Advanced inorganic material for reflection of electromagnetic waves

This application claims the benefit of Chinese application No. CN201210236577.3, filed Jul. 10, 2012, and U.S. Ser. No. 61/685,885, filed Mar. 27, 2012. The entire contents of these applications are incorporated herein by reference into this application.

This invention relates to a material formulation and reaction products having its constituents arranged in a microstructure that controls the reflection and refraction of incident electromagnetic waves according to wave reflection theory.

For thousands of years, many attempts have been made to block the heat flow across surfaces of objects and structures for various reasons including better living environment. In fact, the development of good thermal insulation material has gained great strategic importance especially after energy crisis of the 1970s.

In recent years, China has been adding 1.7 billion m 2 of new floor space on an annual basis (including urban and rural areas). In 2010, the total area of existing buildings in China was approximately 48.6 billion m 2 (Building Energy Efficiency Policies in China—Executive Summary, July 2012, Global Building Performance Network. ISBN: 99-10-91655-01-9). Most of the existing buildings and 30% of the buildings under construction are high energy consumption structures. It is undoubted that a huge potential exists for thermal insulation materials in order for these buildings to achieve energy saving targets.

Objects constantly exposed to radiant energy, such as railway track, develop large thermal stresses which will shorten their working life. Reducing this temperature difference by coating with a thermal insulation material is a possible way to decrease the life cycle cost of these objects.

Central heat supply is provided to an area of 1.0108 billion m 2 in China in 2005 (Chinese Statistical Yearbook of 20054) and, in Beijing alone, the length of pipelines in the heat supply network exceeded 17,000 kilometers in 2008 (Beijing Development and Reform Commission, 2009). This kind of structures enclosing materials with a large temperature gradient with its immediate environment would have a huge demand for thermal insulation materials.

Conventionally, low thermal conductivity is considered as the most important factor in choosing a thermal insulation material. As still air or other gases have low thermal conductivity, most of the thermal insulation materials tend to have a very high void content such that the bulk of the thermal insulation material consists of small bubbles of air.

Due to the high porosity of traditional thermal insulation materials, such as aerated concrete block, foam plastics, expanded perlite, foam cement, expanded polystyrene, most of them are not expected to have sufficient mechanical strength to support a large load. The material will lose its function when subjected to any accidental physical or chemical attacks. As a result, most traditional thermal insulation materials are not durable especially under abrasion and adverse environmental conditions such as moisture and acid gases in the atmosphere. The temperature and relative humidity will also affect the thermal conductivity of the traditional thermal insulation materials. Once the temperature or the humidity exceeds an acceptable range, the thermal conduction of the material will increase dramatically. Flammability is another significant problem with existing thermal insulation materials. Protection is always needed on the surface of thermal insulation materials to resist fire or prevent the release of toxic vapors under high temperature. This incurs additional complexity and cost on the thermal insulation installation.

The most significant problem with traditional thermal insulation materials is their ineffectiveness in resisting radiant heat. The radiant heat, in the form of electromagnetic waves, will cause molecules to vibrate and thereby causes increase in temperature. The wavelengths responsible for heat from sunlight are from 400 nm to 25 μm. Most common thermal insulation materials are capable of absorbing and transferring 90 percent of the radiant energy. In any way, the radiant heat will generate on the surfaces of the traditional thermal insulation materials or be transferred through the materials from one side to the other. The only thing that the traditional thermal insulation can do is to reduce the efficiency of energy transfer across the material. So the tradition thermal insulation is, generally, a kind of passive method in heat resistance.

To overcome the limitations of the traditional thermal insulation materials, the present invention is developed based on the reflection theory with inorganic materials. This invention is directed to a material comprising air-filled glass beads (AGB) and magnesium oxychloride cement (MOC) particles which may contain one or more additives such as titanium dioxide powder, fly ash, pigment powders, and potassium dihydrogen phosphate (KH 2 PO 4 ) or sodium dihydrogen phosphate (NaH 2 PO 4 ) powder ( FIG. 1 ). The MOC reaction product has a layer structure surrounding the shell of glass beads and hence forms a multi-layered structure after application ( FIG. 2 ). If the thickness of two adjacent layers, d i and d j , as well as their refractive indices n i and n j are carefully designed to satisfy the relationship of n i d i +n j d j =λ k /4 to 2 k /2, (Springer Handbook of Electronic and Photonic Materials, 2006, Springer) where λ k is the wave length of incident wave k, the radiant heat energy contained in the k wave will be highly reflected. The optimized values are the range of visible lights and infrared wave lengths, i.e. from 400 nm to 2.5 μm. With the multi-layered structure and the different desirable combination of d i and d j as well as n i and n j , the majority of near-infrared waves and visible light waves will be reflected from the surface of the structure and the radiation heat carried by these waves prevented from transferring across the material. In addition, a combination of MOC, a well-known heat preservation material, and air-filled beads having low thermal conduction is expected to improve the thermal insulation properties of a material. Therefore thermal insulation is achieved by a combination of reflection, refraction, and dissipation.

The present material provides additional advantages such as a small thickness of 0.5 mm to 1.0 mm, insensitivity to high temperature, good bonding strength, and increased fire resistance in addition to thermal insulation.

The following terms shall be used to describe the present invention. In the absence of a specific definition set forth herein, the terms used to describe the present invention shall be given their common meaning as understood by those of ordinary skill in the art.

As used herein, ASTM refers to American Society for Testing and Materials.

As used herein, d refers to thickness.

As used herein, KH 2 PO 4 refers to potassium dihydrogen phosphate.

As used herein, AGB refers to air-filled glass beads.

As used herein, CFCP refers to control fiber cement plate.

As used herein, CB refers to coating with air-filled glass beads.

As used herein, CBT refers to coating with air-filled glass beads and titanium dioxide.

As used herein, CBY refers to coating with air-filled glass beads and yellow pigment.

As used herein, MgO refers to magnesium oxide.

As used herein, MgCl 2 refers to magnesium chloride.

As used herein, MOC refers to magnesium oxychloride cement.

As used herein, n refers to refractive index.

As used herein, NaH 2 PO 4 refers to sodium dihydrogen phosphate.

As used herein, NIR refers to radiation in the near infra-red spectrum.

As used herein, PVC refers to polyvinyl chloride.

As used herein, TiO 2 refers to titanium dioxide.

As used herein, UV refers to radiation in the ultraviolet spectrum.

As used herein, VIS refers to radiation in the visible spectrum.

As used herein, λ refers to wavelength.

FIG. 1 shows a schematic diagram of a mixture comprising AGB and MOC particles.

FIG. 2 shows a multi-layered structure of the present invention after application.

FIG. 3 shows AGB covered with MOC reaction products.

FIG. 4 shows layer of MOC reaction products with AGB beneath.

FIG. 5 shows the shell thickness of a typical AGB.

FIG. 6 shows a schematic diagram of heating test setup.

FIG. 7 shows the inner surface temperature comparison among CFCP without coating, fiber cement plate with MOC coating and fiber cement plate with an embodiment of present invention, CB.

FIG. 8 shows the solar reflectance comparison between fiber cement plate with MOC coating and that with the present invention, CB.

FIG. 9 shows the inner surface temperature comparison among CFCP without coating, fiber cement plate with MOC coating and fiber cement plate with an embodiment of the present invention, CBT.

FIG. 10 shows the solar reflectance comparison between fiber cement plate with MOC and that with an embodiment of the present invention, CBT.

FIG. 11 shows the inner surface temperature comparison between fiber cement plate with an embodiment of the present invention, CBT, and that with commercial coating (B8500).

FIG. 12 shows the inner surface temperature comparison among CFCP without coating, fiber cement plate with MOC and fiber cement plate with an embodiment of the present invention, CBY.

FIG. 13 shows the solar reflectance comparison between fiber cement plate with MOC and that with an embodiment of the present invention, CBY.

To overcome the limitations of the traditional thermal insulation materials, the present invention is developed based on the reflection theory. This invention is directed to a material comprising AGB and MOC particles which may contain one or more additives such as titanium dioxide powder, fly ash, pigment powders, and KH 2 PO 4 or NaH 2 PO 4 powder ( FIG. 1 ). In one embodiment, the MOC act as a binding material for AGB and the additives to form a thin inorganic coating. Said material may form a multi-layered structure after application ( FIG. 2 ). For instance, the thickness of the shell of AGB can range from 10 nanometers to 10 micrometers. In addition, the thickness of the reaction products of MOC can be optimized through the mix portion design. Moreover, it was found that the reaction product of the MOC has a fibrous network layered feature, for example, FIGS. 3 & 4 . If the thickness of two adjacent layers, d i and d j , as well as their refractive indices n i and n i are carefully designed to satisfy the relationship of n i d i +n j d j =λ k /4 to λ k /2, where λ k is the wavelength of incident wave k, the radiant heat energy contained in the k wave will be highly reflected. With the multi-layered structure and the different desirable combination of d i and d j as well as n i and n j , the majority of infrared waves and visible light waves can be blocked. Hence, the heat transfer by radiation across the material will be drastically reduced. As shown in FIG. 4 , the layer thickness of MOC reaction products ranges from 10 nanometers to 5 micrometers. In one embodiment, the thickness is 100 nm. Also, the thickness of the shell of AGB ranges from 10 nanometers to 10 micrometers. In one embodiment, the thickness is 431 nm as in FIG. 5 . The refractive indices of MOC reaction products and air filled glass beads are 1.60-1.80 and 1.40-2.50, for example, 1.70 and 1.51, respectively. Hence, according to the equation, the calculated values fall well into the range of λ k /4 to λ k /2, where λ k is the wavelength of incident wave k. For example, shell thickness and refractive index of air filled glass beads are 431 nm and 1.51, respectively; while the thickness and refractive index of MOC reaction product layer are 100 nm and 1.70, respectively. Through equation calculation (n i d i +n j d j ), a value of 820.81 nm can be obtained, which suggests a large part of near-infrared wavelengths (e.g. from 1642 nm to 3283 nm) can be highly reflected. In addition, a combination of MOC, a well-known heat preservation material, and AGB having low thermal conduction is expected to improve the thermal insulation properties of a material. Therefore thermal insulation is achieved by a combination of reflection, refraction, and dissipation.

In one embodiment, the air-filled beads are made of glass or ceramic and have a density of 0.1 to 2.6 g/cm 3 ; they constitute up to 80% volume fraction of the material.

In one embodiment, said air-filled bead has a refractive index of 1.40-2.50, preferably 1.51.

In another embodiment, said air-filled bead has a shell thickness of 10 nanometers to 10 micrometers, preferably 431 nm.

In one embodiment, said MOC has a molar ratio of MgO to MgCl 2 of 9-17; and a weight ratio of water to particles of 0.3-0.9.

In another embodiment, said MOC has a refractive index of 1.60-1.80, preferably 1.70.

In a further embodiment, said MOC forms fibrous reaction products having its network layer thickness of 10 nanometers to 5 micrometers, preferably 100 nm.

In a further embodiment, said MOC contains one or more of 0-10 volume % of TiO 2 , 0-50 volume % of fly ash, 0.1-5 volume % of KH 2 PO 4 and 0.1-5 volume % of NaH 2 PO 4 .

In yet another embodiment, said pigment powders are iron dioxide and make up 0-20 volume % of the MOC.

In one embodiment, the present invention can be used in thermal insulation coatings in industrial and civil applications to conserve resource and energy.

The present material provides advantages such as a small thickness of 0.5 mm to 1.0 mm, insensitive to high temperature, good bonding strength, and increased fire resistance in addition to thermal insulation.

In one embodiment, the present invention is used for thermal insulation of structures for temporary or permanent sheltering of human beings such as residential and commercial buildings.

In another embodiment, the present invention is used in reducing the thermal stresses caused by radiant heat in an object such as railway tracks exposed to sunlight.

In a further embodiment, the present material is applied onto structures, such as pipelines of a heat supply network, so that materials enclosed within said structures can be maintained at a large temperature gradient with its immediate surroundings.

In one embodiment, the present material is applied onto an object or structure by brushing, spraying, scrape coating or other conventional coating methods.

The invention will be better understood by reference to the Experimental Details which follow, but those skilled in the art will readily appreciate that the specific experiments are provided only for illustrative purposes, and are not meant to limit the invention as described herein, which is defined by the claims that follow thereafter.

Throughout this application, various references or publications are cited. Disclosures of these references or publications are hereby incorporated in their entireties by reference into this application in order to more fully describe the state of the art to which this invention pertains. It is to be noted that the transitional term “comprising”, which is synonymous with “including”, “containing” or “characterized by”, is inclusive or open-ended and does not exclude additional, un-recited elements or method steps.

1. Lang Siwei, China Academy of Building Research, 2007.

2. ASTM C461-81: Standard test methods for mastics and coatings used with thermal insulation.

3. ASTM D3363-05: Standard test method for film hardness by pencil test.

4. ASTM D4541-09e1: Standard test method for pull-off strength coating using portable adhesion testers.

5. ASTM E1175-87(2009): Standard test method for determining solar or photopic reflectance, transmittance, and absorptance of materials using a large diameter integrating sphere.