The possibility of practical application of citrogypsum in engineering

At present, the problem of using as functional materials such materials that are a by-product of technological processes and accumulate in the form of production waste is becoming more relevant. We have studied two groups of samples. The first group became the basis for a new material for the air humidity sensor, which was obtained from the waste products of citric acid production. Samples of citrogypsum (calcium sulfate dihydrate, i.e. CaSO$_4$ $\cdot$ 2H$_2$O) doped with copper sulfate (CuSO$_4$ $\cdot$ 5H$_2$O) were prepared. The dependence of the impedance on the relative humidity of samples of three thicknesses was carried out. The frequency dependences of complex resistance and relative permittivity on relative humidity are measured. The second group of samples obtained from citrogypsum was a powder consisting of CaSO$_4$ $\cdot$ 2H$_2$O whiskers. Whiskers CaSO$_4$ $\cdot$ 2H$_2$O were used to create composites based on epoxy resin. An improvement in the properties of the composite was recorded in the study of tensile and compressive stresses of the samples. This article shows the possibility of practical application of (CaSO$_4$ $\cdot$ 2H$_2$O)$_{0.95}$–(CuSO$_4$ $\cdot$ 5H$_2$O)$_{0.05}$ – as a new air humidity sensor material and improvement of the mechanical properties of the composite based on epoxy resin and CaSO$_4$ $\cdot$ 2H$_2$O whiskers.