CN102303958A - Rice hull ash-paraffin wax phase-change aggregate and preparation method thereof - Google Patents

Abstract

The invention relates to a rice husk ash-paraffin phase change aggregate and a preparation method thereof. A rice husk ash-paraffin phase-change aggregate is characterized in that it is composed of rice husk ash, paraffin and mineral powder, and the quality of the mineral powder accounts for 35% of the mass of rice husk ash, paraffin and mineral powder ~50%, wherein the mass ratio of paraffin to rice husk ash is 1:1~1:1.5. Using industrial rice husk ash and paraffin, after mixing and heating, the paraffin is melted into the pores of the rice husk ash, and a certain negative pressure is formed in the container through the temperature adjustment of high temperature and low temperature, which greatly improves the melting of paraffin wax in the rice husk ash. The composite product of rice husk ash and paraffin was sieved into small particles, and the powder was used to wrap and modify it to prepare rice husk ash-paraffin phase change aggregate. The preparation process of the phase change aggregate is simple and low cost. Low, high paraffin content, good temperature control effect, and good adaptability to concrete.

Description

A kind of rice husk ash-paraffin phase change aggregate and its preparation method

technical field

The invention relates to the field of phase change materials, in particular to rice husk ash-paraffin phase change aggregates used for temperature control of cement concrete.

Background technique

The temperature damage of mass concrete has always been a very serious engineering problem. At present, the application of phase change materials in concrete has become a research hotspot. Phase change materials have heat storage characteristics. When the temperature rises to the phase transition point, the phase change absorbs heat, and when the temperature drops to the phase transition point, it can also phase change and release heat. Therefore, it can be used to suppress the heat of hydration of mass concrete Temperature rise rate, so as to avoid deformation and damage of concrete.

According to the phase change mode, phase change materials can be generally divided into four categories: solid-solid phase change materials, solid-liquid phase change materials, solid-gas phase change materials and liquid-gas phase change materials. The phase change temperature of solid-solid phase change materials is usually high, which is not suitable for application in concrete. Solid-gas phase change materials and liquid-gas phase change materials are not suitable for concrete due to the gas generated during phase change and large volume expansion. , and some solid-liquid phase change materials can just meet the requirements for application in concrete. Among the solid-liquid phase change materials, paraffin is more economical and practical. Now most of the phase change materials used in concrete are paraffin, but because paraffin is not suitable for direct use in concrete, and the paraffin particles are slightly It will stick together at high temperature and is not easy to store. Therefore, it needs to be packaged during application. At present, there are three main methods for preparing shaped phase change composite materials: microencapsulation, porous material adsorption method, and melt blending method.

Microencapsulated phase change materials are solid particles that are stable under normal conditions and are made by covering solid-liquid phase change materials (core materials) with synthetic polymer materials or inorganic compounds by physical or chemical methods using microcapsule technology. However, the process of this method is relatively complicated and the cost is high, and it is not suitable for the application of mass concrete, a material with a large volume and low cost. The porous material adsorption method is currently a widely studied stereotyped packaging technology. It is to immerse the porous material into the phase change solution in the molten state, so that the phase change material is filled in the pores of the porous material. The porous materials used to adsorb phase change materials that have been studied more include expanded perlite, vermiculite, sepiolite, montmorillonite, expanded graphite, ceramsite, etc. The encapsulation efficiency is low, and there is a more obvious floating phenomenon in practical applications. The melt blending method refers to the melting and blending of the phase change material and the polymer at a temperature higher than the melting point of the polymer. When cooled to room temperature, the phase change material is uniformly dispersed in the solidified polymer. Among polymers, to achieve the purpose of shaping, this method has a large capacity of phase change materials, no leakage, and can be processed into any shape required, but its thermal conductivity is poor and the price is high.

Most of the existing phase change materials have serious floating phenomenon when mixed with concrete, and the larger the particle size of the phase change material, the more serious the floating phenomenon. This is because the phase change material is lighter and the particle size is larger. The greater the ratio of buoyancy to gravity, the easier it is to float. Therefore, the phase change material used in concrete should have a smaller particle size, so that the buoyancy it receives in the concrete is not greater than the sum of its gravity and resistance. Good hydrophilicity, thus improving the workability of phase change materials and concrete.

Only when the phase change material used has good compatibility with concrete, does not cause loss or little loss to other properties of concrete, and the phase change material is relatively economical, can the phase change material be widely used in concrete.

The rice husk ash involved in the present invention comes from the incineration of rice husks. my country is a big rice-producing country, and the amount of rice husk ash produced is also very large. At present, rice husk ash is mainly used to prepare white carbon black and activated carbon. , silica and water glass, etc., but the application is limited. Rice husk ash has a rich pore structure, and when it is mixed into fresh concrete, it needs a lot of water, which seriously affects its popularization and application in concrete. However, the large pore structure of rice husk ash is just a good carrier of paraffin, which has great development and utilization value.

Contents of the invention

In order to overcome the above disadvantages, the invention provides an economical and practical rice husk ash-paraffin phase change aggregate and a preparation method thereof.

The technical scheme of the rice husk ash-paraffin phase change aggregate of the present invention is achieved in this way:

A rice husk ash-paraffin phase-change aggregate is characterized in that it is composed of rice husk ash, paraffin and mineral powder, and the quality of the mineral powder accounts for 35% of the mass of rice husk ash, paraffin and mineral powder ~50%, wherein the mass ratio of paraffin to rice husk ash is 1:1~1:1.5.

The paraffin is filled in the pores of the rice husk ash, and the rice husk ash filled with paraffin is agglomerated together in a granular form, as shown in Figure 1 of the specification; the mineral powder is wrapped on the surface of the particles, as shown in Figure 2 of the specification shown.

The mass ratio of the paraffin to the rice husk ash is 1:1˜1:1.5.

The mineral powder is one of fly ash, mineral powder, silica fume, limestone powder or phosphorus slag powder.

The mass of the mineral powder accounts for 35% to 50% of the mass of the rice husk ash-paraffin phase change aggregate.

The present invention further provides the preparation method of this rice husk ash-paraffin phase change aggregate, it is characterized in that it comprises the steps:

1) Selection of raw materials: according to the quality of mineral powder, it accounts for 35% to 50% of the mass of rice husk ash, paraffin and mineral powder, wherein the mass ratio of paraffin to rice husk ash is 1:1 to 1:1.5, and rice husk ash is selected. Shell ash, paraffin and mineral powders;

2) After sieving and mixing the rice husk ash and paraffin wax, place it in a container and seal it, keep it warm in a high temperature environment for 6-10 hours, release the gas in the container, seal it, and then place the container in a low temperature environment to keep warm 2 to 6 hours; take out the container, disperse the composite product of rice husk ash and paraffin into particles with a particle size less than or equal to 1.18mm; then mix the particles with mineral powder to make the mineral powder stick to the surface to obtain rice husk Ash-paraffin phase change aggregate.

The particle size of the rice husk ash material used in the method is less than or equal to 1.18 mm; the paraffin wax material used is solid at normal temperature, and the particle size is less than or equal to 2.36 mm.

The mass ratio of paraffin wax to rice husk ash is 1:1-1:1.5.

The high temperature environment is 1.5 to 3.5 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition, and the low temperature environment is 0.8 to 1.5 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition.

Industrial paraffin has various labels, such as the commonly used No. 48, No. 52, No. 56, No. 58, No. 62, etc. For example, No. 48 means that the average value of the paraffin phase transition point is 48 ° C, and No. 52 refers to the paraffin phase transition point. The average value is 52°C. Paraffin wax is a mixture of hydrocarbons with about 18 to 30 carbon atoms, the main components of which are straight chain alkanes (about 80% to 95%), and a small amount of individual branched alkanes and single rings with long side chains. Alkanes (the total content of the two is less than 20%). Each type of wax is divided into different varieties according to the melting point, generally every 2°C.

The temperature corresponding to the highest point of the endothermic main peak of the paraffin phase transition mentioned in the description, as shown in Figure 3 and Figure 4 of the description, Figure 3 is the DSC curve of No. 48 paraffin, and Figure 4 is the DSC of No. 58 paraffin curve. That is to say, the temperature corresponding to the highest point of the main endothermic peak of the phase transition of different paraffins is different.

The preferred high temperature environment of the present invention is 2.5 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition, and the preferred low temperature environment is 1.2 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition.

In the preparation method of rice husk ash-paraffin phase change aggregate of the present invention, the mineral powder used is one of fly ash, mineral powder, silica fume, limestone powder or phosphorus slag powder, and its consumption is rice husk ash-paraffin wax 35% to 50% of the mass of phase change aggregates.

The present invention also provides a preferred method for making the powder bonded to the particle surface:

Divide the mineral powder into two parts of equal mass, take one part of the powder and mix it with the composite product particles of rice husk ash and paraffin, and place it at 0.9 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition Keep it warm for 20 minutes in an environment, take it out, and mix it with another powder.

The present invention utilizes the porosity of rice husk ash to incorporate paraffin into the voids of rice husk ash, and through the adjustment of high temperature and low temperature, creates a negative pressure environment in the container, thereby increasing the amount of paraffin incorporated into rice husk ash, and greatly Improve the encapsulation efficiency of paraffin, then disperse the composite product of rice husk ash and paraffin into small particles, and then use powder to modify the surface of the product to adapt it to the working requirements of concrete.

Application example 1

The rice husk ash-paraffin phase change aggregate is granular, so it should be used instead of part of the sand when used. The rice husk ash-paraffin wax phase-change aggregates were mixed into two kinds of mortars: equal mass replacement sand and equal volume replacement sand, and the net paraffin content was 15% of the cementitious material. The results showed that when equal mass substitution was used, the mortar’s Poor gelation and no fluidity, fluidity cannot be improved when water consumption and superplasticizer dosage are increased, and severe bleeding occurs, which is equivalent to excessive sand usage. However, when using equal volume replacement, the workability of the mixed mortar is good, even better than that of the reference sample, so the rice husk ash-paraffin phase change aggregate should be replaced by equal volume.

Application example 2

Take 600g of cement and carry out temperature rise test. For the convenience of comparison, the composite product (particle) of rice husk ash and paraffin was added to the test group, and the relative net paraffin content was 15% of the cement mass. Add standard sand and pure paraffin particles, wherein the amount of standard sand is the same volume as the composite product of the test group, and the net amount of pure paraffin wax particles is the same as that of the test group. The test results are shown in Figure 5 of the description.

It can be seen from Figure 5 that the test group has superior temperature control performance, indicating that the composite product of rice husk ash and paraffin is obviously superior to the temperature control performance of pure paraffin wax, which makes the temperature rise rate of cement hydration heat have a relatively large decreased, the temperature peak was significantly reduced. And the test shows that the volume difference between the slurry mixed with the composite product of rice husk ash and paraffin and the slurry mixed with pure paraffin is not large, and the volume of the former is only 1.117 times of the latter.

Application example 3

This test uses a 100mm×100mm×100mm cubic concrete test block, the test water-binder ratio is 0.38, the water reducer is polycarboxylate water reducer, and the solid content is 10%. The concrete mix ratio is shown in Table 1.

Molding scheme:

A. The concrete sample without adding rice husk ash-paraffin phase change aggregate is the reference group sample.

B. Concrete samples mixed with rice husk ash-paraffin aggregates, the relative net paraffin content is 10% and 20% respectively.

Table 1 Concrete mix ratio

Note: R-P is the rice husk ash-paraffin phase change aggregate

As shown in Table 1, the concrete proportioning strength grade is C40, in which the comparison group A is ordinary concrete, the test groups B10 and B20 are phase change concrete mixed with rice husk ash-paraffin phase change aggregate, and the paraffin wax in B10 is relatively pure The amount is 10% of the mass of the cementitious material, and the relative net amount of paraffin wax of B20 is 20% of the mass of the cementitious material. The results of the compressive strength of the concrete at 28 days are: A is 49.8Mpa, B10 is 43.6Mpa, and B20 is 36.3Mpa. The compressive strength of concrete mixed with rice husk ash-paraffin phase-change aggregates is lower than that of ordinary concrete, and the greater the content, the lower the strength. However, when the relative net content of paraffin is 10% of the mass of the cementitious material, it can still Meet the strength level requirements. In the presence of a large amount of fly ash and other admixtures, the ratio of the net paraffin content to the amount of cement is larger, so it can better inhibit the temperature change rate of mass concrete and reduce the temperature peak.

The anti-carbonation and impermeability tests of phase-change concrete show that phase-change concrete has excellent anti-carbonation performance and anti-chloride ion penetration performance. The volume stability of phase change concrete was tested by low temperature-high temperature-low temperature thermal cycle, and the results showed that the volume stability of phase change concrete was slightly better than that of ordinary concrete.

The invention has simple and economical process, high efficiency of paraffin encapsulation, can reduce the temperature peak of cement hydration heat to a large extent, delay the rate of cement hydration temperature rise and temperature drop, and has good performance when mixed with concrete. Adaptability, uniform distribution in concrete, no floating phenomenon.

In summary, rice husk ash-paraffin phase change aggregate has great application value.

Description of drawings

Fig. 1 The internal structure of rice husk ash-paraffin phase change aggregate, in which paraffin is filled in the voids of rice husk ash, and the rice husk ash particles filled with paraffin are agglomerated together in a granular shape.

Marked in the picture: 1 rice husk ash pores 2 paraffin

Figure 2 is the surface morphology of the rice husk ash-paraffin phase change aggregate, with a layer of limestone powder bonded to the surface.

Figure 3 is the DSC curve of No. 48 paraffin

Fig. 4 is the DSC curve of No. 58 paraffin

Figure 5 is a graph of the temperature rise test results

Detailed ways

The present invention will be further elaborated below in conjunction with embodiment and application example:

Example 1

Take 3Kg of rice husk ash with a particle size of less than 1.18mm, and 3Kg of paraffin particles with a particle size of not more than 2.36mm (the temperature corresponding to the highest peak of the endothermic peak of phase transition is 52°C), mix them evenly, and place them in a metal container to seal . Then place the metal container in a high temperature environment of 78°C for 10 hours, open the release valve of the metal container, release the air for 5 seconds, and close the valve to balance the air pressure in the container and the high temperature environment.

Then the metal container was transferred to another 42°C low temperature environment for 6 hours. In a lower environment, a negative pressure state is formed in the metal container, which is more conducive to the entry of paraffin into the pore structure of the rice husk ash.

Take out the metal container, disperse the composite product of rice husk ash and paraffin into particles with a particle size less than or equal to 1.18mm, and obtain composite product particles.

Weigh 3.2Kg of limestone powder, mix the composite product particles and the powder evenly, make the powder bond on the surface of the composite product particles, and obtain the rice husk ash-paraffin wax phase change aggregate.

The rice husk ash-paraffin phase-change aggregate prepared by the method, the paraffin is filled in the pores of the rice husk ash, and the rice husk ash particles filled with the paraffin are agglomerated together, and the mass ratio of the paraffin to the rice husk ash is 1: 1. The limestone powder is wrapped on the particle surface, and its mass accounts for 35% of the mass of the rice husk ash-paraffin phase change aggregate.

Example 2

Take 3Kg of rice husk ash with a particle size of 1.18mm, and 2Kg of paraffin wax particles with a particle size of no more than 2.36mm (the temperature corresponding to the highest peak of the endothermic peak of phase transition is 48°C), mix them evenly, and place them in a metal container to seal . Then place the metal container in an oven at 160°C to keep it warm.

After heating for 6 hours, open the vent valve of the metal container, vent for 5 seconds, and close the valve. In order to balance the air pressure in the container with the air pressure in the oven at 160°C.

The metal container was transferred to another oven at 72°C for 2 hours. In a lower environment, a negative pressure state is formed in the metal container, which is more conducive to the entry of paraffin into the pore structure of the rice husk ash.

Take out the metal container, disperse the composite product of rice husk ash and paraffin into particles with a particle size less than or equal to 1.18mm, and obtain composite product particles.

Weigh 5Kg of fly ash and divide it into two parts, each 2.5Kg. Take one part of it and mix it evenly with the composite product particles of rice husk ash and paraffin, put it in an enamel plate and keep it in an oven at 43°C for 20 minutes, take it out, and mix it fully with the other part of fly ash. The obtained product particles are rice Shell ash-paraffin phase change aggregate.

The rice husk ash-paraffin phase-change aggregate prepared by the method, the paraffin is filled in the pores of the rice husk ash, and the rice husk ash particles filled with the paraffin are agglomerated together, and the mass ratio of the paraffin to the rice husk ash is 1: 1.5. Fly ash wraps on the particle surface, and its mass accounts for 50% of the mass of the rice husk ash-paraffin phase change aggregate.

Example 3

Take 3Kg of rice husk ash with a particle size of less than 1.18mm, and 2.4Kg of paraffin wax particles with a particle size of not more than 2.36mm (the temperature corresponding to the highest peak of the endothermic peak of phase transition is 48°C), mix them evenly, and place them in a metal container seal. Then place the metal container in an oven at 120°C to keep it warm.

After heating for 8 hours, open the vent valve of the metal container, vent for 5 seconds, and close the valve. In order to balance the air pressure in the container with the air pressure in the oven at 120°C.

The metal container was transferred to another oven at 58°C for 4 hours. In a lower environment, a negative pressure state is formed in the metal container, which is more conducive to the entry of paraffin into the pore structure of the rice husk ash.

Take out the metal container, quickly sieve the composite product of rice husk ash and paraffin into a clean enamel plate with a 1.18mm square hole sieve, and place the square hole sieve in an oven at 58°C to preheat in advance. The composite product particles of the obtained rice husk ash and paraffin were cooled at normal temperature.

Weigh 3.6Kg of silica fume and divide it into two parts, each 1.8Kg. Take one part and mix evenly with the composite product particles of rice husk ash and paraffin, put it in an enamel plate and keep it warm in an oven at 43°C for 20 minutes, take it out, and then fully mix it with the other part of silica fume, and the obtained product particles are rice husk Ash-paraffin phase change aggregate.

The rice husk ash-paraffin phase-change aggregate prepared by the method, the paraffin is filled in the pores of the rice husk ash, and the rice husk ash particles filled with the paraffin are agglomerated together, and the mass ratio of the paraffin to the rice husk ash is 1: 1.25. The silica fume is wrapped on the particle surface, and its mass accounts for 40% of the mass of the rice husk ash-paraffin phase change aggregate.

Claims (8)

1. a kind of rice husk ash-paraffin phase change aggregate is characterized in that it is made of three kinds of materials of rice husk ash, paraffin and mineral powder, and the quality of mineral powder accounts for rice husk ash, paraffin and mineral powder quality 35%-50%, wherein the mass ratio of paraffin wax to rice husk ash is 1:1-1:1.5. 2. by the described rice husk ash-paraffin wax phase-change aggregate of claim 1, it is characterized in that described paraffin is filled in the pore of rice husk ash, and the rice husk ash that has been filled with paraffin agglomerates together, is granular; The above-mentioned mineral powder is wrapped on the particle surface. 3. The rice husk ash-paraffin phase-change aggregate according to claim 1 or 2, characterized in that the mineral powder is one of fly ash, silica fume, limestone powder or phosphorus slag powder. 4. a preparation method of rice husk ash-paraffin phase change aggregate, characterized in that it comprises the steps: 1) Selection of raw materials: according to the quality of mineral powder, it accounts for 35% to 50% of the mass of rice husk ash, paraffin and mineral powder, wherein the mass ratio of paraffin to rice husk ash is 1:1 to 1:1.5, and rice husk ash is selected. Shell ash, paraffin and mineral powders; 2) After sieving and mixing the rice husk ash and paraffin wax, place it in a container and seal it, keep it warm in a high temperature environment for 6-10 hours, release the gas in the container, seal it, and then place the container in a low temperature environment to keep warm 2 to 6 hours; take out the container, disperse the composite product of rice husk ash and paraffin into particles with a particle size less than or equal to 1.18mm; then mix the particles with mineral powder to make the mineral powder stick to the surface to obtain rice husk Ash-paraffin phase change aggregate. 5. by the preparation method of the described rice husk ash-paraffin wax phase-change aggregate of claim 4, it is characterized in that described rice husk ash particle diameter is less than or equal to 118mm; Described paraffin is solid at normal temperature, and particle diameter is less than or equal to 118mm; Equal to 2.36mm. 6. by the preparation method of the described rice husk ash-paraffin phase change aggregate of claim 4, it is characterized in that described high temperature environment is 1.5～3.5 times of the corresponding temperature of the endothermic main peak peak peak point of paraffin phase change, so The low temperature environment is 0.8 to 1.5 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition. 7. by the preparation method of claim 4 or 6 described rice husk ash-paraffin phase change aggregates, it is characterized in that described high temperature environment is 2.5 times of the temperature corresponding to the endothermic main peak highest point of paraffin phase change, so The low temperature environment is 1.2 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition. 8. by the preparation method of the described rice husk ash-paraffin phase-change aggregate of claim 4, it is characterized in that making mineral powder bonded on the surface of particle is realized in this way: described mineral powder is divided into equal mass Two parts, take one part of the mineral powder, mix it with rice husk ash and paraffin particles, place it in an environment 0.9 times the temperature corresponding to the highest point of the main endothermic peak of the paraffin phase transition, and keep it warm for 20 minutes, take it out, and mix it with Another part of mineral powder is mixed well.

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