DE1954138A1 - Process for the production of a high-purity alpha-aluminum oxide - Google Patents

Description

W.R. Grace & Co (priority 50 October 1968 -

U ₉ S ₄ 771.9? 9 - 1 ² > O44 - 6468)

New York, N.Y./V.St.A.

Hamburg, October 22, 1969

Process for producing a pure oC -

The invention relates to the production of oC-Älutainiura «oxide. The C-Alurainiuraoxyä produced by the successful process has a size of about 700 to X 000 R and its surface area * / on 10 to IS -wf '/ q, Dieees Aluffiiniümoxyd IEEt sioh cold yevpr-äßeii ;, ^ o that the density without sinfcerv ^ © tv; & 2.4 big Z ^ l'h% / & w '' £ '::> £ . ".-. after sintering V; si 1 500 C WSh ^ as 3 ^ 9 g / sar b ^ trlb ^ = ^ sc-Diohte icann ^v is to 3 * S3 g / ttir »increased" ^? e? iisii _a ¹ InOt ^ ^: "-'ä at higher temperature ^ -: lifter

find -vs Pig ^: «: m ^ ci _f ß.? .-; - J ^ e ^ feiste ι'- ■

ö. · λ- is; i> K'r.i. \ - "1

in Bezifhursi =? t-> i.rt: -.:. * vv- '.-.- silieh .-- ^); ^ :: ^ *. l · - - ^{: ι} · .-.'. ^: - ΐ ^: ~ ^ - \? Yj :: size distribution aes ve ^ weEiuetea Älw ^ intuftiüsords "The smaller particle sizes" obtained by the process according to the invention allow lower firing temperatures and can therefore be used, compact and differently shaped ceramic materials to produce with increased strength *

In the parallel patent armiaXdung P 17 67 724.6, the production of finely divided Alurairiiumqxyde from Aluiainiusasalsen, e.g. nitrates or sulfates, xmu their brines © the precipitation

ORIGINAL

products described by grinding the raw material and, if necessary, subsequent calcination of the ground product «The end product is a mixture of amorphous aluminum oxide with ^ -aluminium oxide or Gt» aluminum oxide or the process thus also leads to the production of oC -aluminium oxide, but only in one concentration from 12 to 20% by weight of the product, while the greater part of the remainder of the product is amorphous aluminum oxide, which shows no X-ray powder diagram.

It has now been found a method with the help of which one practically pure oC aluminum oxide can be obtained at any time. In addition lsi; it is necessary to use defined © R & hsaaterlallen and adhere to certain procedural conditions «

The raw material must either be an aluminum, whose aqueous LiSgsmg © Inen has a pH value of at least 7 u & r * aü: S iPicä at a temperature of 3 * 5 to 815 ° C »that! I, ; Iit άν-Γ ^ aMtesperatiir 5 ^ <»ras" ts5t _s odar after ein FMllungs « PP ¹ JUMiZ ^: -loß ' g ^ l © tees ^ cn'aFtigeü Salses ^ The preferred Sals ί £' ϊ i:;: : li ^^ at «dec- '.κ'', -ύί-i siafe also the Ohlorld wima-mL · ϊτϊζΑ ^ φ PBgilehkwlten st ^ uf das Ölslo ^ at - isid Broiiiid, Bas FMIIyiigsprodukt odes» Sol läSt see hearing- s by treating a usable for the method of aluminum salt with a base to bring * to adjust the pH value to a to a slurry or Aluminiuraoisyd or Aluminlumsol appropriate value, it can be further ₉ although somewhat cumbersome * by treating another aluminum salt with a base to form a slurry or a sol and subsequent separation of the electrolytes by adding nitrate, chloride or other suitable ions When it is used as a raw material, it is generally in an aqueous solution, although it can be present in a mixture with hydrated aluminum oxide.

«. ■■■ * ». 009 3 20/1768

ORTGiNAL

In the inventive method the raw material is added (molten or dissolved salt or a slurry of precipitated alumina or a Alurniniumoxydsol) in a working at 515-815 ⁰ C * jet mill to produce a precursor. The precursor usually contains 10 to 20 ° C. aluminum oxide with a crystallite size of less than 500 ft _g 30 to 70% of an amorphous ot -aluminum oxide precursor, the result being from amorphous

Jf-Aluminiuraoxydvorprodukt consists. The aluminum oxide phases in the product leaving the mill (and the calcination temperature required for the subsequent calcination to completely convert the precursor into et-alurainium oxide) depend on the particular salt, solution, hydrate or sol that was fed to the mill as the starting product are. The products contain less than 0.05 % impurities, except. Water.

In the novel process, the drying and dishydration of the oC -aluminum oxide precursor takes place in a high-temperature jet mill. The jet mill is customary as such in the art and is modified so that it operates at a temperature which is sufficient for the required decomposition or dehydration of the aluminum oxide feedstock with formation of the aluminum oxide precursor or the product containing <X aluminum oxide.

The intermediate product is then converted into pure aluminum oxide by calcining at a temperature of 370 to 54o ° C convicted.

009820/1768

"AWAY

The calcined product can be cold pressed and through Firing or sintering at temperatures below 1,700 ° C Moldings of high density are sintered with a small grain size, so that you get a refractory ceramic material receives «when certain additives are added to the aluminum oxide ceramic materials for use as tool cutting edges * lamp bulbs, ceramic Manufacture seals and the like at unusually low temperatures «These materials have properties which often exceed the favorable values. which conventionally transfer at higher temperatures have known methods obtained substances. The converted powder itself is because of the ultrafine particle size and the absence of agglomerates, which result in microscopically visible scratches on polished surfaces * particularly useful as a polishing agent.

In the previously known methods for producing oil alumina under ordinary conditions Aluminiumoxydhydrate be calcined or salts such as aluminum "sulfate or Hiitrat or other Alusniniutno ^ dübergangs" · form thermally decomposed * All of these methods require temperatures of greater than I 10O ⁰ C ₅ preferably to 1200 ⁰ C _e When the Ä'lumißiuaiöxyd is chemically treated of about 1200, for example, doping silica diirch J5ur preventing the crystal itwachstums * or- by reacting Aiuminiumchlorid with nitrogen dioxide, then heat treatment is required of above ilOÖ ° C * in a To produce product that consists essentially exclusively of "sC-ÄiuaiiriiuiaGxyd.

0DS820 / 1768

- Wm ORiGfMAL

The naturally occurring mineral diaspore can be converted into dL ^{-aluminum oxide below 500 °} C., but the mineral contains too many impurities and does not occur in such large quantities that it would be suitable for the production of pure, ultra-fine eO-aluminum oxide. Synthetic diaspore can be obtained hydrothermally under pressure, but the process is expensive and cumbersome and, moreover, allows undesirable crystallite growth during the complete conversion.

The AlurainiumoxydYorprodukt *, which is formed according to the invention in the jet mill, can be converted into oC-Alurainiumoxyd at temperatures below 1000 ° C Starting material preferably at 750 to 850 ⁰ C.

Before the conversion, the product initially contains XO to 20 % aluminum oxide in the form of crystallites with a particle size of less than 500 L. No other crystalline phase can be detected by X-ray diffraction * After calcining the product in air at atmospheric pressure, the content increases et-Älurainiurnoxyd at a calcination temperature in the range from about 700 to 80O ⁰ C to 50 to 80 % . At this point in time, a microcrystalline phase of aluminum oxide appears, which makes up 20 to 40 % . By continuing the calcination the ^ -Aluminluraoxydphas © disappears again and the oC- »Aluminum oxide phase increases accordingly. Upon reaching a temperature of 700 to IQOO ⁰ U (depends on the used Tliäsatzproduktr) kami's are all crystalline ot-alumina proved by asm Röntgenpulveröiagratais only kr ·

0 0 9 8 2 0/17 $ I.

195 A

These transitions and phases are caused by a thermal Difference analysis confirmed, showing that crystal and Phase changes take place at temperatures that are significantly lower than with conventional 'aluminum' oxide precursors.

In contrast to ά & ® novel product according to the invention, the USA conversion point from X -Alutainiumo ^ d to cC -Aluminium in known processes is at temperatures above 1000 ⁰ C «

It has been found that the properties of the preliminary product depend on the special aluminum salt or mixture that is fed to the high-temperature jet mill. In general, an optimum initial product contains a Maxiraaliaeiige of crystalline oC-alumina or amorphous "t-Älaminiurnoxydvorprodukt and transformed practically completely far below 1000 ⁰ C in

with a particle size below lyu um. The optimal © preliminary product is favored by an acidic environment. «The salts, solutions», hydrates or brines should therefore have a * pH value of less than 7> preferably less than 4. Second, the decomposition temperature of the aluminum acidic acid and the type of acid anion present are important. Relatively high grinding temperatures are required for aluminum sulfate, while input products based on aluminum nitride and aluminum chloride at a grinding temperature of & 76O ⁰ G usable result in preliminary products »

From the prominent ^ follows that as one ^ atzprodukt for dl "mill in question come 3

; 009820/1768 _{M0 0RlGINAL}

1 * Solid or melted Al'jrainiurs salts f ^ / equal

Example I) -J
2 * an aqueous / klumliiiusasalaiasuBS {trergietche example

3 · water-containing alumintmodefrictingprcäiskte * which from an aluminum salt solution and a replaceable base How do you get Äfflnjoniak at a pH value less than 6! be (compare Beiapiel%} * -

4, mixtures bydratisiert-er AltMmiiUHJCMqrde with ^ replaceable season or acids (compare example 2) ι and · *

5 * Aluaiiniuraoxyösolii from zevaetzparefö. Aiasgsngsverbindimgen

^T * md toasonisuc (irrelevant example

"The egg substitute could be, in the form of a solution., An AufsolilSBBBmi5ßg _{s of} a pasta or a partially dehydrated

Pestproäuktes' / © rfsahl ^ w @ rd®s _e The ..solids, Aufri., Solutions © üer 0el # weröea der- Mühle mit

ielui ^ of the most desirable product sufficient-Gesutoflxuligk & -W '? - ^ filled _a If the l «liSgyng example ine rsit Pempf bstrie! StiftifeFges ^ teiiacligtoeife gttesti-5C up to 300 ml / miMa v «sugweise © fcwa ISO up to 220 n & / m3D · Solids can ssit« iaer 0 @ S6hwlsidlgkelt ¥ os. 30 to> 3ö _f . preferably etisa 100 Ms 200 g / min are fed in «

The E & 0hteiDp «r & tuf-Str & hifflQhle -is ^ annoying under Verwfistättitg vtöi Waeserd ^ Bpf at siner i-sape ^ & tur i · ©» Ms 815 ^o C _e vcrcugmrelee 4 £ 5fels 5.4o®0 operated · In

H"! Fall is firm ÄliÄSilniWjsaltrataonialijdrat 20 eia-ö ^f ui? Aifcil © ühl @ Kit elßer Ges-cbwiMigkelt of 250 g / blii augsif-3liF ^ j ^ ater ^ srapf is la-die SÖSliie uater k of 9 # 1 s-tii © £ zagsM®s <atj »w« o @ i the T60 ° C aad the Auglafit ^ temperature 42? ° C

BATH

The feed product is put into the mill together with air introduced under a pressure of 7 to 14 atU "

One of the advantages of the method according to the invention lies in that washing as a special procedural step is no longer necessary and that the Aluralniuraoxyd is obtained free of impurities * The process does not introduce impurities »This is achieved through careful selection of the alurainium oxide precursors achieved «, the preferred input product for the Processes are aluminum salts, hydrous oxides, Hydrogels, brines and solutions. When a precipitant Is used, any decomposable base is suitable * but ammonia is readily available, low in price, and completely decomposed preferred by ammonium salts. Other less inexpensive preliminary products * which also still produce satisfactory results are mixtures of Alurainiumoxydhydrates or Intermediate forms of aluminum oxide with acids or ammonium salts or combinations of oxides, hydrogels, sols and Solutions with aluminum salts.

In the second step of the process according to the invention, the product coming out of the mill is converted into cL aluminum oxide ^{by heating to a temperature below 1000 ° C.} With an increase in the Kalzinierungatemperatur of 400 to 1000 ⁰ C, the crystallite size of the OL-Aluminiuraoxyds increases from 300 to about 1000 S.

The following examples are intended to provide a more detailed explanation of the invention, in which the process according to the invention is compared with unsuitable deviations from the conditions according to the invention.

009820/1768

BATH

example 1

The example shows by comparing that obtained by marrying of aluminum nitrate nonahydrate in a jet mill obtained product with aa by normal calcination Product obtained from aluminum nitrate nonahydrate »such as effective the method according to the invention is "

Example;

The jet milled product was obtained by direct milling of aluminum nitrate nonahydrate in a 20 cra high temperature jet mill. Steam was introduced into the mill with an inlet temperature of 760 ° C and an outlet temperature of 427 ° C. The solid aluminum nitrate was fed to the MtShIe at a rate of 250 g / rain under an air pressure of 10.5 atmospheres. The product contained 11 % cL aluminum oxide and amorphous oC and Jf aluminum oxide precursors. The product was calcined and cooled at a temperature of 95O ° C for 2 hours, whereupon the product was subjected to X-ray analysis. The product was found to be composed entirely of OOC-aluminiumoxide and to have a crystallite size of about 1,000 $. Chemical analysis proved that the product consisted of $ 99 * 95.

Comparison:

The advantages of the process according to the invention are made clear by a comparison in which the alurainlum trate nonahydrate was calcined under customary conditions. A ³ × sample of aluminum nitrate nonahydrate was calcined at temperatures of up to 1200.degree. C. for 2 hours. Material-. were taken at bosttestesi time intervals to read the Hiasöii.:. ·. : * sa,: ii -.- iins «itziÄi?; S and the Krlatallltgröle to jD« r largest proportion of ^

009820/1761

was present in the product at temperatures up to HOO ⁰ C. The OC aluminum oxide formed at 1000 to 1100 ^° C. had a crystallite size of more than 2000 S ₅ accordingly

about twice the particle size of the product obtained in the jet mill. The rapid dewatering in the mill prevents excessive crystal growth by removing up to 90 % of the volatile substances present, especially water, and the grinding action of the mill prevents agglomeration so that subsequent comminution is not necessary *

Example 2

This example shows the use of a mixture of hydrated alumina and ammonia salts or Nitric acid for the production of the invention Aluminum oxide product

A sample of commercially available aluminum oxide trihydrate (aluminum oxide C1) was mixed with 20% by weight of ammonium nitrate and the dry mixture was placed in a 20 cm jet mill. The mill was operated in the presence of steam at an inlet temperature of 76q ⁰ C and an outlet temperature of 427 ⁰ C. The salts were fed into the mill tü at a rate of 250 g / min in air at a pressure of 10.5 »The resulting product was calcined at a temperature of about 10QO ⁰ C and an examination showed that it was composed in wegentliehen pure d -Aluminum oxide.

In a further experiment, commercially available Qt aluminum oxide monohydrate was slurried with a sufficient amount of nitric acid ₉ so that the molar ratio of HNO ^ sAl ^ O, was samples of the monohydrate treated with on (for comparison) and the monohydrate treated with nitric acid (according to Er - -.

009820/178 0 _s * ₀ σ

finding) were ground under the conditions given above. Both products were calcined ^{at 1000 ° C. in air.} The untreated sample consisted essentially of ο-alumina, while the treated with nitric acid sample substantially entirely of oC-alumina "At 900 ⁰ C, the untreated material contained 95% ο -Aluminiumoxyd, while the subject of the Schwefelsäurebehandlüng product 4o% Ot Aluminum oxide and about 60 % ^ aluminum oxide. '

Example 3

This example shows the use of aluminum salt solutions.

Aluminum nitrate was dissolved in water to prepare% alumina to a solution having a content of _S T 2 wt.. The solution was fed to the high-temperature jet mill under the conditions specified in Examples 1 and 2. The product was calcined at a temperature of 975 ° C and consisted essentially entirely of OC-aluminum oxide O

example k

A series of tests was carried out in which the aluminum oxide from Pällungsprodukte, hydrogels and hydrates was produced.

In the first experiment, an aluminum nitrate solution with a content of 28% of the salt in the form of Al (NO,) was heated and reacted with 15 # ammonia solution, the latter being added so much that the pH measured with a pH meter The value of the slurry at the end at 60 ^° C. was 5 to 6. The slurry was for 8 hours

009820/1768 & AD ORIGINAL

aged at a temperature of 40 to 60 ° C and then fed to the jet mill under the conditions specified in Example 1 * The product was at calcined at a temperature of 975 ° C for 2 hours. An investigation showed * that it was essentially pure ot-aluminum oxide »

In a second experiment, a slurry was prepared as above from aluminum nitrate and ammonia, so that the Al ₂ Q, content was 5.9 % and the pH of the slurry was adjusted to 1.5 to 3 * 7 with ammonia. The slurry was fed into a high temperature jet mill operated with steam at an inlet temperature of 76O ⁰ C and an outlet temperature of 482 ° C under a pressure of 12.25 atm. * The product was isolated and for 2 hours at a temperature of Calcined at 95O ° C. The product was tested and found to be essentially pure ot-alumina.

In the third attempt, this series of experiments, the slurry produced in the first experiment was dewatered by filtration 'and the filter cake was dried at room temperature "The filter cake contained I7 OEW _s $ alumina and 21 wt.% Ammonium nitrate. For comparison, half of the filter cake was washed free of ammonium nitrate and dried. The washed and unwashed, dried samples were ground under the conditions given in Example 1. The samples were then calcined at a temperature of 1000 ^° C. for 2 hours. An examination of the products showed that the unwashed filter cow contained "ammonium nitrate, essentially pure" C "aluminum oxide had been obtained as a product.

009820/1768

BATH ORIGINAL

Example 5

This example shows the use of aluminum oxide sols for the production of the aluminum oxide product according to the invention. The preparation of the sol occurs in a similar manner as the preparation of the above Aufschlämmungj, but the Rüekflußbedingungen and the gas supply were adjusted so that the pH in the sol in the narrow between 3.7 and 4 ₉ 1 was *

An aluminum nitrate solution with a content of 7 »5% by weight of aluminum oxide was prepared. The solution was heated to reflux with gaseous aromaite passing through it at such a rate that any precipitate formed was immediately redissolved. These conditions were maintained until a pH of 3-9 was reached and a cloudy sol had formed. The sol was placed in a 20 cm high temperature jet mill operated with steam at an inlet temperature of 76O ⁰ C and an outlet temperature of 427 ° C. The sol was fed at a rate of 250 ml / min. The product was calcined at 95O ° C and examined. The product turned out to be pure ot - aluminum oxide,

Example 6 (comparative test)

The changes in the product occurring during the calcination were observed during the calcination of a product coming from the jet mill and obtained by one of the processes described above at a temperature between 400 and 1000 ^° C. over a period of 2 hours. The samples were calcined in a muffle furnace at 400, 600, 800, and 9OC ⁰ C. Another sample was calcined in a rotary kiln at a temperature of ⁰ C IQOO. The probes were taken periodically and based on their X-ray

009820/1788

powder diagram examined in more detail »The surface that Crystallite size and percent volatiles were also determined. The one in this attempt The measurement results obtained are summarized in the following table.

Tabel

Temperature ⁰ C: 400 600 800 900 1000 % A-Al ₂ O ₃ .13 18th 27 57 100 % ^ -Al ₂ O ₃ - - 40 41 - Surface, m / g 11.1 10.2 9.4 9.4 9.0 Crystal size, R 300 400 600 1000 800 % Fugitives 5.5 7.9 11.2 14.1 I4 _e 5

From the experimental results it is obvious that the content of .alpha.-aluminum oxide at temperatures between 800 and 900 ⁰ C rises sharply. The amount of ^ f-aluminum oxide increases between 800 and 900 ⁰ C to about 40 % , but a conversion into cL aluminum oxide takes place when the temperature reaches 1000 ⁰ C. The sample calcined at 1000 ^° C. in a rotary kiln showed a slower crystalline growth than the product calcined in the muffle furnace. The crystallite size of the ^{product heated to 1000 °} C. was only 800 Å. . "■■■ *

Example 7

This example shows? "The use of the according to the invention obtained Älyminiumoxids for the production of a refractory Materials. That calcined, according to any of the in den

ÖAD ORiGINAL QG962G / 1768

₁₅ ". 1 954 I.

The powder obtained in the method described in Examples 1 to 5 was mixed with polyvinyl alcohol as a binder and pressed cold under a pressure of 060 kg / cm to form a molded body with a density of 2.4 g / cm. The shaped body was fired under hydrogen at 1675 ° C. for 4 hours. The density of the fired body was

5 * 98 g / cm (determined porosimetrically) »

Example 8

An aluminum chloride solution containing about 7% by weight of AlgO was fed into the high-temperature jet mill at a rate of 150 ml / min under a steam pressure of 12.25 atmospheres at a temperature of 677.degree. The water vapor was introduced into the mill at a Einlaßteraperatur of 760 and introduced an outlet temperature of 510 ⁰ C »The product contained 10% crystalline CC-Aluminiumoxydo The product was then calcined at a temperature of 800 ° C for 2 hours and cooled and on the basis of the X-ray powder diffraction examined. The calcined product consisted entirely of ot-alumina. The product can be manufactured in the same purity as the starting materials. For example, a high-purity aluminum ingots with high purity hydrochloric au one äuße2 ^s st pure Äusgangsmateriai be implemented and during the procedure only © occurs in <8 minimal or no © accommodate VePtiBF-elnlgungsn to ₀ if one selects the appropriate materials for the devices used .

bath

O G S S 2 Ö / 1 7 S 8

Claims (12)

Claims VjL process for the production of a high-purity ot -aluminium oxide with a crystallite size of 700 to 1000 S, characterized in that one a) produces a starting mixture which is decomposable under the conditions of process step b), in aqueous solution, an aluminum salt with a pH value below 7 or one made from the salt Contains sol or a slurry obtained from the salt, b) the starting mixture is ground in a jet mill operated at 315 to 815 ° C., and c) the aluminum oxide-containing product leaving the mill is ^{calcined at a temperature of 700 to 1000 0} C « 2. The method according to claim 1, characterized in that that aluminum nitrate or aluminum chloride or an aqueous solution of these salts are used as the starting product ·. 3. The method according to claim 1, characterized in that that a water-containing aluminum oxide is used as the starting product, which is obtained from an aluminum nitrate solution precipitated with a decomposable base 1st. 4. The method according to claim 3 »characterized in that that the precipitation is carried out at a pH value below 6.0 009820/1768 . _1γ . 195Λ 1 5. The method according to claim 1, characterized in that that a mixture of water-containing as feedstock Aluminum oxide with a decomposable salt or a decomposable acid used 6. The method according to claim 1, characterized in that that an aluminum oxide sol which is produced from aluminum nitrate is used as the starting product. 7. The method according to claim 2, characterized in that water-containing aluminum nitrate is used as the starting product and the ground product at 925 Calcined to 975 ° C. 8. A process according to claim 2, characterized in that water-containing feedstock as aluminum chloride used and calcining the vermählene product at a temperature from 750 to 850 ⁰ C. 9. Process according to Claims 1 to 8, characterized in that the starting product is in the form of a solution a sol or a slurry is fed to the mill at a rate of 50 to 300 ml / min. 10. The method according to claim 1 for the production of a high-purity OC-aluminum oxide with a crystallite size of about 800 Å, characterized in that aluminum nitrate or a slurry or a sol made from aluminum nitrate is used in a jet mill in the presence of water vapor at an inlet temperature of about 76O ⁰ C and the aluminum oxide-containing product coming out of the mill is ^{calcined at a temperature of about 750 to 950 0} C, preferably for about 0.1 to 1 hour. 009820/17 68 11. The method according to claim 10, characterized in that that solid aluminum nitrate or an aqueous aluminum nitrate solution is used. 12. The method according to claim 10, characterized in that that a water-containing aluminum oxide is used as the starting product, which is obtained from an aluminum nitrate solution is precipitated by means of a decomposable base, or that an aluminum oxide sol is used which is composed of a Alurainium nitrate solution manufactured 1st. ugsiwy 009820/1768 MDORIGWAL