DE4306234C2 - Finely divided oxide powder and use of the same - Google Patents

Finely divided oxide powder and use of the same

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Publication number
DE4306234C2
DE4306234C2 DE4306234A DE4306234A DE4306234C2 DE 4306234 C2 DE4306234 C2 DE 4306234C2 DE 4306234 A DE4306234 A DE 4306234A DE 4306234 A DE4306234 A DE 4306234A DE 4306234 C2 DE4306234 C2 DE 4306234C2
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Prior art keywords
oxide powder
powder according
coating
maximum
hydration
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Expired - Fee Related
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DE4306234A
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German (de)
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DE4306234A1 (en
Inventor
Andreas Dr Meier
Gerhard Graf
Klaus Doesinger
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Veitsch Radex GmbH and Co OG
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Veitsch Radex GmbH and Co OG
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Publication of DE4306234A1 publication Critical patent/DE4306234A1/de
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Publication of DE4306234C2 publication Critical patent/DE4306234C2/en
Anticipated expiration legal-status Critical
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    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
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Description

Die Erfindung betrifft ein feinteiliges Oxidpulver, ins­ besondere auf Basis Magnesium und Aluminium sowie die Verwendung dieses oberflächenmodifizierten feinteiligen Oxidpulvers.The invention relates to a finely divided oxide powder, ins special based on magnesium and aluminum as well as the Use of this surface-modified fine particle Oxide powder.

Zur Herstellung von keramischen Formteilen und Massen hoher Dichte werden häufig Zusätze feinteiliger Oxidpulver, sogenannter Mikropulver, zum Beispiel auf der Basis SiO2, Cr2O3 und Al2O3 eingesetzt. Die feinteiligen Partikel dieser Mikropulver füllen die Hohlräume zwischen den grö­ beren Körnern des Matrixmaterials aus, wodurch die offene Porosität gesenkt und die Festigkeit sowie die Rohdichte erhöht werden.Additions of fine-particle oxide powders, so-called micropowders, for example based on SiO 2 , Cr 2 O 3 and Al 2 O 3 , are often used to produce ceramic moldings and high-density materials. The fine particles of these micropowders fill the voids between the coarser grains of the matrix material, which reduces the open porosity and increases the strength and bulk density.

Der Einsatz derartiger Mikropulver ist vor allem bei thixo­ tropen feuerfesten Gießmassen bekannt. The use of such micropowder is particularly important at thixo tropical refractory casting compounds.  

So beschreibt die AT 3 92 464 B1 ein Magnesiumoxid-Mikro­ pulver mit einer Teilchengröße kleiner 15 µm, wobei die einzelnen Teilchen eine Beschichtung aus einer hydropho­ bierenden Substanz besitzen. Durch diese Substanzen wird die innere Reibung des Magnesiumoxid-Mikropulvers herabge­ setzt und die Teilchen erhalten im Zusammenwirken mit einem Bindemittel ein hohes Maß an Beweglichkeit, so daß bei der Formgebung der Keramik ein hoher Verdichtungsgrad erreicht wird. Die hydrophobe Beschichtung hat weiterhin den Zweck, eine Hydratation der Oxidteilchen zu Magnesium­ hydroxid soweit wie möglich zu verhindern, wenn diese in wäßrigem Milieu zu feuerfesten Produkten verarbeitet werden. Die Herstellung des MgO-Mikropulvers erfolgt durch Vermischen mit Fettsäuren, Silikonen oder organischen Polymeren.AT 3 92 464 B1 describes a magnesium oxide micro powder with a particle size smaller than 15 microns, the individual particles a coating of a hydropho possessing substance. Through these substances reduce the internal friction of the magnesium oxide micropowder sets and the particles get in cooperation with a binder a high degree of mobility, so that a high degree of compaction when shaping the ceramic is achieved. The hydrophobic coating still has the purpose of hydrating the oxide particles to magnesium prevent hydroxide as much as possible if this processed into refractory products in an aqueous environment become. The MgO micropowder is produced by mixing with fatty acids, silicones or organic polymers.

Aus der Praxis ist es bekannt, daß derartige obenflächen­ modifizierte feinteilige Oxidpulver nach einem relativ kostenintensiven Verfahren durch Vermengen des Beschich­ tungsmittels mit dem feinteiligen Oxidpulver in einem Intensivmischer bei erhöhter Temperatur hergestellt werden. Ziel dieses Beschichtungsvorganges ist es, eine möglichst monomolekulare Schicht des Beschichtungsmittels auf die einzelnen Pulverteilchen aufzutragen und funktionelle Gruppen des Beschichtungsmittels mit der Oberfläche der Pulverteilchen in Reaktion zu bringen. Bei dem bekannten Verfahren kommt es jedoch aufgrund der langen Behandlungs­ zeit und dadurch, daß das Pulver in trockenem Zustand mit dem Beschichtungsmittel gemischt wird, zu Agglomera­ tionen der einzelnen Teilchen. Die Folge ist, daß häufig Pulveragglomerate beschichtet werden, was jedoch uner­ wünscht ist, da sich dann die Eigenschaften der daraus hergestellten Produkte verschlechtern. Zur Verbesserung der Gleichmäßigkeit der Beschichtung (um jedes einzelne Teilchen) ist es deshalb ebenfalls aus der Praxis bekannt, die Beschichtungsmittel in Form verdünnter Lösungen unter Verwendung von nichtwäßrigen, leichtflüchtigen Lösungs­ mitteln einzusetzen. Das Lösungsmittel verdampft beim Beschichtungsvorgang, was eine entsprechende sicherheits­ technische Auslegung der Beschichtungsanlage und eine Entsorgung der Lösungsmitteldämpfe erforderlich macht.From practice it is known that such top surfaces modified fine-particle oxide powder after a relative costly process by mixing the coating with the finely divided oxide powder in one Intensive mixers can be produced at elevated temperatures. The aim of this coating process is one, if possible monomolecular layer of the coating agent on the individual powder particles and functional Groups of the coating agent with the surface of the To bring powder particles into reaction. With the well-known However, procedures come about because of the long treatment time and in that the powder is dry mixed with the coating agent to form agglomerates ions of the individual particles. The result is that often Powder agglomerates are coated, but this is not is desired, because then the properties of it manufactured products deteriorate. For improvement the uniformity of the coating (around each one Particles) it is therefore also known from practice the coating agents in the form of dilute solutions Use of non-aqueous, volatile solution  use funds. The solvent evaporates on Coating process, which is a corresponding security technical design of the coating system and a Disposal of the solvent vapors is required.

Auch das aus DE-Z: cfi/Ber. DKG 68 (1991) No. 5, 219 bekannte Verfahren zur Sprühtrocknung keramischer Pulver geht von einer (wäßrigen) Naßvermahlung aus, die bei hydratationsempfindlichem Material nicht in Frage kommt, da der intensive Kontakt Pulver/Wasser zu einer unerwünschten Hydratation führen würde.Also from DE-Z: cfi / Ber. DKG 68 (1991) No. 5, 219 known processes for spray drying ceramic powders assumes an (aqueous) wet grinding, which at hydration-sensitive material is out of the question, since the intensive powder / water contact becomes an undesirable Hydration would result.

Der Erfindung liegt die Aufgabe zugrunde, ein feinteiliges Oxidpulver anzugeben, das eine möglichst vollständig mono­ molekulare Belegung der Oberflächen der vereinzelten Pulver­ teilchen mit einer Beschichtung aufweist und in einem einfachen Verfahren ohne Einsatz von Lösungsmitteln und ohne wesentliche Hydratisierung herstellbar ist.The invention has for its object a finely divided Specify oxide powder that is as completely mono molecular coverage of the surfaces of the individual powders has particles with a coating and in one simple procedures without the use of solvents and can be produced without substantial hydration.

Dazu beschreibt die Erfindung in ihrer allgemeinsten Aus­ führungsform ein feinteilige, hydratationsempfindliches Oxidpulver, insbesondere auf Basis Magnesium oder Aluminium, mit einem maximalen Hydratationsgrad von 10 Gew.-%, bei dem die einzelnen Oxidteilchen mit einer, eine weitere Hydratation verhindern­ den dünnen Beschichtung versehen sind, und das durch fol­ gende, unmittelbar aufeinanderfolgende Schritte erhalten wurde:To this end, the invention describes in its most general terms leadership form a finely divided, hydration-sensitive oxide powder, in particular based on magnesium or aluminum, with a maximum Degree of hydration of 10 wt .-%, at which the individual Oxide particles with one to prevent further hydration the thin coating are provided by fol receive the steps immediately following one another has been:

  • - zunächst wird eine wäßrige Suspension aus einem reinen Oxidpulver und einem Beschichtungsmittel hergestellt,- First, an aqueous suspension from a pure Oxide powder and a coating agent,
  • - danach wird die Suspension homogenisiert,- the suspension is then homogenized,
  • - anschließend wird die Suspension einer Sprühtrocknung bei maximal 130°C unterworfen.- Then the suspension is spray dried subjected to a maximum of 130 ° C.

Überraschenderweise hat sich gezeigt, daß ein derartiges feinteiliges Oxidpulver mit einem relativ niedrigen Hydra­ tationsgrad auch in wäßriger Suspension hergestellt wer­ den kann, sofern sich an die Aufschlämmung des Ausgangs­ materials unverzüglich der genannte Sprühtrocknungsvor­ gang anschließt.Surprisingly, it has been shown that such a finely divided oxide powder with a relatively low hydra degree of production also in aqueous suspension  that can, provided the slurry of the exit materials immediately the spray drying gang connects.

Aus der US-A-38 43 380 ist ein Verfahren zur Behandlung von mineralischen Pigmentaggregaten bekannt, die zur Ver­ wendung in Farben oder Kunststoffen dienen. Dabei wird ein pumpfähiger wäßriger Schlamm mit 0,1 bis 5 Gew.-% eines in Wasser dispergierbaren Verdickungsmittels versetzt und der so atomisierte Schlamm wird anschließend einer Sprühtrocknungs-Behandlung unterworfen.From US-A-38 43 380 is a method for treatment of mineral pigment aggregates known for ver serve in colors or plastics. Doing so a pumpable aqueous sludge with 0.1 to 5% by weight of a water-dispersible thickener and the sludge so atomized then becomes one Subjected to spray drying treatment.

Die genannten mineralischen Pigmente bestehen beispiels­ weise aus Titandioxid.The mineral pigments mentioned exist, for example wise from titanium dioxide.

Eine Anwendung eines derartigen Sprühtrocknungsverfahrens für die in einem wäßrigen Medium aufgeschlämmten und hydratationsanfälligen Oxidpulver der vorstehend genannten Art erscheint wegen der Hydratationsanfälligkeit des Oxid­ pulvers nicht möglich; gleichwohl wurde festgestellt, daß eine unmittelbar im Anschluß an die Aufschlämmung durchgeführte Sprühtrocknung nicht nur eine (unerwünschte) Hydratationsbildung weitestgehend unterbindet oder stoppt, sondern darüber hinaus in besonderem Maße eine monomoleku­ lare Oberflächenbeschichtung der einzelnen Oxidteilchen begünstigt.An application of such a spray drying process for those slurried in an aqueous medium and hydration-sensitive oxide powder of the above Art appears because of the susceptibility to hydration of the oxide powder not possible; nevertheless it was found that one immediately following the slurry spray drying carried out not only one (undesirable) Largely prevents or stops hydration, but also, in particular, a monomolecule lare surface coating of the individual oxide particles favored.

In diesem Sinne ist es vorteilhaft, die Suspensionsbehand­ lung so kurz wie möglich zu gestalten. Eine Aufschlämmung über einen Zeitraum von 6 Stunden darf als Maximum gelten; nach einer bevorzugten Ausführungsform soll die Behandlung weniger als eine Stunde betragen. Je kürzer die Oxidteilchen vor der Sprühabsorption in der wäßrigen Lösung verbleiben, um so geringer ist der Hydratationsgrad der getrockneten Teilchen, der dabei auf Werte von weit unter 10 Gew.-% (teilweise unter 3 Gew.-%) gesenkt werden kann.In this sense, it is advantageous to use the suspension treatment to make it as short as possible. A slurry over a period of 6 hours may apply as a maximum; according to a preferred embodiment, the treatment less than an hour. The shorter the oxide particles  remain in the aqueous solution before spray absorption, the lower the degree of hydration of the dried Particle that has values far below 10% by weight (partially below 3 wt .-%) can be reduced.

Dabei muß die Suspensionsbehandlung aber zumindest so sorgfältig durchgeführt werden, daß eine homogene Ver­ mischung stattfindet, um die gewünschte monomolekulare Beschichtung sicherzustellen.The suspension treatment must at least be like this be carried out carefully that a homogeneous ver mixing takes place to the desired monomolecular Ensure coating.

Die gestellte Aufgabe wird in besonders vorteilhafter Weise dann gelöst, wenn die Suspension vor der Sprühbehand­ lung eine Temperatur von 40°C nicht übersteigt. Ein Tem­ peraturmaximum von 10°C hat sich als optimal herausge­ stellt.The task is particularly advantageous Way solved when the suspension before the spray treatment temperature does not exceed 40 ° C. A tem temperature maximum of 10 ° C has been found to be optimal poses.

Überraschenderweise ist es also auch bei hydratations­ empfindlichen Oxidpulvern durch die Anwendung des Sprüh­ trocknens möglich, derartige Oxidpulver in einer wäßrigen Suspension zu beschichten, wenn sämtliche Verfahrensstufen vor der Sprühtrocknung bei den angeführten niedrigen Tempe­ raturen und in möglichst kurzen Zeiten durchgeführt werden.Surprisingly, it is also the case with hydrations sensitive oxide powders by using the spray drying possible, such oxide powder in an aqueous Coating suspension when all process steps before spray drying at the specified low temperatures and in as short a time as possible.

Ein weiterer Vorteil besteht darin, daß eine homogene, vollständige Beschichtung auf den Pulverpartikeln bei minimalem Verbrauch des Beschichtungsmittels erreicht wird. Gleichzeitig wird der Einsatz von nichtwäßrigen, leichtflüchtigen Lösungsmitteln nach dem Stand der Technik vermieden, die zur Erzielung desselben Effekts bei den bisherigen Beschichtungstechnologien erforderlich waren und zu den obengenannten Problemen führten. Another advantage is that a homogeneous, complete coating on the powder particles minimal consumption of the coating agent reached becomes. At the same time, the use of non-aqueous, volatile solvents according to the prior art avoided to achieve the same effect in the previous coating technologies were required and led to the problems mentioned above.  

Wichtig ist schließlich auch, daß die Sprühtrocknung bei einer Temperatur durchgeführt wird, bei der die Beschich­ tung stabil bleibt. Das Beschichtungsmittel wirkt gleich­ zeitig als Trennmittel und verhindert weitestgehend eine Agglomeration der Pulverteilchen beim Sprühtrocknen. Inso­ weit zeichnen sich die erfindungsgemäßen feinteiligen Oxidpulver durch eine vollflächige Oberflächenbeschichtung der Primärteilchen aus; Teilchenagglomerate treten so gut wie nicht auf. Insoweit wird auch eine Nachmahlung überflüssig. Ebenfalls entfällt die bei einer solchen Mahlung auftretende Freilegung von unbeschichteten aktiven Pulveroberflächen, was bei der anschließenden Verwendung der feinteiligen Oxidpulver wiederum zu unerwünschten (weiteren) Hydratationsreaktionen führen würde.Finally, it is also important that the spray drying at a temperature is carried out at which the coating tion remains stable. The coating agent works the same as a release agent and largely prevents one Agglomeration of the powder particles during spray drying. Inso the finely divided particles according to the invention are widely distinguished Oxide powder through a full surface coating the primary particles from; Particle agglomerates occur this way well not on. In this respect, there is also a refill superfluous. This also does not apply to such Exposure of uncoated active substances occurring during grinding Powder surfaces what in subsequent use the finely divided oxide powder in turn to undesirable would lead to (further) hydration reactions.

Versuche haben gezeigt, daß - ausgehend von identischen Oxidpulvern und Beschichtungsmitteln - die mittlere Teil­ chengröße d50 durch Anwendung des beschriebenen Verfahrens um etwa die Hälfte gesenkt werden kann. Zur weiteren Redu­ zierung der Teilchengröße kann die Suspension zum Beispiel vor oder nach der Zugabe des Beschichtungsmittels zusätzlich einer Mahlbehandlung unterworfen werden.Experiments have shown that - starting from identical oxide powders and coating agents - the average particle size d 50 can be reduced by about half by using the described method. To further reduce the particle size, the suspension can also be subjected to a grinding treatment, for example, before or after the addition of the coating agent.

Sofern es sich bei dem feinteiligen Oxidpulver um Magnesium­ oxidpulver handelt, eignet sich als Ausgangsmaterial ins­ besondere ein Magnesiumoxid, das durch Pyrohydrolyse einer gereinigten Magnesiumchloridlösung gewonnen wurde.If the finely divided oxide powder is magnesium oxide powder, is suitable as a starting material ins special a magnesium oxide, which by pyrohydrolysis of a purified magnesium chloride solution.

Für die Auswahl des Beschichtungsmittels gelten folgende Kriterien. Das Beschichtungsmittel soll keine unerwünschten Reaktionen mit Wasser eingehen, sein Dampfdruck bei der bevorzugten Temperatur der Sprühtrocknung (circa 100 bis 130°C Produkt-Ausgangstemperatur) soll möglichst niedrig sein, und es soll - wie oben ausgeführt - bei diesen maxi­ malen Temperaturen stabil sein.The following apply to the selection of the coating agent Criteria. The coating agent should not be undesirable React with water, its vapor pressure at the  preferred temperature of spray drying (about 100 to 130 ° C product outlet temperature) should be as low as possible be, and it should - as explained above - with these maxi paint temperatures should be stable.

In diesem Zusammenhang eignen sich besonders Carbonsäuren und deren Derivate (mit reaktiven und funktionellen Gruppen) wie Aminocarbonsäuren, zum Beispiel 6-Aminohexansäure, Crotonsäure sowie gesättigte oder ungesättigte Fettsäuren. Versuche haben gezeigt, daß auch hydrophobe Beschichtungs­ mittel wie Stearin- oder Ölsäure sowie wasserlösliche, organische Polymerverbindungen wie Ligninsulfonate, Poly­ acrylate und/oder Polyvinylalkohole verwendet und auf die genannte Art und Weise aufgebracht werden können.Carboxylic acids are particularly suitable in this context and their derivatives (with reactive and functional groups) such as aminocarboxylic acids, for example 6-aminohexanoic acid, Crotonic acid and saturated or unsaturated fatty acids. Experiments have shown that also hydrophobic coating agents such as stearic or oleic acid and water-soluble, organic polymer compounds such as lignin sulfonates, poly acrylates and / or polyvinyl alcohols used and on the said way can be applied.

Die Erfindung sieht auch vor, der Suspension zusätzlich zum Beschichtungsmittel vor dem Sprühtrocknen Zusatzstoffe zuzugeben. Hierbei ist an Bindemittel, Dispergiermittel oder ganz allgemein oxidische, feinteilige Komponenten gedacht. Hierdurch wird eine homogene Verteilung dieser Komponenten bei der späteren Verarbeitung der beschichteten Pulver zu Formteilen erreicht. Dies ist insbesondere für, die Ausbildung einer homogen verteilten Bindephase von Vorteil.The invention also provides for the suspension in addition Additives to the coating agent before spray drying to admit. Here is binder, dispersant or more generally oxidic, fine-particle components thought. This creates a homogeneous distribution of these Components in the later processing of the coated Powder to molded parts reached. This is especially for the formation of a homogeneously distributed binding phase of Advantage.

Die feinteiligen Oxidpulver eignen sich in hervorragender Weise zur Herstellung von hochdichten keramischen Form­ teilen, beispielsweise feuerfesten, keramischen Steinen, aber auch Massen.The finely divided oxide powders are excellent Way of making high-density ceramic mold parts, for example refractory ceramic stones, but also masses.

Weitere Merkmale der Erfindung ergeben sich aus den Merk­ malen der Unteransprüche sowie den sonstigen Anmeldungs­ unterlagen. Further features of the invention emerge from the note paint the subclaims and other registration documents.  

Die Erfindung wird nachstehend anhand verschiedener Aus­ führungsbeispiele näher erläutert.The invention is based on various examples of management explained in more detail.

Durch Sprührösten einer gereinigten Magnesiumchloridlösung wird ein Magnesiumoxidpulver A erhalten. Dieses Material, dessen physikalische und chemische Daten Tabelle 1 zeigt, wird nun wie folgt weiterverarbeitet:By spray roasting a cleaned magnesium chloride solution a magnesium oxide powder A is obtained. This material, whose physical and chemical data are shown in Table 1, is now processed as follows:

Beispiel 1example 1

Das Magnesiumoxidpulver A wird bei 10°C in Wasser disper­ giert und mit 1 Gew.-% 6-Aminohexansäure (bezogen auf das Magnesiumoxid) homogen vermischt.The magnesium oxide powder A is dispersed in water at 10 ° C. greed and with 1 wt .-% 6-aminohexanoic acid (based on the magnesium oxide) mixed homogeneously.

Die erhaltene Suspension wird danach sofort einer Sprüh­ trocknung unterworfen. Eine vorherige Mahlung zum Beispiel in einer Rührwerkskugelmühle ist optional. Die Eigenschaften des so erhaltenen Magnesiumoxidpulvers B sind ebenfalls in Tabelle 1 aufgeführt. Der Hydratationsgrad nach der Sprühtrocknung beträgt lediglich 2 Gew.-%. Weiters wurde der Hydratationsgrad bestimmt, nachdem die Proben in einem Klimaschrank 48 Stunden lang bei einer Temperatur von 40°C einer Atmosphäre mit 95 Gew.-% relativer Luftfeuchtig­ keit ausgesetzt worden waren.The suspension obtained is then immediately sprayed subject to drying. For example, a previous grind in an agitator ball mill is optional. The properties of the magnesium oxide powder B thus obtained are also listed in Table 1. The degree of hydration after Spray drying is only 2% by weight. Furthermore was The degree of hydration is determined after the samples in one Climatic cabinet for 48 hours at a temperature of 40 ° C of an atmosphere with 95 wt .-% relative humidity had been exposed.

Dabei erfolgte die Berechnung des Hydratationsgrads aus der Gewichtszunahme infolge von Aufnahme von Wasser, wobei ein Hydratationsgrad von 100% der vollständigen Umsetzung des Magnesiumoxids zu Magnesiumhydroxid entspricht.The degree of hydration was calculated the weight gain due to ingestion of water, whereby a degree of hydration of 100% of full implementation corresponds to the magnesium oxide to magnesium hydroxide.

Die Werte d10, d50 und d90 geben jene Teilchendurchmesser an, bei denen 10, 50 beziehungsweise 90% des Materials kleiner als der angegebene Wert sind. The values d 10 , d 50 and d 90 indicate those particle diameters in which 10, 50 and 90% of the material are smaller than the specified value.

Beispiel 2:Example 2:

Das Magnesiumoxidpulver A wird bei 10°C in Wasser dis­ pergiert und mit 1 Gew.-% Hexansäure (bezogen auf das Magnesiumoxid) gemischt. Die Suspension wird unmittelbar danach einer Sprühtrocknung unterworfen. Die chemische Analyse und Versuchsergebnisse des so erhaltenen beschich­ teten Pulvers C zeigt Tabelle 1.The magnesium oxide powder A is dis at 10 ° C in water pergiert and with 1 wt .-% hexanoic acid (based on the Magnesium oxide) mixed. The suspension becomes immediate then subjected to spray drying. The chemical Analysis and test results of the coating obtained in this way Powder C shows Table 1.

Tabelle 1 Table 1

Die Versuchsergebnisse belegen, daß die erfindungsgemäßen Magnesiumoxidteilchen eine hohe Feinteiligkeit aufweisen. Sie zeigen weiters eine deutlich reduzierte Hydratations­ neigung, auch nach längerer Feuchtelagerung, im Vergleich zu Pulver A. Dabei verringert eine geringe Polarität des Beschichtungsmittels die Hydratationsneigung zusätzlich.The test results show that the inventive Magnesium oxide particles have a high degree of fineness. They also show a significantly reduced hydration inclination, even after long periods of moisture storage, in comparison to powder A. A low polarity of the Coating agent additionally the tendency to hydration.

Zur Verdeutlichung der Vorteile der beschriebenen Oxid­ pulver dient das nachfolgende Beispiel.To illustrate the benefits of the oxide described powder is used in the following example.

Beispiel 3Example 3

Es werden Steinmischungen aus 10 Gew.-% des Magnesium­ oxidpulvers A beziehungsweise 10 Gew.-% des Magnesium­ oxidpulvers B und jeweils 90 Gew.-% Sintermagnesia in einer Korngröße kleiner 5 mm, gewonnen aus eisenarmem Naturmagnesit, hergestellt. Die Mischungen werden zu Steinen gepreßt und bei 1850°C gebrannt. Tabelle 2 zeigt die an diesen Steinen ermittelten Prüfwerte.There are stone mixtures from 10 wt .-% of magnesium oxide powder A or 10 wt .-% of magnesium oxide powder B and 90% by weight of sintered magnesia in a grain size less than 5 mm, obtained from low iron Natural magnesite. The mixtures become stones pressed and fired at 1850 ° C. Table 2 shows the test values determined on these stones.

Tabelle 2 Table 2

Es ist deutlich zu erkennen, daß die unter Verwendung der erfindungsgemäßen Magnesiumoxidpulver hergestellten Steine eine höhere Rohdichte, eine deutlich geringere offene Porosität und eine deutlich erhöhte Druckfestigkeit aufweisen.It can clearly be seen that the using the magnesium oxide powder according to the invention produced Stones have a higher bulk density, a significantly lower one open porosity and a significantly increased compressive strength exhibit.

Claims (10)

1. Feinteiliges, hydratationsempfindliches Oxidpulver, insbesondere auf Basis Magnesium und Aluminium, mit einem maximalen Hydratationsgrad von 10 Gew.-%, bei dem die einzelnen Oxidteilchen mit einer, eine weitere Hydratation verhindernden dünnen Beschichtung versehen sind, erhalten durch folgende, unmittelbar aufeinanderfolgende Schritte:
  • 1.1 Es wird eine wäßrige Suspension aus einem reinen Oxidpulver und einem Beschichtungsmittel hergestellt,
  • 1.2 die Suspension wird homogenisiert,
  • 1.3 anschließend wird die Suspension einer Sprühtrock­ nung bei maximal 130°C unterworfen.
1.Fine-particle, hydration-sensitive oxide powder, in particular based on magnesium and aluminum, with a maximum degree of hydration of 10% by weight, in which the individual oxide particles are provided with a thin coating which prevents further hydration, obtained by the following, immediately successive steps:
  • 1.1 An aqueous suspension is produced from a pure oxide powder and a coating agent,
  • 1.2 the suspension is homogenized,
  • 1.3 the suspension is then subjected to spray drying at a maximum of 130 ° C.
2. Oxidpulver nach Anspruch 1 mit einem maximalen Hydra­ tationsgrad von 5 Gew.-%.2. Oxide powder according to claim 1 with a maximum hydra degree of 5 wt .-%. 3. Oxidpulver nach Anspruch 1 oder 2, erhalten durch eine maximale Kontaktdauer der Oxidteilchen und des Beschich­ tungsmittels in der wäßrigen Suspension vor der Sprüh­ trocknung von 6 Stunden.3. oxide powder according to claim 1 or 2, obtained by a maximum contact time of the oxide particles and the coating agent in the aqueous suspension before spraying drying of 6 hours. 4. Oxidpulver nach Anspruch 3, erhalten durch eine maximale Kontaktdauer der Oxidteilchen und des Beschichtungs­ mittels in der wäßrigen Suspension vor der Sprühtrock­ nung von einer Stunde.4. oxide powder according to claim 3, obtained by a maximum Contact time of the oxide particles and the coating by means of the aqueous suspension before spray drying hour. 5. Oxidpulver nach einem der Ansprüche 1 bis 4, erhalten durch eine maximale Temperaturbeaufschlagung der Sus­ pension vor der Sprühtrocknung von 40°C.5. oxide powder according to any one of claims 1 to 4, obtained by a maximum temperature exposure of the Sus pension before spray drying at 40 ° C. 6. Oxidpulver nach Anspruch 5, erhalten durch eine maximale Temperaturbeaufschlagung der Suspension vor der Sprüh­ trocknung von 10°C.6. oxide powder according to claim 5, obtained by a maximum Temperature exposure of the suspension before spraying drying at 10 ° C. 7. Oxidpulver nach einem der Ansprüche 1 bis 6, bei dem das Beschichtungsmittel aus einer Carbonsäure oder deren Derivaten oder wasserlöslichen Polymerverbin­ dungen besteht.7. oxide powder according to any one of claims 1 to 6, in which the coating agent from a carboxylic acid or their derivatives or water-soluble polymer compound exists. 8. Oxidpulver nach einem der Ansprüche 1 bis 7, mit einer monomolekularen Oberflächenbelegung des Beschichtungs­ mittels.8. oxide powder according to one of claims 1 to 7, with a monomolecular surface coverage of the coating by means of. 9. Oxidpulver nach einem der Ansprüche 1 bis 8, erhalten durch Zugabe eines Binde- oder Dispergiermittels in die Suspension vor der Sprühtrocknung. 9. oxide powder according to any one of claims 1 to 8, obtained by adding a binder or dispersant in the suspension before spray drying.   10. Verwendung eines oberflächenmodifizierten feinteiligen Oxidpulvers nach einem der Ansprüche 1 bis 9 zur Herstellung hochdichter keramischer Formteile und Massen.10. Use of a surface-modified fine particle Oxide powder according to one of claims 1 to 9 for Manufacture of high-density ceramic molded parts and Masses.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10058077A1 (en) * 2000-11-23 2002-06-20 Schott Glas Coated particles used in composition and process for producing architectural models, machine parts and medical equipment have hard core and swelling shell
DE10058077B4 (en) * 2000-11-23 2008-05-08 Schott Ag Use of coated particles

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GB2264939B (en) 1995-08-09
FR2688420A1 (en) 1993-09-17
IT1270867B (en) 1997-05-13
DE4306234A1 (en) 1993-09-16
ATA45892A (en) 1994-07-15
ITMI930464A1 (en) 1994-09-10
ITMI930464A0 (en) 1993-03-10
GB2264939A (en) 1993-09-15
GB9304891D0 (en) 1993-04-28
AT398967B (en) 1995-02-27

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