CN116751073B - 具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法 - Google Patents
具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法 Download PDFInfo
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- OJMOMXZKOWKUTA-UHFFFAOYSA-N aluminum;borate Chemical compound [Al+3].[O-]B([O-])[O-] OJMOMXZKOWKUTA-UHFFFAOYSA-N 0.000 title claims abstract description 79
- 239000000919 ceramic Substances 0.000 title claims abstract description 64
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 239000011148 porous material Substances 0.000 title abstract description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 23
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims abstract description 21
- 239000000843 powder Substances 0.000 claims abstract description 21
- 239000013078 crystal Substances 0.000 claims abstract description 16
- 238000004108 freeze drying Methods 0.000 claims abstract description 16
- 229920000936 Agarose Polymers 0.000 claims abstract description 15
- 239000011268 mixed slurry Substances 0.000 claims abstract description 14
- 239000011240 wet gel Substances 0.000 claims abstract description 11
- 238000007710 freezing Methods 0.000 claims abstract description 10
- 230000008014 freezing Effects 0.000 claims abstract description 10
- 238000002156 mixing Methods 0.000 claims abstract description 10
- 238000001354 calcination Methods 0.000 claims abstract description 6
- 238000005303 weighing Methods 0.000 claims abstract description 6
- 238000003756 stirring Methods 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 12
- 229910052796 boron Inorganic materials 0.000 claims description 11
- 239000002149 hierarchical pore Substances 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 8
- 239000011812 mixed powder Substances 0.000 claims description 7
- 238000004321 preservation Methods 0.000 claims description 4
- 238000003837 high-temperature calcination Methods 0.000 claims description 3
- 239000011259 mixed solution Substances 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 101100007699 Emericella nidulans (strain FGSC A4 / ATCC 38163 / CBS 112.46 / NRRL 194 / M139) creB gene Proteins 0.000 claims 1
- 101100402271 Haemophilus influenzae (strain ATCC 51907 / DSM 11121 / KW20 / Rd) molB gene Proteins 0.000 claims 1
- 238000000859 sublimation Methods 0.000 abstract description 4
- 230000008022 sublimation Effects 0.000 abstract description 4
- 239000000463 material Substances 0.000 abstract description 3
- 238000009413 insulation Methods 0.000 abstract description 2
- 230000000052 comparative effect Effects 0.000 description 20
- 238000001878 scanning electron micrograph Methods 0.000 description 14
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 3
- 229910010271 silicon carbide Inorganic materials 0.000 description 3
- 239000007858 starting material Substances 0.000 description 3
- 238000005266 casting Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 239000008367 deionised water Substances 0.000 description 2
- 229910021641 deionized water Inorganic materials 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 1
- 239000004327 boric acid Substances 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 238000005187 foaming Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000000643 oven drying Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 238000004781 supercooling Methods 0.000 description 1
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Abstract
本发明属于硼酸铝多孔陶瓷领域，公开了一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，包括下述步骤：称取B4C粉体和Al2O3粉体，并采用球磨机将两种粉体混合均匀，得B4C与Al2O3混合粉体；称取琼脂糖、水、B4C与Al2O3混合粉体，搅拌混合得混合浆料；将混合浆料倒入模具中，并迅速转移至超低温冰箱中进行冷冻，得湿凝胶；将冷冻后的湿凝胶放入冷冻干燥机中冷冻干燥，得到干燥坯体；将干燥坯体放入箱式炉中，经高温煅烧获得具有多级孔结构的硼酸铝多孔陶瓷。本发明获得的硼酸铝多孔陶瓷具有由冰晶升华形成的宏孔和由硼酸铝晶须搭接形成的微孔，这种多级孔结构赋予了材料轻质隔热的特点。
Description
技术领域
本发明属于硼酸铝多孔陶瓷领域，尤其是涉及一种具有多级孔结构的硼酸铝多孔陶瓷的制备方法。
背景技术
硼酸铝的化学式为xAl2O3·yB2O3，其常见的几种晶型有9Al2O3·2B2O3、2Al2O3·B2O3和Al2O3·B2O3，其中9Al2O3·2B2O3晶体具有良好的热稳定性且应用最为广泛。在硼酸铝的所有晶面中{001}面的面间距最小，这意味着硼酸铝晶体沿{001}面生长的速度最快，因此硼酸铝晶体倾向于沿C轴生长形成硼酸铝晶须。
硼酸铝晶须具有高抗拉强度（8GPa）、高弹性模量（400GPa）、高中子吸收率和良好的耐腐蚀性等特性。硼酸铝晶须的弹性媲美Si3N4晶须，硬度仅次于碳化硅晶须，而价格却仅为碳化硅晶须的1/10。因此从商业角度出发，硼酸铝晶须具有极高的性价比，是碳化硅晶须和Si3N4晶须的优良替代品。
由于其高长径比，硼酸铝晶须在原位生长过程中非常容易形成交织的三维网络结构，从而为硼酸铝多孔陶瓷的制备提供了基础。例如，Hernández等人以氧化铝和硼酸为起始材料，通过干压法成功制造了孔隙率为47%的硼酸铝多孔陶瓷。此外，其他科研人员也采用了诸如添加造孔剂法、发泡法等工艺制备了硼酸铝多孔陶瓷。但上述研究所制备出的硼酸铝多孔陶瓷的密度过高，气孔率过低，从而不利于其在高温隔热领域的进一步应用。
发明内容
本发明的目的在于克服现有技术的不足，提供一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，能够克服现有技术中硼酸铝多孔陶瓷孔结构简单、密度过大、气孔率过低、热导率过高的缺点。
本发明是通过如下技术方案予以实现：
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，包括下述步骤：
（1）按照B、Al摩尔比为6~8:9称取B4C粉体和Al2O3粉体，并采用球磨机将两种粉体混合均匀，获得B4C与Al2O3混合粉体；
（2）按照质量比为1~10:80:2的比例称取琼脂糖、水、B4C与Al2O3混合粉体置于容器中，加热至80~95℃进行搅拌混合，直至琼脂糖完全溶解在水中，得混合浆料，随后将混合浆料倒入模具中，并迅速转移至温度为-20~-60℃超低温冰箱中进行冷冻，得湿凝胶；
（3）将冷冻后的湿凝胶放入冷冻干燥机中冷冻干燥45~50h，冷冻干燥温度为-20~-60℃，压强为1~10kPa，进而得到干燥坯体；
（4）将获得的干燥坯体放入箱式炉中，经高温煅烧获得具有多级孔结构的硼酸铝多孔陶瓷。
优选地，所述的琼脂糖、水、B4C与Al2O3混合粉体的质量比为2~6:80:2。
优选地，步骤（2）冷冻温度为-30~-50℃。
优选地，步骤（3）冷冻干燥温度为-30~-50℃。
优选地，步骤（3）冷冻干燥压强为4~8kPa。
优选地，所述高温煅烧的温度为1200~1400℃，升温速率为2~10℃/min，保温时间为1~3h。
本发明的优点和积极效果是：
针对目前硼酸铝多孔陶瓷的密度过高，气孔率过低的问题，本申请提出采用冷冻浇注成型工艺并结合高温固相反应工艺来制备具有高气孔率、低密度、低热导率的硼酸铝多孔陶瓷。其中在冷冻浇注过程中，混合液中的水在冷源的作用下会生长成片状冰晶，从而推动陶瓷颗粒进行重排。在冷冻干燥阶段，冰晶直接升华成蒸汽，进而在样品内部留下宏孔。在这一阶段，冰晶的生长促进了宏孔的形成，而琼脂糖的三维网络结构抑制了宏孔的形成。所以本申请创新性地通过调控冷冻温度（过冷度）和琼脂糖的含量来达到控制孔结构的目的。在煅烧阶段，混合粉体中的B4C可与Al2O3发生反应生成硼酸铝晶须，晶须和晶须之间会形成交织的网络结构，从而形成微孔，进一步提高整体硼酸铝多孔陶瓷的气孔率。其中要注意的是，硼酸铝的化学式为9Al2O3·2B2O3，其B、Al摩尔比为2:9。但在本申请中所用的硼源量为过量，选用的B、Al摩尔比增加到了6~8：9。过量的硼源可以生成液相，从而促进具有高长径比的晶须生成。此外，所用的硼源为B4C，其在氧化过程中会发生体积膨胀，也有利于晶须的生成。综上，本申请制备的硼酸铝多孔陶瓷具有两种不同的孔结构：一种是由冰晶生长、升华所形成的宏孔，另一种是由硼酸铝晶须交错搭接形成的微孔，这种多级孔结构保证了硼酸铝多孔陶瓷具有较低的密度，较高的气孔率和较低的热导率。
附图说明
图1：实施例1制备的硼酸铝多孔陶瓷放大50倍的SEM图；
图2：实施例1制备的硼酸铝多孔陶瓷放大5000倍的SEM图；
图3：实施例2制备的硼酸铝多孔陶瓷放大50倍的SEM图；
图4：实施例2制备的硼酸铝多孔陶瓷放大5000倍的SEM图；
图5：对比例2制备的硼酸铝多孔陶瓷放大100倍的SEM图；
图6：对比例3制备的硼酸铝多孔陶瓷放大100倍的SEM图；
图7：对比例4制备的硼酸铝多孔陶瓷放大5000倍的SEM图。
具体实施方式
为了更好的理解本发明，下面结合附图对本发明进行进一步详述。在不冲突的情况下，案例中的特征可以相互组合。以下实施例中所使用的原料均为市售的分析纯原料。
实施例1
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，包括下述步骤：
（1）按照B、Al摩尔比为6:9称取B4C粉体和Al2O3粉体，并采用球磨机将两种粉体混合均匀，获得B4C与Al2O3混合粉体；
（2）称取0.2g琼脂糖、8 g去离子水、0.2 g B4C与Al2O3混合粉体置于烧杯中，加热至90℃进行搅拌混合，直到琼脂糖完全溶解在水中，得混合浆料；随后将混合浆料倒入模具中，并迅速放入温度为-50℃的超低温冰箱中进行冷冻，得湿凝胶；
（3）将冷冻后的湿凝胶放入冷冻干燥机进行冷冻干燥48h，冷冻干燥的温度为-50℃，压强为5kPa，进而得到干燥坯体；
（4）将获得的干燥坯体放入箱式炉中高温煅烧，煅烧温度为1300℃，升温速率为2℃/min，保温时间为1h，最终获得具有多级孔结构的硼酸铝多孔陶瓷。
实施例1制备的硼酸铝多孔陶瓷扫描电镜图如图1和图2所示。经测试，制备出的硼酸铝多孔陶瓷的密度为0.16g/cm3，气孔率为94.5%，热导率为0.065 W·m-1·K-1。
实施例2
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，包括下述步骤：
（1）按照B、Al摩尔比为7:9称取B4C粉体和Al2O3粉体，并采用球磨机将两种粉体混合均匀，获得B4C与Al2O3混合粉体；
（2）称取0.4g琼脂糖、8 g去离子水和0.2 g的B4C与Al2O3混合粉体置于烧杯中，加热至95℃进行搅拌混合，直到琼脂糖完全溶解在水中，得混合浆料；随后将混合浆料倒入模具中，并迅速放入温度为-30℃的超低温冰箱中进行冷冻，得湿凝胶；
（3）将冷冻后的湿凝胶放入冷冻干燥机进行冷冻干燥48h，冷冻干燥的温度为-30℃，压强为7kPa，进而得到干燥坯体；
（4）将获得的干燥坯体放入箱式炉中，煅烧温度为1200℃，升温速率为4℃/min，保温时间为2h，最终获得具有多级孔结构的硼酸铝多孔陶瓷。
实施例2制备的硼酸铝多孔陶瓷扫描电镜图如图3和图4所示。经测试，制备出的硼酸铝多孔陶瓷的密度为0.22g/cm3，气孔率为93.4%，热导率为0.072W·m-1·K-1。
对比例1
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，制备方法同实施例1，区别仅在于在步骤（2）中不加入琼脂糖。
由于在对比例1中没有加入琼脂糖，样品在冷冻干燥后没有足够的有机粘结剂来提供强度，所以样品干燥后直接发生粉化现象，无法形成硼酸铝多孔陶瓷。
对比例2
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，制备方法同实施例1，区别仅在于，省去步骤（2）中的冷冻步骤，直接将模具置于空气中室温冷却。
对比例2制备的硼酸铝多孔陶瓷扫描电镜图如图5所示。经测试，制备出的硼酸铝多孔陶瓷的密度为0.61g/cm3，气孔率为78.3%，热导率为0.285W·m-1·K-1。
对比例3
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，制备方法同实施例1，区别仅在于，省去步骤（3）的冷冻干燥过程，采用烘箱来对湿凝胶进行干燥。
对比例3制备的硼酸铝多孔陶瓷扫描电镜图如图6所示。经测试，制备出的硼酸铝多孔陶瓷的密度为0.56g/cm3，气孔率为80.5%，热导率为0.202W·m-1·K-1。
对比例4
一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，制备方法同实施例1，区别仅在于，步骤（1）中按照B、Al摩尔比为2:9称取B4C粉体和Al2O3粉体。
对比例4制备的硼酸铝多孔陶瓷扫描电镜图如图7所示。经测试，制备出的硼酸铝多孔陶瓷的密度为0.43g/cm3，气孔率为85.4%，热导率为0.156W·m-1·K-1。
评价与表征
图1为实施例1制备的硼酸铝多孔陶瓷放大50倍的SEM图，图2为实施例1制备的硼酸铝多孔陶瓷放大5000倍的SEM图。经测试，制备出的硼酸铝多孔陶瓷的密度为0.16g/cm3，气孔率为94.5%，热导率为0.065 W·m-1·K-1。图3为实施例2制备的硼酸铝多孔陶瓷放大50倍的SEM图，图4为实施例2制备的硼酸铝多孔陶瓷放大5000倍的SEM图。经测试，制备出的硼酸铝多孔陶瓷的密度为0.22g/cm3，气孔率为93.4%，热导率为0.072W·m-1·K-1。此外，从上述四幅图中都可以看出，整个硼酸铝多孔陶瓷呈现一个典型的多级孔结构，其中大孔主要由冰晶生长推动颗粒形成的，而小孔主要由硼酸铝晶须搭接而成。这种多级孔结构赋予了材料较低的密度、较高的气孔率和较低的热导率。
图5为对比例2制备的硼酸铝多孔陶瓷放大100倍的SEM图。由于对比例2中省略了冷冻过程，在成型阶段，水溶液无法形成可以推动纤维定向排布的冰晶。所以，与图1和图3相比较可知，样品内部没有由于冰晶升华所形成的大孔。这导致对比例2制备出的硼酸铝多孔陶瓷的气孔率较低，密度和热导率较大。
图6为对比例3制备的硼酸铝多孔陶瓷放大100倍的SEM图。由于对比例3将冷冻干燥替换成了普通烘箱干燥，坯体内形成的冰晶会先变成液体，而后再变成水蒸气排除体外。在这一过程中，坯体会由于水分的挥发而发生严重收缩，所以其内部也无法形成冰晶升华后留下的大孔。因此，对比例2制备出的硼酸铝多孔陶瓷的气孔率也较低，密度和热导率也较大。
图7为对比例4制备的硼酸铝多孔陶瓷放大5000倍的SEM图。对比例4的所述B、Al摩尔比为2:9。由于加入的B4C过少，在煅烧过程中无法形成足够的液相来促进硼酸铝晶须的生成，所以对比例4制备出的硼酸铝多孔陶瓷内部主要形成了片状硼酸铝而非硼酸铝晶须，导致整体材料的气孔率较低，密度和热导率较大。
以上所述的仅是本发明的优选实施方式，应当指出，对于本领域的普通技术人员来说，在不脱离发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。
Claims (5)
1.一种具有多级孔结构的轻质隔热硼酸铝多孔陶瓷的制备方法，其特征在于，包括下述步骤：
（1）按照B、Al摩尔比为6~8:9称取B4C粉体和Al2O3粉体，并采用球磨机将两种粉体混合均匀，获得B4C与Al2O3混合粉体；
（2）按照质量比为1~10:80:2的比例称取琼脂糖、水、B4C与Al2O3混合粉体置于容器中，加热至80~95℃进行搅拌混合，直至琼脂糖完全溶解在水中，得混合浆料，随后将混合浆料倒入模具中，并迅速转移至温度为-20~-60℃超低温冰箱中进行冷冻，得湿凝胶，混合液中的水在冷源的作用下生长成片状冰晶；
（3）将冷冻后的湿凝胶放入冷冻干燥机中冷冻干燥45~50h，冷冻干燥温度为-20~-60℃，压强为1~10kPa，进而得到干燥坯体，在冷冻干燥阶段，冰晶直接升华成蒸汽，进而在样品内部留下宏孔；
（4）将获得的干燥坯体放入箱式炉中，经高温煅烧，B4C粉体和Al2O3粉体发生反应生成硼酸铝晶须，晶须和晶须之间形成交织的网络结构，从而形成微孔，获得具有多级孔结构的硼酸铝多孔陶瓷，所述高温煅烧的温度为1200~1400℃，升温速率为2~10℃/min，保温时间为1~3h。
2.根据权利要求1所述的制备方法，其特征在于，所述的琼脂糖、水、B4C与Al2O3混合粉体的质量比为2~6:80:2。
3.根据权利要求1所述的制备方法，其特征在于，步骤（2）冷冻温度为-30~-50℃。
4.根据权利要求1所述的制备方法，其特征在于，步骤（3）冷冻干燥温度为-30~-50℃。
5.根据权利要求1所述的制备方法，其特征在于，步骤（3）冷冻干燥压强为4~8kPa。
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