CN109095932A - 一种晶须增韧氮化硅泡沫材料及其无压烧结制备方法 - Google Patents
一种晶须增韧氮化硅泡沫材料及其无压烧结制备方法 Download PDFInfo
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Abstract
本发明属于多孔陶瓷泡沫材料领域,特别提供一种晶须增韧氮化硅(Si3N4)泡沫材料及其制备方法。该泡沫材料以多边型封闭环为基本单元,各基本单元相互连接形成三维连通网络;构成三维连通网络的陶瓷筋由氮化硅组成,按体积百分数计,氮化硅固相在25~70%范围内,孔隙率30~75%,陶瓷筋的相对致密度≥90%,材料中平均晶粒尺寸在0.7~5μm。采用有机泡沫浸渍工艺泡沫陶瓷预制体,结合热压致密化提高预制体陶瓷筋致密度,同时添加碳化硅晶须增韧,进行烧结得氮化硅泡沫材料。该方法所得到的材料强度高,抗热冲击能力强,工艺简单、操作方便、无需复杂设备,制造成本低。
Description
技术领域
本发明属于多孔陶瓷泡沫材料领域,特别提供一种晶须增韧氮化硅(Si3N4)泡沫材料及其制备方法。
背景技术
多孔陶瓷泡沫材料由基体材料骨架、可变孔径、较高孔隙率组成,该类材料具有三维网络骨架结构且气孔是相互连通的,是一种重要的多功能材料。目前该类泡沫材料主要有泡沫金属和泡沫陶瓷两大类,其中:泡沫陶瓷除了具有多孔陶瓷所具有的一般特性之外,它还具有高渗透率、高比表面和复杂的孔道结构等特性,这些特性使它在冶金、化工、机械、环保、能源等行业可作为高温过滤、净化、吸收、分离、混合、隔热及换热器件,应用十分广泛。
泡沫陶瓷主要有以下四种方法制备:粉末烧结法、固相反应烧结法、含硅树脂热解法和气相沉积法。粉末烧结法又分为两种不同的过程,其一是将含有一定量烧结助剂的陶瓷粉与连接剂(如:硅酸乙脂水解液、硅溶胶等)调成合适浓度的料浆后,浸挂在聚氨脂泡沫上,固化干燥后,在一定温度范围下脱除连接剂和聚氨脂泡沫。而后,将温度升高到烧结温度下进行烧结便得到泡沫状的陶瓷材料;另一种方法是将含烧结助剂的陶瓷粉与株状发泡剂均匀混合后,用模压或浇注方法成型,通过熔化或气化脱出发泡剂,然后进行高温烧结以获得泡沫陶瓷。固相反应烧结法是将株状发泡剂与陶瓷粉末及烧结助剂均匀混合成型,通过熔化或气化脱出发泡剂,经过高温反应烧结后即获得泡沫陶瓷。含硅树脂热解法主要用来制备泡沫碳化硅材料,是将有机硅前驱体制成高分子凝胶,脱出凝胶中的有机溶剂后得到泡沫状的含硅树脂,经充分予氧化后进行热解即得到泡沫状碳化硅陶瓷。气相沉积法是利用化学气相沉积的方法,将陶瓷沉积到网状碳泡沫上而获得泡沫陶瓷,目前主要用来制备碳化硅泡沫。
上述四种方法均有各自的不足,前三种方法由于没有热压过程,初始密度不高,制备的泡沫陶瓷不致密,因而强度低,并且固相反应烧结法和含硅树脂热解法孔隙体积和尺寸难以控制;而气相沉积法面临制作成本高,速度慢等问题。这些问题使泡沫状陶瓷的应用,特别是新的应用,受到不同程度的制约。
传统泡沫陶瓷材质多为碳化硅、氧化铝、莫来石、高岭土等,由于这些陶瓷材料导热性能不高、高温稳定性差,抗热冲击能力低、尤其是陶瓷内在的固有脆性成为其作为结构元件的最大障碍,而且加工和安装都存在难以克服的技术性难题,目前采用ZrO2粒子或者纤维等第二相对陶瓷材料的增韧研究很多,也有采用制备陶瓷基复合材料来加强结构陶瓷的方法,但是这些方法应用在多孔陶瓷的制备上十分困难,且效果并不明显,氮化硅陶瓷具有高热导率、高抗热冲击能力、高耐腐蚀性、使用温度高(非氧化气氛)、密度低及和石墨材料相近的抗热冲击能力,具有很多的应用方向,将其制备成泡沫材料,同时结合晶须增韧技术,提高其强度和抗热冲击能力,可很好的拓展其功能,使其应用方向更为广泛。
发明内容
本发明的目的在于提供一种晶须增韧氮化硅泡沫材料及其无压烧结制备方法,该氮化硅泡沫材料具有抗热冲击、高强、高韧、高导热率、高孔率、高比表面和高通孔率的特点,且孔结构(孔径和气孔率)可以调控;该制备方法工艺简单、操作方便、无需特别复杂设备,制造成本低。
本发明的技术方案是:
一种晶须增韧氮化硅泡沫材料,该泡沫材料以多边型封闭环为基本单元,各基本单元相互连接形成三维连通网络;构成三维连通网络的陶瓷筋由氮化硅组成,按体积百分数计,氮化硅固相在25~70%范围内,孔隙率30~75%,陶瓷筋的相对致密度≮90%,材料中平均晶粒尺寸在0.7~5μm。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,以固体颗粒粉末和有机高分子粘结剂为原料,以聚胺脂泡沫塑料为模板;其中,固体颗粒粉末为氮化硅粉、碳化硅晶须及烧结助剂,具体制备过程如下:
(1)料浆配制
将固体颗粒粉末、有机高分子粘结剂和溶剂按比例混合,按质量百分比计,固体颗粒粉末40wt%~55wt%,有机高分子粘结剂10wt%~5wt%,溶剂50wt%~40wt%,经机械搅拌后球磨,过滤,得料浆;
(2)浸挂
将聚胺脂泡沫塑料剪裁成所需形状和尺寸,均匀地浸入料浆中、拿出后挤去多余料浆、采用气吹或气吹结合离心的方式除去多余料浆,加热烘干,上述浸料、挤料、固化过程重复两次以上,达到所需要的固相体积百分数25~70%,得到泡沫材料骨架预制体;
(3)热压致密化
将上述得到的泡沫材料预制体表面浸渍浓度为60~90wt%的聚氨酯-丙酮溶液2~4次,每次120~180℃固化0.5~1小时,将在预制体陶瓷筋表面形成一层不透气聚氨酯膜层,而后将表面不透气泡沫预制体放入高压容器内,充入氮气或氩气,高温、高压固化,压力为20~30MPa、温度在100~300℃,升温速率为1~5℃/分钟,保温20分钟~90分钟,得到更加致密化的泡沫陶瓷预制体;
(4)脱脂
将致密的泡沫陶瓷预制体在氩气、氮气或其它惰性气体的保护下或者在真空条件下脱脂,脱除泡沫骨架预制体中的有机物质;其中升温速率为1~10℃/分钟,升温至600~900℃,保温0.5~2小时;
(5)烧结
将脱脂后致密的泡沫陶瓷经机加工成为所需形状和尺寸,然后进行烧结,烧结在高纯氮气保护气氛条件下进行,升温速率为1~10℃/分钟,温度为:1650~1800℃,保温0.5~3小时,得氮化硅泡沫材料。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,有机高分子粘结剂选自聚乙烯醇或聚氨酯。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,氮化硅的平均粒度为0.5~3μm,纯度为99.5wt%以上。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,烧结助剂为硅粉、氧化铝、氧化钇、氧化镁、氧化镧或氧化铈中的一种或者两种以上组成,平均粒度为0.5~1μm,纯度为99.8wt%以上。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,碳化硅晶须的平均直径为0.2~0.5μm,长径比≮20,纯度为90wt%以上。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,采用氮化硅粉、碳化硅晶须和烧结助剂混合粉末时,按质量百分比计,氮化硅粉70~90%,碳化硅晶须10%~5%,烧结助剂20~5%。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,料浆溶液中,固相为总质量的50~60%。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,溶剂为水、乙醇或丙酮。
所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,料浆浸渍过程中的固化采用普通烘箱或收缩机,泡沫骨架预制体热压致密化采用的高压容器为高压反应釜或热等静压机,脱脂用炉为碳管炉或真空感应加热炉,烧结用炉为真空感应烧结炉、真空碳管炉或真空电阻炉。
本发明是在有机泡沫体浸渍工艺制备泡沫陶瓷的工艺基础上发展了一种制备高强、高韧的氮化硅泡沫材料的方法,具有如下优点及有益效果:
1、氮化硅泡沫材料具有高孔率、高比表面、高通孔率、孔径和空隙率易控等特点。
聚氨脂泡沫塑料是获得最终氮化硅泡沫材料的原始模板,因而通过选择不同的模板就可以控制三维网络结构中孔径大小;对于同一模板,可以通过选择浸挂过程中浸挂次数和料浆浓度,实现对泡沫预制体中陶瓷体积百分数和骨架预制体筋的粗细的控制,并消除封闭孔,见图1。
2、高强度、高韧性、高致密度,力学性能优良
本发明采用类似于等静压工艺制备泡沫有机复合骨架预制体的方法,能够显著提高其初始密度和组织均匀性,消除浸渍挂浆过程容易出现的分层现象;采用合理的烧结助剂不仅可以使氮化硅泡沫材料的网络筋具有较高的致密度和微米级均匀细密的显微组织,并促进氮化硅粉末颗粒的结合,从而使网络筋中陶瓷相间具有很高的结合强度。同时添加的碳化硅晶须可以起到很好的增韧效果,以上因素使所得到的氮化硅泡沫材料同时具备高的强度和高的韧性,见图2。
3、很好的成型性和加工性
一则,作为泡沫材料的原始模板,聚氨脂泡沫塑料极易加工成任意形状;二则,预制体经脱脂获得的含陶瓷原料的骨架预制体具有良好的机械加工性能,十分容易加工成各种形状和尺寸要求的件体。上述因素使氮化硅泡沫材料具备很好的成型性和加工性能,从而大大降低其制造加工成本。
综上所述,本发明提供了一种新的、廉价的氮化硅泡沫材料及其无压烧结制备方法,碳化硅晶须的加入显著具有增韧效果,热压工艺可显著提高材料致密度,提高了氮化硅材料性能。在该方法中,有机泡沫体浸渍、热压致密化、脱脂与烧结被有机的结合在一起,使制备出的氮化硅泡沫材料具有高孔率、高比表面、和高通孔率,且孔结构可以调控,孔径、孔隙率易于控制的特点。三维网络筋致密度高(可达近90%以上),三维网络筋表面状态可随意设计,材料导热好,泡沫体高强度,高韧性、抗热冲击能力强等特点。
附图说明
图1为氮化硅泡沫材料的实物照片。
图2为氮化硅泡沫筋的断口形貌。
具体实施方式
在具体实施过程中,本发明提供了一种晶须增韧氮化硅泡沫材料,其中所述氮化硅泡沫材料以多边型封闭环为基本单元,各基本单元相互连接形成三维连通网络,构成多边形封闭环单元的陶瓷筋由晶须增韧氮化硅组成,相对致密度≥90%。
本发明还提供了上述氮化硅泡沫材料的无压烧结制备方法,将固体颗粒粉末(氮化硅粉、碳化硅晶须、烧结助剂二者混合粉末)与低产碳率的有机高分子粘结剂混合制成料浆。选择合适孔径的聚氨脂泡沫塑料,并剪裁成所需要的形状和尺寸,而后将其浸入料浆中,取出后,用挤压、风吹、离心等方式除去多余的料浆,半固化,重复两次以上,至达到所需要的体积百分数,得到泡沫有机复合骨架预制体。在高压容器内高温、高压固化,以提高泡沫有机复合骨架预制体的初始密度。将致密化后的泡沫体在真空或惰性气体保护炉中进行脱脂,得到与原始泡沫聚氨脂形状一样的由泡沫预制体。在此基础上,进行烧结。利用烧结助剂促进氮化硅烧,使得材料中氮化硅粉末晶界连接起来,同时结合碳化硅晶须增韧手段,从而得到高强、高韧的氮化硅泡沫材料。
下面,通过实施例详述本发明。
实施例1
本实施例中,将质量比为85:8:3:2:2的平均粒度3μm氮化硅粉、碳化硅晶须、0.5μm氧化钇、0.5μm氧化铝、0.5μm氧化镁混合成固体颗粒粉末,再加入总质量8%的聚氨酯共混于无水乙醇中,球磨制成料浆,所述料浆溶液中固体颗粒粉末为总质量的55%;将孔径1.5mm的聚胺脂泡沫切割成要求尺寸后均匀地浸入所述料浆中,浸泡1分钟,拿出后挤去多余料浆,并离心处理,使得泡沫孔保持通透,风干后150℃固化15分钟,上述过程反复两次以上,直到达到30%的预定体积百分数(成品中陶瓷筋的体积百分数)。然后浸渍浓度为75wt%的聚氨酯-丙酮溶液三次,每次150℃固化0.5小时,将在预制体陶瓷筋表面形成一层不透气聚氨酯膜层,放入高压容器内,充入氮气使气压达到20MPa,升温速率为2℃/分钟,升温至200℃,保温0.5小时。在氩气保护下脱脂,其中升温速率为2℃/分钟,升温至800℃,保温0.5小时。脱脂后,进行真空炉烧结,充入氮气气氛保护,温度1850℃,升温速率为10℃/分钟,保温0.5小时,得高性能氮化硅泡沫材料,氮化硅陶瓷筋的相对致密度为91%,平均晶粒粒度为3~8μm。
实施例2
本实施例中,将质量比为90:5:2:1:1.5:0.5的平均粒度1μm氮化硅粉、碳化硅晶须、1μm氧化钇、1μm氧化铝、1μm氧化镁、0.5μm氧化镧混合成固体颗粒粉末,再加入总质量10%的聚氨酯共混于丙酮中,球磨制成料浆,所述料浆溶液中固体颗粒粉末为总质量的50%;将孔径2mm的聚胺脂泡沫切割成要求尺寸后均匀地浸入所述料浆中,浸泡1分钟,拿出后挤去多余料浆,并离心处理,使得泡沫孔保持通透,风干后180℃固化25分钟,上述过程反复两次以上,直到达到45%的预定体积百分数(成品中陶瓷筋的体积百分数)。然后浸渍浓度为80wt%的聚氨酯-丙酮溶液三次,每次150℃固化0.5小时,将在预制体陶瓷筋表面形成一层不透气聚氨酯膜层,放入高压容器内,充入氮气使气压达到25MPa,升温速率为5℃/分钟,升温至300℃,保温1.5小时。在氩气保护下脱脂,其中升温速率为5℃/分钟,升温至700℃,保温0.5小时。脱脂后,进入真空炉烧结,充入氮气气氛保护,温度1650℃,升温速率为5℃/分钟,保温1小时,得高性能氮化硅泡沫材料,氮化硅陶瓷筋的相对致密度为92%,平均晶粒粒度为3~5μm。
实施例3
本实施例中,将质量比为70:10:8:3:2:3:2:2的平均粒度3μm氮化硅粉、碳化硅晶须、0.5μm氧化钇、0.5μm氧化铝、0.5μm氧化铈、1μm氧化镁、0.5μm氧化铝、1μm氧化镧混合成固体颗粒粉末,再加入总质量8%的聚氨酯共混于丙酮中,球磨制成料浆,所述料浆溶液中固体颗粒粉末为总质量的52%;将孔径3mm的聚胺脂泡沫切割成要求尺寸后均匀地浸入所述料浆中,浸泡1分钟,拿出后挤去多余料浆,并离心处理,使得泡沫孔保持通透,风干后190℃固化25分钟,上述过程反复两次以上,直到达到60%的预定体积百分数(成品中陶瓷筋的体积百分数)。然后浸渍浓度为80wt%的聚氨酯-丙酮溶液三次,每次150℃固化0.5小时,将在预制体陶瓷筋表面形成一层不透气聚氨酯膜层,放入高压容器内,充入氮气使气压达到30MPa,升温速率为5℃/分钟,升温至200℃,保温1.0小时。在氩气保护下脱脂,其中升温速率为10℃/分钟,升温至750℃,保温1小时。脱脂后,进入真空炉烧结,充入氮气气氛保护,温度1750℃,升温速率为5℃/分钟,保温2小时,得高性能氮化硅泡沫材料,氮化硅陶瓷筋的相对致密度为93%,平均晶粒粒度为3~4μm。
实施例4
本实施例中,将质量比为85:8:4:1.5:1.0:0.5的平均粒度2μm氮化硅粉、碳化硅晶须、1μm氧化钇、0.5μm氧化铝、0.5μm氧化铝、1μm氧化镁混合成固体颗粒粉末,再加入总质量5%的聚乙烯醇共混于纯水中,球磨制成料浆,所述料浆溶液中固体颗粒粉末为总质量的48%;将孔径3mm的聚胺脂泡沫切割成要求尺寸后均匀地浸入所述料浆中,浸泡1分钟,拿出后挤去多余料浆,并离心处理,使得泡沫孔保持通透,风干后180℃固化25分钟,上述过程反复两次以上,直到达到70%的预定体积百分数(成品中陶瓷筋的体积百分数)。然后浸渍浓度为85wt%的聚氨酯-丙酮溶液三次,每次150℃固化0.5小时,将在预制体陶瓷筋表面形成一层不透气聚氨酯膜层,放入高压容器内,充入氮气使气压达到24MPa,升温速率为1℃/分钟,升温至250℃,保温0.8小时。在氩气保护下脱脂,其中升温速率为2℃/分钟,升温至850℃,保温0.5小时。脱脂后,进行真空炉烧结,充入氮气气氛保护,温度1650℃,升温速率为7℃/分钟,保温3小时,得高性能氮化硅泡沫材料,氮化硅陶瓷筋的相对致密度为91%,平均晶粒粒度为2~5μm。
材料性能测试:
测量上述实施例得到氮化硅泡沫材料力学性能,并在950℃铝熔体中浸泡后取出强制风冷循环100次,考察其力学性能变化判定其抗热冲击能力。
Claims (10)
1.一种晶须增韧氮化硅泡沫材料,其特征在于:该泡沫材料以多边型封闭环为基本单元,各基本单元相互连接形成三维连通网络;构成三维连通网络的陶瓷筋由氮化硅组成,按体积百分数计,氮化硅固相在25~70%范围内,孔隙率30~75%,陶瓷筋的相对致密度≮90%,材料中平均晶粒尺寸在0.7~5μm。
2.一种权利要求1所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:以固体颗粒粉末和有机高分子粘结剂为原料,以聚胺脂泡沫塑料为模板;其中,固体颗粒粉末为氮化硅粉、碳化硅晶须及烧结助剂,具体制备过程如下:
(1)料浆配制
将固体颗粒粉末、有机高分子粘结剂和溶剂按比例混合,按质量百分比计,固体颗粒粉末40wt%~55wt%,有机高分子粘结剂10wt%~5wt%,溶剂50wt%~40wt%,经机械搅拌后球磨,过滤,得料浆;
(2)浸挂
将聚胺脂泡沫塑料剪裁成所需形状和尺寸,均匀地浸入料浆中、拿出后挤去多余料浆、采用气吹或气吹结合离心的方式除去多余料浆,加热烘干,上述浸料、挤料、固化过程重复两次以上,达到所需要的固相体积百分数25~70%,得到泡沫材料骨架预制体;
(3)热压致密化
将上述得到的泡沫材料预制体表面浸渍浓度为60~90wt%的聚氨酯-丙酮溶液2~4次,每次120~180℃固化0.5~1小时,将在预制体陶瓷筋表面形成一层不透气聚氨酯膜层,而后将表面不透气泡沫预制体放入高压容器内,充入氮气或氩气,高温、高压固化,压力为20~30MPa、温度在100~300℃,升温速率为1~5℃/分钟,保温20分钟~90分钟,得到更加致密化的泡沫陶瓷预制体;
(4)脱脂
将致密的泡沫陶瓷预制体在氩气、氮气或其它惰性气体的保护下或者在真空条件下脱脂,脱除泡沫骨架预制体中的有机物质;其中升温速率为1~10℃/分钟,升温至600~900℃,保温0.5~2小时;
(5)烧结
将脱脂后致密的泡沫陶瓷经机加工成为所需形状和尺寸,然后进行烧结,烧结在高纯氮气保护气氛条件下进行,升温速率为1~10℃/分钟,温度为:1650~1800℃,保温0.5~3小时,得氮化硅泡沫材料。
3.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:有机高分子粘结剂选自聚乙烯醇或聚氨酯。
4.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:氮化硅的平均粒度为0.5~3μm,纯度为99.5wt%以上。
5.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:烧结助剂为硅粉、氧化铝、氧化钇、氧化镁、氧化镧或氧化铈中的一种或者两种以上组成,平均粒度为0.5~1μm,纯度为99.8wt%以上。
6.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:碳化硅晶须的平均直径为0.2~0.5μm,长径比≮20,纯度为90wt%以上。
7.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:采用氮化硅粉、碳化硅晶须和烧结助剂混合粉末时,按质量百分比计,氮化硅粉70~90%,碳化硅晶须10%~5%,烧结助剂20~5%。
8.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:料浆溶液中,固相为总质量的50~60%。
9.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:溶剂为水、乙醇或丙酮。
10.按照权利要求2所述的晶须增韧氮化硅泡沫材料的无压烧结制备方法,其特征在于:料浆浸渍过程中的固化采用普通烘箱或收缩机,泡沫骨架预制体热压致密化采用的高压容器为高压反应釜或热等静压机,脱脂用炉为碳管炉或真空感应加热炉,烧结用炉为真空感应烧结炉、真空碳管炉或真空电阻炉。
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