Greenhouse heat preservation quilt for agricultural planting and manufacturing method of greenhouse heat preservation quilt

Abstract

The invention discloses a greenhouse heat preservation quilt for agricultural planting and a manufacturing method of the greenhouse heat preservation quilt, and relates to the field of heat preservation quilts.The heat preservation quilt sequentially comprises a photo-thermal management outer layer, an intelligent phase change heat preservation core layer and a humidity response inner layer from outside to inside; the photo-thermal management outer layer is composed of base cloth and a functional composite coating, and the functional composite coating comprises high-infrared-reflectivity filler and photo-thermal conversion filler. Through the synergistic effect of titanium dioxide and carbon black in the photo-thermal management outer layer, bidirectional intelligent photo-thermal regulation and control of high reflection in the daytime to prevent overheating and high emission at night to promote heat dissipation are achieved; the intelligent phase change heat preservation core layer with a stable three-dimensional network is jointly constructed by a plant fiber framework and high-density polyethylene, and it is ensured that efficient and leakage-free heat storage and release circulation of the phase change material is achieved within the crop growth suitable temperature range of 18-25 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of thermal insulation quilt, in particular to a greenhouse thermal insulation quilt for agricultural planting and a manufacturing method thereof. BACKGROUND

[0002] As an important part of modern agriculture, greenhouse technology effectively breaks through the limitations of season and region by creating a controllable growth environment for crops, realizing the counter-season production and high-yield and stable production of agricultural products. In this system, the greenhouse thermal insulation quilt, as a key thermal insulation equipment covered outside the greenhouse film, its core function is to reduce the loss of heat in the greenhouse to the outside environment at night or in low temperature period, so as to maintain the relative stability of the temperature in the greenhouse, which is of great significance to reduce the energy consumption of winter heating, ensure the safety of crops overwintering and improve the efficiency of agricultural production. The performance of the traditional thermal insulation quilt is directly related to the energy consumption cost, the growth period and the quality of crops.

[0003] At present, the common greenhouse thermal insulation quilt on the market adopts a multi-layer composite structure, and its main body is usually composed of an outer base cloth, an intermediate thermal insulation filling layer and an inner protective layer. The intermediate thermal insulation filling layer is usually made of traditional textile materials such as needle-punched cotton, sprayed cotton and foamed plastic, or a simple composite aluminum foil reflective layer is added on the basis of the above materials, and the heat insulation is realized by using the static air layer and the thermal resistance of the material itself. In recent years, some new materials have also been introduced, such as adding phase change material microcapsules to the filling layer to store and release heat by using the latent heat of phase change; or by improving the waterproof performance of the outer layer material and the air permeability of the inner layer material, to deal with rainy and snowy weather and prevent condensation in the greenhouse. These existing technical solutions largely depend on the physical insulation of the material, and their functions are relatively single and passive.

[0004] However, the above prior art solution still has a series of obvious limitations and shortcomings. First, its temperature regulation mode is passive and cannot intelligently respond to changes in the external day-night environment: it cannot effectively manage excess solar radiation during the day, which can cause excessive "greenhouse effect" and burn the crops; at night, it can only slow down heat dissipation and cannot actively supplement or adjust the heat source, and the heat preservation capacity rapidly decreases in extremely low temperatures. Second, the application of existing phase change materials has the problems of leakage risk, poor combination with the base material, poor cycle stability, and mismatch between the phase change temperature and the growth needs of crops, which affect the reliability and effectiveness of long-term use. Third, the humidity management capability of traditional heat preservation blankets is insufficient, and when the air humidity in the greenhouse is high, water vapor is easily accumulated inside, which not only increases the weight and reduces the heat preservation performance, but also creates conditions for mold growth, affecting the health of crops. In addition, the existing structure lacks a mechanism for actively guiding and evenly distributing heat, which can easily cause "hot spots" and "cold spots" in the greenhouse, where the temperature is too high or too low. Therefore, developing a greenhouse heat preservation blanket that can intelligently manage light and heat, efficiently and stably store heat, actively regulate humidity, and have long-term reliability has become a technical problem that needs to be solved in the field. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a greenhouse heat preservation blanket for agricultural planting and a manufacturing method thereof, to solve the technical problems in the prior art that the temperature regulation mode of the greenhouse heat preservation blanket is passive, cannot respond to changes in the day-night environment, the phase change material is prone to leakage and has poor cycle stability, the humidity management capability is insufficient, and the heat preservation effect is poor, the energy consumption is high, the use is short, and the service life is short.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a greenhouse heat preservation blanket for agricultural planting, which comprises, from the outside to the inside, a light and heat management outer layer, an intelligent phase change heat preservation core layer, and a humidity response inner layer. The light and heat management outer layer is composed of a base cloth and a functional composite coating, the functional composite coating contains high infrared reflectivity fillers and light and heat conversion fillers, the high infrared reflectivity fillers are titanium dioxide, the light and heat conversion fillers are carbon black, and the two are mixed by a polymer adhesive and firmly attached to the base cloth. The intelligent phase change heat preservation core layer is a fiber-reinforced shaped phase change material plate, which is composed of a plant fiber skeleton, paraffin with a phase change temperature in the range of 18-25℃ as a phase change material, and high-density polyethylene as a support carrier to prevent the phase change material from flowing. The humidity response inner layer is a hydrophilic and breathable layer treated by a hydrophilic polymer finishing agent.

[0007] The present application further provides that the base cloth of the light and heat management outer layer is a polyester woven fabric, and the mass ratio of titanium dioxide to carbon black in the functional composite coating is 3:1 to 5:1.

[0008] The application further provides that the plant fiber framework in the intelligent phase change heat preservation core layer is jute fiber or sisal fiber, and the length of the plant fiber framework is 3-10 mm; and the mass ratio of the plant fiber framework, paraffin and high-density polyethylene is 3:5:2.

[0009] The application further provides that the high-molecular finishing agent used in the humidity response inner layer is a copolymer emulsion of polyethylene glycol and acrylate, which is solidified on the surface of the non-woven fabric through the padding and baking process.

[0010] The application further provides that a metal-coated reflective layer is arranged between the light-heat management outer layer and the intelligent phase change heat preservation core layer, and the reflective layer is a PET film coated with aluminum in vacuum.

[0011] The application further provides that the intelligent phase change heat preservation core layer is internally embedded with heat-conducting reinforcing fibers distributed in a grid shape, and the heat-conducting reinforcing fibers are copper-plated carbon fibers.

[0012] The application further provides that the grid spacing of the heat-conducting reinforcing fibers is 10-20 cm, and the two ends of the heat-conducting reinforcing fibers extend to the edges of the heat preservation quilt, thereby constituting an optional passive defrosting circuit capable of being connected with an external conductive device.

[0013] The application further provides a method for manufacturing the greenhouse heat preservation quilt for agricultural planting, which comprises the following sequential steps: S1. preparing a light-heat management outer layer: uniformly mixing titanium dioxide, carbon black, a polyurethane adhesive and an organic solvent to prepare a coating slurry, then coating the coating slurry on the surface of a polyester base fabric through a doctor blade coating process, and then drying and high-temperature curing to form the functional composite coating; S2. preparing an intelligent phase change heat preservation core layer: melt blending paraffin and high-density polyethylene under heating, then uniformly mixing the mixture with pretreated plant fiber framework, and then placing the mixture in a hot press to perform mold pressing under the conditions of a temperature of 130-150 DEG C and a pressure of 5-10 MPa, thereby forming a plate-shaped material; S3. preparing a humidity response inner layer: dipping a cotton-spun non-woven fabric in a polyethylene glycol-acrylate copolymer emulsion, controlling the liquid rate of the non-woven fabric through a padder, then performing preliminary drying at 100-120 DEG C, and finally performing baking and setting at 150-160 DEG C, so as to crosslink and solidify the hydrophilic high-molecular finishing agent; and S4. compounding: compounding the light-heat management outer layer, the intelligent phase change heat preservation core layer and the humidity response inner layer prepared in the above steps into an integrated three-layer structure through hot melt adhesive film under heating and pressing.

[0014] The application further provides that in step S4, when the metal-coated reflective layer is compounded, the metal-coated reflective layer is previously attached to the outer surface of the intelligent phase change heat preservation core layer through hot melt adhesive, and then the light-heat management outer layer is attached to the outer surface of the metal-coated reflective layer.

[0015] The application is further configured to, in step S2, performing programmed cooling treatment on the intelligent phase change heat preservation core layer sheet material after hot pressing, controlling the cooling rate to be not more than 0.5℃ / min, and slowly cooling to room temperature, so as to optimize the crystal structure of the phase change material.

[0016] In summary, the application mainly has the following beneficial effects: Through the synergistic effect of titanium dioxide and carbon black in the light and heat management outer layer, bidirectional intelligent light and heat regulation of high reflection to prevent overheating during the day and high emission to promote heat dissipation at night is realized; through the intelligent phase change heat preservation core layer formed by the stable three-dimensional network of the plant fiber skeleton and high-density polyethylene, efficient and leakage-free heat storage and release cycles of the phase change material in the 18-25℃ crop growth suitable temperature range are ensured; through the hydrophilic polymer chain of the humidity response inner layer, water molecules are combined and the micro-pore channels are expanded when the humidity increases, automatic improvement of the moisture permeability in a high humidity environment is realized, and dew condensation is effectively prevented; further, through the embedded copper-coated carbon fiber grid in the core layer, rapid and uniform distribution of heat is realized, and an optional solution of active and low-power defrosting through external power supply at extremely low temperature is provided. These innovative designs synergistically act from multiple dimensions such as light and heat management, phase change energy storage, humidity response and active heat intervention, and together realize dynamic intelligent adjustment of the greenhouse environment, and finally achieve the comprehensive beneficial effects of significant energy saving and consumption reduction, dew condensation prevention, prolonging of service life and improvement of stability of the crop growth environment. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A heat preservation quilt manufacturing method flowchart of the application. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings of the embodiments of the application. The embodiments described below with reference to the drawings are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application.

[0019] The embodiments of the application will be described below according to the overall structure of the application.

[0020] Embodiment one The greenhouse heat preservation quilt provided by the application has a stable three-layer integrated structure formed by the light and heat management outer layer, the intelligent phase change heat preservation core layer and the humidity response inner layer through a hot pressing composite process.

[0021] 1. Material mechanism and manufacturing of the light and heat management outer layer The light and heat management outer layer is composed of a base cloth and a functional composite coating. The base cloth is selected from 210D polyester filament woven cloth, and the grammage is 180g / m 2The material has excellent anti-ultraviolet aging performance and mechanical strength, and can withstand wind and rain erosion during long-term outdoor use.

[0022] The core mechanism of the functional composite coating is to achieve intelligent light and heat management through the synergy of two functional fillers: Titanium dioxide (TiO2): Rutil-type titanium dioxide with a particle size of 0.3 μm is selected, which has a reflectivity of up to 85% or more for the near-infrared band (780-2500 nm) in solar radiation. Its mechanism is to use its high refractive index to directly reflect most of the heat in solar radiation, avoiding excessive warming of the greenhouse during the day.

[0023] Carbon black: Conductive carbon black with a particle size of 40 nm is selected, which has an infrared emissivity of up to 0.95 for the atmospheric window band of 8-13 μm. Its mechanism is to use its blackbody radiation characteristics to efficiently radiate the heat absorbed by the thermal insulation layer to the cold night sky in the form of infrared radiation, accelerating heat dissipation.

[0024] The synergistic mechanism of the two fillers is that during the day, titanium dioxide dominates the reflection effect, preventing heat accumulation; at night, carbon black dominates the radiative cooling, achieving passive cooling. This seemingly contradictory dual function plays a role in different periods, achieving intelligent regulation of the greenhouse environment.

[0025] The manufacturing process is as follows: titanium dioxide and carbon black are mixed in a mass ratio of 4:1 and added to a water-based polyurethane binder with a solid content of 45% (filler to binder solid mass ratio of 1.2:1), 0.5% of a dispersant and an appropriate amount of deionized water are added, and the mixture is stirred with a high-speed disperser at 1000 r / min for 90 min to form a uniform slurry. Using a doctor blade coating method, control the wet film thickness to be 0.3 mm, dry in an oven at 125°C for 8 min, and then cure at 155°C for 5 min to form a functional coating with a thickness of 0.08 mm.

[0026] 2. Material mechanism and manufacturing of intelligent phase change thermal insulation core layer The intelligent phase change thermal insulation core layer is a fiber-reinforced shaped phase change composite material, and its core mechanism is to achieve stable encapsulation and efficient heat management of phase change materials through a three-dimensional network structure: Plant fiber skeleton: Yellow hemp fibers with a length of 5-8 mm are selected, which have a hollow structure and not only act as reinforcing bodies but also form a three-dimensional network to prevent material cracking. When the yellow hemp fiber content is 30 wt%, the bending strength of the composite material can reach 12 MPa.

[0027] Phase change material system: Alkane paraffin with phase change temperature of 22℃ is selected, and its latent heat of phase change is 180J / g. The temperature matches the optimal growth temperature of crops at night. When the ambient temperature is higher than 22℃, the paraffin absorbs heat and melts; when the ambient temperature is lower than 22℃, the paraffin releases heat and solidifies, thereby realizing automatic temperature adjustment.

[0028] Supporting carrier: High-density polyethylene (HDPE) with a melt index of 8g / 10min is selected. When in a molten state, the HDPE forms a bicontinuous phase with the paraffin, and after cooling and solidification, a microcapsule type of wrapping structure is formed, effectively preventing paraffin leakage.

[0029] The synergistic mechanism of the three is: the plant fiber provides a macroscopic skeleton, the HDPE forms a microscopic encapsulation, and the paraffin is responsible for energy storage and temperature adjustment. This multi-level structure ensures that the phase change enthalpy retention rate of the material is still above 95% after 500 cold and hot cycles.

[0030] The manufacturing process includes: first, melt blending the paraffin and HDPE in a 165℃ internal mixer for 15min, then adding the pretreated jute fiber and continuing to mix for 10min. The mixture is placed in a mold preheated to 145℃ and hot pressed at a pressure of 10MPa for 20min to ensure full plastic flow. The key process is: immediately after demolding, transfer to a programmed cooling device to slowly cool to 25℃ at a rate of 0.2℃ / min. This process allows the paraffin to form uniform spherocrystals, avoiding interface separation caused by internal stress due to rapid cooling.

[0031] 3. Material mechanism and manufacturing of the humidity response inner layer The humidity response inner layer is a specific embodiment of the intelligent humidity management system based on the conformational change of high molecular chains: Base material: Cotton / polyester (50 / 50) blended needle-punched non-woven fabric with a grammage of 100g / m 2 , and its three-dimensional fluffy structure provides a channel for humidity exchange.

[0032] Intelligent response material: A graft copolymer of polyethylene glycol (PEG600) and glycidyl methacrylate is used as the finishing agent. Its mechanism of action is: the PEG segment has temperature-sensitive properties. At low temperature and high humidity, the PEG chain forms hydrogen bonds with water molecules and stretches, opening the pores between fibers; at high temperature and low humidity, the hydrogen bonds dissociate and the chain segments curl up, closing the pores.

[0033] The manufacturing process is as follows: prepare a 12% finishing agent solution and add 1% citric acid as a catalyst. Use a two-dip-two-pad process with a pad pickup rate of 85%. Then pre-dry at 110℃ for 5min, and finally cross-link and cure at 160℃ for 3min. Tests show that when the environmental humidity increases from 60% to 90%, the moisture permeability increases from 1200g / m 2 ·24h automatically to 4500g / m 2• 24h, smart response to humidity is achieved.

[0034] 4. Interlayer bonding mechanism and compounding process The bonding between layers uses reactive polyurethane hot melt adhesive film with a thickness of 80μm. Its mechanism of action is: under the conditions of heating and pressure, the adhesive film melts and flows and penetrates into the surface micropores of each layer, and after cooling and solidification, a mechanical interlocking structure is formed, and at the same time the isocyanate groups in the adhesive film react with the active groups on the surface of each layer material to form chemical bonding.

[0035] The compounding process parameters are: three layers of material and two layers of adhesive film are alternately stacked and hot pressed at 120℃ and 0.5MPa pressure for 90s. Under this condition, the adhesive film melts and flows fully but does not penetrate excessively, which ensures the interlayer peeling strength (≥50N / 5cm) and avoids the blocking of the micropore structure of the functional layer.

[0036] Example Two On the basis of the basic structure, a metal-coated reflective layer can be added between the light and heat management outer layer and the intelligent phase change insulation core layer. This layer is a double-sided aluminum-coated PET film with a thickness of 15μm and an aluminum layer thickness of 50nm. Its enhancement mechanism is: taking advantage of the high reflectivity of aluminum metal to long-wave infrared light (>4μm) of up to 97%, a secondary thermal resistance barrier is formed. Especially at night, it can effectively block the radiation of the core layer heat to the outside.

[0037] The compounding process is adjusted as follows: first, the reflective layer is attached to the surface of the core layer with the same hot melt adhesive film, and then the whole is compounded. It should be noted that when attaching, the reflective layer should be completely flat to avoid the generation of thermal bridge effect due to wrinkles.

[0038] Example Three During the manufacturing process of the intelligent phase change insulation core layer, copper-coated carbon fiber heat conduction network can be embedded. The specific implementation is: copper-coated carbon fiber with a single filament diameter of 7μm (copper layer thickness of 1μm) is selected and woven into a 15cm×15cm grid, which is pre-positioned in the mold before hot pressing.

[0039] Its synergistic mechanism is reflected in three aspects: Thermal conductivity enhancement: the axial thermal conductivity of carbon fiber reaches 400W / m·K, which can quickly balance the temperature distribution of the core layer and eliminate local temperature differences.

[0040] Active defrosting: in extreme weather, connect a 24V DC power supply to the exposed end, use the 8Ω / m resistance characteristic of carbon fiber to generate Joule heat, and achieve auxiliary heating of 5-10W / m 2 .

[0041] Structural reinforcement: the grid structure increases the tear resistance of the core layer by about 30%.

[0042] Overall synergistic mechanism and effect of each layer of material Through the above specific implementation, the present application realizes multiple synergies: Space-time synergy: the light-heat management outer layer realizes day-night function switching, the phase change core layer realizes temperature self-adaptive regulation, and the humidity inner layer realizes humidity response, which synergize in the dimensions of time, temperature and humidity, respectively.

[0043] Thermal management synergy: light-heat outer layer reflection / radiation + metal layer reflection + phase change core layer heat storage + carbon fiber network temperature equalization, forming fourfold thermal protection.

[0044] Energy synergy: the latent heat regulation of phase change materials (180J / g) combined with the sensible heat supplement of carbon fibers (joule heat) realizes intelligent energy distribution and management.

[0045] The present application constructs a multi-layer composite structure composed of a light-heat management outer layer with day-night regulation function, an intelligent insulation core layer based on the shaped phase change technology and fiber reinforcement mechanism, and a hydrophilic inner layer with humidity response characteristics, and is supplemented by an optional metal reflection layer and an embedded conductive heat management network. It innovatively uses the synergistic mechanism of various functional materials in different physical dimensions, including the time sequence synergy of light-heat conversion and radiation heat dissipation, the energy synergy of phase change latent heat and sensible heat management, the environmental synergy of humidity sensing and adaptive regulation of air permeability, and the firm combination of interlayer interface realized through a specific composite manufacturing process. Finally, it successfully and integrally solves a series of key technical problems in the prior art, such as passive single temperature regulation, phase change material failure, humidity management deficiency, and lack of emergency heat intervention capability, thereby overall improving the environmental adaptability, functional intelligence, use reliability and energy saving and environmental protection of the greenhouse insulation quilt, and providing a new, high-performance environmental regulation equipment solution for modern agriculture.

[0046] Although the embodiments of the present application have been shown and described, the specific embodiments are merely an explanation of the present application, and are not a limitation of the application. The specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner, and those skilled in the art can make modifications, replacements and variations of the embodiments without creative contribution after reading the specification, as long as they are within the scope of the claims of the present application.

Claims

1. A greenhouse insulation blanket for agricultural planting, characterized in that, From the outside in, it consists of a photothermal management outer layer, an intelligent phase change insulation core layer, and a humidity-responsive inner layer; The photothermal management outer layer is composed of a base fabric and a functional composite coating. The functional composite coating includes a high infrared reflectivity filler and a photothermal conversion filler. The high infrared reflectivity filler is titanium dioxide, and the photothermal conversion filler is carbon black. The two are mixed with a polymer adhesive and firmly attached to the base fabric. The intelligent phase change insulation core layer is a fiber-reinforced shaped phase change material board, which consists of a plant fiber skeleton, paraffin wax with a phase change temperature in the range of 18-25℃ as a phase change material, and high-density polyethylene as a support carrier to prevent the phase change material from flowing. The humidity-responsive inner layer is a hydrophilic and breathable layer made of cotton-nylon blended nonwoven fabric treated with a hydrophilic polymer finishing agent.

2. The greenhouse insulation blanket for agricultural planting according to claim 1, characterized in that: The base fabric of the photothermal management outer layer is a polyester woven fabric, and the mass ratio of titanium dioxide to carbon black in the functional composite coating is 3:1 to 5:

1.

3. The greenhouse insulation blanket for agricultural planting according to claim 1, characterized in that: In the intelligent phase change insulation core layer, the plant fiber skeleton is jute fiber or sisal fiber with a length of 3-10mm; and the mass ratio of the plant fiber skeleton, paraffin and high-density polyethylene is 3:5:

2.

4. The greenhouse insulation blanket for agricultural planting according to claim 1, characterized in that: The humidity-responsive inner layer uses a copolymer emulsion of polyethylene glycol and acrylate as the finishing agent, which is cured onto the surface of the nonwoven fiber through padding and baking processes.

5. A greenhouse insulation blanket for agricultural planting according to claim 1, characterized in that: Between the photothermal management outer layer and the intelligent phase change insulation core layer, a metal-coated reflective layer is also provided, which is a vacuum-aluminized PET film.

6. A greenhouse insulation blanket for agricultural planting according to claim 1, characterized in that: The intelligent phase change insulation core layer is embedded with thermally conductive reinforcing fibers arranged in a grid pattern. The thermally conductive reinforcing fibers are copper-plated carbon fibers.

7. A greenhouse insulation blanket for agricultural planting according to claim 6, characterized in that: The thermally conductive reinforcing fiber has a mesh spacing of 10-20cm, and both ends of the thermally conductive reinforcing fiber extend to the edge of the insulation blanket, forming an optional passive defrosting circuit that can be connected to an external conductive device.

8. A method for manufacturing a greenhouse insulation blanket for agricultural planting as described in any one of claims 1-7, characterized in that, Includes the following sequential steps: S1. Preparation of photothermal management outer layer: Titanium dioxide, carbon black, polyurethane adhesive and organic solvent are uniformly mixed to form a coating slurry, which is then coated onto the surface of polyester base fabric by a scraping process, and dried and cured at high temperature to form the functional composite coating; S2. Preparation of intelligent phase change insulation core layer: Paraffin wax and high-density polyethylene are melt-blended under heating conditions, and then fully and evenly mixed with pretreated plant fiber skeleton. The mixture is placed in a hot press and molded at a temperature of 130-150℃ and a pressure of 5-10MPa to form a plate material. S3. Preparation of humidity-responsive inner layer: The cotton-blend nonwoven fabric is impregnated in polyethylene glycol-acrylate copolymer emulsion, and its liquid carry-over rate is controlled by a rolling mill. Then, it is pre-dried at 100-120℃ and finally baked and shaped at 150-160℃ to crosslink and cure the hydrophilic polymer finishing agent. S4. Composite: The above-prepared photothermal management outer layer, intelligent phase change insulation core layer, and humidity response inner layer are composited into a complete three-layer integrated structure using a hot melt adhesive film under heating and pressure conditions.

9. The manufacturing method according to claim 8, characterized in that, In step S4, when the composite includes a metal-coated reflective layer, the metal-coated reflective layer is pre-attached to the outer surface of the intelligent phase change heat preservation core layer with hot melt adhesive, and then the photothermal management outer layer is attached to the outer surface of the metal-coated reflective layer.

10. The manufacturing method according to claim 8, characterized in that, In step S2, the intelligent phase change insulation core plate material after hot pressing is subjected to a programmed cooling process, and the cooling rate is controlled to not exceed 0.5℃ / minute, so that it is slowly cooled to room temperature to optimize the crystal structure of the phase change material.

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