Transparent glasses obtained by unconventional sintering

openGlasses are conventional manufactured by melting natural sand or silicon compounds at high temperatures. The traditional melting method requires high energy input to reach the melting temperature of precursors. Conventional solid-state sintering of powders is a valid alternative to reduce the processing temperature; however it requires time consuming thermal treatment to obtain densification. With the aim of reducing the environmental impact, energy, temperature and cost, the thesis project carried out in collaboration with the University of Lyon 1 aims to develop new ways of producing glass by employing unconventional sintering approaches. During the experimental work, three different strategies are explored: synthesis of nanoparticles at a low glass transition temperature, cold sintering process on commercial sub-micrometer particles borosilicate glass, the Spark Plasma sintering process on nanostructured silica nanoparticles. - Synthesis of nanoparticles with a low glass transition temperature: using a modifying Stober synthesis, including tetraethyl orthosilicate, as silicon precursor, and boron, calcium and sodium salts or alkoxides as precursors of modifier oxides, capable of lowering the glass transition temperature. Several parameters were investigated such as the type of precursor, the molar ratio of the oxide precursors to TEOS, the concentration of the solution and the calcination temperature. The results showed that particles with a diameter of about 150 nm were obtained, with a strong presence of organic residue. The glass transition temperature was about 950°C, likely due to the lack of successful incorporation of modifier oxides into the silica network. - Cold Sintering Process: a basic sodium hydroxide solution was selected as a liquid phase to promote densification at low temperatures. The main parameters investigated were the following: temperature, pressure, liquid/solid molar ratio and residence time of the powder in the mould. Density measurements by means of the Archimedes test and pycnometer revealed the following best parameter combinations: Pressure P=300MPa, temperature T=250°C, % liquid/mass =40, residence time t in the mould = 30 min; Pressure P=300MPa, temperature T=200°C, % liquid/mass =20, dwell time t in the mould = 120 min, The lack of an unit value of relative density is an indication of sintering having only partially taken place, which is confirmed by the high porosity visible through SEM characterisation analysis, and the lack of transparency. - Spark Plasma Sintering: the silicon oxide particles pre-treated at 900°C (in order to remove water and carbonate groups absorbed) were subjected to the sintering process by Spark Plasma. During the operations, the pressure and dwell time values were chosen and kept fixed (2GPa and 3 minutes respectively), allowing the effect of the key parameter of temperature to be assessed. Characterisation of the samples produced, carried out using SEM and Raman spectroscopy, revealed the following: * Crystallization occurs at 2GPa for temperature above 1000°C * Densification and transparency occur for a temperature of 800°C. In-situ measurements of the process combined with Archimedes density test show, however, that the sintering process is not complete. *An initial sintering step takes place at temperatures around 500°C; one could develop the idea of future experiments by decreasing the temperature, so as to decrease the energy consumption required to achieve densification. This thesis work shows that it is indeed possible to produce transparent glass using unconventional sintering techniques. From these preliminary investigations, it's possibile to confirm an important role of the particles dimension for the obtainment of dense and transparent glass components.Glasses are conventional manufactured by melting natural sand or silicon compounds at high temperatures. The traditional melting method requires high energy input to reach the melting temperature of precursors. Conventional solid-state sintering of powders is a valid alternative to reduce the processing temperature; however it requires time consuming thermal treatment to obtain densification. With the aim of reducing the environmental impact, energy, temperature and cost, the thesis project carried out in collaboration with the University of Lyon 1 aims to develop new ways of producing glass by employing unconventional sintering approaches. During the experimental work, three different strategies are explored: synthesis of nanoparticles at a low glass transition temperature, cold sintering process on commercial sub-micrometer particles borosilicate glass, the Spark Plasma sintering process on nanostructured silica nanoparticles. - Synthesis of nanoparticles with a low glass transition temperature: using a modifying Stober synthesis, including tetraethyl orthosilicate, as silicon precursor, and boron, calcium and sodium salts or alkoxides as precursors of modifier oxides, capable of lowering the glass transition temperature. Several parameters were investigated such as the type of precursor, the molar ratio of the oxide precursors to TEOS, the concentration of the solution and the calcination temperature. The results showed that particles with a diameter of about 150 nm were obtained, with a strong presence of organic residue. The glass transition temperature was about 950°C, likely due to the lack of successful incorporation of modifier oxides into the silica network. - Cold Sintering Process: a basic sodium hydroxide solution was selected as a liquid phase to promote densification at low temperatures. The main parameters investigated were the following: temperature, pressure, liquid/solid molar ratio and residence time of the powder in the mould. Density measurements by means of the Archimedes test and pycnometer revealed the following best parameter combinations: Pressure P=300MPa, temperature T=250°C, % liquid/mass =40, residence time t in the mould = 30 min; Pressure P=300MPa, temperature T=200°C, % liquid/mass =20, dwell time t in the mould = 120 min, The lack of an unit value of relative density is an indication of sintering having only partially taken place, which is confirmed by the high porosity visible through SEM characterisation analysis, and the lack of transparency. - Spark Plasma Sintering: the silicon oxide particles pre-treated at 900°C (in order to remove water and carbonate groups absorbed) were subjected to the sintering process by Spark Plasma. During the operations, the pressure and dwell time values were chosen and kept fixed (2GPa and 3 minutes respectively), allowing the effect of the key parameter of temperature to be assessed. Characterisation of the samples produced, carried out using SEM and Raman spectroscopy, revealed the following: * Crystallization occurs at 2GPa for temperature above 1000°C * Densification and transparency occur for a temperature of 800°C. In-situ measurements of the process combined with Archimedes density test show, however, that the sintering process is not complete. *An initial sintering step takes place at temperatures around 500°C; one could develop the idea of future experiments by decreasing the temperature, so as to decrease the energy consumption required to achieve densification. This thesis work shows that it is indeed possible to produce transparent glass using unconventional sintering techniques. From these preliminary investigations, it's possibile to confirm an important role of the particles dimension for the obtainment of dense and transparent glass components

Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy

IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced colorectal cancers at diagnosis. OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced oncologic stage and change in clinical presentation for patients with colorectal cancer. DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all 17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December 31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period), in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was 30 days from surgery. EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery, palliative procedures, and atypical or segmental resections. MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding, lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery, and palliative surgery. The independent association between the pandemic period and the outcomes was assessed using multivariate random-effects logistic regression, with hospital as the cluster variable. RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years) underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142 (56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR], 1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P < .001), and stenotic lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03). CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for these patients

Effect of centre volume on pathological outcomes and postoperative complications after surgery for colorectal cancer: results of a multicentre national study

Background: The association between volume, complications and pathological outcomes is still under debate regarding colorectal cancer surgery. The aim of the study was to assess the association between centre volume and severe complications, mortality, less-than-radical oncologic surgery, and indications for neoadjuvant therapy.Methods: Retrospective analysis of 16,883 colorectal cancer cases from 80 centres (2018-2021). Outcomes: 30-day mortality; Clavien-Dindo grade >2 complications; removal of >= 12 lymph nodes; non-radical resection; neoadjuvant therapy. Quartiles of hospital volumes were classified as LOW, MEDIUM, HIGH, and VERY HIGH. Independent predictors, both overall and for rectal cancer, were evaluated using logistic regression including age, gender, AJCC stage and cancer site.Results: LOW-volume centres reported a higher rate of severe postoperative complications (OR 1.50, 95% c.i. 1.15-1.096, P = 0.003). The rate of >= 12 lymph nodes removed in LOW-volume (OR 0.68, 95% c.i. 0.56-0.85, P = 12 lymph nodes removed was lower in LOW-volume than in VERY HIGH-volume centres (OR 0.57, 95% c.i. 0.41-0.80, P = 0.001). A lower rate of neoadjuvant chemoradiation was associated with HIGH (OR 0.66, 95% c.i. 0.56-0.77, P < 0.001), MEDIUM (OR 0.75, 95% c.i. 0.60-0.92, P = 0.006), and LOW (OR 0.70, 95% c.i. 0.52-0.94, P = 0.019) volume centres (vs. VERY HIGH).Conclusion: Colorectal cancer surgery in low-volume centres is at higher risk of suboptimal management, poor postoperative outcomes, and less-than-adequate oncologic resections. Centralisation of rectal cancer cases should be taken into consideration to optimise the outcomes