Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium

Definitions

• the present invention relates to novel soda lime silicate glass composition comprising colemanite and a process for the preparation thereof.
• the invention relates to the development of Boron containing soda lime silicate based different compositions yielding lower melting temperature, lower coefficient of thermal expansion, higher surface hardness, higher refractive index, higher glass transition temperature, higher dilatometric softening temperature with improved chemical durability which are suitable for the manufacture of container and flat glasses by float process.
• the development of boron containing soda lime silicate based glasses with lower melting temperature; lower coefficient of thermal expansion, higher surface hardness, higher refractive index, higher glass transition temperature, higher dilatometric softening temperature with improved chemical durability can be used as solar panels, ophthalmic lenses and heat resistant glass cookware.
• Soda lime silicate glass is the most common commercially available oxide glass which is used as flat glass for window panes, and container glass for making containers.
• the composition of these two types of glasses also varies in a narrow range.
• the advantages of these glasses are mainly high transmission in the visible range, smooth surface and chemical durability with moderate surface hardness and low UV transmission.
• the production method for flat glass is float process while conventional blowing and pressing method is utilized to produce container glass.
• the flat glasses are primarily used for the automotive and structural applications as laminated glass and tempered glass for windows and doors. In particular, flat glass with low iron content and possessing high transmission is also used as cover glass for solar panels.
• the container glass finds applications in beverage bottles, food containers, toiletries, cosmetics and laboratory glassware.
• the colored container glasses are also in very much demand especially as amber (dark brown) containers for beer industry, medicine bottles in pharmaceutical industry, green containers used for wine and decorative or architectural purposes.
• the melting temperature of soda lime silicate glass ranges from 1550°C to 1600°C depending on the glass composition.
• the comparatively higher melting temperature of these soda lime silicate glasses may be reduced by lowering the amount of silica with a concomitant increase in the amount of alkali oxides as fluxing agents.
• the additional increase of these alkali oxides reduces the surface durability as well as chemical durability of glasses.
• a reduction in working zone and significant deviation from the desired optical and thermal properties occur.
• B 2 0 3 boron oxide
• introduction of B 2 0 3 in the soda lime silicate composition strengthens the glass network which actually contributes to the improved surface and chemical durability.
• incorporation of B 2 0 3 in the soda lime silicate glass may lower down the melting temperature along with widening up of working range. This may lead to a reduction in the overall energy consumption.
• the maximum amount of boron oxide included into the glass is only limited to 0.1-3.0 %.
• Boron oxide has been introduced into the glass batch in the form of boric acid (H 3 B0 3 ), sodium tetraborate decahydrate (Na 2 B 4 O 7 .10 H 2 0), sodium tetraborate pentahydrate (Na 2 B 4 0 7 , 5H 2 0).
• the main drawback is that such a low concentration of boron oxide in the glass composition could not lead to a substantial reduction in liquidus temperature and no significant improvement in refining.
• compositions either by increase of alkali content with simultaneous reduction of silica or by the aid of other constituent oxides in soda lime silicate systems resulted in negligible reduction in melting temperature. Also, there is no significant reduction in melting temperature even with the inclusion of small amounts (0.1-3 %) of boron oxide in the form of boric acid (H 3 B0 3 ), sodium tetraborate decahydrate (Na 2 B 4 O 7 .10 H 2 0), sodium tetraborate pentahydrate, (Na 2 B 4 0 7 , 5H 2 0) etc. in soda lime silicate glass for solar application.
• boric acid H 3 B0 3
• sodium tetraborate decahydrate Na 2 B 4 O 7 .10 H 2 0
• sodium tetraborate pentahydrate Na 2 B 4 0 7 , 5H 2 0
• Colemanite consists of around 40 wt.% of B 2 0 3 and 25-28 wt.% of CaO with minor constituents like Si0 2 , Al 2 0 3 , MgO, SrO and Na 2 0.
• the dual presence of CaO and B 2 0 3 in this mineral could be utilized as a potential raw material for simultaneous inclusion of both calcia and boron oxide into soda lime silicate glass.
• soda lime silicate glass compositions with inclusion of B 2 0 3 for significant reduction in melting temperature along with better refinement of glass melt and improvement in thermal, optical and mechanical properties of glass using colemanite mineral as a raw material source of both boron oxide (B 2 0 3 ) and calcia (CaO) in compositions of flat and container glasses.
• soda lime silicate composition with inclusion of B 2 0 3 suitable for the preparation of flat glass through float process which possess high transparency and improved thermal and mechanical properties along with reduced melting temperature could be a potential and cost-effective material for solar panels as cover glasses.
• the main objective of the present invention is thus to provide novel composition for soda lime silicate glass for energy efficient processing and involving colemanite which obviates the drawbacks of the hitherto known prior art.
• Another objective of the present invention is to provide soda lime silicate composition containing boron oxide exhibiting reduced melting temperature along with improved thermal and mechanical properties for flat glass specifically destined for solar panels and container glass applications.
• Still another objective of the present invention is to provide soda lime silicate composition containing boron oxide which is introduced in the form of colemanite mineral wherein colemanite mineral also serves as raw material source of calcia (CaO), a major component in the present flat and container glass compositions.
• Yet another objective of the present invention is to provide soda lime silicate composition containing significant amounts of boron oxide and still exhibiting reduced melting temperature, reduced coefficient of thermal expansion, enhanced glass transition temperature, dilatometric softening point and microhardness, along with refractive index and dispersion properties comparable to that of parent soda lime silicate glass.
• the present invention provides soda lime silicate glass compositions for energy efficient processing using colemanite which comprise essentially of 60.82-69.45 wt% silica, 4.26-13.14 wt% B 2 0 3 , 13.00-13.70 wt.% Na 2 0, 8.59-10.30 wt.% CaO, along with other minor components in the indicated proportion of 0.15-1.30 wt% Al 2 0 3 , 0.03-0.30 wt% K 2 0, 0.46- 4.04 wt% MgO, 0.13-0.41 wt% SrO and 0.01-0.02 wt% Ti0 2 with trace amount of impurities comprising of not more than 0.04 wt. % Fe for manufacturing of flat and container glasses.
• soda lime silicate glass compositions for energy efficient processing using colemanite comprise essentially of 60.82-68.80 wt.% Si0 2 , 4.26- 12.24 wt.% B 2 0 3 , 13.70 wt.% Na 2 0, 0.03 wt.% K 2 0, 8.59-8.83 wt.% CaO, 4.00 wt.% MgO, 0.13-0.37 wt.% SrO, 0.15 wt.% Al 2 0 3 0.02 wt.% Ti0 2 and trace amount of Fe coming from raw materials for the manufacturing of flat glasses.
• soda lime silicate glass compositions for energy efficient processing using colemanite comprise essentially of 61.28-69.45 wt.% Si0 2 , 4.97-13.14 wt.% B 2 0 3 , 13.00 wt.% Na 2 0, 0.30 wt.% K 2 0, 9.28-10.30 wt.% CaO, 0.46-1.24 wt.% MgO, 0.15-0.41 wt.% SrO, 1.30 wt.% Al 2 0 3 , 0.01 wt.% Ti0 2 , and trace amount of Fe coming from raw materials for the manufacturing of container glasses.
• additional B 2 0 3 gradually replaces silica and thus the total Si0 2 + B 2 0 3 content does not exceed 73.06 wt% and 74.42 wt% in the flat and container glasses respectively.
• the present invention provides novel soda lime silicate glass composition
• novel soda lime silicate glass composition comprising essentially of 60.82-69.45 wt% silica, 4.26-13.14 wt% B 2 0 3 , 13.00- 13.70 wt Na 2 0, 8.59-10.30 wt% CaO along with other minor components in the indicated proportion of 0.15-1.30 wt% Al 2 0 3 , 0.03-0.30 wt% K 2 0, 0.46-4.04 wt% MgO, 0.13-0.41 wt% SrO and 0.01-0.02 wt Ti0 2 with trace amount of impurities comprising of not more than
• the said glasses have the optical transmission above 90%.
• soda lime silicate glasses for flat glasses specifically for solar panels and container glasses have the refractive indices (nd) ranging from 1.5243 - 1.5345.
• soda lime silicate glasses for flat glasses specifically for solar panels and container glasses have the coefficient of thermal expansion (a SO -3oo) ranging from 86 - 84 x 10 "7 K “1 and 87 - 83 x 10 "7 K “1 with the increased inclusion of boron oxide content respectively.
• soda lime silicate glasses for flat glasses specifically for solar panels and container glasses have the glass transition temperatures varying from 572 - 583°C and 582 - 587°C respectively.
• the present invention provides a process for the preparation of soda lime silicate flat and container glasses using colemanite as one of the source raw material for both B 2 0 3 and CaO and the said process comprising the following steps:
• step (i) melting the homogenous batch mixtures as obtained in step (i) at temperature in the range of 1450 to 1600°C for period of 2.0 h with the intermittent stirring manually at an interval of 45 minutes for two times with quartz rod in order to achieve homogeneity.
• step (ii) The homogeneous melt as obtained in step (ii) was cast on preheated (300°C) cast iron mould to obtain glass slabs followed by its immediate transfer to annealing furnace kept at 550°C to anneal for 4 hrs.
• step [i] recited above Calcium carbonate is gradually and completely replaced by colemanite to get desired calcia (CaO) in the claimed compositions. It means, 0.0 calcium carbonate containing composition will have 10.58 wt% of colemanite which is serving as source for Calcia (CaO).
• the said glass compositions have the isokom temperature at a viscosity of 1 Pa.s ranging from maximum 1413°C to minimum 1234°C.
• the addition of B2O3 incorporated from colemanite in the said glass compositions brings down the batch melting temperature by at least 150°C.
• the present invention provides:
• the present invention provides a composition and a process for the preparation thereof; incorporating colemanite in the chemical composition of soda- lime-silica based flat and container glasses as the source for both calcia (CaO) and boron oxide (B2O3).
• the invented compositions for flat panel glasses comprises of 60.82-68.80 wt.% Si0 2 , 4.26-12.24 wt.% B 2 0 3 , 13.70 wt.% Na 2 0, 0.03 wt.% K 2 0, 8.59-8.83 wt.% CaO, 4.00-4.04 wt.% MgO, 0.13-0.37 wt.% SrO, 0.15 wt.% Al 2 0 3 , and 0.02 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials while the oxide chemicals for container glass comprises of: 61.28-69.45 wt.% Si0 2 , 4.97-13.14 wt.% B 2 0 3 , 13.00 wt.% Na 2 0, 0.30 wt.% K 2 0, 9.28-10.30 wt.% CaO, 0.46-1.24 wt.% MgO, 0.15-0.41 wt.% SrO
• the present invention provides a composition and a process for the preparation thereof, wherein as a result of the incorporation of colemanite in the chemical composition of soda-lime-silica based flat and container glasses the melting process was carried out at lower temperature (1450°C-1550°C) compared to the compositions of soda-lime-silica glasses known in the prior arts.
• the incorporation of B 2 0 3 at its maximum level of 12.24 wt% for flat glass and 13.24 wt% for container glass compositions originating from the addition of colemanite with simultaneous substitution for limestone (CaC0 3 ) up to 100% in the investigated glasses resulted in an energy efficient, cost effective and environment friendly glass melting process.
• the present invention provides a composition wherein additional B 2 0 3 gradually replaces silica and thus the total Si0 2 + B 2 0 3 content does not exceed 73.06 wt%.
• the present invention provides a composition wherein additional B 2 0 3 gradually replaces silica and thus the total Si0 2 + B 2 0 3 content does not exceed 74.42 wt%.
• the present invention provides a composition wherein additional SrO and MgO that are introduced from colemanite mineral have been substituted with CaO and consequently the total alkaline earth content (CaO + MgO + SrO) does not exceed 13.00 wt%.
• the present invention provides a composition wherein additional SrO and MgO that are introduced from colemanite mineral have been substituted with CaO and consequently the total alkaline earth content (CaO + MgO + SrO) does not exceed 10.93 wt%.
• the present invention provides a composition wherein the glass refractive indices (nd) varies from minimum 1.5243 to maximum 1.5339.
• the present invention provides a composition wherein the glass refractive indices (nd) varies from minimum 1.5263 to maximum 1.5345.
• the present invention provides a composition wherein the glass transition temperature varies from minimum 572°C to maximum 583°C.
• the present invention provides a composition wherein the glass transition temperature varies from minimum 582°C to maximum 587°C. In still another embodiment, the present invention provides a composition wherein the dilatometric softening temperature varies from minimum 622°C to maximum 626°C.
• the present invention provides a composition wherein the dilatometric softening temperature varies from minimum 622°C to maximum 635°C.
• the present invention provides a composition wherein the coefficient of thermal expansion varies from maximum 86 x 10 ⁇ 7 K "x to minimum 84 x 10 ⁇ 7 K
• the present invention provides a composition wherein the coefficient of thermal expansion varies from maximum 87 x 10 ⁇ 7 K “1 to minimum 83 x 10 "7 K "
• the present invention provides a composition wherein the transmissions at 580 nm are above 90%.
• the present invention provides a composition wherein the isokom temperature at a viscosity of lPa.s varies from maximum 1372°C to minimum 1234°C.
• the present invention provides a composition wherein isokom temperature at a viscosity of lPa.s varies from maximum 1413°C to minimum 1275°C.
• the present invention provides a composition wherein the melting temperature decreases by at least 150°C from 1600 °C down to 1450 °C with the progressive addition of B 2 0 3 incorporated from colemanite.
• Figure 1 represents UV-vis-NIR transmission spectra of invented flat glass samples FCOl to FC04.
• Figure 2 represents the measured viscosity of FCOl (blank flat glass) and FC04 (flat glass with 100 % Colemanite as raw materials for total CaO) as function of temperature.
• Figure 3 represents UV-vis-NIR transmission spectra of invented container glass samples CCOl to CC04.
• Figure 4 represents the measured viscosity of CCOl (blank container glass) and CC04 (container glass with 100 % Colemanite as raw materials for total CaO) as function of temperature.
• the present invention provides soda lime silicate glass compositions for energy efficient processing using colemanite which exhibit high transmission and reduced melting temperature along with improved thermal and mechanical properties. It is worth mentioning that, the melting temperature of these glasses has got reduced to around 150°C depending upon the successive increase of colemanite mineral in the glass compositions when compared to the melting temperature of commercial soda lime silica glasses. This substantial decrease in melting temperature will certainly diminish the overall power consumption for glass melting.
• the invention thus creates a breakthrough in utilizing colemanite mineral as a raw material which will serve as a source of both boron oxide and calcia resulting in soda lime silica flat and container glass compositions for energy efficient processes with improved optical transmission, thermal and mechanical properties and suitable for solar panels and container glass applications.
• the raw materials for the present invention have been chosen from the minerals such as quartz, soda-ash, feldspar, and colemanite whose compositions have been listed in Table 2. Along with these minerals, fine chemicals like CaC0 3 , Al 2 0 3 , Ti0 2 were chosen as raw materials. Each oxide coming from the raw materials serve a definite purpose in the overall composition resulting in an improvement in high transmission and improved melting, thermal and mechanical properties of the invented glasses. Following is a brief account of the different oxides present in the glasses.
• Si0 2 is a glass forming oxide and was added in the glass composition as network former.
• the Si0 2 content was 60.82-68.80 wt% for flat glass and 61.28-69.45 w% for container glass.
• Table 1 Chemical compositions and properties of blank (FCOl & CCOl) and boron oxide incorporated soda lime silicate flat (FC 02, FC03, FC04); container (CC02, CC03, CC04) glasses
• Table 2 Chemical assay (in wt%) analysis of colemanite and other raw materials used in the investigation
• B 2 0 3 is another glass forming oxide for mainly reducing the melting temperature of the soda lime silicate compositions together with improved thermal and mechanical properties.
• the B 2 0 3 content in the present invention varies from 4.26-12.24 wt% for flat glass and 4.97- 13.14 w% for container glass.
• the total content of the glass formers (Si0 2 + B 2 0 3 ) remains as 73.06 wt% for flat glass and 74.42 wt% for container glass.
• Na 2 0 and 2 0 are used as flux to lower down the melting point of silica.
• the Na 2 0 content for the flat glass is 13.7 wt.% whereas it is 13.00 wt. % for container glass while that of K 2 0 is 0.03 wt.% for flat glass and 0.30 wt% for container glasses, respectively.
• CaO is an alkaline earth oxide which is used in the glass composition to improve chemical durability of the glasses.
• the CaO content varies from 8.59-8.83 wt% for flat glass and 9.28- 10.30 wt% for container glass.
• MgO is added in the glass composition for widening the working range and lowering down the liquidus temperature.
• the MgO content remains 4.00 wt% in flat glass composition and varies from 0.46-1.24 wt% for container glass composition.
• the gradual increase of MgO content in the container glass composition is due to the excess MgO coming from colemanite mineral as shown in Table 2.
• SrO another alkaline earth oxide is being introduced in the glass composition as an additional minor ingredient from colemanite mineral.
• the SrO content varies from 0.13-0.41 wt% for both flat and container glasses.
• Ti0 2 is added as minor component (0.01-0.02 wt.%) in the glass composition to improve the UV-absorption.
• the soda lime silicate glass compositions of the present invention are suitable for preparing the glasses by high temperature melt quenching technique. It is notable to mention that the present invention is not only limited to the listed chemical assay of the raw materials given in table 2 but also can be adopted for similar raw materials with varied chemical assay.
• the glass melting process comprises of the following steps: Appropriately weighed raw materials as per the composition per batch were mixed thoroughly in a porcelain bowl for 30 minutes to ensure uniform mixing of raw materials. At this stage, the batch should be handled with care to avoid any kind of contamination. The batch was charged partly in platinum crucible and the same was introduced in a resistance heating raising hearth electric furnace at temperature of 1350 to 1450 degree C to digest the whole batch by successive charging at the same temperature at an interval of 20 minutes.
• the furnace temperature was increased to 1450°C - 1550°C depending upon the glass composition with a ramp rate of 2.5 °C/min.
• the melting of the chemical batch was done at this temperature for 2 hrs.
• the intermittent stirring of the melt was carried out manually during the melting process at an interval of 45 minutes for two times with quartz rod in order to achieve homogeneity.
• the homogeneous melt was cast on preheated (300°C - 350°C) cast iron mould to obtain glass slab followed by its immediate transfer to annealing furnace kept at 500°C - 550°C to anneal for 4 hrs.
• soda lime silicate glass compositions of the present invention are suitable for preparing in large scale, commercial glass production via float process for flat glass or any other suitable process to yield structured glass panels.
• the soda lime silicate glass compositions of the present invention are also suitable for preparing the glasses via press moulding process for container glass manufacturing.
• soda lime silicate compositions of the present invention for flat and container glasses as shown in Table 1, essentially comprising of 60.82-69.45 wt% silica, 4.26-13.14 wt% B 2 0 3 , 13.00-13.70 wt% Na 2 0, 8.59-10.30 wt% CaO, along with other minor components in the indicated proportion of 0.15-1.30 wt. % Al 2 0 3 , 0.03-0.30 wt. % K 2 0, 0.46-4.00 wt.
• % MgO, 0.13-0.41 wt.% SrO and 0.01-0.02 wt% Ti0 2 with trace amount of impurities comprising of not more than 0.04 wt% Fe are specifically suitable to prepare flat panel glasses by float method as well as container glasses by press moulding process, wherein the total content of the glass formers (Si0 2 + B 2 0 3 ) remains as 73.06 wt.% for flat glass and 74.42 wt.% for container glass while, the total alkaline earth content (CaO + MgO + SrO) does not exceed 13.00 wt% and 10.93 wt% respectively for flat and container glasses.
• the glasses were characterized for their physical, optical, thermal, mechanical and spectral properties in accordance with the standard techniques.
• the glass density is measured following Archimedes' principle using doubled distilled water as immersion liquid on Metler- Tolado electronic mono-pan balance equipped with density kit having an accuracy of ⁇ 0.00005 g.
• refractive indices at five different wavelengths (473 nm, 532 nm, 633 nm, 1064 nm, and 1552 nm) were recorded with an accuracy of 10 "4 on a prism coupler refractometer (Model Metricon M- 2010, Pennington, NJ) built-in with five different lasers as illuminating sources.
• the linear refractive indices at standard wavelengths have been determined from the dispersion curves obtained by the simulation of five coordinate Sellmeier relation.
• the coefficient of thermal expansion (CTE), glass transition temperature (T g ) and dilatometric softening point (Td) were measured using a horizontal-loading dilatometer (Netzsch, Model 402 PC).
• the hardness of the glass was measured by micro-indentation technique on micro-indentation hardness testing system (Clemex CMT, Longueuil, Canada) equipped with a conical Vicker's indenter at an indent load of 500 g. About ten indents were taken for this sample with identical loading condition.
• Optical transmission spectrum was recorded on UV-Vis-NI spectrophotometer (Perkin-Elmer, Lambda 20) at room temperature in the wavelength range 200-1100 nm.
• the high temperature viscosity of the glass was measured on rotating cylinder type viscometer (Behr, VIS403).
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant blank soda lime silicate flat glass of composition 73.06 wt.% Si0 2 , 0.15 wt.% Al 2 0 3; 13.7 wt.% Na 2 0, 0.03 wt.% K 2 0, 9.00 wt.% CaO, 4.00 wt.% MgO, and 0.02 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the blank soda lime silicate flat glass was prepared as a reference glass in order to compare all other glass compositions in the present invention under similar laboratory conditions.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1450°C and melted at 1600°C for 2 hrs.
• the cast glass was annealed at 550°C for 4 hrs.
• the density of the glass was measured to be 2.4981 g/cm 3 .
• the refractive index of the glass at 587.6 nm ⁇ n d ) was 1.5184 and the dispersion (n F -n c ) was calculated as 0.0089.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 91 x 10 "7 K "1 with an accuracy of ⁇ 1%.
• the T g and Td value obtained from dilatometer were 564 °C and 614 °C, respectively.
• the hardness value of the glass was 4.54 GPa with a standard deviation of 0.003.
• the optical transmission of the glass at 580 nm was found to be 91% ( Figure 1).
• the experimental data of viscosity is presented in Figure 2.
• the temperatures at glass viscosity of 10 1 Pa.s and 10 3 Pa.s were found to be 1436°C and 1017°C, respectively.
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant flat glass of composition 68.80 wt.% Si0 2 , 4.26 wt.% B 2 0 3 , 0.15 wt.% Al 2 0 3 , 13.7 wt.% Na 2 0, 0.03 wt.% K 2 0, 8.83 wt.% CaO, 4.00 wt.% MgO, 0.13 wt.% SrO, and 0.02 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1450°C and melted at 1550°C for 2 hrs.
• the cast glass was annealed at 550°C for 4 hrs.
• the density of the glass was measured to be 2.5396 g/cm 3 .
• the refractive index of the glass at 587.6 nm (n d ) was 1.5243 and the dispersion (n F -n c ) was calculated as 0.0086.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 86 x 10 ⁇ 7 K 1 with an accuracy of ⁇ 1%.
• the T g and T d value obtained from dilatometer were 572 °C and 622 °C, respectively.
• the hardness value of the glass was 5.10 GPa with a standard deviation of 0.05.
• the optical transmission at 580 nm was found to be 91% ( Figure 1).
• the temperatures at glass viscosity of 10 1 Pa.s and 10 3 Pa.s were found to be 1372°C and 979
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant flat glass of composition 64.54 wt.% Si0 2 , 8.52 wt.% B 2 0 3 , 0.15 wt.% Al 2 0 3 , 13.7 wt.% Na 2 0, 0.03 wt.% K 2 0, 8.69 wt.% CaO, 4.00 wt.% MgO, 0.27 wt.% SrO, and 0.02 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1400°C and melted at 1500°C for 2 hrs.
• the cast glass was annealed at 560°C for 4 hrs.
• the density of the glass was measured to be 2.5507 g/cm 3 .
• the refractive index of the glass at 587.6 nm [n d ) was 1.5298 and the dispersion (n F -n c ) was calculated as 0.0087.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 85 ⁇ 10 ⁇ 7 K "1 with an accuracy of ⁇ 1%.
• the T g and Td value obtained from dilatometer were 580°C and 625°C, respectively.
• the hardness value of the glass was 5.50 GPa with a standard deviation of 0.02.
• the optical transmission at 580 nm was found to be 91% ( Figure 1).
• the temperatures at glass viscosity of 10 1 Pa.s and 10 3 Pa.s were found to be 1301°C and 944°C,
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant flat glass of composition 60.82 wt.% Si0 2 , 12.24 wt.% B 2 0 3 , 0.15 wt.% Al 2 0 3 , 13.7 wt.% Na 2 0, 0.03 wt.% K 2 0, 8.59 wt.% CaO, 4.00 wt.% MgO, 0.37 wt.% SrO and 0.02 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1350°C and melted at 1450°C for 2 hrs.
• the cast glass was annealed at 570°C for 4 hrs.
• the density of the glass was measured to be 2.5638 g/cm 3 .
• the refractive index of the glass at 587.6 nm ( ⁇ ) was 1.5339 and the dispersion (n F -nc) was calculated as 0.0078.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 84 ⁇ 10 "7 K 1 with an accuracy of +1%.
• the T g and T d value obtained from dilatometer were 583 °C and 626 °C, respectively.
• the hardness value of the glass was 5.10 GPa with a standard deviation of 0.07.
• the optical transmission at 580 nm was found to be 91% ( Figure 1).
• the experimental data of viscosity is presented in Figure 2.
• the temperatures at glass viscosity of 10 1 Pa.s and 10 3 Pa.s were found to be 1234°C and 902°C, respectively.
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant blank soda lime silicate container glass of composition 74.42 wt.% Si0 2 , 1.30 wt.% Al 2 0 3 , 13.00 wt.% Na 2 0, 0.30 wt.% K 2 0, 10.50 wt.% CaO, 0.43 wt.% MgO and 0.01 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the blank soda lime silicate flat glass was prepared as a reference glass in order to compare all other glass compositions in the present invention under similar laboratory conditions.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1450°C and melted at 1600°C for 2 hrs.
• the cast glass was annealed at 560°C for 4 hrs.
• the density of the glass was measured to be 2.5007 g/cm 3 .
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant container glass of composition 69.45 wt.% Si0 2 , 4.97 wt.% B 2 0 3 , 1.30 wt.% Al 2 0 3 , 13.00 wt.% Na 2 0, 0.30 wt.% K 2 0, 10.30 wt.% CaO, 0.46 wt.% MgO, 0.15 wt.% SrO and 0.01 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1450°C and melted at 1550°C for 2 hrs.
• the cast glass was annealed at 560°C for 4 hrs.
• the density of the glass was measured to be 2.5264 g/cm 3 .
• the refractive index of the glass at 587.6 nm (n d ) was 1.5263 and the dispersion (n F -n c ) was calculated as 0.0086.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 87 x 10 "7 K 1 with an accuracy of ⁇ 1%.
• the T g and T d value obtained from dilatometer were 583°C and 622°C, respectively.
• the hardness value of the glass was 4.50 GPa with a standard deviation of 0.3.
• the optical transmission at 580 nm was found to be 91% ( Figure 3).
• the temperatures at glass viscosity of 10 1 Pa.s and 10 3 Pa.s were found to be 1413°C and 991°C,
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant container glass of composition 64.48 wt.% Si0 2 , 9.94 wt.% B 2 0 3 , 1.30 wt.% Al 2 0 3 , 13.00 wt.% Na 2 0, 0.30 wt.% K 2 0, 9.68 wt.% CaO, 0.93 wt.% MgO, 0.31 wt.% SrO and 0.01 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the carefully weighed and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1400°C and melted at 1500°C for 2 hrs.
• the cast glass was annealed at 565°C for 4 hrs.
• the density of the glass was measured to be 2.5540 g/cm 3 .
• the refractive index of the glass at 587.6 nm (n d ) was 1.5323 and the dispersion (n f -n c ) was calculated as 0.0086.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 86 x 10 ⁇ 7 K "1 with an accuracy of ⁇ 1%.
• the T g and T d value obtained from dilatometer were 584 °C and 630 °C, respectively.
• the hardness value of the glass was 5.02 GPa with a standard deviation of 0.03.
• the optical transmission at 580 nm was found to be 91% ( Figure 3).
• the temperatures at glass viscosity of lO ⁇ a.s and 10 3 Pa.s were found to be 1346°C
• the requisite raw materials were weighed in appropriate proportions to obtain the resultant container glass of composition 69.45 wt.% Si0 2 , 13.14 wt.% B 2 0 3 , 1.30 wt.% Al 2 0 3 , 13.00 wt.% Na 2 0, 0.30 wt.% K 2 0, 9.28 wt.% CaO, 1.24 wt.% gO, 0.41 wt.% SrO and 0.01 wt.% Ti0 2 along with 0.04 wt.% Fe coming as impurity from starting raw materials.
• the carefully weighted and thoroughly mixed chemical batch was charged in platinum crucible kept in resistance furnace at 1350°C and melted at 1450°C for 2 hrs.
• the cast glass was annealed at 570°C for 4 hrs.
• the density of the glass was measured to be 2.5568 g/cm 3 .
• the refractive index of the glass at 587.6 nm (n d ) was 1.5345 and the dispersion (n F -n c ) was calculated as 0.0087.
• the measured CTE of the glass cylinder with 25 mm length and 6 mm diameter in the temperature range 50°C-300°C was found to be 83 x 10 "7 K "1 with an accuracy of ⁇ 1%.
• the T g and T d value obtained from dilatometer were 587°C and 635°C, respectively.
• the hardness value of the glass was 5.07 GPa with a standard deviation of 0.05.
• the optical transmission at 580 nm was found to be 91% (Figure 3).
• the experimental data of viscosity is presented in Figure 4.
• the temperatures at glass viscosity of 10 1 Pa.s and 10 3 Pa.s are found to be 1275°C and 916°C, respectively.
• the invented soda lime silicate glass compositions for both flat and container glasses using colemanite in the present invention have showed high visible transmission, increased glass transition temperature, dilatometric softening temperature and better mechanical properties along with decreased coefficient of thermal expansion and melting temperature.

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