32 research outputs found
Glass Foam Made with Silicon Nitride and Manganese Oxide by Microwave Irradiation
A high mechanical strength (6.1 MPa) glass foam was produced by sintering/foaming at 830 潞C in an experimental 0.8 kW-microwave oven. The basic raw material was a colorless flat glass waste and the foaming agent was Si3N4 powder (2 wt.%). As an oxygen supplying agent, a MnO2 powder (3.1 wt.%) was used. The main physical, mechanical, thermal and morphological characteristics of the optimal sample were: apparent density of 0.47 g/cm3, porosity of 77.6%, thermal conductivity of 0.105 W/m路K, compressive strength of 6.1 MPa and pore size between 0.15-0.40 mm. The optimal glass foam sample has the required characteristics of a thermal insulation material usable under mechanical stress conditions in civil engineering. The originality of the paper is the application of the unconventional microwave heating technique, faster and more economical, unlike the other papers in the same area published in the literature, followers of the traditional conventional heating technique
Manufacturing Ceramic Foams at Very High Temperature by the Unconventional Process of Direct Microwave Heating
Abstract
SiC ceramic foams were manufactured by direct microwave heating up to 1520 潞C. Silicon carbide (42-68 wt.%), quartz sand as a silica supplier (20-38 wt.%), coal fly ash (12-20 wt.%) and a constant water addition of 15 wt.% were used as starting materials. The ceramic foam samples had semi-open microstructures in which neighboring cells are partially connected to each other and partially closed. Due to the very dense cellular walls and the very low cells size (below 21 渭m), the compressive strength had very high values (41.3-56.5MPa), the porosity was within an average value range (52.4-57.6%) and the thermal conductivity and the apparent density had relatively high values. In energy terms, the technique of direct microwave heating was very advantageous, the specific energy consumption being very low (1.04-1.21 kWh/kg) compared to the consumptions achieved by conventional methods. The application field of SiC ceramic foams obtained by the bonding method and using silica as a bonding agent includes hot gas or molten metal filters, porous burners, catalytic supports and others. From the four tested experimental variants, it could be concluded that the optimal sample was that achieved at 1520 潞C with 68% silicon carbide, 20% quartz sand, 12% coal fly ash and 15% water addition, having the porosity of 57.6%, thermal conductivity of 0.174 W/m路K, compressive strength of 56.5 MPa and the equivalent pore size between 9-21 渭m
Glass-ceramic Foams Made of Very High Coal Fly Ash Weight Ratio by the Direct Microwave Heating Technique
A high mechanical strength glass-ceramic foam was produced by direct microwave heating at 853 潞C of a very high weight ratio of coal fly ash (82%), calcium carbonate (5%) as a foaming agent, sodium carbonate (13%) as a fluxing agent and water addition (10%). Due to the excellent energy efficiency of the direct microwave heating, the heating rate had a very high value (32 潞C/min), much higher than the heating rate of conventional processes and led to a very low value of the specific energy consumption (0.72 kWh/kg). The physical and mechanical characteristics of the optimal glass-ceramic foam sample were: apparent density of 1.44 g/cm3, porosity of 26.2%, thermal conductivity of 0.281 W/m路K, compressive strength of 41.3 MPa and water absorption of 0.5%. Given the features of the glass-ceramic foam (very high compressive strength, acceptable porosity and thermal conductivity, very low water permeability, fireproof, chemical stability, no-toxicity, etc., the application domain of this material type may include road and railway constructions, bridge abutments and retaining walls, foundations, drainages, sports grounds and other types of constructions that require high mechanical stress
Manufacture of Cellular Glass Using Oak Leaves as a Foaming Vegetable Agent
Abstract
The manufacture experimentation of a cellular glass exclusively from mineral waste and natural residues using the unconventional technique of microwave irradiation was the objective of the research whose results are presented in the paper. The originality of the paper results from the use of oak leaves as a vegetable foaming agent as well as the use of microwave energy in heating processes of the raw material powder mixture for manufacturing thermal insulating materials for the building construction. Worldwide, these processes use only conventional heating techniques. The experimental results led to the conclusion that both the use of waste and residues, as well as the unconventional heating technique allow to obtain porous materials with structural homogeneity having apparent densities and thermal conductivities that can decrease up to 0.34 g/cm3, and 0.071 W/m路K respectively. The compressive strength corresponding to the materials with the lowest values of density and thermal conductivity has an acceptable value (1.2 MPa) for the field of application. The specific energy consumption is around 1 kWh/kg, being approximately at the same level with the values of industrial consumptions achieved by conventional techniques
Unconventional Technique for Producing Borosilicate Glass Foam
The study aims to test an advanced technique but insufficiently valued in the world in the process of experimental manufacture of borosilicate glass foam. It is about the unconventional technique of heating solids by using the microwave radiation converted into heat. The experimental equipment on which the tests were performed was a 0.8-kW microwave oven commonly used in the household with constructive adaptations to be operational at high temperature. The adopted manufacturing recipe was composed of borosilicate glass waste with the addition of calcium carbonate, boric acid and water in different weight proportions. The material was sintered at 829-834 潞C by predominantly direct microwave heating and the optimal foamed product had characteristics similar to those manufactured by conventional techniques (apparent density of 0.33 g/cm3, thermal conductivity of 0.070 W/m鈥, compressive strength of 3.1 MPa and a homogeneous microstructure with pore size between 0.7-1.0 mm). The energy efficiency of the unconventional manufacturing process was remarkable, the specific energy consumption being only 0.92 kWh/kg
Granulated Expanded Glass Manufacturing Method Using Electromagnetic Waves
The paper presents experimental results obtained in the process of experimental manufacture in a microwave oven of lightweight granulated glass aggregates. The process was conducted to obtain the highest dimensional class (between 18-23 mm), the almost spherical shape of the aggregates being facilitated by cold processing of raw spherical pellets (between 11-15 mm) containing the powder mixture formed by glass waste, borax. calcium carbonate, aqueous sodium silicate solution and water addition and then rotation of the high electromagnetic wave susceptible ceramic crucible containing raw pellets during the heat treatment at temperatures between 822-835 潞C. In terms of quality, the expanded glass aggregate granules are almost similar to those manufactured in conventional rotary kilns heated by burning fuel, having the following characteristics: bulk density of 0.17 g/cm3, compressive strength of 2.2 MPa, thermal conductivity of 0.047 W/m路K, water absorption of 1 vol. % and pore size between 0.3-0.6 mm. The experimental product has not yet been tested as a raw material in the manufacture of some light weight concretes, but the use of similar granulated glass aggregates manufactured in the world confirms the ability of this aggregate type to produce light weight and energy efficient concretes for building construction.
 
Experimental Use of Microwaves in the High Temperature Foaming Process of Glass Waste to Manufacture Heat Insulating Material in Building Construction
Abstract
The aim of the paper was the experimental manufacture of cellular glass from glass waste and coal ash as raw material and silicon carbide as a foaming agent, using the unconventional microwave heating technique. This heating technique, although known since the last century and recognized worldwide as fast and economical, is not yet industrially applied in high temperature thermal processes. The cellular glass manufacturing process requires high temperatures and the use of microwaves in this process is the originality of the work. The experiments aimed at producing thermal insulating materials with high porosity and low thermal conductivity for building construction similar in terms of quality to those manufactured industrially by conventional techniques, but with lower energy consumption. The obtained samples had adequate characteristics (apparent density 0.22-0.32 g/cm3, porosity 85.5-90.0%, thermal conductivity 0.043-0.060 W/m路K, compressive strength 1.23-1.34 MPa), and the specific energy consumption was low (0.84-0.89 kWh/kg). Theoretically, given the use of microwave equipment on an industrial scale, this consumption comparable in value to that industrially achieved by conventional techniques could decrease by up to 25%
Granulated Expanded Glass Manufacturing Method Using Electromagnetic Waves
The paper presents experimental results obtained in the process of experimental manufacture in a microwave oven of lightweight granulated glass aggregates. The process was conducted to obtain the highest dimensional class (between 18-23 mm), the almost spherical shape of the aggregates being facilitated by cold processing of raw spherical pellets (between 11-15 mm) containing the powder mixture formed by glass waste, borax. calcium carbonate, aqueous sodium silicate solution and water addition and then rotation of the high electromagnetic wave susceptible ceramic crucible containing raw pellets during the heat treatment at temperatures between 822-835 潞C. In terms of quality, the expanded glass aggregate granules are almost similar to those manufactured in conventional rotary kilns heated by burning fuel, having the following characteristics: bulk density of 0.17 g/cm3, compressive strength of 2.2 MPa, thermal conductivity of 0.047 W/m路K, water absorption of 1 vol. % and pore size between 0.3-0.6 mm. The experimental product has not yet been tested as a raw material in the manufacture of some light weight concretes, but the use of similar granulated glass aggregates manufactured in the world confirms the ability of this aggregate type to produce light weight and energy efficient concretes for building construction
FOAM GLASS GRAVEL MADE OF RECYCLED GLASS WASTE AND SILICON CARBIDE BY MICROWAVE HEATING
The paper presents recent achievements in the microwave use for manufacturing foam glass gravel from recycled glass waste and silicon carbide. The aim was to obtain a product with physical and mechanical characteristics almost similar to those of industrially manufactured materials by conventional heating techniques, but with a higher energy efficiency. A foam glass with the thermal conductivity of 0.075 W/m路K and the compressive strength of 7.5 MPa was experimentally obtained. The specific energy consumption was of 1.0 kWh/kg comparable with the industrial processes and it could reach values up to 25% lower by using a high power industrial microwave equipment
FOAM GLASS GRAVEL MADE OF RECYCLED GLASS WASTE AND SILICON CARBIDE BY MICROWAVE HEATING
The paper presents recent achievements in the microwave use for manufacturing foam glass gravel from recycled glass waste and silicon carbide. The aim was to obtain a product with physical and mechanical characteristics almost similar to those of industrially manufactured materials by conventional heating techniques, but with a higher energy efficiency. A foam glass with the thermal conductivity of 0.075 W/m路K and the compressive strength of 7.5 MPa was experimentally obtained. The specific energy consumption was of 1.0 kWh/kg comparable with the industrial processes and it could reach values up to 25% lower by using a high power industrial microwave equipment