CN112898040B - 一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷的方法 - Google Patents
一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷的方法 Download PDFInfo
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Abstract
一种以高长径比晶须制备无晶间玻璃相β‑Si3N4多孔陶瓷材料的方法,以α‑Si3N4为原料,Y2O3为助剂,通过常压烧结的方法制备高长径比的β‑Si3N4晶须,以制得的β‑Si3N4模压成型后引入碳源,通过碳热还原方法于β‑Si3N4晶须搭接处生成α‑Si3N4,制备Si3N4搭接β‑Si3N4晶须多孔陶瓷材料;本发明解决了现有多孔氮化硅陶瓷室温和高温力学性能之间的矛盾,能够制得室温强度与同气孔率液相烧结氮化硅近似,但直至1500℃强度不下降的多孔氮化硅陶瓷,极大地改善了多孔氮化硅的高温力学性能,大大拓展了多孔氮化硅陶瓷材料的应用范围。
Description
技术领域
本发明属于氮化硅陶瓷烧结技术领域,具体涉及一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷的方法,适用于制备各种高温过滤分离器、催化剂载体、吸声材料及透波材料等。
背景技术
天线罩材料既需要具备较高的气孔率以保证透波性能,又需要具备较高的高温强度以承受飞行器飞行过程中产生的气动力和气动热。随着导弹飞行速度的提高,其工作环境日趋恶劣,当导弹以高超音速在大气中飞行时,气动加热非常严重,其在高超音速飞行过程中会产生大量的热量。此外,为了保护飞行器通讯、遥测、制导、引爆等系统正常工作,天线罩既要适应导弹气动力、气动热和飞行过程中的恶劣环境,又要满足高的制导要求,因此,要求天线罩必须具备耐热、防热、承载、透波等功能。目前我国所使用的透波材料主要为SiO2f/SiO2复合材料,其力学性能较差,高温力学性能更难以有大幅提高。氮化硅材料具有力学性能优异、抗热震性好、耐高温、耐腐蚀等诸多优点,是极具有前景的新一代天线罩材料。
Si3N4存在α、β两种晶型,其中α-Si3N4为等轴状而β-Si3N4为六棱柱状。Si3N4陶瓷的高强度得益于β-Si3N4的棒状晶结构,具有高长径比的β-Si3N4晶粒,可以形成交织互锁的特殊结构,从而提高Si3N4陶瓷的强度和韧性。因此高长径比晶粒互相搭接形成自锁结构的β-Si3N4陶瓷的室温强度远高于α-Si3N4陶瓷。但在绝大多数情况下β-Si3N4的获得只能借助于液相烧结得到,而液相冷却后会形成玻璃相分布于晶间,所以,当材料在高温环境中使用时,晶间相会发生软化而使氮化硅的高温力学性能迅速衰减,因此氮化硅陶瓷的室温力学性能和高温力学性能之间存在矛盾。
发明内容
为了克服上述现有技术的缺陷,本发明的目的在于提供一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷的方法,该方法以α-Si3N4为原料,Y2O3为助剂,通过常压烧结的方法制备高长径比的β-Si3N4晶须,以制得的β-Si3N4模压成型后引入碳源,通过碳热还原方法于β-Si3N4晶须搭接处生成α-Si3N4,制备Si3N4搭接β-Si3N4晶须多孔陶瓷材料,克服晶间玻璃相对氮化硅高温性能的不利影响;本发明一方面高长径比的β-Si3N4晶须在成型压力的法平面内存在着定向排列性,提高了Si3N4陶瓷的抗弯强度和断裂韧性;另一方面β-Si3N4搭接处生成的α-Si3N4将其紧密结合形成适当的界面结合强度,增加氮化硅陶瓷材料强度的同时,解决了液相烧结氮化硅的玻璃相在高温下易软化的问题。
为了达到上述目的,本发明所采用的技术方案是:
一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷材料的方法,具体包括如下步骤:
步骤1:按照质量百分比称取90-95wt%α-Si3N4以及5-10wt%稀土氧化物混合粉末,混合均匀后,松装放入石墨坩埚中;
步骤2:将装有混合粉末的坩埚放入多功能烧结炉中,充入氮气作保护气氛,控制升温速率<12℃/min,高温保温2-3h后随炉冷却;
步骤3:将步骤2中所得反应物放入装有氢氟酸的聚四氟乙烯容器中,60℃-90℃加热并间歇性超声处理,直至块体变为粉末,蒸馏水多次漂洗,至pH=7后烘干,得到β-Si3N4晶须;
步骤4:向β-Si3N4晶须中添加粘结剂,根据不同的制备需求通过模压、等静压、挤出成型的方式制成生坯;从而能够在后续真空浸渍过程中保持形态完整。
步骤5:所得试样真空浸渍在10wt%-20wt%的酚醛树脂酒精溶液中并在烘箱内150℃-180℃保温6h-8h后固化;
步骤6:通入流动的保护气,在高温下保温使固化后的树脂裂解为碳;
步骤7:坩埚内放置石墨架,石墨架上放置碳化后的试样,石墨架下放置SiO粉体,以N2做保护气,使C在高温下和SiO、N2反应生成α-Si3N4,分布于β-Si3N4搭接处,通过其结合作用制得Si3N4搭接的β-Si3N4多孔陶瓷。
所述步骤1中,选用氮化硅粉的型号为UBE-E10,平均粒径为 0.2-0.5μm,采用不同粗细颗粒级配的α-Si3N4为原料或烧结工艺,使得β-Si3N4晶须的长径比在10-19之内可控;选用的稀土氧化物为Y2O3。
所述步骤2中,N2压强为5atm,高温下指保温温度在1600-1750℃间变动,室温至1100℃的升温速率为10℃/min,1100℃以上的升温速率为5℃/min。
所述步骤3中,氢氟酸的浓度可在1-2mol/L之间变动。
所述的步骤4中粘结剂包括酚醛树脂、聚乙烯醇、聚乙烯醇缩醛或聚碳酸醋,只需保证生坯在浸渍过程中能保持形态即可。
所述步骤4中生坯成型压力在20-250MPa范围内变动,从而有效调节生坯致密度,从而调节烧结体气孔率。
所述步骤5中真空浸渍过程中,体系的真空度为-0.09MPa,从而保证酚醛树脂能够进入试样内部,有利于提高材料的均匀性。
所述的步骤5中试样成型后的浸渍过程中,酚醛树脂能够替换为其余含碳材料,只需保证该含碳材料可裂解为C,其溶液的流动性满足浸渍要求即可。
步骤5中酚醛树脂可采用热固型和热塑性两种,若采用热固型酚醛树脂,则只需加热固化,固化温度根据树脂牌号不同而有所差异;若采用热塑型酚醛树脂,则需加入固化剂后加热固化,具体固化方式由树脂牌号决定,本发明采用热固型树脂。
所述的步骤6碳化过程中保护气为不与体系反应的任意惰性气体。
所述步骤7中,N2压强为5atm,使C在高温下和SiO、N2反应生成α-Si3N4时,室温至1100℃的升温速率为10℃/min,1100℃以上的升温速率为5℃/min,高温下保温温度可在1600-1700℃间变动。
与现有技术相比,本发明的优点在于:
1)本方法使用制得的高长径比β-Si3N4晶须作为原料制备氮化硅多孔陶瓷,由于材料内部高长径比的β-Si3N4晶须形成交织互锁的特殊结构,使其抗弯强度和断裂韧性得到明显提高;
2)通过本方法制得的多孔氮化硅材料仅有α-Si3N4和β-Si3N4两相,无晶间玻璃相,其抗弯强度在1600℃下无明显下降,克服了晶间玻璃相对液相烧结多孔氮化硅陶瓷高温力学性能的不利影响;
3)本方法制备多孔氮化硅材料无需添加烧结助剂,因此烧结后坯体不发生收缩,可实现净尺寸烧结,利于材料的后续加工;
4)由于采用模压成型方法,使得β-Si3N4晶须二维方向定向排布,使其同时具有高的强度和断裂韧性,在保持51.2%气孔率的同时其强度可达98.3MPa,断裂韧性可达3.1;
5)通过调整成型压力、浸渍液浓度及浸渍次数,可以控制材料的气孔率,使气孔率可在74-50%之间变动,便于满足不同场景的应用要求。
附图说明:
图1为本发明制备的高长径比β-Si3N4晶须的微观形貌图。
图2为实施例1与实施例4碳热还原烧结后试样断口的微观组织图,图2中的(a)是实施例1的20MPa成型压力下试样断口组织照片,图2 中的(b)是实施例4的80MPa成型压力下试样断口组织照片。
图3为实施例5碳热还原烧结后试样的XRD图。
图4为实施例6中β-Si3N3多孔氮化硅陶瓷抗弯强度随温度的变化图。
具体实施方式:
以下结合实施例对本发明做进一步说明:
本发明提供的一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷的方法,其实施例组成如表1所示,在表1所示的实施例1~ 10中,向氮化硅中添加一定比例的Y2O3作为烧结助剂,制备具有更高长径比的β-Si3N4晶须,通过模压成型、浸渍酚醛树脂、固化、碳化和碳热还原,于β-Si3N4晶须搭接处生成α-Si3N4,通过其结合作用制得β-Si3N4多孔陶瓷。
本发明的制备方法,结合下面步骤以及表1中的具体参数,实施如下:
步骤1:按照质量百分比称取取90-95wt%α-Si3N4以及 5-10wt%Y2O3混合粉末,混合均匀后松装放入石墨坩埚中;
步骤2:将装有混合粉末的坩埚放入多功能烧结炉中,充入氮气做保护气氛,控制升温速率<10℃/min在1650-1750℃保温2-3h后随炉冷却;
步骤3:将步骤2中所得反应物放入装有1mol/L氢氟酸的聚四氟乙烯容器中,60℃-90℃加热并间歇性超声处理,直至块体变为粉末,蒸馏水多次漂洗,至pH=7后烘干,得到β-Si3N4晶须;
步骤4:β-Si3N4晶须要先采用质量分数为10wt.%的低浓度酚醛树脂酒精溶液进行抽滤,使其表面均匀附着一层酚醛树脂,便于后续模压成型;抽滤后的β-Si3N4晶须在20-80MPa的压力下模压成型,使其在后续的酚醛树脂酒精溶液真空浸渍过程中保持形态完整;
步骤5:将样品放入三口烧瓶内,接真空泵和恒压漏斗,漏斗内装入酚醛树脂的酒精溶液。启动真空泵,使体系内真空度达到-0.09 MPa后持续20min,旋开恒压漏斗旋钮,使漏斗内酚醛树脂溶液流入三口烧瓶,保持体系负压20min。样品先在常温下干燥,干燥后试样置于烘箱中150℃-180℃保温6h-8h固化;
步骤6:通过管式炉碳化试样,以流动Ar气做保护气体,在400℃保温2h后,在800℃保温2h,使固化后的酚醛树脂裂解为碳;
步骤7:将试样及SiO粉末放入石墨坩埚中,在N2气氛下 1600-1750℃保温3-4h,使试样中的碳、SiO和N2发生碳热还原反应生成α-Si3N4,通过其结合作用制得Si3N4搭接的β-Si3N4多孔陶瓷,如图1所示,为实施例1产物,具有高长径比β-Si3N4晶须。
由上述方法获得的多孔氮化硅陶瓷,INSTRON-1195型万能试验机测量样品抗弯强度,每个样品测量3次的平均值作为最终结果,样品尺寸3mm×4mm×30mm(跨距16mm),加载速率0.5mm/min;用阿基米德排水法测定开气孔率;使用Gemini SEM 500型扫描电子显微镜(加速电压15.0KV,二次电子成像模式)观察制得的β-Si3N4晶须与样品断口的微观形貌;Bruker D8 ADVANCE型X射线衍射仪分析试样的相组成,测试条件:Cu Kα辐射源,扫描速率12(°)/min,管电压40kV,管电流40mA。所得到的数据见表2。
由表2可以看出,实施例1采用95.0wt%的氮化硅粉作为原料, 5.0%wt%的Y2O3为烧结助剂,经过1700℃保温2.5h常压烧结后制得平均长径比为14.5的β-Si3N4粉体,20MPa模压成型后,单次浸渍后碳化,碳化后的试样在1650℃下保温3h进行碳热还原烧结,所得多孔Si3N4材料的气孔率为66.1%,常温抗弯强度可达17.5MPa,在1500℃高温下抗弯强度可达16.9MPa。
由表2可以看出,实施例4采用95.0wt%的氮化硅粉作为原料, 5.0%wt%的Y2O3为烧结助剂,经过1750℃保温2.5h常压烧结后制得平均长径比为17.2的β-Si3N4粉体,80MPa模压成型后,单次浸渍后碳化,碳化后的试样在1650℃下保温3h进行碳热还原烧结,所得多孔Si3N4材料的气孔率为59.5%,常温抗弯强度可达57.7MPa,在1500℃高温下抗弯强度可达57.1MPa。
由表2可以看出,实施例6采用95.0wt%的氮化硅粉作为原料, 5.0%wt%的Y2O3为烧结助剂,经过1750℃保温2h常压烧结后制得平均长径比为16.5的β-Si3N4粉体,40MPa模压成型后,三次浸渍后碳化,碳化后的试样在1650℃下保温3.5h进行碳热还原烧结,所得多孔Si3N4材料的气孔率为51.2%,常温抗弯强度可达98.3MPa,在1500℃高温下抗弯强度可达97.9MPa。
由表2可以看出,实施例10采用95.0wt%的氮化硅粉作为原料, 5.0%wt%的Y2O3为烧结助剂,经过1700℃保温2.5h常压烧结后制得平均长径比为13.6的β-Si3N4粉体,40MPa模压成型后,两次浸渍后碳化,碳化后的试样在1650℃下保温3.5h进行碳热还原烧结,所得多孔Si3N4材料的气孔率为55.2%,常温抗弯强度可达81.2MPa,在 1500℃高温下抗弯强度可达79.1MPa。在与比较例1即长径比为5.3 的市售短β-Si3N4晶须制备的多孔氮化硅材料对比实验中,其抗弯强度提高了35.8%,其力学性能得到极大提高。
由表2可以看出,比较例2采用95.0wt%的氮化硅粉作为原料, 5.0%wt%的Y2O3为烧结助剂,混料过筛后直接40MPa模压成型,在 1750℃下保温2h进行常压烧结,所得多孔氮化硅材料的气孔率为 56.4%,常温抗弯强度达71.4MPa,但在1500℃高温下抗弯强度仅为32.6MPa,较常温抗弯强度下降了54.3%。本发明的一种以高长径比晶须制备无晶间玻璃相β-Si3N4多孔陶瓷的方法与比较例2相比,能够制得室温强度与同气孔率液相烧结氮化硅近似,但直至1500℃高温强度不下降的多孔氮化硅陶瓷。
实施例1与实施例4的断口组织如图2所示,可以看到高长径比的微米级氮化硅棒状晶之间相互搭接形成了多孔陶瓷。与20MPa压力成型的实施例1相比,80MPa下成型的实施例4的抗弯强度提高了 3-4倍,β-Si3N4棒状晶在受力方向的法平面内晶粒定向排列程度有所增强。
图3为实施例5获得的多孔氮化硅材料XRD图。如图所示,碳热还原烧结后,所获得的相为α-Si3N4与β-Si3N4。
图4为实施例6获得的多孔氮化硅材料抗弯强度随温度的变化曲线。如图所示,随着温度的升高,其抗弯强度基本不变。在1500℃的高温依然能保持82.9MPa的高强度。
表1:本发明10个实施例制备高长径比β-Si3N4晶须工艺参数
表2:本发明氮化硅多孔陶瓷的烧结工艺参数与性能
Claims (6)
1.一种以高长径比晶须制备无晶玻璃相β-Si3N4多孔陶瓷材料的方法,其特征在于,具体包括如下步骤:
步骤1:按照质量百分比称取90-95wt%α-Si3N4以及5-10wt%稀土氧化物混合粉末,混合均匀后,松装放入石墨坩埚中;
步骤2:将装有混合粉末的坩埚放入多功能烧结炉中,充入氮气作保护气氛,控制升温速率<12℃/min,高温保温2-3h后随炉冷却;
步骤3:将步骤2中所得反应物放入装有氢氟酸的聚四氟乙烯容器中,60℃-90℃加热并间歇性超声处理,直至块体变为粉末,蒸馏水多次漂洗,至pH=7后烘干,得到β-Si3N4晶须;
步骤4:β-Si3N4晶须要先采用粘结剂进行抽滤,使其表面均匀附着一层酚醛树脂,便于后续模压成型;抽滤后的β-Si3N4晶须模压成型,使其在后续的酚醛树脂酒精溶液真空浸渍过程中保持形态完整;
步骤5:所得试样真空浸渍在10wt%-20wt%的酚醛树脂酒精溶液中并在烘箱内150℃-180℃保温6h-8h后固化;
步骤6:通入流动的保护气,在高温下保温使固化后的树脂裂解为碳;
步骤7:坩埚内放置石墨架,石墨架上放置碳化后的试样,石墨架下放置SiO粉体,以N2做保护气,使C在高温下和SiO、N2反应生成α-Si3N4,分布于β-Si3N4搭接处,通过其结合作用制得Si3N4搭接的β-Si3N4多孔陶瓷;
所述步骤2中,N2压强为5atm,室温至1100℃的升温速率为10℃/min,1100℃以上的升温速率为5℃/min,高温下指保温温度在1600-1750℃间变动;
所述步骤3中,氢氟酸的浓度在1-2mol/L之间变动;
所述的步骤4中粘结剂包括质量分数为10%的酚醛树脂、聚乙烯醇、聚乙烯醇缩醛或聚碳酸醋的酒精溶液中的一种或多种,只需保证生坯在浸渍过程中能保持形态即可;
所述步骤4中生坯成型压力在20-250MPa范围内变动;
所述步骤7中,N2压强为5atm,使C在高温下和SiO、N2反应生成α-Si3N4时,室温至1100℃的升温速率为10℃/min,1100℃以上的升温速率为5℃/min,高温下保温温度可在1600-1700℃间变动。
2.根据权利要求1所述的一种以高长径比晶须制备无晶玻璃相β-Si3N4多孔陶瓷材料的方法,其特征在于,所述步骤1中,选用氮化硅粉的型号为UBE-E10,平均粒径为0.2-0.5μm;选用的稀土氧化物为Y2O3。
3.根据权利要求1所述的一种以高长径比晶须制备无晶玻璃相β-Si3N4多孔陶瓷材料的方法,其特征在于,所述步骤5中真空浸渍过程中,体系的真空度为-0.09MPa。
4.根据权利要求1所述的一种以高长径比晶须制备无晶玻璃相β-Si3N4多孔陶瓷材料的方法,其特征在于,所述的步骤5中试样成型后的浸渍过程中酚醛树脂能够替换为其余含碳材料,只需保证该含碳材料可裂解为C,其溶液的流动性满足浸渍要求即可。
5.根据权利要求1所述的一种以高长径比晶须制备无晶玻璃相β-Si3N4多孔陶瓷材料的方法,其特征在于,步骤5中酚醛树脂采用热固型或热塑型,若采用热固型酚醛树脂,则只需加热固化;若采用热塑型酚醛树脂,则需加入固化剂后加热固化。
6.根据权利要求1所述的一种以高长径比晶须制备无晶玻璃相β-Si3N4多孔陶瓷材料的方法,其特征在于,所述的步骤6碳化过程中保护气为不与体系反应的任意惰性气体。
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