Method for making improved ceramic cement compositions containing a dispersed seeded phase and a method and apparatus for producing seed crystals

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of ceramics, and more specifically to a cementitious composition containing a dispersed seeded phase and a method and apparatus for producing seed crystals.

BACKGROUND OF THE INVENTION

Concrete is one of the most ubiquitous of all structural materials, consisting generally of aggregates, such as rock or gravel, bound together in a cement matrix. While the aggregate phase comprises about 80% of the volume of the concrete, it is the cement binder phase that is most important regarding the physical properties and ultimate performance of the concrete.

There is a wide variety of different cements, including organic polymer cements, amorphous cements, and ceramic cement compositions. Ceramic cements are generally mixtures of water and reactive metal oxides that undergo chemical reactions causing them to harden and fasten after they are mixed and allowed to set. In addition to providing the binding matrix for concrete, cements have a variety of familiar uses, such as glues or adhesives for bonding porous materials, providing the bonding layer that holds bricks together to form walls, and as structural building materials such as patio or garage slabs. The cement of choice for the majority of commercial uses is Portland cement, a mixture of water and calcined lime (CaO) and silica (SiO

2

)-containing minerals. Upon curing, the primary constituents of Portland cement are dicalcium silicate (2CaO·SiO

2

), tricalcium silicate (3CaO·SiO

2

), and tricalcium aluminate (3CaO·Al

2

O

3

) phases and a ferrite phase containing calcia (CaO) and alumina (Al

2

O

3

). In commercial Portland cement, none of these phases are chemically pure; rather, they are solid solutions with such impurities as Mg and Al dispersed throughout.

Portland cement has the commercial advantage of being relatively cheap to produce and easy to mix and pour. Part of the reason Portland cement is so cheap is because the silica-containing mineral component may come from a wide variety of sources, usually silica-containing clays, and also because these clays are not required to be especially pure or consistent.

Portland cement also suffers from some disadvantages, with inconsistency of the physical properties of the cement being chief among them. The inconsistencies arise from the inherent inconsistency of the source materials, both in composition and quality. Typically, the raw constituents of Portland cement are ground clinkers containing hydraulic calcium silicates of varying compositions, calcium sulfates, and also various aluminates, manganates, and other impurities present in varying and uncontrolled amounts. Moreover, there is no real control of the grinding process, yielding cement powders with extremely variable particle size distributions (PSDs). The lack of consistency of the compositions and PSDs of the raw materials relates directly to a lack of consistency in the physical properties of the resultant Portland cement.

Portland cement also has the disadvantage of having a relatively high viscosity. While it is well adapted to pouring and spreading, Portland cement is too thick for most pumping and/or spraying operations. Another disadvantage of Portland cement is that it does not readily bond to itself. Portland cement-containing structures, such as cement driveways or road segments, must be formed in essentially one step. If there is an interruption in the forming of a Portland cement body sufficient to allow the cement to begin to cure, a structural discontinuity or “cold joint” can result. Moreover, Portland cement cannot be used to patch a Portland cement structure absent costly and time consuming surface pre-treatment at the patch interface.

Portland cement also has the limitation of having a slow setting or “drying” time, during which the cement remains plastic and may be easily deformed. While the cement sets up and hardens, it is subject to damage and deformation by vandals, animals, and the elements; moreover, until the cement hardens it cannot support a load and in fact must itself be supported. This results in a potentially costly “sit and wait” period during which further construction depending on the structural strength of the freshly poured cement form is necessarily suspended.

Another important limitation of Portland cement is that it is relatively soft, and is therefore not suited for those applications requiring a very hard surface, body, or bond. Portland cement also has limited toughness, relatively low tensile and fracture strength, and is relatively quickly worn down. Portland cement is also fairly porous and permeable to liquids, and thus quickly suffers from the deleterious effects of water intrusion and chemical degradation, such as from entrapped water expanding upon freezing and from seasonal exposure to de-icing salts.

There are other ceramic cements available that are tougher, harder, stronger, less porous, and/or chemically more stabile. For example, phosphate cements, resin-modified cements, and carbon-fiber composite cements are all harder and tougher than Portland cement. These cements also have the advantages of having more consistent and reliable physical properties. However, these cements have the disadvantages of being much more expensive and in much shorter supply than Portland cement. Hence, there is a need for a method of controlling the consistency of the physical properties of Portland cement and for altering the physical properties as desired. The present invention is directed at satisfying this need.

SUMMARY OF THE INVENTION

One form of the present invention contemplates controlling the physical properties of cement by adding a predetermined amount of a second phase to the cementitious precursor. The second phase is added in the form of seed crystals having controlled sizes, shapes, and compositions. Upon curing, the seed crystals provide growth sites for a second phase in the cement body. Curing is accelerated by the presence of the seed crystals. Control of the physical properties of the resultant cement is achieved by controlling its microstructure through the morphology, orientation, distribution and growth of the seed crystals.

One object of the present invention is to provide an improved method of producing a cement.

Another object of the present invention is to provide an improved method of producing small spherical particles via precipitating them in a drop-tube.

Still another object of the present invention is to provide an improved method of producing fine catalyst particles having high surface-area-to-volume ratios.

Yet another object of the present invention is to provide an improved method of coating particles and of making compounds and/or composites from precursors. Related objects and advantages of the present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A

is a front elevational view of a typical seed precursor of a first embodiment of the present invention.

FIG. 1B

is a front partial sectional view of a coated seed crystal of the embodiment of FIG.

1

A.

FIG. 2A

is a front elevational view of a typical seed precursor of a second embodiment of the present invention.

FIG. 2B

is a front partial sectional view of a coated seed crystal of the embodiment of F IG.

2

A.

FIG. 3

is a perspective view of a multistage drop tube for producing cement additive powders according to a third embodiment of the present invention.

FIG. 4

is a perspective view of a multistage drop tube for producing cement additive powders having a plurality of intermediate segments according to a fourth embodiment of the present invention.

FIG. 5

is a perspective view of a single-stage drop tube according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

The physical properties of cements, including compressive strength, hardness, toughness, porosity, tensile strength, water resistance, and chemical stability are dependent on the cement's microstructure. As used herein, the microstructure of a cement or cementitious material is defined to be a measure of the composition, distribution, size, and size distribution of its component phases and their boundaries. Additives and/or admixtures have been used in the past to control various cement properties. For example, U.S. Pat. No. 1,310,520 to Bennett discloses the addition of copper stamp sand to harden Portland cement; U.S. Pat. No. 4,832,746 discloses the additions of metal fibers to Portland cement and other cements to increase their structural strengths; and U.S. Pat. No. 5,527,387 discloses the addition of fly ash and/or silica fume to decrease the amount of water required to produce a workable cementitious mixture and to increase the strength of the cement. However, while the use of cement additives is not new, additives have primarily been used to provide an additional stable phase or composite component to the cement that does not change or grow as the cement cures.

The present invention is directed towards the controlled distribution in ceramic precursors of seed crystal additives of predetermined size, shape, hardness, and PSD to control the microstructure and final physical properties of the ceramic body. The seed crystals provide growth sites upon which one or more distributed crystalline phases may grow while the cement cures. The addition of one or more controlled crystal phase to a ceramic body results in a tailored and controlled microstructure, which in turn gives rise to ceramic bodies having consistent, controlled and reliable physical properties that may be enhanced and tailored to suit a particular need.

There are two ways in which kinetics may be used to control the microstructure of a polycrystalline material, by controlling the nucleation kinetics of the individual crystals and/or by controlling the growth kinetics of already nucleated crystals. The ranges of physical conditions under which crystals nucleate and grow often have little or no common overlap. Therefore, sometimes during processing a material moves through the crystal growth regime for a given type of crystal before any crystals nucleate. Seed crystals may be used to provide controlled distribution of already nucleated crystals that may grow while the material is in the growth regime.

Likewise, nucleation agents may be introduced that act as catalysts upon which crystals may nucleate under conditions that are otherwise unfavorable for nucleation (i.e., while the material is in the growth regime but not in the nucleation regime). The nucleation agents do not have the same composition as the desired crystals, but may enable nucleation of those crystals under conditions wherein crystals could not otherwise spontaneously nucleate. Nucleation agents may also be used to provide controlled distribution of crystals that may grow while the material is still in the growth regime.

One form of the present invention uses substantially spherical seed crystals of predetermined size, PSD, and composition to control the microstructure of a cementitious ceramic composition and to achieve a cement having a set of predetermined, microstructure-related physical properties. A typical seed crystal

10

is illustrated in

FIGS. 1A and 1B

. Preferably, the seed crystals

10

have tightly controlled PSDs and median sizes. The preferred median sizes range from a few nanometers to a few microns in diameter, depending on the compositions of the seeds

10

and of the cement, and also on their desired impact on the cement's physical properties and curing times.

The composition of the seeds

10

added to a given cement is a function of the desired property change they are to effect on the cement. Table I inexhaustively illustrates some of the desired physical effects and some of the seed compositions useful in achieving those effects in both Portland and phosphate cements. The contemplated phosphate cements include, but are not limited to, phosphates of calcium, magnesium, zinc, sodium, potassium, ammonia, and mixtures thereof.

TABLE 1

Portland Cement

Phosphate Cement

Desired Effect

Seed Composition

Seed Composition

Accelerators

NaCL, KCL, polyelectrolytes, acid

Uncalcined CaO or MgO and hyroxides

or base coated or drop-tubed seeds,

thereof; polyelectrolytes, acid or base

sodium aluminate, magnesium

coated or drop-tubed seeds, volcanic ash,

aluminate, wollastonite, Al (foil,

flyashes under 10 micros in size,

powder), liquid phosphoric acid,

polyelectrolytes

flyashes under 10 microns in size,

polyelectrolytes.

Hardeners

Ground blast furnace slag; CaCO3,

Ground blast furnace slag; CaCO3,

MgAl-silicates; Catalyst seeds,

Sn; MgAl-silicates; Catalyst seeds,

Reactive seeds, feldspars, N and

Reactive seeds, feldspars, N and potassium

potassium silicates, agar, iron, iron

silicates, agar, iron, iron oxide, metals,

oxide, metals, hard aggregates,

hard aggregates, silica fume, MetaMax,

silica fume, MetaMax, smaller

smaller cements, smaller seeds, smaller and

cements, smaller seeds, smaller and

harder aggregates, multiple sizes of

harder aggregates, multiple sizes of

particles, smaller particles sizes, fly ashes,

particles, smaller particles sizes, fly

silica fume, colloidal silica, fumed silica

ashes, silica fume, colloidal silica,

and silica flour, methyl methacrylates with

fumed silica and silica flour

initiators, dolomite, well graded and

narrow gradient mixtures of flyashes or

other silicas and oxides

Water Resistance

Sodium nitrate, agar, smaller

Plastics, agar, smaller particles sizes, fly

particles sizes, fly ashes, silica fume,

ashes, silica fume, colloidal silica, fumed

colloidal silica, fumed silica, silica

silica, silica flour, Na silicate, K silicate,

flour

Ductal

Chemical

Sodium nitrite, smaller particles

Smaller particles, fly ashes, silica fume,

Resistance

sizes, fly ashes, silica fume,

colloidal silica, fumed silica

colloidal silica, fumed silica

Retardation

Boric Acid, acetic acid, citric acid,

Ammonium nitrate, ice water, dry ice,

borates, ammonium nitrate, strong

mixing in the acid and base ingredients

water reducers, CMC’s including

separately in water, strong water reducers,

carboxyl, methyl and ethyl, starch

Boric Acid, acetic acid, citric acid,

borates, strong water reducers, CMC’s

including carboxyl, methyl and ethyl,

starch, deionized water, large sized base

oxides and hydroxides, gradient sizes of

acid salts

Reduced rebound

Saw dust, CMC’s; water reducers,

Saw dust, CMC’s; water reducers,

For sprayed

Na and K silicates, silica flour,

Na and K silicates, silica flour, gums, guar,

cements

CMC’s (including carboxyl, methyl

silica flour, k silicate

and ethyl).

Increased ductile

Ground rubber crumbs, fibers,

Ground rubber crumbs, fibers, celluloses,

and fracture

celluloses, CMC’s, buytl

CMC’s, buytl methacrylates, elastomeric

strengths and

methacrylates, elastomeric plastics,

plastics, non-deforming plastics, smaller

elasticity

non-deforming plastics, smaller

particle sizes, spherical particles, smaller

particle sizes, spherical particles,

and more spherical aggregates, latex,

smaller and more spherical

potassium silicate, sodium silicate, water-

aggregates, latex, potassium silicate,

activated polyurethanes and epoxies

sodium silicate, Ductal, water-

activated polyurethanes and epoxies

Less heat

Agar; carboxyl methyl cellulose,

Agar; carboxyl methyl cellulose,

shrinkage

celluloses, sawdust, curing

celluloses, sawdust, curing compounds,

compounds, guar, ethyl and methyl

Berylex, methyl and ethyl celluloses

and carboxyl CMC’s, starch,

Berylex, starch

Self-leveling

Agar; carboxyl methyl cellulose,,

Agar; carboxyl methyl cellulose, gums,

Self-filling / Self-

ethyl and methyl CMC’s, starch,

smaller more spherical aggregates,

consolidating

Berylex, gums, smaller more

cementious particles and no rocks, flyashes

spherical aggregates, cementious

and super plasticizers and water reducers,

particles and no rocks, small sized

higher pH for the mix, less reactive

flyashes and super plasticizers,

cementitious particles and aggregates,

micronized and amorphous silicas,

lower valence oxides, weaker acids,

and water reducers. Replacing sand

diluted acids, less active acid phosphate

and rock with spherical small sized

salts ex. K rather than ammonium or

flyashes and other micronized

magnesium, separate mixing of the acid

sililcas, feldspars, pre-wetting the

and base reactants and pre-wetting the

aggregates, feldspars, K and Na

aggregates, feldspars, K and Na silicates

silicates

Generally, smaller seeds

10

are preferred since the smaller particles more readily fill the interstitial voids between the cement particles and result in more complete packing. As the cement powder is more completely packed, void space is reduced and the amount of water necessary for achieving workability is decreased. Reducing void space and excess water typically results in a cement with reduced porosity, increased compressive strength, a more even microstructure (more uniform phase domain size and distribution), and generally more uniform and consistent physical properties.

The shape of the seeds

10

is preferably at least substantially spherical. Spherical particles pack more readily and can more closely achieve theoretical packing density. Moreover, substantially spherical seeds

10

are preferred in order to produce an even growth of the seeded phase in the cement. Irregular seed particles

10

act as growth sites for crystallites having irregular morphologies, and oblong seeds

10

tend to grow oblong crystallites and/or whiskers. While these microstructural morphologies may be result in cement properties desirable for some special applications, they are generally undesirable.

The character of the seed surfaces is also important, affecting both the growth rate and morphology of the seeded crystallites as well as how the seeds mix into the cementitious precursor powder or slurry. One important characteristic of the seed surfaces is their hardness. Harder seeds

10

are preferred as they are more resistant to damage and deformation during mixing and blending with the cement. Seed hardness is even more critical if the blended cement is the bonding component of concrete, since the seeds

10

must resist additional grinding by the concrete aggregate media.

Another important characteristic of the seed surfaces is electrical charge. Seeds

10

having a net positive or negative charge will be less likely to agglomerate with each other and will more readily mix and become evenly distributed in the cementitious precursor. Charged seeds

10

may even be used to impart a net electrical charge to uncured, wet cements or mortar pastes, allowing for electrostatic manipulation of the flowable cement or mortar and electrostatic control over the adhesion of the cement, coating or mortar to a substrate.

Another important aspect of the seed surfaces is the presence of a thin coating layer

22

, as illustrated in FIG.

2

. The coating layer

22

may be as thin as a few atoms thick, and may do no more than provide the above-discussed surface charge. The surface coating layer

22

may also add to the hardness, toughness, and/or chemical stability of the seeds

10

. For example, a relatively hard and substantially chemically inert aluminosilicate layer

22

may be deposited on a softer and more reactive phosphate cement seed crystal

10

to provide resistance to chemical and physical degradation during the mixing process.

If the surface layer

22

is made substantially thick, it can be considered to be a shell

24

. One or more shells

24

may be formed about a seed core

10

. Each shell

24

may have the same composition as the seed core

10

or they may have different compositions, as desired. This may be advantageous in applications requiring a delayed introduction of the seeds

10

into the cement growth medium. An outer, soluble shell

24

may be formed around the seed

10

with the thickness and dissolution rate of the shell

24

governing when the seed

10

is effectively introduced into the growth medium. Alternately, a relatively insoluble ablative shell

24

may be formed around the seed

10

such that the mixing action of the seed

10

in the cementitious or concretious medium releases the seed

10

at the desired time.

It is also possible to have some shells

24

carry one component of the seeded crystal phase with the other component supplied by the cementitious growth medium. The growth rate and morphology of the seeded phase may then be controlled by the amount of the essential growth component present in the shell

24

.

Preferably, the seeds

10

are introduced as a dry additive to a cement powder and mixed until thoroughly dispersed. Alternately, the seeds

10

may be introduced as a dry powder into a cement slurry or as a seed slurry into a cement slurry. In the case of a sprayed cement, the seeds

10

may be mixed prior to spraying or may be introduced into the sprayed cement during the spraying process as an injected stream from a second sprayer or spray nozzle. In any embodiment, it is important that the seeds

10

be evenly distributed throughout the cement to yield a cement body having a uniform microstructure and accordingly uniform physical properties.

In addition to uniform seed distribution, some of the other factors affecting the physical properties of the seeded cement/cementitious body are the concentration of the seeds

10

in the cement, the relative compositions of the seeds

10

and of their cementitious growth medium, the amount of water present, the temperature at reaction or hydration time, the curing temperature, and the curing time. The seed crystals

10

are introduced as batches of seeds

10

having tightly controlled PSDs and median particle sizes ranging from a few nanometers to a few microns, and therefore a volume of seeds

10

equal to a small percentage (preferably about 0.01 to 5.0 percent) of the volume of cement powder contributes enough seeds

10

to control the microstructure of the resulting cement. Preferably, the seeds

10

are introduced with median sizes ranging from about 5 nanometers (5×10

−9

meters) to about 20 microns (20×10

−6

-meters). As soon as seed crystals

10

are introduced into a cementitious growth medium (i.e., when the cement-seed powder mixture is hydrated, when the naked seeds

10

are mixed into hydrated cement, or when the protective shells

24

are removed from seeds

10

in a hydrated cement matrix) they begin to grow at a rate influenced by such factors as the composition of the seeds

10

, the composition of the growth medium, the concentration of seeds

10

in the growth medium, and the temperature of the system.

In the case of Portland cement, most of the elements (usually cations) necessary for the growth of most of the seed crystal compositions are already available in the Portland cementitious growth medium; when seeding other cement compositions, it should be remembered that seeds

10

cannot grow if the necessary compositional elements are not present in the cement growth medium. If it is desired to seed and grow phases requiring elements not already present in the cement, those elements need to be added either as part of the seeds

10

(i.e., as shells

24

) or as a separate component. Control of the above-discussed factors allows control of the microstructure of the final cementitious form and of its microstructure-dependent physical properties.

For example, to achieve accelerated curing or hardening of a cement, the seeding might be highly concentrated, the seeds

10

might be given a reactive surface treatment, the seeded phase composition might be chosen having fast reaction/growth kinetics, and/or the seeded phase might be chosen to remove impurities from the cement that would otherwise retard cement formation. To achieve increased strength, a medium concentration of seeds

10

might be used, the seeded phase composition might be chosen to have growth kinetics on a par with those of the cement, and/or the seeded phase might be chosen for having high strength properties which it would add as a dispersed composite phase. To achieve low porosity, a medium to low concentration of seeds might be used, the seeded phase composition might be chosen to have slow growth kinetics, and/or the composition of the seeds might be chosen to be the same as that of the cement. To increase the toughness of the cement, the seeded phase composition might be chosen to be the same as the cement or one that contributes an even microstructure with no secondary grain growth.

Another form of the present invention, illustrated as

FIGS. 2A and 2B

, contemplates the use of batches of substantially spherical particles

26

having controlled PSDs as nucleation sites in cements to control the microstructure of the resulting cement body. In this embodiment, the nucleation control particles are preferably single crystals or polycrystalline particles having median sizes ranging from a few nanometers to a few microns in diameter. As with the seed crystals

10

, the nucleation control particles

26

are introduced into the cement precursor and distributed substantially evenly throughout. Upon curing of the cement, the nucleation control particles

26

act as nucleation sites for one or more of the cement phases to promote controlled its controlled growth and distribution. Microstructure control is influenced by the concentration of the nucleation control particles

26

in the cement precursor, particle size, surface area, particle composition and particle shape.

Of particular importance is the particle composition. Since the nucleation control particles

26

are extremely small, the addition of nucleation control particles

26

equal to a small percentage of the volume or mass of the total cement powder (preferably about 0.1 to 5.0 percent by volume) is sufficient to provide enough nucleation sites to significantly control the resulting cement microstructure. The cement phase nucleated depends on the composition of the nucleation control particle

26

and the similarity of its crystal structure to that phase. For example, if the nucleation control particle

26

has a crystal structure similar to that of dicalcium silicate (i.e., is an isomer of dicalcium silicate), dicalcium silicate (2CaO·SiO

2

) will grow on the nucleation control particle

26

much more readily than the other cement phases. Likewise, some or all of the major phases may be nucleated by the controlled additions of different types of nucleation control particles

26

formulated to nucleate each different phase. Since the overall composition of the cement is not substantially changed by the addition of the nucleation control particles

26

, controlled nucleation of one or more phases results in a cement having a microstructure wherein the individual crystallites or phase domains are smaller and more evenly distributed. This results in an increased phase boundary area relative to the phase domains, and contributes to the consistency of the physical properties of the cement. Moreover, smaller and more evenly distributed grains also generally contribute to increased strength, hardness, density, and toughness and decreased porosity.

Nucleation control particles

26

may also be used to disperse additives into the cementitious material. For example, the nucleation control particles

26

may include strength enhancing substances, such as plastics, elastomers, proteins, and the like that may be distributed to produce an non-brittle, compressible second phase in an otherwise brittle material to increase its toughness and fracture resistance. The nucleation control particles

26

may likewise contain mounts of water-activated polyurethanes, epoxies or other like materials for introduction into Portland or phosphate cements to decrease the curing time. The addition of such polymers also yields cements having decreased porosity and increased hardness. And heat resistance, hardness, and fracture strength may all be enhanced through the addition of particulate polyhedral oligomeric silsequioxanes.

A further example of the use of nucleation control particles

26

to enhance the performance of a cement is illustrated by the addition of one or more particulate potassium-containing materials (such as potassium hydroxide, potassium silicate, feldspar, or the like) to ammonium phosphate cement. The resulting, and still inexpensive, phosphate cement cures with increased smoothness, decreased pin-holing and pock marking, decreased evolution of ammonia gas during curing, and increased hardness. Likewise, less acidic phosphate salts may be added to further eliminate ammonia gas evolution and the accompanying pin-holing and strength loss. Moreover, the substitution of iron oxides, and/or less reactive TiO

2

, ZrO

2

or the like for calcined MgO also works to improve the smoothness, hardness, and integrity of the cured phosphate cement.

In general, particulate ZrO may be added to a cement to impart or improve color. Silicates of K and Na may be added to impart a surface gloss, smoothness and hardness.

Seed crystals

10

and nucleation control particles

26

can be made by chemically treating relatively pure crystalline or polycrystalline powder precursors to produce substantially spherical particles falling into a predetermined PSD.

FIG. 3

illustrates a preferred embodiment of a device for producing seed crystals

10

from powder precursors, nucleation control particles

26

, drop tower or drop tube

30

through which the powder precursors fall under the pull of gravity. The drop tube

30

has a top portion

32

, a middle portion

34

, and a bottom portion

36

in fluid communication with each other. Each portion

32

,

34

,

36

is filled with a liquid chemical treatment through which the precursor powders sequentially fall or pass. Preferably, the composition, concentration, viscosity, turbulence, and temperature of each portion of the drop tube

30

may be individually controlled and maintained.

The composition of the powder precursor to be introduced into the drop tube

30

is predetermined according to the composition of the cement to which it is to be added and the desired effects it is to have on that cement's physical properties. While the powder precursor does not necessarily have to have the same composition as the desired seed crystal

10

, it preferably should be able to support the growth of a layer of that crystalline composition. The powder precursor is preferably provided having a mean size and PSD close to the target mean size and PSD desired for the resultant seed crystal population. The powder precursor is then introduced into the top portion

32

of the drop tube

30

. The powder precursors are preferably introduced into the center of the drop tube

30

, since it is desirable to prevent them from making excessive contact with the walls of the drop tube

30

in order to better control the travel time of the powders through the tube

30

, prevent uneven growth of the seed crystals

10

and prevent particle agglomeration. Moreover, it is preferred that the drop tube

30

be slightly conical in shape, flaring from top to bottom, to further prevent contact of the falling particles with the sides of the tube and to assist in minimizing the agglomeration of the seed particles at the bottom of the tube

30

, note the seeds

10

may be continually removed.

The top portion

32

of the drop tube

30

preferably contains a first fluid

38

. The first fluid

38

may be an etching solution used to further control the size and PSD of the introduced powder precursor. The etching solution also helps shape the seed crystals

10

by dissolving the outer surfaces of the powder precursors to achieve smaller and more perfectly spherical particles upon which the seed crystals

10

will grow. The etching process may also leave the etched particles with pH driven surface charges, enabling them to readily accept deposition of the seed crystal composition from solution. The etching solution is also preferably formulated to further purify the seed precursor powder by preferentially dissolving impurities introduced with the powder precursor. The composition of the etching solution may be dilute or concentrated acid or base, with the composition and concentration of the etchant tailored to the composition of the powder precursor and the desired effect it is to have thereon.

The rate at which the etching occurs is generally a function of temperature, insofar as the etching rate increases with increasing temperature and decreases with decreasing temperature. Therefore, the etching rate may be controlled by controlling the temperature of the etching solution. External means may be employed, such as surrounding the drop tube

30

with heaters and/or refrigerators. Internal means may likewise be employed, such as bubbling a temperature controlled inert or otherwise non-reactive gas through the etching solution

38

, or by introducing an exothermic or endothermic chemical into the etchant (for example, ammonium nitrate to cool the etchant and other solutions or suspensions in the same or other layers of the tube or wash solution).

In some alternate embodiments, the fist fluid

38

is not an etching solution; instead the first fluid

38

is a wash bath. In other embodiments, the top portion

32

contains a first fluid etching solution

38

to which deflocculents, dispersants, sequestrants, plasticizers, defoamers, self-leveling agents, self-consolidating/filing agents, catalysts, water reducers, gases and/or surfactants have been added to prevent the precursor particles from agglomerating. In yet other embodiments, the top portion

32

contains a nutrient first fluid

38

from which the seed crystals

10

are grown. The first fluid

38

is normally envisioned as an aqueous solution, but may be any solution conducive to the growth of a given crystal, such as an organic liquid or a gas. In still other alternate embodiments, the top portion

32

of the drop tube

30

contains inlet and outlet valves

33

A, B through which etchant fluid is continually flowed to maintain a constant pH/chemical concentration.

The middle portion

34

of the drop tube

30

preferably contains a second fluid

40

which is more preferably the nutrient bath from which the seed crystals

10

are grown. The composition and concentration of the nutrient bath is selected to grow seed crystals

10

of the desired composition on the precursor particles passing through the middle portion

34

of the drop tube

30

, and may contain the growth medium in solution, as a colloidal suspension, a gas, or in any other convenient chemical medium. The growth rate of the seed crystals

10

is influenced by the concentration, turbulence (stirring), pH, and temperature of the nutrient bath and the time the growing crystals spend in the second nutrient fluid growth medium

40

. For most seed crystals

10

, a pH range between about 5.5 and about 8.0 is preferred. These factors can be controlled to allow the even, steady growth of substantially spherical seed crystals

10

of the desired size in the nutrient bath. While substantially spherical seed crystals

10

are preferred for most uses, some crystal morphologies tend away from the spherical and toward the cubic. However, the above-detailed processing parameters influencing crystal growth rate may still be used to produce uniformly sized and substantially perfectly shaped non-spherical crystals. Control of the growth rate is not only important as a tool for assuring the proper seed crystal size and PSD, but is also important because crystals grown at a slow and even rate tend to have less defects and more prefect shapes than those grown at fast and/or uneven rates. The temperature of the nutrient bath may be easily controlled using any of the methods described above regarding the temperature control of the etching solution.

In some alternate embodiments, the middle portion

34

of the drop tube

30

contains inlet and outlet valves

35

A, B through which the second fluid nutrient solution

40

is continually flowed to maintain a constant concentration. In other embodiments, the middle portion

34

contains deflocculents, dispersants, sequestrants, plasticizers, water reducers, defoamers, self-leveling agents, self-consolidating/filling agents and/or surfactants, cooling chemicals or gas(es), added to the nutrient solution to prevent the growing seed crystal particles

10

from agglomerating and to help maintain the desired small crystal size and spherical crystal shape.

The bottom portion

36

of the drop tube

30

preferably contains a wash bath

42

. Preferably, the wash bath

42

is composed of cool or chilled deionized water. The seed crystals

10

passing through the wash bath

42

are rinsed of the nutrient solution to prevent further, uncontrolled growth. The lower temperature of the wash bath

42

relative to the nutrient solution also helps to prevent further crystal growth.

In some alternate embodiments, the wash bath

42

is not cooled. In other alternate embodiments, the wash bath

42

is composed of water. In still other alternate embodiments, the wash bath

42

is pH controlled to neutralize the pH of the crystals passing through the acidic or alkaline etch and/or nutrient solutions. In yet other embodiments, the bottom portion

36

of the drop tube

30

contains inlet and outlet valves

37

A,B and the wash bath

42

is flowing. In still other embodiments, the seed crystals are maintained in the wash bath for extended lengths of time, or until they are used. In yet other alternate embodiments, an electric field may be generated in the drop tube to impart a net surface charge or to preferentially orient and/or segregate forming seeds (see FIG.

5

).

After the seed crystals pass through the wash bath

42

, they are dried and collected. The crystals

10

exiting the drop tube

30

are preferably of the desired size, shape, and PSD for immediate use, although they may be sieved or otherwise sized if so desired.

In one alternative embodiment, illustrated as

FIG. 4

, the drop tube

30

′ contains one or more intermediate portions

50

between the top portion

32

and the bottom portion

36

. Each intermediate portion

50

preferably contains a separate nutrient solution, the composition and concentration of which is individually controlled, such as through the use of inlet and outlet valves

51

A,B. Crystals passing through an intermediate portion

50

of the tube

30

′ acquire a layer or shell

24

having a different chemical and/or physical composition. By passing the growing seed

10

through several different intermediate portions

50

, several shells

24

of different compositions may be built up on the seed

10

to produce a layered polycrystalline or composite seed

10

.

In yet another alternate embodiment, shown as

FIG. 5

, the drop tube

30

″ comprises a single stage containing a single solution bath containing at least one nutrient fluid

56

. The seed precursors are passed through the bath and are grown in transit. Removal from the nutrient fluid

56

halts the growth of the seed crystals

10

.

The drop tube environment of any embodiment may also be manipulated to impart other desired properties onto the particles processed therein. For example, electric field coils

60

may be positioned to generate an electric field extended through the drop tube

30

to impart a net charge onto the particles processed therein, as shown by ghost lines in

FIG. 5

, for example. Such an imparted charge discourages agglomeration (since like charges repel) and is also useful in evenly distributing the seeds

10

evenly throughout a cementitious powder or slurry. Further, if the particles

10

,

26

are sufficiently charged and/or a great enough concentration of charged particles are added to a cementitious material, the disposition of the cementitious material may be aided through the application of like or unlike fields to direct the flow of the cementitious material and/or to influence the adhesion of the cementitious material onto a given substrate. Such a control process enjoys the advantages of being quick and efficient with reduced waste and clean-up time requirements. This is especially true in the case of phosphate cements, since phosphate cements are highly reactive and set and cure rapidly. This technique can be adapted to the process of tuckpointing in the form of a mortar gun (or spray gun). The use of a mortar gun would greatly speed and greatly reduce the expense of tuckpointing, which is currently done by hand with a trowel and pallet.

The drop tube

30

may also be used to produce coatings

22

of controlled, substantially uniform thickness on the seed particles

10

nucleation control particles

26

, or other larger objects passing therethrough. For instance, transparent coatings of magnesium phosphate may be applied by adding nanosize precursors of magnesium oxide into an aqueous phosphoric acid solution. A magnesium phosphate coating is resultingly formed on seeds

10

or other objects passing therethrough. The thickness of the coating

22

is a function of the time the coated object spends in the solution and the concentration of the solution. Interestingly, the magnesium phosphate coating tends to be transparent rather than opaque when the MgO precursors are nanosized.

Tables 2-4 below illustrate general examples of four different types of seeds

10

(Types I-III) made from the above-described process. Each type of seed

10

is made through its own general processing parameters and has its own set of identifying properties. While the above-described process is not limited to making seeds

10

falling into one of the four types described in the following tables, the mechanism of defining four distinct seed types is instructive of the versatility of the process as well as convenient for describing four varied and useful classes of cementitious seeds, reactive seeds and catalysts.

TABLE 2

TYPE I: Seeds for all Portland cements/mortars/concretes and coatings

PROPERTIES OF

SOLUTION / COLL.

HARDENED SEEDED

SUSPEN.

CEMENTS / COATINGS /

PRECURSOR(S)

CONTENTS

RESULTANT SEEDS

CHEM. COMPOUNDS.

HES-OPC = High

“WS” = water & silica:

“SSS” = Small Spherical

“OPC-P” = Accelerated

Early Strength

(fumed silica &/or

Seeds, of Portland

set times, more

Portland cement.

colloidal &/or silica

Cement consisting of:

compressive, fracture,

Precursor sizes =

fume &/or silica flour

Hydrated cement

tensile and flexibility /

preferably

&/or small sized flyash =

particles or clusters

ductile strengths,

nano or micron size

20 micron and smaller)

consisting mostly of bi-

smoother, easier to

although larger sizes

and optionally: a

and tri-Ca silicates with

finish. Less total

can be used in baths

sequestrant &/or

some Fe and AL

porosity and smaller

or the drop-tube,

surfactants / water

silicates. The colloidal

pore size, increased

preferably the drop-

reducers &/or retardants

silica, fumed silica, silica

self- leveling and self-

tube.

or accelerants &/or super

fume and smaller sized

filling/consolidating

plasticizers (prefer-ably a

fly ashes react much

properties. When

3

rd

or 4

th

generation

more quickly with the

used in OPC or HES-

super plasticizer).

CaOH, than does sand

OPC. Smaller particles

Colloidal tin, potassium

and yields a spherical

also yield greater

or sodium feldspars and

shaped seed in the drop-

adhesion to substrates

K or Na silicates,

tube, and a somewhat

and to itself and other

carbonates and other

spherical shape when just

cement types, it

materials. Ground blast

bathed in the nutrient

makes the resultant

furnace slag or iron

solution. Seeds charged

product easier to

oxide(s), iron oxide and

with a positive or

spray, less porous and

other magnetic materials

negative electrical charge

more dense. Resulting in

and polyelectrolytes and

or having a magnetic

end products = more self-

other

field or having

leveling and self-filling

materials/metals/compounds,

ferromagnetic or

and able to have an

chemicals. Using

paramagnetic character.

electrical and/or

sequestrants such as:

magnetic charge or being

DEQUEST 2000 ™,

conductive. Can be used

DEQUEST 2006 ™ and

in electrostatic sprays.

colostrum.

OPC (Ordinary

WS & chilled water or

SSS with even smaller

“OPC-P”

Portland Cement)

ammonium nitrate (for

particle sizes.

cooling) or cooling gas

added

OPC

WS & CO2 or CaCO3 or

SSS

OPC-P”

SN or Ground blast

furnace slag or iron

oxide(s) or SiC or flyash

combinations thereof.

TABLE 3

TYPE II: Seeds for phosphate cements/mortars/concretes/coatings

PROPERTIES OF

SOLUTION / COLL.

HARDENED SEEDED

SUSPEN.

CEMENTS / COATINGS /

PRECURSOR(S)

CONTENTS

RESULTANT SEEDS

CHEM. COMPOUNDS

Calcined

“PCS”=

“SPS” = Small Spherical

“PC-PROP” = PC

MgO or CaO

Ammonium phosphate

Phosphate Seeds of:

Properties.

or ZrO or NI or Mb or

salt(s) and/or alkaline

Nano or micron sized

Accelerated set times,

Cr or Al or Ca or Mg

earth phosphate salts (or

particles or clusters of:

more compressive,

oxides and hydroxides

phosphoric or phosphoric

chemically bonded

fracture, tensile and

thereof and

acids) or Zn or Al or Na

reactive powder cement

flexibility strengths,

combinations thereof

phosphate salts, or

consisting of:

smoother, easier to

also ground iron ore

combinations thereof,

ammonium and/or

finish, less total

trap rock (which

and optionally along with

alkaline earth phosphate

porosity and smaller

contain a mixture of

water & silica: (fumed

salts (or phosphoric or

pore size, increased

hard metal oxides such

silica &/or colloidal &/or

phosphoric acids).

self-leveling and self-

as vanadium) and

silica fume &/or flour

Mortars, coatings,

filling properties.

ground blast furnace

&/or flyash) and

concretes and paints.

Smaller particles

slag. Precursor sizes =

optionally a sequestrant

Nano and micron size

also yield greater

preferably nano- or

&/or surfactants / water

particles and clusters,

adhesion to substrates

micron- size although

reducers or retardants or

Seeds charged with a

and to itself and other

larger sized particles

accelerants. Also one

positive or negative

cement types, it

and clusters can be

can add in super

electrical charge or

makes the resultant

used in baths or the

plasticizers (prefer-ably a

having a magnetic field.

product easier to

drop-tube, preferably

3

rd

or 4

th

generation