der Elektronenbeugung und der Viskosität der Sole in Abhängigkeit von p_H, Elektrolytgehalt und Alter konnten nachweisen, daß das Nachleuchten auf einem Festkörpereffekt der Substanzen beruht, bei dem durch als Verunreinigungen in geringer Konzentration vorhandene Fremdstoffe (Al₂O₃) oder Gitterdefektstellen (SiO₂) durch Licht anregbare Aktivatorzentren gebildet werden. Die Lumineszenzintensität wird in erster Linie vom Ordnungszustand (Kristallinität) der Partikelbausteine bestimmt. Da der Anteil geordneter Bereiche auch von der Partikelgröße abhängt, ist diese ebenfalls ein bestimmender Faktor. Ein sehr deutlicher Einfluß des p _H und des Elektrolytgehaltes oder auch der Koagulation ist nur zu verstehen, wenn eine Zunahme der negativen Nettoladung in der Grenzschicht der Partikel zu einem Abbau positiv geladener Desaktivierungszentren führt. Das Eingreifen von Desaktivierungszentren solcher Art setzt voraus, daß das Nachleuchten durch Photoionisation des Aktivators, Einfangen der Elektronen in Haftstellen und Rückführung zum Aktivator und Desaktivator stattfindet. Dies steht auch im Einklang mit der Beobachtung, daß die Lumineszenzfähigkeit durch längeres Belichten (UV) zerstört, im Dunkeln aber zurückgebildet wird.

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Summary Similar but not identical emission spectra between 350 and 550 nm were observed for the long living luminescence of colloidal silica and alumina as gel and as sol. Their excitation spectra situated in the UV-region. show strong bands at 220 (Al₂O₃) and 290 nm (SiO₂). Whilst the spectral distribution of the luminescence of Al₂O₃ is markedly influenced by the wavelength of excitation there is no such dependence for SiO₂. With heating up to 900°C the luminescence of both gels dissappears and is very slowly regenerated at room temperature, for SiO₂ this takes place in the presence of water, only.Parallel measurements of luminescence, light scattering, electron diffraction, surface and viscosity as function of p_H, electrolyte content, and age of the sols could prove the luminescence as due to a solid state effect of the colloidal particles. Activator centres excited by light absorption are impurities of minute concentrations (Al₂O₃) or vacancies in the host lattice (SiO₂). The intensity of the luminescence is mainly ruled by the perfection of the crystal structure. Because the part of indistorted lattice areas depends on the particle size this term itself is a ruling factor. The very distinct influence of p_H and electrolyte content or coagulation, as well, is only conceivable when an increase of the negative surface charge causes a breaking down of positively charged killer centres.The engagement of such centres presupposes that the process of luminescence consists, here, of photoionization of the activator, trapping of the photoelectron, and its transition to the activator or killer centre. This coincides with the observation that the luminescence vanishes with prolonged UV-illumination and reappears after storage in the dark.

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Mit 11 Abbildungen in 13 Einzeldarstellungen und 6 Tabellen     

Luminescence Properties of Mn2+-Doped Sol-Gel Glasses

Mn²⁺-doped 1Al₂O₃-99SiO₂ glasses have been prepared by a sol-gel method and their photoluminescence (PL) properties have been studied for the first time. The effect of ZrO₂ and TiO₂ on the luminescence properties has also been studied. In addition, the PL of Mn: 1Al₂O₃-99SiO₂ is compared with Mn:SiO₂. The emission spectra of all the samples containing Al₂O₃ show a band around 620 nm, and the sample without Al₂O₃ shows two bands around 620 and 650 nm. These emission bands are all assigned to the ⁴T₁ ⁶A₁ transition of octahedrally coordinated Mn²⁺ · ZrO₂ and TiO₂ have fluorescence quenching effect. The relative fluorescence intensity of Mn²⁺-doped sol-gel 1Al₂O₃-99SiO₂ is much stronger than that of Mn²⁺-doped sol-gel SiO₂. The difference of the emission wavelength between host materials is explained in terms of the ligand field effect.     

Preparation of superhydrophobic PET fabric from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> hybrid: geometrical approach to create high contact angle surface from low contact angle materials

In this work we prepare high contact Poly Ethylene Terephthalate (PET) fabric surface from low contact angle materials. Superhydrophobic PET fabric is prepared by coating the fabric with hybrid Al₂O₃–SiO₂ sol. In this case, the high contact angle Al₂O₃–SiO₂ hybrid is created from low contact angle Al₂O₃ and SiO₂ precursors. PET treated with hybrid Al₂O₃–SiO₂ exhibit Water Contact Angle (WCA) as 150°, while PET treated with individual Al₂O₃ sol or SiO₂ sol exhibits lower WCA, (Al₂O₃ WCA = 137°; SiO₂ WCA = 141°). FESEM and AFM investigations show that the hybrid Al₂O₃–SiO₂ sol and individual Al₂O₃ or SiO₂ sol imparted different roughness geometry on the PET fabric surface. We observe surface structure of fish fin-like, particle-like and hybrid fin-particle for treated PET fabric with; Al₂O₃, SiO₂ and hybrid Al₂O₃–SiO₂ sol, under FESEM and AFM observations.AFM observations show the evolution of roughness (Ra) dimension of different surface structures with the order of: SiO₂ < Al₂O₃ < Al₂O₃–SiO₂ (Ra = 31, 63 and 273 nm). We believe that the disparity of the surface geometries lead into different surface WCA. FTIR spectra of Hybrid Al₂O₃–SiO₂ shows additional peak at 902, 850, 557, and 408 cm⁻¹ which can be ascribed to the hybridization structure.     

Towards Microwave Absorbing Metal-Oxide Nanocomposites: The Problem of Metal/Matrix Reaction

Thermostable microwave absorbing materials are of considerable interest for the applications with the tailored radar cross-section. Nanocomposites metal (Co, Fe)-dielectric (Al₂O₃, Al₂O₃2SiO₂, 3Al₂O₃2SiO₂) prepared by sol-gel route have been studied by electron microscopy and ⁵⁷Fe Mössbauer spectroscopy. The relationships between the micro/meso porosity, the composition and the state of the matrix precursor and the metal particle size are discussed with emphasis on the oxidation of nanoparticles. The size are discussed with emphasis on the oxidation of nanoparticles. Fe-based nanocomposites are obtained only using microporous host matrices. The interfacial reaction between iron nitrate solution precursor and host matrix promotes the formation of -(Fe_1-XAl₉)₂O₃ phase. The metal content is maximized by the use of highly concentrate iron solution and/or mixing with cobalt nitrate, in which case alloying particles are obtained.     

The role of ligand coordination on the spectral features of Yb3+ ions in lead aluminum silicate glasses

The glasses of the composition (40 ? x)PbO–(5 + x)Al₂O₃–54SiO₂:1.0Yb₂O₃ (in mol%) with x ranging from 5 to 10 have been synthesized. The IR spectral studies of these glasses have indicated that there is a gradual transformation of Al³⁺ ions from tetrahedral to octahedral coordination with increase of Al₂O₃ content in the glass network. The optical absorption and luminescence spectra have exhibited bands originating from ²F_7/2 → ²F_5/2 and ²F_5/2 → ²F_7/2 transitions, respectively. From these spectra, the absorption and emission cross-sections and fluorescence lifetime of Yb³⁺ ions have been evaluated. Quantitative analysis of these data indicated a decreasing radiative trapping and increasing fluorescence lifetime of Yb³⁺ ions with increasing Al₂O₃ content. This may be explained by structural variations in the vicinity of Yb³⁺ ions due to variation in the concentration of Al₂O₃ in the glass network.     

Pentacoordinated Al3+‐Stabilized Active Pd Structures on Al2O3‐Coated Palladium Catalysts for Methane Combustion

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO₂ catalysts with porous Al₂O₃ overlayers coated by atomic layer deposition (ALD). ²⁷Al magic angle spinning NMR analysis showed that Al₂O₃ overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al³⁺ sites capable of strongly interacting with adjacent surface PdO_x phases on supported Pd particles. Consequently, Al₂O₃‐decorated Pd/SiO₂ catalysts exhibit active and stable PdO_x and Pd–PdO_x structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al₂O₃ overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.     

Eco-friendly synthesis of high silica zeolite Y with choline as green and innocent structure-directing agent

Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure-directing agents (OSDAs), which are chronically hazardous to humans and the environment. It is a growing trend to develop an eco-friendly and nuisanceless OSDA for zeolite synthesis. Herein, choline is employed as a non-toxic and green OSDA to synthesize high silica Y zeolite with SiO₂/Al₂O₃ ratios of 6.5–6.8. The prepared Y zeolite samples exhibited outstanding (hydro)thermal stability at ultrahigh temperature owing to the higher SiO₂/Al₂O₃ ratio. The XRF, SEM, ²⁹Si-NMR and ¹³Na+ results suggested that choline plays a structure-directing role in the synthesis of Y zeolite, while the feed molar fraction of Na⁺ is a crucial determinant for the framework SiO₂/Al₂O₃ ratio and the crystal morphology.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XVI. Reduktionsverhalten amorpher NiO?Al2O3/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al₂O₃/SiO₂ Catalysts The reduction behaviour of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al₂O₃/SiO₂ catalysts is enhanced and the nickel dispersity is decreased at low Al₂O₃ contents. The decrease of the reducibility at Al₂O₃ contents >5 mole% is caused by the formation of nickel spinels and the decrease of the Ni^II ion surface concentration.     

Catalytic properties of Fe/SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> systems,obtained via sol–gel method

The high efficacy of iron-containing catalysts based on SiO₂–Al₂O₃ systems obtained via sol–gel method in the oxidative destruction of carmoisine azo dye in aqueous solutions is demonstrated. It is found that the stability of the catalysts with respect to the leaching of iron ions into a solution during catalysis grows along with the aluminum content in the composition of aluminosilicate supports. It is concluded that the synthesized catalysts are promising materials for purifying wastewaters contaminated with organic dyes.     

Densification mechanisms of alumina,aluminosilicates and aluminoborosilicates gels,glasses and ceramics

The thermal evolution of gels, glasses and ceramics of various more or less refractory compositions (Al₂O₃, 3Al₂O₃2SiO₂, 7Al₂O₃3SiO₂, Al₂O₃2SiO₂, Al₂O₃2SiO₂0.7B₂O₃, Al₂O₃2SiO₂2B₂O₃, Al₂O₃2SiO₂6B₂ O₃) have been studied by dilatometry, DTA, and helium density measurements. Comparison is made for materials prepared by rapid (powder) or by very slow gelation (optically clear monoliths). The influence of atmosphere sintering (air, H₂, vacuum) is reported. Densification and kinetic laws are discussed.Also at LASIR, CNRS, 2 rue Henry Dunant, 94320 Thiais, France.     

系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XV. Oberflächenchemische Eigenschaften von NiO/Al2O3?SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XV. Surface Chemical Properties of NiO/Al₂O₃-SiO₂ Catalysts Surface chemical properties of precipitated NiO/Al₂O₃? SiO₂ catalysts different compositions and the corresponding Al₂O₃? SiO₂ carriers have been investigated. Infrared spectroscopic measurements (before and after adsorption of pyridine and ammonia), ¹H-n.m.r. and ammonia adsorption measurements showed that the number of the Lewis-acidic sites are increased mainly by incorporation of the nickel component on the X-ray amorphous Al₂O₃? SiO₂ carriers, whereas the number of the hydroxide groups do not change significantly. With growing alumina content the number and the strength of the Lewis-acidic sites are increased where the part of the Ni^II surface sites decreases and those of the Al^III surface sites increases. Brönsted-acidic sites are detectable at high alumina contents.     

Hydrolysis of the uranyl ion in sodium nitrate medium

Studies on Nickel Oxide Mixed Catalysts. VIII. Catalytic Properties of NiO? Al₂O₃/SiO₂ Catalysts Catalytic properties of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitation-deposition and impregnation have been investigated in dimerization of ethene and isomerization of but-1-ene. It was found that the catalytic activity is mainly determined by the interaction between the catalyst components where a X-ray amorphous nickel alumolayersilicate is formed. The dimerization of ethene proceeds by participation of coordinatively unsaturated nickel ions with aluminum ions in the neighbourhood. The catalytic activity in the isomerization of but-1-ene depends on the surface acidic properties of the catalyst.     

Multi‐instrument characterization of the surfaces and materials in microfabricated,carbon nanotube‐templated thin layer chromatography plates. An analogy to ‘The Blind Men and the Elephant’

We apply a suite of analytical tools to characterize materials created in the production of microfabricated thin layer chromatography plates. Techniques used include X‐ray photoelectron spectroscopy (XPS), valence band spectroscopy, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) in both positive and negative ion modes, Rutherford backscattering spectroscopy (RBS), and helium ion microscopy. Materials characterized include: the Si(100) substrate with native oxide: Si/SiO₂, alumina (35 nm) deposited as a diffusion barrier on the Si/SiO₂: Si/SiO₂/Al₂O₃, iron (6 nm) thermally evaporated on the Al₂O₃: Si/SiO₂/Al₂O₃/Fe, the iron film annealed in H₂ to make Fe catalyst nanoparticles: Si/SiO₂/Al₂O₃/Fe(NP), and carbon nanotubes (CNTs) grown from the Fe nanoparticles: Si/SiO₂/Al₂O₃/Fe(NP)/CNT. The Fe films and nanoparticles appear in an oxidized state. Some of the analyses of the CNTs/CNT forests appear to be unique: (i) the CNT forest appears to exhibit an interesting ‘channeling’ phenomenon by RBS, (ii) we observe an odd–even effect in the SIMS spectra of C_n^‐ species for n = 1 – 6, with the n ≥ 6 ions showing a steady decrease in intensity, and (iii) valence band characterization of CNTs using X‐radiation is reported. Initial analysis of the CNT forest by XPS shows that it is 100 at.% carbon. After one year, only ca. 0.25 at.% oxygen is observed. The information obtained from the combination of the different analytical tools provides a more complete understanding of our materials than a single technique, which is analogous to the story of ‘The Blind Men and the Elephant’. The raw XPS and ToF‐SIMS spectra from this study will be submitted to Surface Science Spectra for archiving. Copyright © 2013 John Wiley & Sons, Ltd.     

Indirect radiotracer study of the adsorption of chromate ions on γ-Al2O3 and direct study of the adsorption of sulfate ions on Cr2O3 using 35S-labelled H2SO4

The specific adsorption of sulfate ions on Cr₂O₃ was studied by a radiotracer technique using ³⁵S-labelled sulfuric acid in low concentrations (c<10^–3 mol dm^–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. It was found that the extent of adsorption is determined by the protonation of the surface sites, similar to other oxides studied previously. A comparison of Cr₂O₃ and Al₂O₃ in this respect shows that the protonation of the former takes place at significantly lower pH values than that of the latter. The indirect radiotracer study of the adsorption of chromate on Al₂O₃ was carried out using labelled sulfate ions as indicator species. The results obtained show that the adsorption strength of chromate species is very low in comparison to sulfate ions and a regular Langmuir-like adsorption behaviour can be observed. It is believed that the observations presented may contribute to a better understanding of the behaviour of surface layers with a mixed oxide content. Electronic Publication     

The effect of calcination on the surface properties of the systems Al2O3-TiO2, SiO2-Al2O3, and SiO2-TiO2 prepared from metal alkoxides

Summary The effect of calcining temperature on the surface properties of the systems Al₂O₃-TiO₂, SiO₂-Al₂O₃, and SiO₂-TiO₂ prepared by co-hydrolysis of the corresponding metal alkoxide mixtures was studied from the crystal structure, the specific surface area, the heat of immersion in water and the surface acidity.Generally, the crystal growth of the systems accelerates with the rise of temperature of calcination. The specific surface area diminishes markedly with the rise of temperature of calcination, while the surface acidity remains almost constant. But the heat of immersion depends on the composition of the systems.

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Zusammenfassung Die Systeme Al₂O₃-TiO₂, SiO₂-Al₂O₃ und SiO₂-TiO₂ wurden durch die Hydrolyse der korrespondierenden Metallalkoxyde hergestellt. Von den Systemen wurden die spezifische Oberfläche, die Kristallstruktur, die Benetzungswärme in Wasser und das Oberflächen-p_H in Abhängigkeit von der Glühtemperatur gemessen.Im allgemeinen wird das Kristallwachstum mit der Erhöhung der Glühtemperatur beschleunigt und die spezifische Oberfläche vermindert. Hingegen ist der Oberflächen-p_H-Wert mit der Erhöhung der Glühtemperatur fast unveränderlich. Aber die Benetzungswärme hängt von der Komposition der Systeme ab.

     

Über den Mechanismus der Polymerisationsreaktionen

Zusammenfassung Beim Erhitzen gefällter Kieselsäure zeigen sprunghafte Änderungen in der Emanationsabgabe Umwandlungen bei etwa 570⁰ bzw. 870⁰ C an.Calciumoxyd reagiert mit SiO₂ erst nach 900⁰ C.Die Umwandlung eines -Al₂O₃ in Korund erfolgt zwischen 840⁰ und 950⁰ C. Diese Umwandlang schreitet von außen nach dem Inneren des Al₂O₃-Partikels vor; daraus wird auf einen größeren Energieinhalt der Atome an der Oberfläche der Partikeln gegenüber jenen in deren Innerem geschlossen.Kobaltcarbonat zeigt auf Aluminiumhydroxyd bis etwa 400⁰ C keinen Einfluß; zwischen 400⁰ und 800⁰ C tritt eine den Austritt der Emanationsatome stark blockierende Wirkung ein. Die Oberfläche des entstehenden -Al₂O₃ wird stark verdeckt bis nach 800⁰ C, also beim Beginn der —-Umwandlung, ein E.V.-Anstieg einsetzt: Das Kobaltoxyd reagiert mit dem Al₂O₃ unter Bildung von Thenardsblau und der Beginn der Reaktion ist mit einer starken Auflockerung verbunden.CaCO₃ wirkt auf die Oberfläche von Al₂O₃ nach 600⁰ C stark ein. Zu Beginn der Reaktion von CaO mit Al₂O₃ tritt eine starke Auflockerung der Al₂O₃-Oberfläche ein.Die Bildung von Calciumferrit erfolgt zwischen 550⁰ und 600⁰ C unter erheblicher Erhöhung der Dispersität beim Beginn der Reaktion.Für Unterstützungen zu großem Dank verpflichtet bin ich den Herren Professoren H.Mark und St.Meyer.