A Novel Method for Calcium Carbonate Deposition in ...

In this work, we synthesized CaCO 3 inside the microstructure of radiata pine samples using a novel process that consisted in vacuum impregnation of an aqueous solution of calcium chloride (CaCl 2 ) and subsequent sequential diffusion of gaseous ammonium (NH 3 ) and CO 2 . The main objective of the study was to verify the feasibility of an innovative treatment to accumulate CO 2 inside wood that simultaneously could improve the response of wood against the action of fire, as the CO 2 involved in the reaction becomes part of the salt crystals of CaCO 3 accumulated in the wood microstructure. Specifically, we planned to verify the level of fire protection offered by the best conditions of the treatment, if any, and the amount of CO 2 accumulated inside the wood in such conditions.

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Mineralization treatments can certainly be accounted as an option to protect wood against fire while reducing the risk of releasing toxic compounds during its thermal degradation. Examples of innovations in such area can be found in the development of treatments promoting an accelerated petrification of wood [ 9 10 ] and others based on the formation of a wide range of minerals with inherent fire resistance properties inside the wood cells [ 11 12 ]. Several authors have proposed calcium carbonate (CaCO) as a fire protection agent for wood products [ 13 16 ]. During the endothermic decomposition of CaCO, the release of carbon dioxide (CO) apparently dilutes and cools combustion gases, reducing the effectiveness of the combustion [ 14 ]. The thermal degradation of CaCOdoes not generate toxic compounds and therefore is considered an environmentally friendly treatment [ 14 19 ]. Cone calorimetry tests on wood treated with CaCOhave shown up to a 65% decrease in heat release capacity, demonstrating the great potential of the treatment. In addition, the intrinsic properties of wood are not significantly affected, expanding its reliability in construction uses [ 14 17 ].

Fire retardancy in wood products is regularly achieved by superficial or integral impregnation with chemical formulations. In this sense, a wide range of very effective formulations, mostly based on the action of phosphorus, nitrogen, and boron compounds, have been developed [ 5 ]. However, nowadays many of these formulations have been questioned because of their possible toxic effects on living organisms [ 6 8 ]. For instance, the release of chlorinated and brominated dioxins and dibenzofurans during accidental fires or waste incineration is a recurrent concern [ 8 ]. Consequently, the development of new and innovative technologies for wood&#;s fire protection, capable of meeting the current environmental demands, is an evident necessity.

The increasing interest in wood as a building material is driven by its outstanding physical and mechanical behavior and versatility, but also by its biodegradable nature and ability to act as a carbon reservoir [ 1 ]. For these characteristics, many final users, seeking materials supporting sustainable development, have turned their attention to wood and wood products [ 2 ]. The use of wood in construction ensures that an important portion of the carbon incorporated by trees during their growth will remain sequestered in wood fibers for a long time [ 3 ]. Unfortunately, wood&#;s ability to act as a carbon reservoir ends when it is degraded, and carbon is released to the atmosphere [ 4 ]. Among the agents of deterioration, fire stands out because of its devastating effects, which can almost wholly degrade wood cells in a very short time. Thus, fire is a significant risk in any construction containing wooden elements.

Analysis of variance (ANOVA) was used to evaluate the mineralization and fire resistance of the wood samples. The mineralization experiment was conducted according to a factorial design that tested the concentration of CaCl 2 and the number of cycles of treatment as factors, while the weight gain of the samples after treatment was considered as the main response. Similarly, ANOVA was used to test the effect of the fire-retardant treatment on the wood samples. Such analysis considered as responses the weight loss due to combustion and the carbonization index. In all cases, after ANOVA ( p < 0.05), significant differences were estimated using Fisher&#;s least significant test (l.s.d.) and expressed as error bars in the different result charts.

Before the combustion test, all samples were oven-dried at 50 °C until constant weight (±0.002 g), and their mass recorded. After the combustion, the samples were allowed to cool down, and their mass was recorded again and used to calculate the weight loss due to combustion (Equation (3)). In addition, the maximum extension of the carbonization in each axis of the samples was recorded in mm and used to calculate the carbonization index according to Equation (4).where mand mare the mass of the samples before and after the combustion, respectively.where L, L, and Lare the maximum extension of the carbonization at the length, width, and depth of the sample, respectively.

Wood samples, 6 mm × 150 mm × 300 mm (= 15), were mineralized using the conditions that resulted in the highest accumulation of calcium carbonate, treated with the commercial fire-retardant agent AF (AF Fire Protection, Industrial y Comercial Ciprés Ltda, Santiago, Chile), or left without treatment to act as control samples. The fire-retardant agent was selected due to its commercial availability and chemical composition based on boric and phosphoric acid and ammonium sulfate [ 20 ]. The fire-retardant agent was applied by brushing, according to the manufacturer&#;s instructions, on samples previously conditioned at 65% R.H. and 21 °C for 2 weeks.

The fire resistance of the wood samples was tested according to Chilean Standard NCh ( Figure 1 ). The samples were ignited in controlled conditions inside a 400 mm × 700 mm × 810 mm cabinet, under a constant air flux (0.2 m·s). In the test, the samples are individually placed in the middle of the cabinet laying at 45°. Then, in a stainless-steel container, a known volume of absolute ethanol is burned directly under the samples. The test lasts until the total combustion of the fuel is achieved and the flames in the sample are completely off.

In addition, 2.5 mg of each grinded sample was used to conduct a thermogravimetric analysis (TGA) in a TG 209F3 Tarsus from NETZSCH Instruments (Selb, Germany) thermogravimetric analyzer. These tests were conducted in an ultra-high purity nitrogen atmosphere with a heating rate of 20 °C·min &#;1 , from 50 to 600 °C. The weight loss relative to the temperature values was used to perform the derivative thermogravimetric analysis (DTG). All TGA tests were performed in triplicate.

The Fourier transform infrared spectroscopy (FTIR) spectra of the untreated and mineralized samples, as well as of the pure CaCO 3 standard, were measured by direct transmittance using the KBr pellet technique. The spectra were recorded in the range of &#;400 cm &#;1 using a Thermo-Nicolet Nexus 670 FTIR (Thermo Fischer Scientific, Waltham, MA, USA). Pretreatment was carried out by grinding the samples in a mill to 200 mesh and, subsequently, by compressing the mixture of each sample and KBr (where KBr has a ratio of 0.5 wt.%&#;1 wt.%).

Calcium concentration in the samples was measured by Atomic Absorption Spectroscopy (AAS) by using 20 mm × 20 mm × 40 mm wood samples ( n = 5). These samples were sawn in half to obtain 10 paired samples of 20 mm × 20 mm × 20 mm. Five of the paired samples remained as controls without treatment, and the other five were mineralized until reaching a 20% weight gain. After treatment, the samples were grounded in a small grinder to 200 mesh, and then the ash content was determined according to ASTM -01(). The grounded samples were digested using a mixture of 18 mL HNO 3 and 7 mL HCl (final volume 25 mL). The samples were boiled for 2 h in covered beakers on a hot plate. Then, the digested samples were transferred and diluted to 100 mL with distilled water. The resultant products were measured and analyzed in an iCE Series Atomic Absorption Spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). The initial content of calcium in the samples was subtracted from the content of calcium measured after the mineralization treatment. This information was used to calculate the mol of calcium per gram of anhydrous wood and hence the content of CO 2 .

The concentration of COaccumulated inside the wood microstructure due to the mineralization treatment was indirectly determined by assessing the gain of calcium in the samples. According to the chemical reaction associated with the mineralization treatment, each molecule of calcium acquired by the wood due to the accumulation of CaCOreacted with one molecule of CO(Equation (2)). Thus, for each mol of calcium accumulated in the wood, at least one mol of COwas captured due to the treatment.

Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were used to observe the accumulation of salt crystals inside the wood microstructure and assess their chemical composition. SEM and EDS evaluations were performed on samples that achieved the higher weight gains. Primarily, observations were made at the surface and then at 5 and 10 mm depth, using a JEOL-JSM (Tokyo, Japan) scanning electron microscope and an acceleration voltage of 20 kV.

CaCOaccumulation inside the wood microstructure was conducted on the 20 × 20 × 20 mm (= 100) conditioned samples. The samples were vacuum-impregnated (&#;1 atm, 120 min) with CaCl(7.5%, 15%, 30%, and 60% w/v) in a stainless-steel vessel (30 L, approx.). After that, the samples were removed and then sequentially exposed to gaseous ammonia (40 °C for 60 min, atmospheric pressure) inside a vaporing chamber and to CO(99%, 60 min, 4 bars, room temperature) inside the stainless-steel vessel. The aim of using gaseous ammonia was to promote a rapid change of pH throughout the wood section, creating an alkaline environment, in which the presence of COcould initiate the reaction of mineralization of CaClinto CaCO. Similarly, the use of gaseous COwas expected to improve the penetration of the mineralization treatment. After the treatment, the samples were washed overnight in distilled water at neutral pH to remove residual salts and byproducts. The whole process was consecutively repeated, producing cycles of treatment from 1 to 5. The treated samples were oven-dried at 50 °C until constant weight (±0.002 g), and the anhydrous mass was recorded and afterwards used to calculate the weight gain of the treatment according to Equation (1):where mand mare the anhydrous mass of the samples before and after the mineralization treatment, respectively.

Radiata pine ( Pinus radiata D. Don) wood pieces, acquired at a local lumber store, were used to prepare two sets of samples. The first set consisted of cubic sapwood pieces with perfectly tangential, radial, and transverse faces (20 mm × 20 mm × 20 mm). The second set consisted of 6 mm × 150 mm × 300 mm wood pieces with the tangential section on the main face and the end grain oriented along the longest axis. These samples were not screened for the presence of sapwood or heartwood. All samples were dried to anhydrous conditions in a convection oven at 50 °C, and their anhydrous mass was recorded. After that, the samples were conditioned at 65% relative humidity (R.H.) and 21 °C for two weeks, prior to the impregnation treatment.

The appearance of the wood samples after the fire-resistance test is shown in Figure 7 . It can be observed that the mineralized samples maintained their structural integrity, which was not the case for some of the samples treated with the fire-resistant-agent and for the control samples. The integrity of the mineralized samples supports their reliability if used in a wooden structure subjected to fire, pointing out the great potential of the mineralization treatment for wood fire protection.

The weight gain of the mineralized samples in the fire-resistance test is shown in Table 2 . The results of the fire resistance tests are summarized in Figure 6 . The ANOVA results, available as Supplementary Data (Figures S2 and S3) show differences between the treatments (-values < 0.05). Thus, a significant improvement in fire resistance was observed for the mineralized samples treated with four cycles of CaCl30% compared to the control samples left without treatment. However, differences between the mineralized samples and those treated with the commercial fire-retardant agent AF were not significant. In terms of weight losses, the mineralized samples reached an average value that was about 20 percentage points lower than that of the samples treated with the fire-retardant agent and more than 40 percentage points lower than that of control samples. A similar trend was observed for the carbonization index, which was almost 30 percentage points lower for the mineralized samples compared to the samples treated with the retardant agent and approximately 60 percentage points lower compared to the control samples.

TGA of the untreated wood samples showed a large signal at 367 °C, which implied a mass loss of almost 80% ( Figure 5 a). In contrast, the samples previously treated with CaCOshowed a different thermal degradation profile. It is possible to observe in Figure 5 b the important increase of the signal (shoulder) near 300 °C that appeared in the untreated samples. This signal in CaCO-treated samples appears at lower temperatures (283 °C) with a DTG of &#;3.87%/min. The DTG curve of CaCO-treated samples presents two important decomposition stages: the first one appears as a signal in the form of a slight curve after 200 °C, and the second stage presents the highest peak of decomposition near 350 °C. In all replicates, the mineralized samples showed a maximum decomposition peak before that of untreated wood. Therefore, these TGA results suggest that, at the beginning, CaCO-treated wood lost weight faster than untreated wood; however, after 350 °C, the opposite behavior was observed, and the untreated wood lost weight faster ( Figure 5 a), reaching a loss of about 92% compared with a weight loss of only 64% of the CaCO-treated samples.

The FTIR spectrum of pure CaCOshowed the presence of a strong band centered around cm, characteristic of the C&#;O stretching mode of carbonate, together with a narrow band around 873 cmcharacteristic of the bending mode ( Figure 4 B). These bands were also observed in the CaCO-treated wood sample, showing an increased absorbance in both wavenumbers ( Figure 4 A). Additionally, when both spectra were compared, it was observed that the treated wood sample showed differences at cmthat corresponded to C=C stretching vibrations in the aromatic structure. Interestingly, a variation was seen at cmassociated with the stretching vibrations of unconjugated C=O and related to carbonyl groups in the hemicellulose structure [ 21 22 ].

The gains of weight, calcium, and CO, of selected wood samples are shown in Table 1 . The average carbon dioxide gain was 0.467 (mmol of CO·gof anhydrous wood) for samples that achieved about 20% weight gain (wt.%) due to the mineralization treatment. These samples were treated with an initial CaClconcentration of 30% in four consecutive cycles.

SEM images of samples treated with 30% CaCl, five cycles, show that the treatment induced an extended mineralization of the external area of the samples ( Figure 3 ). Mineralization was less prevalent at 5 mm depth, forming semispherical particles, and apparently absent at 10 mm depth. EDS analysis of the samples showed that the amount of calcium present at the surface of the observed samples was 35.6% ( Figure 3 a). This amount decreased to 3.6% at 5 mm depth and to 1.08% at 10 mm depth ( Figure 3 b,c), which was almost equal to that measured in an untreated sample. The EDS analysis of the semispherical particles found in the interior and at the surface of the samples ( Figure 3 d) and at 5 and 10 mm depth in the treated samples was stoichiometrically sufficient to determine CaCOpresence. This clearly contrasts with the results obtained for the untreated surface, where the content of C, O, and Ca were 52.85%, 46.39%, and 0.79%, respectively.

The results of the mineralization experiments are depicted in Figure 2 . The ANOVA results, available as Supplementary Data (Figure S1) , indicated a significant effect (-value < 0.05) of CaClconcentration, the number of treatment cycles, and the interaction of these two factors. Figure 2 shows that the increment of the treatment cycles had a significant effect only until the fourth cycle. Similarly, 30% CaClconcentration yielded significantly higher weight gains values compared to other concentrations. Nevertheless, relevant interactions detected among factors showed that the highest weight gain, 22% in samples treated with five cycles using CaClat a concentration of 30%, was not significantly different than those obtained in samples treated with five cycles; 15% CaCl, and 4 cycles; 15% and 30% CaCl. With the goal to establish adequate conditions for the treatment of larger samples, four cycles and 30% CaClwere chosen as treatment conditions to mineralize the fire-resistant test samples.

4. Discussion

The results obtained in this work support the hypothesis that a mineralization treatment based on wood impregnation with an aqueous solutions of CaCl2, followed by sequential diffusion of ammonia and carbon dioxide, promotes CaCO3 deposition into the wood microstructure, resulting in improved fire resistance and in the accumulation of CO2. In the process of mineralization, the main product synthesized on the surface and inside the wood was CaCO3. In the process, CO2 reacted in presence of CaCl2 in an alkaline environment (NH3) to form CaCO3. The best conditions of mineralization reached for radiata pine sapwood led to a weight gain of 20 wt.%, with an average of 0.467 (mmol·g&#;1 wood) of CO2 captured into the wood.

A significant increment of weight due to the mineralization after cycle 4 was apparently made difficult by the saturation of the wood surfaces and penetration pathways with CaCO3. These pathways may include pits, rays, and cell lumens in a transverse section. In support of this, SEM images and EDS analysis showed a compact layer of minerals on the wood surface and a scarce presence of CaCO3 at 10 mm depth. The ideal process of wood mineralization requires that the reaction occurs from the center of the sample towards the surface. In most mineralization processes, this is difficult to achieve, as the precursors of the chemical reaction are all first available at the surface, and consequently, the synthesis of minerals and byproducts will inevitably saturate the surface after several cycles of replications, if not during the first. In this case, diffusion of gaseous CO2 apparently occurs in parallel with the formation of CaCO3. In such conditions, it is likely that gaseous CO2 would follow only free passages in the microstructure of the wood, avoiding the already coated surfaces and clogged lumens. Further testing, increasing CO2 pressure or reaction times and using methods to promote the liberation of pathways before CO2 injection into the system (such as sonication), may be valid strategies to improve the efficiency of the treatment.

&#;1, suggest a chemical interaction between CaCO3 impregnated in the wood and the hemicellulose matrix. Evidence of this has been attributed to the absorption of calcium cations into pectin and lignin surfaces, which are rich in metal-complexing groups and are negatively charged [3-treated samples [3-treated wood samples was due to the early degradation of CaCO3, H2O, and CO2 [3-treated samples become more stable to combustion due to aragonite transforming into calcite at 387 °C [2 at temperatures above 850 °C [

Changes detected by FTIR, specifically, the decrease in absorbance of the band cm, suggest a chemical interaction between CaCOimpregnated in the wood and the hemicellulose matrix. Evidence of this has been attributed to the absorption of calcium cations into pectin and lignin surfaces, which are rich in metal-complexing groups and are negatively charged [ 14 ]. The TGA results showed that the mineralized samples degraded faster at the beginning of the test, but after 350 °C, this behavior reversed, and finally the untreated samples were more extensively degraded. These results are in agreement with those reported previously in the literature for different CaCO-treated samples [ 15 23 ]. It has been proposed that a fast initial degradation of CaCO-treated wood samples was due to the early degradation of CaCO, HO, and CO 24 ] before reaching 100 °C ( Figure 5 ). However, at higher temperatures (>350 °C), CaCO-treated samples become more stable to combustion due to aragonite transforming into calcite at 387 °C [ 25 ], which afterwards is decomposed into CaO and COat temperatures above 850 °C [ 26 ].

In terms of fire resistance, it is relevant to remark that the conditions of mineralization&#;CaCl2 30% and 4 cycles&#;only produced a weight gain of 8 wt.% for the fire-resistant test samples. This may be due to the presence of heartwood within large samples, which is more difficult to impregnate than sapwood. Despite this, the results showed that the mineralized samples performed to a similar level as the samples treated with a commercially available fire-retardant agent, while maintaining their structural conformation. This suggest the great potential of the treatment. The experimental results indicated that the main portion of the synthesized CaCO3 was located at the surface of the samples, which is also the main area coming in contact with fire. Thus, it appears that, in terms of fire resistance, the specific concentration of CaCO3 at the wood surface is more relevant than the total amount of CaCO3 accumulated within the sample.

3 has been proposed by several authors to increase wood&#;s fire resistance, but to our knowledge, a method comprising sequential gas diffusion has not been reported. Most of the reported treatments use liquid diffusion of CaCl2 in combination with a number of agents, such as sodium hydroxide and supercritical carbon dioxide [15,

The mineralization of wood with CaCOhas been proposed by several authors to increase wood&#;s fire resistance, but to our knowledge, a method comprising sequential gas diffusion has not been reported. Most of the reported treatments use liquid diffusion of CaClin combination with a number of agents, such as sodium hydroxide and supercritical carbon dioxide [ 23 ], aqueous sodium carbonate with dodecanoic acid [ 11 ], sodium bicarbonate [ 14 27 ], ammonium carbonate [ 28 ], sodium carbonate, alkaline hydrolysis of dimethyl carbonate [ 17 ], and calcium dimethylcarbonate in methanol [ 13 ]. In addition, a novel method was recently proposed consisting in impregnating wood with calcium acetoacetate [ 16 ]. The mineralization treatment used in this work yielded weight gains that were comparable to those obtained by using sodium bicarbonate and calcium acetoacetate as precursors [ 14 16 ], generating weight gains close to 35% for spruce samples and of about 28% and 8.3% for beech samples.

Common drawbacks of CaCO3 mineralization treatments include the impossibility to achieve a deep deposition of minerals, the toxicity of certain precursors, and the complexity of the treatments. Although this was partially confirmed for the treatment proposed in this study, as certainly gaseous ammonia can be categorized as toxic, the diffusion of ammonia, in practical terms, can be achieved in a closed system in which the residual gases can be recovered and recycled. In addition, it is expected that the increment of reaction time with NH3 and CO2 may also increase the weight gain and the depth of mineralization.

The development of new and innovative technologies for fire protection capable of meeting the current environmental demands is a necessity. The method presented in this paper indicates that it is possible to promote the deposition of CaCO3 inside the wood microstructure using a hybrid process that includes the use of liquid and gaseous reagents, resulting in the retention of CO2 and improving wood&#;s fire resistance. This opens the way for the development of wood products with enhanced performance and environmental characteristics that can be very attractive for many final users.

A kind of preparation method of flame-retardant calcium carbonate

Technical field

The invention belongs to chemical material technical field, more particularly, the present invention relates to a kind of flame-retardant calcium carbonate crystal (Marinco H Mg (OH) 2/ lime carbonate CaCO 3) the preparation method, with the flame-retardant calcium carbonate of this method preparation be used for sheath or the shell of power cable, electronics, electrical equipment etc. fire-retardant/toughener, and fire-retardant/toughener of share with fields such as furred ceilings of interior decoration.

Background technology

Lime carbonate is widely used in industry as a kind of enhancement additive:

(1) application of lime carbonate in plastics

China has become the big country of plastics production and consumption, and the output of plastics in has surpassed 4,000 ten thousand t.The quantity of the inorganic mineral powder material that uses in the plastics is pressed 10% of plastic material and goods ultimate production usually and is calculated, and promptly the inorganic powder material of the annual use of China's plastic working industry at present is at least more than 4,000,000 t (ten thousand t, that is: ten thousand tons).Lime carbonate (comprising coarse whiting and fine particle calcium carbonate) is to use the most extensively, the maximum inorganic mineral powder material of consumption; In employed inorganic mineral powder total amount of material; Lime carbonate accounts for more than 70%; Be not only because lime carbonate aboundresources, cheap, the good stability of lime carbonate, simple, the low abrasion of color and luster, be prone to dry, be prone to processing, plurality of advantages such as nontoxic also is to obtain general a large amount of major reasons of using.

(2) application of lime carbonate in rubber

Lime carbonate has that resource is wide, toxicity and characteristics such as contaminative is low, whiteness is high, loading level is big and price is low, in rubber industry, be widely used, and be the main light filler of rubber item.In recent years, along with the fast development of China's rubber industry, the consumption of lime carbonate improves constantly.Total consumption of China's rubber industry light calcium carbonate in and water-ground limestone is 580,000 t, is about 700,000 t in .

2.1 tire

The normal part of light calcium carbonate substitutes subnormal structure black and WHITE CARBON BLACK is used for cycle tyre cover tire glue (consumption is above 70 parts) and tube glue, in auto tyre casing cord ply compound, air/tight layer rubber, air retaining wall glue and the tube glue (consumption can reach 58 parts) to reduce production costs.

2.2 sebific duct and adhesive tape

Light calcium carbonate and nano-calcium carbonate are used for sebific duct and adhesive tape, and the one, play white reinforcing filler, the 2nd, improve the dispersiveness of sizing material.Lime carbonate can be used for common sebific duct, colored sebific duct, hydralic hose and staple fibre reinforcement sebific duct etc. in sebific duct, in adhesive tape, can be used for conveying belt, transmission belt and synchronous band etc.

2.3 rubber overshoes

Lime carbonate can adapt to different color requirements, can improve the mixing and extrusion performance of sizing material, in rubber overshoes, uses very extensively, and normal and carbon black, WHITE CARBON BLACK, white titanium pigment and potter's clay etc. also are used for the positions such as vamp, sole and heel of rubber overshoes.

2.4 electric wire

Lime carbonate is general with carbon black, WHITE CARBON BLACK, potter's clay and talcum powder etc. and be used as the reinforcing filler of sheath such as mining electric wire, electric wire peculiar to vessel, high-tension bus-bar cable and electrical equipment electric wire sizing material.At chloride rubber; Do in the electric wire sizing material of main body material like CR, chlorinated polyethylene rubber (CM) and chlorination cis-1,4-polybutadiene rubber etc.; Lime carbonate is except that playing reinforcing filler; Also rise and reduce the hydrogenchloride that produces in the sizing material acidity and the absorption sizing material course of processing, thereby avoid the effect of the sizing material appearance sulfuration delay and the phenomenon of reverting, improve the extrusion performance of sizing material simultaneously.

In sum; Lime carbonate is the filler of a kind of cheapness, excellent property, but since the heat decomposition temperature of lime carbonate more than 800 &#;, if be used on the plastics; Because plastics are inflammable; Therefore its temperature of lighting in the initial combustion stage, hopes that divided calcium carbonate separates that to discharge carbonic acid gas be impossible about 400 &#;.The favourable part that lime carbonate exists only is to reduce the amount of combustiblematerials, and calcium carbonate content is high more, and the combustiblesubstance in same volume is just few more, helps fire-retardant certainly.But because the existence of lime carbonate; Form countless micropores in the process that expands rapidly during the macromolecular material burning and gasify; Increased the surface-area that combustiblematerials contacts with oxygen greatly, made more combustiblematerials participate in burning, and further improve the temperature of fire area; More help the expansion and the gasification of combustiblematerials, the flame retardant resistance that makes lime carbonate is of no consequence.If lime carbonate not only has enhanced in some product especially electronic product, also have certain flame retardant resistance, the effect of lime carbonate is just more remarkable.Yet in the preparation method of numerous composite calcium carbonates, also there is not a kind of method to relate to the preparation of the lime carbonate of flame retardant properties at present.

Summary of the invention

The technical problem that the present invention will solve is: a kind of flame-retardant calcium carbonate crystal (Marinco H Mg (OH) is provided 2/ lime carbonate CaCO 3) preparation method, to solve the problems referred to above that exist in the prior art, its crystal habit of flame-retardant calcium carbonate for preparing with the present invention is good, purity is high, and is remarkable as its fire-retardant/reinforced effects of fire-retardant/toughener.

The preparation method of flame-retardant reinforced lime carbonate provided by the invention is prepared by following component by mole concentration:

Sal epsom (MgSO 4) 0.82mol/L&#;1.6mol/L

Sodium hydroxide (NaOH) 7.6mol/L&#;9.2mol/L

Yellow soda ash (Na 2CO 3) 4.84mol/L&#;5.3mol/L

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Calcium hydroxide (Ca (OH) 2) 0.18mol/L--2.4mol/L

Calcium chloride (CaCl 2) 3.8mol/L&#;4.7mol/L

In the said components, sal epsom MgSO 4Provide the preparation basic magnesium chloride required mg ion; Calcium chloride CaCl 2, calcium hydroxide Ca (OH) 2Required calcium ion is provided, and calcium chloride, calcium hydroxide are also favourable to crystal growth, and calcium hydroxide also is used to adjust the pH value; Sodium hydroxide NaOH provides required hydroxide ion, controls the pH value of reaction soln simultaneously, yellow soda ash Na 2CO 3Provide reaction required carbanion.

It is as shown in Figure 1 that liquid phase method prepares the experimental installation of flame-retardant calcium carbonate.Reactor drum is an open container 1, adopts electric furnace 3 heating; Whisking appliance 4 carries out mechanical stirring, and stirring velocity is at 50&#;rmin -1Adjustable continuously in the scope.

The present invention prepares flame-retardant calcium carbonate and carries out according to the following steps:

The first step is also filtered sal epsom by the aqueous solution that said ratio is mixed with ml;

Second step; In this Adlerika, (in the suspension liquid, the calcium hydroxide amount is by the said ratio preparation slowly to add the calcium hydroxide of preparation and the mixing suspension liquid of sodium hydroxide; The pH value that sodium hydroxide only helps to regulate this mixing suspension liquid is controlled in 8.5&#;9 scopes); In about 65 &#;, water bath with thermostatic control reaction 20 minutes, and continue to stir;

The 3rd step under high stirring velocity, slowly was added dropwise to the calcium chloride solution that is mixed with by said ratio again in this reaction solution, in about 70 &#;, and water bath with thermostatic control reaction 3 hours, and continue to stir; Constantly measure the pH value of solution therebetween, the pH value is controlled in 8.5&#;9 scopes;

In the 4th step, after reaction solution becomes white suspension liquid fully, stop heating, leave standstill, at room temperature cooling.Put it in the ultrasonic cleaning machine under the frequency of 59KHz ultrasonic 20 minutes then;

The 5th step changed the white suspension liquid after ultrasonic in baking oven ageing, and wherein: the ageing temperature is: 45 &#;&#;55 &#;.Digestion time is: 24 hours&#;36 hours.Can obtain white basic magnesium chloride crystal;

With above-mentioned component proportioning and the prepared basic magnesium chloride of process method, through ESEM (SEM) observation, prepared needle-like basic magnesium chloride crystalline footpath: 1.5 microns&#;2 microns, long: as 6 microns&#;10 microns, to see Fig. 2.Through the XRD test, its chemical constitution is Mg 2(OH) 3Cl4H 2O sees Fig. 3.

The 6th goes on foot, and yellow soda ash is mixed with the aqueous solution of 500ml by said ratio;

The 7th step added sodium hydroxide in white basic magnesium chloride crystal that after the 5th step ageing, obtains and the solution thereof, and its pH value is controlled in 10&#;10.5 scopes.Then with ultrasonic cleaning machine with its ultrasonic 5 minutes, generate white suspension liquid;

The 8th step under stirring velocity slowly, added the sodium carbonate solution that is mixed with by said ratio in the white suspension liquid of this basic magnesium chloride, in about 90 &#;&#;100 &#;, and water bath with thermostatic control reaction 6&#;8 hours, and continue slowly to stir; Constantly measure the pH value of solution therebetween, the pH value is controlled in 10&#;11 scopes;

The 9th step then stopped heating, leaves standstill, and treated to put into baking oven after the suspension liquid deposition fully, carried out skillfully according to corresponding temperature and time;

Wherein: skilled TR is: 60 &#;&#;75 &#;.Skilled period, scope was: 2 days&#;3 days;

In the tenth step, after skilled the completion, be precipitated to neutrality with the deionized water repetitive scrubbing, and repetitive scrubbing removes the redundant impurities cl ions Cl that adsorbs on the precipitation surface -Filter then, obtain flame-retardant calcium carbonate crystal (Marinco H Mg (OH) 2/ lime carbonate CaCO 3).

With above-mentioned component proportioning and the prepared flame-retardant calcium carbonate of process method, through ESEM (SEM) observation, prepared is flaky thick: 0.1 micron&#;0.2 micron, directly: 0.5 micron&#;1 micron, see Fig. 4 (b)&#;Fig. 8 (b).Through the XRD test, its chemical constitution is Marinco H Mg (OH) 2/ lime carbonate CaCO 3Complex phase is seen Fig. 4 (a)&#;Fig. 8 (a).

Compared with prior art, the present invention has following characteristics:

(1) the tabular crystal Marinco H Mg (OH) of preparation submicron order under normal pressure 2/ lime carbonate CaCO 3Compound fire-retardant toughener; Avoid Carbonization Preparation lime carbonate CaCO 3The time, because of the feeding of dioxide gas, complicacy on the technology.

(2) technological process is simple, does not require specific installation, and raw materials used sufficient cheap, is suitable for industrialized production fully;

(3) observation from ESEM shows, the tabular crystal Marinco H Mg (OH) of submicron order 2/ lime carbonate CaCO 3The crystal habit homogeneity of compound fire-retardant toughener is good; Through the XRD test shows, the tabular crystal Marinco H Mg (OH) of this submicron order 2/ lime carbonate CaCO 3Compound fire-retardant toughener phase composite is stable;

(4) the tabular crystal Marinco H Mg (OH) of this submicron order 2/ lime carbonate CaCO 3Compound fire-retardant toughener whiteness is good;

(5) the tabular crystal Marinco H Mg (OH) of submicron order of the present invention 2/ lime carbonate CaCO 3Compound fire-retardant toughener had both had Marinco H Mg (OH) 2The fire retardant effect has lime carbonate CaCO again 3The strengthening agent effect.And,, help further compound with polymkeric substance because it is the tabular crystal of submicron order.

(6) the tabular crystal Marinco H Mg (OH) of this submicron order 2/ lime carbonate CaCO 3Compound fire-retardant toughener has Halogen, smoke elimination, nontoxic characteristics, helps the protection and the human health of environment, is a kind of new variety of inorganic strengthening agent efficiently of very promising flame retardant type.It is further to develop the flame-retardant reinforced matrix material of lime carbonate/polymkeric substance, and basic substance and wide research and development space are provided.

(7) the tabular crystal Marinco H Mg (H) of this submicron order 2/ lime carbonate CaCO 3Compound fire-retardant toughener is flaky thick: 0.1 micron&#;0.2 micron, directly: 0.5 micron&#;1 micron, compare with pure micro-calcium carbonate, improved lime carbonate CaCO 3Fineness and flowability, had both the advantage of nano-calcium carbonate.

Description of drawings

Fig. 1 the present invention prepares the experimental installation synoptic diagram of sample, and wherein: 1 is that adjustable resistance electric furnace (1K Ω max) 2 is pH meter for asbestos gauge 3 for Stainless Steel Ware 4, and 5 is the boosting-type electric mixer

Fig. 2 basic magnesium chloride crystalline ESEM (SEM) photo (amplify times, middle scale is 10 microns)

The homemade basic magnesium chloride crystalline of Fig. 3 XRD figure spectrum shows that its chemical constitution is Mg 2(OH) 3Cl4H 2O

The XRD figure spectrum of the compound fire-retardant toughener of tabular crystal of Fig. 4 (a) submicron order shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3

The tabular crystal Marinco H Mg (OH) of Fig. 4 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron)

The XRD figure spectrum of the compound fire-retardant toughener of tabular crystal of Fig. 5 (a) submicron order shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3

The tabular crystal Marinco H Mg (OH) of Fig. 5 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 5 microns)

The XRD figure spectrum of the compound fire-retardant toughener of tabular crystal of Fig. 6 (a) submicron order shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3

The tabular crystal Marinco H Mg (OH) of Fig. 6 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron)

The XRD figure spectrum of the compound fire-retardant toughener of tabular crystal of Fig. 7 (a) submicron order shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3

The tabular crystal Marinco H Mg (OH) of Fig. 7 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron)

The XRD figure spectrum of the compound fire-retardant toughener of tabular crystal of Fig. 8 (a) submicron order shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3

The tabular crystal Marinco H Mg (OH) of Fig. 8 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron)

Embodiment:

Below in conjunction with preferred embodiment content of the present invention is elaborated.

Embodiment 1

Getting the magnesium ion concentration that is mixed with by sal epsom is 0.82mol/L, and NaOH is 7.6mol/L, Na 2CO 3Be 4.84mol/L, Ca (OH) 2Be 0.18mol/L, calcium chloride is 4.7mol/L, reacts according to above step.Wherein prepare basic magnesium chloride crystal (Mg 2OH) 3Cl4H 2O) time: its temperature of reaction is that 70 &#;, reaction times are 3 hours, and ageing temperature subsequently is that 55 &#;, digestion time are 36 hours.And preparation flake magnesium hydroxide Mg (OH) 2/ lime carbonate CaCO 3During compound fire-retardant toughener: its temperature of reaction is that 90 &#;, reaction times are 8 hours, and skilled TR subsequently is that 70 &#;, skilled period are 3 days.Obtain thick: 0.1 micron&#;0.15 micron, directly: the compound fire-retardant toughener of 0.8 micron&#;1 micron sheet, see Fig. 4.Wherein, the XRD figure of the compound fire-retardant toughener of tabular crystal of Fig. 4 (a) submicron order spectrum shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3The tabular crystal Marinco H Mg (OH) of Fig. 4 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron)

Embodiment 2

Getting the magnesium ion concentration that is mixed with by sal epsom is 1.42mol/L, and NaOH is 8.86mol/L, Na 2CO 3Be 5.04mol/L, Ca (OH) 2Be 1.18mol/L, calcium chloride is 4.08mol/L, reacts according to above step.Wherein prepare basic magnesium chloride crystal (Mg 2OH) 3Cl4H 2O) time: its temperature of reaction is 70 &#;, and the reaction times is 3 hours, and ageing temperature subsequently is that 50 &#;, digestion time are 32 hours.And preparation flake magnesium hydroxide Mg (OH) 2/ lime carbonate CaCO 3During compound fire-retardant toughener: its temperature of reaction is that 95 &#;, reaction times are 7 hours, and skilled TR subsequently is that 60 &#;, skilled period are 3 days.Obtain thick: 0.15 micron&#;0.2 micron, directly: the compound fire-retardant toughener of 0.6 micron&#;1 micron sheet, see Fig. 5.Wherein, the XRD figure of the compound fire-retardant toughener of tabular crystal of Fig. 5 (a) submicron order spectrum shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3, the tabular crystal Marinco H Mg (OH) of Fig. 5 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 5 microns).

Embodiment 3

Getting the magnesium ion concentration that is mixed with by sal epsom is 1.6mol/L, and NaOH is 9.2mol/L, Na 2CO 3Be 5.3mol/L, Ca (OH) 2Be 1.52mol/L, calcium chloride is 4.05mol/L, reacts according to above step.Wherein prepare basic magnesium chloride crystal (Mg 2OH) 3Cl4H 2O) time: its temperature of reaction is 70 &#;, and the reaction times is 3 hours, and ageing temperature subsequently is that 45 &#;, digestion time are 24 hours.And preparation flake magnesium hydroxide Mg (OH) 2/ lime carbonate CaCO 3During compound fire-retardant toughener: its temperature of reaction is that 100 &#;, reaction times are 6 hours, and skilled TR subsequently is that 70 &#;, skilled period are 2 days.Obtain thick about 0.1 micron, directly: the compound fire-retardant toughener of 0.5 micron&#;1 micron sheet, see Fig. 6.Wherein, the XRD figure of the compound fire-retardant toughener of tabular crystal of Fig. 6 (a) submicron order spectrum shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3The tabular crystal Marinco H Mg (OH) of Fig. 6 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron).

Embodiment 4

Getting the magnesium ion concentration that is mixed with by sal epsom is 0.98mol/L, and NaOH is 8.62mol/L, Na 2CO 3Be 5.13mol/L, Ca (OH) 2Be 0.48mol/L, calcium chloride is 4.68mol/L, reacts according to above step.Wherein prepare basic magnesium chloride crystal (Mg 2OH) 3Cl4H 2O) time: its temperature of reaction is 70 &#;, and the reaction times is 3 hours, and ageing temperature subsequently is that 55 &#;, digestion time are 24 hours.And preparation flake magnesium hydroxide Mg (OH) 2/ lime carbonate CaCO 3During compound fire-retardant toughener: its temperature of reaction is that 100 &#;, reaction times are 8 hours, and skilled TR subsequently is that 60 &#;, skilled period are 2 days.Obtain thick about 0.1 micron, directly: the compound fire-retardant toughener of 0.5 micron&#;0.8 micron sheet, see Fig. 7, wherein, the XRD figure of the compound fire-retardant toughener of tabular crystal of Fig. 7 (a) submicron order spectrum shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3The tabular crystal Marinco H Mg (OH) of Fig. 7 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron)

Embodiment 5

Getting the magnesium ion concentration that is mixed with by sal epsom is 1.06mol/L, and NaOH is 8.53mol/L, Na 2CO 3Be 5.24mol/L, Ca (OH) 2Be 1.58mol/L, calcium chloride is 3.8mol/L, reacts according to above step.Wherein prepare basic magnesium chloride crystal (Mg 2OH) 3Cl4H 2O) time: its temperature of reaction is that 70 &#;, reaction times are 3 hours, and ageing temperature subsequently is that 45 &#;, digestion time are 36 hours.And preparation flake magnesium hydroxide Mg (OH) 2/ lime carbonate CaCO 3During compound fire-retardant toughener: its temperature of reaction is that 95 &#;, reaction times are 7 hours, and skilled TR subsequently is that 65 &#;, skilled period are 2 days.Obtain thick about 0.1 micron, directly: the compound fire-retardant toughener of 0.5 micron&#;0.9 micron sheet, see Fig. 8.Wherein, the XRD figure of the compound fire-retardant toughener of tabular crystal of Fig. 8 (a) submicron order spectrum shows that its chemical constitution is: Marinco H Mg (OH) 2/ lime carbonate CaCO 3The tabular crystal Marinco H Mg (OH) of Fig. 8 (b) submicron order 2/ lime carbonate CaCO 3The ESEM of compound fire-retardant toughener (SEM) photo (amplify times, middle scale is 1 micron).

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