Phase Formation of Ca-alpha-sialon by Reaction Sintering

In this study the reaction sintering route for the formation of Ca-a-sialon with a composition on the line Si3N4/CaO · 3AlN (Ca0.8 Si9.6 Al2.4 O0.8 N15.2, m = 1.6, N = 0.8) has been investigated. This is compared with the hot-pressing of Ca-a-sialon and the reaction sintering of Y- or lanthanide-a-sialons. The reaction follows the same sequence: first, the formation of a Ca-rich a-sialon phase (m = 1.9) which is gradually transformed to a Ca-a-sialon with a lower Ca concentration (m = 1.2). The gehlenite phase (Ca2Al2SiO7, melilite group) is observed as an intermediate product. A potential advantage of Ca-a-sialon over Ln-a-sialon Full-size image is liquid phase formation at a lower temperature, which has a positive influence on the processing temperature. Moreover, Ca is cheaper than the lanthanides. The solubility of Ca in the a-sialon is in agreement with values found in the literature

Total aqueous processing of carbothermally produced beta-sialon

ß-Sialon with chemical formula Si3Al3O3N5 is synthesized from meta-kaolin/coal mixtures which are pelletised and heat treated at 1500 °C in flowing nitrogen. Typically batches produced contain 300 g powder with 90 wt% ß-sialon and 10 wt% 15-R phase. The powders are attrition milled to submicron size, suspended in water and mixed with yttrium oxide as a sintering aid. Suspensions are pH and polyelectrolyte stabilised. The suspensions are used to slip cast discs which are sintered in a nitrogen atmosphere of 100 kPa at 1450 °C for 150 minutes. Typical properties are ball-on-ring strength at room temperature 450 MPa, density 3.31 g/ml, HV2 Vickers hardness 12.5 GPa and KIC 5.4 MPa v

Total aqueous processing of carbothermally produced beta-sialon

ß-Sialon with chemical formula Si3Al3O3N5 is synthesized from meta-kaolin/coal mixtures which are pelletised and heat treated at 1500 °C in flowing nitrogen. Typically batches produced contain 300 g powder with 90 wt% ß-sialon and 10 wt% 15-R phase. The powders are attrition milled to submicron size, suspended in water and mixed with yttrium oxide as a sintering aid. Suspensions are pH and polyelectrolyte stabilised. The suspensions are used to slip cast discs which are sintered in a nitrogen atmosphere of 100 kPa at 1450 °C for 150 minutes. Typical properties are ball-on-ring strength at room temperature 450 MPa, density 3.31 g/ml, HV2 Vickers hardness 12.5 GPa and KIC 5.4 MPa v

Neoadjuvant chemoradiotherapy plus surgery versus active surveillance for oesophageal cancer: A stepped-wedge cluster randomised trial

Background: Neoadjuvant chemoradiotherapy (nCRT) plus surgery is a standard treatment for locally advanced oesophageal cancer. With this treatment, 29% of patients have a pathologically complete response in the resection specimen. This provides the rationale for investigating an active surveillance approach. The aim of this study is to assess the (cost-)effectiveness of active surveillance vs. standard oesophagectomy after nCRT for oesophageal cancer. Methods: This is a phase-III multi-centre, stepped-wedge cluster randomised controlled trial. A total of 300 patients with clinically complete response (cCR, i.e. no local or disseminated disease proven by histology) after nCRT will be randomised to show non-inferiority of active surveillance to standard oesophagectomy (non-inferiority margin 15%, intra-correlation coefficient 0.02, power 80%, 2-sided α 0.05, 12% drop-out). Patients will undergo a first clinical response evaluation (CRE-I) 4-6 weeks after nCRT, consisting of endoscopy with bite-on-bite biopsies of the primary tumour site and other suspected lesions. Clinically complete responders will undergo a second CRE (CRE-II), 6-8 weeks after CRE-I. CRE-II will include 18F-FDG-PET-CT, followed by endoscopy with bite-on-bite biopsies and ultra-endosonography plus fine needle aspiration of suspected lymph nodes and/or PET- positive lesions. Patients with cCR at CRE-II will be assigned to oesophagectomy (first phase) or active surveillance (second phase of the study). The duration of the first phase is determined randomly over the 12 centres, i.e., stepped-wedge cluster design. Patients in the active surveillance arm will undergo diagnostic evaluations similar to CRE-II at 6/9/12/16/20/24/30/36/48 and 60 months after nCRT. In this arm, oesophagectomy will be offered only to patients in whom locoregional regrowth is highly suspected or proven, without distant dissemination. The main study parameter is overall survival; secondary endpoints include percentage of patients who do not undergo surgery, quality of life, clinical irresectability (cT4b) rate, radical resection rate, postoperative complications, progression-free survival, distant dissemination rate, and cost-effectiveness. We hypothesise that active surveillance leads to non-inferior survival, improved quality of life and a reduction in costs, compared to standard oesophagectomy. Discussion: If active surveillance and surgery as needed after nCRT leads to non-inferior survival compared to standard oesophagectomy, this organ-sparing approach can be implemented as a standard of care

Phase Formation of Ca-alpha-sialon by Reaction Sintering

In this study the reaction sintering route for the formation of Ca-a-sialon with a composition on the line Si3N4/CaO · 3AlN (Ca0.8 Si9.6 Al2.4 O0.8 N15.2, m = 1.6, N = 0.8) has been investigated. This is compared with the hot-pressing of Ca-a-sialon and the reaction sintering of Y- or lanthanide-a-sialons. The reaction follows the same sequence: first, the formation of a Ca-rich a-sialon phase (m = 1.9) which is gradually transformed to a Ca-a-sialon with a lower Ca concentration (m = 1.2). The gehlenite phase (Ca2Al2SiO7, melilite group) is observed as an intermediate product. A potential advantage of Ca-a-sialon over Ln-a-sialon Full-size image is liquid phase formation at a lower temperature, which has a positive influence on the processing temperature. Moreover, Ca is cheaper than the lanthanides. The solubility of Ca in the a-sialon is in agreement with values found in the literature

Densification behaviour of Ca-α-sialons

In this paper three methods of densification of Ca- -sialon are compared. It is shown that both reaction hot pressing and reaction sintering are convenient methods to obtain densities close to theoretical values. For the densification of carbothermally prepared Ca- -sialon powders the influence of the amount of CaO as a sintering additive has been shown to be significant. The highest density was reached with 15 wt.% CaO (~ 97% relative density). The `mechanisms' of sintering using the three mentioned methods (reaction hot pressing, reaction sintering and sintering Ca-a-sialon powder with CaO as a sintering additive) appear to be similar. First a rearrangement of the particles takes place due to the presence of a liquid phase, followed by a solution/precipitation mechanism. The mechanism for liquid phase sintering of Ca- -sialon is similar to that described in literature for other Ln- -sialon (Ln=Y, lanthanide's) materials

Total aqueous processing of carbothermally produced beta-sialon

ß-Sialon with chemical formula Si3Al3O3N5 is synthesized from meta-kaolin/coal mixtures which are pelletised and heat treated at 1500 °C in flowing nitrogen. Typically batches produced contain 300 g powder with 90 wt% ß-sialon and 10 wt% 15-R phase. The powders are attrition milled to submicron size, suspended in water and mixed with yttrium oxide as a sintering aid. Suspensions are pH and polyelectrolyte stabilised. The suspensions are used to slip cast discs which are sintered in a nitrogen atmosphere of 100 kPa at 1450 °C for 150 minutes. Typical properties are ball-on-ring strength at room temperature 450 MPa, density 3.31 g/ml, HV2 Vickers hardness 12.5 GPa and KIC 5.4 MPa v

Carbothermal Preparation and Characterisation of Ca-alpha-sialon

Ca-a-sialon can be synthesised by simultaneous carbothermal reduction-nitridation of a mixture of fine SiO2, Al2O3, CaSiO3 and carbon black powder at 1500 °C. For the first time a single phase material is obtained in a one step process. The main intermediate product in these processes is a ß-sialon with a low z-value (z <1.2). After formation of this ß-sialon the calcium is incorporated in the lattice to form the Ca-a-sialon