Pengaruh tekanan kompaksi dan suhu sintering terhadap sifat fisis dan mekanis kaolin

AMIN, Muh, Ir. M. Waziz Wildan, M.Sc.,Ph.D

2005 | Tesis | S2 Teknik Mesin

Kaolin pada umumnya memiliki kandungan 40-50 wt% Al2O3 dan 50-60 wt% SiO2, sehingga dapat digolongkan sebagai jenis refraktori alumina rendah. Dalam aplikasinya kaolin telah banyak dipakai sebagai bahan bahan porcelain, chinaware, furnace lining, crucible, batu tahan api dan abrasive. Tujuan dari penelitian ini adalah mengetahui pengaruh tekanan kompaksi dan suhu sintering terhadap densitas, kekerasan, fracture toughness dan kekuatan bending dari kaolin. Pembuatan spesimen dilakukan dengan metode pressureless sintering dengan variasi tekanan kompaksi (20, 25, 30, 35, 40, 45 dan 50) MPa dan suhu sintering (1350, 1400, 1450 dan 1500)oC. Serbuk kaolin dengan ukuran 325 mesh dibuat spesimen berbentuk silindris (diameter, d=15 mm, tebal, t=5 mm), spesimen balok (panjang, L= 40 mm, lebar, B= 8 mm, tinggi, W= 7 mm) dan spesimen balok (panjang, L= 40 mm, lebar, B= 8 mm, tinggi, W= 7 mm) dengan sebuah notch di tengah batang spesimen balok dengan uniaxial-pressing. Spesimen disinter dengan laju pemanasan 5oC/menit dengan waktu penahanan selama 60 menit. Pendinginan dilakukan di dalam furnace dengan cara mematikan power furnace sampai suhu kamar. Pada suhu sinter yang sama kenaikan tekanan kompaksi meningkatkan densitas kaolin. Demikian juga untuk setiap tekanan kompaksi dengan naiknya suhu sinter menaikkan densitas kaolin. Densitas diukur dengan metode Archimedes . Densitas tertinggi sebesar (2,57±0,01) gr/cm3 diperoleh pada suhu sinter 1500oC dan tekanan kompaksi 50 MPa. Kekerasan naik seiring dengan naiknya suhu sinter dan tekanan kompaksi. Pengujian kekerasan Vickers dilakukan dengan beban 153,2 N diperoleh harga kekerasan sebesar 8.372 MPa pada spesimen dengan tekanan kompaksi 50 MPa dan suhu sinter 1500oC. Pengujian fracture toughness pada spesimen dengan tekanan kompaksi 25 MPa dan suhu sinter 1500oC dengan menggunakan metode Indentasi Kekerasan Vickers diperoleh harga fracture toughness sebesar 3,12 MPa.m0,5. Sedangkan dengan menggunakan metode Single- Edge Notched Beam (SENB) untuk spesimen yang sama diperoleh harga fracture toughness sebesar (0,32±0,004) MPa.m0,5. Pengujian kekuatan bending pada spesimen dengan tekanan kompaksi 25 MPa dan suhu sinter 1500oC dengan menggunakan three-point bending test diperoleh hasil sebesar (107,33±24,80) MPa.

Kaolin is a ceramic material that usually consists of (40-50) % wt Al2O3 and (50-60) % wt SiO2 and can be classified as low alumina refractory. Kaolin is widely used in porcelain, chinaware, furnace lining, crucible, firebrick and abrasive. This research aim to investigate the effects of compacting pressure and sintering temperature on physical and mechanical properties of kaolin. The material used was kaolin with 325-mesh size. Green body of specimens were uniaxially pressed with various pressures of (20, 25, 30, 35, 40, 45 and 50) MPa. There were three different shapes of specimens, cylindrical (diameter, d= 15 mm and thickness, t= 5 mm), square bar (40 x 8 x 7) mm3 and square bar with a notch (Single-Edge Notched Beam) (40 x 8 x 7) mm3. The cylindrical specimen were pressureless sintered at various temperature of (1350, 1400, 1450 and 1500)oC with a heating rate of 5oC/minutes with holding time for 1 hour. The sintered temperature which gave the highest density was then used as sintered temperature for square bar and SENB specimens. Density of sintered samples was measured using Archimedes method. Vickers indentation method was used to measure the hardness and by using the crack generated from the corner of the indent can be used to estimate the fracture toughness. The fracture toughness was also measured by using SENB test. Bending strength of the specimens was measured using three point bending test. Optical microscopy and SEM were used to observe the microstructures. The results show that for each compacting pressure the density increases with increasing temperature and also for each sintering temperature the density increases with increasing compacting pressure. The highest density of 2.57 gr/cm3 is achieved on the specimens with compacting pressure of 50 MPa and sintering temperature of 1500oC. The highest Vickers hardness is also obtained on the specimens with compacting pressure of 50 MPa and sintering temperature of 1500oC. The highest value of fracture toughness measured using Indentation method is 3.12 MPa0.5, which is obtained on the specimens with compacting pressure of 50 MPa and sintering temperature of 1500oC. However the fracture toughness measured using SENB method gives lower values. The bending strength of (98,79±28,74) MPa is achieved on the specimen compacting pressure of 50 MPa and sintering temperature of 1500oC.

Kata Kunci : Kaolin,Tekanan Kompaksi,Densitas dan Kekerasan, density, fracture toughness, Vickers hardness, bending strength, pressureless sintering, compacting, uniaxially pressing.