CA1117990A

CA1117990A - Alumina-containing calcium silicate and process for producing same

Info

Publication number: CA1117990A
Application number: CA000340473A
Authority: CA
Inventors: Akira Takahashi; Kenichi Oohashi
Original assignee: Osaka Packing Seizosho KK
Current assignee: Osaka Packing Seizosho KK
Priority date: 1979-11-23
Filing date: 1979-11-23
Publication date: 1982-02-09

Abstract

Abstract of the disclosure:
Alumina-containing calcium silicate being in the form of secondary particles, shaped bodies and a process for preparing the same, said secondary particles being composed of alumina-containing calcium silicate crystals having an index of crystallite antigrowth of at least 8 and interlocked with one another in the form of a globular shell, the particles being about 5 to about 70 µm in diameter, up to about 0.13 g/cm3 in apparent density and at least 10 g per particle in initial breaking load, and said shaped bodies being composed of the secondary particles.

Description

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Alumina-Containing Calcium Silicate and Process for Producing Same - This invention relates tD alurnina-containing calcium silicate and a process for producing the same, and more particularly to secondary particles of alumina-containing calcium silicate, shaped bodies of such secondary particles of alumina-containing calcium silicate, aqueous slurries of such secondary particles of alumina-containing calcium silicate and processes for producing these secondary particles, shaped bodies and slurries.
Calcium silicate has found ~ide use in industries ~ for refractory heat-insulating materials, fillers, ` adsorbents, reinforcing materials, building materials, etc. Since calcium silicate shaped bodies have the features of having high specific strength and heat-insulating properties and being light, highly dielectric and resistant to fire, they are expected to have wider application as inorganic materials. These characteristic properties appear attributable primarily to the form of calcium silicate crystals and to the structure of secondary ` particles of calcium silicate crystals in which the crystals are agglomerates and interconnected in a reticular ~ arrangement.
`~ We conducted research on the production and :; . !
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structure of secondary particles into which calcium s,ilicate crystals are agglomerated :Ln a peculiar mode and provlded secondary particles of needlelike crystals ~' of wollastonite group calcium silicate in the form of a porous shell which is globular to withstand external pressure most effectively with high stability and strength and whlch has a hollow interior and an outermost layer composed of closely interlocked crystals. We found that `-the secondary particles have high strength afforded by the globular shell-like form thereof and by the outermost layer of closely interlocked crystals and further possess ` an exceedingly low density because of their high degree of hollowness. We also found that shaped bodies with a very low density and high strength can be prepared ,' 15 from an aqueous slurry of such secondary particles merely by shaplng the slurry and drying the shaped mass. Based on these findings, we accomplished an invention, which has matured to U.S. Patent No.4,162,924.
` While the secondary particles described above have the distinct features that they are shaped to most . effectively withstand external pressure with high ` stability and high strength and have a remarkably low apparent density, we have carried out continued research on various crystals in an attempt to rep]ace the calcium silicate crystals constituting the secondary particles ' ~, .

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by other crystals withou~ impairing these features in any way, and unexpectedly found that alumina-contalning calcium silicate crystals are useful for reali~ing ~his entirely nove~ attempt and afford shaped bodies having further improved properties.
Accordingly an object of this invention is to provide secondary particles composed of alumina-containing calcium silicate crystals, shaped to withstand external forces with the highest stability and strength and having a remarkably low apparent density.
Another object of this invention is to provide shaped bodies composed of alumina-containing calcium ~ silicate crystals, having an extremely low density and `~ high strength and retaining great strength after having been fired at a high temperature of at least l,000C.
Another object of the invention is to provide aqueous slurries of alumina-containing calcium silicate crystals capable of giving such shaped bodies of alumina-containing calcium silicate crystals.
. .
Still another object of the invention is to provide processes for producing globular shell-like secondary particles of alumina-containing calcium silicate, and above-mentioned shaped bodies ahd slurries.
Stated more specifically, the present invention provides super llghtweight se^ondary partlcles of alumina-;..
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1, containing calcium silicate characterized in that the particles are composed of alur~ina~containing calcium silicate crystals having an index of crystallite antigrowth of at least 8, preferably at least 10, and interlocked with one another in the form of a globular shell, the particles being about 5 to about 70 ~m in . ~ diameter, up to about 0.13 g/cm3 in apparent density and at least 10 g per particle in initial breaking load.
The present invention also provides alumina-containing calcium silicate shaped bodies composed of such secondary particles as joined to one another, aqueous s].urries com-prising such secondary particles.as uniformly dispersed in water, and processes for producing these secondary particles, shaped bodies and slurries.
The term "index of crystallite antigrowth" as used in this specification refers to an index given by ~'`
the following equation:
Index of crystallite antigrowth (S) =DDa~XxDDb~x DxCDc, x 100 :~` where Da~ Db and Dc are the dimensions of the crystallite-size in the planes of (400), (040) and (001) of an alumina-containing calcium silicate crystal, such as alumina-containing xonotlite crystal, and Da', Db' and.Dc' are the dimensions of the crystallite-size in the planes of (400), (020) and (002) of the ~-wollastonite crystal 25 obtained by firing the crystal at 1,000C for three .` . .

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hours. Each of the dimensions (Da to Dc r ) can be determined by X-ray diff'ractiornetry and calculation f'rom the following equation (Scherrer's equation):
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where: D is the dimension ln crystallite-size, ~ is diffraction angle, K is 0.9, shape factor, ~ is 1.5418 A, the wavelength of x-rays -~ 10 (target CuK~), and is the half maximum line breadth of reflection plane.
Briefly stated, the index of crystallite r antigrowth indicates the degree of difficulty with which the crystallites of ~-wollastonite crystals grow when alumina-containing calcium silicate crystals are trans-formed into ~-wollastonite crDstals by being fired at 1,000C for 3 hours. Thus the index shows the degree of difficulty with which the size of the original crystals alter.
The term "initial breaking load" as used in ` the specif'lcation refers to the load applied to the ; globular shell-like secondary particle of alumina-contain-. ing calcium silicate crystals and ~ust sufficient to at least partially crack the globular shell of the particle.
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175~3 Accordingly the initial breaking load o~ 1~ g per particle means that when a progressively increasing load is applied to the secondary particle, the shell of the particle cracks at least partially under a load of 10 g. The initial breaking load can be determined by placing three secondary particles on a slide glass plate in an equilateral triangular arrangement, placing a covering glass plate on the particles and applying a gradually increasing load to the covering glass plate while observing the particles under an optical microscope to measure the load just sufficient to crack the shell of any one of the particles at least partially.
The apparent density of the secondary particles of this invention is meausred by the following method.
The water of a slurry of secondary particles is replaced by acetoneg and the mixture of the particles and acetone is dried at 80C for 24 hours to obtain a powder without breaking the particles. A W g quantity of the powder is placed into a beaker, and water is applied to the secondary particles with a burette. ~1hen .,he particles have just been impregnated with water (i.e. when the viscosity of the secondary particles abruptly rises), the quantity of water applied, V ml, is measured. The apparent density is calculated from the following equation.

; 25 Apparent density p(g/cm3) = W (g) W

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I'he secondary particles of alumina-contalning `
calcium-silicate crystals of this invention have the following characteristics.
,; . i (1) The alumina-containing calcium silicate crystals include alumina-containing xonotlite~ alumina-` containing tobermorite and like crystals. The alumina-containing calcium silicate crystal means one in which ~ . .
some of the constituent silicon atoms have been replaced by aluminum atoms. The amount of aluminum atoms sub-stituting for silicon atoms in the alumina-containing `t calcium silicate crystal is such that the ratio of silicon atoms to aluminum atoms is up to 5 : 1. Whlle alumina-containing calcium silicate crystals are-prepared by subjecting a siliceous material, lime material and alumina material to hydrothermal reaction, the mixture of the . starting materials, if containing alumina in excess of - a certain amount, will not afford alumina-containing calcium silicate crystals but give other crystals as of hydrogarnet, or the resulting calcium silicate crystals , will contain a limited amount of alumina, permitting an excess of alumina to remain as such or in some other form. Such limit of the alumina contained in the starting m~xture ~s us~ally about 8~ by weight. ~hen the starting , .

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mixture is subjected to hydrothermal reaction with its alumina content not exceeding the above limit, alumina-containing calcium silicate crystals are obtained.
If the reaction product is placed into a mixture of 1 part by weight of concentrated hydrochloric acid and 1 part by weight of distilled water and the resulting insolubles are sub~ected to X ray diffraction, no X ray peak will be observed for the alumina component of the starting mixture used. Furthermore, X-ray diffraction of the product will reveal a peak for calcium silicate crystals only. This means that the alumina material : in the starting mixture has been incorporated into the calcium silicate crystals as a component thereof.
The alumina content of the product can be determined by placing the reaction product into hydrochloric acid, collecting the resulting precipitate by filtration, placing the precipitate into an aqueous solution of sodium hydroxide, filtering the mixture and chemically analyzing the filtrate obtained.
2G Such alumina-containing calcium silicate crystals afford alumina-containing calcium silicate shaped bodies having the peculiar secondary structure to be described later, an extremely low density and high strength, retaining remarkably enhanced residual strength when fired at 1,000C and exhibiting a greatly reduced : , , , :,: ;
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, _ g _ linear shrinkage on drying. It is noteworthy that even when a siliceous ma~erial having a relatively high alumina content is used for the preparation of alumina-: containing calcium silicate crystals with an alumina content of 1 to 8% by weight, the crystals have an indexof crystallite antigrowth of less than 8 and give a shaped body which fails to exhibit noticeably enhanced residual strength when fired at 1,000C. Thus, only when an alumina material is used in combination with a siliceous material and lime material although siliceous materials usually contain an amount of alumina, the resulting alumina-containing calcium silicate crystals have an index of crystallite antigrowth of at least 8.
: (2) The alumina-containing calcium silicate crystals useful in this invention are at least 8 in the index of ;~
crystallite antigrowth. Because of this feature, the secondary particles of such crystals can be fired with deformation effectively inhibited and therefore provide shaped bodies having greatly improved thermal stability, namely outstanding residual strength.

(3) Observations under an electron microscope and an optical microscope reveal that the secondary particles are in the form of globular shells about 5 to about 70~m in outside diameter and made up of three-dimensionally interlocked calcium silicate crystals, at least 80% of . . , .' I

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the particles being 10 to 60 ~m in outside diameter.
The term "globular shell" is not uged in a strict sense but means that the particle appears globular or spherical and has a hollow interior. The globular shell may have projections or indentations over part of its surface.
The above appearance and outside diameter will be apparent from Fig. 1 which is an optical photomicrograph taken at a magnification of 400X and showing secondary particles of Example 1 according to the invention.
The hollow shell structure will be apparent from Fig. 2 which is a scanning-type electron photomicrograph taken at a magnification of 3,000X and showing the same secondary particles as above. Furthermore Fig. 2 and Fig. 3 ( electron photomicrograph at 15,000X) show that the secondary particles have an outer shell portion com-posed of needlelike crystals of alumina-containing calcium silicate as closely three-dimensionally interlocked with one another. Fig. 4 is an opt-ical photomicrograph taken at a magnification of lllOOX and showing a slice specimen prepared by embedding such secondary particles in a synthetic resin piece and microtoming the piece.
It is seen that the shells of the secondary particles are about 1 to about 25 ~m in thickness.

(4) The secondary particles of this invention are up to about 0.13 g/cm3, primarily in the range of 0.03 ;~ :
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to 0.13 g/cm3, in apparent denslty and are extrernely light.

(5) The secondary particles of this invention are at least 10 g-per particle in initial breaking load and are characterized by exceedingly high plasticity such that they are compressed to a flat shape free of any cracking even when sub~ected to a load of 20 g. It appears that the initial breaking load relates to the structure of the secondary particles, especially to ; the density of alumina-containing calcium silicate crystals forming the outer shell portion, as well as to the outside diameter and the apparent density of the particles. The shaped bodies prepared from these secondary partlcles with such high resistance to deformation have the feature that they retain extremely high residual strength when fired at a temperature of not lower than l,000C.

(6) An analysis with use of 2 thermobalance indicates that the~secondary particles have an ignition loss of up to about 10%.
The alumina-containing calcium silicate shaped bodies of this invention will now be described. The shaped bodies are composed of secondary particles of alumina-containing calcium silicate crystals joined to one another as compressed and deformed by the pressure applied for shaping. Because of this structure, the .

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globular shell-like form peculiar to the secondary particles and the unique characteristics of the component alumina-containing calcium silicate crystals, the shaped bodies have the features of possessing an extremely low density and high strength, exhibiting greatly reduced linear shrinkage when fired at 1,000C and retaining outstanding ` residual strength.
The aqueous slurries of alumina-containing calcium silicate crystals of this invention comprise secondary particles of this invention as uniformly dispersed in water.
The amount of water is usually at least 15 times, pre-ferably at least 18 times, the amount of the solids. The aqueous slurries, when shaped and dried, afford shaped bodies made up of alumina-containing calcium silicate crystals.
The secondary particles of alumina-containing calcium silicate crystals of thiS invention are prepared by the following process.
An amorphous siliceous material containing Na2O and/or K2O in a total amount of at least 0.5% by weight is admixe~ with a lime material and water to obtain a slurry in which 50% of the particles are up to 7 ~m in diameter. An alumina material is admixed with the slurry -~ to obtain a starting slurry containing water in an amount f at least 15 times the weight of the solids of the `
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starting slurry. The starting slurry is then sub~ected to hydrothermal reaction with application of pressure and heat and with stirring to prepare an aqueous slurry contalning numerous globular shell-like secondary particles of this invention as dispersed in water. The aqueous slurry is dried without breaking the globular " shell-like particles. Examples of useful lime materials are various and include quick lime. Also usable are slaked lime and carbide slug, but quick lime is most preferable. Useful siliceous materials are amorphous siliceous materials having an average particle size of up to 10 ~m and containing Na2O and/or K2O in a total i amount of at least 0.5% by weight. Such materials preferably contain at least 75% by weight of S~O2.
The Na2O and K2O contents can be determined by chemical analysis. Ex~emplary of useful siliceous materials is amorphous silica, namely so-called silicon dust or silica dust, resulting in large quantities from the production of metallic silicon or ferrosilicon as a by product.
Silicon dust or silica dust is usually about 0.05 to 0.5 ~m in average particle size, and is found to be amorphous or vitreous by X-ray diffraction. Chemical analysis of this material reveals that it comprises 0 to 7% by J
weight of ignition loss, 80 to 99% by weight of SiO2, 0 to 4% by weight of A12O3, and 0.5 to 4% by weight of ,:, ; , . .
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Na20 and/or K20. Silicon dust or silica dust, which ls a by-product, is relatively inexpensive and is one of preferable siliceous materials. Our research has shown that when silicon dust or silica dust containing at least about 0.5% by weight, preferably about 0.5 to about 4% by weight, of Na20 and/or K2O is used, additional use of a specified amount of an alumina-containing material in combination therewith imparts the resulting product higher strength after heating at l,000C than when the alumina-containing material is not used. In the present invention only when having at least 0.5% by weight of Na2O and/or K2O, a siliceous material may contain a small amount of crystalline silica.
When milk of lime having a sedimentation volume of at least 5 ml is used as the lime material, the secondary particles obtained have a bulk density of about 0.03 to about 0.07 g/cm3 and are exceedingly light-weight.
The sedimentation volume of milk of lime referred to in this specification is a value obtained by preparing 50 ml of milk of lime having a water to solids ratio by weight of 120:1, allowing the milk to stand for 20 minutes i in a cylindrical container 1.3 cm in diameter and at least 50 cm3 in capacity and measuring the volume (ml) of the resulting sedimen' of the particles of the lime. Thus a , ~ . ,, '' . ' - ' . .; , : ; ., , ~ ' ' , . ' ' , .
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't30 sedimentation volume o~ 5 ml means that the volume of such sediment is 5 ml, with 45 ml of a supernatant above ~-the sediment in the container. Accordingly 'che value - of the sedimentation volume is indicative of the degree of fineness of the lime particles in the water; the value~
if large, indicates that the lime particles are very fine.
Alumina materials use~ul in this invention are a wide variety of materials containing alumina. Typical of such materials are clays consisting primarily of at least one of minerals such as kaolinite, halloysite, hydrated halloysite, illite, pyrophyllite, dickite, sericite, attapulgite, etc.; mordenite, clinoptilolite, zeolite containing such minerals, etc.; alumina; etc.
The ratio of the lime material to the mixture of siliceous material and alumina material to be mixed therewith is suitable determined in accordance with the kind of the alumina-containing calcium silicate crystals desired. In the case of alumina-containing xonotlite, for example, the Ca/Si ~ Al atomic ratio is 0.80 to~1.3, preferably 0.85 ~to 1.1. The amount of alumina material to be used is about 1 to about 8% by weight, preferably about 1 to about 5% by weight, calculated as A1203 based on the combined amount of SiO2 and CaO in the mixture.
The staring slurry prepared contains water in an amount of at least 15 times, preferably at least 18 times, the `` ~ ~

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amount of the solids contained in the slurry. Although larger proportlons of water are in no way ob~ectionable, the amount of water is usually 20 to 100 times ~he amount of the combined solids.
For the preparation of the starting slurry of this invention, the mixture of sillceous material, lime material and water must be so treated that the starting slurry obtained contains dispersed particles 50% of which are up to 7 ~m in diameter. Such slurry can be prepared by adding water to the siliceous material and lime material in an amount at least equal to the amount of the solids of the materials by weight to prepare a slurry and treating the slurry, for example, with a fan turbine blade mixer (homomixer) equipped with a draft tube at about 8,ooo r.p.m. or some other useful agitator.
Alternatively the~starting slurry can be prepared by treating a mixture of water and the siliceous material, for example, with the above-mentioned homomixer and : admixing milk o~ lime with the treated mixture. These methods may be adopted in combination.
In this way the desired starting slurry can be prepared in which 50% by weight of the particles are up to 7 ~m in diameter (hereinafter expressed as "particles at cumulative weight percent of 50% are up to 7 ~m in diameter). This expression indicates the , ' .
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dispersibility of solid particles in water. To obtain the desired slurry, solid particles are dispersed in varying amounts of water by various dispersing methods to prepare slurries each 1,000 ml in quantity-and containing 35 g of solids, and the distribution of particle sizes in each of the slurries is measured according to the method of JIS A 1204-1970 to identify the slurry havlng the specified particle sizes. Particles of varlous materials generally tend to agglomerate into larger particles in water although this tendency varies with the kind and properties of the particles. For this reason, fine particles, when merely placed into water, usually will ~ not provide a uniform slurry but agglomerate in the water, ;' with the result that the particles at cumulative weight percent of 50% become larger in diameter. Slurries con-taining particles of such low dispersibility will present difficulty in the production of the shaped bodies contem-plated by the invention, ~hereas such difficulty is avoidable for the production of the desired product with use o~ a slurry in which fine siliceous particles have been dispersed in water by hlgh-speed or forced stirring as with a homomixer SQo that the particles at cumulative weight percent of 50% are up to 7 ~Im in diameter. Further accord-; ing to this invention, all the solid particles of the ~` 25 siliceous material, lime material and alumina material in . .
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The starting slurry is then subjected to hydrothermal reaction with application of pressure and heat and with continuous or temporarily interrupted stirring. The starting slurry can be stirred by any of various methods insofar as the solids in the slurry can be hold dispersed uniformly in the aqueous medium The slurry can be stirred, for example, with a mechanical device, air or liquid or by vibration. The reaction conditions such as pressure, stirring speed, etc. are suitably determined in accordance with the type of the reactor, stirring device and reaction product, etc.
The preferred pressure is usually about 8 to 50 kg/cm , while the preferred temperature is about 175 to about 264C. The reaction can be completed within a shorter period of time w-ith an increase in the pressure.
The hydrothermal reaction of the invention can be carried out continuously or batchwise. For continuous reaction, the starting slurry is continously forced into the reactor while drawing off the reaction product (slurry of calcium silicate crystals? therefrom at atmospheric ..
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pressure. Precautions should be taken not to impair the secondary particles when they are drawn off. It is al50 possible to reduce the proportion of water in the starting slurry for reaction in the reactor and to run off the . 5 reaction product with a specified quantity of water added thereto.
For the preparation of the alumina-containing calclum silicate~ it is possible to use a reaction accelerator, catalyst and inorganic fibers such as asbestos, ceramic fiber, alkali-resistant glass fiber, etc.
The hydrothermal reaction gives a slurry in which numerous secondary particles of alumina-containing calcium silicate crystals are dispersed in water. When dried without impairing the shape of the secondary particles, the slurry affords secondary particles of super-lightweight alumina-containlng calcium silicate of this invention.
The secondary particles of this invention thus obtained can be readily dispersed or suspended in water without impairing the structure thereof to prepare a slurry.
According to this invention, shaped bodies can be produced by shaping and drying a slurry comprising numerous secondary particles of alumina-containing calcium silicate crystals as dispersed in water and thus prepared. With this invention, it is also possible to produce I

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shaped bodies by shaping a mass of alumina-containing calcium silicate secondary particles of this invention as wetted with water and drying the shaped mass. In the former case, although the proportion of-water is variable over a wide range, water is used usually in an amount about 15 to about 100 times the amount of the solids by weight. In the latter case, an amount of water is about 3 to about 14 times the amount of the solids by weight.
When desired, various reinforcing materials can be incorporated into the aqueous slurry of secondary particles or the wet mass of secondary particles. A
wide variety of re~nforcing materials are usable, including inorganic fibers such as asbestos, rock wool, glass fiber, ceramic fiber, carbon fiber, metallic fiber, etc. and organic fibers such as pulp, hemp, rayon, polyacrylonitrile, polyporpylene, wood fiber, polyamide, polyester, etc.
These fibrous materials impart-greatly enhanced mechanical strength to the shaped body. Cements, gypsum, starch, binder of the phosphoric acid or water glass type, etc.
are usable for reducing or eliminating the shrinkage of the wet shaped mass during drying or for adding to the surface strength of the shaped body. Metal nets, metal wires or rods, etc. can also be incorporated into the shaped body. According to this invention, the aqueous .:

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slurry or wet mass o~ secondary particles can be made into shaped bodies as by injectlon molding, dewatering with a press or rolls, sheet making and extrusion The globular secondary particles of this invention have an extremely low apparent density and high resistance to heat. Suspensions of these particles in water or solutions can be easily made into shaped bodies, which are very useful as refractory building materials and heat-insulating materials. The secondary particles, as such or as suitably shaped, are also usable as fillers, adsorbents, deodorants, pigments, carriers for catalysts and for various chemicals. They are further useful for agricultural chemicals, coating compositions, tooth powders, etc.
The features of this invention will be described below in greater detail with reference to examples, in which the parts or percentages are all by weight unless otherwlse specified.
~ Example 1 Quick lime (43.3 parts, containing 95.2% of CaO) is slaked in hot water at 80C, and 4~5.8-parts of ferrosllicon dust 0.23 ~m in average particle slze (con-taining 92.3% of SiO2, 0-1% of Al2O3, 1.20% of K2O and 0.54% of Na2O) is added to the mixture. The resulting r1xture 15 treated ln a homomlxer for 20 mlnutes to . . . . .

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disperse the solids in water and obtain a slurry (the - particles at cumulative weight percent of 50% are 5.2 ~m in diameter). To'the slurry are added 10.9 parts of clay (containing 49.6% of SiO2 and 28.0% of A1203) con-- sisting primarily of halloysite and kaolinite and water to obtain a starting slurry (Ca/Si ~ Al atomic ratio:
0.86) containing water in 24 times the amount by weight of the solids. The starting slurry is sub~ected to hydrothermal reaction at saturated water vapor pressure 10 of 12 kg/cm at a temperature of 191C for 8 hours in an autoclave having an inside diameter of 15 cm, with a stirrer blade driven at 540 r.p.m. to obtain a slurry of crystals. The slurry is dried at 105C for 24 hours and thereafter subjected to X-ray diffraction. The diffraction pattern, shown as ~L-~R~ reveals no diffraction peak for the c,lay used as a-material but,indicates diffraction peaks ~or xonotlite crystals only (at d=
1.8455, 1.5259 and 2.3330 (A) ).
, A quantity of the dried particles are decomposed with an aqueous solution of hydrochloric acid (1 part of conc.~HCl and 1 part of water), and the resulting pre-cipitate is filtered off. An aqueous solution of sodium hydroxide is added to the precipitate~ and the mixture lS filtered. The separated cake is dried and then sub-jected to X-ray diffraction, which reveals no diffraction .~
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. peak for the clay. Chemical analysis of the filtrate gives 2.61% of A1203.
The above results of X-ray diffraction and chemical analysis show that some o~ the~Si atoms in the xonotlite crystals ~ormed by the hydrothermal reaction have been replaced by Al atoms in the clay, thus indicating that the crystals in the slurry are alumina-containing xonotlite crystals.
The same slurry of crystals as above is dried on slide glass and then photographed under an optical microscope at a magnification of 400X. The photograph reveals globular shell-like secondary particles 30 ~m in average outside diameter as shown in Fig. 1. An observa-tion of the particles by the reflection method reveals distinct contours and a substantially transparent interior.
~An amount of the dry slurry of crystals is fixed with a mixture of methyl methacrylate, ethyl methacrylate and n-butyl methacrylate resins and then microtomed to~a thickness of about 3 ~m. The slice is photographed under an optical microscope at a magnification ;
of l,lOOX. Fig. 4 is the photograph, which shows that the globular shells of particles have a thickness of 1 to 25 ~m, an average thickness of 3.8 ~m and an interior a ma~or portion of which is hollow. When observed under an electron microscope at a magnification of 15,000X as ~ ~ .

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~ 3 shown in Fig. 3, the shells are found to have numerous whiskers of alumina-containing xonotlite crystals on the surface. Further when observed under a scanning electron microscope as seen in Fig. 2 (3~000X), the-globular shells are found to have a hollow interior and to be made up of a large number o~ alumina-containing xonotlite crystals three-dimensionally interlocked with one another.
Fig. 5 shows some of the alumina-containing xonotlite crystals (primary particles) forming the secondary particles as observed under an electron micros~ope at a magnification of 5,000X. It is seen that ~he crystals are needlelike and about 1 to about 20 ~m in length and ~- about 0.05 to about 1.0 ~m in width. A differential thermal analysis of the crystals reveals hardly any peak, while an analysis with use of a thermo-balance shows a reduction at 750 to 820C. When~such crystals are fired at 1,000C for 1 hour and then subjected to X-ray diffraction, ~ the resulting diffraction pattern (P.cf. Fig. ~) indicates : that they are ~-wollstonite crystals. An observation of the crystals under an electron microscope reveals exactly the same form as alumina-containing xonotlite crystals .
and an extinction contour-line.
Table 1 æhows properties of the secondary part~cles.

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Table 1 Properties r~easurements Average particle diameter (~m) 30 Apparent density of secondary 0,12 particles (g/cm3) Average shell thickness of 3.8 secondary particles (~m) Initial breaking load Flattened but free of on secondary particles breaking under load of 10 g/particle or higher Index of crystallite Zl anti-growth Ignition loss (%) 6.5 True specific gravity 2.70 of crystals at 22C
t 15 With 90 parts (calculated as solids) of the same slurry of crystals as above are admixed 4 parts of glass fiber, 3 parts of portland cement and 3 parts of pulp, and the mixture is shaped under pressure by a press and then dried at 120C ~or 20~hours to obtain a shaped body I. The~same procedure as above is repeated except that a different pressure is applied to the mixture to obtain a shaped body II. Fig. 6 is a scanning electron photomicrograph taken at a magnification of 600X and showing a fractured surface of the shaped body I. The shaped 1-bodles are impregnated with the same mixture of resins as ~. used above and microtomed to a thickness of about 3 ~m, and the slices are observed under optical and electron ~ ' :

: ' ~17q~9~

microscopes, with the result that the particles are found identical with those of the slwrry of crystals in average particle size and shell thickness. Table 2 shows pro-perties of these shaped bodies.
- Table 2 ~ cimen No.
Properties -~~~~----____ I II
Density (g/cm3) 0.098 0.205 Bending strength (kg/cm2) 9.3 32.5 Sepcific strength 94.9 158.5 Linear shrinkage 0.31 0.22 on drying (%) The properties listed above are measured by the following methods.
Bending strength: According to JIS A 9510.
bending strength Specific strength: Given bD density ~The-specimens exhibit the properties shown in Table 3 when baked at 1,000C ~or 3 hours.
Table 3 ~ ecimen No.
Properties ~ I II
; Density (g/cm3) 0.095 0.201 ` Bending strength (kg/cm2) 6.2 22.6 Specific strength 65.3 112.4 Linear shrinkage 0.81 o.76 - on heating (%) Residual strength (%) 66.7 69.5 i.~

' ' . ,: ' , ~, .

9~3 The residual strength is calculated ~rom the following equation.
Residual strength (%) _ Bendin~ strength after bakin~ x 100 ~i Bending strength before baking ` Example 2 Quick lime (47.0 parts, containing 95.5% of CaO) is slaked in hot water at 80C, and 21.9 parts of - ~ ferrosilicon dust 0.24 ~m in average particle size (containing 92.5% of SiO2, 0.2% of A12O3~ 1033% of K2O and 0.62% of Na2O) is added to the mixture. The resulting mixture is treated in a homomixer for 20 minutes to disperse the solids in water and obtain a slurry (the particles at cumulative weight percent of 50% are 4.8 ~m in diameter). To the slurry are added 31.1 parts of clay (containing 68.1% of SiO2 and 20.8%
f A12O3) consisting primarily of illite and kaolinite and water to obtain a starting slurry (Ca/Si -~ Al atomic ratio: 0.98j containing water in 24 times the amount by ~ weight of the solids. The starting slurry is subjected - to hydrothermal reaction at saturated water vapor pressure of 12 kg/cm2 at~a temperature of 191C for 8 hours in the same autoclave as used in Example 1, with a stirrer blade driven at 112 r.p.m. to obtain a slurry of crystals.
The slurry is dried at 105C for 24 hours and thereafter analyzed in the same manner as in Example 1, with the result that the o~ystsle are alumina-contalning xonotlite I~

:- ~- . . - .. .. :

' ', :, . - ' ,, , ' crystals and alumina-containing tobermorite crystals mixed therewith. Subsequently the slurry is treated in the same manner as in Example 1 to obtain secondary particles with the properties shown in Table 4 below.
5 - Table 4 ~ Properties Measurements _ Average particle diameter (~m) 36 Apparent density3 of secondary 0.112 particles (g/cm ) Average shell thickness of 3.8 secondary particles (~m) Initial breaking loadFlattened but ~ree of break-; on secondary particlesing under load of 10 g/
particle or higher Index of crystallite 18 anti-growth Ignition loss (%) 8.8 ` True specific gravity 2.66 of crystals~at 22C
With 90 parts (calculated as solids) of the same slurry o~f crystals as abo-ve are admixed 4 parts of glass s `fiber, 3 parts of portland cement and 3 parts of pulp, and the mixture~ is shaped under pressure by a press and then~dried at 120C for 20 hours to obtain a shaped body I.
The same procedure as above is repeated except that a different pressure is applied to the mixture to obtain a shaped body II. Table 5 shows properties af these shaped - bodies.

"

.
, . . , :
-.

...

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Table 5 - ~ 5Q~cimen No.
Properties ~ I II
Density (g/cm3) 0.107 0.199 Bending strength (kg/cm2) 4.7 18.1 Specific strength 43.9 91.0 Linear shrinkage 0.41 0.10 on drying (%) The shaped bodies exhibit the properties shown in Table 6 below when baked at l,000C for 3 hours.
Table 6 ~~~-----____~pecimen No.
Properties ~
Density (g/cm3) 0.104 0.195 t~ 15 Bending strength (kg/cm2) 3.0 11.6 ~ Specific strength 28.8 59.5 : Linear shrinkage 0.90 o.67 ; on-heating (%) Residual strength (%) 63.8 64.1 Example 3 Quick lime (47.0 parts, containing 95.5% of ~ CaO) is slaked in hot water at 80C, and 33.7 parts of ; ferrosilicon dust 0.24 ~m in average particle size (con-taining 92.5% of SiO2, 0-2% o~ A1203, 1.33% o~ K20 and . 25 0.62% o~ Na20) is added to the mixture. The resulting ` mixture is treated in a homomixer for 20 minutes to :` disperse the solids in water and obtain a slurry (the ,. ~
~ .

'~ particles at cumulative weight percent of 50% are 5.4 ~m in diameter). To the slurry are added 19.3 parts of clay (containing 68.1% of SiO2 and 20.8~ of A1203) consisting primarily of illite and kaolinite and water to obtain a starking slurry (Ca/Si ~ Al atomic ratio: 0.98) con-taining water in 24 times the amount by weight of the solids. The starting slurry is subjected to hydrothermal reaction at saturated water vapor pressure of 12 kg/cm2 ; at a temperature of 191C for 8 hours in the same autoclave as used in Example 1, with a stirrer blade driven at 112 r.p.m. to obtain a slurry of crystals. The slurry is dried at 105C for 24 hours and thereafter analyzed in the same manner as in Example 1, with the result that the crystals are alumina-containing xonotlite crystals and a small amount of alumina-containing tobermorite crystals mixed therewith. Subsequently the slurry is treated in the same manner as in Example 1 to obtain secondary particles with the~properties shown in Table 7 below.
Table 7 PropertiesMeasurements ` Average particle diameter (~m) 31 Apparent densit~ of secondary 0.124 particles (g/cm~

Average shell thickness of3.7 secondary particles (~m) ` Initial breaking loadFlattened but free of on secondary particlesbreaking under load of 10 g/particle or higher . . ;. .

~L7~3V
~`

_ Properties _ _ _ Measurements :
Index of crystallite 24.5 anti~growth Ignition loss (%) 7~3 True specific gravity 2.69 of crystals at 22C
With 90 parts (calculated as solids) of the same slurry of crystals as above are admixed 4 parts of glass fiber, 3 parts of portland cement and 3 parts of pulp, and the mixture is shaped under pressure by a press and then dried at 120C for 20 hours to obtain a shaped body I. The same procedure as above is repeated except that a different pressure is applied to the 1 mixture to obtain a shaped body II. Table 8 shows pro-perties of these shaped bodies.
' Table 8 ,3~ecimen No.
Properties ~ I II
Density (g/cm3) 0.101 0.203 ; 20 Bending strength (kg/cm2) 8.1 27.3 : Speclfic strength 80.2 134.5 Linear shrinkage 0.31 0.12 on drying (%) The shaped bodies exhibit the properties shown ; 25 in Table 9 below when baked at 1,000C for 3 hours.

.
.
~ ''''''~ ' :

!

Table 9 ~~~~---_____~pecimen No.
:Propertles ~~
. Density (g/cm3) 0.097 0,198 Bending strength (kg/cm2) 5.3 17.2 Specific strength 54.6 86.9 : . Linear shrinkage 0.84 0.71 on heating (%) Residual strength (%) 65.4 63.o " 10 Example 4 Quick lime (47.0 parts, containing 9:5.5% of CaO) is slaked in hot water at 80C, and 44.2 parts of ferrosilicon dust 0.24 ~m in average particle size ~. (containing 92.5% of SiO2, 0.2% of A1203, 1.33% of i 15 K2O and 0.62% of Na2O) is added to the mixture. The resulting mixture is treated in a homomixer for 20 minutes to disper-se the solids in water and obtain a slurry (the partlcles at cumulative weight percent of 50% are 5.0 ~m in diameter):. To the:slurry are added

8.8 parts of clay (containing 68.1% of SiO2 and 20.8%
of A12O3) consisting primarily of illite and kaolinite and water to obtain a starting slurry (Ca/Si ~ Al atomic ratio: 0.98) containing water in 24 times the amount ., , I
by weight of the solids. The starting slurry is sub-25 jected to hydrothermal reaction at saturated water vapor pressure of 12 kg/cm2 at a temperature of 191C

,, .

,: :" ~ : ..... , : , .
, .

~ ~1 7~

for 8 hours in the same autoclave as used in ~xample 1, with a stirrer blade driven at 112 r.p.m. to obtain a slurry of crystals. The slurry is dried at 105C for 24 hours and thereafter analyzed in the same,manner as ' . 5 ln Example 1, with the result that the crystals are alumina-containing xonotlite crystals. Subsequently the slurry is treated in the same manner as in Example 1 to obtain secondary particles with the properties shown in Table 10 below.
- 10 Table 10 .. Properties _ _ _Measurements Average particle diameter (~m) 27 Apparent density, of secondary 0.121 particles (g/cm~) Average shell thickness of3.6 secondary particles ( ~m) Initial breaking load onFlattened but free of secondary particlesbreaking under load of : 10 g/particle or higher ` 20 Index of crystalllte 17.5 anti-growth ' Ignltion loss (%) 6.1 True speciflc gravity 2.71 of crystals at 22C
With 90 parts (calculated as solids) of the same slurry of crystals as above are admixed 4 parts of glass~fiber,~ 3 parts of portland cement and 3 parts of , pulp, and the mixture is shaped under pressure by a press .
.

. ~
and then dried at 120C for 20 hours to obtain a shaped body I. The same procedure as above is repeated except -- that a d:Lfferent pressure is applied to the mlxture to obtain a shaped body II. Table 11 shows properties of these shaped bodies.
Table 11 :: - = ecimen No.
Pro~erties -~~~~----___ I II
- - . ~
, Density (g/cm3) 0.102 0.203 . 10 Bending strength (kg/cm2) 9.4 32.2 Specific strength 92.2 158.6 Linear shrinkage 0.35 0.19 on drying (%) `I The shaped bodies exhibit the properties shown 15 in Table 12 below when baked at 1,000C for 3 hours.

Table 12 ecimen No.
Properties ' ~

20 ~Density (g/cm3) 0.099 - 0.197 ` Bending streng:th (k~g/cm23 6.3 21.9 Specific strength 63.6 111.2 -~

Linear shrinkage 0.82 0.74 on heating (%) Residual strength (%) 67.o 6~8.o Example 5 ~ Ferrosilicon dust 0.24 ~m in average particle ize (44.2 pDrts, containing 92.5~ f SiO2~ 0.2% of ' ., `
-:, A12O3, 1.33% of K2O and 0.62% of Ma2O) is treated in a homomixer for 20 minutes to disperse the dust in water - and obtain a slurry (the particles at cumulative weight , percent of 50% are 4.7 ~m in diameter). To the slurry ~is added a mixture prepared by slaking quick 1-~me (47.0 parts, containing 95.5% of CaO) in water at 80C. To `` the resulting mixture are added 8.8 parts of clay (con-taining 68.1% of SiO2 and 20.8% o~ A12O3) consisting primarily of illite and kaolinite and water to obtain 10 a staring slurry (Ca/Si ~ Al atomic ratio: 0.98) con-taining water in 2ll times the amount by weight of the solids. The starting slurry is subjected to hydrothermal reaction at saturated water vapor pressure of 12 kg/cm2 at a temperature of 191C for 8 hours in the same autoclave 15 as used in Example 1, with a stirrer blade driven at 112 r.p.m. to obtain a~slurry of crystals. The slurry is dried at 105C for 24 hours and thereafter analyzed in the same manner as in Example 1, with the result that the crystals are alumlna-containing xonotlite cry-stals.
: 20 Subsequently the slurry is treated in the same manner ~as in Example 1 to obtain secondary particles with the properties shown in Table 13 below.

~ .
. :

.

Table 13 Properties ~
. Average particle diameter (~m) 26 ,; Apparent densitx of secondary0.120 particles (g/cm~) ` Average shell thickness of 3.6 secondary particles (~m) : - Initial breaking loadFlattened but free of on secondary particlesbreaking under load of lO g/particle or higher Index of crystallite 17 anti-growth Ignition loss (%) 5.7 True specific gravity 2.71 of crystals at 22C
t With 90 parts (cal~culated as solids) of the same slurry of crystals as above are admixed 4 parts of glass fiber, 3 parts of portland cement and 3 parts of pulp, and the~mixture is shaped under pres~sure b:y a press and then dried at 120C for 20 hours to obtain a shaped body I. The same~procedure as above is repeated except that a different pressure is applied to the mixture to obtain a shaped body II. Table 14 shows properties of these shaped bodies.

I

I

, ., ~ . . i . . . :
`': ''. ~ ,:,,`
:, :: i , .
. . .
, - \
3~

Table 14 Specimen No.
:Properties ~ I ~
Density (g/cm3) 0.099 0.207 5 . Bending strength (kg/cm2) 9.4 30.8 Specific strength 94.9 148.3 Linearshrinkage 0.34 0.18 on drying (%) The shaped bodies exhibit the properties shown in Table 15 below when baked at 1,000C for 3 hours.
Table 15 ~ S~ecimen No.
- Properties = I II
Density (g/cm3) 0.096 0.201 ; 15 Bending strength (kg/cm ) 6.2 21.6 Specific strength 64.6 107.5 Linear shrinkgae 0.79 0.68 on heating (%) Residual strength (%) 66.o 70.1 Example_6 ~ Ferrosilicon dust 0.25 ~m in average particle size (45.5 partsy containing 93.3% of SiO2~ 0,2% of A1203, 1.68% of K20 and 0.74% of Na20) is treated in a homomixer for 20 minutes to disperse the dust in water and obtain a slurry (the particles at cumulative weight ~` percent of 50% are 5.9 ~m in diameter). To the slurry is added a mlxture prepared by slaking quick lime (45.9 ~l~l17~9~3 : parts, containing 95.5% of CaO) ln water at 80C. To the resulting mixture are adcled 6.6 parts of clay (containing 49.3% of SiO2 and 27.5% of A1203) consisting primarily o~ halloysite and kaolinite, 2.0 parts of rock wool and water to obtain a starting slurry (Ca/Si ~ Al atomic ratio: o.g8) containing water in 24 times the amount by weight of the solids. The starting slurry is sub-jected to hydrothermal reaction at saturated water vapor pressure of 12 kg/cm at a temperature of 191C ~or 8 hours ln the same autoclave as used in Example 1, with a stirrer blade driven at 112 r.p.m. to obtain a slurry o~ crystals. The slurry is dried at 105C for 24 hours and thereafter analyzed in the same manner as in Example 1, with the result that the crystals are alumina-containing xonotlite crystals. An observation of the slurry of crystals under an optic-al mi~croscope in the same manner as in Example 1 reveals globular secondary particles 27 ~m in average ou~side diameter and partly joined to rock wool fiber. Subsequently the slurry is treated in the same manner as in Example 1 to obtain secondary particles with the properties shown in Table 16 below.
Table 16 ; Properties Measurements _ _ Average particle diameter (~m) 27 Apparent densit~ of secondary 0.118 particles (g/cm~) 1.
~ , . .. ...

- ~ i '7~<3i~
.
`:.

. ~
; Pro~erties Measurements Average shell thickness of 3.5 secondary particles (~m) : Initial breaking load Flattened but free of on secondary particles breaking under load of ` - 10 g/particle or higher Index of crystalllte 18 anti-growth Ignition loss (%) 5.9 True specific gravity 2.72 - of crystals at 22C

With 92 parts (calculated as solids) of the same slurry of crystals as above are admixed 2 parts of - glass fiber, 3 parts of portland cement and 3 parts of pulp, and the mixture is shaped under pressure by a t press and then dried at 120C for 20 hours to obtain a shaped body I. The same procedure as above is repeated except that a differe-nt pressure is applied to the mixture to obtain a shaped body II. Table 17 shows properties of these shaped bodies.
Table 17 ~ Specimen No.
Properties Density (g/cm3) o.og7 0.198 Bending strength (kg/cm ) 9.7 33.9 " Speclfic strength 100.0 171.2 Linear shrinkage 0.41 0.20 on drylng (%) .

.
.

3~

:.
The shaped bodies exhiblt the properties shown in Table 18 below when baked at 1,000C ~or 3 hours.
Table 18 ~ cimen No.
Properties ~ I II
_ _ Density (g/cm3) 0.0940.195 Bending strength (kg/cm ) 6.5 23.8 Specific strength 69.1,122.1 Linear shrinkage o.83 0.70 on heating t%) Residual strength (%j 67.o 70.2 Example 7 Ferrosilicon dust 0.24 ~m in average particle ,~ size (47.0 parts, containing 92.5% of SiO2, 0.2% of Al2033 1.33% of K20 and 0.62% of Na20) is treated in a homomixer for 20 mlnutes to disperse the dust in water ~ and obtain a slurry (the particles at cumulative weight : percent of 50% are 5.2 ~m in diameter). To the slurry is added a mixture~pre,pared by slaking quick lime (47.0 parts, containing 95.5% of CaO) in water at 80~C. To the resulting mixture are added 4.5 parts of clay (containing 68.1% of SiO2 and 20.8% of A1203) consisting primarily of illite and kaolinite and water to obtain a starting slurry (Ca/Si ~ Al atomic ratio: 0.98) containing water ~ 25 in 24 times the amount by weight of the solids. The starting slurry is subJeoted to hydrothermal reaction ., , . '' ` " ~ ;'' .-~. , .

_ 41 -at saturated water vapor pressure of 12 kg/cm2 at a temperature of 191C for 8 hours in the same autoclave as used in Example 1, with a stirrer blade driven at 112 r.p~m. to obtain a slurry of crystals. The slurry . 5 is dried at 105C for 24 hours and thereafter analyzed in the same manner as in Example 1, with the result that the crystals are alumina-containlng xonotlite crystals. Subsequently the slurry is treated in the same manner as in Example 1 to obtain secondary particles 10 with the properties shown in Table 19 below.
Table 19 Properties _Measurements Average particle diameter (~m) 29 Apparent density of secondary 0.109 particles (g/cm~) Average shell thickness of3.6 secondary particles (~m) Initial Breaking load onFlattened but free of secondary particlesbreaking under load of 10 g/particle or higher Index of crystallite 17 antl-growth Ignition loss (%) 6.0 True specific gravity 2.74 of crystals at 22C
With 90 parts (calculated as solids) of the i ~ same slurry of crystals as above are admixed 4 parts of glass fiber, 3 parts of portland cement and 3 parts of : - 42 -; pulp, and the mixture is shaped under pressure by a press - and then dried at 120C for 20 hours to obtain a shaped : ~ ~ody I. The same procedure as above is repeated except that a different pressure is applied to the mixture to obtain a shaped body II. Table 20 shows properties of these shaped bodies.
, Table 20 ~ pecimen No.
Properties ~~~~~ - ---_____ I II
Density (g/cm3) 0.103 0.202 - Bending strength (kg/cm2) 8.9 29.8 Specific strength 86.4 147.5 Linear shrinkage 0.33 0.21 . on drying (%) The shaped bodies exhibit the properties shown in Table 21 below when baked at 1,000C for 3 hours.
Table 21 ~ imen No.
Properties -- _ I II
Densi~y (g/cm3) 0.100 0.198 Bending strength (kg/cm ) 5.8 19.1 Specific strength 58.o 96.5 Linear shrinkage o.89 0.73 on heating (g) Resldual strength (%) 65.2 64.1 ., .
~.

A

' ' ' ~ ' .

!

- 1~ 3 -Exarnple 8 - Quick lime (47.0 parts~ containing g5.5% of CaO) is slaked in hot water at 80C and treated in a homomixer for 3 minutes in watex to obtain a milk o~ lime having a sedimentation volume of 17 ml. 43 parts of ferrosilicon dust 0.24 ~m in average particle size (containing 92.5%
of SiO2, Q-2% of A12O3, 1.33% of K2O and 0.62% of Na2O) is treated in a homomixer for 20 minutes to disperse the dust in water to obtain a disperaion. The milk of lime is added to th~e ~ispersion to produce a slurry (the particles at cumulative weight percent of 50% are 4.0 ~m in diameter). To the slurry are added 6.7 parts of clay (containing 68.1% of SlO2 and 20.8% of A12O3) con-sisting primarily of illite and kaolinite and water to obtain a starting slurry (Ca/Si + Al atomic ratio: o.98) containing water in 50 times the amount by ~!eight ~o-f the solids. The starting slurry is sub~ected to hydrothermal react-ion~at saturat~ed water vapor pressure of 12 kg/cm at a temperature of 191C for 8 hours in the s2me autoclave ,~
as used in Example 1, with a stirrer blade~driven at~112 r.p.m. to o~btain a slurry of crystals. The slurry is dried at 105C for 24 hours and thereafter analyzed in the same manner as in Example 1, with the result that the crystals are alumina-containing xonotlite crystals.
Subsequen~ly the slurry is treated in the same manner as ': ' :
,, :. . , , ~ ' . ' .
;. :

- 44 ~

in Example 1 to obtain secondary particles with the pro-perties shown in Table 22 below.
Table 22 Pro~erties Measurements ........ . .. .. _ .....
. 5 Average particle diameter (~m) 28 Apparent densit~ of secondary 0.054 particles (g/cm ) Average shell thlckness of 2.3 secondary particles (~m) Initial breaking load on Flattened but free of secondary particles breaking under load of - lO g/particle or higher Index of crystallite 18 anti-growth Ignition 1QSS (%) 5.8 :~ True specific gravity 2.73 `. of crystals at 22C
With 88 parts (calculated as solids) of the same . slurry of crystals~as above are admixed S parts of glass flber, 3 parts of portland cement and 4 parts of pulp, and the mixture is shaped under pressure by~a .press and then dried at 120C ~or 20 hours to obtain a shaped body I.
The samè pr~ocedure as above :is repeated except that a .
different pre:ssure is applied to the mixtu~e to obtain a shaped body II. Table 23 shows properties of these shaped bodies. .
- , !

: :
, .

, - .. . .

~ . i ;
., !, . ` ' "
' .'' . . :.
'` , ' ~ . ' 7~<3~) -- ~5 --Table 23 ecimen No.
Pro~erties ~ ~ I II
Density (g/cm3) 0.056 0.084 Bending strength (kg/cm2) 3.1 8.9 Specific strength 55.4 106.0 Linear shrinkage 0.37 0.18 on drying (~) The shaped bodies exhibit the properties shown in Table 24 below when baked at 1,000C for 3 hours.
- Table 24 ~ lmen No.
Properties ~
Density (g/cm3) 0.052 0.080 Bending strength (kg/cm2) 2.0 5.8 Specific strength 38.5 72.5 Linear shrinkage 0.87 0.71 on heating t%) Residual strength`(%) 64.5 65.2 Comparison Example 1 Quick lime (47.0 parts, containing 95.5% o~
CaO) is slaked in hot water at 80C, and~53.0 parts of ferrosilicon dust 0.24 ~m in average particle size (con-taining 92.5% of SiO2, 0.2% of A12O3, 1.33% of K2O~and 0.62% of Na2O) ls treated in a homoml~er for 20 minutes - in water to produce a dispersion. Then the resulting dispersion is mixed with the above slaked lime to obtain ,.'' `, , , '" ''` ' ` ': ,:

., ~ . ,

9~3 a slurry (the particles a~ cumulative weight percent of 50% are 4.8 ~m in diameter). Subsequently water i8 added to the slurry to obtaln a s~arting slurry, which is subjected to hydrothermal reaction at saturated water 5 vapor pressure o~ 12 kg/cm2 at a temperature Or 191C
for 8 hours in the same autoclave as used in Example 1, with a stirrer blade drlven at 112 r.p.m. to obtain a slurry of crystals. The slurry is dried at 105C for 24 hours and thereafter analyzed in the same manner as

10 in Example 1, with the result that the crystals are found to be xonotlite crystals (having diffraction peaks at 1.8410, 1.5229 and 2.3406 (A) ). Subsequently the t slurry is treated in the same manner as in Example 1 to obtain secondary particles with the properties shown 15 in Table 25 below.
Table 25 _Properties _ Measurements Average particle diameter ~(~m) 26 - Apparent densit~ of secondary 0.122 20 particles (g/cm~) Average shell thickness of 3.6 ! secondary particles (~m) Initial breaking load onFlattened but free of secondary particlesbreaking under load of 10 g/particles or higher ~ 25 Index of crystallite 2.5 ant1-growth .

Properties _ Measurements Ignition loss (%) 5.8 True specific gravity 2.76 of crystals at 22C
5 . With 90 parts (calculated as solids) of the same slurry o~ crystals as above are admixed 4 parts of glass fiber, 3 parts of portland cement and 3 parts of ` pulp, and the mixture is shaped under pressure by a press and then dried at 120C for 20 hours to obtain a shaped body I. The same procedure as above is repeated except that a different pressure is applied to the mixture to : obtain a shaped body II. Table 26 shows properties of these shaped bodies.
Table 26 ~ ~ 4L_~imen No.
Properties ~
Density (-g/cm3) 0.107 0.206 Bending strength (kg/cm2~ 4.2 15.4 $pecific strength 39.3 ~74.8 Linear shrinkage 0.41 0.17 on drylng (%) : The shaped bodies exhibit the properties shown in Table 27 below when baked at 1,000C for 3 hours.

.
." I

, I
- I
.. ~. '. , '.'~. - ' , ,.~ . : , ' '' ' ~ ' :

- ~8 -Table 27 ~~~~~~----_SL~imen No.
Properties ~ I II _ Density (g/cm3) 0.103 0.200 Bending strength (kg/cm2) 1.4 5.0 Specific strength 13.6 25.0 Linear shrinkage 1.20 0.99 on heating (%) Residual strength (%) 33.3 32.5 Comparison Example 2 Quick lime (47.0 parts, contain~ng 95.5% of CaO) is slaked in hot watér at 80C, and 44.2 parts of ferrosilicon dust 0.24 ~m in average particle size t~ (containing 92.5% of SiO2, 0.2% of A1203, 1.33% of K2O
and 0.62% of Na2O) is added to the mixture to obtain a 15 slurry (the particles at cumulative weight percent of 50% are 8~2 ~m ln diameter). To the slurry are added ; 8.8 parts of clay (containine 68.1% of SiO2 and 20.8% of A12O3) consisting primarily of illite and kaolinite and water to obtain a starting slurry (Ca/Si + Al atomic ratio:
o.98) containing water in 24 times the amount by weight of the solids. The starting slurry is sub~ected to hydrothermal reaction at saturated water vapor pressure of 12 kg/cm2 at a temperature of 191C for 8 hours in the ~ same autoclave as used in Example 1, with a stirrer blade driven at 112 r.p.m. to obtain a slurry.

.
.~ .

., - : .

.~.`' ' ' ,' ', , ,, With 90 parts (calculated as solids) of the slurry are admlxed 4 parts of glass fiber, 3 parts o~
: portland cement and 3 parts of pulp, and the mixture is shaped by a press, but since the resulting mass has a 5 low ability to retain its shape, it is imposslble to obtain a shaped body havlng a density of about 0.1 g/cm3.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Super-lightweight secondary particles of alumina-containing calcium silicate characterized in that the particles are composed of alumina-containing calcium silicate crystals having an index of crystallite anti-growth of at least 8 and interlocked with one another in the form of a globular shell, the particles being about 5 to about 70 µm in diameter, up to about 0.13 g/cm3 in apparent density and at least 10 g per particle in initial breaking load.

2. Secondary particles as defined in claim 1 wherein the alumina-containing calcium silicate crystals have an index of crystallite antigrowth of at least 10.

3. Secondary particles as defined in claim 1 wherein the alumina-containing calcium silicate crystals are needlelike crystals of alumina-containing xonotlite.

4. Secondary particles as defined in claim 1 wherein the alumina-containing calcium silicate crystals are needlelike crystals of alumina-containing xonotlite and other calcium silicate in mixture therewith.

5. An aqueous slurry of calcium silicate crystals comprising the secondary particles defined in claim 1 and uniformly dispersed in water.

6. An aqueous slurry as defined in claim 5 which contains a reinforcing material.

7. An aqueous slurry as defined in claim 6 which contains an inorganic fiber as joined to the secondary particles.

8. A shaped body of alumina-containing calcium silicate characterized in that the shaped body comprises super-lightweight secondary particles of alumina-containing calcium silicate jointed to one another and composed of alumina-containing calcium silicate crystals,the calcium silicate crystals having an index of crystallite anti-growth of at least 8 and being interlocked with one another in the form of a globular shell, the particles before shaping being about 5 to about 70 µm in diameter, up to about 0.13 g/cm3 in apparent density and at least 10 g per particle in initial breaking load.

9. A shaped body as defined in claim 8 wherein the alumina-containing calcium silicate is an alumina-containing xonotlite.

10. A shaped body as defined in claim 8 wherein the alumina-containing calcium silicate is a mixture of alumina-containing xonotlite crystals and other calcium silicate crystals.

11. shaped body as defined in claim 8 which contains a reinforcing material as uniformly dispersed therein.

12. A shaped body of .beta.-wollastonite prepared by firing the shaped body defined in claim 8 at 800 to 1,050°C.

13. A process for preparing an aqueous slurry of alumina-containing calcium silicate crystals defined in claim 5 characterized by mixing together water, a lime material and an amorphous siliceous material con-taining Na2O and/or K2O in a total amount of at least 0.5% by weight, treating the resulting mixture so that 50% of the particles contained therein are up to 7 µm in diameter, admixing an alumina material with the treated mixture to obtain a starting slurry containing water in an amount of at least 15 times the amount of the solids in the slurry by weight and subjecting the starting slurry to hydrothermal reaction with application of heat and pressure and with stirring.

14. A process as defined in claim 13 wherein the alumina material is at least one of clay, zeolite and alumina.

15. A process as defined in claim 13 wherein the alumina material is used in an amount of about 1 to about 8% by weight, calculated as A12O3, of the combined amount of SiO2 and CaO contained in the siliceous material, lime material and alumina material.

16. A process for preparing the secondary particles defined in claim 1 characterized by drying the aqueous slurry of alumina-containing calcium crystals defined in claim 5.

17. A process for preparing a shaped body of alumina-containing calcium silicate characterized by shaping the aqueous slurry of alumina-containing calcium silicate crystals defined in claim 5 and drying the shaped mass.

18. A process for preparing a shaped body of alumina-containing calcium silicate characterized by shaping the aqueous slurry of alumina-containing calcium silicate crystals defined in claim 6 and drying the shaped mass.

19. A process for preparing a shaped body of .beta.-wollastonite characterized by firing the shaped body of alumina-containing calcium silicate defined in claim 8.