WO1995007379A9

WO1995007379A9 - Inorganic composite hardened material containing carbon fibrils

Info

Publication number: WO1995007379A9
Application number: PCT/US1994/010120
Authority: WO
Filing date: 1994-09-09
Publication date: 1995-04-20

Abstract

An inorganic composite hardened material containing carbon fibrils obtained by mixing 0.05 to 20 % by weight of carbon fibril material comprised of an aggregate in which carbon fibrils of an outside diameter of 3.5 to 75 nm are intertwinned with 100 parts by weight of water hardening inorganic powder. The hardening precursor is suited to the manufacture of immediate mold release type cement products and the hardened material is of superior conductivity and strength.

Description

INORGANIC COMPOSITE HARDENED PRODUCT CONTAINING CARBON FIBRILS

FIELD OF THE INVENTION This invention relates to a composite hardened material containing carbon fibrils and a water hardening inorganic powder. This material can be used in fields requiring high strength and conductivity and in manu acturing immediate mold release products.

BACKGROUND OF THE INVENTION Fiber of organic polymers such as polyvinyl alcohol and polyimides, fibers of metals such as steel, and copper and reinforcing fillers such as carbon fibers have been developed for the purpose of improving the strength of mortar and concrete in which hydrates of water hardening inorganic powders serve as the matrix.

Known procedures for improving the conductivity of mortar and concrete include a procedure in which a conductive fi Ller such as conductive carbon black, carbon fibers, metal fibers or glass fibers coated with metal is mixed. with water hardening powder, water, or aggregate, and, as required, with various additives such as cement builders, and the mixture is hardened.

The use of a reinforcing conductive filler is desirable for the purpose of improving the strength and conductivity of mortar and concrete. Of these substances, metal fibers are of high specific gravity and present a problem in regard to chemical safety. On the other hand, there are few of these problems with carbonaceous fillers. However, conductive carbon black and carbon fibers are of poor dispersibility in water and they are difficult to disperse uniformly in mortar and concrete products.

Known methods of improving dispersibility include methods in which the surfaces of carbonaceous materials are modified and methods in whiόh extremely large quantities of surfactant are used. However, these methods significantly raise the cost of the carbonaceous hardened material or lower the strength of the hardened material due to addition of surfactant. Most recently, immediate mold release products have been employed to increase productivity. Fresh mortar and fresh concrete can be put into a suitably dry state for manufacture of immediate mold release products without hardening the material with the addition of a minute quantity.

OBJECTS OF THE INVENTION It is therefore a general object of the invention to eliminate the aforementioned problems and to obtain a composite hardened substance containing a suitable water hardening inorganic powder for the purpose of meeting the aforementioned needs.

These and other objects, features and advantages of the invention will become readily apparent from the ensuing description, and the novel features will be particularly pointed out in the appended claims.

SUMMARY OF THE INVENTION The invention is directed to a hardened substance containing a water hardening inorganic powder and carbon fibrils and to an inorganic composite hardened material containing carbon fibrils obtained by mixing 0.05 to 20% by weight of carbon fibril material comprised of an aggregate in which carbon fibrils of an outside diameter of 3.5 to 75 nm are intertwined with 100 parts by weight of water hardening inorganic powder.

DETAILED DESCRIPTION OF THE INVENTION The invention is broadly directed to a hardened substance containing a water hardening inorganic powder and carbon fibrils. The carbon fibrils that are used in this invention are comprised of a tubular aggregate of a median diameter (the median value of the particle diameter distribution) of 0.1 to 30 pm in which fine, filiform carbon fibrils of 3.5 to 75 nm in outside diameter and these carbon fibrils were intertwined. The median diameter of the aggregate should be 0.2 to 20 μm. When the median diameter of the aggregate exceeds 30 μm, the carbon fibril material is poorly dispersed in the hardened material, the tensile strength of the hardened material is decreased and the external appearance of the compact surface is impaired. It is difficult to manufacture an aggregate of a median diameter of less than 0.1 μm.

The proportion of aggregate in the carbon fibril material should be greater than 30%, and, preferably, greater than 50%.

The carbon fibrils that form the carbon fibril aggregate are filaments in which the variation in the outside diameters should be less than 15% of the average outside diameter of several tens of fibrils and of which the aspect ratio should ordinarily be greater than 5, preferably, greater than 100, and, more preferably, greater than 1000. Moreover, they should ordinarily be tubular fibrils the cores of which are hollow.

Further, these carbon fibrils have several graphite layers that are parallel to the fibril axis without having a continuous hot carbon coating. The proportion of the surface area that is coated with this hot carbon coating should ordinarily be less than 50%, preferably, less than 25%, and, more preferably, less than 5%.

A method of manufacturing the carbon fibril material that is used in this invention is described in Japanese Patent Early Disclosure No 2-503334 [1990]. A specific example is described below. The carbon fibers are manufactured tubular reactor by introducing catalyst metal into a gas flow containing carbon weight or by injection of a gas such as reaction temperature is 550 to 1200°C. The catalyst particles may be formed in the reaction vessel by decomposition of a precursor compound, for example, ferrocene. The reaction vessel is equipped with an internal plug of quartz wool for catching the catalyst particles and a quartz tube equipped with a thermocouple for monitoring the temperature of the reaction vessel. In addition, it is equipped with an inlet port for introducing the catalyst, the reaction gas and a purge gas such as argon and with an outlet port for removing the gas from the reaction vessel.

Suitable gases containing carbon include saturated hydrocarbons, for example, methane, ethane, propane, butane, hexane and cyclohexane, unsaturated hydrocarbons, for example, ethylene, propylene, benzene, toluene, and hydrocarbons containing oxygen, for example, acetone, methanol and tetrahydrofuran and carbon monoxide. The preferred gases are ethylene and propane. Preferably, hydrogen gas is added. Typically, the ratio of gas containing carbon to hydrogen gas is in the range of 1:20 to 20:1. Desirable catalysts include iron, molybdenum-iron, chromium-iron, cerium-iron and manganese-iron particles that are attached to deposited alumina. In order to cause the fibrils to grow, the reaction tube is heated to 550-1200°C, and, at the same time, purging is performed with, for example, argon. When the reaction tube reaches a specified temperature, introduction of the hydrogen flow and the flow of gas containing carbon is begun. A hydrogen flow volume of approximately 100 milliliterε/ inute and a flow volume of gas containing carbon of approximately 200 milliliters/minute are suitable for a reaction tube of 1 inch in thickness. After the reaction tube has been purged for over 5 minutes with the reaction gases at the aforementioned flow volumes, the catalyst - s dropped onto the quartz wool plug. Next, the reaction ases are reacted with the catalyst (typically, for 0.5 to 1 hour) throughout the entire body of the reaction vessel. When the reaction period is completed, the flow of reaction gases is stopped, purging is effected with a gas not containing carbon, for example, argon, the reaction vessel is cooled to room temperature and the fibrils are recovered from the reaction tube. The yield of fibrils is greater than 30 times the iron content of the catalyst. The carbon fibril materials that are used in this invention are carbon fibrils manufactured as described above, or, in many cases, are prepared to a specified size by pulverization. The pulverization apparatus may be, for example, a pneumatic grinder (jet mill) or an impact grinder. Because these grinders can operated continuously and the quantity treated per unit time is greater than that with a ball mill or a vibrating mill, pulverization costs can be lowered. In addition, a carbon fibril aggregate of a narrow particle size distribution can be obtained by installing a classifying mechanism in the grinder or by installing a classifier such as a cyclone in the line.

The surfaces of the carbon fibrils which have been denatured can also be used. For example, they can be denatured by chemical reactions such as oxidation with nitric acid and by coating with polymers such as epoxy resins. As required, the carbon fibrils of this invention can be mixed with other conductive fillers. Examples of other conductive fillers include carbonaceous fillers such as carbon black, graphite powder and various types of carbon fibers, fibers of metals such as steel, copper and aluminum and glass fibers coated with metals such as nickel.

Examples of water hardening powders that can be used in this invention include Portland cements such as ordinary Portland cement, moderate heat Portland cement, (super) early strength Portland cement and sulfate resistant Portland cement, mixed cements such as blast furnace cement, silica cement and fly ash cement, special cements such as alumina cement, white cement, ultra-fast setting cement and expansive cement, water hardening substances such as gypsum dehydrate and gypsum hemihydrate and water hardening substances in which blast furnace slag is the principal material.

In this invention, 0.05 to 20 parts by weight, and, preferably, 0.1 to 15 parts by weight, of carbon fibrils is used per 100 parts by weight of water hardening powder. When the amount of carbon fibrils is less than 0.05 parts by weight, no appreciable effect is attributable to the carbon fibrils. When the carbon fibrils are greater than 20 parts by weight, dispersion of the carbon fibrils and the fluidity of the hardening precursor are markedly impaired and the strength of the hardened material is decreased.

The water hardening inorganic powder hardened material containing carbon fibrils of this invention is manufactured by hardening a mixture obtained by mixing water hardening powder, water and aggregate, and, as required, additives such as various types of cement builders or some of these.

There are no particular limitations on the methods of manufacturing the hardened material of this invention. Because the carbon fibrils that are used in this invention are easily dispersed in water, a hardened material in which carbon fibrils are well dispersed can easily be manufactured. In preparing the aforementioned mixture, the carbon fibrils and the water hardening powder may be mixed in advance, or, when a water hardening powder paste, mortar or concrete are used, they may be mixed successively or at the same time. The mixing machine may be, for example, a mortar mixer, an inclined mixer, a hand mixer or a ball mill.

Additives that can be used as required include inorganic fillers such as calcium carbonate, mica, tobermorite and kaolinite, organic fibers such as natural pulp, cotton, polyvinyl alcohol, polyimides, polyamides and polyesters, cement separation inhibitors such as cement water reducing agents comprised of naphthalene sulfonic acid/for amide condensates or alkali or alkaline metal salts thereof and lignin sulfonates, ultra fine particles and silica and aqueous dispersions of neutral and ionic organic polymers such as styrene-butadiene copolymeric latex and acrylic polymer emulsions.

The invention will be more fully described and understood with reference to the following examples which are given by way of illustration.

The diameter of the carbon fibril aggregate that was used as the raw material was determined using a laser diffraction-scattering type particle size distribution meter on materials obtained by dispersing the carbon fibrils with an ultrasonic homogenizer in water to which a surfactant was added. Examples 1 to 5 and Comparative Examples 1 to 3

Water was added to and mixed with a carbon fibril material of an average diameter of 0.013 pm and of an aggregate average particle diameter of 3.5 pm, after which Portland cement and standard sand were added and the materials were mixed for two minutes using a mortar mixer. The proportions in which the raw materials were compounded are shown in Table 1. The flow value and the specific gravity of the raw mortar that was obtained were determined. The raw mortar was poured into a 4 cm x 16 cm mold of 4 cm in depth and it was allowed to stand indoors for two days at 100% humidity, after which it was released from the mold and it was then cured for 5 days in water at 20°C, with a mortar test material being prepared. The test material was subjected to compressive strength tests and bending strength tests. These tests were performed in accordance with JIS A-5201. In addition, the raw mortar was introduced into a 1 cm x 10 cm mold of 1 cm in depth. It was then allowed to stand indoors for 7 days at 100% humidity and hardened. This test material was dried, after which volumetric intrinsic resistance values were determined. The results are tabulated in Table 1.

A cement water reducing agent was added to the cement mortar of Example 1 to increase its fluidity. A material to which it had not been added did not flow. The carbon fibrils in Example 3 consisted of the carbon fibrils of Example 1 that had been oxidized with nitric acid.

From a comparison of Examples 1 and 2 and Comparative Examples 1 and 2 , it can be seen that the flow values of raw mortar containing carbon fibrils were lower and that the bending strength and the compressive strength of the hardened materials were greater.

In Examples 3 through 5 and Comparative Example 3, the volumetric intrinsic resistance of the hardened materials was determined. The volumetric intrinsic resistance values were determined using an electrode made by applying silver paste to both ends of the test material. When the carbon ^ibril content was increased from 0 to 24 parts, the res_stance value decreased from 10⁷ Ω.cm to 10 Ω.cm. Examples 6 and 7 and Comparative Examples 4 to 8

Raw mortar was prepared in the same way as in Example 1 and in the compounding proportions shown in Table 2. Except in Comparative Example 5, the flow values of the raw mortar were low and the mortar was in a dry state.

In Examples 6 and 7 and in Comparative Examples 6 and 8, the raw mortar was loaded into the mold under good control. It was placed on a stainless steel block vibration of an amplitude of 1.0 mm and a vibration frequency of 15 seconds was applied with a table vibrator (manufactured by Maruhigashi Seisakujo) while a load was being applied. The water that was exuded was absorbed with filter paper. The operation in which vibration was applied and water was absorbed was repeated three times, raw mortar was then replenished and the operation of vibration and water absorption was performed two times. When the raw mortar did not fill 4 cm of the mold, it was supplemented to make 4 cm. It was then removed from the mold and was allowed to stand indoors for 2 days at 100% humidity. Next, it was cured for 20 days in water at 20°C, after which its physical properties were determined.

The hardened materials of the examples were of a gray color that appeared more stable than that of the comparative examples which did not contain carbon fibrils. In Comparative Examples 4, 5 and 7, the raw mortar was loaded into the mold under good control and was allowed to stand in this state indoors for 2 days at 100% humidity. It was then removed from the mold and was cured for 20 days in water at 20°C, after which its physical properties were determined. The results are shown in Table 2 below.

A flow value of the mortar of 100 mm indicates a dry state. The raw mortar of Comparative Example 4 did not contain carbon fibrils as did that of Example 6.

Although it exhibited fluidity, its physical properties on hardening were poorer than the raw mortar containing carbon fibrils. In Comparative Examples 5 and 6, the materials were drier with decreased water content. However, the physical properties on hardening were poorer in Comparative Example 6, in which molding was carried out with application of vibration. The physical properties on hardening in Comparative Examples 7 and 8 (molding in comparative Example 8 having been carried out with application of vibration) , in which the quantity of water was comparable to that in Example 6, in which the quantity of sand was increased and in which a smooth state was effected, were not as good as those in Example 6. Physical properties on hardening were not as good when water reduction (Comparative Example 5) and sand (Comparative Example 7) was used as means of obtaining dry mortar, as in Examples 6 d 7 in which a dry state was obtained using carbon fibrils.

From Examples 6 and 7, it can be seen that cement mortar containing the carbon fibrils of this invention is suited to the manufacture of immediate mold release products.

Examples 1 2 3 4 5

Comparative Examples 1 2 3

P¹ π>

(note) a b

Composition (parts by *— * weight)

Carbon fibrils 0.23 — 0.32 - 1.81 — 10.5 24

Water 45 45 65 65 60 60 180 270

Cement 100 100 100 100 100 100 100 100

Standard sand 200 200 200 200 200 200 40 — P>

Mortar

Flow value (mm) 125 123 173 232 131 205 - —

Specific gravity

(g/cm³) 2.11 2.07 2.07 2.08 2.09 2.08 - —

Hardened material

Bending strength

(kg/ cm²) 85.1 79.6 5 3 46.6 53.4 53.3 — —

Compressive strength (kg/cm²) 355 299 260 212 290 278 Volumetric intrinsic 1.5X10⁶ 2.2X10⁷ 1.4X10² 4.4X10 resistance (Ω-cm)

Notes a: cement water reducing agent added b: carbon fibrils oxidized with nitric acid used

Examples 6 7

Comparative Examples 4 5 6 7 8

0)

(notes) vibra¬ vibra¬ vibra¬ vibra¬ u⁴

Composition (parts by tion tion tion tion to t weight)

Carbon fibrils 1.05 1.58 — - - - -

Water 50 50 50 33 33 50 50

Cement 100 100 100 100 100 100 100

Standard sand 200 200 200 200 w

200 300 300

Mortar

Flow value (mm) 100 100 115 100 100 100 100

Specific gravity 2.24 2.19 2.13 2.00 2.10 2.01 2.10 (g/cm³)

Hardened material

Bending strength

(kg/cm²) 81.3 72.1 69.8 46.2 50.8 44.8 66.6

Compressive strength 512 460 371 190 265 177 350 (kg/cm²) Volumetric intrinsic resistance (Ω.cm)

Example 8

Concrete samples were prepared using commercial Sandmix (Sa rete) . Sandmix is a concrete formulation consisting of cement paste and fine aggregate. Samples were cast in plastic molds and placed in a humid atmosphere to cure immediately after casting. Batches were prepared with and without fibrils. The fibrils used were red-deviled BN (125-35-B) , in a 3 wt% aqueous dispersion with 35 wt% Tamol dispersant (Rohm and Haas) by weight of fibrils (pH was adjusted to 10.5 by NaOH addition) . This slurry had been blended 5 min, ball- milled 24 hr, and ultrasonicated 30 sec. For each batch, two cylindrical samples (d=l", h=L/2") and one half- cylindrical sample (d=-l", h-2") were cast. The formulations used to prepare concrete specimens are given in Table 3. Water/cement ratio is one of the most important variables in concrete-making, as it effects cure rate, strength, durability, etc. The reason the water/cement ratio differed between samples was due to use of fibrils from a previously-prepared aqueous slurry. The ratio was an approximation based on an assumption of 30 wt% cement paste in Sandmix, therefore these numbers are not accurate on an absolute scale, but are accurate on a relative scale. The fibrils added amount to 0.6 wt% of the dry concrete mix.

Table 3. Concrete formulations used for initial test.

COMPONENT T% IN FORMULATION Sandmix Fibril-reinforced Sandmix

Sandmix 87.7 81.8 water 12.3 15.7 fibrils 0.0 0.49 Tamol 0_₁0 0.12 /C ratio % 0.47 0.64 fibrils/dry concrete 0.0 0.006 Samples were removed from the molds after 4 days. Compressive strength was assessed using a Carver press on cylindrical samples. The results are summarized in Table 4. Pressure was manually applied and load was recorded as a function of sample deformation (strain) . "Compressive strength" is reported as the maximum sustainable load, the accompanying strain is also given. Area under the stress-strain curve indicates a measure of material toughness (qualitatively, the opposite of brittleness) . Fibril-reinforced Sandmix showed areas 2 to 3 times those of non-reinforced samples, after 5 and 8 days of cure. Geometric densities before and after compression are indicated for 8-day samples. No quantitative measure of bleed was accomplished, though observations indicate that the presence of fibrils in wet concrete causes formulations to appear significantly dryer, probably due to the fibrils' ability to absorb water.

Table 4. Compressive testing of concrete samples.

Area

"Strenth" Strain under in psi at max stress- Density (g/cc)

(tg/cm³ load strain before after

5-DAY ( :URED SAMPLES no fibrils 3100 (217) 0.04 0, .87 0.6 wt% fibrils 2970 (208) 0.17 2. .26

8-DAY CURED SAMPLES no fibrils 2600 (183) 0.11 0.97 2.01 2.29

0.6 wt% fibrils 3680 (258) 0.11 2.08 1.93 2.16

The composite hardened materials containing carbon fibrils of this invention exhibit good strength and conductivity and the hardening precursors are suited for the manufacture of immediate mold release products. These materials can be used in mortar and concrete for which conductivity, strength and immediate mold release properties are sought. They can be used in engineering works and buildings, for example, in inside and outside walls, curtain wool, floors, ceilings, roofing materials, tile and blocks. In addition, they can be battened and colored to make light boards and boards can be laminated to make laminated panels. The use of carbon fibrils is effective for coloring from gray to black depending on the quantity compounded with the mortar or concrete. Having thus described in detail preferred embodiments of the present invention, it is to be understood, that the invention defined by the appended claims is not limited to particular details set forth in this description as many variations thereof are possible without departing from the spirit or scope of the present invention.

WHAT IS CLAIMED IS:

An inorganic composite hardened material containing carbon fibrils comprised of 0.05 to 20 parts by weight of carbon fibrils of an outside diameter of 3.5 to 75 nm per 100 parts of a water hardening inorganic powder.