WO1995032929A1

WO1995032929A1 - Improved water-resistant magnesite cement and process for its manufacture

Info

Publication number: WO1995032929A1
Application number: PCT/US1995/006650
Authority: WO
Inventors: Itzhak Yaniv
Original assignee: Baran Advanced Materials (94) Ltd.; Baratz, Yael
Priority date: 1994-05-30
Filing date: 1995-05-25
Publication date: 1995-12-07
Also published as: AU2762695A; IL111032A0

Abstract

Improved magnesite cements comprises a cement selected from magnesium oxychloride and/or magnesium oxysulphate cements together with one or more organic carboxylic acid(s) having a '120h Weight Loss Coefficient' of less than 5 %, and/or their anhydrides and/or their carboxylate salts. Illustrative cements are those that comprise carboxylic acids of the formula: R-(COOH)p, wherein: p = 1 to 5; R = Alkyl (linear or branched; saturated or unsaturated; cyclic or acyclic); or Aryl (substituted or unsubstituted), wherein R contains up to 10 carbon atoms, and one or more of its carbon or hydrogen atoms may be replaced by oxygen, nitrogen, phosphor or sulfur atoms.

Description

TMPROVED WATER-RESISTANT MAGNESTTE CEMENT AND PROCESS

FOR ITS MANUFACTURE

Field of the Invention

The present invention relates to magnesite cements, magnesium oxychloride and oxysulfate cements, having improved properties, particularly increased water resistance. The invention further relates to a process for the manufacture of such cements and to methods for their utilization in the hardened form as construction elements, fillers and flame retardants in plastics and composite materials for special applications (e.g. ions adsorption).

Background of the Invention

The magnesite cement referred to hereinafter is magnesium oxychloride cement having a composition defined by nMgO-MgCb-mHbO. The art deals with compositions in which n = 3 and m = 1 , or in which m = 5 and n = 13, or the like. The present invention is not limited to a specific composition and includes any cement the composition of which comprises MgO and MgCl2- and generally molecular water. Whenever H2O is mentioned herein, it should be understood that the reference is to molecular water, unless otherwise specified. The magnesium cement may also be oxysulfate cement, the composition of which can be described by the formula m'MgO-MgSθ4-n'H2θ. Various possible values of n' and m' are known in the art, e.g., n' = 5 and m' = 3. The expression "magnesite cements" also includes mixtures of oxychloride and oxysulfate cements.

Obviously, the structure and compositions of the cements change during the curing or hardening process, in manners that are well known to skilled persons and are discussed in the pertinent literature. When magnesium cements are mentioned in this specification and claims, it will be understood that reference is made to cured or uncured or both to cured and uncured cements, as the case may be.

In the specification and claims, the expression "magnesite cement" is intended to include both magnesium oxychloride or Sorel cement, magnesium oxysulfate cement, and mixtures thereof.

Magnesite cements, in particular Sorel cement, have been known in the art for many years. However, their physical properties are considerably inferior to those of, e.g., Portland Cement and therefore their utilization is quite limited. Compositions and products including said cements and various fillers are also known. Yet, such cement compositions and products have inadequate water resistance. Because of this disadvantage their industrial uses are also extremely limited. Many attempts have been made in the past to overcome the problem of water-resistance, by adding various additives to magnesite cements, and a few examples will be mentioned hereinafter:

The addition of phosphoric acid and metal phosphates to improve the properties of the magnesite cements is mentioned, for example, in E.I. Ved et al: "Water-resistant magnesia cement based on caustic dolomite"; Budirelni Mater. Konstr. (1) 35-6 (1969) (also CA. 103399C Vol. 72 (1970)), H. T. Stamboliev: "Magnesia-Zement -

Verbesserung der wasser-bestandigkeit durch phosphatzusatz "; Tonind. - Ztg. 100

(1976) Nr. l. pp. 34-37. and Israeli Patent No. 81807.

The use of sulfur to improve the magnesite cements is reported in J.J. Beaudoin et al "Impregnation of magnesium oxychloride cement with sulfur": Ceramic Bull. Vol. 56, No. 4 (1977), pp. 424-7. USP 5,004,505 discloses magnesium oxychloride cement compositions and products obtained by mixing magnesium oxide, a magnesium chloride solution, a strong acid and aggregate particles, and the resulting cement products are said to exhibit increased strength and water resistance. The references cited in the said patent are illustrative of the state of the art.

EPA 454,660 discloses and claims a Sorel cement, said to have improved water resistance, based on mixtures of MgO, MgCb and inorganic fillers, characterized in that it contains water soluble polymeric or polycondensed synthetic resins, including water soluble polycarboxylic acids.

USP 4.699,822 discloses the use of acrylic latex and acrylic powders in the production of magnesite cements.

USP 4,814.014 discloses the use of graft copolymers of polyether backbones and side chains prepared by polymerization of an ethylenically unsaturated monomers, including acrylic acid and similar compounds.

USP 4.992.481 discloses the use of polycarboxylic acids and their salts, among many other organic polymeric materials, in the production of magnesite cements.

DE 3832-287 discloses the use of citric acid and oxalic acids to improve the water resistance of maεnesite cements. USP 4,041,929 discloses the use of a frothing agent - "Norgan Expander", which is actually Mg metal plus lactic acid that react, in situ, during the production of the magnesite cement.

However, none of the suggestions of the prior art is fully satisfactory, from the viewpoint of water-resistance and cost-effectiveness.

It is a purpose of the present invention to provide an inexpensive magnesite cement having improved properties.

It is a further purpose of the invention to provide such cement mixtures, which can be produced by utilizing readily available and inexpensive raw materials.

It is still another purpose of the invention to provide simple and inexpensive methods to produce and use such cement mixtures.

Other purposes and advantages of the invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

Surprisingly, it was found that magnesite cements of outstanding water-resistance may be formed by mixing MgO, MgCb or MgSθ4 and water with certain organic carboxylic acids (nitrlotriacetic acid (NTAH3), ethylenediaminetetracarboxylic acid (EDTAH4), gluconic acid, tartaric acid and malic acid and mixtures thereof). The -o-

product can be casted or injected into molds and after hardening for a short duration at ambient pressure and temperature, solid specimens are formed.

This invention is not at all limited to the components discussed above and may contain additional components. Addition of fillers like sand, clay, calcium based minerals, gravel, aggregates, light aggregates. Acidic Fly-Ash (AFA), graphite, coal and synthetic materials (e.g. Kevlar fibers, Nylon fibers, etc.) in suitable forms may further improve the properties of the final product and allow it to meet different economical and physical requirements.

Moreover, the above carboxylic acids and/or their anhydrides and/or their carboxylate salts may be mixed with other carboxylic acids and/or their anhydrides and/or their carboxylate salts that are capable of foaming the magnesite cements in order to get improved foamed magnesite cements. The use of foaming carboxylic acids to form foamed magnesite cements is disclosed in copending Israeli Patent Applications of the same applicants herein, Nos. 109825, filed May 30, 1994 and 11 1031, filed September 22. 1994.

Detailed Description of Preferred Embodiments

The invention relates to an improved magnesite cement, comprising a cement selected from magnesium oxychloride and magnesium oxysulphate cement, or a mixture thereof, together with one or more organic carboxylic acid(s), having a "120h Weight Loss Coefficient", as hereinafter defined, of less than 5%, and/or their anhydrides and/or their carboxvlate salts. According to a preferred embodiment of the invention, the carboxylic acid has the formula:

R-(COOH)p wherein: p = 1 to 5

R= Alkyl (linear or branched: saturated or unsaturated; cyclic or acyclic); or Aryl (substituted or unsubstituted). wherein R contains up to 10 carbon atoms, and one or more of its carbon or hydrogen atoms may be replaced by oxygen, nitrogen, phosphor or sulfur atoms.

In order to determine which organic carboxylic acid is capable of forming "Water- Resistant cements" of a suitable quality, an "Enhanced Water-Resistance Test" was devised, following the procedure described in the following literature:

1) J. Kovler, et al; "Durability of Glass Fiber Reinforced Composites with Different Cement Matrixes"; National Building Research Institute; Technion - Israel Institute of Technology; Haifa; Israel (1993).

2) A.J. Majumdar, et al; "glass Fibers Reinforced Cement"; BSP Professional Books; Oxford (1991).

Clearly, different water-resistance tests could be devised and it will be easy, for skilled persons, to determine when the addition of a organic carboxylic acid produces a cement which is significantly better than that of a comparable cement prepared without the addition of the acid or with acids that give rise to cements of inferior water-resistance.. Preferably, the following organic carboxylic acids are selected, based on the above mentioned "Enhanced Water-resistance Test" and the resulting "120h Weight Loss Coefficients": nitrilotriacetic acid (NTAH3), ethylenediaminetetracarboxylic acid (EDTAH4), gluconic acid, tartaric acid and malic acid and mixtures thereof. Although the above mentioned carboxylic acids pass the "Enhanced Water-resistance Test", their effect on the setting kinetics of the magnesite cements is quite different. This phenomenon may be useful in some applications.

As can be seen in the examples to follow, other organic carboxylic acids and/or their anhydrides and/or their carboxylate salts, which do not pass the "Enhanced Water- resistance Test", can still improve the performance of the magnesite cements. Therefore, their blending with the top performing carboxylic acids that are covered in the present patent application is a straight forward mode of operation, which does not exceed the scope of the invention

Moreover, the above carboxylic acids and/or their anhydrides and/or their carboxylate salts may be mixed with other carboxylic acids and/or their anhydrides and/or their carboxylate salts that are capable of foaming the magnesite cements in order to obtain improved foamed magnesite cements, as disclosed in the aforementioned copending Israeli patent applications.

Compounds that are able to undergo fast hydrolysis to form the carboxylic acids or carboxylate salts during the cements preparation can also be used in this invention. Examples of such materials are acid halides [of the general formula R(COX)p; X=halide, e.g. X=C1]. However, these materials are usually more expensive than the respective carboxylic acids and carboxylate salts. According to another preferred embodiment of the invention the cement comprises carboxylate salts. Illustrative but non-limitative salts are the Na⁺, Mg^"1-*^", Al^"1-*^""1" and Ca^4"1" salts. The carboxylate salts may give somewhat different results than the corresponding acids or anhydrides. However, these differences are usually quite small, especially if the quantities used in the production are based on the respective molecular masses.

Of course, as will be appreciated by the skilled person, the cement according to the invention may further comprise suitable additives and/or fillers. Illustrative, but non- limitative examples of such additives include sand, clay, calcium based minerals, gravel, aggregates, light aggregates, coal, ashes (especially Acidic Fly-Ash) and synthetic materials in suitable forms. According to a preferred embodiment of the invention, the Acidic Fly-Ash contains about 35%-55% by weight of Siθ2 , about 15%-32% of AI2O3 no more than 15% by weight of CaO. and has an Loss On Ignition (1000°C) greater than 2.5 %wt. The technology of formulating magnesite cements further comprises the addition of additives like phosphoric acid and salts, oily materials like paraffin, silicones. long chain fatty acid esters and various polymers, as mentioned in the prior art.Such additives may also be used in combination with the formulations of the invention, when desired, but their presence is of course not a requirement of the invention.

The invention is also intended to cover shapable composition comprising a cement of the invention. Such shapable compositions are useful in manufacturing formed bodies. Illustrative formed bodies comprising a cement which has hardened include cast articles. structural elements, pressed articles, injected articles, extruded articles, and articles in pelletized form or in crushed form.

The articles manufactured according to the invention, as explained above, may be used for a variety of well known uses of magnesite cements, such as adsorbent materials, e.g., as ion sequestering agents, as pet litter, as gas adsorbents for adsorbing noxious gases, such as SO3 or SO2 and as flame retarding agents which can be used as flame-retarding additives in synthetic resins.

All the above and other characteristics and advantages of the invention will be better understood through the following illustrative and non-limitative examples.

Experimental

In the examples given hereinafter, the following raw materials were used:

- calcined MgO, a product of Dead Sea Periclase ("MgP");

- calcined MgO, a product of Grecian Magnesite;

- calcined MgO, a product of Grecian Magnesite - Type C-85;

- grade "Normal F" - "MgF";

- grade "Normal K" - "MgK";

- MgS04 solution having a density of d=1.2 g/cm^J were the ratio H2θ/MgSθ4 - 3.1 ; -MgCb solution having a density of d=l.267-1.27 g/cm^J were the ratio

H2θ/MgCb=2.61 ;

- Quartz sand powder (-200 mesh)

- Acidic Fly-Ash (AFA) from Hadera power station (contains the major constituents: 50 % wt Siθ2, 25% wt AI2O3, 9 % wt CaO); Examples of carboxylic acid materials (supplied by Aldrich) that were used, and which will be indicated in the examples by the symbols of the right-hand column of the following list, are:

- Maleic anhydride - P2

- Nitrilotriacetic acid (NTAH3) - P3

- NTANa3^»H2θ - Nitrilotriacetic acid trisodium salt monohydrate - P3-1.

- Ethylenediaminetetracrboxylic acid (EDTAH4) - P4

- EDTA Na4 - Tetrasodium salt ethylenediaminetetraacetic acid - P4-1

- DL-aspartic acid - P5

- DL-malic acid - P6

- Adipic acid - P7

- Acrylic acid - P10

- Phthalic acid - PI 1

- Phthalic anhydride - P12

- Methacrylic acid - P14

- Fumaric acid - PI 5

- Oxalic acid - PI 6

- Tartaric acid - PI 7

- Isophthalic acid - P18

- Gluconic acid - PI 9

- Propionic acid - P20

- Acetic acid - P21

- Formic Acid - P22 -Terephthalic Acid - P27 -Trimellitic Acid - P28

- Citric Acid - P29

- Lactic Acid - P97 -Polyacrylic acid of Fluka (#81140) - P98

-Ethylene Acrylic Copolymer of Allied Signal

(Grade A-C540; Lot #095406AC) - P99

It should be noted that the purity of the raw materials that can be used is not of prime importance. A variety of commercially available materials can be used as suitable and inexpensive substitutes.

Production and Performance Tests of Magnesite Cements

The raw materials, in the desired amounts, were introduced in a Retch Mill type KM-1 and subjected to a grinding/mixing operation for a period of 20 minutes. A viscous mass was thus produced, which was introduced in dies of the dimensions 40x40x160 mm and left there to cure for a period of ten days at room temperature. After being cured the cast or pressed bodies were exposed to an accelerated drying/freezing (D/F) cycles for the purpose of evaluating their water resistance and stability. The accelerated D/F cycle included the following stages: a) drying at 80°C for 24 hours; b) immersion in water for 24 hours; c) freezing of the wet bodies at -18°C for 24 hours; and d) dropping the cold bodies into boiling water and keeping them therein for 4 hours. The reaction of the bodies to such a treatment reveals their water resistance and stability, resistance to thermal shock, water absorption, weight loss and density changes. The modulus of rapture and compressive strength were measured before and after applying five cycles as herein before described.

In the examples below, the following abbreviations are used: CS - Compressive Strength (MPa) MOR - Modulus Of Rupture (MPa) CM - Carboxylic acid Material d - Density W.A. - Water Absorption W.L. - Weight Loss AFA - Acidic Fly Ash K-Clay - Kaolin Clay.

Example 1 (comparative)

Table I:

Oxysulfate Cement

Calculated weight ratio

Test No. MgO/MgS0₄ H,0/MgS0 MgO H₂0 Type of MgO

A 9.57 5.57 1.72 MgP

B 6.14 4.12 1.49 MgP

C 5.00 3.56 1.40 MgP

D 4.10 3.10 1.32 MgP

E 2.73 3.10 0.88 MgP

F 1.75 3.10 0.56 MgP

G 4.10 3.10 1.32 MgF

Without exception, the products developed cracks and/or decomposed during the drying and/or wetting stage of the first cycle.

Table II: Oxychloride Cement

CALCULATED WEIGHT RATIO

Test No. MgO/MgCl₂ H₂0/MgCI₂ MgO/H₂0 Type of MgO

A 3.61 2.99 1.20 MgP

B 2.84 2.61 1.09 MgP

C 2.70 2.61 1.04 MgP

D 2.70 2.61 1.04 MgF

E 2.70 2.61 1.04 MgK

F 2.40 2.61 0.92 MgP

G 1.94 2.61 0.74 MgP

H 1.55 2.61 0.52 MgP

I 1.27 2.61 0.48 MgP

J 1.08 2.61 0.41 MgP

Without exception, the products developed cracks and/or decomposed during the drying and/or wetting stage of the first cycle. Example 2 Oxysulphate Cements Including Water Resistant Additives

The products shown in the following table were prepared. The following cement formulations were used:

Table III

CALCULATED WEIGHT RATIO

Test No. MgO/ AFA H_:0/ MgO/ Type of % CM/ Type of MgS0₄ MgS0 MgS0₄ H,0 CM MgO MgO

51 6.16 6.83 5.68 1.080 P3 1.0 MgP

54 4.10 8.20 5.08 0.807 P4 1.0 MgP

57 2.73 10.25 5.15 0.530 P7 1.0 MgP

59 1.75 3.30 3.10 0.560 P6 1.0 MgP

After applying the test procedure, the following results were obtained:

Table IV

Before D/F cycles After D/F cycles

Test % d CS MOR % % d CS MOR No. W.A. g/m³ W.A. W.L.* g/m³

51 10.7 1.66 24.5 3.85 7.5 + 1.0 1.71 22.5 3.85

54 11.9 1.58 18.0 4.55 10.2 +0.8 1.63 19.5 5.15

57 13.2 1.52 16.0 2.35 12.9 +0.5 1.56 16.0 2.25

59 14.3 1.45 31.0 6.25 14.1 0 1.45 30.0 5.90

*%W.L. = % weight gained Example 3

A combination of MgCb and MgS04 solutions was used. Normally, bodies cast out of MgCb solutions tend to expand, while bodies cast out of MgSθ4 solutions tend to shrink.

By preparing a cement based on a mixture of these solutions, one can control the rate of shrinking/expansion, and in addition enjoy the other properties of the mixture, such as density, water absorption, reaction acceleration, by adding the sulfate solution.

The following table gives an example of this experiment.

Table V

CALCULATED WEIGHT RATIO

Test No. MgO/ AFA MgSθ₄/ MgO/ Type of % CM Type of Brine MgCl, MgCl₂ H₂0 CM MgO MgO

258 2.725 5.47 0.325 1.0 P3 1.0 MgP

After applying the test procedure, the following results were obtained:

Table VI

Before D/F cycles After D/F cycles

Test % d CS MOR % % d CS MOR

No. W.A. g/m³ W.A. W.L. g/m³

258 5.0 1.85 56.0 7.0 5.0 - 1.85 56.0 7.65 Example 4 Oxychloride cements including additives.

Test 1 : Pure cement.

The following cement formulation was used in the test work.

Table VII

CALCULATED WEIGHT RATIO

Test No. MgO/ Additive/ H₂0/ Type of Type of MgCl₂ MgCl₂ MgCb Additive MgO

2-3 2.70 4.1 1 0.63 AFA MgP

281 2.40 4.01 0.65 AFA MgP

336 2.40 4.01 0.65 K-Clay MgP

JJ / 2.40 4.01 0.65 K-Clay MgP

Composite products by casting technology.

As stated before, by adding various materials to the mixing stage together with the cement ingredients, one can produce composite structural materials. The following table gives some examples of these composites:

Tahle VIII

After applying the D/F procedure, the following results were obtained:

Table IX

Before D/F cycles After D/F cycles

Test % d CS MOR % % d CS MOR

No. W.A. g/m³ W.A. W.L. g/m³

2-3 2.3 1.99 81.50 17.50 2.2 - 1.99 84.0 19.75

292 1.2 2.27 61.50 10.65 0.9 - 2.27 64.0 10.3

295 4.8 0.95 4.50 2.65 4.7 - 0.95 5.5 3.45

300 1.8 2.07 77.00 13.45 2.2 0.9 2.05 79.0 9.35

293 2.1 2.16 53.50 8.15 2.5 0.9 2.14 51.50 8.25

Test 2 - Pressing technology.

Composite products by pressing technology

Pressing technology is commonly used in the tile industry. It has some advantage over casting technology, mainly because it produces an instant green body of a sufficient strength, which can be handled to a curing place.

In addition to the cement, which acts as a binder between the various fillers, the most important parameters influencing the product quality are:

- Size distribution of the fillers.

- Magnitude of the pressing force.

In this experiment, quartz sand of different mesh size was used as filler. Three fractions were used:

Fraction 1 - -20 + 30 mesh

Fraction 2 - -80 + 200 mesh

Fraction 3 - -200 mesh.

Various mixtures were prepared where the pressing force was kept constant at a value of 100 Kg/cm-. The products prepared are summarized in Table X below.

Table X c /o W e i g h t R a t i o

Test No. Cement Cement Fraction Fraction Fraction Type of % CM/ Type of Formu¬ 1 2 3 CM MgO MgO lation

3 2-3 20.0 54.8 18.3 6.9 P3 1.0% MgP

19 2-3 17.0 67.7 10.2 5.1 P7 1.0% MgP

32 2-3 15.0 72.0 15.0 - P4 1.0% MgP After pressing these bodies into shapes of 4 x 4 x 16 cm-⁵, the bodies maintain sufficient green strength and can be carried by any conventional way of industrial transportation into the curing place.

The D/F test procedure was applied to these products.

The product properties were measured before and after these tests, and are summarized in the following table:

Table XI

Before cycle After cycles

Test % d CS MOR % % d CS MOR

No. W.A. g/m³ W.A. W.L. g/m³

3 5.2 2.20 52.0 9.5 5.0 0 2.20 53.0 9.8

19 2.4 2.40 70.0 15.0 2.3 0 2.40 72.0 14.5

32 2.8 2.35 61.0 13.2 2.7 0 2.35 61.0 13.4

Example 5 White Cement Test 1 - Pure cement.

The following materials were prepared:

Table XII

CALCULATED WEIGHT RATIO

Test No. MgO/ SiO,/ H,0/ H,0/ Type of %CM/ Type of MgCl, MgCl, MgCl, SiO, CM MgO MgO

Material

271 2.40 4.01 2.61 0.65 P3 5% MgP

272 2.40 4.01 2.61 0.65 P4 5% MgP

After applying the drying/freezing procedure, the following results were obtained:

Table XIII

Before cycle After cycles

Test % d CS MOR % % d CS MOR

No. W.A. g/m³ W.A. W.L. g/m³

271 1.80 2.04 93.5 9.70 2.1 0 2.04 93.5 8.60

272 1.60 1.96 101.0 8.60 1.9 0 1.96 102.0 9.00

Test 2 - Addition of fine alumino-silicates

The following samples were prepared:

Table XIV

% Weight Ratio

Test No. MgO/ Additive H,0/ H,0/ Type of Type of % CM/ Type of MgCl₂ MgCl, MgCl, Additiv Additive CM MgO MgO Materia

281 2.40 4.01 2.61 0.65 AFA P3 3% MεP

336 2.40 4.01 2.61 0.65 K. CLA P3 5% MgP

Table XV

Before cycle After cycles

Test % d CS MOR % % d CS MOR

No. W.A. g/m³ W.A. W.L. g/m³

280 1.8 1.95 79.0 10.15 1.3 0.7- 1.97 72.5 7.15

336 2.5 2.03 80.0 14.00 1.8 0 2.04 60.0 9.05

Test 3 - Composite products.

The following samples were prepared:

Table XVI

% W e i gh t R a t i o

Test No. Cement Cement Additive Type of Type ( % CM/ Type of Formu¬ Additive CM MgO MgO lation Material

301 236 50.0 50.0 quartz P4 5% MgP sand -100 mesh

302 236 50.0 50.0 P6 5% MgP

303 236 50.0 50.0 P3 5% MgP

308 286 50.0 50.0 P4 5% MgP

322 310 50.0 50.0 P3 2.5% MgP

After applying the D F cycle procedure, the following results were obtained: Table XVII

Before D/F cycles After D/F cycles

Test % d CS MOR % % d CS MOR

No. W.A. g/m³ W.A. W.L. g/m³

301 1.8 2.07 1 17.0 10.35 1.3 0 2.07 1 18.5 13.95

302 1.0 2.09 109.5 15.85 0.5 0 2.03 1 14.0 17.45

303 1.2 2.1 91.5 20.45 1.2 0 2.1 108.0 14.65

308 1.2 2.13 90.0 6.7 1.2 0 2.19 100.5 8.10

322 2.2 2.08 47.5 8.25 2.3 0 2.08 56.5 8.85

In addition, samples 302, 303 and 322 were cast in dies (dimensions: 20 x 70 x 70 mm) for attrition test purposes.

The following results were obtained:

Table XVIII

Test

No. Before D/F cycles After D/F cycles

Attrition MM (440 rpm) Attrition MM (440 rpm)

302 2.26 2.40

303 2.08 2.02

322 2.80 2.54

Example 6 Comparative test, acid vs. salt form

The following additive materials were tested and compared:

1.0- EDTA - Ethylenediaminetetraacetic acid - P4

1.1- EDTA a4 - Tetrasodium salt ethylenediaminetetraacetic acid - P4-1 2.0- NTA - Nitrilotriacetic acid - P3

2.1 - NTANa3^»H2θ - Nitrilotriacetic acid trisodium salt monohydrate - P3-1.

The cement products were prepared according to the patent procedure and by weight proportions given by the following table:

Table XIX

% W E I G H T R A T I O

Test No. MgO/ Siθ2 H2O/ H2O/ Type of C % CM/ Type of

MgCh MgCl2 MgCh Siθ2 Material MgO MgO

271 2.40 4.01 2.61 0.65 P3 5% MgP

271 - 1 2.40 4.01 2.61 0.65 P3-1 5% MgP

272 2.40 4.01 2.61 0.65 P4 5% MgP

272-2 2.40 4.01 2.61 0.65 P4-1 5% MgP

-2δ-

Table XX

Test % % CS CS No. W.A. W.L. Reduc-tion %

271 2.1 0 93.5 -

271-1 4.4 2.5 77.0 17.6%

272 1.9 0 102.0

272-1 3.0 1.0 85.0 16.6%

The comparative tests show the following:

1. The salt forms are somewhat inferior to the acid forms additives by means of water absorption weight loss and compressive strength.

2. During the D/F cycles, samples 271-1, 272-1 (i.e. the salt forms) tended to crack under thermal shock.

3. The results could be much more closer, had the CM. weights been based on the molecular weights.

Example 7 "Enhanced Water-resistance Test" and "120h Weight Loss Coefficient"

Cement mixtures consisting of the following materials: 60g MgO (calcined MgO, a product of Grecian Magnesite - Type C-85), 90g MgCb brine, 50g quartz sand powder and the 1.5g of the organic carboxylic acid being tested, are mixed in a laboratory mixer (Retchtype KM"1) for 10 mins.. The mixtures obtained are cast into dies of the dimensions 20x20x70 mm and allowed to cure at room temperature and pressure for 14 days. The specimens are subjected to the following operations:

a. Immersion in water at 25°C for three days and measuring the weight of the wet samples and drying the samples at 90°C for fifteen hrs. to obtain the initial % Water Absorption (%W.A.₀ );

b. Immersion of the dried samples of "a" in water at 60°C for one day and drying the samples at 90°C for fifteen hrs. to obtain the % Water Absorption (%W.A. ₄ hrs.)- ^Tne difference between the dried samples in b and a gives the % Weight Loss (%W.L.₂₄ hrs.);

c. Immersion of the dried samples in water at 60°C for additional four days and drying the samples at 90°C for fifteen hrs. to obtain the % Water Absorption (%W.A.-₂0hrs.)- The difference between the dried samples in c and a gives the % Weight Loss (%W.L.₁₂o hrs.);

The results are summarized in Table XXI: Table XXI

24 hrs. at 60 °C 120 hrs. at 60 °C

Test# CM. %W.A₀ %W.A. %W.L. %W.A. %W.L. Notes

El None 17.1 19.0 6.30 42.7 24.5 Reference - Failed

E2 P3 7.0 6.7 0.2 6.8 2.2 %W.L._120hrs<5%

E3 P4 7.6 5.6 +0.2 7.5 1.1 %W.L._120hrs<5%

E4 P6 10.0 6.9 0.8 7.2 2.1 %W.L._120hrs<5%

E5 P7 8.2 9.3 3.2 17.2 10.7 Failed

E6 P12 7.3 6.8 1.5 17.5 1-5.-5 Failed

E7 P16 15.0 12.4 1.0 26.8 14.4 Failed

E8 P17 7.5 6.3 1.5 8.2 %W.L._120hrs<5%

E9 P 19 6.3 4.7 0.6 7.8 2.6 %W.L._120hrs<5%

E10 P21 6.7 8.3 3.9 14.4 10.9 Failed

Ell P22 6.9 6.8 2.4 10.2 6.5 Failed

E12 P27 11.8 18.1 7.7 36.6 24.7 Failed

E13 P28 5.6 7.7 4.3 26.8 22.1 Failed

E14 P29 9.7 7.8 1.6 14.9 8.3 Failed

E15 P97 16.2 14.2 3.1 30.2 19.8 Failed

E16 P98 15.1 22.0 6.0 32.1 22.1 Failed

E17 P99 16.3 23.1 5.8 31.8 21.8 Failed

Note 1 : + XX means W'eight Gain.

Note 2: Immersion of the cement specimens for one day in hot water at 60 is simulating a nine month of exposure of the material under a regular English weather.

Note 3: The "120h Weight Loss Coefficient" of a carboxylic acid is defined as the

%W.L._]2ohrs °f ^a magnesite cement that incorporates the respective carboxylic acid. Those carboxylic acids that lead to %W.L.ι o hrs 5% are operative according to the present invention.

All the above description and examples have been provided for the purpose of illustration, it being understood that they are not intended to limit the scope of the invention in any way. except as defined in the appended claims.

Claims

C L A I M S

1. Improved magnesite cement comprising a cement selected from magnesium oxychloride and/or magnesium oxysulphate cements together with one or more organic carboxylic acid(s) having a "120h Weight Loss Coefficient", as defined in the specification, of less than 5%, and/or their anhydrides and/or their carboxylate salts.

2. A cement according to claim 1, comprising a carboxylic acid of the formula:

R-(COOH)p wherein: p = 1 to 5;

R= Alkyl (linear or branched; saturated or unsaturated; cyclic or acyclic); or Aryl (substituted or unsubstituted), wherein R contains up to 10 carbon atoms, and one or more of its carbon or hydrogen atoms may be replaced by oxygen, nitrogen, phosphor or sulfur atoms.

3. A cement according to any one of claims 1 and 2, in which the organic carboxylic acids are selected from nitrlotriacetic acid (NTAH3), ethylenediaminetetracarboxylic acid (EDTAH4), gluconic acid, tartaric acid and malic acid and mixtures thereof.

4. A cement according to any one of claims 1 to 3, further comprising one or more carboxylic acid(s) and/or their anhydrides and/or their salts, which are capable of inducing foaming.

5. A cement according to any one of claims 1 to 4, further comprising one or more carboxylic acid(s) and/or polycarboxylic acids and/or their anhydrides and/or their salts, which are not capable of inducing foaming.

6. A cement according to any one of claims 1 to 5, further comprising suitable additives and/or fillers.

7. A cement according to claim 6, wherein the fillers are chosen from among sand, clay, calcium based minerals, gravel, aggregates, light aggregates, coal, ashes (especially Acidic Fly-Ash) and synthetic materials in suitable forms.

8. A cement according to claim 7, wherein the Acidic Fly-Ash contains about 35%-55% by weight of Siθ2 , about 15%-32% of AI2O3 no more than 15% by weight of CaO, and has an LossOn Ignition (1000°C) greater than 2.5 %wt.

9. A shapable composition comprising a cement according to any one of claims 1 to 8.

10. Formed bodies comprising a cement according to any one of claims 1 to 8, which has hardened.

1 1. Formed bodies according to claim 10, which are cast articles.

12. Formed bodies according to claim 10, which are pressed articles.

13. Formed bodies according to claim 10, which are injected articles.

14- Formed bodies according to claim 10, which are extruded articles.

15. Formed bodies according to claim 10, which are in pelletized form..

16. Formed bodies according to claims 11 to 15, which are in crushed form.

17. Formed bodies according to claims 11 to 16, which are structural elements.

18. An adsorbent material comprising a cement according to any one of claims 1 to 8.

19. An adsorbent material according to claim 18, for use as a sequestering agent for ions.

20. An adsorbent material according to claim 18, for use as a pet litter.

21. An adsorbent material according to claim 18, for use as a gas adsorbent.

22. An adsorbent material according to claim 21, wherein the gas is SO3 or Sθ2-

23. A flame retarding composition, comprising as an active ingredient a cement according to any one of claims 1 to 8.

24. A water-resistant magnesite cement, substantially as described and exemplified.

25. A composition comprising a magnesite cement, substantially as described and exemplified.

26. Formed bodies comprising a magnesite cement, substantially as described and exemplified.

27. A process for the manufacture of magnesite cements as claimed in claim 1, comprising adding to the components mixture, prior to foaming, an effective amount of a polymerization initiator.

28. Process for making a water-resistant magnesite cement, substantially as described and exemplified.