Cold sintering process on molybdenum disilicide and graphite composite electrodes
Molibden disilisit ve grafit kompozit elektrotlarına soğuk sinterleme yönteminin uygulanması
- Tez No: 635746
- Danışmanlar: PROF. DR. CÜNEYT ARSLAN
- Tez Türü: Doktora
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2020
- Dil: İngilizce
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Metalurji ve Malzeme Mühendisliği Bilim Dalı
- Sayfa Sayısı: 100
Özet
Sinterleme, toz malzemelere uygulanan bir sıkıştırma yöntemi olup difüzyon prosesi ile malzemelerin yüzey enerjilerinin azaltılarak yoğunlaştırılmasını sağlar. Geleneksel yaklaşımda etkin bir yoğunlaştırma genellikle ilgili malzemenin ergime sıcaklığının yaklaşık %50 ile %75 civarındaki bir sıcaklıkta gerçekleştirilir (Dejonghe and Rahaman 2003; German 1996; S.-J L Kang 2005). Sıkıştırma prosesinin etkinliğini artırmak maksadıyla bazı uygulanan yöntemlerde eş basıçlı sıcak presleme gibi 200 MPa'a kadar bir basınç uygulaması gercekletirilmiştir (German 1996; S.-J L Kang 2005; Li et al. 1996; Stanciu et al. 2001). İlgili yöntemlerde basıncın uygulanması tanecik seviyesinde yoğunlaştırmanın performansını artırsa da, meydana gelen yavaş katı hal difüzyonu, uygulamanın yüksek sıcaklıklara bağımlı kalmasına neden olur. Yürütülen bu çalışmada, Soğuk sinterleme yöntemi (Cold sintering Process) olarak anılan metod, seçilen kovalent bağlı yapılara ve toz metal malzemelere uygulanmıştır. Soğuk sinterleme yöntemi, bir konsolidasyon metodu olup, bir geçiş-sıvının yardımı ile ve son derece düşük sıcaklıklarda (
Özet (Çeviri)
Sintering is a compaction process of particulate matters with a diffusional process that minimizes surface energy to densify particles against the competitive force of coarsening (Dejonghe and Rahaman 2003; German 1996; S.-J L Kang 2005). In a conventional aspect, effective consolidation is usually accomplished at 50-75% of melting temperatures of sintered materials and with an occasional aid of pressure. The primary driving force behind the consolidation process is a reduction of surface free energy. In order to improve the effect of sintering, some of the processing techniques, such as hot isostatic pressing, field-assisted sintering (FAST), utilize pressure up to 200 MPa (German 1996; S.-J L Kang 2005; Li, Liao, and Hermansson 1996; Stanciu, Kodash, and Groza 2001). Although, the application of pressure improves the performance of densification in the particle-particle level, densification is still highly dependent on high temperature, due to the slow solid-state diffusional process. Cold sintering process (CSP) is a densification process at a low-temperature provides an opportunity to sinter a wide range of ceramic materials at extremely low temperatures ( direction in both produced pellets and films. Microscopy analysis with SEM showed that the sintered constituents were incorporated with the structure and small MoS2 flakes formed on the surface of the constituents and enabled their bonding. The chemistry information acquired with EDS also supports the incorporation with homogeneous dispersion of LAGP and graphite flakes in the structure. The EBSD analysis of both pellet and films were conducted to reveal the anisotropic feature of the samples. The pellets were scanned in both directions (c- and a-axis) while the film was only investigated on the surface, due to lack of thickness on the cross-section. The pole figure for {0001} planes of the pellets, which is measured perpendicular to the pressure loading, had shown a strong intensity along the direction, which is a strong basal orientation with ~24x randomly distributed intensity. The measurements parallel to applied pressure had a texture mainly orientated along the a-axis with ~15x randomly distributed intensity that shows an anisotropy between the two directions of cold sintered pellets. The findings are also in a consensus with the XRD results showing proof of stacked platelets along the c-axis that are arranged by applied uniaxial force. In order to evaluate the impact of Graphite in the system, electrical resistivities of the pellets were measured by a four-probe method. The resistivity measurements of samples in different graphite contents are conducted with respect to the temperature. The directional dependencies seen in the previous results were also investigated with this electrical testing with measuring samples in both directions, which are a, and c-axes. According to the results, the resistivities of a pure MoS2 pellet in a- and c-directions are 400 ohm.m and 120 ohm.m while MoS2-Graphite pellet (containing 20 wt.% Graphite) had 5 ohm.m and 1.5 ohm.m, respectively. It is believed that the preferential stacking of MoS2 planes along c-direction induced a higher resistivity along this direction. The results also suggest that the preferred orientation of the planes can create a barrier during current flow that increases the resistivity. The ratio of the resistivities between the two axes is found as~ 4.1, which is lower than the reported values (~1000) (El Beqqali et al. 1997; Hermann et al. 1973; Hippalgaonkar et al. 2017; Kam 1982; Souder and Brodie 1971). The testing of the electrodes in terms of electrochemical capabilities was conducted after preparing a half-cell in the argon-filled glove box. The results were displayed as Cyclic voltammetry (CV), and charge, and discharge profiles. The CV graphs of the MG electrode showed cathodic peaks at 0.28, 1.1, and 1.8V and anodic peaks at 0.29, and 2.5V, which are consistent with reported redox peaks of MoS2 electrodes. The cathodic peaks are signatures of Li+ insertion into MoS2 galleries and phase transformation of the structures. The first encountered anodic peak represents the lithium de-intercalation, graphite oxidation, and Mo oxidation to MoS2. The charge and discharge profiles have an agreement with CV curves, and the discharge curve depicts two visible plateaus at 1V vs. Li+/Li, the indicative formation of LixMoS2 and 0.5V vs. Li+/Li, the reduction of Mo4+ to Mo metal with Li2S formation. Cycling capability and capacity retention of the composites were significantly improved with the addition of solid electrolyte during the cold sintering process. The modified electrodes showed a first cycle capacity retention as 85.7%, and specific capacity as ~ 1000 mAh/g between 0 to 2.5 V vs. Li+/Li, after the 10th cycle. In summary, the thesis investigated the cold sintering of MoS2/Graphite composite structures, and results showed that consolidation of the composites was accomplished at low-temperatures with the aid of transient liquid-slurry, which includes AHM/Thiourea. The slurry provides a facile production of MoS2 flakes that can act as if cement between the pristine MoS2 and Graphite constituent and enables their bonding during the cold sintering process. It is believed that the uniaxial pressure, which is applied during the process, is amplified the anisotropy of the composite structure. The argument is supported by EBSD pole figures and electrical resistivity measurements, which are showed discrepancies between the a and c-directions. Another important finding is that increased graphite ratio improved both electrical conductivity electrochemical performance due to increased electron transfer during charge and discharge. The obtained charge and discharge profile in ~20-30wt% of graphite contents showed a typical plateau of MoS2 with increased capacity and cycling performance. The electrochemical performance was further increased by introducing a solid electrolyte, Li1.5Al0.5Ge1.5(PO4 )3(LAGP), to the system, which is improved Li+ ion intercalation capabilities of the electrodes. As a result, electrochemically active MoS2 and Graphite electrodes are produced with ~1000 mAh/g specific capacity using the cold sintering method.
Benzer Tezler
- Östemperlenmiş toz metal çeliklerin mekanik ve mikroyapı özelliklerinin araştırılması
Investigation of mechanical and microstructural properties of austempered steel powder metal
NURULLAH SARIÇİÇEK
Yüksek Lisans
Türkçe
2012
Metalurji MühendisliğiGazi ÜniversitesiMetal Eğitimi Ana Bilim Dalı
YRD. DOÇ. DR. AHMET GÜRAL
- Mekanik alaşımlama süreçleriyle MoS2-grafit katı yağlayıcı katkılı Fe-C esaslı kompresör parçalarının geliştirilmesi ve karakterizasyonu
Development and characterization of iron based and MoS2, graphite solid lubricant reinforced compressor parts synthesized by mechanical alloying
MERVE UYSAL
Yüksek Lisans
Türkçe
2016
Metalurji Mühendisliğiİstanbul Teknik ÜniversitesiMetalurji ve Malzeme Mühendisliği Ana Bilim Dalı
PROF. DR. MUSTAFA LUTFİ ÖVEÇOĞLU
- Toz metalurjisi yöntemleri ile üretilen çeşitli W-Ni-Fe ve W-Ni-Cu ağır alaşımların mikroyapısal ve fiziksel karekterizasyonu
Microstructural and physical characterization of various W-Ni-Fe and W-Ni-Cu heavy alloys manufactured via powder metallurgy methods
GÜNKUT ERNAS
- Enhancement of dispenser cathode fabrication with pre – design activation simulations and polymer doping
Polimer katkılandırma ve ön aktivasyon tasarımı benzetim çalışmaları ile dispenser katotların üretim süreçlerinin geliştirilmesi
NERGİS YILDIZ ANGIN ATMACA
Doktora
İngilizce
2023
Fizik ve Fizik Mühendisliğiİstanbul Teknik ÜniversitesiFizik Mühendisliği Ana Bilim Dalı
PROF. DR. ESRA ALVEROĞLU DURUCU
- Synergistic effects of Mo and Ti element addition on microstructure, mechanical and corrosion properties of 316 L stainless steels produced by PM method
TM yöntemiyle üretilen 316 L paslanmaz çeliklerin mikro yapı, mekanik ve korozyon özellikleri üzerinde Mo ve Ti element ilavesinin sinerjik etkileri
MOHAMMED FARAJ ALI ABU SHAALAH
Yüksek Lisans
İngilizce
2023
Makine MühendisliğiKarabük ÜniversitesiMakine Mühendisliği Ana Bilim Dalı
DOÇ. DR. HARUN ÇUĞ
PROF. DR. MEHMET AKİF ERDEN