WO2002002477A1

WO2002002477A1 - Magnesic foam panel, and relevant production method

Info

Publication number: WO2002002477A1
Application number: PCT/IB2001/001591
Authority: WO
Inventors: Alberto Vaghini; Rosa Di Maggio
Original assignee: Alberto Vaghini; Rosa Di Maggio
Priority date: 2000-07-03
Filing date: 2001-07-02
Publication date: 2002-01-10
Also published as: ITPC20000025A1; ITPC20000025A0; AU2001282396A1

Abstract

A panel is described, designed for making cabins and compartments for boats and the like, which comprises at least one layer of magnesium oxide foam. In particular the panel comprises one layer of material having the following composition: A) Magnesium oxide MgO 100 parts B) Compound B 90 parts C) Naphthalene sulphonate NNO 0.1 % to 3 % D) Hydrogen peroxide H2O2 0 to 20 % in which compound B comprises : Water H2O 50 parts (45 % A) Magnesium chloride MgC12 50 parts (45 % A) Phosphoric acid H3PO4 0.5 % A.

Description

MAGNESIC FOAM PANEL AND RELEVANT PRODUCTION METHOD

This invention relates to a magnesium foam panel with marked characteristics of lightness, resistance to chemical and atmospheric agents and fire resistance, together with good mechanical strength.

The panel in accordance with the invention, which has good heat insulation properties, is particularly suitable to make partition walls and/or cabin walls in boats and the like. The panel is made from a mixture comprising magnesium oxide, naphthalene sulphonate and a compound of water, magnesium chloride and phosphoric acid. A percentage of hydrogen peroxide is added to the formulation and combines with the metal ions present in the mixture to form a foam, thus producing a panel that combines good characteristics of rigidity and mechanical strength with considerable lightness.

As it consists wholly of inorganic materials, the panel presents excellent fire- resistance characteristics, and in particular does not produce toxic fumes in the event of fire. The panel manufacturing process in accordance with the invention involves steam curing, preferably in a carbon dioxide environment, to accelerate the consolidation time of the material and at the same time increase its mechanical strength. All materials and components used in the construction of ships, aircraft and the like are subject to very strict regulations that specify the safety requirements with which these materials must comply. In particular, in the case of the panels used to make the cabins of ships and boats in general, designers have to solve problems which often have conflicting solutions.

On the one hand increasingly severe regulations impose minimum safety requirements such as fire and heat resistance, mechanical strength and durability of the material, while on the other hand project specifications require increasingly lightweight, tough, strong panels, characteristics which are hard to reconcile with those imposed by the new regulations in the major European countries.

Until a few years ago, the panels used for ship's cabins comprised a metal framework with curtain walling panels made of wood or the like; however, they were heavy, posed considerable problems relating to the installation of equipment, and above all possessed very poor fire resistance.

More recently, panels with a honeycomb structure have been proposed. However, they are very expensive to manufacture, and it is very difficult to make passages in them for cables to pass through; it is also difficult to apply loads to the wall, as this type of panel is not designed to withstand concentrated loads, with the result that stiffening needs to be added in the load application area, for example by glueing on suitable reinforcement plates or the like.

Moreover, this kind of material does not present fire resistance characteristics. AS a result, the need is felt in the industry for means which produce lightweight panels that also feature good mechanical strength, and above all excellent fire resistance characteristics.

This problem is now solved by the present invention, which relates to a panel and the corresponding manufacturing process, and involves mixing magnesium oxide, magnesium chloride, water and possibly phosphoric acid and naphthalene sulphonate, with the addition of hydrogen peroxide as foaming agent.

This invention will now be described in detail, by way of example but not of limitation, by reference to the annexed figures in which:

• figures 1 to 6 are six photos taken with a scanning electron microscope which illustrate the structure of the material constituting a panel made in accordance with the invention

• figure 7 is the graph of an X-ray analysis of the various types of panel in accordance with the invention. The panel in accordance with the invention basically consists of a layer of porous, rigid, lightweight material obtained by foaming a compound with the basic formula indicated below:

Formulation (1):

A Magnesium oxide MgO 100 parts

B Compound B 90 parts

C Naphthalene sulphonate NNO 0.1% to 3%

D Hydrogen peroxide H₂0₂ 0 to 20% in which compound B comprises: Water H₂0 50 parts (45% A)

Magnesium chloride MgCl₂ 50 parts (45% A) Phosphoric acid H3PO4 0.5% A Foam formation is due to the reaction of the hydrogen peroxide, catalysed by the metal ions present in the mixture.

This layer of light, porous material is preferably sandwiched between two outer layers which may consist of layers of the same material, unfoamed, subsequently called "levelling compound" (a material obtained by mixing the same constituents as stated above without hydrogen peroxide) or of other materials such as sheet metal, possibly shaped, or MDF cement.

For example, the panel could be advantageously made by joining two sheets of metal, suitably shaped and connected, as described in Italian patent application no.

PC 98A 036, and filling them with foam produced as stated above. The material constituting the core of the panel thus produced is fire-resistant and has a density of 400 to 1000 kg/m , depending on the amount of hydrogen peroxide used as foaming agent.

In the absence of hydrogen peroxide, the volume of the material does not increase and no porosity is formed; a levelling compound with a density of 1200 kg/mβ is thus formed. The material which constitutes the core of the panel can be lightened further by adding suitable materials such as sawdust or polystyrene foam balls, but only at the expense of its fire resistance and safety characteristics (polystyrene, like other organic materials, develops harmful substances during combustion). The material would preferably be lightened by adding hollow microspheres of silica, an inorganic, non-combustible material, to the mixture.

The hardening of the material is due to two parallel phenomena: firstly the formation of an oxychloride hydrate, presumably with the composition 3MgO-MgCl₂-l lH₂0, and secondly carbonation of the residual magnesium hydroxide or the oxychloride hydrate.

The first phenomenon is a process which takes a few days at ambient temperature. Carbonation (such as the formation of magnesium carbonate MgC03, a hard material which constitutes some rocks together with calcium carbonate or other types of carbonate) is a slow process that takes years. Thus the mechanical resistance of the foam tends to increase with time.

The overall hardening process is accelerated by modifying one of the two phenomena.

If the formation of oxychloride hydrate is modified, consolidation of the foam is accelerated, whereas if carbonation is modified, the increase in the mechanical resistance of the solid foam is accelerated.

To consolidate the material in a short time and produce good mechanical strength, the invention introduces into the manufacturing process a steam-curing stage in an environment enriched with carbon dioxide. To prevent the risk of evaporation of the necessary water from the mixture, especially in the cortical areas, leading to a reduction in the final characteristics of the material, the invention provides for heating to be performed in an environment saturated with steam (steam curing). In order to prevent the final characteristics of the material from being adversely affected by the fact that some of the water in the atmosphere passes into the hardening mixture, the invention provides for the initial mixture to contain less than the stoichiometric amount of water. In fact, it has been found that water in the form of steam possesses sufficient mobility to spread throughout the mixture, thus accelerating setting and hardening, and experiments have demonstrated that mere exposure to a jet of steam for around ten minutes consolidates the foam. To accelerate the time taken by the foam to develop mechanical strength even more, it was decided to modify the carbonation reaction of the main constituents, magnesium hydroxide and magnesium chloride, two examples of which are set out below.

0.5 3MgO-MgCl₂-l lH₂0_(solid) + C0_2(gas)₅ Mg₂(OH)-Cl-C0₂-3H₂0_(solid)

+ 2H₂0(ii_qui Mg(OH)₂(_soiid) + C0₂(_gas) Mg₂C0₃(_soι_id) + H₂0(ϋ_quid)

As will be seen, the formation of carbonates, which contributes to strength, is obtained by reaction with carbon dioxide, a gas naturally present in the air. As a result, the reaction speed considerably benefits from heating of the material in an atmosphere enriched with C0₂.

It can be demonstrated that heating at 80°C for one hour in a carbon dioxide atmosphere doubles the strength of the foam, overall curing time being equal. In accordance with a further preferred embodiment of the invention, the following alternative formula is used: Formulation (2)

MgO 100 g

MgCl₂-6H 0 45 g

H3PO4 0.5 g

H₂0 18 g

NNO 0.3 g

H₂0₂ 8 g

The mixture prepared with this formulation hardens when it is treated with steam for 15 minutes, and its strength is doubled by heat treatment at 80°C in carbon dioxide. The density of the solid foam ranges between 250 and 300 kg/m3. The reduction of water in the mixture is designed to increase the durability of the material, making it less sensitive to water. The density of the foam can predictably fall, increasing the foaming agent content by up to 12-14 g, obviously at the expense of mechanical strength if the curing times are short, because greater porosity is introduced and the strong section is reduced. The mechanical behaviour of the material could be improved by adding mineral fibres. Moreover, steam and carbon dioxide treatment can be performed simultaneously.

The treatment can be performed by curing the mixture with steam and carbon dioxide for at least 10-15 minutes, or causing the sheet of mixture to pass through a chamber containing carbon dioxide and steam at a sufficient speed to ensure that it is affected by that atmosphere for at least 10-15 minutes. Of the various types of coating, levelling compound appears to be the most interesting, because it would allow the foam to be produced continuously and polypropylene channels for installations to be introduced with no need to use organic adhesives, while still meeting soundproofing and fire resistance requirements. A first panel with a thickness of approx. 30 mm was made, consisting of a layer of foam sandwiched between two layers of levelling compound made of the same material, but unfoamed. The process used to make the prototype involved preparing the foam, shaving the foam to the desired thickness (approx. 28 mm), positioning the foam on a layer of liquid levelling compound and Velovetro until dry, and repeating the operation on the opposite side. The interfaces between the foam and the levelling compound were strong enough to withstand handling of the panel. An alternative method which is more suitable for industrial product involves making the foam on a sheet of aluminium approx. 1.5 mm thick, shaving, and application by rolling of a plastic laminate of MDF cement approx. 1 mm thick. The strength of an aluminium-foam interface (adhesion) is greater than that of a levelling compound-foam interface. Morphological and structural analysis

Observations were made under a scanning electron microscope (SEM) and with X- ray diffraction analysis (XRD) to analyse foams made with both formulations. Some samples were then analysed to evaluate the effects of steam-curing, carbon dioxide treatment and reduction of water content. Observation of the materials under the scanning electron microscope showed the shape of the pores and the appearance of the crystals responsible for the strength of the material. First of all, attention focused on the magnesium foam with formulation (1) prepared by weighing and mixing the various constituents at ambient temperature (Sample A, figures 1 and 2). The subsequent photos show the foam with formulation (1) cured with steam (figures 3 and 4, sample B) and the foams with formulation (1) treated with steam and C0₂ (figures 5 and 6, sample C). As will be seen, sample (A) has regular spherical pores inside which the formation of lamellar crystals can be seen. The walls of the pores consist of powders of unreacted substances entwined with lamellar crystals.

The other foams are characterised by more irregular porosity and reduced growth of lamellar crystals (if the photos of the materials are compared at the same magnitude, the average length of the lamellae will be found to be shorter). Two types of crystal can be seen in the sample treated with C0 : a lamellar crystal similar to the one present in the two preceding samples, and another, more specifically needle-shaped crystal which must necessarily be attributed to a different product. The information supplied by direct observation under the microscope is clarified by X-ray analysis.

The main compounds contained in sample A (Figure 7) are magnesium oxychloride with the formula Mg3(OH)5CTH₂0 (lamellar crystals) and magnesium oxide MgO (the non-hydrated reagent, which appears in the photos as a mass of granules). Magnesium hydroxide Mg(OH ) is also present, though in a very modest amount, but no carbonated form is present.

The steam-cured samples with formulation B mainly contain magnesium hydroxide and magnesium oxychloride with the formula Mg3(OH)5ClΗ₂0, the latter in smaller quantities than those present in the foam from which sample A was taken. Very modest quantities of magnesium oxide and magnesium chlorocarbonate hydrate Mg3(OH)-Cl-C03-3H₂0 are also present. Sample C treated with C0₂ contains a significant amount of magnesium chlorocarbonate hydrate (needle-shaped crystals), together with magnesium hydroxide and magnesium oxychloride. It can therefore be said that the lower water content in formulation C allows the formation of products of carbonation, and that the presence of magnesium chloride does not seem to thermodynamically promote the formation of magnesium carbonate, but rather of the chlorocarbonate. In any event, the results of the analysis confirm the hypotheses formulated about the curing process. The samples cured for the longest time contain oxychloride and chlorocarbonate fractions which are much greater in terms of volume than the reagents in their original state. Moreover, if the results obtained with the steam-cured sample are compared with those of the sample also treated with carbon dioxide, the volume of chlorocarbonate will be found to be some 30-40% greater than the volume of oxychloride hydrate.

Figure 7 also shows the analysis of a foam B', containing only 40%> of the amount of water used in the traditional formulation, immediately after the steam treatment. It can be deduced that although magnesium oxide is the main constituent, some forms of oxychloride hydrate are already present. Mechanical tests

The modulus of elasticity of foams cannot be determined experimentally with precision, due to the impossibility of measuring the deformation of the specimens exactly, because they are friable. The values reported are deduced from the experimental curves with a certain degree of approximation, and only express the order of magnitude of the real value. It was only possible to measure the modulus of elasticity fairly accurately with a resonance measuring instrument in the case of levelling compound with sawdust. All samples were analysed with compression tests (except for levelling compound with sawdust), and the mechanical behaviour recorded was the brittle type, as was to be expected of ceramic materials. However, some significant differences were found.

Foam sample A, which represents the standard reference material, exhibited perfectly elastic, brittle behaviour, i.e. presented definite yielding of the sample at a mean applied force of 0.384 + 0.024 Mpa, with a modulus of elasticity between 10 and 20 GPa. Other samples yielded at a given load; when it was increased, the strength remained constant until the final collapse (see Table 1). As will be seen by comparing sample 891110.2S with sample 891110. IS, the strength of the material declines in proportion to the increase in foaming agent, and consequently to the variation in the overall porosity of the material.

Table 1

Sample ^σmean (Mpa) E(Mpa)

891110.2S 0.770 + 0.040 20-30

891110.1S 0.515 + 0.063 15-20

89008.1.6 0.594 + 0.034 40-50

In a second set of samples a first yield was recorded; then, when the load was increased, a plateau was reached at which strength remained constant until the collapse of the material (Table 2). Table 2

Sample σ_mean (Mpa) E(Mpa)

891105.15 0.262 + 0.009 30-40

990212 0.115 ± 0.003 10-20

7/04/98 0.233 ± 0.007 10-20

Finally, the sample of levelling compound contairiing sawdust as toughening filler was analysed for flexural strength. The stress-strain curve proved to be the pseudoplastic type, with a yield stress of 14.32 ± 0.11 Mpa and a fracture stress of 23.35 ± 0.28 Mpa. Measurement of the modulus of elasticity supplied a very high value of 80 GPa. The value of the modulus of elasticity of levelling compound without filler is presumably much higher; in fact, the presence of less rigid fillers or porosity leads to a reduction in the modulus of elasticity in accordance with their percentage in terms of volume. Other samples, which were prepared with formulations A and therefore cured in air at ambient temperature, did not yield at a given value when subjected to increasing loads, but slowly disintegrated. The fracture resistance of these materials therefore cannot be defined, and Table 3, which summarises the results, refers to the stress at which the foam begins to yield. In addition, it was found that the development of strength slows with aging, with the result that substantial modifications can only be recorded over the long term, not over a period of 1 or 2 months. The yield stress values measured are therefore much lower than for samples cured for over six months, foaming agent being equal.

^' Table 3 Sample ^σmean (Mpa) E(Mpa) Sample 8% H₂0 5 days p = 600 kg/m3 0.119 + 0.011 10-20 Sample 8% H 0₂ 7 days p = 600 kg/m3 0.127 + 0.024 10-20 Sample 1.5% H 0₂ 5 days p = 1200 kg/m³ 0.956 ± 0.043 30-40 Sample 1.5% H₂0₂ 7 days p = 1200 kg/m³ 0.994 + 0.109 30-40 The results shown in this table again confirm that the use of a larger amount of foaming agent reduces the density, and above all the strength of the material. The samples cured in steam and carbon dioxide remained more compact before the final yield. When the load was increased, they presented an initial yield; then, when the load was increased further, they exhibited an increase in strength until a plateau was reached that remained constant until the collapse of the material (see Table 4).

Table 4 Steam-cured samples σ_mean (Mpa) E(Mpa) Sample 8% H₂0₂ 1 day p = 300 kg/m³ 0.067 + 0.017 5-10 Sample 8% H 0₂ 7days p = 300 kg/m3 0.066 + 0.012 5-10

Steam- and C0 -cured samples Sample 8% H₂0₂ 1 day p = 300 kg/m3 0.108 + 0.009 10-15 Sample 8% H₂0 7days p = 300 kg/m3 0.142 + 0.019 10-15 The results shown in the table demonstrate that rapid consolidation of the mixture following steam treatment does not lead to an equally rapid development of strength, and that samples cured in steam are far less strong than those cured in air, aging time being equal. The time when setting begins appears to be crucial to commencement of the chemical processes which form strong compounds. In fact, although treatment in carbon dioxide cancels out the differences between steam- cured and air-cured samples, the compound to which the greatest mechanical strength is attributed is magnesium chlorocarbonate hydrate, while the crystallisation nuclei of the compound, which increase with time, may form more readily in a mixture that is still plastic. These hypotheses confirm the need for curing to be performed in steam enriched with C0 .

Claims

CLAIMS 1) Panel designed in particular for making cabins and compartments for boats and the like, characterised in that it comprises at least one layer of magnesium oxide foam. 2) Panel designed in particular for making cabins and compartments for boats and the like, as claimed in claim 1, characterised in that it comprises at least one layer consisting of a mixture of magnesium oxide and magnesium chloride foam. 3) Panel designed in particular for making cabins and compartments for boats and the like, as claimed in claim 2, characterised in that it comprises one layer of material having the following composition:

A) Magnesium oxide MgO 100 parts

B) Compound B 90 parts

C) Naphthalene sulphonate NNO 0.1% to 3%

D) Hydrogen peroxide H₂0₂ 0 to 20% in which compound B comprises:

Water H₂0 50 parts (45% A)

Magnesium chloride MgCl₂ 50 parts (45% A)

Phosphoric acid H3PO4 0.5% A

4) Panel as claimed in claim 1, characterised in that hollow microspheres of silica are added as lightening material.

5) Panel as claimed in claim 1, characterised in that polystyrene foam is added as lightening material.

6) Panel as claimed in claim 1, characterised in that sawdust is added as lightening material.

7) Process for the manufacture of a panel in accordance with each of the preceding claims, characterised in that it involves mixing at ambient temperature: A) Magnesium oxide MgO 100 parts

B) Compound B 90 parts

C) Naphthalene sulphonate NNO 0.1% to 3% In which compound B comprises:

Water H₂0 50 parts (45% A)

Magnesium chloride MgCl₂ 50 parts (45% A) Phosphoric acid H3PO4 0.5% A, and the addition of hydrogen peroxide H₂0₂ 0 to 20%), as foaming agent

8) Process for the manufacture of a panel as claimed in the preceding claim, characterised in that it includes a stage involving steam-curing of the said mixture.

9) Process for the manufacture of a panel as claimed in claim 8, characterised in that the said steam-curing stage takes place in a C0₂ atmosphere.

10) Process for the manufacture of a panel as claimed in claim 9, characterised in that the mixture includes less than the stoichiometric amount of water in order to offset water absorption by the mixture during the steam-curing stage.

11) Panel as described and illustrated.

12)Method for manufacture of panels as described and illustrated.